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POTENTIALLY TOXIC ELEMENTS, SOURCES, PATHWAYS, AND FATE THROUGH2.1.SOURCES AND PATHWAYS OF POTENTIALLY TOXIC ELEMENTS IN UWW AND SS2.1.1 DOMESTIC SOURCES 2.1.2 COMMERCIAL SOURCES 2.1.3 U

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Luxembourg: Office for Official Publications of the European Communities, 2001

AND SEWAGE SLUDGE

Prepared by ICON

Dr Mark Nieuwenhuijsen

Adrienne Pitman

Dr Radu Rautiu Richard Sawyer

Dr Steve Smith

Dr David White

Technical University Munich

Professor Peter Wilderer

Stefania Paris

IRSA Rome

Dr Dario Marani

Dr Camilla Braguglia

2 POTENTIALLY TOXIC ELEMENTS, SOURCES, PATHWAYS, AND FATE THROUGH

2.1.SOURCES AND PATHWAYS OF POTENTIALLY TOXIC ELEMENTS IN UWW AND SS2.1.1 DOMESTIC SOURCES

2.1.2 COMMERCIAL SOURCES

2.1.3 URBAN RUNOFF

2.2 INFLUENCE OF VARIOUS TREATMENT PROCESSES ON THE FATE OFPOTENTIALLY TOXIC ELEMENTS THROUGH WASTEWATER TREATMENT SYSTEMS(WWTS) AND SEWAGE SLUDGE TREATMENT (SST)

2.3 QUANTITATIVE ASSESSMENT OF POTENTIALLY TOXIC ELEMENTS INUNTREATED UWW, TREATED UWW AND TREATED SS

3 ORGANIC POLLUTANTS: SOURCES, PATHWAYS, AND FATE THROUGH URBAN

3.1 SOURCES AND PATHWAYS OF ORGANIC POLLUTANTS IN UWW AND SS

3.1.1 DOMESTIC AND COMMERCIAL

4 HEALTH AND ENVIRONMENTAL EFFECTS OF POLLUTANTS IN UWW AND SS 94

4.1 POTENTIALLY TOXIC ELEMENTS

4.2 ORGANIC POLLUTANTS

5 A REVIEW OF EU AND NATIONAL MEASURES TO REDUCE THE POTENTIALLY TOXIC ELEMENTS AND ORGANIC COMPOUNDS CONTAMINATION OF UWW AND SS

102

(A) PLATINUM GROUP METALS IN URBAN ENVIRONMENT

(B) SUSTAINABLE URBAN DRAINAGE

(C) POLLUTANT SOURCES AND LOAD FROM ARTISANAL ACTIVITIES IN URBANWASTEWATER (THE MUNICIPALITY OF VICENZA, INCL GOLD JEWELLERY SHOPS)(D) PHARMACEUTICALS IN THE URBAN ENVIRONMENT

(E) PERFUME COMPOUNDS IN WASTEWATER AND SEWAGE SLUDGE

(F) SURFACTANTS IN URBAN WASTEWATERS AND SEWAGE SLUDGE

(G) USE OF POLYELECTROLYTES; THE ACRYLAMIDE MONOMER IN WATERTREATMENT

(H) CASE STUDY: LANDFILL LEACHATE

(I) PTE (POTENTIALLY TOXIC ELEMENTS) TRANSFERS TO SEWAGE SLUDGE

(J) EFFECT OF CHEMICAL PHOSPHATE REMOVAL ON POTENTIALLY TOXICELEMENT CONTENT IN SLUDGE

YEARS

POLLUTANTS IN URBAN WASTE WATER AND SEWAGE SLUDGE

EXECUTIVE SUMMARY

Water policy in the European Union is aiming to promote sustainable water use and a majorobjective of the new Water Framework Directive (2000/60/EC) is the long-term progressivereduction of contaminant discharges to the aquatic environment in urban wastewater(UWW) Sewage sludge is also a product of wastewater treatment and the Urban WasteWater Treatment Directive (91/271/EEC) aims to encourage the use of sludge wheneverappropriate Potentially toxic elements and hydrophobic organic contaminants largelytransfer to the sewage sludge during waste water treatment with potential implications for theuse of sludge although some may be emitted with the effluent water

Inputs of metals and organic contaminants to the urban wastewater system (WWTS) occurfrom three generic sources: domestic, commercial and urban runoff A review of availableliterature has quantified the extent and importance of these various sources and the inputsfrom different sectors In general, urban runoff is not a major contributor of potentially toxicelements to UWW Inputs from paved surfaces due to vehicle road abrasion and tyre andbrake-lining wear have been identified and losses from Pb painted surfaces and Pb and Znfrom roofing materials represent localised sources of these elements

Platinum and Pd are components of vehicle catalytic converters and emissions occur as theautocatalyst deteriorates Catalytic converters are the main source of these metals emitted

to the environment and releases have increased with the expansion in use of autocatalysts.Platinum group metals (PGMs) potentially enter UWW in runoff and transfer to sewagesludge in a similar way to other potentially toxic elements The Pt content in sludge is

PGMs are inactive and immobile in soil

In contrast to potentially toxic elements, inputs of the main persistent organic pollutants ofconcern, including: PAHs, PCBs and PCDD/Fs, to UWW are principally from atmosphericdeposition onto paved surfaces and runoff Combustion from traffic and commercial sourcesaccounts for the major PAH release to the environment, although inputs from foodpreparation sources also represent an important and often under-estimated contribution ofcertain PAH congeners PCDD/Fs are released during waste incineration and also by coalcombustion Soil acts as a long-term repository for these contaminant types andremobilisation by volatilisation from soil is an important mechanism responsible for recyclingand redistributing them in the environment For example, the industrial use of PCBs wasphased out in Europe during the 1980s-1990s, but 90 % of the contemporary emissions ofPCBs are volatilised from soil Since emission controls are already in place for the mainpoint sources and PAHs, PCDD/Fs or PCBs enter UWW principally from diffuse atmosphericdeposition and environmental cycling, there is probably little scope, from source control, tofurther reduce inputs and concentrations of these persistent organic substances in UWW orsewage sludge

Being strongly hydrophobic these organic pollutants are efficiently removed during urbanwastewater treatment (WWTS) and bind to the sludge solids However, the increasing body

of scientific evidence has not identified a potential harmful impact of these substances on theenvironment in the context of the urban wastewater system Therefore, on balance, theimportance of these contaminants in UWW and sewage sludge has significantly diminishedand there may be little practical or environmental benefit gained from adopting limits orcontrols for PAHs, PCBs or PCDD/Fs in UWW or sewage sludge This is emphasised further

by the high cost and specialist analytical requirements of quantifying these compounds insludge and effluent

Potentially toxic element contamination of urban wastewater and sewage sludge is usuallyattributed to discharges from major commercial premises However, significant progress hasoccurred in eliminating these sources and this is reflected in the significant reductions inpotentially toxic element concentration in sewage sludge and surface waters reported in allEuropean countries where temporal data on sludge and water quality have been collected.However, potentially toxic element concentrations remain higher in sludge from large urbanwastewater treatment plant (WWTP) compared with small WWTP and they are also greater

in sludges from industrial catchments compared with rural locations These patterns insludge metal content suggest that commercial sources may still contribute significantly to thetotal metal load entering UWW Indeed, recent regional surveys of metal emissions fromcommercial premises confirm that further reductions in most elements could be achievedfrom this sector The primary targets for source control include health establishments, smallmanufacturing industries (particularly metal and vehicle related activities) and hotel/cateringenterprises, as 30 % of medical centres and 20 % of the other types of activity could bedischarging significant amounts of potentially toxic elements in UWW Mercury is a specificcase where compulsory use of dental amalgam separators, and substituting Hg withalternative thermoreactive materials in thermometers, may be effective in reducingdischarges of this element to the WWTS wastewater treatment system

Faeces contribute 60 – 70 % of the load of Cd, Zn, Cu and Ni in domestic wastewater and

>20 % of the input of these elements in mixed wastewater from domestic and industrial

wastewater are body care products, pharmaceuticals, cleaning products and liquid wastes.Plumbing is the main source of Cu in hard water areas, contributing >50 % of the Cu loadand Pb inputs equivalent to 25 % of the total load of this element have been reported indistricts with extensive networks of Pb pipework for water conveyance Adjusting waterhardness in order to reduce metal solubilisation from plumbing is technically feasible, but islikely to be impractical at the regional scale necessary to significantly reduce metalconcentrations in UWW and sludge and may be unpopular with consumers in hard waterareas The gradual replacement of Pb water pipes can be achieved during building renewaland renovation programmes

Reductions in domestic discharges of metals may be possible through increased publicawareness of appropriate liquid waste disposal practices and the provision of accessibleliquid waste disposal facilities It may be impractical to eliminate the use of metals in bodycare products when they are an important active ingredient, but advice and labelling could

be improved to minimise excessive use Cadmium may be a contaminant present inphosphatic minerals and removing phosphate from detergent formulations can reduceassociated potential discharges of Cd from domestic sources

Detergent residues (e.g.nonyl phenol, NP), surfactants (e.g linear alkyl benzenesulphonates, LAS), plasticising agents (e.g di-(2-ethylhexyl)phthalate, DEHP) andpolyacrylamide compounds, added to sludge to aid dewatering, are quantitatively amongstthe most abundant organic contaminants present in UWW and/or sewage sludge.Dewatering agents based on polyacrylamide may contain traces of the potentially toxicacrylamide monomer, but this is rapidly degraded and polyacrylamide itself is biologicallyinactive Detergent residues and DEHP are primarily of domestic origin and they areeffectively degraded during aerobic wastewater treatment and are not considered torepresent a potential environmental problem from the discharge of treated effluents to

alternative products This has been successful when supported by extensive publicawareness campaigning For example, the market share for ecolabelled detergents inSweden increased to 95 % and the consumption of LAS has decreased to a similar extent.Surfactant residues and plasticisers degrade quickly when added to aerobic soils Theoestrogenic activity of NP is however, a principal concern and measures are proposed toeliminate the discharge of this substance to UWW.

Natural and synthetic oestrogens are degraded in WWT, but trace amounts remain andrepresent the main source of oestrogenic activity in treated effluents Further work isnecessary to link these substances to oestrogenic responses in aquatic life, but it may benecessary in future to consider the requirement for tertiary treatment processes (e.g.ozonation) to eliminate these substances from treated effluents

A number of other groups of organic compound are identified as being potentially resistant towastewater and sewage sludge treatment and the most significant of these are brominateddiphenyl ethers (PBDEs) and chlorinated paraffins Further research is warranted, inparticular to assess the persistence and potential environmental significance of thesecompounds Synthetic nitro musks are used in perfumed products and traces may bepresent in UWW and sludge Little is known about the environmental fate of thesecompounds, but effects on human health from this route seem unlikely given that the mainexposure route is through direct contact

The degree of removal and biodegradation of pharmaceutical compounds during WWTvaries considerably, although many common analgesic drugs rapidly biodegrade They aresoluble and transfer to sludge is only of minor concern Significant amounts of prescribeddrugs are excreted from the body and controlling these inputs from the general populationwould be impractical However, the disposal of unused drugs into UWW should be reviewedand alternative methods of disposal should be encouraged The potential significance ofpharmaceuticals in the environment should be assessed in context of the major inputs andpresence arising from widespread veterinary administration of drugs to livestock and farmwaste disposal to land

A general recommendation to protect the water and soil environment is that a hazard,biodegradability and fate assessment should be required for all new synthetic chemicals,irrespective of their purpose or end-use, to determine the potential from them to transfer toUWW or sewage sludge and the subsequent implications for the environment Specifiedcriteria regarding toxicity and biodegradation could be set for compounds that exhibit apropensity to enter the WWTS and restrictions could be enforced regarding production anduse if these were not met These decisions would need to balanced against the potentialbenefits to health derived from the administration of pharmaceutical drugs

Strategies aimed at controlling pollutant discharges can only focus on those sources that can

be identified and quantified Published mass balance calculations indicate there is a highdegree of uncertainty regarding inputs of potentially toxic elements entering the WWTS.Indeed, unidentified sources may contribute as much as 30 - 60 % of the total metal loadentering the WWTS, although more than 80 % of the Cd discharged is from identified inputs.This apparent discrepancy could be related to difficulties in measuring the highly variableinputs of metals in urban runoff and the underestimation of discharges from commercialpremises that have not been subjected to trade effluent control

The European Commission has proposed a list of 32 priority and 11 hazardous substances(COM/2001/17) with the aim of progressively reducing emissions and discharges of thesechemicals to the environment Current developments also suggest that Zn, Cu and LAS may

be the most limiting constituents in sludge if the proposed maximum permissibleconcentrations for these substances in soil (Zn and Cu) and sludge (LAS) are carriedthrough in the revised of Directive 86/278/EEC, but they are not listed as priority substances.Consideration should be given to designating Zn, Cu and LAS as priority substances to

minimise their to UWW as far as is practicable and to ensure there is a consistent link andapproach to defining the environmental quality standards for sludge with those forsustainable water use and contaminant discharge reduction.

The main identified priorities for future research relating to contaminant sources, fate andbehaviour in the WWTS are:

and surveying specific sources to determine the potential for controlling inputsparticularly from small commercial sources and medical establishments;

investigations in relation to precipitation frequency and changes in sludge quality;

environmental consequences of alternative surfactant and plasticing compounds, incollaboration with the related chemical manufacturing industries, to inform decisions ofthe benefits and disadvantages of product substitution in detergent formulations andplastics manufacture;

pollutants in the environment, identifying the processes controlling the extent andmagnitude of diffuse inputs of these substances to UWW and to provide long-termpredictions of changes in release patterns and the consequences for UWW and sludge;

composition data presented in surveys of sewage sludge quality

1 INTRODUCTION

The primary objective of this study is to determine the sources of pollution in urbanwastewater (UWW) treated in wastewater treatment systems (WWTS) This includes thepollutants introduced into the UWW collecting system with run-off rainwater, from domesticand small commercial sources The pollutant contents in urban wastewater and sewagesludge has been evaluated by review of the existing literature, in order that measures may

be proposed to reduce pollution at source

1.1 Introduction to pollutants in urban wastewater

The pollutants of interest can be divided into two main groups;

VI), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn),

furans (PCDF) Over 6,000 organic compounds have been detected in raw watersources most of which are due to human activities While some of these are highlypersistent, others are easily biodegradable in WWTS

Other pollutants of interest are the metalloids, arsenic and selenium and the metal silver.Platinum group metals (PGMs), and pharmaceuticals are covered in detail in case studies.The sources of metal pollution in the wastewater system can be classified into three maincategories:

Figure 1.1: Sources of pollutants in wastewater [after Lester, 1987]

A summary of the various inputs, outputs and pathways followed by water and associatedcontaminants from both natural and anthropogenic sources encountered in urbanenvironments is shown in Figure 1.1 It depicts the drainage area as an open system [Ellis,1986] A more detailed urban catchment figure is included in Appendix A

Wastewater contains many constituents and impurities arising from diffuse and pointsources Large point sources are easily quantifiable and result from specific activities in thearea that are connected to UWW collecting systems The contribution from small pointsources, such as households and small businesses, is much more difficult to identify andquantify, compared to point sources which are usually regulated UWW is also vulnerable toillegal discharges of pollutants

Diffuse sources, such as atmospheric deposition and road runoff have also beencharacterised and this study will attempt to present an overview of the available information

in this area Different methods have been used to estimate point sources and diffuse point) sources contributions to the pollution load [Vink, 1999] Inventories of point and diffusesources, can link observed water quality trends to changes in socio-economic activities

WASTEWATER TREATMENT WORKS

Receiving Water

The type of pollutants and the magnitude of the outfall loadings are a complex function of:

A review of the sources and pathways of potentially toxic element pollutants in urbanwastewater is presented in Section 2.1 and for organic pollutants in Section 3.1

1.2 Objectives and Goals

The main goals of the study were:

domestic, commercial, and urban run-off wastewater, which end up in the UWWcollecting system

wastewater and runoff rainwater on the basis of the available data in the literature

sewage sludge and the percentage of pollutants released in the environment with thetreated effluents

measures to prevent pollution at source The most important practices to treatwastewater and sewage sludge in Europe will be closely examined

further research directions in those areas with insufficient data

This report presents a thorough literature review and is primarily based on the analysis andpresentation of case studies from a wide variety of sources and test catchments acrossEurope, covering a time range from 1975 to date Databases used during this project arelisted in the reference section As theoretical approaches, such as modelling of pollutantsources and predicted concentrations, are scarce the report attempts to summarise themonitoring, sampling and measurement of numerous studies, thus providing a conciseoverview of pollution source types and concentration ranges The reader must keep in mindthat there are significant differences between the experiments (in duration, location,measurement methods, measurement targets and initial conditions), and thus conclusions

on mean or extreme values of pollutants will have to be drawn carefully

2 POTENTIALLY TOXIC ELEMENTS: SOURCES, PATHWAYS, AND FATE THROUGH URBAN WASTEWATER TREATMENT SYSTEMS

The aim is to reduce inputs of pollutants entering the wastewater system to backgroundlevels because this represents the minimum potential extent of contamination that can beachieved Potentially toxic elements are of concern because of their potential for long-termaccumulation in soils and sediments

The majority of metals transfer to sewage sludge (see Fig 2.1) However, 20% may be lost inthe treated effluent, depending on the solubility and this may be as high as 40% - 60% forthe most soluble metal, Ni Although the use of sludge on agricultural land is largely dictated

by nutrient content (nitrogen and phosphorus), the accumulation of potentially toxic elements

in sewage sludge is an important aspect of sludge quality, which should be considered interms of the long-term sustainable use sludge on land Application of sludge to agriculturalland is the largest outlet for its beneficial use and this is consistent with EC policy of wasterecycling, recovery and use This is a critical issue due to the increasing amount of sludgeproduced, the increasingly stringent controls on landfilling, the public opposition toincineration (a potential source of further atmospheric pollution), and the ban on disposal atsea Consequently sludge quality must be protected and improved in order to secure theagricultural outlet as the most cost effective and sustainable option

Figure 2.1: Origin and fate of metals during treatment of wastewater [from ADEME,

1995]

2.1 Sources and pathways of potentially toxic elements in UWW

The average concentrations of potentially toxic elements in domestic and commercialwastewater are given in Table 2.1 The maximum concentrations of potentially toxicelements found in commercial wastewater are generally greater than those in domesticwastewater This is supported by Scandinavian studies [SFT-1997a, 1997b, 1999]considering all urban sectors together, which judged that commercial and light industrialsectors contributed larger loads of potentially toxic elements to urban wastewater thanhousehold sources

Table 2.1 Concentrations of metals in domestic and commercial wastewater

[Wilderer and Kolb, 1997 in Munich, Germany]

Wastewater [mg.l -1 ]

Commercial Wastewater [mg.l -1 ]

Table 2.2 Potentially toxic elements in UWW from various sources

(% of the total measured in the UWW)

Pollutant Country Domestic

Wastewater

Commercial Wastewater

Urban Runoff

Not Identified

Cd distribution

Domestic Storm events Commercial Non Identified

Cu distribution

Domestic Storm events Commercial Non Identified

Cr distribution

Domestic Storm events Commercial Non Identified

Hg distribution

Domestic Storm events Commercial Non Identified

Pb distribution

Domestic Storm events Commercial Non Identified

Ni distribution

Domestic Storm events Commercial Non Identified

Zn distribution

Domestic Storm events Commercial Non Identified

The data in Table 2.2 and Figure 2.2 show that for some elements over 50% of thepotentially toxic elements in wastewater are unaccounted for This is in line with findings byCritchley & Agy [1994] Better source inventory data is essential in order to effectively targetreductions in emissions from all the different sources It may be that identification of some ofthe industrial sources will require increased trade effluent discharge controls ifconcentrations of pollutants are to be reduced Domestic and urban run-off sources mayrequire different types of action, such as changes in products used.

Emissions of potentially toxic elements from industrial point sources were the major sources

of pollution to urban wastewater However, stringent and more widespread limits applied toindustrial users has reduced the levels of potentially toxic elements emitted by industry intourban wastewater considerably This continues a general decline of potentially toxicelements from industrial sources since the 1960s, due to factors such as cleaner industrialprocesses, trade effluent controls and heavy industry recession For example, the liquids

[Barnes, 1987] However, metal finishing industries are now required to pre-treat theseliquids before disposal, reducing toxic discharges by 80-90%

In the Netherlands, a survey of potentially toxic element load in UWW influent [SPEED,1993], also made estimations for 1995 and forecasts up to 2010 The overall prevalence ofpotentially toxic elements in the UWW system is expected to decrease, mainly due to adecrease in runoff and industrial sources, while the potentially toxic elements share inWWTS loads from households was expected to increase As industrial sources of potentiallytoxic elements in UWW decline, the relevant importance of diffuse sources will increase.Wiart and Reveillere [1995] carried out studies at the Achères WWTS in France Theirstudies showed a significant decrease (50-90%) in the potentially toxic element content ofsewage sludge since 1978, following the application of the "at-source discharge reduction"policy [Bebin, 1997] However, the main concern is now with organic pollutants, and currentregulations require monitoring of the influent, in order to set up a baseline database fromwhich limits may then be devised

2.1.1 Domestic sources

Domestic sources of potentially toxic elements in wastewater are rarely quantified due to thedifficulty in isolating them Domestic sources include the potentially toxic elementsdischarged from the household to UWW collecting systems and, in addition, corrosion frommaterials used in distribution and plumbing networks, tap water and detergents

A study by RIVM (Dutch Institute of Public Health and the Environment) in the Netherlands[SPEED, 1993], quantified the waterborne emissions of potentially toxic elements fromhousehold sources, dentistry and utility buildings in the urban environment Table 2.3 showsthe data of waterborne potentially toxic elements emissions in tonnes per annum

Table 2.3 Emissions by Dutch households of potentially toxic elements

[adapted from SPEED, 1993].

Gross waterborne emissions* tonnes.y -1 to surface

water (1993)

Potentially

toxic element

Household sources

Dentistry Utility buildings

Cadmium: is predominantly found in rechargeable batteries for domestic use (Ni-Cd

batteries), in paints and photography The main sources in urban wastewater are fromdiffuse sources such as food products, detergents and bodycare products, storm water[Ulmgren, 2000a and Ulmgren, 2000b]

Copper: comes mainly from corrosion and leaching of plumbing, fungicides (cuprous

chloride), pigments, wood preservatives, larvicides (copper acetoarsenite) and antifoulingpaints

Mercury: most mercury compounds and uses are now banned or about to be banned,

however, mercury is still used in thermometers (in some EU countries) and dentalamalgams Also, mercury can still be found as an additive in old paints for water proofingand marine antifouling (mercuric arsenate), in old pesticides (mercuric chloride in fungicides,insecticides), in wood preservatives (mercuric chloride), in embalming fluids (mercuricchloride), in germicidal soaps and antibacterial products (mercuric chloride and mercuriccyanide), as mercury-silver-tin alloys and for "silver mirrors"

for uses in glazes), also in "crystal glass" Lead has also been found in wines, possibly fromthe lead-tin capsules used on bottles and from old wine processing installations.

Zinc: comes from corrosion and leaching of plumbing, water-proofing products (zinc

formate, zinc oxide), anti-pest products (zinc arsenate - in insecticides, zinc dithioamine as

fungicide, rat poison, rabbit and deer repellents, zinc fluorosilicate as anti-moth agent), woodpreservatives (as zinc arsenate), deodorants and cosmetics (as zinc chloride and zincoxide), medicines and ointments (zinc chloride and oxide as astringent and antiseptic, zincformate as antiseptic), paints and pigments (zinc oxide, zinc carbonate, zinc sulphide),printing inks and artists paints (zinc oxide and carbonate), colouring agent in variousformulations (zinc oxide), a UV absorbent agent in various formulations (zinc oxide), "healthsupplements" (as zinc ascorbate or zinc oxide)

Silver: originates mainly from small scale photography, household products such as

polishes, domestic water treatment devices, etc [Shafer, et.al, 1998, Adams and Kramer,

1999]

Arsenic and Selenium: are among the potentially toxic metalloids found in urban

wastewaters These are of importance due to their potential effects on human/animal health.Only a limited number of studies have taken these into account Arsenic inputs come fromnatural background sources and from household products such as washing products,medicines, garden products, wood preservatives, old paints and pigments Selenium comesfrom food products and food supplements, shampoos and other cosmetics, old paints andpigments Arsenic is present mainly as DMAA (dimethylarsinic acid) and as As (III) (arsenite)

in urban effluents and sewage sludge [Carbonell-Barrachina et.al., 2000].

Household products

Household products were investigated as potential sources of PTE pollution entering theWWTS Table 2.4 shows metal concentrations in various household products in UK

Table 2.4 Metal concentrations in household products

[Comber and Gunn, 1996, WRc report, 1994]

(µg g -1 )

Copper (µg g -1 )

Cadmium (µg g -1 )

Nickel (µg g -1 )

Washing Powders

‘Big Box’

abc

37.935.93.3

1.4

<0.5

<0.5

74.3 136.0

<0.12.31.0

<0.51.401.38

24.010.611.8

0.1

<0.10.1

<0.5

<0.5

<0.5

9.49.010.7

<0.11.01.70.5

<0.51.4

<0.51.4

16.817.28.6

13.610.4

mining source [Hutton et al reported in WRc report 1994] Reducing the amount of

phosphate in washing powders, or choosing phosphate ores with low Cd concentration couldlead to a reduction in Cd in wastewater from diffuse sources In Sweden the amount of

1999], and cadmium discharges from households in the Netherlands have been substantiallyreduced due to the switch to phosphate-free detergents [SPEED, 1993] The 'Ultra' washingpowders, usually phosphate-free, have smaller potentially toxic element contents than thetraditional powders, and are designed to be used in smaller quantities A shift to these newerproducts will reduce the overall metal load from this source

The products with the highest metal contents are shown in bold in Table 2.4 The medicated(anti-dandruff) shampoos contain zinc pyrithione and the high zinc concentrations will thusraise the zinc inputs to the UWW collecting system In 1991 these shampoos were estimated

Table 2.5 provides a general picture of some of the potentially toxic elements in variousdomestic products including food products [after Lester, 1987 and WRc report 1994].Sources for each metal are marked with a tick In addition to the main metals considered inthis study, cadmium, chromium (III and VI), copper, mercury, nickel, lead and zinc, silver,arsenic, selenium and cobalt are also included Other metals and metalloids for which moreinformation is necessary include manganese, molybdenum, vanadium, antimony and tin.

TABLE 2.5 Domestic sources of potentially toxic elements in urban wastewater

[modified from Lester, 1987, and WRc, 1994]

Estimates of the mean potentially toxic element inputs to UWW collecting systems fromdomestic activities are presented in Table 2.6 The results show that for the particular UK(hard water) catchment studied in 1994, the domestic inputs of copper and zinc are majorcontributors to the overall level of potentially toxic elements reaching the WWTS Most of thezinc is derived from faeces and household activities such as washing and cleaning.Chromium, lead and cadmium were also found to be mainly from domestic activities ratherthan from plumbing.

Table 2.6 Potentially toxic element loads to the UWW collecting systems from domestic activities [adapted from Comber and Gunn, 1996]

Load (µg.person -1 day -1 ) Activity (study in a hard

Washing

6624452

6859977

36.0515

0.611

2752

4238Dishwashing

(machine)

Input WaterWashing

3942

698

2.96

0.031.3

22

0.310Dishwashing

(hand)

Input WaterWashing

5911010

6125

<20

3246

0.57.8

24138

3.7136.7

Bathing

11401095

1065167

4645

1.013.1

409

5.97.4

Faeces

253111400

80822104

63121

2.048.0

77284

8.551.5

Measured mean from

housing estates

CatchmentPopulation

50 000

Predicted load to UWW

collecting systems from

domestic sources (kg/day)

Measured mean total load to

the WWTS kg per day

It is noted that, while the quantities of potentially toxic elements dissolved in water fromplumbing will vary across the Europe they will make up a significant proportion of thepotentially toxic element loading going to any WWTS

Table 2.7 summarises the percentages of the domestic inputs at the Shrewsbury WWTS, inthe UK As can be seen over a fifth of the copper, zinc, cadmium and nickel entering the

Table 2.7 Potentially toxic elements entering wastewater, breakdown by source [WRc, 1994]

Percentages of total load

Break down of domestic sources as percentage of total metal entering WWTS

WashingMachine

Concentrations are expected to vary with the intake of metals in the diet, drinking water andmedication and may also be influenced by the increasing prevalence of mineralsupplementation of food, for example with zinc, iron, selenium, and manganese One study

in France (ADEME 1997) found the following concentrations of potentially toxic elements in

For some elements, such as Cd, the weighted average concentration in sludge (e.g 3.3 mg

concentrations of Cd in different EU member states is discussed in section 2.3

Domestic water and heating systems

Studies in the USA [Isaac et.al, 1997], and Europe [WRc 1994] show that corrosion of the

distribution-plumbing-heating networks contribute major inputs of Pb, Cu and Zn Lead

the output

It has been found that concentrations of copper in sewage sludge are directly proportional to

water hardness [Comber et al 1996] Hard water (high pH) is potentially more aggressive to

copper and zinc plumbing, increasing leaching However, the opposite is true for lead in that

it dissolves more readily in than soft, acidic water The high lead levels in drinking water inScotland due to its soft waters are a major concern

Reductions in the amounts of copper and lead in wastewater have been reported by pHadjustment of tap water and addition of sodium silicate The addition of alkali agents to water

at the treatment stage and the replacement of much lead piping has led to reductions in lead

concentration [Comber et al., 1996] Adjusting the pH of tap water may be limited by

practical and economic factors

Zinc in domestic plumbing comes from galvanised iron used in hot water tanks but is lessproblematic than lead and copper because the amount decreases with the ageing of theinstallations Copper corrosion and dissolution is also greater in hot water than in cold water

supplies [Comber et al 1996] The 'first draw' (initial flow of water in the morning) has higher amounts of copper and lead compared to subsequent draws [Isaac et.al., 1997] The Cu

would be recommended for certain water domestic uses, such as boilers and heatingsystems, in order to reduce the metal corrosion

The type of housing was also found to be important by the WRc report [1994] Table 2.8gives an average concentration of effluent from two types of estates, "1960s residential" and

"1990s residential" from daily bulk- and flow-weighted samples The larger copper levelsfrom the "modern estate" can be explained by the newer plumbing system In manycountries copper is the major element used in plumbing In the UK it has been estimated thatleaching from copper plumbing accounts for over 80% of the copper entering domestic

wastewater [Comber et al 1996] The higher lead level found in the newer housing did not

correlate with similar studies comparing old and new housing and could not be explainedsatisfactorily; as in general older houses in the UK contain more lead plumbing Lead fromsolders in the piping system may also be an important source In other regions of the EUsteel and zinc galvanised iron are used widely This may explain why zinc in sludge isproportionally greater than Cu in other member states compared with the UK

Table 2.8 Mean concentration of potentially toxic elements in the effluent from households in two types of residential areas [WRc Report, 1994]

and quantities of the products used

2.1.2 C OMMERCIAL S OURCES

Limited data is available for the potentially toxic element contribution from commercialsources and health care inputs (such as hospital and clinical wastes) Inputs from artisanalsources are looked at in more detail in a separate Case Study in Section 6

Cadmium could originate from laundrettes, small electroplating and coating shops, plastic

manufacture, and also used in alloys, solders, pigments, enamels, paints, photography,batteries, glazes, artisanal shops, engraving, and car repair shops Data from ADEME[1995], estimated that worldwide, 16000 tonnes of cadmium were consumed each year; 50-60% of this in the manufacture of batteries and 20-25% in the production of colouredpigments

Chromium is present in alloys and is discharged from diffuse sources and products such as

preservatives, dying, and tanning activities Chromium III is widely used as a tanning agent

in leather processing Chromium VI uses are now restricted and there are few commercialsources

Copper is used in electronics, plating, paper, textile, rubber, fungicides, printing, plastic, and

brass and other alloy industries and it can also be emitted from various small commercialactivities and warehouses, as well as buildings with commercial heating systems

Lead, as well as being used as a fuel additive (now greatly reduced or banned in the EU) it

is also used in batteries, pigments, solder, roofing, cable covering, lead jointed waste pipesand PVC pipes (as an impurity), ammunition, chimney cases, fishing weights (in somecountries), yacht keels and other sources

Mercury is used in the production of electrical equipment and is also used as a catalyst in

chlor-alkali processes for chlorine and caustic soda production The main sources in effluentare from dental practices, clinical thermometers, glass mirrors, electrical equipment andtraces in disinfectant products (bleach) and caustic soda solutions

Nickel is used in the production of alloys, electroplating, catalysts and nickel-cadmium

batteries The main emission of nickels are from corrosion of equipment from launderettes,small electroplating shops and jewellery shops, from old pigments and paints It also occurs

in used waters from hydrogenation of vegetable oils (catalysts)

Zinc is used in galvanisation processes, brass and bronze alloy production, tyres, batteries,

paints, plastics, rubber, fungicides, paper, textiles, taxidermy (zinc chloride), embalming fluid(zinc chloride), building materials and special cements (zinc oxide, zinc fluorosilicate),dentistry (zinc oxide), and also in cosmetics and pharmaceuticals The current trend towardselectrolytic production of zinc which, in contrast to thermally produced zinc, has virtually nocadmium contamination This means that cadmium pollution to UWW due to the corrosion ofgalvanised steel will in time become negligible [SPEED 1993]

Platinum and platinum group metals (PGMs) such as palladium and osmium can enter

UWW from medical and clinical uses, mainly as anti-neoplastic drugs The amount in

and Helmers, 1997, Kümmerer et.al., 1999] giving a total emission of 84-99 kg per annum

from hospitals in Germany Other sources of platinum metals in the environment related tocommercial activities come from catalysts used in petroleum/ammonia processing andwastewaters, from the small electronic shops, jewellery shops, laboratories and glassmanufacturing Section 6 contains a detailed Case Study (a) on PGMs in urban waste waterand sewage sludge

Silver could potentially be emitted from photographic and printing shops, from jewellery

manufacturers and repairers, plating and craft shops, glass mirror producers and scale water filters

small-Studies in Spain showed the presence of elevated concentrations of Cd, Cu, Hg, Pb and Zn

in urban wastewater and in the coastal environment [Castro, et.al., 1996], with large

concentrations of copper and zinc possibly due to the use of fungicides in glass-houses

A summary of concentrations of metals found in effluent from commercial sources indifferent regions in Europe is given in Table 2.9

Table 2.9 Summary of potentially toxic elements in UWW from commercial sources ( g l -1 )

Element Country Industry Industrial Effluent

3-1,250300-400

37-26,0005,000-10,00020,500700-1,900(max.13,300)

Wilderer et al 1997

NTUA, 1985EBAV, 1996

Greece

Italy

All sectorsMetal and electrical industriesTanneries

Artisanal galvanic shops

<10-20,100500-13,000100-7,000,00016,000

Wilderer et al 1997

NTUA, 1985EBAV, 1996

Greece

Italy

All sectorsMetal and electrical industriesCeramics and photoceramicsshops

<50-13,4005006,000

Wilderer et al 1997

NTUA, 1985EBAV, 1996

Greece

Italy

All sectorsMetal and electrical industriesArtisanal galvanic shops

<10-7,300500-14,50019,700

Wilderer et al 1997

NTUA, 1985EBAV, 1996

Greece

Italy

All sectorsMetal and electrical industriesGoldsmiths and jewelleryshops

30-133,00060-2,8301,000 (max 7,000)

Wilderer et al 1997

NTUA, 1985EBAV, 1996

1993

In 1999, a project carried out by Anjou Recherche [LIFE, 1999], attempted to classify allcommercial sources of wastewater pollution based on a matrix of 73 main pollutantsincluding many potentially toxic elements and certain organic pollutants The UWWcollecting system of Louviers, for example, had listed 1054 establishments of which 39%were capable of emitting at least one of these pollutants Ten classes of activities wererecorded, of which health and social action (33.5%), manufacturing industry (20%), hotelsand restaurants (17.8%), and collection services (10%) appeared most often as potentialpolluters It was found on average, that between a third and a half of the activities emittedpollutants In the Louviers area, it was found that 53 urban businesses and institutions couldpotentially emit cadmium, 168 chromium, 147 copper, 35 nickel, 167 mercury, 50 lead, and

63 zinc This suggests that more can be done to reduce trade effluent discharges

Collaborative projects were developed both for research, product development andeducational programmes Local commercial organisations (particularly the Swedish DentalFederation) co-operated in the project; new technologies were developed and an evaluation

of alternative products was carried out Pollution limits were imposed that were determined

to be appropriate to encourage the purchase of the endorsed environmental products Thisprogramme of research, and earlier work during the 1980s led to a reduction of between 50and 80% of potentially toxic elements in sewage sludge [Ulmgren 2000a]

The results of some more specific investigations into sources of potentially toxic elements inUWW are outlined below

Motor industry - vehicle washing

Scandinavian studies [SFT-1997a, 1997b, 1999] showed that the motor industry, followed byvehicle workshops contribute most to the potentially toxic element load in UWW Vehiclewashing, particularly heavy goods vehicles (HGVs), was found to be an important source ofpotentially toxic element contamination

In Sweden, oil separators are commonly used in vehicle washing and motor industriesbefore discharging effluent to UWW collecting systems Most facilities in Sweden arereported to be equipped with combined oil separators and sludge traps where the dispersedoil and sludge should be retained However, tests at one of the light vehicle (LV) washingfacilities showed that this equipment was ineffective with practically no difference betweenthe influent (before the separator) and the effluent (after the separator) This was due to theformation of stable emulsions in the wastewater caused by the detergents in themicroemulsion formulations used for vehicle washing [Paxéus, 1996b]

A study by the Norwegian Pollution Control Authority [SFT, 1999] examining potentially toxicelement pollutants in Norway found that out of six petrol stations investigated, only one had

an oil separator/sand trap that worked effectively Although designed to reduce thecontamination of urban wastewater, oil separating devices are generally ineffective atreducing pollutant emissions from vehicle washing and motor industry facilities

Dental practices and healthcare (mercury)

In the late 1980s, the high concentration of mercury in sewage sludge (SS) at HenrikdalWWTS, Stockholm, prompted an investigation to identify potential sources (Table 2.10) Itwas concluded that the high mercury content of sludge was attributable to dental practicesand the use of mercury in dental amalgams Amalgam separators were ineffective atretaining mercury and new legislation was introduced to combat this [Ulmgren, 2000a].Recent reduction or bans on the use of mercury in various products, such as batteries andthermometers, has led to a reduction of mercury input into UWW [Ulmgren, 2000a andUlmgren, 2000b] Mercury recycling schemes have also proved to be successful, and could

be extended to other countries and activities

Other discharges from dental technicians shops are covered in detail in Section 6, CaseStudies

Table 2.10 Sources of mercury in urban wastewater in Sweden

[Table adapted from text, Ulmgren 2000a]

Source Comments Heavy Industry no Ruled out as a source of mercury to UWW and SS as these were

not connected to the UWW collecting system

Small and

Medium

Enterprises

(18 Companies)

no Ruled out as they were operated in such a way that no

contamination of the wastewater was likely

Storm Drains yes 20% of the total mercury load came from storm drains This was

largely traced to the deposition of particulates emitted fromcrematoria which are estimated to be about 50 kg of mercury a year

Household

Wastewater

yes About 15% of the mercury entered the waste water system through

the use of mercury thermometers in the home, and also from smallamounts of mercury in food and amalgam fillings in teeth

Dentists and

Dental

Technicians

yes High mercury content of sludge was largely attributable to dental

practices and the use of mercury in dental amalgams

Hospitals yes Samples indicated that hospitals emit 10% of the mercury loading

Old Sewage

Pipes

yes Investigations in the last few years have found many sources of

mercury in old pipes

Similar findings have been reported in other countries A WRc report [1994] established that

in the UK mercury emissions are much higher from commercial, rather than domesticsources, mainly due to dental practices In France, it is estimated [Agence de l'Eau, 1992]that between 73 and 80 % of the mercury in UWW is from dental practices and amalgamfillings corrosion In the Louviers area of France, the analysis of wastewater and sewagesludge showed that out of the total load of mercury, 50% was lost from medical practices,13% from dentistry practices, 28% from medical auxiliaries (nurses etc.), 4% from hospitalactivities, 4% from veterinary activities, and 1% from ambulance activities Thus, in thisinstance, targeting medical/dental practices may help reduce pollution from mercury [LIFE,1999]

Other sources of mercury

In 1993, the amount of mercury entering France was 209 tonnes, the amount leaving Francewas 87 tonnes, and hence 122 tonnes were entering the environment in the form of waste[AGHTM, 1999-2000] (see Table 2.11)

Table 2.11: Mercury contained in waste

[from Dossier sur les dechets mercuriels en France: AGHTM, 1999]

Activity Amount (tonnes) % Treated and recycled

et.al, 1998] There appears to be potential for improved control and recycling of mercury

waste associated with these activities

Sources of chromium

Mine production of chromium in Finland has increased from 348 thousand tonnes to justover a million tonnes in 1990 [Mukherjee 1998], representing just under 10% of worldproduction The main sources of chromium in wastewater are from the metal, chemical andleather industries (Table 2.12) As can be seen, the chemical industry contributes over half

of the total emissions to UWW and surface waters in this region

Table 2.12 Chromium emissions to water in Finland [adapted from Mukherjee, 1998]

Emissions to water (not exclusively UWW) Source Category

tonnes per annum % of total contribution

Mukherjee [1998] reports that in Scandinavia, chromium compounds are also used in wood

chemicals (phenol and creosol)

All wet-textile processing in Finland discharges its wastewater, containing chromium andother metals, to the WWTS The textile companies studied [Kalliala, 2000] producedbetween 50 and 500 litres of wastewater per kg of textile produced Wastewater analyseswere carried out at six major Finnish textile companies (two of these include analysis forpotentially toxic elements (Table 2.13)):

Table 2.13 Potentially toxic elements in wastewater from textile processing in Finland

There is a very high variation in the process emissions between these two plants Company

2 was noted to use cellulose blends while company 4 was noted to have mainly polyesterand polyester blends

Sources of lead

Data from ADEME [1995] showed that worldwide consumption of lead is around 5.4 milliontonnes per year In a Swedish study [Palm, Östlund, 1996] in the Stockholm area the totalamount of lead used in products such as those listed previously, was estimated at between44,000 and 47,000 tonnes per annum Clearly the potential for lead entering UWW fromthese sources will vary greatly The largest amount of lead that finds its way to the WWTS islikely to be contributed by piping Estimates for the amount of lead used are 8,000 tonnes inlead jointed water pipes used inside buildings, followed by 2,000 tonnes used in lead jointedwater pipes used outdoors (higher replacing rate), and 120 tonnes used in PVC piping

In the case of Finland, the Ministry of the Environment report that the drinking waterpipelines are predominantly plastic (85% PVC and PEH), with 11% cast iron; no lead is usedfor pipes conveying water The wastewater pipes for the UWW collecting system are 57%concrete and 41% plastic

2.1.3 U RBAN RUNOFF

Runoff to UWW collecting systems and waterways has been intensely studied due to itspotentially high loading of potentially toxic elements [WRc, 1994] Atmospheric inputs to theurban runoff depend on the nature of surrounding industries, on the proximity of majoremission sources such as smelters and coal fired power stations and the direction of theprevailing wind Potentially toxic element loads can be five fold greater in runoff nearcommercial activities, than in residential areas far from industrial emitters Roof runoff andbuilding runoff also contribute to the total runoff loading and may be a source of considerableamounts of potentially toxic elements such as zinc, lead, copper and cadmium Road androof runoff sources are particularly important during storm events, which will allow flushing ofpotentially toxic elements and other pollutants from surfaces Furthermore, it is important tonote that the metal species released are usually in a freely dissolved, bioavailable form.Nevertheless, these sources are very variable, as every event is different and depends ontraffic, material and age of roofs and other surfaces, and meteorological and environmentalconditions

Although a number of studies had focused on the effects of urban land use in the

studies were undertaken [Palmer, 1950 and 1963; Wilkinson, 1956] Table 2.14 providesconcentrations for a number of potentially toxic elements in urban runoff, as a summary ofvarious investigations from 1975 to 1978 It is important to note that the measuredconcentrations differ considerably The main sources of pollution in urban precipitation runoffcan be summarised as follows [based on Mitchell, 1985]:

Table 2.14 Maximum and mean concentrations of potentially toxic elements (mg l -1 )

in urban precipitation runoff pollutants [after Mitchell, 1985]

Droste and Hartt, 1975

Mance and Harman,

1978

Mattraw and Sherwood, 1977

1

Focusing on pollutant loads in rainfall runoff

Table 2.15 Mean concentrations in rainwater runoff (in µg/l)

Garnaud et.al., [1999] attempted a comparative study between the main sources of pollution

in urban precipitation in Paris In this recent study of individual rain events, bulk sampleswere collected within four gutter pipes (roof runoff), three yard-drainage pipes (yard runoff),six gullies (street runoff) and one combined UWW collecting system, at the catchment outlet.The results can be seen in Figure 2.3 The values are median values

Figure 2.3 Comparison between main elements contributing to precipitation runoff in

respect to potentially toxic elements pollution load [after Garnaud et al., 1999]

A comparison of samples from consecutive phases of precipitation runoff (precipitation toroof runoff to urban runoff to catchment outlet) indicated that the potentially toxic elementconcentration increased by a factor of 12, 30, 30 and 60 for cadmium, copper, lead and zinc,respectively Corrosion of roof and urban surfaces as well as human activities contributes tothis contamination, including corrosion or emission from vehicles and commercial activities.Bulk metal concentrations were similar within all urban runoff samples except for zinc andlead, which were particularly concentrated in roof runoff samples, due to their contamination

by corrosion of roof materials At all sites it appeared that bulk metal concentrations could beranked as: Cd << Cu < Pb << Zn

Differences in potentially toxic elements concentration in precipitation water and runoff fromroofs and streets have also been found in a German study (Table 2.16) In this case it can

Table 2.16 Concentration changes of certain contaminants in precipitation water and runoff from different outflow paths, Germany.

[Xanthopoulos and Hahn, 1993] LOD Limit of detection

Pollutant Precipitation

[µg/l]

Run-off from roofs [µg l -1 ]

Run-off from streets [µg l -1 ]

A study carried out by Rougemaille (1994) analysed the wastewaters of the treatment plant

in Achères in the Paris region and found that lead concentrations varied between 0.05 and

four different urban areas The study showed that lead concentrations were 3 times largerduring wet weather than during dry weather, hence proving the importance of the runoffsources

A study carried out around the region of Nantes in France in 1999, analysed road runoff from

a major highway for a year showing that lead and zinc are the main pollutants present inrunoff waters (Table 2.17)

Table 2.17: Analysis of raw runoff waters [Legret, 1999]

PAH (ng l -1 )

Pb ( g l -1 )

Cu ( g l -1 )

Cd ( g l -1 )

Zn ( g l -1 )

A Road and vehicle contribution

Roads are a major source of pollution in urban environments and contribute to wastewaterpollution both directly and indirectly (airborne pollutants generation) Sartor and Boyd[USEPA, 1972] determined the major constituents of road related runoff to be inorganicmatter, but the total mass of inorganic matter present seemed to increase as the antecedentdry period (ADP) increased Sources of the organic and inorganic fraction of road-producedpollutants are summarised as follows:

Potentially toxic elements in runoff occur from motor fuel combustion, brake linings, tyrewear and road surface wear Motor fuel combustion was the largest source of lead to runoffbut it is on the decrease due to the gradual phasing out of leaded fuel in the EU Othermetals emitted from exhausts are zinc, chromium and more recently tin from thereplacement anti-knock compounds in petrol The presence of Zn and Cd in road surfacesediments can also be explained by the addition of Zn dithiophosphate in the manufacturing

of lubricating oil, Cd being present as an impurity of the original Zn Brake lining wearcontributes copper, nickel, chromium and lead to runoff Tyre abrasion contributes to theload of zinc, lead, chromium and nickel due to the soot and metal oxides constituents.Cadmium in car tyres is attributed to zinc-diethylcarbonate, which is used during thevulcanisation process Road surface wear contributes to emissions of nickel, chromium,lead, zinc and copper

Legret and Pagotto (1999) produced estimates of potentially toxic element content fromvehicle related pollution sources (Table 2.18), and contributions to road runoff (Table 2.19)

Table 2.18 Potentially toxic element contents in vehicle and road materials (mg kg -1 )

[after Legret and Pagotto, 1999]

Table 2.19 Emissions fluxes in precipitation runoff (kg km -1 annum) and percentage removed in drainage waters [after Legret and Pagotto, 1999]

Brakelinings

Vehicles

-Safetyfence

Road

De-icingagent

The percentages of these potentially toxic elements entering the drainage systems show that

a large proportion of the pollutants released do not end up in the runoff waters but areprobably emitted into the atmosphere The Zn content in urban runoff remains highly variabledepending on the use of safety barriers made from galvanized steel or from an alternativematerial All parameters are affected by traffic and by variables connected to themeteorological and environmental conditions of the sites concerned, which make the

comparison highly uncertain (Montrejaud-Vignoles et al., 1996).

The following mechanisms summarise the way the pollutants are transported (pathways)from the catchment over the roads and finally in the drainage network:

contaminants which are transported by the runoff water [Ellis, 1976; Sylvesterand DeWalle, 1972]

atmosphere either as dry particles or dissolved in surface water

Note that the first two mechanisms above result in pollutants being transferred ultimately intoreceiving waters or sewage sludge, while the last mechanism removes pollutants prior totheir ultimate disposal The general conclusion, however, is that the majority of road surfacerunoff contamination is sediment associated In particular, the prime transport mechanismsand pathways with respect to road-runoff sediment transport are [Sartor and Boyd, 1972]:

heavy fluid transport process

The transportation of surface particulates is sporadic in nature [Mitchell, 1985] Metal levelstend to fall after periods of rain, whilst elevated concentrations have been recorded afterprolonged dry periods Also introduced in the movement patterns are local storage andresidence effects due to the intrinsic configurations and micro-topography of the roadsurface [Harrop, 1983] The fact that contaminants move through this sequence is wellknown, however, the relationship between the contaminants and the various mechanismsinvolved are poorly understood Comparison of metal distribution during particle transport,

2

For value >100% the research identified larger concentrations in the samples than expected from the sources that were taken into account This is particularly true for Cd concentrations Additional sources of Cd (such as lubricating oils, as discussed earlier) may account for this underestimation.

from atmosphere to receiving water body, clearly demonstrates a metal mobility evolution

(Garnaud et al., 1999) Extremely labile (i.e hydrosoluble or exchangeable), within dry

atmospheric deposits Cd, Pb and Zn, become bio-available within street runoff and stablewithin UWW collecting system or river sediment In conclusion particulate metal mobility may

be classified as: Cu<<Cd<Pb<Zn<Fe

Potentially toxic elements are predominantly associated with inorganic particles andresearch indicates that potentially toxic element concentrations increase as particle sizedecreases (Sansalone and Buchberger, 1997; Lloyd and Wong, 1999) In particularColandini and Legret (1997), found a bimodal distribution with the highest concentrations of

Cd, Cu, Pb and Zn being associated with particles of less than 40 µm in size Table 2.18indicates the potentially toxic elements distribution across the particle size distribution for anumber of potentially toxic elements

Table 2.20 Approximate concentration of potentially toxic elements associated with particles [after Colandini and Legret, 1997]

Approximate concentration of potentially toxic elements

associated with particles (mg kg -1 )

Vehicle emissions:

more than 90% of atmospheric lead pollution Although the main source of lead in theaverage urban atmosphere is lead from fuel additives, it appears that only 5% of the leadcan be traced in runoff water The greatest part may, therefore, disperse in the atmosphere

or settle on the soil by the roadside (Hewitt and Rashed, 1990) The actual rate and form oflead emission is crucially dependent on driving conditions High engines speeds and rapidacceleration can increase emission levels due to reactivation of particles deposited on theexhaust system Total lead emissions can double if the engine and/or weather is cold The

the case of lead-containing fuel, approximately 75% of lead is discharged to the atmosphere(Hewitt and Rashed, 1990) and a further 20% is retained in engine sump oil (Wilson, 1982).Concentration of lead added to petrol has rapidly declined in the EU during the 1980s due tolegislation In Austria for example, the lead emissions between 1985 and 1995 have beenreduced by approximately 88 % [UBA, 1999] Figure 2.4 is indicative of this period of policychange (between 1972 and 1992) Note the high correlation between lead in petrol and leadair pollution despite the large rise in traffic flow experienced in the same period

Figure 2.4 Reduction in lead concentrations in air and petrol between 1972-1992

in the EU [after Montague and Luker, 1994]

and can be traced in the urban environment [Farago et al., 1995] These are covered in

detail in Section 6, case studies

3

Amid mounting concern that the lead dispersed in the environment was causing damage to humans and the environment, a series of regulations and directives have been adopted in Europe since the 1980s, in order to phase out the use of leaded petrol Lead content of petrol has been reduced from 0.4g l-1 to 0.15gl-1, following the Lead In Petrol Directive 85/210/EEC Further regulations on air quality have now come into force limiting the levels of lead in air, with an attainment date of 2005 Some countries, namely: Austria, Denmark, Finland, Germany, the Netherlands, Norway, Sweden, and the UK have already phased out its use.

However, in some countries in Eastern Europe, higher levels of lead are permitted, up to 0.4g l-1 In most of the newly independent states and the Russian Federation, permitted lead levels are 0.15-0.37 g l-1 Various strategies for reduction

of lead in petrol have been made in these countries, though it is expected that some will have difficulty in achieving these targets.

4

Platinum, palladium in vehicle exhaust catalysts and rhodium in three-way catalysts

Vehicle degradation:

Tyre wear releases lead, zinc and hydrocarbons, either in particulate form or in larger pieces

as a result of tyre failure The deposition of Zn on the road surface from tyres has been

nickel, are released by wear of clutch and brake linings Additionally, the presence of Ni and

Cr in storm runoff can result from the degradation of car bumpers and window sealingswhere both metals are used in the manufacture of chrome plating Copper is a commonconstituent of piping and other components of the engine and chassis work The contribution

to road surface material of vehicle tyres and brake linings from different road types has beensummarised in Table 2.22

Table 2.22 Input from tyre wear and brake lining degradation for each road category

[after Muschack, 1990]

Individual elements (g ha of road-1 annum-1)

Tyre wear

Brake lining

Tyre wear

Brake lining

Tyre wear

Brake lining

Tyre wear

Brake lining

Tyre wear

Brake lining Residential

These findings are also supported by evidence in non-EU countries Drapper et al (2000) in

an experimental site in Australia concluded that brake pad and tyre wear, caused by rapid

Laser particle sizing indicated that the median size (by volume) of the sediment found was

100 µm, but have settling times of around 24 hours under laboratory conditions Theexplanation offered to this unexpected behaviour is the presence of potentially toxicelements One of the most important findings of this study (which took into account bothAustralian and US research), was that traffic volume cannot account for more than 20-30%

of the variability of pollutant load variations and therefore a traffic volume criterion onwhether or not the precipitation runoff should be treated may not be acceptable Drapper et

al (2000) also stated that precipitation intensity and preceding dry days could be asignificant factor influencing actual pollutant concentrations It can be argued that a moresuitable criterion for treatment need assessment would be the environmental significance ofthe receiving waters

Road related sources:

Pollution in precipitation runoff from road-related sources stems mainly from maintenancepractices including de-icing, road surface degradation and re-surfacing operations

and it is suggested it may affect the solubility and mobility of other metals, notably of lead,which may precipitate more readily in the presence of sodium [Laxen and Harrison, 1977].The use of NaCl as a de-icing agent may change the behaviour of the accumulatedcontaminants in roadside soils In soils exposed to high Na concentrations with asubsequent supply of lower salinity water, as in snowmelt periods and storm flow events,there is a risk of colloid dispersion and mobilization [Norrstrom and Jacks, 1998] Soilcolumn leaching experiments with NaCl and low-electrolyte water have provided evidencefor the mobilisation of organic colloids and Fe-oxides, suggesting that potentially toxic

elements may reach the groundwater via colloid-assisted transport [Amrhein et al., 1992,

1993] Moreover, the use of road-salt may result in the increased mobilisation of potentially

toxic elements due to complexation with chloride ions [Doner, 1978; Lumsdon et al., 1995].

Complexed cyanide ion (in the form of sodium ferrocyanide) is added as anti-caking agent to de-icing agents, and compounds containing phosphorus may also be added as

rust inhibitors Novotny et al (1998) argue that although ferrocyanide is non-toxic in its

original form, its instability under predominant natural surface waters conditions, results in

cyanide form is only stable within the pH range 8 to 14 and zero to –600mV redox potential

al (1992) estimated similar rates of decomposition

Road surface degradation is likely to release various substances: bitumen and aromatichydrocarbons, tar and emulsifiers, carbonate and metals depending on the road constructiontechniques and materials used The following table provides some indication of theconcentrations of potentially toxic elements released from road surface abrasion, classified

by type of road encountered in urban areas

Table 2.23 Emissions from abrasion of urban streets surface material

[after Muschack, 1990]

Individual elements (g ha of road -1 annum -1 )

Type

of street

Total abrasion (kg ha of road -1

on wastewater treatment plants or directly to water receptors is hard to estimate due to therandom nature and the unpredictability to both the extent of the spill and its position relative

to the precipitation runoff system

In the case of chemical accidents, water or foam medium are used for road cleaningpurposes or for fire fighting The compositions of a typical and unusual load of the surfacerun-off are compared in Table 2.24

Table 2.24 Example of a typical and unusual load in run-off water from a German motorway [Ascherl, 1997, Krauth and Klein, 1982]

Parameter Run-off rain water- mean value

Table 2.25 Accidental spillages in Thames Region (UK)