EXPOSURE ANALYSIS -CHAPTER 14 docx

The results demonstrate that concentrations of many toxic pollutants lead, pesticides, and polycyclic aromatic hydrocarbons in homes often exceed the soil “screening levels” established

Part V

Multimedia Exposure

House Dust

John W Roberts

Engineering-Plus, Inc

Wayne R Ott

Stanford University

CONTENTS

14.1 Synopsis 319

14.2 Characteristics and Measurement of House Dust 320

14.3 Major Pollutants in House Dust 326

14.3.1 Lead: Sources, Pathways, Trends, and Effects 326

14.3.2 Reducing Lead Exposure from House Dust 330

14.3.3 Pesticides, Polycyclic Aromatic Hydrocarbons (PAHs), Phthalates, and Other Toxic Pollutants 332

14.4 Control of House Dust 337

14.4.1 Cleaning 337

14.4.2 Why Vacuum Cleaners Do and Do Not Work 338

14.5 Master Home Environmentalist™ Program 339

14.6 Health Care Cost Savings 341

14.7 Making a Plan to Reduce Your Personal Exposure 342

14.8 Questions for Review 342

14.9 Acknowledgments 343

References 343

14.1 SYNOPSIS

House dust presents a special problem: it is not routinely measured; it has been found to contain

a large number of toxic pollutants; and it presents potential health problems for infants and children who have small body mass and developing organs, spend large amounts of time near floors and carpets, and engage in hand-to-mouth activities Specially designed vacuum cleaners, the HVS3 and HVS4, have been developed to collect large samples of house dust from carpets and bare floors,

as well as dust from outdoor surfaces such as streets, sidewalks, and lawns These standardized vacuums have been used since 1990 to collect house dust samples as part of numerous studies of American homes The results demonstrate that concentrations of many toxic pollutants (lead, pesticides, and polycyclic aromatic hydrocarbons) in homes often exceed the soil “screening levels” established for Superfund sites There has been a dramatic reduction in the lead in gasoline and children’s blood since 1990 However, one in three children under 6 years of age still lives in a house with a lead-based paint hazard Homes built before 1940 present the most risk for toddlers

A major cause of the high pollutant concentrations in house dust is the preferential “track-in” ofsmall dust particles from outdoor soil containing exterior paint of older homes, pesticides fromlawns and gardens, air pollution fallout, allergens, and vehicular pollutants found on streets andsidewalks Deep dust in ordinary carpets acts as a sink and source of these pollutants and is themajor source of pollutants in surface dust Human activity in a room causes carpet dust to beresuspended The present expenditure of public funds at most Superfund sites is not efficient inreducing total exposure The exposures from indoor dust and air are usually much higher than thosedue to many Superfund sites Fortunately, pollutant concentrations and loadings from house dustcan be reduced in most homes by relatively simple steps, such as removing shoes before enteringthe home, using a commercial-grade door mat, reducing carpets indoors, selecting carpets and floorsurfaces that are easy to clean, dusting, and vacuuming frequently with a vacuum cleaner equippedwith an agitator brush and a dirt finder Many environmental pollutants reach people through onlyone carrier medium For example, we are exposed to carbon monoxide (CO) only through the air

we breathe For single-medium pollutants, a multimedia exposure analysis is not appropriate Forothers, a multimedia analysis may be necessary to determine the concentrations of each pollutant

in each medium, which may include house dust, ambient air, drinking water, and food Pollutantsfor which multimedia exposure analyses are appropriate include lead (Pb) and polycyclic aromatichydrocarbons (PAHs)

14.2 CHARACTERISTICS AND MEASUREMENT OF HOUSE DUST

It should come as no surprise to anyone who has cleaned the interior of a home that a layer ofparticles called “house dust” accumulates rapidly on surfaces, such as floors, shelves, and window-sills We have all observed layers of dust that have settled on tables, chairs, sofas, light fixtures,bookshelves, floors, cupboards, figurines, and on other surfaces in a home Even after just a fewweeks, the layer of dust becomes thick enough to be visible to the eye and is easily picked up onfingers touching horizontal surfaces Anyone who has operated a vacuum cleaner can rememberemptying clumps of gray-brown matter from the collection bag after an hour or two of vacuuming.Indeed, removal of house dust is such a common household chore that the vacuum cleaner, amotorized air movement filtering system equipped with a moving agitator brush, was invented tohelp residents collect house dust Feather dusters, invented to dislodge the dust from householdobjects and surfaces, simply spread dust around and are of dubious value Area rugs have beenused for thousands of years and can be cleaned by hanging them on a wire and beating them orwashing them with water Wall-to-wall carpets were not popular before the vacuum cleaner wasinvented, in part because they could not be cleaned adequately

How does one go about measuring quantitatively the exposures of children and adults topollutants in house dust? In 1987, engineers John Roberts and Mike Ruby, working under a contractwith the U.S Environmental Protection Agency (USEPA), developed the High Volume SurfaceSampler (HVS2), a special-purpose vacuum cleaner designed to collect house dust from surfaces

in a standardized manner for subsequent chemical analysis for exposure assessment purposes(Roberts et al 1991a) The HVS2 has a known and reproducible dust removal rate on various types

of test surfaces and relatively constant efficiency at different loadings of surface dust The HVS2weighed 55 lbs, was expensive ($8,000), and difficult to operate This first test model soon evolvedinto the HVS3, a 24-lb vacuum cleaner costing around $3,000 that could be used to collect a large,representative sample of house dust from indoor sources such as carpets, rugs, and bare floors, anddust from outdoor surfaces such as streets, sidewalks, lawns, and bare, packed dirt (Roberts et al.1991b) (Figure 14.1) The HVS3 vacuum is recognized in American Standard of Testing Materials(ASTM) method 5438-00 and is now available commercially from CS3, Inc (Sandpoint, Idaho).Due to its high airflow volume (17–20 cubic feet per minute [cfm] or 8.1–9.5 l/s), the HVS3dust sampler can collect a 10-minute sample that is large enough (2–200 grams, [g]) to permitsubsequent laboratory chemical analyses and bioassays This specialized vacuum cleaner system

maintains uniform sampling conditions by measuring and controlling the airflow and pressure dropacross a 5-inch (14-cm) nozzle A 3-inch (7.5-cm) cyclone collects more than 99% of the housedust that enters without any reduction in airflow The cyclone “catch cup” can be used to transportthe sample for laboratory analysis The dust that is collected in the cyclone cup is usually sievedthrough a 100-mesh sieve so that only dust below 150 microns in diameter is analyzed This cutpoint was selected because these particles stick to skin and hands better and present more risk.Approximately 140 of these specialized vacuum cleaners were in use throughout the world in 2005,and a number of scientific papers using the HVS3 have reported results for lead, pesticides, andother pollutants in house dust These results can be compared with each other, since the operators

of the HVS3 are all using the same standardized method The HVS4, developed in 2001, is a17-pound simplified version of the HVS3 that is easier to carry, operate, and purchase

House dust, because of its proximity to pets, children, and adults, has considerable potentialfor exposing the occupants of a home to toxic and hazardous pollutants Pollutants in dust increasethe potential exposure of all people and pets, especially infants and toddlers who crawl and mouththeir hands and other objects Dogs and cats that clean their fur with their tongue will also ingestpollutants in house dust and soil that they contact These animals may have high health risks from

Pb in an old house that is being painted or remodeled The average infant’s daily dust ingestionrate, estimated to be 100 milligrams per day (mg/day), is more than two times that of adults Elevenpercent of toddlers may exhibit pica behavior, eating nonfood items, and may consume up to 10 g

of soil and dust per day (Calabrese and Stanek 1991; Mahaffrey and Annest 1985) Potential risks

to small children, when compared to adults, are further increased due to their smaller size, higherratio of surface area to body weight, and the stage of development of their organs, nervous systems,and immune systems (Woodruff et al 2003; Roberts et al 1992) Figure 14.2 illustrates the role

of house dust as a carrier medium for pollutants reaching a baby, compared with the quantity offood eaten, air breathed (6.3 m3/day), and water drunk (1 liter/day) House dust gets into indoorair, food, and water However these routes of exposure to house dust are not important whencompared with the 100 mg that the average infant ingests (Calabrese and Stanek 1991) A baby’sdust intake from indoor air is estimated to be 0.1 mg/day A general finding from research conductedthus far is that house dust often contains a great variety of pollutants that should be of concern forthe health of residents (Roberts et al 1992; Camann and Buckley 1994; Rudel et al 2003; Maertens,Bailey, and White 2004) Pollutants found in house dust include lead, cadmium, chromium, mercury,arsenic, other toxic metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls(PCBs), dichloro diphenyl trichloroethane (DDT), phthalates, fire retardants, and other persistent

FIGURE 14.1 Special purpose vacuum, the HVS3, designed to collect a large quantity of dust in a

standard-ized manner for laboratory analysis of the sample’s chemical composition and pollutant concentration tesy of Dr Robert Lewis, USEPA; see also Chapter 15 and Figure 15.4.)

(Cour-pesticides House dust is a major pathway for children and adults for the flame retardantspolybrominated diphenylethers (PBDEs) (Stapleton et al 2005; Jones-Otazo et al 2005) Housedust also contains pollutants that come from window cleaners, laundry detergents, spot removers,plastics, electronics, and carpeting Concentrations of these pollutants may exceed USEPA health-based standards (Rudel et al 2003).

Most of the pollutants in the ambient air may be deposited with particles on the roof and siding

of houses and be washed down to the foundation soil and walkways Measurements (Adgate et al.1998) show that carrying the pollutant indoors on the shoes, or “track-in,” is one of the largest sources

of house dust in most U.S homes (Figure 14.3) There appears to be a preferential track-in of smallparticles because they stick to shoes better (Roberts et al 1996) The small particles have a highersurface area (and toxicity) per unit mass This is the best theory to explain why the concentration oftoxic pollutants found in house dust are higher than those found in soil around the house and canequal or exceed street dust concentrations found in front of the house (Roberts et al 1992) Mostparents do not allow their infants to play in street dusts because of the known toxic pollutants invehicle exhaust, motor oil, and asphalt However, increased awareness of the pollutants in house dustmay cause parents to put a clean sheet down before they allow a baby to play on a carpet and also

to learn effective methods of cleaning to protect themselves and their children

House dust on carpets is easily resuspended into the air of a room where occupants breathe it

as airborne particulate matter In an experiment by one of the authors (Ott) in a Palo Alto, CA,home, two occupants purposely “stomped” on the carpet, plush shag, for 18 minutes after eatingdinner and relaxing (Figure 14.4) The mass concentration of particulate matter of 5 micrometers

or smaller (PM5) measured at a height of 30 inches above the floor rapidly increased in the room

as soon as the stomping began The doors and windows were closed as usual, and the particleconcentrations did not return to normal levels until about 1 1/2 hours later

Most people may be unaware of the ease by which particles are stirred up in their homes, orresuspended, after just a small amount of physical indoor activity Because of their small size,resuspended fine particles are not easily seen by the eye, even though they may surround us indoors.Indeed, one might conclude that we live in a “sea of particles” in our homes The “particle loading”

is often higher inside than outside and in some homes is much higher than in others, depending

on the activities of the occupants, the presence of pets, and the steps taken to reduce house dust

FIGURE 14.2 Estimated quantity of dust per day reaching a small child from dust ingestion, drinking water,

breathing, food ingestion, and dermal contact.

DRINKING WATER

1 liter/day

BREATHING 6.3 m 3 /day

FOOD

DERMAL CONTACT WITH DUST

Overall, five important steps can help reduce the levels of house dust:

• Wiping shoes twice on a commercial grade door mat before entering the home

• Removing shoes while in the home

• Frequent and thorough vacuuming of carpets and furniture

• Removing deep dust from carpets with a vacuum with a power head and an embeddeddirt finder

• Cleaning all surfaces inside the home on a regular basis

A commercial-grade doormat can be obtained by making a special order at a large hardwarestore The “twister” mat often found in front of department stores is an example of a high-qualitymat

FIGURE 14.3 Dust tracked in from outdoors contains lead, pesticides, and other pollutants The dust collects

on floors and surfaces and becomes embedded deep in the weave of carpets It becomes resuspended when people walk on floors, exercise, or breathe particles It can be ingested directly by toddlers engaging in hand- to-mouth activities Using a doormat, removing shoes, and frequently cleaning with an agitator-equipped vacuum can reduce indoor concentrations of these pollutants.

WY Califo rnia

Dust containing

pesticides

▼

pick up toxics

in dust

▼

Dust tracked-in

Persons with allergies, asthma, and heart problems have special health risks due to resuspended

particles indoors Books such as Allergy-Free Living (Howarth and Reid 2000) list dozens of steps

a resident can take to decrease exposure to the major interior allergens and irritants by creating ahealthy, allergy-free home and lifestyle Asthma is a leading cause of chronic disease and absen-teeism among schoolchildren in the United States, and an increasing incidence of asthma in theUnited States suggests that efforts to reduce fine particles (that include dust mites, mold, and catdander) indoors could produce health benefits for both children and adults (Krieger et al 2005).Although it is possible to reduce resuspension of carpet dust by frequent vacuuming and otherpractical steps, many people do not realize that an extremely thorough vacuuming is needed toremove embedded dust particles Even after extensive vacuuming, large amounts of dust remaindeeply embedded in the fabric of the carpet Some new vacuum cleaners are equipped with anembedded dirt finder, an electronic sensor system with red and green signal lights that the operatorcan easily see while vacuuming The light is red when the vacuum is picking up particles, but itturns green when the noise made by the particle stream hitting a sensor plate drops below a fixedlevel Removing the deep dust from an old carpet for the first time may require vacuuming someareas of the carpet for surprisingly long time periods, sometimes up to 45 minutes per square meter(min/m2) of carpet, to get a green light on the dirt finder In two studies of 11 and 10 older carpets

in the Seattle area, the median time to remove the deep dust was 8 and 20 min/m2, respectively(Roberts et al 1999; Roberts, Glass, and Mickelson 2004) Once the “deep dust” is removed, it isrelatively easy to keep it out by frequent vacuuming and use of a commercial grade doormat A 6-meter long high-quality doormat reduced dirt track-in at an elementary school from 12 to 2milligrams (mg) per person (Lehen 1983), a reduction of 83%

One of the authors (Roberts, Glass, and Mickelson 2004) developed a “3-spot test,” a method

to estimate how much deep dust resides in a carpet and the time required to remove the dust Themethod uses a vacuum cleaner equipped with an embedded dust finder, such as the upright HooverVacuum Model U 6445-900 The 3-spot test consists of the following procedure:

FIGURE 14.4 Particle mass concentration measured indoors before, during, and after 18 minutes of stomping

activity by two people on an old shag carpet in an efficiency apartment in Palo Alto, CA, with the doors and windows closed The piezobalance fine particle monitor was located at a height of 30 in (0.76 m) and within

4 ft (1.2 m) of the two stomping persons, who rested before and after the stomping activity.

Talking, Relaxing

Resting, Talking

• Choose a spot in the center of the carpet.

• Start the vacuum and a stopwatch at the same time Hold the vacuum in one place untilthe light turns green

• Then move the vacuum quickly without stopping it to a second spot 3 feet away andhold it in one place until the light turns green Repeat this procedure for a third spot.The three spots should form a triangle with equal sides

• Note the total time required to clean all three spots

When the time required for the dust detector light to turn green is less than 11 seconds for all

3 spots, the carpet is considered relatively clean with 6 seconds being an achievable goal Roberts,

Glass, and Mickelson (2004) found that the surface dust (g/m2), deep dust (g/m2), and dust collectionrate (g/min) tended to drop rapidly at first and then much more slowly during vacuuming An HVS4was used to measure the surface dust For this study the starting surface dust loading was 0.7–21.1g/m2, which decreased by 85–99% when the deep dust was removed Vacuuming times rangingfrom 2.3–95 min/m2 were required to remove the deep dust

Until the deep dust is removed, it will tend to rise to the surface of the carpet and becomesurface dust Activity in the room brings up deep dust Lead concentrations from two sequentialsamples of surface dust on a carpet in a remodeled house increased from 180 parts per million(ppm) to 59,800 ppm (Roberts, Glass, and Mickelson 2004) The surface lead loading increased

by a factor of 60 on the second sample We theorized that a layer of lead paint from remodelingactivity was uncovered as the deep dust was removed Measuring the lead surface loading, in units

of micrograms per square meter (µg/m2), is one of the best ways to predict the amount of lead inthe blood of an infant who crawls on such a carpet in an old house (Davies et al 1990) Estimatingdeep dust with the 3-spot test and measuring the lead in the deep dust collected in the 3-spot testand a small area inside the 3-spot triangle, may also predict lead in the blood of an infant Surfacedust shows much more variation than deep dust Since deep dust is the major source of the pollutantsthat appear in surface dust, removal of deep dust tends to reduce the risk from surface dust bymore than 90% (Roberts, Glass, and Mickelson 2004)

There may be an analogy between vacuuming the deep dust from a carpet in a home anddigging at an archeological site; both efforts uncover the historical record of past events Everyindividual who enters a home interacts with its dust history They take dust from a room when theyleave and make a unique contribution to the dust with skin scales, clothing fibers, dust falling offclothes, and tracked-in dust The DNA in skin scales and unique clothing fibers can theoretically

be used to identify past room occupants (National Institute of Justice 2002) They take away a

“fingerprint” of the dust from the room that collects on their clothes

Replacing house carpets with bare wood floors will eliminate the tendency for carpets andbacking to act as a reservoir for pollutants Bare floors are easiest to clean Flat and level loopcarpets are also easy to clean, with carpet cleaning difficulties increasing for short plush carpets,deep plush, and shag carpets, respectively Spilled liquids may initiate mold growth in a carpet that

is not dried in 24 hours Interface (www.interfaceinc.com) as well as Collins and Aikeman(www.powerbond.com) make carpets with low volatile organic compound (VOC) emissions andwaterproof backing that are around 50% easier to clean The cost of installing a Powerbond carpet

in a Seattle apartment in 2005 was $3.50/ft2

While there may be health advantages for bare floors, the homeowner must consider the costsand benefits of different types of floor coverings Ceramic, solid hardwood, laminated hardwood,and linoleum floors are long lasting but more expensive Vinyl tile floors are lower in cost but haveVOC emissions Carpets reduce noise, are softer to walk on, and may reduce falls Bare floors inclassrooms may require architectural and surface material changes to reduce noise

14.3 MAJOR POLLUTANTS IN HOUSE DUST

14.3.1 L EAD : S OURCES , P ATHWAYS , T RENDS , AND E FFECTS

Lead is unique among the toxic heavy metals because of its abundance in the Earth’s crust Because

of its easy isolation and low melting point, lead was among the first metals to be used by humansthousands of years ago The environmental significance of lead is a result both of its utility and itsabundance World production of lead, about 4 million tons per year, is larger than the commercialproduction of any other toxic heavy metal (USEPA 1986)

Lead is present in food, water, air, soil, dustfall, paint, and other materials with which thegeneral population comes into contact Each of these is a potential pathway for human exposure

to lead through inhalation or ingestion The actual lead content in each environmental medium mayvary by several orders of magnitude Individual exposure is further complicated by different activitypatterns and differences in indoor and outdoor microenvironments

Centuries of mining, smelting, and usage have made the natural background concentration oflead difficult to determine Geochemical data indicate that the concentrations of lead in most surfacesoils in the United States range from 10–30 ppm or µg/g (USEPA 1986) Unlike gaseous pollutants,where 1 ppm denotes a part-per-million by volume, trace metals like lead usually are reported inmass ppm units, and 1 ppm by mass is equivalent to 1 microgram of lead per gram of soil, or 1 µg/g.Trace amounts of lead occur naturally in air and water as a result of wind and rain erosion,and in air as a result of volcanic dusts, forest fires, sea salt, and the decay of radon Naturalbackground concentrations of airborne lead have been estimated as approximately 0.0006 µg/m3

or 5 × 10–7µg/g Estimated natural fresh water and ocean water lead concentrations are about 0.5

µg/L of water (5 × 10–4µg/g water) and 0.05 µg/L (5 × 10–5µg/g water), respectively (USEPA 1986)

As a consequence of the diverse uses of lead in products, including its extensive history of use

in gasoline and house paint in the United States, the present concentrations of lead in air, soil, andwater are higher than these estimated background levels Typical average nonurban lead concen-trations in air are about 0.01 µg/m3 (USEPA 2004) Prior to restrictions on the lead content ingasoline in the United States, typical ambient lead concentrations in U.S cities averaged about 1.5

µg/m3 (Woodruff et al 2003)

Concentrations of lead in most urban water supplies are well below 10 µg/L standard for water(0.01 µg/g water) (Woodruff et al 2003) However, values above 50 µg/L have been reported insome locations on occasion Suspended solids contain the major fraction of lead in river waters.Concentrations of lead in tap water may be considerably higher than those in municipal supplies.Lead values as high as 2,000 µg/L have been reported for homes with lead pipes and lead-linedstorage tanks Efforts to reduce the effect of lead solder joints in copper pipes and fittings andgreater use of plastic pipe has reduced the levels of lead in residential tap water Running the tap

a few minutes before using tap water can help reduce lead concentrations in cases where lead isadded by a home’s plumbing system

The contribution of food to human exposure to lead is highly variable and not well quantified.Estimates of the daily intake of lead from food vary from about 100–350 µg/day Historically, foodsstored in lead-soldered cans or stored or served in imported glazed pottery were identified as havinghigh lead content (ATSDR 1989) In the United States there have been efforts to reduce the contactbetween lead-containing containers and foods

Use of lead as an antiknock additive in gasoline historically accounted for a major share ofU.S lead production Consequently, motor vehicles constituted the major source of atmosphericlead emissions As a result of legislation that limited the lead content of gasoline, the productionand use of alkyl lead additives decreased in the United States beginning around 1978 Beginning

at this same time, concentrations of lead in ambient air have shown a similar downward trend In

1977 ambient air lead concentrations at 78 sites in the United States averaged 1.5 µg/m3 By 1984ambient air lead levels in the United States had dropped to an average of 0.3 µg/m3 In 1995 ambient

air lead concentrations in the United States had continued to decline, reaching an average of about0.1 µg/gm3, which is close to the background concentrations measured years earlier in nonurbanareas (USEPA 1986; Woodruff et al 2003).

Lead happens to be one of the few environmental pollutants for which long-term data areavailable on an important biomarker of dose, the concentrations in the blood of U.S citizens.Elevated blood lead levels are a predictor of adverse health effects, including anemia and braindamage The U.S National Center for Health Statistics periodically conducts the National Healthand Nutrition Examination Survey (NHANES) In this survey, as many as 22,000 respondents arestatistically selected and given a physical examination that includes a detailed questionnaire abouttheir current health, diet, and activities Blood drawn from a subset of the NHANES respondents

is analyzed by the U.S Centers for Disease Control (CDC) to determine blood lead concentrations.The results indicate a downward trend for blood lead concentrations of Americans over the 14-yearperiod from 1976–1990 (Figure 14.5) This downward trend is continuing to the present time androughly correlates with a similar downward trend in the lead content of gasoline (Woodruff et al.2003) Measurements of average blood lead levels for the U.S population based on NHANES-II,NHANES-III, and follow-up national surveys indicate that average blood lead levels for the U.S.population have continued to drop through 1999, but at a lower rate (Figure 14.6)

The median blood lead concentration of children 5 years old and younger dropped from 15micrograms per deciliter (µg/dL) for the 1976–1980 period, to 2.2 µg/dL for the 1999–2000 period.However, 10% of children during 1999–2000 still had blood lead concentrations above 4.8 µg/dL,

a level which is still of considerable concern (Woodruff et al 2003) The data presented in thischapter suggest that over 50% of adults 25–35 years of age in 2005 have had their intellectualpotential reduced by exposure to lead in childhood

Despite this downward trend in blood lead levels nationwide, many children and adults stilllive in older homes that contain risks from lead-based paints The possibility that elevated blood

FIGURE 14.5 Measurements of blood levels in Americans based on the National Health and Nutrition

Examination Survey (NHANES) from NHANES-II (1976–1980) and NHANES-III (1988–1991), compared with the amount of lead used in U.S gasoline (Personal communication with David M Mannino, Centers for Disease Control, Atlanta, GA, 2002.)

lead concentrations is due to indoor contaminants continues to warrant scrutiny A U.S Department

of Housing and Urban Development (HUD) (Clickner et al 2001) national survey of lead from arepresentative sample of U.S housing found that one in three children under the age of 6 live in

a house with a lead-based paint (LBP) hazard In this study, the term “LBP hazard” referred todeteriorating paint, which indicated problems of lead-contaminated dust indoors or lead-contami-nated soil from lead-based paint outdoors A significant LBP hazard is defined by the HUD safehousing rule on lead as follows:

Lead-contaminated dust — Dust on floors (bare or carpeted) with greater than or equal to

40 µg/ft2 lead, dust on windowsills greater than or equal to 250 µg/ft2 lead as measuredwith wipe method

interior or damage to 10% of the total surface area of interior small surface area components(window sills, baseboard, trim) LBP is defined as paint or other surface coatings (varnish,lacquer, or wallpaper over paint) that contains lead equal to or greater than 1.0 mg/cm2

to or greater than 2,000 ppm lead, or 400 ppm for soil frequented by child under the age

of 6 years

Of the 16.4 million homes with children under the age of 6, 5.7 million (34%) have LBPhazards About 17 million houses have interior dust hazards, 14 million houses have deterioratedLBP, and 6 million houses have soil lead hazards Some 39% of homes with interior LBP exceedthe LBP hazard rule Some 6% of the 67 million houses without interior LBP exceed the samestandard Lead may be tracked in from the outside or tracked home from the job Hobbies mayalso contaminate house dust with lead Only 2% of the 87 million homes without deteriorated LBPhave lead in the soil above 2000 ppm Clean homes have fewer LBP hazards Some 15% of allhousing showed no evidence of cleaning (Clickner et al 2001)

FIGURE 14.6 Measurements of blood lead levels in Americans based on the National Health and Nutrition

Examination Survey (NHANES) from NHANES-II (1976–1980), NHANES-III (1988–1991), and NHANES for 1999 and beyond (Personal communication with Larry Needham, Centers for Disease Control and Prevention, Atlanta, GA, 2004.)

1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

Median Blood Lead for Children Aged 5 Years or Less (1999 to 2000 Period)

Year

BLOOD LEAD LEVELS IN THE U.S POPULATION 1976–1999

There are various physiological effects of lead that occur at the subcellular, cellular, and organsystem level A number of significant effects of lead on the blood have been observed in leadpoisoning These effects are prominent in clinical lead poisoning but are still present to a lowerdegree in persons with a lower level of lead exposure Although a level of health concern for bloodlead has been set at 10 µg/dL, it is believed that there is no true lower threshold at which adverseeffects are nonexistent (Canfield et al 2003) Anemia is a clinical feature of lead poisoning Inchildren, symptoms of anemia occur at blood lead levels of 40 µg/dL and in adults at levels of 50

µg/dL The effects of lead on the nervous system range from acute intoxication behavior and fatalbrain damage to more subtle changes associated with lower levels of exposure, such as reducedcoordination and reduced intelligence (USEPA 1986, 1990; ATSDR 1989)

The most extreme effects of lead poisoning, severe irreversible brain damage, chronic alopathy (brain damage) symptoms, or death, have been known to occur at surprisingly low levels

enceph-of blood lead However, for most adults such damage does not occur until blood lead levelssubstantially exceed 120 µg/dL, although some evidence suggests that acute encephalopathy (braindamage) and death may occur at blood lead levels slightly below 100 µg/dL (ATSDR 1989) Forchildren, the effective blood levels for producing encephalopathy or death are lower than for adults,with such effects being seen somewhat more often starting at blood lead concentrations of approx-imately 100 µg/dL Studies also suggest that severe neural damage can exist without obvioussymptoms, and children with high blood lead concentrations (greater than 80–100 µg/dL) arepermanently impaired cognitively (USEPA 1986, 1990; ATSDR 1989)

The blood lead concentrations at which neurobehavioral deficits occur in children who exhibit

no other symptoms appear to start at about 50–60 µg/dL Mounting concerns about the adversehealth effects of lead on children have given rise to a protective concentration set at 10 µg/dL, butthere are concerns that subtle neurological and cellular effects such as lowered IQ could occur insome children below this level Canfield et al (2003) measured the blood lead concentrations of

172 children every 6 months for 5 years starting at age 6 months The intelligence (IQ) was measured

at 3 and 5 years The IQ was inversely and significantly associated with lead in blood showing adecline of 4.6 points for every 10 µg/dL increase in blood lead concentrations The IQ decline forchildren whose blood lead concentrations remained below 10 µg/dL was greater IQ declined 7.4points as average blood lead concentrations increased from 1 to 10 µg/dL

Two pollutants for which multimedia exposure assessments are important are lead (Pb) andpolycyclic aromatic hydrocarbons (PAHs) Multimedia scientific studies, although limited, havesought to quantify the contributions of outdoor air, indoor air, house dust, food, and drinking water

to population exposures for these two multimedia pollutants

The most effective exposure analysis for some pollutants in house dust is one that examinesall relevant environmental carrier media by which the pollutant reaches a particular target, such as

a human being Ideally, this multimedia exposure analysis determines how often individuals in apopulation are exposed to concentrations that exceed critical thresholds, and the contribution ofindividual sources to the total exposure A frequency distribution provides information on thepercent of individuals exposed to different concentration levels for an averaging time of interest,such as 24 hours For example, the percent of people exposed to outdoor air quality concentrationsgreater than the 24-hour air quality standard is useful for planning health-based initiatives.Surprisingly, few multimedia exposure analyses have been carried out for several reasons.Significant concentrations of the pollutant of interest found only in one medium negate the need

to study other media The pollutant of interest may only travel through one carrier medium Data

on a pollutant in a specific carrier media are usually not available Exposure levels themselves areimprecisely known, or it is unclear how the exposure actually occurs Thus, there are few multimediaexposure analyses available in the literature

Multimedia exposure analyses can be extremely important for setting regulatory policies.Determining the amount of exposure attributable to each carrier medium can help provide a decisionmaker with guidance about reducing total exposure in a manner that protects public health

effectively and is least costly to society Fortunately, the absence of complete multimedia exposureanalyses for many agents is not as limiting as it might seem Many pollutants, such as carbonmonoxide (CO), reach human beings through only one carrier medium, inhaled air It is notnecessary to consider house dust, food, or drinking water when evaluating contact with CO.Similarly, many toxic volatile organic compounds (VOCs) present in the air we breathe are alsofound in food and drinking water at negligible concentrations For these pollutants, a reasonablyaccurate exposure analysis may be done on indoor and outdoor air.

14.3.2 R EDUCING L EAD E XPOSURE FROM H OUSE D UST

Adgate et al (1998) used a chemical mass balance approach to find the major contributors of lead

to indoor house dust obtained from 64 homes in Jersey City, NJ To apply the chemical massbalance approach, the authors looked at the relative concentrations of lead and 16 other elements

to help identify the “chemical profiles” of individual sources For both coarse particles (up to 60micrometers) and PM10 (particulate matter with aerodynamic diameters 10 microns or less) outdoorair was responsible for approximately two-thirds of the lead found in house dust Suspended crustalmaterials from soil and deposited airborne particulate matter comprised the outdoor air sources.Interior lead-based paint sources contributed the remaining third Thus, about one-third of theindoor lead was associated with old paint on surfaces, while two-thirds of the lead was from outdoororigin, including tracked-in yard soils and street dusts

Lioy et al (1998) studied the effectiveness of cleaning protocols in homes of children found

to have moderate lead poisoning (blood lead levels of 10–20 µg/dL) Samples were collected inthe homes at least twice, and in some cases three times, during the course of a yearlong randomizedstudy in which half the homes used a heavy-cleaning protocol and the other half used a light-cleaning protocol Both wipe sampling and a standard vacuum sampling were employed to evaluatethe dust and Pb loading on bare and carpeted surfaces When compared with the values seen onthe first visit vacuum sampling, the results showed statistically significant decreases in lead anddust loading for the heavy-cleaning protocol For the light-cleaning protocol, the sampling resultsfound no significant reductions in dust and lead loading among any of the room surfaces sampled

In contrast, there were 75% and 50% reductions observed on the windowsills and on the bedroomfloors of the homes in which the heavy-cleaning intervention took place

The Superfund law requires a risk assessment when the concentrations of pollutants in dential outdoor soil exceed limits specified as the Preliminary Remediation Goals (PRGs) PRGlevels for many toxic pollutants are listed in USEPA tables as the upper concentration limitsacceptable for protecting people, including crawling children, from the health risks associated withoutdoor soil (Smucker 1995) These levels are used by risk assessors to help decide the level ofremediation at these sites Surprisingly, concentrations of pollutants found in the dust of ordinaryhomes often exceed these Superfund PRG remediation limits When these laws initially werewritten, the initial framers may not have been aware of the high residential indoor pollutantconcentrations in American homes For example, the PRG level for lead is 400 mg of lead per kg

resi-of material (that is, 400 µg/g or 400 ppm by mass)

Over a 7-year period from 1993–2000, more than 150 Master Home Environmentalist volunteers

in Seattle agreed to collect house dust samples in their homes as part of their training and for astudy conducted by one of the authors (Roberts) They used upright vacuums, most of which wereequipped with dirt finders, to collect the samples on a section of carpet in their homes The samplessubsequently were sieved and analyzed by x-ray fluorescence mass spectrometry for lead content.The results showed that the percent of Seattle homes built before 1940 with indoor house dust leadconcentrations above the 400 ppm Superfund PRG screening limit was 51% as shown in Figure14.7 The horizontal axis of this logarithmic-probability graph lists the proportion of the housesbelow the stated concentration level given on the vertical axis By comparison, only 4% of thehomes built after 1940 had indoor house dust lead concentrations above 400 ppm by mass This

dramatic difference in indoor dust concentrations with the age of a home is evident in the difference

in mean lead concentrations for these two groups of homes; the mean lead concentration for the

63 older homes was 519 ppm, vs 146 ppm for the homes built after 1940

The lead content of paint began to drop after 1940, and strict limits on the lead content of paintwere imposed in 1978 Much of this lead found in house dust can be attributed to the soil aroundthe homes Lead in yard soil is attributed to a home’s exterior paint and to road dust, but cannot

be attributed to Superfund sites (Adgate et al 1998) These results show that many American homeshave interior lead concentrations on floors and carpets that are higher than the soil lead levelsrequired to trigger a risk assessment under the Superfund Act Remediation goals may be loweredbelow the PRG for individual chemicals when there are multiple pollutants at or near the PRGlevels as found in house dust (Roberts 1998)

Children probably visit most Superfund sites rarely, if ever They are much more likely to beexposed to lead while playing on floors and surfaces in their own homes, particularly if their home

FIGURE 14.7 Distributions of lead concentrations measured in the house dust of 154 Seattle homes,

com-paring homes built before 1940 with those built after 1940 The Superfund Primary Remediation Goal of 400 ppm by mass ( µ g/g) also is shown (horizontal dashed line).

Cumulative Frequency, %

Superfund PRG

400 ppm

Homes Built before 1940

n = 63

Homes Built after 1940

n = 9 1

10000 10000

1000

1000