Environmental Life Cycle Costing - Chapter 13 pptx

Pesticides and Related Materials 13.1 INTRODUCTION A pest, broadly defined, is any organism — plant, animal, or microorganism — to any chemical intended to prevent, deter, destroy, or ot

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Pesticides and Related Materials

13.1 INTRODUCTION

A pest, broadly defined, is any organism — plant, animal, or microorganism —

to any chemical intended to prevent, deter, destroy, or otherwise impair the ability

of pests to compete with desired organisms such as crops, animals, or humans.Pesticides can be classified in various ways, such as by their target, chemical nature,physical state, and mode of action Classification based on the target is perhaps themost widely known, as the following examples indicate: insecticides, herbicides,

chemistry, characteristics, and health effects of several representative groups ofpesticides and herbicides We will then discuss several halogenated hydrocarbonsthat have become of much concern to us in recent years, including PCBs and dioxins

13.2 INSECTICIDES

Insecticides are those compounds that are effective against insects Many ticides have been developed and used to control various species of insects Whilemost insecticides are applied as sprays, others are applied as dusts, aerosols, fumi-gants, and baits The majority of insecticides used today are synthetic organicchemicals and most of them are nerve poisons They act by inhibiting the organism’senzymes or interacting with other target sites vital to the proper functioning of theinsect’s nervous system Other insecticides act by blocking essential processes such

insec-as respiration Although there are many synthetic organic insecticides, in this chapter

we will focus on three main groups: chlorinated hydrocarbons, organophosphoruscompounds, and carbamates

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(dichlorodiphenyl-in a number of less developed countries.

DDT is characterized by its very low vapor pressure, extremely low solubility

in water (1.2 ppb), and high solubility in oils Because of this latter property, DDTcan be readily absorbed through the skin in the fatty tissues of living organisms,and can biomagnify as tissues pass through the food chain DDT is released slowlywhen the stored fat is called upon as a source of energy Of the two isomers of DDT,

DDT and other chlorinated hydrocarbons are typically persistent broad-spectruminsecticides Their residues persist in the environment for long periods of time,

estimated to be 7 to 30 years, depending on the environment The organochlorineshave broad-spectrum characteristics, enabling them to affect many species of insects.Environmental persistence of this group of chemicals is due to the fact that they arenot readily degraded by the action of water, heat, sunlight, or microorganisms DDTrapidly accumulates in invertebrates to several thousand times the exposure level in

Table 13.1 Classification of Pesticides Method of

By target Insecticides, herbicides, fungicides, rodenticides, algicides,

nematocides

By chemical nature Natural organic compounds, inorganic compounds, chlorinated

hydrocarbons, organophosphates, carbamates

By physical state Dusts, dissolved solutions, suspended solutions, volatile solids

By mode of action Contact poisons, fumigants, stomach poisons

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PESTICIDES AND RELATED MATERIALS 189

DDT adversely alters several physiological characteristics, including normalratios of serum amino acids, thyroid activity, and the ability to withstand stress.Although DDT was not shown to influence gonad maturation, the mortality of fryproduced by DDT-treated parents was high, especially during the terminal stages of

DDT and other chlorinated hydrocarbons are very resistant to metabolic down Nevertheless, in animals and humans, DDT is degraded to DDE (ethylene1,1-dichloro-2,2-bis(p-chlorophenyl) or dichlorodiphenyl dichloroethylene) or DDD

Figure 13.1 Chemical structures of some chlorinated hydrocarbon insecticides.

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190 ENVIRONMENTAL TOXICOLOGY

DDT to DDE occurs in human subjects The conversion is catalyzed by DDTdehydrogenase, and the resultant DDE is a stable metabolite

persistence and biomagnification of chlorinated hydrocarbons These researchers ied the residues of organochlorine pesticide in adipose tissue samples of 25 persons(M: 19; F: 6) from El Paso, TX None of the tissue was taken from people known tohave occupational exposure to pesticides They observed eight organochlorine com-pounds in the tissue samples The pesticide residue levels were in the moderate range.DDE was found in all the samples tested, with an average level of 4.96 ppm, whereasthe average level of DDT was 1.50 ppm Since DDE is a stable breakdown product

stud-of DDT (Figure 13.2), its presence in the tissue represents mainly past ingestion Itcould also represent low-level indirect exposure from food and water coming fromareas of past use where DDT persists in the environment

A main health effect of DDT, DDE, and a number of other chlorinated carbons is on the endocrine system Many studies show evidence suggesting thatchlorinated hydrocarbon residues found in the environment may be responsible forinterfering with the functioning of the endocrine system and disrupting reproduction.Published reports related to such disruption involve alligators in Lake Apopka,

hydro-Figure 13.2 Metabolism of DDT.

Table 13.2 Summary of DDT’s Acute

Toxicity for Fish

Test Organism

Stage or wt (g)

96-h LC 50 (µ g/L)

&O & &O

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Florida, sea gulls in Tacoma and bald eagles on the Columbia River in the state ofWashington, and trout in Britain, among others Louis Guillette, a zoologist, wascredited with the initial observation that many of the Lake Apopka alligators exhib-ited abnormal reproductive systems and meager male hormones, apparently due topesticide residues Field and laboratory studies have shown similar effects of anumber of toxicants on wildlife Observed effects include: (a) feminization of malealligators and trout when exposed to hormone-like chemicals in laboratories; (b)poor reproduction among bald eagles along the Columbia River (seemingly linked

to exposure to DDE and PCBs); (c) the offspring of exposed pregnant female miceshowing elevated testicular cancer and delayed puberty, malformed sex organs inrats, and reduced sperm counts in hamsters; and (d) salmon in the Great Lakes withenlarged thyroids and males with premature sexual development Some scientistssuggest that exposure to these chemicals could be related to the surge of disorders

in human reproductive organs — from declining sperm counts to increasing breastand prostate cancers — in the industrialized world since World War II

The effect of organochlorine compounds on birds has been widely known ever

equally, however Birds of prey are especially susceptible to the persistent nochlorine insecticides, and levels that inhibit reproduction can be very much lowerthan those that kill For example, common species used in the laboratory, such aschicken, pheasant, pigeon or sparrow, can cope with insecticides far more success-fully than other species Birds that migrate lay down large amounts of fat prior tomigration to serve as a store of energy for the long journey Because many pesticidesare soluble in fat, birds accumulate the poison in their fat before migrating and thepoison is released to do its damage when fat is consumed during the journey

orga-Note: Delegates from about 110 countries met in Geneva in September 1999 towork on a treaty to control 12 persistent organic pollutants [POPs] They agreed tothe international phaseout of the pesticides aldrin, endrin, and toxaphene They alsodecided to severely restrict the use of four others — chlordane, dieldrin, heptachlor,and mirex — and one industrial chemical, hexachlorobenzene, allowing only someresidual uses Countries are aiming for a global treaty because these persistentbioaccumulative chemicals can be transported by wind and water far from wherethey are originally used and can cause damage to wildlife Even at low doses, thesechemicals are suspected of causing diseases of the immune system, reproductivedisorders, and abnormal child development in humans However, the countries wereunable to make decisions on DDT, PCBs, dioxins, and furans The World HealthOrganization (WHO), public health specialists, and some developing countrieswanted DDT kept available for malaria control until equally inexpensive alternatives

Organophosphorus insecticides are the most toxic among the insecticides; theyare dangerous not only to insects but also to mammals Many of these compounds,such as parathion, paraoxon, timet, and tetram are in the “super toxic” category ofhuman poisons Human fatal doses for these toxicants are < 5 mg/Kg, along withLA4154/frame/C13 Page 191 Thursday, May 18, 2000 11:46 AM

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children Figure 13.3 shows the chemical structures of three representative phosphorus insecticides: parathion, malathion, and tetraethyl pyrophosphate (TEPP).Symptoms of poisoning by organophosphate insecticides in humans includenausea, vomiting, diarrhea, cramps, sweating, salivation, blurred vision, and mus-cular tremors Severe cases may be fatal, with respiratory failure Even thoughorganophosphates are usually more toxic to humans and mammals than chlorinatedhydrocarbons, they are more easily biodegraded than the organochlorines Becauseorganophosphates do not persist in the environment or accumulate in fatty tissue,

The mode of action of this group of insecticides in vertebrates and invertebrates

for the breakdown of the neurotransmitter acetylcholine (ACh) (Equation 13.1) inthe insect and vertebrate nervous systems Inhibition of the enzyme results in accu-mulation of ACh at the nerve endings, leading to disruption of nervous activity As

choline In this case, the resultant acetic acid is first converted to acetyl CoA before

it reacts with choline Resynthesis of ACh is mediated by cholineacetyl transferase,

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Evidence suggests that the vertebrate AChE contains two binding sites, and it islikely that the insect enzyme is similar The anionic site, which may contain aglutamate residue, interacts with the positively charged N atom of ACh, while theesteratic site is responsible for the cleavage of the ester link of ACh The esteraticsite contains a serine residue, whose nucleophilicity (i.e., the extent to which it willreact with a relatively positive center) is enhanced by hydrogen bonding to theimidazole group of a neighboring histidine residue Chemicals that can inactivate

by forming a covalent bond

Just as organophosphate insecticides such as parathion and malathion are atives of phosphoric acid, the carbamates are derivatives of carbamic acid,

-(methylcarbamoyl) oxime)) (Figure 13.5) and carbofuran 7-benzofuranyl methylcarbamate) The mode of action of the carbamates is the same

(2,3-dihydro-2,2-dimethyl-as that of organophosphates, i.e., inhibition of AChE

Figure 13.4 Diagrammatic representation of the action of acetylcholine and

acetylcholin-esterase.

Figure 13.5 Chemical structure of aldicarb.

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31 to 75 ppb, and 16% more than 75 ppb Studies did not reveal any cases of

Another episode occurred in four western states (California, Washington, gon, and Alaska) and one Canadian province (British Columbia) in 1986 About 300people were made ill over the long July 4 weekend after eating watermelons con-taminated with aldicarb The melons were grown on farms in southern California.Forty of 550 California watermelon fields were shown to be contaminated with thepesticide As a result, about one million melons were destroyed

Ore-Aldicarb is manufactured by Union Carbide It is approved for use on a number

of crops to control nematodes, aphids, and other insects that feed on parts of cropplants It is not approved for use on watermelons It was reported that a concentration

of aldicarb at 0.2 ppm in watermelon meat caused illness The contaminated melonshad concentrations up to 3 ppm Symptoms resembled those of influenza, i.e., blurredvision, perspiration, nausea, dizziness, and shaking These symptoms usually disap-pear after a few hours In the episode mentioned above, none of the cases proved fatal

13.3 HERBICIDES

During the Vietnam War years, the U.S Air Force defoliation program applied

a huge amount of undiluted 2,4-D (2,4-dichlorophenoxy acetic acid) and 2,4,5-T

between 1965 and 1970 In addition to military use of the phenoxyherbicides (PHs)

in Vietnam, PHs were widely used in the United States for weed control in agricultureand rangeland, lakes and ponds, and in forestry

As shown in Figure 13.6, 2,4-D and 2,4,5-T are identical esters except for theadditional chlorine atom present on the benzene ring of 2,4,5-T During production

of these two compounds, chlorinated dioxins (TCDD) (to be discussed later in thechapter) were found to contaminate the final product, a compounding factor inanalysis because of its high toxicity Prior to its ban in 1978, 2,4,5-T was used incombination with other chemicals in forestry primarily for “releasing” conifer spe-cies from competition with broad-leafed species PHs are also used after logging toclear the brush so that seedlings can be planted

In plants, the biochemical actions of PHs are complex After application, thechemicals are absorbed primarily through stomata and secondarily through root hairswith water In resistant species, detoxification results after decarboxylation andconjugation In sensitive plants, as the chemicals are translocated through vasculartissue, they disrupt growth and various metabolic processes The most importantchange is the stimulation or inhibition of many enzymes, which in turn affects growthLA4154/frame/C13 Page 194 Thursday, May 18, 2000 11:46 AM

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and metabolic processes, possibly leading to plant death Certain species, such asDouglas fir, are tolerant when PHs are mixed with a water carrier

Numerous clinical reports on humans have described peripheral neuropathy(degeneration of nervous tissue) and acute myopathy (disorder of muscle tissue ormuscles) after dermal exposure or oral ingestion of 2,4-D Clinical symptoms ofseverely poisoned farmers include pain and weakness in the lower extremities,slowed nerve conduction velocity, twitching, and muscle spasms In addition, behav-ioral changes such as nervousness, inability to concentrate, irritability, impotence,

workers employed at PH manufacturing plants In the early studies, the degree ofTCDD contamination was often unknown In later studies, exposure is primarilydue to the formulated product

The neurotoxic and mycotoxic mechanisms of 2,4-D are not well studied In

velocity measurement (NCV) Such studies have become increasingly valuable inxenobiotic assessment, because slowed NCV is associated with histological as well

as behavioral changes NCV is an excellent starting point for epidemiology in thatthe techniques involved are rapid, accurate, and noninvasive In 1979, a survey wasconducted of 190 current, former, and retired workers of a Jacksonville, Arkansas,

carefully screened in order to minimize factors that could possibly affect NCV Threenerves were tested (median motor, median sensory, and sural), measured, andrecorded for 56 workers at the plant Regression statistics were applied to the data

to equilibrate age differences Velocity was adjusted to a temperature of 36°C,because it is known that temperature affects NCV The results showed that 46% ofthe study group had one or more slowed nerve conduction velocities In addition,slowed sural nerve conduction velocity was correlated to duration of employment

at the factory

Figure 13.6a Chemical structure of 2,4-D.

Figure 13.6b Chemical structure of 2,4,5-T.

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The widespread use of phenoxyherbicides during the Vietnam War has beenassociated with a large variety of health problems Again, TCDD is a complexingfactor Specific neurotoxic effects of 2,4-D have recently been examined in response

to reports of episodic increase in intracranial skull pressure associated with

neural metabolism of 2,4-D, specifically concerning the accumulation and transportwithin the brain and spinal cord

Phenoxyherbicides were banned for forestry in 1979 due to a combination ofpublic pressure and the results of EPA’s Alsea II report This widely criticized reportfound significantly greater spontaneous abortion rates inside a residential areaexposed to PH spray compared to a similar area without spray Although banned foruse in forestry, PHs are still widely used as herbicides for cotton, wheat, corn, andrice crops

13.4 POLYCHLORINATED BIPHENYLS (PCBs)

Polychlorinated biphenyls (PCBs) are a class of synthetic chlorinated organiccompounds with biphenyl as the basic structural unit Chlorination of the basicstructure can theoretically yield 209 chlorobiphenyls substituted with 1 to 10 chlorineatoms, but the probable number of compounds is estimated to be 102 The generalchemical structure of PCBs is shown in Figure 13.7 Although PCBs belong tochlorinated hydrocarbons, they are not pesticides However, because of their wideuse and resistance to degradation in the environment, PCBs are known as one of themajor organochlorine pollutants found in the environment Extensive PCB-contam-ination exists in the food chain

The properties of PCBs are similar to those of DDT PCBs are soluble in fat orfat solvents, but hardly soluble in water The solubility of PCBs in water and inorganic solvents affects their transport and persistence in the environment Theirsolubility in water generally decreases with increase in the degree of chlorination.Individual chlorobiphenyls vary in their solubility from about 6 ppm for monochlo-

nondry-ing, and nonflammable in that they are stable after long heating at 150°C, do notsupport combustion when alone above 360°C, and can withstand temperatures up

to 650°C (1600°F) They are not affected by boiling with NaOH solutions

Electri-Figure 13.7 Chemical structure of PCBs (m + n = 1 ~ 10)

Cl m Cl n

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cally, PCBs are nonconducting They also have very low vapor pressures, which,like their solubility in water, decreases with increased chlorination

PCBs tend to bind tightly to particulate matter, such as soils and sediments.Thus, surface waters with low particulate loads may have very low concentrations

of PCBs, while high concentrations may exist in the bottom sediments

PCBs were first manufactured commercially in 1929 in the United States by the

numbers such as 1221, 1248, and 1268, etc The numbers in the last two digits refer

to the percentage of chlorine in the products Because of their unique properties,PCBs are widely used Industrial uses include manufacture of plastics, paints, var-nishes, asphalt, rubber, carbon paper, carbonless paper, printing inks, syntheticadhesives, sealers in waterproof material, lubricating oils, fire retardants, electrical

pesti-cides, they were previously added to DDT to extend its “kill effect.”

The U.S banned the use of PCBs in 1976 in the wake of concern about publichealth In 1985, the Environmental Protection Agency (EPA) issued a final rulerequiring removal of PCB fluids or the electrical transformers containing PCBs fromcommercial buildings by October 1, 1990

Similar to DDT, PCBs are ubiquitous in the environment Contamination ofPCBs may occur through (a) spills and losses in PCB and PCB-containing fluidmanufacture; (b) vaporization and/or leaching from PCB formulations; (c) leaksfrom sealed transformers and heat exchangers; (d) leaks of PCB-containing fluidsfrom hydraulic systems that are only partially sealed; and (e) disposal of waste PCBs

through incineration of rubber and plastics; and through addition of the compounds

to insecticide formation to increase “kill-life” of the products

One of the most important routes by which PCBs can contaminate the ment is air The airborne PCBs can rapidly and efficiently dissipate from point sources

environ-to distant areas In addition environ-to the airborne route, marine environments receive PCBsfrom various sources, including rivers, urban runoff, wastewater discharges, anddumped sewage sludge Once in the aquatic environment, PCBs, like DDT, tend tobioaccumulate PCBs and DDT are similar to each other in terms of their low water

13.4.4.1 Wildlife Exposure

PCBs were identified in birds’ feathers as early as 1944, and many investigatorshave since reported varying levels in wildlife in Canada, Germany, Great Britain,the Netherlands, Sweden, and the United States High concentrations of the com-

-( methylcarbamoyl) oxime)) (Figure 13. 5) and carbofuran 7-benzofuranyl methylcarbamate) The mode of action of the carbamates is the same

(2,3-dihydro-2,2-dimethyl-as that of... forestry

As shown in Figure 13. 6, 2,4-D and 2,4,5-T are identical esters except for theadditional chlorine atom present on the benzene ring of 2,4,5-T During production

of these... factory

Figure 13. 6a Chemical structure of 2,4-D.

Figure 13. 6b Chemical structure of 2,4,5-T.

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