CHAPTER 7 Summary and Conclusions This book reviews more than 400 studies of pesticides in bed sediment and aquatic biota of United States rivers conducted over the last three decades. Considered together, the existing literature provides a basis for at least partial assessment of the extent of pesticide contamination of rivers and estuaries in the United States, although there are areas where our current understanding is incomplete. The majority of studies reviewed were monitoring studies, ranging in scale from local to national. There was little consistency among the studies reviewed in terms of site selection strategy, sample collection methods, species of organisms sampled, tissue type analyzed, and analytical detection limits. In contrast, there was great consistency in the types of pesticides that were target analytes in bed sediment and aquatic biota studies—the vast majority of studies focused on organochlorine insecticides. Since the 1960s, there has been a decrease in process- type studies (or field experiments) designed to assess the general environmental fate and persistence of individual pesticides, and an increase in monitoring-type studies that focused on analytes known to be present in bed sediment and aquatic biota (as the environmental fate of hydrophobic pesticides became more generally understood). Results of the hundreds of state and local monitoring studies are difficult to compare because of the large variability in study design (which includes factors such as site selection, sampling methods, and analytical detection limits). However, several national programs have been conducted that constitute individual data sets large enough to provide a nationwide perspective on pesticide occurrence and distribution. Together, these national monitoring studies have provided good geographic coverage of pesticides in bed sediment and aquatic biota of United States rivers and estuaries. Temporally, the national studies have provided the fewest data for freshwater sediment, which was sampled only during the 1970s. The focus of state and local monitoring studies was fairly evenly divided between bed sediment and aquatic biota. Geographically, state and local monitoring efforts have been heaviest in the Great Lakes region, along the Mississippi River, and in western states, especially California. In aquatic biota monitoring studies, pesticide residues were more often measured in fish than in other aquatic organisms, with other invertebrates and mollusks placing a distant second and third. In studies that sampled fish, there was little consistency in the types of tissue analyzed (such as whole fish, fillets, liver, or other organs). No national studies measured pesticide residues in plants, algae, or amphibians, whereas a number of both local monitoring studies and process-type studies did. © 1999 by CRC Press LLC Analytical detection limits varied among studies and were not always reported. In general, detection limits tended to be lower and to be reported more frequently in more recently published studies. Changes in analytical methods over time (especially the change from packed-column to capillary column gas chromatography) tended to lower detection limits. The monitoring studies reviewed show that a large number of pesticides have been detected in bed sediment and aquatic biota at some time over the last 30 years. Forty-one of 93 target analytes (44 percent) were detected in bed sediment in one or more studies, and 68 of 106 analytes (64 percent) were detected in aquatic biota in one or more studies. Most of the target analytes detected were organochlorine insecticides, by-products, or transformation products, despite the fact that most organochlorine insecticides were banned or severely restricted by the mid-1970s. This reflects both the environmental persistence of these compounds and the bias in the target analyte list (which typically was limited to organochlorine compounds). DDT and metabolites, chlordane compounds, and dieldrin were the most commonly detected pesticide analytes in both bed sediment and aquatic biota. Other organochlorine insecticides that sometimes were detected included endosulfan compounds, endrin and metabolites, heptachlor and heptachlor epoxide, mirex, lindane, α - and β -HCH, kepone, methoxychlor, and toxaphene. Besides the organochlorine insecticides, a few compounds in other pesticide classes were detected in some studies. Most of these pesticides contained chlorine or fluorine substituents and were intermediate in hydrophobicity. Examples in bed sediment included the herbicides ametryn, dacthal, 2,4-DB, dicamba, and diuron; the organophosphate insecticide zytron; and the fungicide/wood preservative pentachlorophenol. In aquatic biota, examples included the herbi- cides dacthal, oxadiazon, and trifluralin; the organophosphate insecticides zytron and chlor- pyrifos; and the fungicide/wood preservative pentachlorophenol and (its metabolite) pentachloro- anisole. Of pesticides from other chemical classes that were analyzed in bed sediment or aquatic biota, most were targeted at relatively few sites nationwide, and those sites generally came from one or a few studies. Aggregate detection frequencies (calculated by combining data from the studies reviewed) are not necessarily representative of freshwater resources in the United States. If a given pesticides is absent from the list of pesticides detected in bed sediment or aquatic biota, it does not necessarily mean that the individual pesticide is not present in these sampling media, but that it may not have been looked for in the studies reviewed. Even for those compounds with zero or few detections, the results may have been biased by sampling location or study design. The monitoring studies reviewed suggest that pesticides were detected more often in aquatic biota than in bed sediment. More pesticides (both the total number and the percentage of those targeted) were detected in aquatic biota than in bed sediment and the cumulative detection frequencies for a given pesticide generally were higher. Moreover, in direct comparison between benthic fish and associated surficial sediment samples collected by the National Oceanic and Atmospheric Administration’s (NOAA) National Status and Trends (NS&T) Program (Benthic Surveillance Project), detection frequencies and concentrations (dry weight) of most hydro- phobic organic contaminants tended to be higher in estuarine fish liver than in associated sediment. The exceptions were aldrin and heptachlor, both of which are metabolized rapidly in aquatic biota. Their transformation products (dieldrin and heptachlor epoxide, respectively) showed the expected pattern, that is, they were found at higher levels in fish liver samples than in associated sediment. © 1999 by CRC Press LLC About 1 billion pounds of pesticides currently are used each year in the United States in a wide variety of agricultural and nonagricultural applications. Total pesticide use and the number of different chemicals applied have grown steadily since the early 1960s, when the first reliable records were kept. More than 75 percent of total pesticide use is applied in agriculture. However, pesticides also are applied on lawns and gardens, to control nuisance insects (both indoors and outdoors), in subterranean termite control, in landscape maintenance, to control public-health pests, in industrial settings, in forestry, along roadways and rights-of-way, and in direct application to aquatic systems. Although quantitative estimates of pesticide use are available for agriculture, there is relatively little quantitative data available on nonagricultural uses of individual pesticides. Agricultural use of insecticides declined during the 1980s. Also, there was a pronounced change in the types of insecticides used from the 1960s to the 1980s as organochlorine insecticides were replaced by organophosphate, carbamate, and other insecticides. The only four organochlorine insecticides used in agriculture in 1988 (endosulfan, dicofol, methoxychlor, and lindane) are less hydrophobic and less persistent than DDT and the other restricted compounds in the organochlorine family. In contrast, agricultural use of herbicides has increased markedly since the 1960s. Most herbicide classes contributed to this rise, except the chlorophenoxy acid herbicides. Over 60 percent of the herbicides used in agriculture in 1988 were triazine, amide, or carbamate herbicides. The principal pesticides used in and around the home and garden today tend to differ from those used in agriculture. However, almost all of the restricted organochlorine insecticides (except endrin) once had extensive urban use. Several organochlorine insecticides were used in homes and gardens in 1990, but they accounted for fewer than 4 percent of products or outdoor applications. Home and garden insecticide use was dominated by pyrethroid insecticides, pyrethroid synergists, and the insect repellent diethyltoluamide. As a first approximation, the geographic distribution of pesticides detected in bed sediment and aquatic biota may be expected to relate directly to the quantities of pesticides applied. To this end, aggregate detection frequencies (which represent a crude composite detection frequency from the 1960s to 1993) were calculated for individual pesticides on the basis of combined data from all of the monitoring studies reviewed. These aggregate detection frequencies were compared with estimates of national agricultural use in either 1966 (for organochlorine insecticides) or 1988 (for currently used pesticides). There was no clear relation in either case. Factors that may obscure this relation include pesticide use in nonagricultural settings, sources other than pesticide application (such as hexachlorobenzene from industrial sources), the influence of physical and chemical properties, and bias introduced by combining data from studies that have different study designs and methods. To increase the chances of detecting a relation between pesticide occurrence and pesticide use, the variability in both data sets was reduced: Pesticide occurrence data were taken from a single national program at a time, and pesticide use estimates by agricultural production region or by county were employed. For several organochlorine insecticides, there was a moderately strong relation between detection in both bed sediment and whole fish from major United States rivers during the 1970s and agricultural use by region in 1966. This was observed for total DDT and total dieldrin in bed sediment sampled by the U.S. Geological Survey (USGS) and the U.S. Environmental Protection Agency (USEPA) during 1972–1982, and for total DDT, total dieldrin, chlordane, and total heptachlor in whole fish sampled by the Fish and Wildlife Service (FWS) © 1999 by CRC Press LLC during 1976–1979. In all cases, however, higher than expected concentrations were observed in some parts of the United States, possibly due to intensive nonagricultural use, heavy local use (in excess of average regional use), incidental industrial release, and atmospheric deposition. The geographic distributions of some organochlorine insecticides in whole fish measured by the FWS were associated with specific uses such as corn production (dieldrin, chlordane, heptachlor) or red fire ant control (such as mirex) or with manufacturing inputs (such as kepone and mirex). In estuarine bed sediment and mollusks sampled by NOAA, the geographic distributions of most organochlorine insecticides (during 1984–1989) were related to human population levels. Contaminated coastal or estuarine sites sampled by NS&T Program in 1986 were sometimes, but not always, associated with contaminated inland sites sampled by the FWS’s National Contaminant Biomonitoring Program (NCBP) also in 1986. Relatively few national studies monitored currently used pesticides in bed sediment or aquatic biota. Although the USGS and USEPA analyzed bed sediment from major United States rivers (during 1975–1980) for a few organophosphate insecticides, and chlorophenoxy acid and triazine herbicides, there were too few detections of any pesticides other than the organochlorine insecticides to permit association with pesticide use. In fish sampled by the U.S. Environmental Protection Agency (1986–1987), three organochlorine insecticides that were still used in agriculture in 1988 (dicofol, methoxychlor, and lindane) had higher detection frequencies than might be expected on the basis of agricultural use alone. These organochlorine insecticides, although less persistent than DDT and other canceled organochlorine insecticides, still have longer environmental lifetimes than most other chemical classes. They also can be applied in residential or urban settings. Several currently used pesticides were detected in association with agricultural drainages in three large-scale studies that analyzed for them in fish tissues. The studies were the USEPA’s National Study of Chemical Residues in Fish (NSCRF), the NCBP, and California’s Toxic Substances Monitoring Program (TSMP). The currently used pesticides that were associated with agricultural drainages were chlorpyrifos (NSCRF and TSMP); dacthal (NCBP and TSMP); diazinon, endosulfan, and parathion (TSMP); and dicofol and trifluralin (NSCRF). Insufficient data are available at this time to assess trends for organochlorine insecticides in either river or estuarine bed sediment. Some national studies were of sufficient duration, however, to provide information on organochlorine insecticide trends in fish and shellfish contamination. In whole freshwater fish sampled by the FWS, hexachlorobenzene residues appeared to decline in frequency and magnitude nationwide from 1976 to 1986. Concentrations of dieldrin, total DDT, endrin, and α -HCH appeared to decline during the 1970s, then level off in the early 1980s. Toxaphene residues in whole fish appeared to peak nationally around 1980, declining afterwards through 1986. For most organochlorine insecticides, high concentrations appear to be persisting in some areas in the United States. In coastal and estuarine biota, DDT residues have declined nationally in the last two decades, especially during the 1970s. There is evidence for declining dieldrin residues at some marine sites, but it remains to be determined whether there is a nationwide trend for coastal and estuarine areas, especially for dieldrin residues in fish. Toxaphene residues in coastal and estuarine biota appear to have declined nationally, although local “hot spots” remain. For estuarine biota, insufficient data exist to evaluate national trends in residues of chlordane, endrin, total heptachlor, and hexachlorobenzene. Ongoing collections of coastal and estuarine bivalve mollusks and benthic © 1999 by CRC Press LLC fish (as well as bed sediment) under the NS&T Program are expected to provide additional data for chlordane, dieldrin, and lindane. Of currently used pesticides, long-term national data are available only for lindane, one of the four moderately persistent organochlorine insecticides still used in agriculture (in 1988). In whole freshwater fish sampled by the FWS, lindane concentrations appeared to decline in the late 1970s, then level off in the 1980s. Several other currently used pesticides (1988) were analyzed for a limited period of time in one or more national programs, but not long enough to permit assessment of trends. Sources of pesticides to bed sediment and aquatic biota include agricultural and nonagricultural applications and atmospheric contamination. The frequent detection of organochlorine insecticides in bed sediment and aquatic biota in remote areas of the United States and the world has been attributed to atmospheric transport from high-use or contaminated areas, and subsequent deposition. Agriculture is undoubtedly a major contributor to pesticide contamination of bed sediment and aquatic biota. There is considerable evidence that the source of DDT in bed sediment and fish in many rivers in the United States is from past insecticide use in agriculture. Many agricultural areas still contain soil residues of hydrophobic, persistent pesticides that were applied in the 1970s or earlier. Field monitoring studies indicate that DDT half-lives in soil are on the order of 15 years or longer, that soil contaminated with total DDT may enter drains as a result of normal field and irrigation practices (such as land leveling), and that the rate of DDT degradation appears to increase slightly once it enters a river or other waterway. DDD and DDE, the most common transformation products of DDT, also are resistant to degradation. High residues of total DDT (the sum of DDD, DDE, and DDT) and a high ratio of DDT/total DDT in soil, bed sediment, or biota samples do not necessarily indicate recent use of DDT. A high ratio of DDT/total DDT in river sediment or aquatic biota probably indicates that the residues recently entered the hydrologic system, such as by erosion of DDT- contaminated soil. Existing monitoring data suggest that various nonagricultural uses of pesticides may contribute to residues of some pesticides in bed sediment and aquatic biota, at least in some areas. Pesticides used in forestry and in urban areas, like those used in agriculture, have changed over time. Of the pesticides currently used in forestry, only a few have been targeted in any studies that monitored bed sediment and aquatic biota (2,4-D, picloram, carbaryl, and glyphosate), and these were detected at very few (less than 10 percent) sites. Some process- oriented studies were conducted in which pesticides and their transformation products were measured in forest streams following known applications of those pesticides. Results indicate that the behavior of pesticides in forest streams is in agreement with their behavior in agricultural streams. DDT and metabolites appear to have a long residual lifetime in bed sediment of forest streams. Concentrations of less hydrophobic pesticides may be detected in bed sediment and aquatic biota for some time following application, but would be expected to decline in these media more rapidly than the organochlorine insecticides. In urban areas, organochlorine insecticides have been largely replaced over time by insecticides in other classes. However, several organochlorine insecticides were used around homes and gardens in 1990, including dicofol, chlordane, endosulfan, heptachlor, lindane, and methoxychlor. Many monitoring studies have reported the frequent detection of organochlorine pesticides in bed sediment, aquatic biota, and water in rivers in urban areas. The actual sources of these pesticide residues are not completely known, however, because the organochlorine © 1999 by CRC Press LLC insecticides had both urban and agricultural uses, and many urban sites are also located near agricultural areas. Most pesticides found in bed sediment and aquatic biota in such urban areas probably derive from both agricultural and urban sources, with their relative importance varying by location and chemical compound. Taken together, the studies reviewed in this book provide a good understanding of processes affecting the fate, transport, and transformation of pesticides within the hydrologic system and how these relate to the physical and chemical properties of a given pesticide. Pesticides may enter surface-water bodies via surface runoff and drainage, ground-water discharge (for hydrophilic pesticides), atmospheric deposition (for volatile pesticides), or direct application to the water body. Once a pesticide enters a hydrologic system, its environmental fate is controlled by the physical and chemical properties of the pesticide and by environmental conditions in the hydrologic system. Environmental processes that occur may be categorized as phase-transfer, transport, or transformation processes. Pesticides with low water solubility and high n -octanol-water partition coefficients ( K ow , a measure of lipophilicity) tend to associate with organic matter in the hydrologic system, including dissolved organic matter, particulates, and biota. Pesticides associated with particulate matter in the water column may be deposited to bed sediment. Once there, pesticides may be remobilized by chemical diffusion or biological and physical mixing or both. Remobilized pesticides can reenter the water column and be carried downstream and(or) redeposited again. Aquatic biota may take up pesticides by partitioning (diffusion through surface membranes) from water, by ingestion of contaminated food or particles, or by direct contact with sediment. Once the pesticide is taken up by living biota tissue, it can be stored, metabolized, or depurated. Final removal of the pesticide from bed sediment or biota in a hydrologic system can occur either by physical removal (such as burial of bed sediment in long-term depositional zones, sediment discharge to the oceans, or consumption of contaminated fish by humans or other terrestrial animals) or by chemical transformation (such as biodegradation or hydrolysis). Bioaccumulation in an organism is the net effect of competing processes of uptake and elimination. Contaminant accumulation by aquatic biota is affected by biological factors (such as species, sex, body size, age, reproductive state, lipid content, metabolic capability, growth rate, blood flow, and gill ventilation volume), chemical characteristics (such as molecular size and shape, solubility in lipid and water, and chemical stability), and environmental conditions (such as temperature, pH, salinity, concentrations of dissolved organic matter and particulates, and degree of water oxygenation). There has been some disagreement in the literature as to whether biomagnification (the process whereby the tissue concentrations of a chemical increase as it passes up the food chain through two or more trophic levels) occurs in hydrologic systems. An opposing view has held that contaminant accumulation by aquatic organisms can be described using equilibrium partitioning theory, in which contaminant concentrations in water, blood, and tissue lipids approach equilibrium; regardless of the mechanism of uptake, the contaminant partitions into and out of these phases according to its relative solubility (bioconcentration). The relative importance of contaminant uptake from the diet, and from water via partitioning, has also been debated in the literature. The relative importance of dietary uptake and uptake from water by partitioning, and of biomagnification and bioconcentration, in hydrologic systems appears to depend on the chemical, as well as on the type of organisms involved. From a review of field, laboratory, and model ecosystem studies that assessed bioconcentration, dietary uptake, and potential biomagnification of organic chemicals, it appears that biomagnification may occur © 1999 by CRC Press LLC under conditions of low water concentration for compounds of high lipophilicity, high persistence, and low water solubility. Biomagnification is most likely to occur for chemicals with log K ow values greater than 5 or 6. The predominant route of uptake also appears to depend on the organism involved. At one extreme are air-breathing vertebrates such as sea birds, seals, and whales. These organisms have no external surface for rapid exchange, such as gills in fish, so that contaminant accumulation is by biomagnification. At the other extreme are autotrophic organisms that draw their food from dissolved components in water; for such organisms, bioconcentration is the uptake mechanism. For intermediate organisms, both mechanisms probably occur, with their relative importance depending on the organism, the chemical, and various other factors. The process of biomagnification initially was believed to result from the loss of food substances due to respiration, whereas resistant contaminants were retained by the organism. This mechanism is now considered unlikely. It has been proposed that food digestion and absorption from the gastrointestinal tract, accompanied by inflow of more contaminated food, may increase the concentration of the chemical in the gastrointestinal tract relative to that in the original food. This also increases the fugacity (a thermodynamic measure of the escaping tendency of a chemical from a phase, equivalent to chemical activity) of the chemical in the gastrointestinal tract relative to that in the original food. This creates a fugacity gradient (or fugacity pump) that drives the passive diffusion of chemical from the gastrointestinal tract into the organism, raising the fugacity of the predator over that in the prey (the consumed food). This modified fugacity (partitioning) theory subscribes to and attempts to explain observations of biomagnification. As such, it represents a convergence of the previously competing theories of equilibrium partitioning and biomagnification. Seasonal events that strongly affect the movement of pesticides to and within surface waters also may influence the accumulation of pesticide residues in bed sediment and aquatic biota. These include agricultural management practices (such as seasonal application of pesticides, irrigation practices, land leveling, and tillage practices), seasonal or episodic water- management practices (such as reservoir release and impoundment), weather-driven events (such as precipitation, snowmelt, and strong winds), seasonal environmental conditions (such as temperature and salinity), and, in the case of residues in aquatic biota, seasonal biological or physiological factors (such as lipid content, reproductive cycle, and enzyme activity). Although few studies attempted to measure seasonal changes in contaminant residues in bed sediment, the studies that were conducted (together with current knowledge of seasonal and episodic events that may affect contaminants in sediment) suggest that seasonal perturbations of bed sediment can cause changes in the concentrations of hydrophobic organic chemicals. Irrigation and rains will increase the water discharge and velocity of a river, which are likely to resuspend some of the bed sediment. At this time, surficial bed sediment will have its lowest total DDT concentration and the water column its highest concentration. As the irrigation or rains subside, the water discharge and velocity will decrease, and the suspended particles will settle out of the water to the depositional zones of bed sediment. The cycle may repeat itself, depending on the timing of each irrigation or rain event. Reservoir release, which tends to occur on an episodic rather than seasonal basis, would have similar effects on soil erosion, streamflow velocity, and bed sediment disturbance. Deeper bed sediment that is generally protected from resuspension is not affected by this seasonal cycle, but it may be moved by infrequent catastrophic events, such as flooding. © 1999 by CRC Press LLC In aquatic biota, seasonal variations in pesticide residues have been observed in both saltwater and freshwater systems. Most of the factors that affect seasonality in aquatic biota appear to act by influencing organochlorine availability (determined by a combination of pesticide application, industrial discharge rates, streamflow, runoff, etc.) or physiological changes (especially those related to lipid content and the reproductive cycle), or both. Contaminant availability and physiological condition (lipid content and reproductive stage) do not necessarily correspond, so that multiple peaks may be observed in seasonal profiles. Differences in the timing of seasonal maxima and minima may occur among different species at the same location and among organisms of the same species from different locations. Given the number of factors involved and the interaction between them, it may be difficult to attribute seasonal profiles observed in the field to individual factors or combinations of factors. The occurrence of seasonal fluctuations, whatever the cause, points out the importance of considering seasonality in study design and data interpretation. The physical and chemical properties of a pesticide influence its tendency to accumulate in bed sediment and aquatic biota. Two types of properties are particularly important. First are those characteristics of the pesticide that promote its association with sediment or biota (such as low water solubility and high K ow ). Second, a pesticide must be environmentally persistent for it to accumulate to substantial levels over time in bed sediment or aquatic biota. Pesticides with low water solubility, high K ow , and long soil half-life (which is the best measure of persistence that is available for a large number of pesticides) generally were observed in bed sediment and aquatic biota in the monitoring studies reviewed, whereas those pesticides with high water solubility, low K ow , or short soil half-life generally were not. However, a number of moderately hydrophobic, moderately persistent pesticides (such as endosulfan, lindane, chlorpyrifos, permethrin, trifluralin, dacthal, oxadiazon, and pentachlorophenol) also were detected in bed sediment and aquatic biota, although at lower frequencies than the more persistent organochlorine insecticides. These intermediate compounds generally have water solubilities of 0.01–1 mg/L or log K ow values of 3–5, and soil half-lives of 30–150 days. Some of these compounds (such as chlorpyrifos and trifluralin) are very high use pesticides in agriculture today. Their presence in bed sediment and aquatic biota in the studies reviewed suggests that other currently used pesticides of intermediate hydrophobicity and persistence also might be found, if they were target analytes in these media. Most pesticides in high use during the 1990s are more water soluble and have a shorter environmental residence time than the organochlorine insecticides. Several have a water solubility less than 1 mg/L, a log K ow value greater than 3, and a soil half-life greater than 30 days, but have not been analyzed in bed sediment or aquatic biota at many sites nationwide. Examples are the insecticides esfenvalerate, fenthion, fenvalerate, and propargite; the herbicides benfluralin, bensulide, ethalfluralin, pendimethalin, and triallate; and the fungicide dichlone. These pesticides have the potential to be found in bed sediment and aquatic biota, if analyzed in these media. However, such moderately hydrophobic, moderately persistent compounds would probably be found at much lower frequencies than the more persistent organochlorine insecticides (such as DDT or dieldrin). Because these intermediate pesticides are not as resistant to degradation as DDT, concentrations of these intermediate pesticides would be expected to decline following application or introduction to the hydrologic system. Currently used pesticides that are intermediate in hydrophobicity and persistence, however, may reach fairly high © 1999 by CRC Press LLC concentrations and detection frequencies in bed sediment and aquatic biota in areas of high or repeated use. The probability of detection would be likely to increase if study designs considered location and time of application. Detection of hydrophobic pesticides in bed sediment and aquatic biota serves as an indicator that these compounds are present as contaminants in the hydrologic system. Their biological significance is more difficult to assess. Organochlorine pesticides such as DDT have been shown to adversely affect the survival of various organisms in laboratory tests (including aquatic invertebrates, fish, birds, and mammals); to disrupt the reproduction of fish and birds in the field; and to accumulate to high levels in fish-eating mammals. Pesticide contamination in the field also has been associated with fish kills and fish diseases. Potential effects of pesticide residues measured in the monitoring studies reviewed were assessed by comparing the reported pesticide residue levels with appropriate standards and guidelines designed for protection of aquatic life, wildlife, and human health. Despite the limitations of this kind of analysis, some important points emerge. For both bed sediment and aquatic biota, a substantial number of recently published studies (1984–1994) reported maximum concentrations of some pesticides that exceeded applicable guidelines for protection of aquatic organisms or wildlife. Residue levels for some pesticides at the most severely contaminated site in each study reviewed appear to be sufficient to adversely affect benthic organisms (in 25–50 percent of studies, depending on the pesticide), fish (10–20 percent of studies), and fish-eating wildlife (25–75 percent of studies). The pesticides most frequently present at levels that may cause toxicity were DDT and metabolites, dieldrin, and chlordane. Because this analysis was based on the maximum concentrations in each study, these results indicate potential adverse effects only at the most contaminated site in each study. They give no information on how often, or at how many sites within these studies, these guidelines were exceeded. Also, the concentrations observed in the monitoring studies reviewed are not necessarily representative of the water resources in the United States. It is important to consider site selection and other aspects of study design in interpretation of study findings. Human exposure to organochlorine contaminants is demonstrated by their frequent, almost universal, detection in samples of human breast milk, blood, and various tissues, including adipose and reproductive organ tissues. These organochlorine contaminants include pesticides, as well as polychlorinated biphenyls (PCB), polychlorodibenzodioxins (PCDD), and polychlorodibenzofurans (PCDF). Several studies indicate that food consumption is the principal mode of intake of hydrophobic pesticide contaminants. Fish and shellfish consumption was reported to be a major source of human exposure (relative to other foods) for a number of organochlorine compounds, including DDT, mirex, kepone, dieldrin, hexachlorobenzene, HCH isomers, PCBs, and tetrachlorodibenzo- p -dioxins (TCDD). Moreover, organochlorine residues in human blood have been shown to be related to consumption of contaminated fish. To estimate potential effects on human health due to consumption of fish and shellfish contaminated at the levels found by the monitoring studies reviewed in this book, the maximum pesticide concentrations reported in these monitoring studies were compared with applicable standards and guidelines for the protection of human health. These consist of USEPA tolerances for pesticides in food, Food and Drug Administration (FDA) action levels for unavoidable pesticide residues in food, and USEPA screening values for pesticides in edible fish (part of USEPA’s guidance for use in setting fish consumption advisories). USEPA tolerances exist only © 1999 by CRC Press LLC for currently registered pesticides, and so, do not apply to most organochlorine insecticides. Both FDA action levels and USEPA screening values exist for most of the commonly detected organochlorine insecticides. The maximum concentrations of most organochlorine compounds in edible fish tissues reported in recently published (1984–1994) studies did not exceed applicable FDA action levels. The exceptions were total chlordane, mirex, total DDT, and toxaphene. FDA action levels for these compounds were exceeded at the most contaminated sites in 56 percent (total chlordane), 40 percent (mirex), 13 percent (total DDT), and 6 percent (toxaphene) of recently published (1984–1994) studies. For the affected sites, if the contaminated fish were in interstate commerce, the pesticide residues would be high enough to warrant enforcement action by FDA to remove them. Generally, USEPA screening values were exceeded by maximum concentrations from a higher percentage of recently published (1984–1994) studies than were FDA action levels, because USEPA screening values for most organochlorine insecticides are lower than FDA action levels. This occurs because FDA action levels are based on a different risk assessment methodology than that used by USEPA in setting guidance for use in fish consumption advisories. Moreover, FDA action levels are not based on health considerations alone, but also consider factors such as the economic costs of banning a foodstuff, analytical detection limits, and the extent to which residues cannot be avoided by good agricultural or current good manufacturing practice. USEPA screening values for several pesticides were exceeded by maximum concentrations in at least 40 percent of recently published (1984–1994) studies: total DDT (in 100 percent of studies), total chlordane (75 percent), dieldrin (73 percent), heptachlor epoxide (50 percent), and mirex (40 percent). This analysis suggests that pesticide residues at the most severely contaminated site in each of these monitoring studies would be high enough to cause adverse human health effects if the fish from these sites were consumed at average rates by the general adult population over a 70-year lifetime. For these five organochlorine compounds (total DDT, total chlordane, dieldrin, heptachlor epoxide, and mirex), the expected effects would be cancer, and the excess cancer risk may exceed 1 in 100,000 people. Adverse health risks may be higher for sport or subsistence fishers or for sensitive subpopulations such as children or pregnant women. The standards and guidelines discussed above generally were based on chronic toxicity and (for human health) carcinogenicity. It is possible, however, that additional effects on develop- ment and reproduction in fish, wildlife, and humans may occur at concentrations below existing standards and guidelines. This is currently a research area of great interest and controversy. More than 50 synthetic and naturally occurring chemicals have been shown to disrupt the endocrine systems of humans and other animals. An environmental endocrine disruptor is an exogenous agent that interferes with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development, or behavior. The list of known endocrine disruptors include several persistent organochlorine insecticides and their transformation products (DDT, DDE, dicofol, dieldrin, heptachlor, hexachlorobenzene, kepone, lindane and other HCH isomers, methoxychlor, mirex, and toxaphene), as well as synthetic pyrethroids, triazine herbicides, and ethylene bis- dithiocarbamate fungicides. A number of field studies have shown an association between exposure to endocrine-disrupting chemicals in the environment and adverse effects on reproduction, development, and the immune system in birds, fish, shellfish, turtles, and © 1999 by CRC Press LLC [...]... Still, there are gaps in our understanding of the distribution and trends in pesticide contamination in bed sediment and aquatic biota First, it would be worthwhile to determine whether residues of DDT and other organochlorine contaminants have continued to decline or have reached a plateau since last measured nationwide in bed sediment (late 1 970 s) or aquatic biota (mid-1980s) of United States rivers Although... of contamination of currently used pesticides, including the few organochlorine insecticides still permitted for use in agriculture The presence of currently used pesticides, such as chlorpyrifos, dacthal, trifluralin, and oxadiazon, in bed sediment and aquatic biota suggests that other pesticides that are moderately hydrophobic (water solubility less than 1 mg/L or log Kow greater than 3) and moderately... most organochlorine insecticides have declined nationally since they were banned or severely restricted, the largest declines took place during the 1 970 s and early 1980s Legitimate questions remain regarding the biological significance of very low residues of organochlorine compounds to fish, wildlife, and humans Also, it will be important to continue to monitor these compounds in the contaminated areas... considered individually), synergistic (where the mixture is more toxic than the chemicals considered individually), and additive (where the mixture has toxicity equivalent to the sum of the toxicities of the individual chemicals in the mixture) This is another important area of ongoing research Clearly, there is a wealth of information in the existing literature on pesticides in bed sediment and aquatic biota. .. adult; effects are usually seen in the offspring and not the exposed parent; the timing of exposure is critical in determining the effects; and effects of exposure in utero may not be observed until maturity Animals in the environment generally are exposed to a mixture of contaminants The potential for interactions among mixtures of chemical contaminants exists Possible interactions are generally categorized... in United States rivers and estuaries These are the sampling media best suited to investigate the presence of hydrophobic contaminants in hydrologic systems The hundreds of national, multistate, state, and local studies that have been conducted during the last 30 years have indeed given us a national perspective on hydrophobic pesticides in United States rivers Still, there are gaps in our understanding... xenobiotics has been suggested as contributing to the increased incidence of breast, testicular, and prostate cancers, ectopic pregnancies, and cryptorchidism, and to a decrease in sperm count However, the role of environmental endocrine disruptors in these human health trends remains uncertain With a few exceptions (such as diethylstilbesterol, TCDD, and DDT and its metabolite DDE), epidemiological... understanding of hydrologic systems, the environmental behavior of chemicals in the environment, and the effects of pesticides on the ecosystem and on human health These are formidable tools to be used by the next generation of multidisciplinary research efforts that combine chemistry, hydrology, and ecotoxicology A more complete national perspective of the occurrence, distribution, and significance of pesticides. .. (soil half-life greater than 30 days) may be detected in these sampling media Although nationwide monitoring of these compounds may not be warranted, it may be © 1999 by CRC Press LLC reasonable to monitor such pesticides in areas of known high or repeated use, or in association with specific land uses or crops Third, the detection of pesticides at urban and suburban sites, when targeted in the studies... combined with the little available data on urban and residential uses of pesticides, strongly suggests a need for a systematic, large-scale study of pesticides in the urban environment Fourth, there is a real need for more quantitative information on pesticide use, particularly in nonagricultural applications Finally, there is much to be learned about the biological significance of pesticide residues in . understanding of the distribution and trends in pesticide contamination in bed sediment and aquatic biota. First, it would be worthwhile to determine whether residues of DDT and other organochlorine. pesticide contamination of bed sediment and aquatic biota. There is considerable evidence that the source of DDT in bed sediment and fish in many rivers in the United States is from past insecticide use in. as chlorpyrifos and trifluralin) are very high use pesticides in agriculture today. Their presence in bed sediment and aquatic biota in the studies reviewed suggests that other currently used pesticides of intermediate