Some pesticides and organic compounds were in widespread use for nearly 40 years until banned or restricted in the 1970's and 1980's (Smith and others, 1988), when it was learned that many of these compounds are toxic and also accumulate in the food chain. These compounds include organochlorine pesticides (such as DDT and chlordane) and polychlorinated biphenyls (PCBs, formerly used as electrical insulators). Because of the low chemical reactivity, resistance to oxidation, and resistance to other degenerative processes, residues of these compounds have been shown to be persistent in the environment (Great Lakes Basin Commission, 1975). These compounds generally are not soluble in water but can accumulate in the tissues of organisms that live in the water. As a result, tissue samples of fish are collected and analyzed for the presence of these compounds.
Organochlorine pesticides (many of which are now banned) are persistent in the environment. Trace amounts are present in streambed sediment and fish. Fish are collected for study by a team of biologists using equipment like this barge-mounted electroshocker. (Photograph by Steven F. Siwiec, U.S. Geological Survey.)
Twenty sites were sampled from 1992 to 1995 to determine the occurrence and distribution of selected organochlorine compounds. Whole-body tissue samples of white sucker were collected at 19 of the 20 sites and smallmouth bass were collected at 5 sites. Organic compounds were detected in whole-body fish tissue and the streambed sediment at all 20 sites sampled, which represented a variety of settings. Of the 28 compounds analyzed for, 12 were detected.
Although some of the detected compounds are known human-health risks, an interagency work group on fish-tissue contaminants (composed of representatives of the Pennsylvania Department of Environmental Protection, Pennsylvania Fish and Boat Commission, and Pennsylvania Department of Health) reviewed the data collected by the USGS, compared the data to FDA action levels, and concluded that no public-health advisories were warranted for the fish species (white sucker or smallmouth bass) collected at any of the sampling sites. Concentrations in the whole body of fish and the edible portions (fillets) are not directly comparable. Nevertheless, the FDA action level for human consumption for total chlordane [300 µg/kg (micrograms per kilogram)], total DDT (5,000 µg/kg) (U.S. Food and Drug Administration, 1992), or total PCBs (2,000 µg/kg) (U.S. Food and Drug Administration, 1995) in the edible portion was not exceeded in the whole-body tissues at any of the sample locations. The collection of whole fish and fillet data in future studies would aid in identifying problem sites and evaluating the need for fish-consumption advisories.
PCBs in fish tissue were associated with urban and industrial land use. The organochlorine pesticides and their degradation products in fish tissue showed an association with agricultural land use. Organochlorine concentrations detected in fish tissue were evaluated in terms of the major land uses present in the basin (agricultural, forested, urban) as shown in the graph below. The two sites representing basins with a mixture of agricultural, urban, and industrial land uses had the highest concentrations of total PCBs, total DDT, and total chlordane. DDT and chlordane were associated with the highest percentages of agricultural land use. Tissue samples from sites whose drainage included the greatest percentage of urban land use, although never a dominant land use, had higher total PCB concentrations than those at sites downstream from less urban use. Samples from sites categorized as forest dominant (greater than 50 percent of the basin area forested) had the lowest number of detectable organochlorine compounds and the lowest concentrations overall.
The fish-tissue data indicate that DDT and chlordane have degraded over time and that no recent influx of these compounds has occurred. Organochlorine pesticides such as DDT and chlordane degrade in the environment over time into a series of breakdown products called metabolites. The most persistent metabolite of DDT-- p,p'-DDE --made up about 50 percent of the total DDT detected in fish tissue. Because the metabolite p,p'-DDE is the most persistent, it can be expected to be the major metabolite present late in the degradation process. The high percentage of p,p'-DDE indicates no recent influx of total DDT within the basin. Concentrations of two components of total chlordane, cis-chlordane and trans-nonachlor, were the highest among the chlordane components detected in fish tissue. These are the most abundant and persistent components of chlordane. The high concentrations of more persistent components indicate that degradation has taken place.
At four sites, concentrations of total DDT or total chlordane in streambed sediment exceeded USEPA Tier 1 guidelines for protection of aquatic life (U.S. Environmental Protection Agency, 1996b). Tier 1 guidelines for total PCBs were not exceeded at any of the sites. Of the 32 compounds analyzed for, 15 were detected. The highest concentrations were for metabolites of DDT and components of total chlordane, more specifically, the concentrations of the p,p'- forms of DDD, DDE, and DDT, trans-nonachlor, and cis-nonachlor. Further analysis of the data shows a strong correlation between the concentrations of these compounds and PCBs in the streambed sediments and whole-fish tissues, indicating the possibility of a direct contaminant pathway. For example, the highest concentrations of total DDT and chlordane in streambed sediments were in Quittapahilla Creek. The fish-tissue samples at that site also had the highest concentrations of DDT and chlordane. Codorus Creek had the highest concentrations of total PCBs in both streambed sediment and fish tissue.
The concentration patterns for streambed sediment and fish tissue with respect to land use were similar (see graph below). Sites representing basins with agricultural and mixed urban and industrial land use had the highest concentrations of total PCBs, total DDT, and total chlordane. Sites representing basins with the highest percentage of agricultural land use showed the highest concentrations of total DDT and total chlordane. Sites representing basins with the greatest percentage of urban and industrial land use (though never dominant) had the highest concentrations of total PCBs. Streambed sediments from the forest-dominated sites had the lowest concentrations of all organochlorine compounds and PCBs.
Median concentrations of total organochlorine pesticides and total PCBs in white sucker tissue and streambed sediment are grouped by the predominant land use in the basin to illustrate the effects of land use.
Sites representing basins with a mixture of agricultural, urban, and industrial land uses had the highest concentrations of total PCBs, total DDT, and total chlordane. PCB concentrations were associated with the highest percentages of urban land use, and DDT and chlordane were associated with the highest percentages of agricultural land use.
At most sites where DDT was detected, the DDE/DDT ratio was greater than 1, indicating long-term degradation of the DDT. At only 3 of the 21 sites did concentrations of DDT in the sediment and DDE/DDT ratios indicate a recent influx of DDT. At six of the sites, data were available to compare concentrations of organic compounds in sediment detected in 1974 (Hollowell, 1975) to the concentrations detected in the 1992-95 NAWQA survey. At most of these sites, total DDT and total chlordane concentrations declined between 1974 and 1995. The concentrations of the most persistent metabolite -- p,p'-DDE -- increased at most of these sites, illustrating the continued degradation of DDT. Concentrations of total DDT and total PCBs increased significantly at the Codorus Creek site, indicating a recent influx of these contaminants. This is also one of the sites where the DDE/DDT ratio indicated a recent influx of DDT. The evidence of a recent influx of DDT at the Codorus Creek site or the other two sites was not apparent from the analysis of DDT in fish tissue.
Concentrations of semivolatile organic compounds (SVOCs) in streambed sediment exceeded USEPA Tier 1 guidelines for protection of aquatic life at 4 of the 21 sites. All the SVOCs that exceeded the guidelines were polycyclic aromatic hydrocarbons (PAHs), a group of organic compounds that result from incomplete combustion of fossil fuels, wood, and municipal solid waste or are present naturally in coal. A nationwide study using NAWQA data (Lopes and others, in press) showed concentrations of PAHs were strongly correlated with population density, urban land use, and toxic releases to the air.
The sites where concentrations of PAHs exceeded Tier 1 guidelines include Quittapahilla Creek and Codorus Creek. These basins have agricultural land mixed with urban and industrial land use (see graph below) and also have the highest concentrations of PCBs, DDT, and chlordane in streambed sediment and fish tissue. Concentrations of PAHs also exceeded guidelines at Swatara Creek, which drains an area of significant coal-mining activity, and at the Susquehanna River at Conowingo Reservoir.
The sum of PAHs was well above the NAWQA medians even at sites with little urban, industrial, or mining land use. The proximity of the Study Unit to major metropolitan areas of the northeastern United States is a probable explanation for this fact because PAHs are also distributed regionally by atmospheric deposition. The sum of phthalates also was higher than the national NAWQA median at all of the sites. Phthalates are commonly from industrial sources. The sum of phenols ranged from well below the national median to well above the national median. Phenols are used in industrial, agricultural, and sanitation activities and also can occur naturally.