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A non-lethal biopsy method for monitoring mercury (Hg) concentrations in smallmouth bass (Micropterus dolomieu; smallmouth) from the Eleven Point River in southern Missouri USA was evaluated. A biopsy punch was used to remove a muscle tissue plug from the area immediately below the anterior dorsal fin of 31 smallmouth. An additional 35 smallmouth (controls) were held identically except that no tissue plug was removed. After sampling, all fish were held in a concrete hatchery raceway for 6 weeks. Mean survival at the end of the holding period was 97 % for both groups. Smallmouth length, weight and Fulton's condition factor at the end of the holding period were also similar between plugged and non-plugged controls, indicating that the biopsy procedure had minimal impact on growth under these conditions. Tissue plug Hg concentrations were similar to smallmouth Hg data obtained in previous years by removing the entire fillet for analysis.

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The Big River (BGR) drains much of the Old Lead Belt mining district (OLB) in southeastern Missouri, USA, which was historically among the largest producers of lead-zinc (Pb-Zn) ore in the world. We sampled benthic fish and crayfish in riffle habitats at eight sites in the BGR and conducted 56-day in situ exposures to the woodland crayfish (Orconectes hylas) and golden crayfish (Orconectes luteus) in cages at four sites affected to differing degrees by mining. Densities of fish and crayfish, physical habitat and water quality, and the survival and growth of caged crayfish were examined at sites with no known upstream mining activities (i.e., reference sites) and at sites downstream of mining areas (i.e., mining and downstream sites). Lead, zinc, and cadmium were analyzed in surface and pore water, sediment, detritus, fish, crayfish, and other benthic macro-invertebrates. Metals concentrations in all materials analyzed were greater at mining and downstream sites than at reference sites. Ten species of fish and four species of crayfish were collected. Fish and crayfish densities were significantly greater at reference than mining or downstream sites, and densities were greater at downstream than mining sites. Survival of caged crayfish was significantly lower at mining sites than reference sites; downstream sites were not tested. Chronic toxic-unit scores and sediment probable effects quotients indicated significant risk of toxicity to fish and crayfish, and metals concentrations in crayfish were sufficiently high to represent a risk to wildlife at mining and downstream sites. Collectively, the results provided direct evidence that metals associated with historical mining activities in the OLB continue to affect aquatic life in the BGR.

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We studied the ecological effects of mining-derived metals on riffle-dwelling benthic fishes at 16 sites in the Viburnum Trend lead-zinc mining district of southeast Missouri. Fish community attributes were compared to watershed features and to physical and chemical variables including metal concentrations in sediment pore water and fish. Ozark sculpin (Cottus hypselurus), rainbow darter (Etheostoma caeruleum), Ozark madtom (Noturus albater), and banded sculpin (Cottus carolinae) were the most abundant fishes collected. Species richness and density of riffle-dwelling benthic fishes were negatively correlated with metal concentrations in pore water and in fish. Sculpin densities were also negatively correlated with metal concentrations in pore water and in fish, but positively correlated with distance from mines and upstream watershed area. These findings indicate that metals associated with active lead-zinc mining adversely affect riffle-dwelling benthic fishes downstream of mining areas in the Viburnum Trend. Sculpins may be useful as a sentinel species for assessing mining-related impacts on fish communities.

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Lead (Pb) and other metals can accumulate in northern hog sucker (Hypentelium nigricans) and other suckers (Catostomidae), which are harvested in large numbers from Ozark streams by recreational fishers. Suckers are also important in the diets of piscivorous wildlife and fishes. Suckers from streams contaminated by historic Pb-zinc (Zn) mining in southeastern Missouri are presently identified in a consumption advisory because of Pb concentrations. We evaluated blood sampling as a potentially nonlethal alternative to fillet sampling for Pb and other metals in northern hog sucker. Scaled, skin-on, bone-in "fillet" and blood samples were obtained from northern hog suckers (n = 75) collected at nine sites representing a wide range of conditions relative to Pb-Zn mining in southeastern Missouri. All samples were analyzed for cadmium (Cd), cobalt (Co), Pb, nickel (Ni), and Zn. Fillets were also analyzed for calcium as an indicator of the amount of bone, skin, and mucus included in the samples. Pb, Cd, Co, and Ni concentrations were typically higher in blood than in fillets, but Zn concentrations were similar in both sample types. Concentrations of all metals except Zn were typically higher at sites located downstream from active and historic Pb-Zn mines and related facilities than at nonmining sites. Blood concentrations of Pb, Cd, and Co were highly correlated with corresponding fillet concentrations; log-log linear regressions between concentrations in the two sample types explained 94% of the variation for Pb, 73-83% of the variation for Co, and 61% of the variation for Cd. In contrast, relations for Ni and Zn explained <12% of the total variation. Fillet Pb and calcium concentrations were correlated (r = 0.83), but only in the 12 fish from the most contaminated site; concentrations were not significantly correlated across all sites. Conversely, fillet Cd and calcium were correlated across the range of sites (r = 0.78), and the inclusion of calcium in the fillet-to-blood relation explained an additional 12% of the total variation in fillet Cd. Collectively, the results indicate that blood sampling could provide reasonably accurate and precise estimates of fillet Pb, Co, and Cd concentrations that would be suitable for identifying contaminated sites and for monitoring, but some fillet sampling might be necessary at contaminated sites for establishing consumption advisories.

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The Viburnum Trend mining district in southeast Missouri, USA is one of the largest producers of lead-zinc ore in the world. Previous stream surveys found evidence of increased metal exposure and reduced population densities of crayfish immediately downstream of mining sites. We conducted an in-situ 28-d exposure to assess toxicity of mining-derived metals to the woodland crayfish (Orconectes hylas). Crayfish survival and biomass were significantly lower at mining sites than at reference and downstream sites. Metal concentrations in water, detritus, macroinvertebrates, fish, and crayfish were significantly higher at mining sites, and were negatively correlated with caged crayfish survival. These results support previous field and laboratory studies that showed mining-derived metals negatively affect O. hylas populations in streams draining the Viburnum Trend, and that in-situ toxicity testing was a valuable tool for assessing the impacts of mining on crayfish populations.

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We evaluated three potentially nonlethal alternatives to fillet sampling for the determination of mercury (Hg) concentrations in smallmouth bass (Micropterus dolomieu). Fish (n = 62, 226-464 mm total length) from six sites in southern Missouri were captured by electrofishing. Blood samples (1 mL) from each fish were obtained by caudal veinipuncture with a heparinized needle and syringe. Biopsy needle (10 mm x 14 gauge; three cuts per fish; 10-20 mg total dry weight) and biopsy punch (7 mm x 5 mm in diameter, one plug per fish, 30-50 mg dry weight) samples were obtained from the area beneath the dorsal fin. Fillet samples were obtained from the opposite side of the fish. All samples were freeze-dried and analyzed for total Hg by combustion amalgamation atomic absorption spectrophotometry. Mean relative standard deviations (RSDs) of triplicate samples were similar for all four methods (2.2-2.4%), but the range of RSDs was greater for blood (0.4-5.5%) than for the muscle methods (1.8-4.0%). Total Hg concentrations in muscle were 0.0200-0.8809 microg/g wet weight; concentrations in plug, needle, and fillet samples from each fish were nearly identical. Blood Hg concentrations were 0.0006-0.0812 microg/mL and were highly correlated with muscle concentrations; linear regressions between log-transformed blood and fillet Hg concentrations were linear and statistically significant (p < 0.01), and explained 91-93% of the total variation. Correlations between fillet Hg concentrations and fish size and age were weak; together they explained

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The H4IIE cell bioassay has proven utility as a screening tool for planar halogenated hydrocarbons (PHHs) and structurally similar chemicals accumulated in organisms from the wild. This bioassay has additional applications in hazard assessment of PHH exposed populations. In this review, the toxicological principles, current protocols, performance criteria, and field applications for the assay are described. The H4IIE cell bioassay has several advantages over the analytical measurement of PHHs in environmental samples, but conclusions from studies can be strengthened when both bioassay and analytical chemistry data are presented together. Often, the bioassay results concur with biological effects in organisms and support direct measures of PHHs. For biomonitoring purposes and prioritization of PHH-contaminated environments, the H4IIE bioassay may be faster and less expensive than analytical measurements. The H4IIE cell bioassay can be used in combination with other biomarkers such as in vivo measurements of CYP1A1 induction to help pinpoint the sources and identities of dioxin-like chemicals. The number of studies that measure H4IIE-derived TCDD-EQs continues to increase, resulting in subtle improvements over time. Further experiments are required to determine if TCDD-EQs derived from mammalian cells are adequate predictors of toxicity to non-mammalian species. The H4IIE cell bioassay has been used in over 300 published studies, and its combination of speed, simplicity, and ability to integrate the effects of complex contaminant mixtures makes it a valuable addition to hazard assessment and biomonitoring studies.

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Fish were collected in late 1995 from 34 National Contaminant Biomonitoring Program (NCBP) stations and 13 National Water Quality Assessment Program (NAWQA) stations in the Mississippi River basin (MRB) and in late 1996 from a reference site in West Virginia. Four composite samples, each comprising (nominally) 10 adult common carp (Cyprinus carpio) or black bass (Micropterus spp.) of the same sex, were collected from each site and analyzed for organochlorine chemical residues by gas chromatography with electron capture detection. At the NCBP stations, which are located on relatively large rivers, concentrations of organochlorine chemical residues were generally lower than when last sampled in the mid-1980s. Residues derived from DDT (primarily p,p'-DDE) were detected at all sites (including the reference site); however, only traces (or= 0.05 microg/g) at only 35% of the stations, mostly in the more industrialized parts of the MRB.

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Specific detection of amanitins in body fluids is necessary for an early diagnosis of an intoxication with amanita mushrooms. In this paper, a liquid chromatographic-mass spectrometric assay after immunoaffinity extraction (IAE-LC-MS) is described for the determination of alpha- and beta-amanitin in urine. The method has been validated according to the criteria established by the Journal of Chromatography B. The assay was found to be selective. The calibration curves for alpha- and beta-amanitin were linear from 5 to 75 ng/ml. Intra- and inter-day accuracy and precision were inside the required limits. Amatoxins in frozen urine samples or immunoaffinity extracts were stable for more than 6 months, and the IAE columns could be used more than fifty times without remarkable loss in performance. LOD for alpha- and beta-amanitin was 2.5 ng/ml and LOQ for both was 5.0 ng/ml. The absolute recoveries of alpha- and beta-amanitin were 63% and 58% for the low quality control and 61% and 57% for the high quality control. The absolute recovery for the internal standard gamma-amanitin methyl ether at 25 ng/ml was 60%. The analysis of 5 authentic urine samples from patients intoxicated by amanita mushrooms showed a good correlation between the results measured by radioimmunoassay and the IAE-LC-MS assay. A partial validation showed that the assay was also suitable for plasma analysis.

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This review compiles and evaluates existing scientific information on the use, limitations, and procedural considerations for EROD activity (a catalytic measurement of cytochrome P4501A induction) as a biomarker in fish. A multitude of chemicals induce EROD activity in a variety of fish species, the most potent inducers being structural analogs of 2,3,7,8-tetracholordibenzo-p-dioxin. Although certain chemicals may inhibit EROD induction/activity, this interference is generally not a drawback to the use of EROD induction as a biomarker. The various methods of EROD analysis currently in use yield comparable results, particularly when data are expressed as relative rates of EROD activity. EROD induction in fish is well characterized, the most important modifying factors being fish species, reproductive status and age, all of which can be controlled through proper study design. Good candidate species for biomonitoring should have a wide range between basal and induced EROD activity (e.g., common carp, channel catfish, and mummichog). EROD activity has proven value as a biomarker in a number of field investigations of bleached kraft mill and industrial effluents, contaminated sediments, and chemical spills. Research on mechanisms of CYP1A-induced toxicity suggests that EROD activity may not only indicate chemical exposure, but also may also precede effects at various levels of biological organization. A current research need is the development of chemical exposure-response relationships for EROD activity in fish. In addition, routine reporting in the literature of EROD activity in standard positive and negative control material will enhance confidence in comparing results from different studies using this biomarker.

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The analysis of PCBs in fish tissues by immunoassay methods was evaluated using fish collected from a US monitoring program, the National Contaminant Biomonitoring Program of the US Department of Interior, Fish and Wildlife Service. Selected composite whole fish samples, which represented widely varying concentrations and sources of PCBs, were extracted and subjected to congener PCB analysis by gas chromatography (GC) and total PCB analysis using an ELISA (ePCBs) calibrated against technical Aroclor 1248. PCB congener patterns in these fishes were different from the patterns found in commercial Aroclors or their combinations as demonstrated by principal component analysis of normalized GC congener data. The sum of the PCB congeners measured by GC (total-PCBs) ranged from 37 to 4600 ng/g (wet weight). Concentrations of PCBs as determined by the ELISA method were positively correlated with total-PCBs and the ePCBs/total-PCBs ratios for individual samples ranged from 1 to 6. Ratios of ePCBs/total-PCBs for dilutions of Aroclors 1242, 1254, and 1260 and for matrix spikes range from 0.6 for 1242 to 2.5 for 1254 and 1260. These results suggest that higher chlorinated PCB congeners have higher affinity for the anti-PCB antibodies. Partial least squares with latent variable analysis of GC and ELISA data of selected Aroclors and fish samples also support the conclusion that ELISA derived PCB concentrations are dependent on the degree of chlorination.

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As part of the National Contaminant Biomonitoring Program (NCBP, formerly a component of the National Pesticide Monitoring Program), the U.S. Fish and Wildlife Service periodically determined concentrations of organochlorine chemical residues and elemental contaminants in freshwater fish collected from a nationwide network of stations. In late 1986 and early 1987, the last time the network was sampled, a total of 319 composite fish samples were collected from 97 NCBP stations. The samples were analyzed for residues of organochlorine chemicals and the elements As, Cd, Cu, Hg, Pb, Se, and Zn. The mean concentration of total DDT and its homologs (p,p'-constituents) declined from 1984 to 1986, thus continuing a trend that began in 1970. The most persistent DDT homolog (p,p'-DDE) was detected at all stations sampled in 1986, and averaged 74% of total DDT residues, up from 70% in 1974-1979 but essentially unchanged from 1984. Collectively, these findings indicated a low rate of influx and continued weathering of DDT in the environment; nevertheless, DDT concentrations in fish from some stations in the South remained high enough to constitute a threat to piscivorous wildlife. Residues of polychlorinated biphenyls (PCBs) also remained widespread, but a significant downward trend in total PCB concentrations and incidence was evident, and PCB mixtures containing early eluting components were present at fewer stations than in the past. PCB concentrations were generally highest in fish from the industrialized rivers of the Northeast and Midwest and from the Great Lakes. Concentrations of toxaphene also declined, as did its incidence, from 88% of the stations sampled in 1980-1981 to 64% in 1986; however, analytical problems with the 1986 samples may have contributed to the latter. The risks represented by PCBs and toxaphene could not be evaluated on the basis of our data. Among cyclodiene insecticides, dieldrin and chlordane-related residues were the most widespread. Mean concentrations of dieldrin declined through 1986, but remained consistently highest in the Great Lakes. For chlordane-related residues, mean concentrations were lower that reported previously, and trans-nonachlor continued to replace cis-chlordane as the most abundant component. Collectively, these findings suggested a lower rate of chlordane influx to the aquatic environment; however, a point source of cyclodiene insecticides to the Mississippi R. near Memphis, TN, remained evident. Residues of mirex, PCA, BHC isomers, endrin, heptachlor, and HCB were either found at relatively few (< 25%) of the stations sampled in 1986 or were characterized by relatively low concentrations. Concentrations of the herbicide Dacthal (DCPA) were also low, but incidence increased from 46% of the stations sampled in 1984 to 61% in 1986. In general, organochlorine chemical concentrations were lower in 1986 than at any time reported previously. For elemental contaminants, the geometric mean, maximum, and 85th percentile concentrations (respectively, all in microgram/g wet weight) in 1986 samples were as follows: As, 0.083, 1.53, 0.24; Cd, 0.011, 0.32, 0.04; Cu, 0.794, 11.0, 1.7; Hg, 0.087, 0.44, 0.18; Pb, 0.058, 1.90, 0.21; Se, 0.417, 3.41, 0.66; and Zn, 21.191, 94.5, 31.7. Mean concentrations of Cu increased and concentrations of As decreased relative to the 1984 collection, but these changes may reflect subtle differences in the species composition of the 1986 collection relative to other collections; concentrations of both elements differ greatly among fishes. There were no other statistically significant changes from 1984 to 1986; however, mean concentrations of As, Cd, Pb, and Zn declined from 1976, when elemental contaminants in fish were first measured in the NCBP, and 1986. In contrast, mean concentrations of Hg and Se did not change appreciably. Moreover, and in contrast to the other elements measured in 1986, concentrations of Hg and Se were high enough to constitute a threat to pisc

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GC-MS is the method of choice for toxicological analysis of toxicants volatile in GC while non-volatile and/or thermally labile toxicants need LC-MS for their determination. Studies are presented on the toxicological detection of the amphetamine-like anorectic clobenzorex in urine by GC-MS after acid hydrolysis, extraction and acetylation and by fluorescence polarization immunoassay (FPIA, TDx (meth)amphetamine II). After ingestion of 60 mg of clobenzorex, the parent compound and/or its metabolites could be detected by GC-MS for up to 84 h or by FPIA for up to 60 h. Since clobenzorex shows no cross-reactivity with the used immunoassay, the N-dealkylated metabolite amphetamine is responsible for the positive TDx results. The intake of clobenzorex instead of amphetamine can be differentiated by GC-MS detection of hydroxyclobenzorex which is detectable for at least as long as amphetamine. In addition, the described GC-MS procedure allows the simultaneous detection of most of the toxicologically relevant drugs. Furthermore, studies are described on the atmospheric pressure ionization electrospray LC-MS detection of alpha- and beta-amanitin, toxic peptides of amanita mushrooms, in urine after solid-phase extraction on RP-18 columns. Using the single ion monitoring mode with the ions m/z 919 and 920 the amanitins could be detected down to 10 ng/ml of urine which allows us to diagnose intoxications with amanita mushrooms.

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Specific and sensitive detection or precise quantification of xenobiotics in biosamples (e.g. blood, urine, saliva, sweat, hair) are great challenges in analytical toxicology. GC-MS is the most sensitive, specific and universal analytical method for low mass xenobiotics. Precise quantification can be performed using the selected ion mode (SIM) and stable isotopes as internal standards. Negative chemical ionization (NCI) can improve severalfold the sensitivity for the determination of compounds with electronegative sites (e.g. halogens). For screening and identification of most of the basic and neutral drugs (e.g. drugs of abuse, psychotropics, hypnotics, analgesics, cardiacs) in urine, a systematic toxicological analysis procedure (STA) was developed using GC-MS after acid hydrolysis, extraction and acetylation. for detection of acidic xenobiotics (e.g. anticoagulants, ACE inhibitors, diuretics, antirheumatics) in urine, a further GC-MS procedure was developed using extractive alkylation. For the detection of non-volatile xenobiotics (e.g. toxic peptides like alpha- and beta-amanitin or phase II metabolites) electrospray LC-MS procedures were developed. The procedures and examples show that in analytical toxicology GC-MS is the method of choice for low mass xenobiotics while LC-MS is that for non-volatiles.

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We developed and evaluated a total toxic units modeling approach for predicting mean toxicity as measured in laboratory tests for Great Lakes sediments containing complex mixtures of environmental contaminants (e.g., polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pesticides, chlorinated dioxins, and metals). The approach incorporates equilibrium partitioning and organic carbon control of bioavailability for organic contaminants and acid volatile sulfide (AVS) control for metals, and includes toxic equivalency for planar organic chemicals. A toxic unit is defined as the ratio of the estimated pore-water concentration of a contaminant to the chronic toxicity of that contaminant, as estimated by U.S. Environmental Protection Agency Ambient Water Quality Criteria (AWQC). The toxic unit models we developed assume complete additivity of contaminant effects, are completely mechanistic in form, and were evaluated without any a posteriori modification of either the models or the data from which the models were developed and against which they were tested. A linear relationship between total toxic units, which included toxicity attributable to both iron and un-ionized ammonia, accounted for about 88% of observed variability in mean toxicity; a quadratic relationship accounted for almost 94%. Exclusion of either bioavailability components (i.e., equilibrium partitioning control of organic contaminants and AVS control of metals) or iron from the model substantially decreased its ability to predict mean toxicity. A model based solely on un-ionized ammonia accounted for about 47% of the variability in mean toxicity. We found the toxic unit approach to be a viable method for assessing and ranking the relative potential toxicity of contaminated sediments.

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Brown bullheads were given a single intraperitoneal dose of 0, 5, 25 or 125 mg kg-1 benzo[a]pyrene (BaP), a carcinogenic polycyclic aromatic hydrocarbon, and evaluated over 18 months. Flow cytometric analyses of hepatocyte DNA content indicated an increase in DNA synthesis in BaP-exposed fish prior to day 14 post-exposure. Thereafter, all flow cytometric variables returned to initial levels. Histopathological evaluation of livers from fish sampled at 18 months revealed significant differences among treatments in the amount of hepatic macrophage ceroid pigmentation and basophilic staining intensity. No neoplasms or changes in blood cell DNA content were detected. Significant morphometric variations existed among fish, but differences between sexes overshadowed differences attributable to dose. Flow cytometry yielded no evidence of long-term DNA alterations from a single exposure to BaP; however, the differences detected by DNA analysis shortly after the toxic event suggest that flow cytometric cell cycle analysis may be useful for documenting continuing exposures.

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Sediments from four inshore industrial sites and a reference site in the Great Lakes were extracted with organic solvents to produce a crude extract, which was separated on alumina into two fractions: predominantly polycyclic aromatic hydrocarbons; and predominantly nitrogen-containing polycyclic aromatic compounds. Crude extracts were redissolved in acetone and analyzed by gas chromatography and gas chromatography-mass spectrometry. The acetone-redissolved crude extracts from the four industrialized sites contained 5.6-313.3 micrograms total polycyclic aromatic compounds/g sediment and 3.0-36.4 micrograms other compounds/g sediment. In addition to the typical EPA priority pollutants, a substantial amount (228.7 micrograms/g sediment) of alkyl-polycyclic-aromatic compounds was detected in sediments from one of the industrialized sites. Extracts from the reference site contained 1.55 micrograms total polycyclic aromatic compounds/g sediment. Medaka (Oryzias latipes) were exposed to multiple pulse doses of acetone-redissolved extracts and fractions. Medaka were also exposed to a known carcinogen, methylazoxymethanol acetate, to verify that chemicals produced tumors in the test fish. Acetone-redissolved extracts and fractions from contaminated sediments were toxic to medaka. Fin erosion and non-neoplastic liver abnormalities were more prevalent in medaka after exposure to acetone-redissolved extracts and fractions from contaminated sediments. Neoplasms previously associated with chemical exposure in wild fishes were induced in medaka exposed to acetone-redissolved extracts and fractions from two of the contaminated sites, but not from the reference site or controls. These findings further support the hypothesis that chemical contaminants in sediments are involved in epizootics of neoplasms in wild fishes at contaminated sites.

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From late 1984 to early 1985, the U.S. Fish and Wildlife Service collected a total of 315 composite samples of whole fish from 109 stations nationwide, which were analyzed for arsenic, cadmium, copper, lead, mercury, selenium, and zinc. Geometric mean, maximum, and 85th percentile concentrations (µg/g wet weight) for 1984 samples were as follows: arsenic-0.14, 1.5, 0.27; cadmium-0.03, 0.22, 0.05; copper-0.65, 23.1, 1.0; mercury-0.10, 0.37, 0.17; lead-0.11, 4.88, 0.22; selenium-0.42, 2.30, 0.73; and zinc-21.7, 118.4, 34.2. The mean concentrations of selenium and lead were significantly lower than in the previous NCBP collection (1980-81). Mean concentrations of arsenic and cadmium also declined significantly between 1976, when elemental contaminants in fish were first measured in the NCBP, and 1984. Of greatest significance, lead concentrations declined steadily from 1976 to 1984, suggesting that regulatory measures have successfully reduced the influx of lead to the aquatic environment.

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The U.S. Fish and Wildlife Service periodically determines concentrations of organochlorine chemicals in freshwater fish collected from a nationwide network of stations as part of the National Contaminant Biomonitoring Program (NCBP, formerly a part of the National Pesticide Monitoring Program). From late 1984 to early 1985, a total of 321 composite fish samples were collected from 112 stations and analyzed for organochlorine chemical residues. The mean concentrations of total DDT did not change from 1980-81 to 1984, following a period of steady decline through the 1970's; however, the mean concentrations ofp,p'-DDT declined significantly. The most persistent DDT homolog (p,p'-DDE) was detected at 98% of the stations sampled in 1984, and constituted 73% of total DDT residues, up from 70% in 1974-79. Collectively, these findings indicate a low rate of influx and continued weathering of DDT in the environment. Residues of polychlorinated biphenyls (PCBs) also remained widespread, but a significant downward trend in total PCBs was evident, and early eluting PCB components were present at fewer stations than in the past. Mean concentrations of dieldrin have not changed since 1978-79; concentrations remained highest in Hawaii and in the Great Lakes. Toxaphene concentrations declined from 1980-81 to 1984, especially in the Great Lakes, and the incidence of toxaphene declined from 88% of the stations sampled in 1980-81 to 69% in 1984. Mean chordane concentrations did not change from 1980-81 to 1984, following a period of decline; however,trans-nonachlor replacedcis-chlordane as the most abundant component, suggesting a lower influx of chlordane to the aquatic environment. Residues of other organochlorines-mirex, pentachloroanisole (PCA), benzene hexachloride (BHC) isomers, endrin, heptachlor, hexachlorobenzene (HCB), and Dacthal(®) (DCPA)-were either found at relatively few (<25%) of the stations sampled in 1984 or were characterized by relatively low concentrations. In general, organochlorine concentrations were lower in 1984 than at any time reported previously.

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