Fate and biological effects of methyl parathion in outdoor ponds and laboratory aquaria. I. Fate

Three outdoor ponds were treated with methyl parathion (MEP) applied beneath the water surface at a concentration of 100 micrograms liter-1. Laboratory aquaria containing either tap water, pond water, tap water plus plants, tap water plus sediment, or tap water plus sediment and plants were similarly treated. Samples of water, sediment, and fish were analyzed for residues of MEP. The rate of loss from water and concentrations found in sediment were compared with predictions based on a calculated rate of biodegradation and a sediment:water partition coefficient. The rate of loss of MEP from pond water isolated in an aquarium was similar to the predicted rate. However, the rate of loss from outdoor ponds, or from aquaria containing plants and sediment, was greater than predicted. MEP was not detected in sediment even though predicted concentrations far exceeded the limit of detection. These results are discussed and it is suggested that the rate of biodegradation in shallow bodies of water may be determined predominantly by bacteria attached to sediments and plants, rather than by planktonic bacteria. Bioaccumulation in fish was predicted from empirical equations based on the octanol:water partition coefficient. Observed values were in good agreement with predictions.     

Long-term fate of organochlorine xenobiotics in aquatic ecosystems : Distribution, residual behavior, and metabolism of hexachlorobenzene, pentachloronitrobenzene, and 4-chloroaniline in small experimental ponds

Hexachlorobenzene (HCB), pentachloronitrobenzene (PCNB), and 4-chloroaniline (4-CA) were dosed into the water of small experimental ponds in Southern Germany. The average concentration of the chemicals in the pond water during the application period (4–6 weeks) was about 50 μg/liter. Chemical residue concentrations were determined in water, sediment, and flora and fauna species up to 166 weeks after application. The decrease of all chemicals in the water phase follows exponential functions and can be correlated to some extent with the physicochemical properties such as volatility from water and vapor pressure. Although chemically quite different, the residual behavior of the model compounds followed a similar pattern resulting in relatively high initial concentrations in biota and a slow buildup and subsequent decline of concentrations in the sediment. As to some fauna species (backswimmers and libellula larvae) and to sediment (0- to 20-cm layer), even 3 years after application, ¹⁴C residues of about 0.1 mg/kg could be found. In all analyzed flora species, however, no more residues could be measured in the new vegetation period after application. The amounts of the chemicals used did not cause detectable symptoms of poisoning over the investigation period. Anisols and azo compounds were found to be conversion products of pentachloronitrobenzene and 4-chloroaniline.     

Kinetics of adsorption and desorption of some organochlorine compounds on black carbon in a sediment

Rate constants for adsorption and desorption of four organochlorine compounds on black carbon in a sediment were determined from measurements of the rate of removal, by gas purge, of the organochlorine compounds as single solutes from a water-sediment mixture immediately after addition of the solute to the system. The rates of removal fitted to a kinetic scheme based on Langmuir adsorption onto two types of sites in black carbon. The first-order rate constants for desorption from these sites were comparable to those for slow and very slow desorption from sediment. The time needed to reach apparent equilibrium in the experimental setup, with 10 g sediment/L water, ranged from 13 to 166 h, depending on the sorbate and the adsorption process. These short times to equilibrium suggest no need to assume rate-limiting diffusion from and to adsorption sites in this sediment. Average Gibbs free energies for adsorption of the four organochlorine compounds from the pure solid state were -10 +/- 3 and -20 +/- 3 kJ/mol for low-energy and high-energy sites, respectively, pointing to two different adsorption mechanisms.     

Accumulation and food chain transfer of fluoranthene and benzo[a]pyrene in Chironomus riparius and Lepomis macrochirus

This research investigated the accumulation of polycyclic aromatic hydrocarbons (PAHs) by Chironomus riparius from sediments and transfer of these contaminants to bluegill, Lepomis macrochirus. Experiments were conducted in laboratory microcosms containing sediments spiked with either benzo[a]pyrene (BAP) or fluoranthene (FLU). Chironomids rapidly accumulated PAHs from sediments. Concentrations of BAP and FLU in chironomids increased with sediment concentration; however, FLU accumulated to a much greater extent. At sediment concentrations ranging from 47 to 4,040 g/kg, levels of FLU in chironomids ranged from below detection to 181,000 g/kg. In contrast, the maximum concentration of BAP measured in chironomids at similar sediment levels was 6,030 g/kg. Levels of FLU and BAP in bluegill that were fed contaminated chironomids were generally low, indicating either low uptake or rapid metabolism of these compounds.Bioturbation of sediments by chironomids decreased water clarity and released sediment-associated BAP to overlying water. BAP in water and in C. riparius increased significantly with chironomid density. In experiments where bluegill were exposed to BAP from water, direct contact with sediments, and chironomids, each source contributed to total body burden. The results of the experiments indicated that PAHs in sediments may be mobilized and made available to benthic invertebrates and fish.     

Bioaccumulation of Benzo(<Emphasis Type="Italic">a</Emphasis>)pyrene from Sediment by Fathead Minnows: Effects of Organic Content,Resuspension and Metabolism

The accumulation of ¹⁴C-benzo(a)pyrene (BaP) sorbed to sediment was examined in fathead minnows (Pimephales promelas) to compare uptake from sediment with a high organic carbon (OC) content (7.7%), to that with a low OC content (2%). Ingestion of sediments was quantified by co-labeling the sediment with ¹⁴¹Cerium, which was not assimilated by the fish. Results of this study indicated that (1) significantly greater quantities of BaP were dissolved in water over low-OC sediment, compared to water over high-OC sediment, (2) fish disturbed the sediment and increased the concentration of BaP in centrifuged (particle-free) water, (3) fish ingested significantly more of the low-OC sediment than high-OC sediment, perhaps in response to the lower food quality of the low-OC sediment, and (4) uptake of BaP from sediment ingestion contributed <3% of the total flux of BaP into the fish. Primarily as a result of the greater concentration of BaP in water, fish from the low-OC exposures had significantly higher rates of BaP accumulation. However, after 48 h the body burdens in these fish declined by 50%, likely due to the induction of MFO enzymes in response to accumulation of BaP. A smaller effect was apparent in the fish from the high-OC exposures, consistent with the lower dose of BaP they experienced. These results illustrate the complex, and sometime counterintuitive, interactions that affect the uptake and bioaccumulation of sediment-associated contaminants.     

Dose reduction associated with various countermeasures in freshwater fish contamination in Hong Kong.

Based on a model developed specifically for the local freshwater fish culture system, a dose transfer coefficient for 137Cs of 1.15 mSv per MBq m(-2) is obtained for the consumption of freshwater fish in the first year after deposition. Several countermeasures are suggested to reduce the ingestion dose resulting from a nuclear accident. These countermeasures include suspension of fish culture for a period of time after deposition of radionuclides, the removal of the contaminated pond water and, in the more severe cases, the removal of the sediment. The dose reductions that could be achieved by these countermeasures and the effects of their implementation times relative to the input are investigated. The time of resumption of fish culture in affected ponds and the resulting ingestion dose have also been studied in detail. It is found that reusing a pond for fresh fish culture after 6 months would reduce the ingestion dose in the following year by half as compared with that if the pond was reused a short period of time after deposition. An empirical formula linking the peak concentration in fish and the ingestion dose has been derived. The results are useful to decision-makers in limiting the ingestion dose arising from consumption of contaminated freshwater fish after nuclear accidents.     

Persistence and distribution of azinphos-methyl following application to littoral enclosure mesocosms

The organophosphorus insecticide azinphos-methyl was applied once to the surface of 12 of 18 littoral enclosure mesocosms (5x10 m) constructed in a 2-ha pond near Duluth, Minnesota. Water, sediment, macrophytes, and adult fathead minnows were analyzed for residue to determine the persistence, distribution, and mass balance of azinphos-methyl. Nominal treatment concentrations were 0, 0.2, 1, 4, and 20 microg/liter active ingredient. The maximum residue concentration in the water was measured 1h after treatment. The half-life in the water column ranged from 1.2 to 2 days and 95% of the residue dissipated in 5.4 to 10.2 days. Measurable residues were found in the sediment, macrophytes, and fish. Maximum residues in these media were measured at 4, 1, and 0.12 days. respectively. The water and sediment were the most important sorptive compartments for azinphos-methyl residue. The macrophytes and fish were of minor importance, containing only trace amounts of the mass applied.     

Desorption of pyrethroids from suspended solids

Pyrethroid insecticides have been widely detected in sediments at concentrations that can cause toxicity to aquatic organisms. Desorption rates play an important role in determining the bioavailability of hydrophobic organic compounds, such as pyrethroids, because these compounds are more likely to be sorbed to solids in the environment, and times to reach sorptive equilibrium can be long. In the present study, sequential Tenax desorption experiments were performed with three sorbents, three aging times, and four pyrethroids. A biphasic rate model was fit to the desorption data with r(2) >?0.99, and the rapid and slow compartment desorption rate constants and compartment fractions are reported. Suspended solids from irrigation runoff water collected from a field that had been sprayed with permethrin 1 d before were used in the experiments to compare desorption rates for field-applied pyrethroids with those for laboratory-spiked materials. Suspended solids were used in desorption experiments because suspended solids can be a key source of hydrophobic compounds in surface waters. The rapid desorption rate parameters of field-applied permethrin were not statistically different from those of laboratory spiked permethrin, indicating that desorption of the spiked pyrethroids is comparable to desorption of the pyrethroids added and aged in the field. Sorbent characteristics had the greatest effect on desorption rate parameters; as organic carbon content of the solids increased, the rapid desorption fractions and rapid desorption rate constants both decreased. The desorption rate constant of the slow compartment for sediment containing permethrin aged for 28 d was significantly different compared to aging for 1 d and 7 d, whereas desorption in the rapid and slow compartments did not differ between these treatments.     

Spatially distributed ecological risk for fish of a coastal food web exposed to dioxins

The ecological risk posed by 2,3,7,8-polychlorodibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorobiphenyl (PCB) congeners to five edible fish species of the aquatic food web of Venice Lagoon, Italy, was estimated by applying a state-of the-art kinetic bioaccumulation model. Site-specific data were used to define a representative food web. The experimental data set for model validation and application included PCB and PCDD/F congener concentrations in sediments, in water, and in five organisms (both invertebrates and fish). The spatial distribution of risk was evaluated by dividing the lagoon into six homogeneous areas, and for each area, sediment, water, and organism dioxins concentrations were calculated. The bioaccumulation model was calibrated for both nonmetabolizing and metabolizing congeners, the metabolic elimination rates of which were estimated. The model validation showed an acceptable bioaccumulation estimation, evaluated using the model bias parameter. The calibrated model was applied to the six areas of the lagoon to estimate the fish predicted exposure concentration as 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity equivalents from sediment concentration. Internal no-effect concentrations were calculated for each fish species from literature data. Risk was estimated by applying the hazard quotient (HQ) approach, obtaining the ecological risk for each fish species on the basis of 90 and 99% protection levels, in each of the six lagoon areas. The sediment dioxins concentration does not pose a significant risk to the selected fish species at the 90% protection target (HQ<1), whereas risk is significant (HQ>1) at the 99% protection target. Risk results were higher near the Porto Marghera industrial district, Italy, and in lagoon zones characterized by a low water-exchange rate and freshwater basin inputs.     

Fate and effects of the insecticide-miticide chlorfenapyr in outdoor aquatic microcosms

The concentrations of chlorfenapyr in water and sediment in a lentic pond following early and late applications in a Florida crop treatment program were predicted using PRZM and EXAMS modeling and incorporating 30 years of actual rainfall data. An outdoor microcosm study was also conducted to determine the fate of chlorfenapyr and its effects on zooplankton, macroinvertebrates, phytoplankton, and fish in a freshwater system under exposure conditions representing simulated surface runoff and/or spray drift. The microcosm design used a regression model with five treatments (i.e., 300 microg/L spray, 30 microg/L spray, 15 microg/L spray and 30 microg/L runoff, 1.2 microg/L spray and 2.5 microg/L runoff, 30 microg/L runoff) plus a control. Chlorfenapyr was applied as an aqueous suspension concentrate (36% a.i.) to six microcosm tanks (30.9 m3). The no-observed-effect-concentration (NOEC) for zooplankton was the water concentration produced from the combination 1.2 microg/L spray and 2.5 microg/L runoff treatment. The NOEC for bluegill sunfish was the water concentration produced from the 30 microg/L runoff, which was significantly higher than the exposure concentrations from the lowest combination treatment. Chlorfenapyr was more toxic via spray to the water than via an exposure simulating surface runoff. The 96-h time weighted average concentrations (TWAs) from the lowest joint treatment and the 30 microg/L runoff treatment in the microcosm study were similar to model-predicted water 96-h TWA concentrations from early and late applications. The toxicity data from laboratory and microcosm studies along with water exposure data indicate low hazard to zooplankton species in the water column. Although chlorfenapyr remained in sediment, TWAs concentrations from the microcosm study along with model-predicted concentrations indicate low hazard to benthic invertebrate species based on acute toxicity to amphipods in the laboratory. Results from this assessment indicate that with appropriate measures to mitigate spray drift to shallow water bodies, applications of chlorfenapyr do not present a hazard to aquatic organisms during labeled uses.     

Bacterial and metal quality of tilapia (Oreochromis nilotica) aquaculture systems

Bacterial quality of four tilapia (Oreochromis nilotica) growing pond systems based on total coliforms, Aeromonas hydrophila, Yersinia enterocolitica and Campylobacter jejuni occurrence was examined. Surveys were conducted during the rainy and dry seasons. Results showed that the bacteria were present in feed, pond water and sediment. Seasonality in the incidence of the bacteria was observed, with higher numbers recorded in the dry than in the rainy season. Site‐specific sampling programmes were conducted to determine levels of metals (K⁺, Ca²⁺, Fe²⁺, Mg²⁺, Cu²⁺and Cr³⁺) in the fish environment. Higher metal levels were encountered in sediment than in the water column. The metal concentrations showed an inconsistent seasonality.     

Bioaccumulation of Polychlorinated Biphenyls (PCBs) in Fish Host-Parasite Bentho-Pelagic Food Chain in Epe Lagoon,Lagos, Nigeria

This paper investigates the concentrations of PCBs in the water and sediment media and its bio-concentration in the fish host-parasite bentho-pelagic food chain in Epe lagoon. Samples of water, sediment, plankton, mollusks, fish and intestinal helminth parasites were collected from three stations (Oriba, Imode and Ikosi) in Epe Lagoon. Concentration of total PCBs in the surface water and sediment across the stations ranges from 3.20 to 6.00 ppb and 405.50–860.70 ppb respectively. Imode had the highest concentrations. The plankton bio-concentrates most PCBs in Ikosi (286.70 ppb) followed by Imode concentration (165.40 ppb), then Oribo (92.60 ppb) with total bio-concentration of 544.60 ppb. Surface water temperature negatively and strongly correlates with PCBs in the plankton. The planktons bio-concentrates total PCBs 44 times than that in the surface water. Chrysichthys nigrodigitatus bio-concentrates total PCBs 48 times than that in the surface water. Bioaccumulation of PCBs in human food chain could pose health risk.

     

Levels of contaminants in effluent,sediment, and biota from Bai Bang,a bleached kraft pulp and paper mill in Vietnam

Chemical analyses of organochlorine compounds in effluents, sediment, and biota samples were done for the Bai Bang Paper Company (BAPACO), a bleached kraft pulp and paper mill in Vietnam. High chlorine consumption in the bleaching process resulted in a high specific discharge of adsorbable organic halogens (AOX), 4.7 kg/ton of air dried pulp (ADP), and polychlorinated phenolic compounds (31 g/ton ADP) in the effluent. The extractable organochlorine content in the accumulated fiber sludge of the sedimentation tank (70–100 g/g) was more than 100 times higher than the sediment from the receiving river. Chlorinated compounds including dioxins were detected at low levels in sediment and rice, crab, mollusc and fish samples. Significant amounts of the chlorinated persistent compounds are probably transported by the Red River to the river mouth and coastal area. Heavy metal content was high in sediment and mollusc samples from the receiving rice field and fish pond. There may be a possible risk for human intoxication of the metals through the aquatic food chain via the mollusc but not via the rice.     

Heavy Metal Concentrations in Food Chain of Lake Velenjsko jezero, Slovenia: An Artificial Lake from Mining

The concentration of metals (Pb, Cd, Zn, Hg) in different ecosystem components (lake water, sediment, plankton, macrophytes, and fish tissues) has been determined in Velenjsko jezero, an artificial lake resulting from mining activity. The risk to humans from consuming fish has been evaluated from the heavy metal load of fish muscle tissue. Heavy metals are transferred through the food chain at different levels, and Hg is found to be the element of the highest ecotoxicological concern. Although both sediment and plankton contain relatively low concentrations of Hg, this element accumulates in high levels in fish, especially in the benthivorous species Abramis brama danubii and predator species Perca fluviatilis. Moreover, Hg appears to be very mobile in the fish organism. Whereas the other metals remained mostly in liver (Cd) or gills (Zn, Pb), levels of Hg in fish muscle and liver were the same and markedly higher than in gills. However, in muscle, the average concentrations of each metal were below their maximum limits, determined either by Slovenian legislation or by the Food and Agriculture Organization.     

Fate of 2,5,4'-trichlorobiphenyl in outdoor ponds and its uptake via the food chain compared with direct uptake via the gills in grass carp and rainbow trout

A field experiment was carried out to investigate the fate and the extent to which food chain transfer of a PCB congener (2,5,4'-trichlorobiphenyl; 3-CB) could affect its potential for bioaccumulation. Three 35-m3 ponds were each stocked with 25 rainbow trout (a carnivore) and 20 grass carp (a herbivore). 3-CB was supplied to each pond at a nominal concentration of 14 micrograms liter-1. Samples of water, sediment, grass carp, rainbow trout, aquatic plants, and invertebrates were removed at intervals from 0 to 28 days after treatment and residues of 3-CB were determined using gas-liquid chromatography with electron-capture detection. The fate of 3-CB in the ponds was determined by transport rather than degradation processes. Evaporation accounted for 86-87% loss and sorption onto sediment and biota for 11-12% loss of 3-CB from the pond water after 28 days. The kinetics of transport between water, air, sediment, and biota were studied after fitting the data to a three-compartment model. This model was used to calculate rates of evaporation (ke) and sorption. The calculated value for ke was in good agreement with predictions based on fundamental relationships between Henry's constant, windspeed, and ke. Residues of 3-CB in rainbow trout accumulated to a significantly greater extent (P less than 0.05) than in grass carp. This difference could not be explained by differences in growth rates, distribution of lipids, or by a difference in rates of metabolism. The most plausible explanation is that there was a difference in accumulation of 3-CB residues via the food chain. This experimental work supports the conclusion, suggested by a modeling approach of other workers, that food chain accumulation of PCBs can be an important route for uptake when environmental concentrations are very low.     

不同水体富营养化程度与水中鱼鸭体内微囊藻毒素相关分析

目的为了解不同水体微囊藻毒素(MC-LR)污染状况以及鱼鸭食品中的富集量。方法 2009-09分别采集池塘水、鱼、鸭,长江水(涪陵段)和鱼;用sep-pakc18(ODS)柱分离,酶联免疫吸附(ELISA)法测定含量。结果池塘水体MC-LR是长江水的6.696倍,平均含量分别为1.366μg/L和0.204μg/L,差异有统计学意义(t=22.27,P0.01);池塘鱼是长江鱼1.98倍,平均含量分别为1.008ng/kg和0.514ng/kg,差异有统计学意义(t=2.26,P0.05);鸭肝MC-LR是鸭肉的1.59倍,平均含量分别为0.748ng/kg和0.470ng/kg,差异有统计学意义(t=3.20,P0.05)。结论池塘水和鱼中MC-LR含量高于长江水和鱼中含量,鸭肝MC-LR含量高于鸭肉。     

Relative Contributions of Aqueous and Dietary Uptake of Hydrophobic Chemicals to the Body Burden in Juvenile Rainbow Trout

This study assessed the relative contributions of aqueous versus dietary uptake of three hydrophobic chemicals, 1,2,4-trichlorobenzene (1,2,4-TCB), 1,2,3,4,5-pentachlorobenzene (PeCB), and 2,2′,4,4′,6,6′-hexachlorobiphenyl (HCBP). Juvenile rainbow trout (Oncorhynchus mykiss) were exposed separately to chemically spiked water and food for 4 days and 12 days, respectively. Chemical concentrations were measured in the food, water, and tissues, and this allowed calculation of uptake rate constants (k₁ from water exposure, k_d from food exposure). The k₁ values for the three test chemicals were approximately five orders of magnitude greater than the k_d values. Using these measured uptake rate constants, a simulation model was used to predict the relative aqueous versus dietary uptake when fish were exposed simultaneously to water and food contaminated with these hydrophobic chemicals. The model predicted for all three test chemicals that the two uptake routes would contribute equally to the chemical body burden in fish whenever the food:water chemical concentration ratio was near 10⁵. However, using food:water chemical concentration ratios that might be expected in nature, the model predicted that gill uptake could account for over 98% of fish body burden for both 1,2,4-TCB and PeCB uptake (log K_ow values of 3.98 and 5.03, respectively). For HCBP (log K_ow of 7.55), the model predicted that the dietary uptake could contribute over 85% of the body burden. Thus, depending on the actual food:water chemical concentration ratio, aqueous uptake via the gills can predominate even when the chemicals have a log K_ow value greater than 5.0. In addition, we confirmed that dietary uptake of hydrophobic xenobiotics increases with increasing log K_ow. Received: 30 November 1999/Accepted: 3 May 2000     

Effect of Maintaining Rainbow Trout in Creosote Microcosms on Lens Optical Properties and Liver 7-Ethoxyresorufin-O-Deethylase (EROD) Activity

Previously, exposure of fish to polycyclic aromatic hydrocarbons (PAHs) in both field and laboratory settings has been associated with eye damage, but this has only been expressed qualitatively. In this study, an automated scanning laser system has been employed to quantitatively evaluate changes in lens optical quality in rainbow trout (Oncorhynchus mykiss) following their in vivo exposure to creosote, which is a complex mixture with many PAHs. Rainbow trout were placed in 12,000-L outdoor microcosms dosed with 0, 3, or 10 μl/L liquid creosote for a 28-day period. Collected fish were examined for changes in focal length variability (FLV), lens size, and weight. These measurements were compared with induction of hepatic ethoxyresorufin-O-deethylase (EROD) activity and hepatic and water concentrations of priority pollutant PAHs. The optical quality of rainbow trout lenses was significantly reduced following creosote exposure, as indicated by increased FLV. Lens damage was significantly related to hepatic EROD activity, and both effects rose with creosote dose. Analytical measurements of microcosm water indicated elevated concentrations of PAHs in creosote-dosed ponds, including compounds capable of inducing rainbow trout EROD activity in vitro. Hepatic concentrations of PAHs were low and not related to creosote dose, likely due to rapid metabolism and elimination. This study demonstrates for the first time employment of a highly sensitive and quantitative technique to measure lens damage in fish exposed to contaminants in situ. The relationship between this effect and hepatic CYP1A activity may suggest a mechanistic linkage, which could lead to the use of EROD activity as an indicator of toxic effect rather than just chemical exposure. Received: 17 May 1999/Accepted: 24 September 1999     

Lead accumulation rates in tissues of the estuarine teleost fish,Gillichthys mirabilis: Salinity and temperature effects

Tissue-specific lead accumulation rates were determined in the estuarine teleost fish,Gillichthys mirabilis, as a function of four variables; sea water lead concentration, duration of exposure to lead, salinity, and temperature. Distinct tissue-specific accumulation rates were found. Spleen, gills, fins, and intestine accumulated the greatest amounts of lead; liver and muscle accumulated the least lead.Decay of lead from tissues of lead-exposed fish was observed only for gills, fins, and intestine, tissues which all possess an outer or inner covering of mucus. Our data suggest that the rapid turnover of lead in these mucus-covered tissues is a result of lead complexing with mucus and subsequent loss of lead when the mucus layer is sloughed off. In spleen and vertebrae, lead levels continued to rise in fish returned to natural (unspiked) sea water from lead-spiked sea water.The rate of lead accumulation was dependent on both the holding salinity and the temperature. Fish held at high temperature accumulated lead more rapidly than fish held at low temperature. The rate of lead accumulation was inversely proportional to the salinity of the medium. Both of these environmental effects on lead accumulation rates could be significant in estuarine habitats where lead concentrations, salinity, and temperature are all apt to vary seasonally.     

Concentrations of Chlorinated Organic Compounds in Biota and Bed Sediment in Streams of the San Joaquin Valley, California

Samples of resident biota and bed sediments were collected in 1992 from 18 sites on or near the floor of the San Joaquin Valley, California, for analysis of 33 organochlorine compounds. The sites were divided into five groups on the basis of physiographic region and land use. Ten compounds were detected in tissue, and 15 compounds were detected in bed sediment. The most frequently detected compound in both media was p,p′-DDE. Concentrations of ΣDDT (sum of o,p′- and p, p′ forms of DDD, DDE, and DDT) were statistically different among groups of sites for both tissue and sediment (Kruskal-Wallis, p < 0.05). Concentrations in both media were highest in streams draining the west side of the valley. Concentrations of ΣDDT in tissue were significantly correlated with specific conductance, pH, and total alkalinity (p < 0.05), which are indicators of the proportion of irrigation return flows in stream discharge. Concentrations in sediment on a dry-weight basis were not correlated with these water-quality parameters, but total organic carbon (TOC) normalized concentrations were significantly correlated with specific conductance and pH (p < 0.05). Regressions of the concentration of ΣDDT in tissue, as a function of ΣDDT in bed sediment, were significant and explained up to 76% of the variance in the data. The concentration of ΣDDT in sediment may be related to mechanisms of soil transport to surface water with bioavailability of compounds related to the concentration of TOC in sediment. The results of this study did not indicate any clear advantage to using either bed sediment or tissues in studies of organochlorine chemicals in the environment. Some guidelines for protection of fish and wildlife were exceeded. Concentrations of organochlorine chemicals in biota, and perhaps sediment, have declined from concentrations measured in the 1970s and 1980s, but remain high compared to other regions of the United States. Received: 6 August 1996/Accepted: 5 May 1997