Seasonal and annual distribution of organic contaminants in marine sediments from Elkhorn slough, moss landing harbor and nearshore Monterey Bay, California

This 3-year study provides data on the spatial, seasonal and annual variability of hydrocarbons and total organic carbon present in marine sediments at three sites: Elkhorn Slough, Moss Landing Harbor and nearshore Monterey Bay in the vicinity of Moss Landing, California. The study provides baseline information that could be used to evaluate the potential impacts of future fuel oil releases occuring in the Moss Landing area. Groups of hydrocarbons were chosen to represent the hydrocarbon inputs into the Moss Landing area. These included the pesticide dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyl (PCB), phthalic acid ester (PAE), polycyclic aromatic hydrocarbon (PAH) and combustion PAHs (SigmaCOMBs). For SigmaDDTs, SigmaPCBs, SigmaPAEs, SigmaPAHs and SigmaCOMBs, the major sources of variability were between sites and random effects. Subsites within each site contributed little variability. No significant seasonal differences in any chemical contaminant group were found at any site. Significant seasonal differences in total organic carbon (TOC) and significant annual differences in SigmaPCBs, SigmaPAHs, SigmaCOMBs and SigmaPAEs were found at the nearshore Monterey Bay site. Significant annual differences in SigmaPAEs and TOC were found within Moss Landing Harbor, and significant annual differences in SigmaPAEs were found within the Elkhorn Slough site. Implications for future sampling designs in the Moss Landing area are that given the current baseline conditions (a stable, low rate of hydrocarbon input), a variability of 75-150 m(2) may not need to be heavily sampled. Spatial variability, not seasonal or annual variability, is the major source of hydrocarbon variability in Moss Landing sediments, although 3 years may not be long enough to establish long-term annual trends. Further research to determine the SigmaPAH spatial sampling scale for oil spills is needed.     

Bioavailability of PAHs in the Biobio river (Chile): MFO activity and biliary fluorescence in juvenile Oncorhynchus mykiss.

Cytochrome P450-dependent monooxygenase (MFO) activity and levels of bile PAH metabolites were measured in fish (Oncorhynchus mykiss) exposed to Biobio river (Chile) water. Experiments were performed simultaneously in both the field and laboratory to investigate whether the river water contained notable bioavailable PAH fractions. The field experiment was conducted using fish caged for 41 days at La Mochita (Biobio river mouth) whereas the laboratory experiment involved a 21-day exposure treatment with water collected in the same area. Induction of hepatic MFO, assayed by benzo(a)pyrene monooxygenase activity (BaPMO), and levels of PAH metabolites in the bile were measured in groups of eight (field experiment) and four specimens (laboratory experiment) sampled after 5, 10, 21 and 41 days of exposure. BaPMO was induced by a factor of 23 and 25 in fish caged for 21 and 41 days, respectively. Likewise, a significant BaPMO induction was found in the fish group experimentally exposed to river water for 21 days. Biliary fluorescence measurements, recorded by fixed wavelength fluorescence (FF) and synchronous fluorescence spectroscopy (SFS), revealed significantly high levels of PAH metabolites in bile samples of fish caged for 21 and 41 days. A positive relationship was found between BaPMO activity and biliary PAH metabolites. This study provides evidences that (i) Biobio river water contains a significant bioavailable PAH fraction in terms of marked effects on fish and (ii) the biological indicators MFO activity and bile PAH metabolites represent an excellent screening methodology to assess PAH exposure.     

Isolation of MFO inducers from tissues of white suckers caged in bleached kraft mill effluent

White sucker (Catostomus commersoni) caged for 3 days in a bleached kraft mill effluent (BKME) stream had elevated mixed function oxygenase (MFO) activities 15-90 fold those of fish caged in a reference stream. Liver composites of male and female fish were ground and extracted with dichloromethane (DCM), methanol or 50% DCM/methanol, and tested for MFO activity in rat hepatoma cells (H4IIE). There was no difference in the potency of H4IIE EROD induction among the three solvents, so DCM extracts were split into 31 fractions using reverse phase high pressure liquid chromatography (HPLC). H4IIE MFO activity was elevated in several fractions, with three early peaks and several later peaks of induction, indicating several classes or compounds causing MFO induction were present in the fish livers. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and chlorinated diphenylethers (CDPEs) were detected in several late-eluting fractions, but concentrations were not high enough for these compounds to be solely responsible for the observed induction. Induction by liver extracts decreased as cell exposure times increased (24, 48 or 72 h), suggesting that some inducers were more easily metabolized and eliminated from the H4IIE cells. In contrast, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2378-TCDD) had similar potency over 24, 48 and 72 h, as it was relatively resistant to metabolism.     

Seasonal and diurnal measurements of carbon monoxide and nonmethane hydrocarbons at Mt. Wilson,California: Indirect evidence of atomic Cl in the Los Angeles basin

We present a study of the seasonal and diurnal variability of carbon monoxide and selected volatile organic compounds in the Los Angeles area. Measurements were made during four different nine-day field campaigns in April/May, September, and November, 2007, and February, 2008, at the Mt. Wilson sampling site, which is located at an elevation of approximately 1700 m in the San Gabriel Mountains overlooking Pasadena and the Los Angeles basin. The results were used to characterize the Mt. Wilson site as a representative location for monitoring integrated Los Angeles basin emissions, and, by reference to carbon monoxide emissions, to estimate average annual emissions. The considerable seasonal variability of many hydrocarbons, in both their measured mixing ratios and their relationship to carbon monoxide, was indicative of variable source strengths. Most interestingly, perturbation of C₄ hydrocarbon ratios suggested an enhanced role for chlorine chemistry during the month of September, likely as the result of Los Angeles’ coastal location. Such coastal influence was confirmed by observations of enhanced mixing ratios of marine halocarbons, as well as air mass back trajectories.     

Effect of long term exposure to petroleum on mixed function oxygenases in fish: Further support for use of the enzyme system in biological monitoring

A number of long term, low level petroleum hydrocarbon exposures were carried out from 1978 to 1981 in order to further evaluate use of the mixed function oxygenase (MFO) system in biological monitoring. The studies involved exposure, at ambient temperatures, of fish from three separate families including (a) spawning codfish ($\text{Gadus morhua}$), (b) post-spawned sculpins ($\text{Myoxocephalus octodecemspinosus}$), and (c) gonadally maturing flounder ($\text{Pseudopleuronectes americanus}$). MFO activity remained elevated approximately four-fold in the liver, and three-fold in the gills of codfish exposed for four months to water concentrations of 0.30–0.60 ppm petroleum, at ?1-1°C. Similarly, liver enzyme activity remained elevated approximately three-fold in sculpins exposed to very low levels (0.15–0.20 ppm) of petroleum for three months, at 4–12°C. Results indicate that several years may be required before hydrocarbon concentrations are reduced in petroleum contaminated sediments, such as those heavily impacted by oil spills, to non-inducing threshold levels. Oil contaminated sediment was, even after a year of weathering, quite effective in inducing a high level of MFO activity (seven-fold) in flounder, at 11-6°C. A number of factors that might detract from use of the mixed function oxygenase system in biological monitoring were not realized in these long term studies with petroleum hydrocarbons.     

Evaluation of the genotoxic and cytochrome P450 monooxygenase-inhibitory potential of Dicuran on procaryotic and eucaryotic test systems

The effect of the herbicide Dicuran 500 FL (formulated product) on the phenotypical and genotypical changes in procaryotic and eucaryotic organisms was investigated using short-term tests for detecting genotoxins. Since pesticides discharged in the water environment can modulate the mixed-function monooxygenases (MFO) detoxification system of water organisms, the in vivo and in vitro effects of Dicuran on hepatic cytochrome P450 (cyt P450) monooxygenase activities were also examined in juvenile carp (Cyprinus carpio L.). By measuring the activities of MFO in experimental carp exposed to Dicuran an attempt was made to establish whether Dicuran could be bioactivated by MFO into ultimate mutagens. Our results on the bacterial strains Salmonella typhimurium TA100 and TA98 show that Dicuran does not possess either mutagenic or premutagenic characteristics. The micronucleus test on the erythrocytes of experimental carp did not establish any clastogenic effect either. However, Dicuran significantly inhibited the MFO activity of 7-ethoxyresorufin-O-deethylase (EROD) and benzo[a]pyrene monooxygenase (BaPMO) in the liver of experimental carp in vitro, as well as in in vivo conditions. These findings demonstrate the potentially damaging effect of Dicuran on the xenobiotic metabolizing enzyme systems of fish, and suggest the applicability of described methods for the prediction of the ecotoxicological significance of the presence of pesticides in the water environment.     

A laboratory exposure procedure for screening pulp and paper mill effluents for the potential of causing increased mixed function oxidase activity in fish

To better understand the relationships between pulp manufacturing processes and mixed function oxidase (MFO) enzyme induction in fish, a practical and standardized exposure procedure is required. This study was undertaken to develop a laboratory-based exposure procedure to quantify the relative MFO induction potencies of different types of pulp and paper mill effluents. One major consideration in developing the procedure was to ensure that the protocol was practical so that tests could be performed in a short time, with small volumes of effluents and using simple experimental conditions. A series of concentration-response and time-course experiments were conducted to find the minimum time and effluent concentration which could distinguish the ability of different effluents to cause significant MFO induction in rainbow trout in the laboratory. Experiments were also conducted to determine the effects of biotic and abiotic factors such as loading density, fish size and feeding regime. This study showed that the exposure of rainbow trout in the laboratory to 10% concentration of secondary-treated effluent for 96 h caused significant increases in hepatic MFO activity. The magnitude of MFO induction was comparable to other field and laboratory observations. While fish size, loading density and feeding regime were found to affect the test results, consistent responses within a laboratory using this protocol are possible, provided that these factors are standardized. Therefore, the short-term exposure approach described in this paper could be a relevant tool for assessing the ability of different types of pulp and paper mill effluents to cause MFO induction in fish.     

Regional variations in sulfate and nitrate on annual, seasonal, and synoptic time scales

Ambient data from Interagency Monitoring of Protected Visual Environments (IMPROVE) monitors are analyzed to evaluate the spatial structure of SO4 and NO3 aerosols in the mid-Atlantic region. Sub-weekly, seasonal, and annual data values are compared between the IMPROVE Washington, DC, site and three rural sites. Synoptic perturbations are compared between sites to quantify similarities in short-term temporal perturbations of SO4 and NO3. Based on these comparisons between the rural and urban IMPROVE monitors, the spatial structure of SO4 shows broad regional homogeneity that is recognizable from both the long-term average values and the short-term variations. NO3 data on a seasonal and annual basis show much larger spatial gradients between the urban Washington monitor and the three rural monitors than do SO4 data. Short-term NO3 perturbations at the three rural monitors also differ significantly from those at the Washington site. These dissimilarities in NO3 levels between the rural and urban IMPROVE monitors on both short-term and longer-term time scales indicate little homogeneity of NO3 aerosols in the mid-Atlantic region considered here. The volatility of NO3 aerosols and the removal rate of HNO3 via dry deposition could contribute to the spatial variability differences shown here between SO4 and NO3.     

Impact of dredged urban river sediment on a Saronikos Gulf dumping site (Eastern Mediterranean): sediment toxicity,contaminant levels,and biomarkers in caged mussels

Impacts of chemical contaminants associated with dumping of dredged urban river sediments at a coastal disposal area in Saronikos Gulf (Eastern Mediterranean) were investigated through a combined approach of sediment toxicity testing and active biomonitoring with caged mussels. Chemical analyses of aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), Cu, and Zn in combination with the solid phase Microtox® test were performed on sediments. Concentrations of PAHs, AHs, Cu, and Zn as well as multiple biomarkers of contaminant exposure and/or effects were measured in caged mussels. Sediments in the disposal and neighboring area showed elevated PAHs and AHs concentrations and were characterized as toxic by the solid-phase Microtox® test during and after dumping operations. Biomarker results in the caged mussels indicated sublethal effects mainly during dumping operations, concomitantly with high concentrations of PAHs and AHs in the caged mussel tissues. Cu and Zn concentrations in sediments and caged mussels were generally not elevated except for sediments at the site in the disposal area that received the major amount of dredges. High PAHs and AHs levels as well as sublethal effects in the caged mussels were not persistent after termination of operations. The combined bioassay–biomarker approach proved useful for detecting toxicological impacts of dredged river sediment disposal in sediments and the water column. Nevertheless, further research is needed to evaluate whether sediment toxicity will have long-term effects on benthic communities of the disposal area.     

Microsomal monooxygenase activity in Tilapia (Oreochromis mossambicus) exposed to a bleached kraft mill effluent using different exposure systems.

Bleached kraft pulp and paper mill effluents (BKMEs) are known to have adverse effects on aquatic organisms. One of the effects of BKMEs is its ability to induce cytochrome P4501A activity in exposed fish. 7-Ethoxyresorufin O-deethylase (EROD) activity is the most common biomarker used to measure the mixed-function monooxygenase activity. In this study, Tilapia were exposed to BKMEs using different exposure systems and their hepatic EROD activity, as well as liver/somatic index (LSI), were determined. In the Phase I study, Tilapia treated with betaNF and a whole (100%) BKME using a static, non-renewal system exhibited statistically significant EROD induction, but LSI values were not altered. In the Phase II study, fish were either caged in the mill's fishpond with the whole effluent passing through or cultured in tanks receiving 100% of the BKME continuously using a flow-through system in the laboratory. Their EROD activities were then compared with the non-exposed fish (control). The EROD activities in both groups of fish were elevated significantly with the greatest induction being observed in the field-exposed group. The LSI values in all of the field-exposed fish were significantly greater than the control Tilapia. The EROD assay was sensitive in detecting biological changes in fish exposed to the BKME. Further studies are warranted to better understand the impacts of BKMEs on aquatic organisms in Taiwan.     

Organophosphorus pollutants (OPP) in aquatic environment at Damietta Governorate, Egypt: implications for monitoring and biomarker responses

The study was carried out from spring 1999 to spring 2001 to monitor the residue levels of organophosphorus pollutants (OPP) in aquatic environment of the drainage canal surrounding a pesticide factory at Damietta Governorate. Water, sediment, and fish samples were collected at six different seasonal periods. OPPs were analyzed by GLC and confirmed using GC-MS. Chlorpyrifos, chlorpyrifos-methyl, malathion, diazinon, pirimiphos-methyl and profenofos were detected in most samples. Chlorpyrifos was dominant in all water and sediment samples. It was ranged from 24.5 to 303.8 and 0.9 to 303.8 ppb in water and sediment samples, respectively. Diazinon level was slightly similar to chlorpyrifos in fish samples. Data based on the grand total concentration of OPP showed that the most polluted samples were collected either at spring 1999 or autumn 2000. They were 675.5 and 303.8 ppb in water samples and 43.0 and 52.2 ppb in fish collected at spring 1999 and autumn 2000, respectively. The obtained results are in parallel to that found in case of cholinesterase activity where the activity of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) was declined at these seasonal period. The activity levels of AChE and BuChE were found to be 77.18% and 59.67% of control at spring 1999 and 78.62% and 85.80% of control, at autumn 2000, respectively. Thus, AChE and BuChE could be used as biomarkers for tracing and biomonitoring OPP pollution.     

Evaluation of the genotoxic and cytochrome P450 monooxygenase‐inhibitory potential of dicuran on procaryotic and eucaryotic test systems

Abstract

The effect of the herbicide Dicuran 500 FL (formulated product) on the phenotypical and genotypical changes in procaryotic and eucaryotic organisms was investigated using short‐term tests for detecting genotoxins. Since pesticides discharged in the water environment can modulate the mixed‐function monooxygenases (MFO) detoxification system of water organisms, the in vivo and in vitro effects of Dicuran on hepatic cytochrome P450 (cyt P450) monooxygenase activities were also examined in juvenile carp (Cyprinus carpio L.). By measuring the activities of MFO in experimental carp exposed to Dicuran an attempt was made to establish whether Dicuran could be bioactivated by MFO into ultimate mutagens. Our results on the bacterial strains Salmonella typhimurium TA100 and TA98 show that Dicuran does not possess either mutagenic or premutagenic characteristics. The micronucleus test on the erythrocytes of experimental carp did not establish any clastogenic effect either. However, Dicuran significantly inhibited the MFO activity of 7‐ethoxyresorufin‐O‐deethylase (EROD) and benzo[a]pyrene monooxygenase (BaPMO) in the liver of experimental carp in vitro, as well as in in vivo conditions. These findings demonstrate the potentially damaging effect of Dicuran on the xenobiotic metabolizing enzyme systems of fish, and suggest the applicability of described methods for the prediction of the ecotoxicological significance of the presence of pesticides in the water environment.     

Polybrominated biphenyl ethers in marine fish, shellfish and river and marine sediments in Japan

The presence of polybrominated biphenyl ethers (PBBEs), commonly used as flame retardants, was confirmed in marine fish, shellfish and river and marine sediments in Japan. These compounds were detected in seven out of 17 marine fish and shellfish, though at low levels. Tetrabrominated biphenyl ether was a major component in marine organisms. However, sediment pollution by PBBEs, particularly that by decabrominated biphenyl ether, pose a serious problem in the rivers of Osaka but not in marine areas.     

Nationwide monitoring of mercury in wild and farmed fish from fresh and coastal waters of Korea

Mercury (Hg) concentrations were monitored in wild and cultured fish collected from fresh and coastal waters in the Korean peninsula from April 2006 to August 2008 nationwide. Total Hg concentrations were reported for 5043 fish samples, including 78 species from 133 locations. Significant interspecies variation was noted in the Hg levels. The average Hg concentration in each fish species ranged from 6.31 μg kg⁻¹ for mullet (Mugil cephalus) to 200 μg kg⁻¹ for mandarin fish (Siniperca scherzeri). Among the species collected, the maximum concentration of Hg, 1720 μg kg⁻¹, was measured in an Amur catfish (Silurus asotus). Only wild freshwater fish exceeded the WHO ingestion standard. Wild freshwater piscivorous fish samples from a large artificial upstream lake contained the highest Hg levels. Hg concentrations were compared between fish groups categorized as wild and farmed fish from freshwater and coastal waters. Although the wild freshwater fish had similar size ranges, their Hg concentrations were higher than those of the other groups. Compared to the feed of farmed marine and freshwater fishes, the prey of wild freshwater fish had a higher Hg concentration, and the total Hg concentrations in freshwater and associated sediment samples were higher than those in coastal water and associated sediment samples. In the freshwater environment, piscivorous fish bioaccumulated two times more Hg than carnivorous and omnivorous fish and four times more than planktivorous fish. The difference in Hg concentrations among trophic groups might have been due to differences in the size of fish, in addition to the variations among different trophic groups. These data will be useful for developing the fish consumption advisory as a management measure to reduce Hg exposure.     

Effects of complex waste mixtures on hepatic monooxygenase activities in brown bullheads (Ictalurus nebulosus)

Hepatic MFO components (cytochrome P-450, cytochrome b(5), and ethoxyresorufin O-deethylase, EROD) were measured in brown bullheads (Ictalurus nebulosus) inhabiting a creek receiving a complex mixture of organics and trace metals. The activities of these same enzymes were also measured in bullheads from an uncontaminated reference site to assess the relative ability of MFO parameters to serve as a biomarker of aquatic pollution. Bullheads analyzed from the polluted site had lower hepatic microsomal P-450 (p < 0.01) concentrations and similar EROD activities per mg protein as compared to bullheads from the reference site. However, analysis of enzyme turnover ratios revealed greater EROD activity per mg cytochrome P-450 (p < 0.05) in the fish from the polluted site. No difference in cytochrome b(5) activities were observed between the two groups. As compared to the reference site, bullheads collected from the polluted creek had an increased occurrence of lip and lower jaw lesions and liver damage, including elevated liver/body weight ratios. Accordingly, the monooxygenase activities measured in this study were not reliable indicators of chemical pollution or contaminant stress in bullheads in the polluted creek. Further research is needed concerning contaminant interactions, particularly among organic pollutants and metals and their effects on monooxygenase activities.     

Assessing the biological status of fish in a river receiving pulp and paper mill effluents

This study compared the use of sentinel species- and community-based field approaches for assessing the biological status of fish living in a river receiving pulp and paper mill effluents. Three approaches were compared. Two approaches used sentinel species. One of these involved an internal/external examination of the fish that leads to the calculation of a fish health assessment index (HAI) and the other involved biochemical measurements of hepatic mixed function oxidase (MFO) activity and plasma steroid levels. The third approach characterized the fish community structure according to an index of biotic integrity (IBI). The comparison focused on how the methods respond to the hypothesis that recent process modifications/effluent treatment changes, resulting in demonstrable improvements in effluent quality, have beneficial effects on fish. Neither of the approaches using sentinel fish indicated clear mill-related influences either before or after the process modifications/effluent treatment changes. There was no evidence of depressed plasma steroids and increased MFO activity in fish frequently associated with mill effluent exposure in previous studies. While the HAI was higher at stations downstream from two mills, this could not be linked to effluent exposure alone. In contrast, the study of community structure showed a substantial improvement in fish assemblages at all the mill sites.     

Strong links between metal contamination, habitat modification and estuarine larval fish distributions

Changes to larval fish assemblages may have far reaching ecological impacts. Correlations between habitat modification, contamination and marine larval fish communities have rarely been assessed in situ. We investigated links between the large-scale distribution of stressors and larval fish assemblages in estuarine environments. Larval fish communities were sampled using a benthic sled within the inner and outer zones of three heavily modified and three relatively unmodified estuaries. Larval abundances were significantly greater in modified estuaries, and there were trends towards greater diversity in these systems. Differences in larval community composition were strongly related to sediment metal levels and reduced seagrass cover. The differences observed were driven by two abundant species, Paedogobius kimurai and Ambassis jacksoniensis, which occurred in large numbers almost exclusively in highly contaminated and pristine locations respectively. These findings suggest that contamination and habitat alteration manifest in substantial differences in the composition of estuarine larval fish assemblages.     

Trace elements in two marine fish cultured in fish cages in Fujian province, China

Two cultured marine fish, the Japanese seabass (Lateolabrax japonicus) and red seabream (Pagrus major) were collected from eight fish cage sites along the coast of Fujian province in China. The concentrations of Ag, As, Cd, Co, Cu, Fe, Mn, Se, and Zn in their muscle, stomach and liver tissue were quantified. The risk of these trace elements to humans through fish consumption was then assessed. The highest concentrations of As, Cd, Se and Zn in fish feed from fish cages were found in Dongshan Station. Moreover, the As levels in the muscles of both species at all sites were generally higher than China's national standard (>1.0 μg/g). Trace element concentrations in two marine fish followed the order of livers > stomachs > muscles. Although the As levels in two marine caged fish exceeded the permissible standards, the estimated daily intake of As did not exceed the reference dose guideline established by US EPA. For other trace elements examined in this study, their concentrations did not exceed the permissible concentrations of the international standards.     

In vitro inhibition of hepatic cytochrome P450 and enzyme activity by butyltin compounds in marine mammals

The present study attempted to examine the in-vitro inhibition of hepatic microsomal P450 content and activity by butyltins in marine mammals and discussed on their possible effects in animals in the wild. Decreases in P450 content and the activities of ethoxyresorufin O-deethylase (EROD, catalyzed by CYPIA subfamily) and penthoxyresorufin O-depentylase (PROD, catalyzed by CYP2B subfamily) by tributyltin (TBT) were observed in in-vitro experiments using hepatic microsomes of a pinniped and a cetacean. Among P450 family, EROD activity is more sensitive to TBT than P450 content and PROD activity, indicating a specific mode of action of TBT on different P450 forms. On the other hand, dibutyltin and monobutyltin have no inhibitory effect on EROD activity at concentrations less than 0.5 mM, indicating that the inhibition of enzyme activity in hepatic microsome of marine mammal is mainly by TBT. TBT concentrations that affect P450 contents and activities are above 10 times higher than the values found in the liver of various marine mammals.     

Environmental and industrial factors relating to flavor tainting of fish in the upper Wisconsin river

Extracts from Large Toothed Aspen (Populous grandidenta Michx.) and Jack Pine (Pinus banksiana Lamb.) contained many odor compounds found in flavor-tainted walleye from the Wisconsin River, including alkylphenols. Aspen wood contained 8 ppb of 2-isopropylphenol, and river sediments also contained low ppb levels of many alkylphenols, including 2-isopropylphenol. Thiophenol and thiocresol which sporadically cause offensive sulfury taints in Wisconsin River fish were also found in river sediment. Quantitative analysis of fish for alkylphenols supported a hypothesis involving a food chain-mediated seasonal fluctuation of alkylphenol levels in fish. Thiophenols are postulated to be derived from pulp mill activities on the river.