Ethoxyresorufin-O-deethylase (EROD) activity in fish as a biomarker of chemical exposure

Summary results from a pilot study conducted around an oil production platform on the Northwest Shelf of Australia

The Australian Institute of Marine Science (AIMS) conducted a pilot study around the Harriet A oil production platform on the Northwest Shelf of Australia. We evaluated hepatic ethoxyresorufin-O-deethylase (EROD) activity, fluorescent aromatic compounds (FACs) in bile and immunodetection of CYP1A-like proteins in two Australian tropical fish species, Gold-Spotted Trevally (Carangoides fulvoguttatus) and Bar-Cheeked Coral Trout (Plectropomus maculatus) to assess exposure to petroleum hydrocarbons associated with produced formation water (PFW). Additionally, the incidence of hydrocarbon-degrading bacteria isolated from the liver and bile of all fish captured was examined. Low EROD activity was found in both species, with EROD activity in C. fulvoguttatus showing significant site differences. FACs and CYP1A protein levels in C. fulvoguttatus showed a clear trend in hydrocarbon exposure consistent with hydrocarbon chemistry data: Harriet A>Harriet C>reference site. P. maculatus showed elevated levels of FACs at Harriet A as compared to the reference site and demonstrated detectable levels of CYP1A-like proteins at these two sites. Hydrocarbon-degrading bacteria were found in the liver and bile of both species, yet there was no correlation by sites. Our results demonstrate that C. fulvoguttatus and P. maculatus have potential as indicator species for assessing the effects from exposure to petroleum hydrocarbons. Both FACs and CYP1A are providing warning signs that there is potential for biological effects on fish populations exposed to PFW around the Harriet A production platform.

Environmental contaminants and biomarker responses in fish from the Rio Grande and its U.S. tributaries: spatial and temporal trends

We collected, examined, and analyzed 368 fish of seven species from 10 sites on rivers of the Rio Grande Basin (RGB) during late 1997 and early 1998 to document temporal and geographic trends in the concentrations of accumulative contaminants and to assess contaminant effects on the fish. Sites were located on the mainstem of the Rio Grande and on the Arroyo Colorado and Pecos River in Texas (TX), New Mexico (NM), and Colorado. Common carp (Cyprinus carpio) and largemouth bass (Micropterus salmoides) were the targeted species. Fish were examined in the field for internal and external visible gross lesions, selected organs were weighed to compute ponderal and organosomatic indices, and samples of tissues and fluids were obtained and preserved for analysis of fish health and reproductive biomarkers. Whole fish from each station were composited by species and gender and analyzed for organochlorine chemical residues and elemental contaminants using instrumental methods, and for 2,3,7,8-tetrachloro dibenzo-p-dioxin-like activity (TCDD-EQ) using the H4IIE rat hepatoma cell bioassay. Overall, fish from lower RGB stations contained greater concentrations of organochlorine pesticide residues and appeared to be less healthy than those from sites in the central and upper parts of the basin, as indicated by a general gradient of residue concentrations and biomarker responses. A minimal number of altered biomarkers and few or no elevated contaminant concentrations were noted in fish from the upper RGB. The exception was elevated concentrations [up to 0.46 microg/g wet-weight (ww)] of total mercury (Hg) in predatory species from the Rio Grande at Elephant Butte Reservoir, NM, a condition documented in previous studies. Arsenic (As) and selenium (Se) concentrations were greatest in fish from sites in the central RGB; Se concentrations in fish from the Pecos River at Red Bluff Lake, TX and from the Rio Grande at Langtry, TX and Amistad International Reservoir, TX exceeded published fish and wildlife toxicity thresholds. In the lower RGB, residues of p,p'-DDT metabolites (<or=1.69 microg/g ww), chlordane-related compounds (<or=0.21 microg/g ww), dieldrin (<or=0.0.05 microg/g ww), and toxaphene (<or=2.4 microg/g ww) were detected in fish from most sites; maximum concentrations were in channel catfish (Ictalurus punctatus) from the Arroyo Colorado at Harlingen, TX. Concentrations of one or more residues exceeded toxicity thresholds for fish and wildlife in fish from this site and from the Rio Grande at Mission, TX and Brownsville, TX; however, concentrations were lower than those reported by previous studies. In addition, the proportional concentrations of p,p'-DDT at all sites were low, indicating weathered DDT rather than the influx of new material. Concentrations of total PCBs (<0.05 microg/g ww) and TCDD-EQ (<or=6 pg/g ww) were comparatively low in all samples. Hepatic ethoxyresorufin O-deethylase (EROD) activity in some fish was elevated relative to reference rates at most sites, but was generally lower than previously reported activity in fish from heavily contaminated locations. The comparatively low PCB and TCDD-EQ concentrations together with elevated EROD activity may reflect exposure to polycyclic aromatic hydrocarbons. Reproductive biomarkers were consistent with chronic contaminant exposure at lower RGB sites; comparatively large percentages of intersex male largemouth bass, relatively low gonadosomatic indices, and elevated plasma vitellogenin concentrations in male fish were noted at three of the four stations. Large percentages of atretic eggs were also observed in the ovaries of female common carp from the Rio Grande at Brownsville, TX. Although many of the conditions noted may have other causes in addition to contaminant exposure, the biomarker results for the lower RGB sites are consistent with subtle responses of fish to contaminants, an interpretation supported by the chemical data of this and other investigations.

EROD activity and biliary fluorescence in Schroederichthys chilensis (Guichenot 1848): biomarkers of PAH exposure in coastal environments of the South Pacific Ocean

Schroederichthys chilensis is a common shark that lives in Chilean coastal environments. In this work, the relationship between liver 7-ethoxyresorufin-O-deethylase dealkylation (EROD) activity and Fluorescent Aromatic Compounds (FAC) in bile of S. chilensis sampled in three bays with different degrees of pollution were performed including a reference area. Sixty individuals were collected, 20 for each site; (10 males and 10 females per site) livers and bile samples were obtained and immediately frozen. EROD activity and FAC were measured according to three standard methods. EROD activity and FAC were higher in polluted areas than in the reference area. Synchronous Fluorescence Spectra of the bile from the fish collected at the most polluted area showed a peak at 347nm representing a metabolite corresponding to 1-hydroxypyrene. The low EROD activity in the reference area is likely related to the low level of PAH in sediments. We propose that this species is a good indicator of exposure to FACs, since it presents a series of characteristics that make it suitable for monitoring PAH exposure in coastal zones.

Individual variability in esterase activity and CYP1A levels in Chinook salmon (Oncorhynchus tshawytscha) exposed to esfenvalerate and chlorpyrifos

Acetylcholinesterase (AChE) activity has traditionally been monitored as a biomarker of organophosphate (OP) and/or carbamate exposure. However, AChE activity may not be the most sensitive endpoint for these agrochemicals, because OPs can cause adverse physiological effects at concentrations that do not affect AChE activity. Carboxylesterases are a related family of enzymes that have higher affinity than AChE for some OPs and carbamates and may be more sensitive indicators of environmental exposure to these pesticides. In this study, carboxylesterase and AChE activity, cytochrome P4501A (CYP1A) protein levels, and mortality were measured in individual juvenile Chinook salmon (Oncorhynchus tshawytscha) following exposure to an OP (chlorpyrifos) and a pyrethroid (esfenvalerate). As expected, high doses of chlorpyrifos and esfenvalerate were acutely toxic, with nominal concentrations (100 and 1 microg/l, respectively) causing 100% mortality within 96 h. Exposure to chlorpyrifos at a high dose (7.3 microg/l), but not a low dose (1.2 microg/l), significantly inhibited AChE activity in both brain and muscle tissue (85% and 92% inhibition, respectively), while esfenvalerate exposure had no effect. In contrast, liver carboxylesterase activity was significantly inhibited at both the low and high chlorpyrifos dose exposure (56% and 79% inhibition, respectively), while esfenvalerate exposure still had little effect. The inhibition of carboxylesterase activity at levels of chlorpyrifos that did not affect AChE activity suggests that some salmon carboxylesterase isozymes may be more sensitive than AChE to inhibition by OPs. CYP1A protein levels were approximately 30% suppressed by chlorpyrifos exposure at the high dose, but esfenvalerate had no effect. Three teleost species, Chinook salmon, medaka (Oryzias latipes) and Sacramento splittail (Pogonichthys macrolepidotus), were examined for their ability to hydrolyze a series of pyrethroid surrogate substrates and in all cases hydrolysis activity was undetectable. Together these data suggest that (1) carboxylesterase activity inhibition may be a more sensitive biomarker for OP exposure than AChE activity, (2) neither AChE nor carboxylesterase activity are biomarkers for pyrethroid exposure, (3) CYP1A protein is not a sensitive marker for these agrochemicals and (4) slow hydrolysis rates may be partly responsible for acute pyrethroid toxicity in fish.

Tissue levels and biomarkers of organic contaminants in feral and caged chub (Leuciscus cephalus) from rivers in the West Midlands, UK

The Birmingham conurbation (West Midlands, UK) has traditionally been a major centre of UK industry and population and consequently has a legacy of pollution, which is reflected in the water quality of local rivers. Three of these rivers, exhibiting good, intermediate and poor overall water quality, were the subject of a study in which the effects of contamination on hepatic biomarkers and tissue contaminant loads in feral and caged chub (Leuciscus cephalus) were investigated. Muscle polychlorinated biphenyls and organochlorine pesticides (PCBs and OCPs), as well as bile pyrene and benzo[a]pyrene-like metabolite levels, were variable in both caged and feral fish, but were generally higher in tissue from the more polluted sites. OCPs were, in most cases, higher in the feral fish than in the caged fish, although the opposite was true of bile PAH metabolites, possibly due to differences in relative accumulation rates. Hepatic CYP1A activity (via ethoxyresorufin-O-deethylase (EROD) activity) in both feral and caged fish was also generally higher at the more polluted sites. EROD activity in feral and caged fish was statistically associated with polycyclic aromatic hydrocarbon (PAH) contamination and specific PCB congeners. Other biomarkers measured (reduced glutathione in liver, and serum aspartate aminotransferase) showed little consistent evidence of relationships with water quality. The assessment of these parameters during different seasons also revealed relatively little evidence of temporal variation. Overall, the caged chub appeared to reflect the pattern of general water quality more accurately than did feral fish, particularly with respect to EROD activity and to some degree bile PAH metabolites, thus supporting their use as sentinel species. However, the fact that muscle OCPs were generally higher in the feral fish suggests that the use of feral fish may be more indicative of exposure to certain classes of contaminant, and so biological monitoring programs should be designed with such considerations in mind.

Seasonal variability of metallothioneins, cytochrome P450, Bile metabolites and oxyradical metabolism in the European eel Anguilla anguilla L. (Anguillidae) and striped mullet Mugil cephalus L. (Mugilidae)

The European eel Anguilla anguilla (Anguillidae) and the striped mullet Mugil cephalus (Mugilidae) are typical inhabitants of Mediterranean brackish lagoons, and their utility as bioindicator organisms has already been suggested. The seasonal variability of several potential biomarkers was investigated during a field study carried out in the Orbetello lagoon (Tuscany, Italy). Organisms were sampled on a seasonal basis, and analyzed parameters included the levels of hepatic metallothioneins, the activity of cytochrome P450 1A (EROD), and the presence of biliary PAH metabolites. Special attention was also paid to antioxidant defenses, including catalase, glutathione peroxidases, glutathione reductase, glutathione S-transferases, and total glutathione concentration. Total Oxyradical Scavenging Capacity (TOSC-assay) was measured as an indication of the overall biological resistance to toxicity of different forms of oxyradicals (peroxynitrite, peroxyl and hydroxyl radicals). Obtained results suggest that natural variations of analyzed responses are associated with seasonality of both environmental and biological factors, mainly temperature and reproductive cycle which, however, have a different influence in these two species. Striped mullets exhibited the strongest variations in October when spawning occurs; eels are not influenced by a seasonal sexual maturation and showed more marked changes during the summer, likely related to the elevated seawater temperature and light irradiance in the lagoon. This study confirms the importance of characterizing seasonal variations and the influence of different factors on biological responses that can be used as biomarkers in monitoring programs.

Cytochrome P4501A induction in brown trout exposed to small streams of an urbanised area: results of a five-year-study

This case study examines the ability of the cytochrome P4501A (CYP1A) biomarker to distinguish the pollution status of two small streams, Krähenbach and Körsch, receiving different levels of urban and agricultural impact, with low to moderate contamination by arylhydrocarbon receptor (AhR)-binding PAHs and PCBs. Brown trout, Salmo trutta, exposed in enclosure restrictions, showed significant between-stream differences of hepatic CYP1A levels. EROD activities were the better discriminator than CYP1A protein levels. The CYP1A response was consistent and repeatable over the 5-year observation period from 1995 to 1999. In contrast to brown trout, hepatic CYP1A of stone loach, Barbatula barbatula, did not clearly distinguish the streams. The findings of this long-term study lend support to the use of CYP1A as a biomarker of degraded environmental conditions, provided that sufficiently long observation periods are used to average out confounding factors, that sufficiently sensitive detection methods are used, and that a responsive monitoring species is chosen.

Evaluation of chromosomal damage by flow cytometry in turbot (Scophthalmus maximus L.) exposed to fuel oil

Flatfishes, turbots (Scophthalmus maximus), were injected intraperitoneally with two doses of fuel oil number 2. Biliary metabolites were evaluated by fixed fluorescence to verify the efficiency of intoxication. Ethoxyresorufin-O-deethylase (EROD) activity was compared with chromosomal damage measured by flow cytometry. The analysis of biliary metabolites showed a good dose-response relation and constitutes a clear reference for the subsequent measurements. Comparing flow cytometry and EROD results, a shorter delay of response for EROD activity was obtained, but chromosomal damage was significant only after one week. The persistence of the EROD response was shorter, while the genotoxic signal still persisted after one month. The measurement of chromosomal damage allowed a good differentiation between the two tested doses. In the case of EROD activity, the results were less clear. The results suggest that within a few weeks after exposure to fuel oil number 2, the measurements of chromosomal damage by flow cytometry can be used to detect a dose-dependent genotoxic response in fish.

Impact assessment of various rearing systems on fish health using multibiomarker response and metal accumulation

European sea bass were reared in three different systems: one flow-through (FTS), one recirculating (RAS), and one recirculating with a high-rate algae pond (RAS + HRAP). After 1 year of rearing, the final fish weight was 15% lower in the RAS compared to the FTS. The accumulation of a growth-inhibiting substance in the RAS is the main hypothesis explaining this difference. As in environmental risk assessment, fish bioaccumulation markers and biomarkers were used to demonstrate exposure to and effects of the rearing water in the three rearing systems. Thirty fish per system were sacrificed before their condition factor (CF) and liver somatic index (LSI) were calculated. Nine biomarkers, including ethoxyresorufin-O-deethylase (EROD) and superoxide dismutase (SOD), were measured in liver and twelve metals including As, Cd, Cu, Pb, Cr, and Zn, for which there are regulations regarding human consumption, were measured in liver and muscle. In all systems, CF and LSI were not significantly different and no correlation was found with biomarker activity or metal concentration. EROD and SOD activities were significantly increased in RAS. Accumulation of seven and four metals in muscle and liver, respectively, was significantly higher in the RAS relative to FTS. The HRAP prevented metal accumulation except for chromium and arsenic. Eight metal concentrations were significantly higher in liver than in muscle. Concentrations of toxic metals were similar to reported values and below FAO/WHO recommended values for human consumption.

The distribution and relative toxic potential of organic chemicals in a PCB contaminated bay

For reliable monitoring of environmental improvement, the PCB contaminated bay Orserumsviken on Sweden's Baltic coast was investigated prior to remediation. We examined PCB congener patterns and the relative toxic potential of PCBs in extracts of three matrices: bottom sediment, settling particulate matter and the dissolved phase (obtained from semi-permeable membrane devices). Congener patterns were similar in all matrices. Three fractions were isolated from the extracts: (1) aliphatic and monocyclic aromatic compounds (MAC-fraction), (2) dicyclic aromatic compounds (DAC-fraction), including PCBs, and (3) polycyclic aromatic compounds (PAC-fraction), including PAHs. Total extracts and fractions were injected into newly fertilised rainbow trout eggs. At larval stage, hepatic EROD activities were quantified. Though high, the PCB contamination could explain only an estimated 1-5% of the total EROD induction. The order of EROD induction potential was: total extract > PAC-fraction > DAC-fraction > MAC-fraction in all matrices, suggesting that in Orserumsviken PACs made a larger contribution to the EROD induction potential than PCBs and other DACs.

Reproductive responses of common carp (Cyprinus carpio) exposed in cages to influent of the Las Vegas Wash in Lake Mead, Nevada, from late winter to early spring

The Las Vegas Wash (LW) delivers tertiary-treated municipal wastewater effluent, nonpotable shallow groundwater seepage, and runoff from the urbanized Las Vegas Valley to Las Vegas Bay (LX) of Lake Mead. To investigate the potential for contaminants in LW influent to produce effects indicative of endocrine disruption in vivo, adult male and female common carp (Cyprinus carpio) were exposed in cages for 42-48 d at four sites in Lake Mead: LW, LX, and two reference locations in the lake. End points examined included gonadosomatic index; gonad histology; concentrations of plasma vitellogenin (VTG) and plasma sex steroids (17beta-estradiol (E2), testosterone (T), 11-ketotestosterone (11-KT)); plasma estrogen:androgen ratios (E2:T, E2:11-KT), in vitro production of T by gonad tissue, and hepatopancreas ethoxyresorufin O-deethylase activity. Few differences among fish caged at different sites were potentially attributable to exposure to contaminants

Xenobiotic substances such as PCB mixtures (Aroclor 1254) and TBT can influence swimming behavior and biotransformation activity (GST) of carp (Cyprinus carpio)

Different groups of carp were treated with polychlorinated biphenyl (PCB) or tributyltin (TBT), and possible effects of the chemicals on the swimming behavior of the carp were examined using the BehavioQuant system. By evaluating quantitative behavioral parameters of the animals, it became evident that exposure to high concentrations of chemicals (organotin, 7 microg L(-1), or polychlorinated biphenyl, 22 microg L(-1)) severely affected the carp, causing a significant change in their swimming speed. TBT stress led to a rapid decrease in mean swimming activity. A decrease in the preferred swimming depth was observed in TBT- and PCB-exposed fish. Animals exposed to PCB reduced their mean daily activity and increased their mean swimming speed in the nighttime during the second week of exposure. Therefore, our findings imply that the fish were adapted to cope with the chemicals after the second week of exposure. Furthermore, our results showed that low concentrations (TBT, 0.3 and 2 microg L(-1), or PCB, 14 microg L(-1)) did not significantly alter any quantified parameters of swimming behavior. In addition, the direct effects of chemicals on enzyme activity (GST) were determined. Measurement of soluble glutathione-S-transferase activity of fish liver or gills showed a significant elevation after exposure to PCB (0.1 or 22 microg L(-1)) or TBT (0.8 or 7 microg L(-1)). We had to conclude that the two different end points tested generally are useful as biomarkers of exposure and for investigations of energy resources in organisms under the influence of toxic stress.

Effects of the brominated flame retardants hexabromocyclododecane (HBCDD), and tetrabromobisphenol A (TBBPA), on hepatic enzymes and other biomarkers in juvenile rainbow trout and feral eelpout

Brominated flame retardants (BFRs) leak out in the environment, including the aquatic one. Despite this, sublethal effects of these chemicals are poorly investigated in fish. In this study, a screening of selected biomarkers in juvenile rainbow trout (Oncorhynchus mykiss) and feral eelpout (Zoarces viviparus) was performed after exposure to hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA). Rainbow trout was injected intraperitoneally (i.p.) with HBCDD or TBBPA. Two out of four short-term experiments with HBCDD showed an increase in the activity of catalase. A 40% increase in liver somatic index (LSI) could be observed after 28 days. HBCDD did also seem to have an inhibitory effect on CYP1A's activity (ethoxyresorufin-O-deethylase (EROD)). A putative peroxisome proliferating activity of the compound was investigated without giving a definite answer. HBCDD did not seem to be estrogenic or genotoxic. TBBPA increased the activity of glutathione reductase (GR) after 4, 14 and 28 days in rainbow trout suggesting a possible role of this compound in inducing oxidative stress. The compound did not seem to be estrogenic. TBBPA seemed to compete with the artificial substrate ethoxyresorufin in vitro, during the EROD assay. In eelpout, only one 5 days in vivo experiment was performed. Neither of the compounds gave rise to any effect in this fish. This was the first screening of sublethal effects of the two chemicals in fish, using high doses. Our results indicate that there is a need for further studies of long-term, low-dose effects of these two widely used flame retardants.

Applicability of the black slug Arion ater for monitoring exposure to polycyclic aromatic hydrocarbons and their subsequent bioactivation into DNA binding metabolites

The applicability of terrestrial black slugs Arion ater (Mollusca, Gastropoda) was studied for biomonitoring environmental exposure to polycyclic aromatic hydrocarbons (PAHs). In laboratory experiments, slugs were orally exposed to benzo[a]pyrene (BaP) for a short term (3 days) or a long term (119 days) period. Test animals were collected in the field, or were reared under laboratory conditions to ensure that they had no history of PAH-exposure. Benzo[a]pyrene hydroxylase (BPH) activity was measured in the digestive gland as a biomarker for BaP exposure. Bulky DNA adduct formation in kidney was measured as an effect biomarker for BaP bioactivation into DNA-binding metabolites. Although success of clutching was relatively low (5 out of 18 slugs produced egg packages), sufficient number of slugs were obtained to perform exposure experiments due to high hatching (89%) and survival rates (79%). After a short exposure to a relatively high BaP doses of 20 and 200 microg/g fresh feed, a dose-dependent and significant increase of BPH activity and bulky DNA adduct levels could be demonstrated in A. ater. Induction factors were low (two times control level), but optimization of the test conditions yielded a higher BPH induction factor of 4.8 times control level. BPH activity and bulky DNA adduct levels, however, did not increase after a long-term exposure to environmentally relevant BaP doses (upto 0.25 microg/g fresh feed). Based on this lack of response after realistic exposure it is concluded that A. ater is not sensitive to BaP exposure and, therefore, not suitable for monitoring environmental exposure to PAHs.

Hazard assessment of a simulated oil spill on intertidal areas of the St. Lawrence River with SPMD-TOX

Phytoremediation in a simulated crude oil spill was studied with a "minimalistic" approach. The SPMD-TOX paradigm-a miniature passive sorptive device to collect and concentrate chemicals and microscale tests to detect toxicity-was used to monitor over time the bioavailability and potential toxicity of an oil spill. A simulated crude oil spill was initiated on an intertidal freshwater grass-wetland along the St. Lawrence River southwest of Quebec City, Quebec, Canada. Several phytoremediation treatments were investigated; to dissipate and ameliorate the spill, treatments included nutrient amendments with inorganic nitrogen sources (ammonium nitrate and sodium nitrate) and phosphate (super triple phosphate) with and without cut plants, with natural attenuation (no phytoremedial treatment) as a control. Sequestered oil residues were bioavailable in all oil-treated plots in Weeks 1 and 2. Interestingly, the samples were colored and fluoresced under ultraviolet light. In addition, microscale tests showed that sequestered residues were acutely toxic and genotoxic, as well as that they induced hepatic P(450) enzymes. Analysis of these data suggested that polycyclic aromatic hydrocarbons were among the bioavailable residues sequestered. In addition, these findings suggested that the toxic bioavailable fractions of the oil spill and degradation products dissipated rapidly over time because after the second week the water column contained no oil or detectable degradation products in this riverine intertidal wetland. SPMD-TOX revealed no evidence of bioavailable oil products in Weeks 4, 6, 8, and 12. All phytoremediation efforts appeared to be ineffective in changing either the dissipation rate or the ability to ameliorate the oil toxicity. SPMD-TOX analysis of the water columns from these riverine experimental plots profiled the occurrence, dissipation, and influence of phytoremediation on the bioavailability and toxicity of oil products (parent or degradation products).

Biomarker responses in juvenile rainbow trout (Oncorhynchus mykiss) after single and combined exposure to low doses of cadmium, zinc, PCB77 and 17beta-oestradiol

The objective of this study was to examine (i) the biochemical responses of rainbow trout exposed to sublethal water concentrations of the metals cadmium (Cd) (1.5 microg l(-1)) and zinc (Zn) (150 microg l(-1)); and (ii) the potential combined effects when applied in mixture (Cd/Zn) with and without co-exposure to model organic chemicals 3,3',4,4'-tetrachlorobiphenyl (PCB77) (1 mg kg (-1)) and 17beta-oestradiol (E2) (0.5 mg kg(-1)). After 21 days of exposure, several biomarkers were assessed in the liver (enzymatic and nonenzymatic antioxidants, heat shock proteins [HSP70 and HSP60], ethoxyresorufin-O-deethylase [EROD]) and in the plasma (vitellogenin [Vtg], aminotransferases). Plasma aminotransferases were not affected, whereas the other biomarkers showed different patterns of response depending on the treatment. For example, Cd, and Zn to a lesser extent, induced an adaptive response in the liver shown by an increase in antioxidant defences (total glutathione [GSH], superoxide dismutase, Trolox equivalent antioxidant capacity [TEAC]), without any impairment of GSH redox status or induction of heat shock proteins. Antagonistic effects were observed in GSH-related biomarkers after Cd/Zn exposure. PCB77 strongly induced EROD activity, HSP70 and TEAC. Co-exposure with metals did not modulate significantly the effects of PCB77. E2 induced Vtg and inhibited liver antioxidants and basal EROD activity. These inhibitory effects were suppressed in fishes exposed to E2 + Cd/Zn, suggesting additive effects of E2 and metals. In addition, E2-induced Vtg was not altered by metals. Multivariate analyses confirmed some correlation between the biomarkers. The use of complementary biomarkers is necessary to discriminate different treatments and to highlight interactive effects.

Hepatic ethoxyresorufin O-deethylase (EROD) activity in flounder (Platichthys flesus) from contaminant impacted estuaries of the United Kingdom: continued monitoring 1999-2001

The determination of hepatic ethoxyresorufin O-deethylase (EROD) has been used to assess the induction of the mixed function oxygenase system (MFO) of flounder (Platichthys flesus) in UK estuaries. Induction of the MFO system denotes possible exposure to certain organic contaminants (e.g. polycyclic aromatic hydrocarbons, polychlorinated biphenyls) and its measure has been incorporated in national monitoring programmes. This study presents EROD monitoring data from 5 UK estuaries taken between 1999 and 2001 and builds on data from previous years. The results reveal that for all sampled estuaries EROD values have been significantly (p < 0.05) elevated on the majority of occasions in comparison with the reference estuary, the Alde in Suffolk, UK. However, the limited temporal scale of the reported monitoring does not allow any conclusions to be drawn with respect to trends in the data. Possible factors influencing the data (size, gender, seasonality, reproductive status, etc.) are discussed and recommendations for continued monitoring are made.

Reduction of cytochrome P4501A with age in Atlantic tomcod from the St. Lawrence Estuary, Canada: relationship with emaciation and possible effect of contamination

This study reports a reduction of ethoxyresorufin-O-deethylase (EROD) activity in large-sized, older Atlantic tomcod (Microgadus tomcod) collected in the St. Lawrence Estuary (Quebec, Canada) and investigates its relationship over a 4-year period to sex, gonadosomatic index (GSI), condition factor (CF) and cytochrome P4501A (CYP1A) mRNA levels. In addition, the concentrations of polychlorinated biphenyls (PCBs) were measured in a subsample of fish. The reduction of EROD activity with age was observed each year in both sexes and was not related to the GSI. A high proportion of large-sized fish, with a body length greater or equal to 225 mm, were emaciated (CF < or = 0.55). A 6-16-fold reduction of EROD activity and a 2-4-fold reduction of CYP1A mRNA levels were observed in large-sized emaciated females compared to small-sized non-emaciated females. Concentrations of PCBs in liver increased from 1000 to 4000 ng/g lipid weight as the hepatic lipid content and the CF decreased. The inter-annual variation of EROD activity was associated with the variation in CF with lowest EROD activity and CF in 1999. When emaciated fish were excluded from the analyses, EROD activity was still lower (2-5-fold) in large compared to small fish and was no longer related to CF. For similar levels of CYP1A mRNA, EROD activity was lower in large compared to small fish. Thus, there was post-transcriptional inhibition of CYP1A activity in large-sized tomcod, indicative of cellular dysfunction. This response may be related to aging, chronic exposure to toxic contaminants or to selective pressures favoring less responsive individuals. This study demonstrates that fish age, size, and CF are important variables to consider in studies using EROD activity as an indicator of environmental contamination. The main finding was that a large part of the reduction of CYP1A with age in St. Lawrence Estuary tomcod was associated with severe emaciation of a large proportion of large-sized fish. Hepatic concentrations of contaminants covaried with the CF and the effects of these two variables on CYP1A could not be discriminated.

Some polybrominated diphenyl ether (PBDE) flame retardants with wide environmental distribution inhibit TCDD-induced EROD activity in primary cultured carp (Cyprinus carpio) hepatocytes

Ethoxyresorufin-O-deethylase (EROD) activity, a catalytic function of the cytochrome P450 1A (CYP1A) microsomal oxygenase subfamily, is a popular biomarker for exposure to xenobiotics, polyhalogenated aromatic hydrocarbons (PHAHs) in particular. It has found wide use in aquatic pollution assessment both in vivo and in vitro. In such studies, subjects are often exposed to complex mixtures where various constituents can interfere with EROD-activity, possibly resulting in inadequate estimation of toxic hazard or biological response. The present study investigates the effects of polybrominated diphenyl ethers (PBDEs), a relatively new and increasingly detected group of environmental contaminants, on the validity of EROD activity as exposure marker in carp (Cyprinus carpio) hepatocytes. Freshly isolated hepatocytes of a genetically uniform strain of male carp were co-exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at concentrations of 0, 1, 3, 10, 30, and 100 pM, and one of the highly purified PBDE/PCB congeners (at concentrations of 0, 0.25, and 2.5 microM) or cleaned-up and untreated DE-71 samples (0, 0.1, and 1 microM). PBDEs were selected from the 209 possible congeners based on their relative abundance in environmental samples: BDE-47, BDE-99, BDE-100, and BDE-153. A tentative metabolite of BDE-47, 6OH-BDE-47, was also included. In addition, a commercial pentabrominated dipenylether mixture (DE-71) was tested for interference with EROD activity both with and without clean-up by carbon fractionating which removed possible planar contaminants. Polychlorinated biphenyl (PCB)-153, a reported inhibitor of EROD activity in flounder, was included for comparison. Cells were cultured for a total period of 8 days; exposure started at day 3 after cell isolation. After 5 days of exposure, cell pellets were frozen before EROD activity was determined. Upon exposure to TCDD, the cells responded with increased EROD activity as expected. Significant reduction of TCDD-induced EROD activity was found in the presence of BDE-47, BDE-99, and BDE-153, but not with BDE-100 and 6-hydroxylated BDE-47. Of these PBDE congeners, the most abundant congener in environmental samples, BDE-47, exhibited the strongest inhibition (down to 6% of the TCDD control value). The cleaned-up fraction of commercial penta-BDE (DE-71) mixture proved an even more potent inhibitor, resulting in reduction of EROD activity to 4% of the control values observed at 1.0 microM. BDE-47 and BDE-153 did not reduce TCDD-induced EROD activity when added shortly prior to measurement, suggesting possible interaction with TCDD at the level of CYP1A biosynthesis. PCB-153 did not show significant effects on EROD activity in carp in this study. The present results indicate that environmentally relevant PBDEs can interfere with determination of EROD activity in vitro, at levels reported earlier for PCBs. The observation that detected PBDE levels are rising, stresses the need for caution when interpreting EROD data on environmental samples.

Testing the ecotoxicology of vegetable versus mineral based lubricating oils: 2. Induction of mixed function oxidase enzymes in barramundi, Lates calcarifer, a tropical fish species

An increasing number of vegetable-based oils are being developed as environmentally friendly alternatives to petroleum products. However, toxicity towards key tropical marine species has not been investigated. In this study we used laboratory-based biomarker induction experiments to compare the relative stress of a vegetable-based lubricating oil for marine 2-stroke engines with its mineral oil-based counterpart on tropical fish. The sub-lethal stress of 2-stoke outboard lubricating oils towards the fish Lates calcarifer (barramundi) was examined using liver microsomal mixed function oxidase (MFO) induction assays. This study is the first investigation into the use of this key commercial species in tropical North Queensland, Australia in stress assessment of potential hydrocarbon pollution using ethoxyresorufin O-deethylase (EROD) induction. Our results indicated that barramundi provide a wide range of inducible rates of EROD activity in response to relevant organic stressors. The vegetable- and mineral-based lubricants induced significant EROD activity at 1.0 mg kg(-1) and there was no significant difference between the two oil treatments at that concentration. At increasing concentrations of 2 and 3 mg kg(-1), the mineral-based lubricant resulted in slightly higher EROD activity than the vegetable-based lubricant. The EROD activity of control and treated barramundi are found to be within ranges for other species from temperate and tropical environments. These results indicate that vegetable-based lubricants may be less stressful to barramundi than their mineral counterparts at concentrations of lubricant > or =2 mg kg(-1). There is great potential for this species to be used in the biomonitoring of waterways around tropical North Queensland and SE Asia.

Hepatic CYP1A levels and EROD activity in English sole: biomonitoring of marine contaminants in Vancouver Harbour

To assess chemical contaminant stress in the marine environment, ethoxyresorufin-O-deethylase (EROD) activity and cytochrome P450 1A (CYP1A) expression were measured in 88 English Sole (Pleuronectes vetulus) collected during May and June 1999 from four sites in Vancouver Harbour and at an expected reference site outside the harbour. Hepatic microsomes were prepared from the fish and analyzed for total CYP content, EROD activity, and CYP1A protein levels. Hepatic EROD activity and CYP1A protein levels were elevated in fish from two sites in the inner harbour. A comparison with sediment chemistry data showed that fish with increased EROD activity and CYP1A levels came from sites containing relatively high levels of polycyclic aromatic hydrocarbons and polychlorinated biphenyls. Unexpectedly high levels of EROD activity and CYP1A protein were also found in fish from a reference site near Gibsons, in Howe Sound. The elevated EROD activity and CYP1A expression in fish from this site cannot be explained by the chemical analysis data collected.

Brown trout as a sentinel organism for organic pollution in the field using catalytic and immunochemical assays of cytochrome P-450 1A

The measurement in some living organisms of adequate biomarkers (e.g. cytochrome P-450) to assess the organic pollution in freshwater ecosystems is well established. However, the sensitivity of this approach depends on the analytical measurement method employed and on the chosen living organism for the biomonitoring. Three analytical methods were compared for measuring cytochrome P-450 1A levels in wild brown trout (Salmo trutta): a catalytic one, based on measurement of the ethoxyresorufin-O-deethylase (EROD) activity, and two immunochemical methods, namely, enzyme-linked immunosorbent assay (ELISA) and western blotting. The P-450 1A levels in those animals from a river located in an industrialized area (Trubia River, Northern Spain) and also from individuals living in a low-contamination reference area have been studied. Significant differences (Mann-Whitney U-test, P < 0.01) between rivers were found (ELISA and EROD assays), with the values for Trubia river being similar to those observed in laboratory experiments with well known P-450 1A inducers. However, no significant differences were observed in terms of sex and age. Western blot analysis confirmed the presence of a single band of 56 kDa (corresponding with P-450 1 A protein) in microsomes of fish caught in the Trubia river. On the other hand, and associated with the chemical analysis of PAHs in the waters of both rivers by SPME-GC-MS, high levels of naphthalene (P-450 1A inducer) in the contaminated river were found. In brief, a wide difference between basal levels and P-450 1A induction levels could be detected in trout living in natural field conditions using both EROD activity assay and immunochemical methods. Therefore, brown trout could constitute a good sentinel organism to biomonitor the exposure to PAHs in rivers using P-450 1A measurements.

Characteristics and application of established luciferase hepatoma cell line that responds to dioxin-like chemicals

AIM: To establish a luciferase reporter cell line that responds dioxin-like chemicals (DLCs) and on this basis to evaluate its characteristics and application in the determination of DLCs.

METHODS: A recombinant luciferase reporter plasmid was constructed by inserting dioxin-responsive element (DREs) and MMTV promoter segments into the pGL₃-promoter plasmid immediately upstream of the luciferase gene, which was structurally demonstrated by fragment mapping analysis in gel electrophoresis and transfected into the human hepatoma cell line HepG₂, both transiently and stably, to identify the inducible expression of luciferase by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). The time course, responsive period, sensitivity, structure-inducibility and dose-effect relationships of inducible luciferase expression to DLCs was dynamically observed in HepG₂ cells stably transfected by the recombinant vector (HepG₂-Luc) and compared with that assayed by ethoxyresorufin-O-deethylase (EROD) in non-transfected HepG₂ cells (HepG₂-wt).

RESULTS: The inducible luciferase expression of HepG₂-Luc cells was noted in a time-, dose-, and AhR-dependent manner, which peaked at 4 h and then decreased to a stable level at 14 h after TCDD treatment. The responsiveness of HepG₂-Luc cells to TCDD induction was decreased with culture time and became undetectable at 10^th month of HepG₂-Luc cell formation. The fact that luciferase activity induced by 3, 3', 4, 4'-PCB in HepG₂-Luc cells was much less than that induced by TCDD suggests a structure-inducibility relationship existing among DLCs. Within the concentrations from 3.5 × 10^-12 to 5 × 10^-9 mol/L, significant correlations between TCDD doses and EROD activities were observed in both HepG₂-luc and HepG₂-wt cells. The correlation between TCDD doses from 1.1 × 10^-13 to 1 × 10^-8 mol/L and luciferase activities was also found to be significant in HepG₂-luc cells (r = 0.997, P < 0.001), but not in their HepG₂-wt counterparts. For the comparison of the enzyme responsiveness between cell lines to TCDD, the luciferase sensitivity and reproducibility in HepG₂-luc cells were both better than that of EROD in HepG₂-wt cells, the former was at 1.1 × 10^-13 mol/L and 3.5 × 10^-12 mol/L, and the coefficients of variation (CV) of the latter was 15%-30% and 22%-38%, respectively.

CONCLUSION: The luciferase expression of HepG₂-luc cells established in the present study could sensitively respond to the DLCs stimulation and might be a prospective tool for the determination of DLCs.

Fish bioaccumulation and biomarkers in environmental risk assessment: a review

In this review, a wide array of bioaccumulation markers and biomarkers, used to demonstrate exposure to and effects of environmental contaminants, has been discussed in relation to their feasibility in environmental risk assessment (ERA). Fish bioaccumulation markers may be applied in order to elucidate the aquatic behavior of environmental contaminants, as bioconcentrators to identify certain substances with low water levels and to assess exposure of aquatic organisms. Since it is virtually impossible to predict the fate of xenobiotic substances with simple partitioning models, the complexity of bioaccumulation should be considered, including toxicokinetics, metabolism, biota-sediment accumulation factors (BSAFs), organ-specific bioaccumulation and bound residues. Since it remains hard to accurately predict bioaccumulation in fish, even with highly sophisticated models, analyses of tissue levels are required. The most promising fish bioaccumulation markers are body burdens of persistent organic pollutants, like PCBs and DDTs. Since PCDD and PCDF levels in fish tissues are very low as compared with the sediment levels, their value as bioaccumulation markers remains questionable. Easily biodegradable compounds, such as PAHs and chlorinated phenols, do not tend to accumulate in fish tissues in quantities that reflect the exposure. Semipermeable membrane devices (SPMDs) have been successfully used to mimic bioaccumulation of hydrophobic organic substances in aquatic organisms. In order to assess exposure to or effects of environmental pollutants on aquatic ecosystems, the following suite of fish biomarkers may be examined: biotransformation enzymes (phase I and II), oxidative stress parameters, biotransformation products, stress proteins, metallothioneins (MTs), MXR proteins, hematological parameters, immunological parameters, reproductive and endocrine parameters, genotoxic parameters, neuromuscular parameters, physiological, histological and morphological parameters. All fish biomarkers are evaluated for their potential use in ERA programs, based upon six criteria that have been proposed in the present paper. This evaluation demonstrates that phase I enzymes (e.g. hepatic EROD and CYP1A), biotransformation products (e.g. biliary PAH metabolites), reproductive parameters (e.g. plasma VTG) and genotoxic parameters (e.g. hepatic DNA adducts) are currently the most valuable fish biomarkers for ERA. The use of biomonitoring methods in the control strategies for chemical pollution has several advantages over chemical monitoring. Many of the biological measurements form the only way of integrating effects on a large number of individual and interactive processes in aquatic organisms. Moreover, biological and biochemical effects may link the bioavailability of the compounds of interest with their concentration at target organs and intrinsic toxicity. The limitations of biomonitoring, such as confounding factors that are not related to pollution, should be carefully considered when interpreting biomarker data. Based upon this overview there is little doubt that measurements of bioaccumulation and biomarker responses in fish from contaminated sites offer great promises for providing information that can contribute to environmental monitoring programs designed for various aspects of ERA.

Seasonal variation of plasmatic and hepatic vitellogenin and EROD activity in carp, Cyprinus carpio, in relation to sewage treatment plants

Concern about the health of aquatic fauna living in waters containing biologically active levels of estrogenic compounds is particularly focused on the effects on their reproductive success. To that end, carp, Cyprinus carpio, a feral fish living in warm waters of Southern Europe (NE Spain), were selected for signs of estrogenicity. The study area covered two tributaries (the Anoia and the Cardener) of the Llobregat River both known to be polluted by estrogenic compounds. The estrogenicity in the carp was measured as vitellogenin (VTG) presence in males and alterations in VTG levels in females, over a 6-month period, embracing both the pre- and post-spawning seasons. VTG content was measured in both the plasma and liver, the latter being the organ that synthesizes it. Also, hepatic 7-ethoxyresorufin O-deethylase (EROD) activity was recorded, as interactions of xenoestrogens and oestradiol have been reported to affect this enzymatic activity. The estrogenicity of these rivers was more evident in the Anoia at the location downstream from the sewage treatment plant (STP), by elevated levels of VTG in males and by the presence of some intersex individuals. In the Cardener, no intersex fish were found and male plasmatic VTG was not so highly elevated. However presence of hepatic VTG, in up to 54% of the male fish analyzed, proved exposure to xenoestrogens. In females, VTG fluctuated according to the biological cycle with a plasmatic peak in May and an earlier maximal in the liver. However, this pattern was altered in the locations with higher xenoestrogens presence. EROD activity showed differences between sexes, with higher activity in males than females, as well as site-related differences (up to one order of magnitude) in the same river. These differences were even greater than those detected between rivers. A seasonal trend was also seen in EROD activity with higher induction towards the summer in both males and females.

Effects of benzo[a]pyrene exposure on a fish population resistant to the toxic effects of dioxin-like compounds

Effects of a model polycyclic aromatic hydrocarbon (PAH) were compared in populations of the estuarine fish Fundulus heteroclitus indigenous to a reference site and one highly contaminated with polychlorinated biphenyls (PCBs) and other compounds. The fish population resident to the PCB-contaminated site is genetically resistant to those PCB congeners categorized as dioxin-like compounds (DLCs) that act through the aryl hydrocarbon receptor (AHR). In response to DLC exposures, these DLC-resistant fish showed poor inducibility for enzymes known to be regulated by the AHR pathway and important for the metabolism of xenobiotics including some PAHs that also act as AHR agonists. Therefore, a laboratory study using the model PAH, benzo[a]pyrene (BaP), was conducted to evaluate how PAHs might affect these wild fish populations that differed in their inherent sensitivities to DLCs and in their tissue concentrations of contaminants. Following BaP treatment, the activities of two xenobiotic metabolizing enzymes and the concentrations of BaP-DNA adducts, as measured using the 32P-postlabeling method, were lower in the livers of DLC-resistant than reference fish. These results suggest that DLC-resistance could provide protection following chronic exposures to PAHs from the long-term consequences of DNA adduct formation, such as cancer. Alternatively, reduced metabolism and elimination of toxic or photo-activated PAHs could have acute consequences to the health and reproduction of these DLC-resistant fish and their progeny. These fish populations provide useful models to evaluate the potential costs and benefits of genetic adaptation in wildlife populations subject to anthropogenic stress.

Exposure to hydrocarbons 10 years after the Exxon Valdez oil spill: evidence from cytochrome P4501A expression and biliary FACs in nearshore demersal fishes

Three biomarkers of hydrocarbon exposure, CYP1A in liver vascular endothelium, liver ethoxyresorufin O-deethylase (EROD), and biliary fluorescent aromatic compounds (FACs), were examined in the nearshore fishes, masked greenling (Hexagrammos octogrammus) and crescent gunnel (Pholis laeta), collected in Prince William Sound, Alaska, 7-10 years after the Exxon Valdez oil spill (EVOS). All biomarkers were elevated in fish collected from sites originally oiled, in comparison to fish from unoiled sites. In 1998, endothelial CYP1A in masked greenling from sites that were heavily oiled in 1989 was significantly higher than in fish collected outside the spill trajectory. In 1999, fishes collected from sites adjacent to intertidal mussel beds containing lingering Exxon Valdez oil had elevated endothelial CYP1A and EROD, and high concentrations of biliary FACs. Fishes from sites near unoiled mussel beds, but within the original spill trajectory, also showed evidence of hydrocarbon exposure, although there were no correlations between sediment petroleum hydrocarbon and any of the biomarkers. Our data show that 10 years after the spill, nearshore fishes within the original spill zone were still exposed to residual EVOS hydrocarbons.

Estrogen-mediated suppression of cytochrome P4501A (CYP1A) expression in rainbow trout hepatocytes: role of estrogen receptor

Hepatic CYP1A expression in fish can be modulated by the female sex hormone, 17beta-estradiol (E2), however neither the mechanism of E2 suppression of CYP1A nor the capacity for hormonal regulation to overcome CYP1A induction by xenobiotics are known. The present study investigates for the first time in fish if the estrogen receptor (ER) is involved in the suppressive action of E2 on CYP1A gene expression. The study further examines, if the E2 effect is able to overcome xenobiotic induction of CYP1A. As experimental model, in vitro cultures of rainbow trout, Oncorhynchus mykiss, hepatocytes were used. The effect of E2 on CYP1A was assessed by measuring the CYP1A-associated 7-ethoxyresorufin-O-deethylase (EROD) enzyme activity, and CYP1A mRNA contents. E2 at non-cytotoxic concentrations caused a significant time- and concentration-dependent decline of basal but not of induced hepatic EROD activities. The inhibitory action of E2 on basal CYP1A was also evident at the mRNA level. The presence of the ER antagonist tamoxifen abolished the inhibitory action of E2 on CYP1A expression. The results from these in vitro experiments provide evidence (a) that the ER is involved in the suppressive action of E2 on CYP1A, and (b) that E2 inhibitory action does not overcome xenobiotic induction of CYP1A.

In vivo and in vitro inhibition of CYP1A-dependent activity in Fundulus heteroclitus by the polynuclear aromatic hydrocarbon fluoranthene

Certainpolynuclear aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BaP) induce CYP1A-dependent enzyme activities. Because PAHs are ubiquitous environmental contaminants, and some are aryl hydrocarbon agonists, CYP1A has been used as a biomarker for PAH exposure. However, PAHs exist in the environment in complex mixtures that may confound biomarker results. In in vitro studies, the PAH fluoranthene (FL) failed to increase or enhance CYP1A1-dependent ethoxyresorufin-O-deethylase (EROD) activity in cells, but rather inhibited activities induced by AhR agonists such as 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo(k)fluoranthene. In order to determine the in vivo effects of FL on CYP1A and DNA adduct levels, Fundulus heteroclitus were given single ip injections of either BaP (5 mg/kg), BaP + FL (5 mg/kg each), BaP + FL (5 and 50 mg/kg, respectively), FL (5 mg/kg), FL (50 mg/kg), or corn oil control. BaP-treated fish had liver microsome EROD activities significantly higher than controls, whereas FL-treated fish were not different from controls. EROD activities in BaP + FL cotreatments were significantly lower compared to fish treated with BaP alone. When FL was incubated with BaP-induced microsomes, the IC50 for inhibition of EROD activity was 1.4 x 10(-5) M FL. Kinetic studies indicated a significant noncompetitive component to the FL inhibition. When fish were treated with [(14)C]FL, the concentration of radiolabel associated with microsomal preparations was four orders of magnitude lower than the IC50. Therefore, the presence of FL or a FL metabolite was insufficient to account for the inhibition by a kinetic mechanism. In contrast to cell studies, CYP1A immunoreactive protein was significantly decreased in vivo by FL cotreatment, indicating that FL may inhibit EROD activity by down-regulating the CYP1A protein. A covalent interaction of [(14)C]FL with CYP1A was not detected. Total (32)P-postlabeled DNA adducts were not significantly changed by cotreatment of FL and BaP; however, cotreatment with 50 mg/kg FL decreased one adduct and increased another significantly. Because FL and perhaps other inhibitory PAHs, co-occur in the environment with CYP1A inducers, CYP1A-dependent bioassays may cause an underestimation of PAH exposures.

Hepatic 7-ethoxyresorufin O-deethylase activity in eel (Anguilla anguilla) from the Thames Estuary and comparisons with other United Kingdom Estuaries

Hepatic microsomal 7-ethoxyresorufin O-deethylase (EROD) activities (indicative of exposure to polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs)) were measured in eel Anguilla anguilla from the Thames Estuary. Fish were collected from up to 13 sites during November 1997, May and August 1998 and October 1999. Throughout this period no clear seasonal variation could be identified at every site along the Thames. However, during the summer months, fish sampled from sites in the middle to the upper estuary (Woolwich, Greenhithe and West Thurrock) reported up to 3-fold higher EROD activities compared to sites either at the upper reaches (Richmond and Brentford) at the same time of the year, or fish sampled in winter, along the entire length of the estuary. A laboratory exposure experiment demonstrated a 3-fold elevation of EROD activity 2 days after injection with beta-naphthoflavone (beta-NF). However, higher levels of activity could be determined in fish sampled from the Weston canal near the Merseyside. The lowest levels of A. anguilla EROD activity were observed in fish sampled from the upper reaches of the River Tamar, Devon, and were comparable to activities determined in fish from the Wear and Humber estuaries. A. anguilla sampled along the Thames, Tyne and Tees estuaries reported between 2.5- and 7-fold higher EROD activities compared to fish collected from the Tamar. These results indicate that a low to moderate induction of A. anguilla CYP1A had occurred (indicative of low to moderate exposure to PAHs and planar PCBs) in fish collected from the Thames, Tyne, Wear, Tees, Humber and Tamar estuaries. However, the highest level of EROD activity was observed in fish from the Weston Canal (Merseyside).