Organochlorine concentrations in diseased vs. healthy gull chicks from the northern Baltic

Diseases of wild birds in southern Rio Grande do Sul, Brazil

ABSTRACT: Necropsy protocols of the “Laboratório Regional de Diagnóstico” of “Faculdade de Veterinária” of the “Universidade Federal de Pelotas” were reviewed, ranging the period from 2000 to 2018. Three hundred eighty one necropsies, 25 refrigerated and/or formaline fixed organs, and seven biopsies were received, representing 413 samples. Most of these materials were sent by the “Núcleo de Reabilitação da Fauna Silvestre” of “Universidade Federal de Pelotas” (NURFS-CETAS-UFPel) and were from municipalities within the range area of LRD-UFPel influence. Of the 413 cases 55 (13.31%) corresponded to metabolic/nutritional diseases; 50 (12.10%) to trauma; 35 (8.47%) to bacterial diseases/toxi-infections; 30 (7.26%) to parasitic diseases; 28 (6.77%) to fungal diseases; four (0.97%) to viral diseases and 17 (4.11%) to other diseases. Cases where it was not possible to determine the etiology, were in severe autolysis or were inconclusive totaled 194 (46.97%). Metabolic/nutritional diseases and traumatic injuries were the main cause of death in wild birds’, being Passeriformes the most affected order.

Polychlorinated Biphenyls in the Plasma and Preen Oil of Black-Footed Albatross (Diomedea nigripes) Chicks and Adults on Midway Atoll, North Pacific Ocean

Polychlorinated biphenyls (PCBs) are ubiquitous in the environment. Midway Atoll, located in the North Pacific Ocean, was occupied by the military during and after World War II. However, Midway Atoll has become a national wildlife refuge and home to many different seabirds today, including the black-footed albatross (Diomedea nigripes) (BFAL). The profiles and toxic equivalents (TEQ) of PCB congeners in the plasma and preen oil of BFAL chicks and adults were determined in this study. The concentrations of the total PCBs in the plasma samples of chicks and adults collected in Midway Atoll ranged from 2.3 to 223.8 (mean 80.1) and 22.8 to 504.5 (mean 158.6) ng g(-1) (wet weight, ww), respectively. The TEQs ranged from 0.2 to 0.6 (mean 0.4) and 0.4 to 1.6 (mean 0.9) pg g(-1) ww, respectively, in the plasma samples of chicks and adults from Midway Atoll. The major congeners in the plasma samples of chicks and adults included PCBs 31, 87, 97, 99, 118, 138, 153, and 180, accounting for 70% of the total PCBs. The concentrations of the total PCBs in the adult preen oil samples ranged from 1693 to 39404 (mean 10122) ng g(-1) (ww), of which 97% were PCBs 105, 118, 128, 138, 153, 161, 172, and 183.

Persistent organic pollutant concentrations in fledglings of two arctic seabird species

Persistent organic pollutants (POPs) and stable isotopes were measured in muscle from fledglings of two arctic seabird species, Northern fulmar (Fulmarus glacialis) and Black-legged kittiwakes (Rissa tridactyla). The purpose was to compare POP concentrations between species, in an age class that is highly vulnerable to POPs but little studied, relate to diet using stable isotopes, and quantify differences across life stages (egg to adult). Northern fulmar fledglings had significantly higher POP concentrations than kittiwake, consistent with results reported for adults of these species. Surprisingly, carbon and nitrogen stable isotopes did not differ between species, which does not match data for, or the known feeding ecology, of the adults. Fulmar/kittiwake POP concentration ratios varied across life stages indicating variable POP exposure and accumulation with age in seabirds, indicating that of the use of avian species-specific thresholds should only be done with caution in ecosystem-based POP risk management.

Bioamplification as a bioaccumulation mechanism for persistent organic pollutants (POPs) in wildlife

Persistent organic pollutant bioaccumulation models have generally been formulated to predict bioconcentration and biomagnification. A third bioaccumulation process that can mediate chemical fugacity in an organism is bioamplification.Bioamplification occurs when an organism loses body weight and the chemical partitioning capacity occurs at a rate that is faster than the chemical can be eliminated.Although bioamplification has not been widely recognized as a bioaccumulation process, the potential consequences of this process are significant. Bioamplification causes an increase in chemical fugacity in the animal's tissues and results in there distribution of contaminants from inert storage sites to more toxicologically sensitive tissues. By reviewing laboratory and field studies, we have shown in this paper that bioamplification occurs across taxonomic groups that include, invertebrates,amphibians, fishes, birds, and mammals. Two case studies are presented, and constitute multi-life stage non-steady state bioaccumulation models calibrated for yellow perch and herring gulls. These case studies were used to demonstrate that bioamplification is predicted to occur under realistic scenarios of animal growth and seasonal weight loss. Bioamplification greatly enhances POP concentrations and chemical fugacities during critical physiological and behavioral events in an animal's life history, e.g., embryo development, juvenile stages, metamorphosis, reproduction, migration, overwintering, hibernation, and disease. Consequently,understanding the dynamics of bioamplification, and how different life history scenario scan alter tissue residues, may be helpful and important in assessing wildlife hazards and risks.

Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish

Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.

Organochlorine compounds and their metabolites in seven Icelandic seabird species - a comparative study

The present study is designed to assess the occurrence of a few organochlorine contaminants and their metabolites in eggs of different marine bird species in Iceland, a country located in the sub-Arctic of the North-Western Atlantic. Previous investigations from e.g. Sweden and The Netherlands have shown some obvious differences in contaminant concentrations, including e.g. hydroxylated polychlorinated biphenyl metabolites (OH-PCBs) in guillemot (Uria aalge) and other bird species. Eggs from seven marine bird species, Arctic tern (Sterna paradisaea), common eider (Somateria mollissima), guillemot, fulmar (Fulmarus glacialis), great black-backed gull (Larus marinus), lesser black-backed gull (Larus fuscus), and great skua (Stercorarius skua), that all breed in Iceland, were collected and analyzed for several persistent organic compounds and their metabolites. The contaminant levels varied between the species investigated. The highest concentrations were found in eggs from the great skua (18 and 23 microg/g l.w. of CB-153 and 4,4'-DDE, respectively). The concentration difference was generally 2 orders of magnitude higher in great skua for all organochlorine compounds analyzed with the exception of HCB. HCB did not vary as much between the seven species (ranging from 34 to 710 ng/g l.w). OH-PCB and MeSO(2)-PCB metabolites congener concentrations and patterns showed differences in metabolic capacity between bird species. Guillemot and great skua seem to distinguish themselves most from other species i.e. with the absence of 4-OH-CB187 and low relative levels of 4-OH-CB146 in guillemot and the low abundance of OH-PCBs in great skua.

Temporal variations of polybrominated dibenzo-p-dioxin and methoxylated diphenyl ether concentrations in fish revealing large differences in exposure and metabolic stability

The concentrations of polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated methoxylated diphenyl ethers (MeO-PBDEs) were investigated in perch (Perca fluviatilis) collected from a Baltic Sea background contaminated area between 1990 and 2005. No temporal trend was found, but large variations were observed - up to 5-fold and 160-fold differences in MeO-PBDE and PBDD concentrations, respectively - between consecutive years, suggesting that retention of these compounds, particularly the PBDDs, is limited. Examination of the congener profiles using principal component analysis (PCA) and correlation analysis indicated that MeO-PBDEs without adjacent substituents (6-MeO-BDE47) or with two adjacent substituents (2'-MeO-BDE68 and 6-MeO-BDE90) are retained more than MeO-PBDEs with three adjacent substituents (6-MeO-BDE85 and 6-MeO-BDE99) and that 1,3,6,8-tetraBDD and 1,3,7,9-tetraBDD are retained more than the other PBDDs which have vicinal hydrogen. Debromination could explain the limited retention of 6-MeO-PBDE85 and 6-MeO-BDE99 and the absence of 2-MeO-BDE123 and 6-MeO-BDE137, and cytochrome P-450 mediated oxidation could explain the limited retention of PBDDs containing vicinal hydrogen. The levels of organobromines, especially MeO-PBDEs, were found to covary with water conditions related to primary production, for example temperature, depth visibility, and inorganic nutrient concentrations, which also favor fish productivity. The results suggest natural production of MeO-PBDEs and PBDDs and imply that they fluctuate considerably over time, as do common marine toxins in fish. Thus, assessments of human and environmental risk should consider both the average and peak concentrations of these contaminants in marine biota.

Perfluorinated and chlorinated pollutants as predictors of demographic parameters in an endangered seabird

Despite global occurrence of several perfluorinated compounds (PFCs) the potential ecological effects of such substances on natural populations are not known. In endangered lesser black-backed gulls (Larus fuscus fuscus) on the Norwegian Coast, the blood concentrations of PFCs were as high as legacy organochlorines (OCs), and here we examined whether PFCs show associations similar to those of OCs to factors potentially affecting population growth, by evaluating relationships between contaminant concentrations and demographic parameters (reproductive performance and the probability of adults returning between breeding seasons). PFCs were not adversely associated with demographic parameters, while the most persistent OCs; notably PCB and p,p'-DDE, were adversely associated with early chick survival, and adult return rate. This study thus suggests that when the concentrations of PFCs and OCs are of similar magnitude in a gull population, OCs are more likely to cause adverse ecological effects.

Brominated dibenzo-p-dioxins: a new class of marine toxins?

Levels of polybrominated dibenzo-p-dioxins (PBDDs) were measured in marine fish, mussels, and shellfish. PBDDs were nondetectable in samples from freshwater environments, and their levels were successively higher in samples from the marine environments of the Bothnian Bay and Bothnian Sea, the West Coast of Sweden, and the Baltic Proper. In Baltic Proper littoral fish the levels of PBDDs generally exceeded those of their chlorinated analogues (PCDDs). This is alarming as some Baltic fish species already are contaminated by chlorinated dioxins to such an extent that they cannot be sold on the European market. By comparing spatial trends in PBDD and PCDD distributions, and PBDD patterns in fish, mussels, and algae, we show that the PBDDs are probably produced naturally, and we propose a route for their biosynthesis. We further show that the levels of PBDDs are high (ng/g wet weight) in mussels, and that the levels increase over time. Finally, we discuss the possibility that the PBDDs have adverse biological effects, and that the levels are increasing as a result of global warming and eutrophication.

Environmental pollutants in endangered vs. increasing subspecies of the lesser black-backed gull on the Norwegian Coast

Organochlorine (OC) residues were measured in eggs and blood of different subspecies of the lesser black-backed gull, Larus fuscus, on the Norwegian coast: a) increasing L. f. intermedius in the North Sea; b) endangered L. f. fuscus near the Arctic Circle; c) L. f. fuscus and greyish-mantled gulls, with a L. f. intermedius appearance, in the Barents Sea region. The dominating OCs in lesser black-backed gulls were polychlorinated biphenyls (PCB) and p,p'-dichlorodiphenyldichloroethylene (DDE). DDE and beta-hexachlorocyclohexane (beta-HCH) residues were higher in L. f. fuscus compared to L. f. intermedius and greyish-mantled birds in the Barents Sea region. In the latter area, blood residues of PCB and DDE in lesser black-backed gulls were as high as in great black-backed gulls, Larus marinus, while in the other regions they were lower. The higher DDE residues in endangered L. f. fuscus compared to increasing L. f. intermedius and greyish-mantled birds, which are invading northern Norway, suggest that OCs may have played a role in the population decline of L. f. fuscus, possibly in combination with nutrient stress.

Multivariate data analysis of organochlorines and brominated flame retardants in Baltic Sea guillemot (Uria aalge) egg and muscle

Concentrations of organochlorines (OCs) and brominated flame-retardants (BFRs) were determined in guillemot (Uria aalge) eggs from the island of Stora Karlsö in the Baltic Sea where 10 eggs/year were collected in the years 2000, 2001 and 2002. The dominating contaminant in egg was p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) with a geometric mean (GM) concentration of 18200 ng/g lipid weight (lw). The GM concentration in egg of hexabromocyclododecane (HBCD) of 140 ng/glw, was significantly higher than that of polybrominated diphenyl ether (summation operatorPBDE) of 77 ng/glw. For the evaluation of the data multivariate data analysis techniques namely principal components analysis (PCA), partial least squares regression (PLS), soft independent modelling of class analogy (SIMCA classification), and PLS discriminant analysis (PLS-DA), were used. We investigated whether the eggs' biological characteristics co-varied with egg concentrations of OCs and BFRs, and found e.g., significant negative correlations between egg weight and concentrations of HCB and p,p'-DDE. A PLS model with analyzed BFRs as the Y matrix and OCs as the X matrix could, with varying accuracy, calculate the concentrations of BFRs in the individual egg from their concentrations of OCs (e.g., R(2)Y of 0.89 for BDE47, and of 0.50 for HBCD). Lastly, we compared the contaminant concentrations in the eggs to those in previously analyzed pectoral muscles from adult guillemots from Stora Karlsö, from the year 2000. A PLS-DA model, showed that some of the contaminants (e.g., HBCD and CB28) had significantly higher concentrations in egg than in muscle, although 7 of the 14 contaminants showed no difference in concentrations between the two matrices.

Accumulation profiles of persistent organochlorines in liver and fat tissues of various waterbird species from Greece

Waterbirds are particularly subject to accumulation of persistent organic pollutants (POPs) that have been shown to constitute a major hazard for this group of birds. Liver and fat tissue from ten species belonging to the orders Ciconiformes (Ardeidae, Ciconiidae, Phoenicopteridae) and Pelicaniformes (Pelecanidae, Phalacrocoracidae) were used as bioindicators in order to assess environmental pollution by POPs (HCHs, DDTs, cyclodienes, PCBs) in Greek wetlands. To our knowledge, this is the first study on POPs in livers of water birds in Greece and Eastern Mediterranean area. The DDTs consisted mainly of p,p'-DDE with percentages over 60% in the great majority of the samples. The highest summation SigmaDDT concentrations were measured in the liver and subcutaneous fat of Phoenicopterus rubber and in Ardea purpurea liver (15565, 24706 and 10406 ng g(-1) wet weight, respectively). Low concentrations of cyclodienes (Cycls) and HCHs were detected occasionally and the contamination pattern of OCPs in most species of waterbirds followed the order summation SigmaDDTs> summation SigmaCycls> summation SigmaHCHs. Individual values of total PCBs reached the levels of 4468 and 3252 ng g(-1) wet weight, for Nycticorax nycticorax and Egretta garzetta samples respectively. Some of the recorded differences in organochlorine concentrations could be due to different causes of death, with a subsequent effect on body lipid levels. Organochlorine pesticides and PCBs residues were lower than those commonly associated with mortality and reduced reproductive success in most species. However, low level exposure to these contaminants may constitute one of the many stressors that in combination could adversely affect bird populations.

Persistent organochlorine contaminants in liver and fat of birds of prey from Greece

The concentrations of persistent organic pollutants, such as DDT and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), cyclodienes (Cycls), and polychlorinated biphenyls (PCBs), were measured in livers and subcutaneous fat tissues of six Accipitridae and four Falconidae bird species from different areas in Greece. This is the first report of persistent organochlorine (OC) pollutants in birds of prey tissues presented for Greece and the Eastern Mediterranean region. Accumulation patterns of OCs found in birds suggested that the predominant contaminants were p,p'-dichlorodiphenyldichloro-1,1-ethylene (DDE) and PCBs, whereas Cycls and HCHs occurred at low concentrations only. Concentration values of p,p'-DDE ranged from nondetected to 19,518.72 ng/g wet wt in livers and from nondetected to 2679.19 ng/g wet wt in fat. Total PCB levels ranged from 1.01 to 7419.43 ng/g and from 3.25 to 490.10 ng/g wet weight for liver and fat samples, respectively. Higher-chlorinated PCBs such as 118, 138, 153, and 180 predominated in both the liver and subcutaneous fat samples, a pattern comparable to that observed in birds from other European countries. No significant differences in mean concentrations of OCs are detected between species. Hepatic concentrations were in general higher than the fat concentrations showing depleted fat stores in most birds. Concentration ranges were also found in lower or similar levels to those reported for birds in other regions. Variation of OCs levels in bird tissues could be due to different causes of death, with a subsequent effect on body lipid levels, and different feeding and migration habits. The liver PCB levels reported in this study are below the concentrations currently believed to exert mortality or ecotoxicological effects. On the contrary, in some cases p,p'-DDE concentrations were higher than the reported effect values for birds of the same families and could be associated with sublethal effects.

Organochlorines in antarctic and arctic avian top predators: a comparison between the South Polar Skua and two species of northern hemisphere gulls

Different organochlorine compounds (OCs) were measured in the blood of breeding south polar skuas (Catharacta maccormicki) at Svarthamaren, Dronning Maud Land (Antarctica) and compared to those in two species of northern hemisphere gulls: the Arctic glaucous gull (Larus hyperboreus) and the subarctic great black-backed gull (Larus marinus). The skuas had 8% and 29% of the SigmaOC levels (45 ng/g, wet weight) of glaucous gulls (591 ng/g) and great black-backed gulls (158 ng/g), respectively. Polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) were very low in skuas compared to northern gulls, but the mean hexachlorobenzene (HCB) level was 1.7 times higher than in great black-backed gulls and one-third of the glaucous gull level. Mirex levels in skuas were among the highest reported in birds, the mean level being 3 and 26 times higher than those in glaucous gull and great black-backed gulls, respectively. In skuas, the mean levels of HCB, oxychlordane, p,p'-DDE, and PCBs increased by about 30% during a 2-week period, and mirex increased by nearly 60%. In glacuous gulls, HCB, p,p'-DDE, and PCBs increased by 10-20%. For HCB, mirex, and oxychlordane, only a relatively small proportion of the increase in skuas could be explained by changes in lipid pools and the levels at first sampling, compared to glaucous gulls. Thus, skuas were probably accumulating these compounds when present in Antarctica. p,p'-DDE and PCB levels, in contrast, seemed much more stable in the skuas. Relatively high levels of mirex and HCB in south polar skuas are concerning with regard to potential adverse effects.

Multivariate data analyses of chlorinated and brominated contaminants and biological characteristics in adult guillemot (Uria aalge) from the Baltic Sea

Adult guillemot (Uria aalge) birds, 10 females and 10 males, drowned in trawl nets near Stora Karlsö in the Baltic Sea, were collected in 2000. Several of the animals' biological characteristics were recorded. The birds' pectoral muscles were individually analyzed for their concentrations of organochlorines (OCs) and brominated flame retardants (BFRs), dichlorodiphenyltrichloroethanes (DDTs), polychlorinated biphenyls (PCBs), hexachlorocyclohexanes, trans-nonachlor, hexachlorobenzene, hexabromocyclododecane (HBCD), and polybrominated diphenyl ethers (PBDEs). The dominating contaminant was p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) with a geometric mean concentration of 12 900 ng/g lipid weight (lw). The concentration of sigmaPBDE (80 ng/g lw) was similar to that of HBCD (65 ng/g lw). The total concentration of all OCs was approximately 150 times higher than that of all BFRs. For the statistical evaluation of the data, we used multivariate analysistechniques such as principal components analysis, partial least-squares (PLS) regression, and PLS discriminant analyses. No differences between the two sexes were found, either in contaminant concentrations or in biological characteristics. We found that some biological characteristics covaried with the concentrations of several OCs and BFRs, e.g., a negative correlation between liver weight and concentration of contaminants. The concentrations of most OCs but not of BFRs showed a decrease with increasing lipid content. Further, a PLS model with OCs as X and BFRs as Y showed that the contaminants formed two groups, each with distinctive correlation patterns. The PLS model could be used to predict with varying accuracy the concentration of BFRs in the individual muscles from their concentration of OCs.

Estrogenic and toxic effects of polychlorinated biphenyls on cultured ovarian germ cells of embryonic chickens

Polychlorinated biphenyls (PCBs) are man-made ubiquitous pollutants that have detrimental effects on reproduction and endocrine functions in a variety of species. In the present study, estrogenic and toxic effects of PCBs on embryonic chicken ovarian development were evaluated by a germ-somatic cell co-culture system. Ovarian cells were cultured in serum-free medium and challenged with a mixture of PCBs (Aroclor 1254). Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release. Results showed that lower PCBs (0.1-1 microg/ml) manifested mainly estrogenic effect to stimulate germ cell proliferation, while higher PCBs (10 microg/ml) imposed severe toxicity on germ and somatic cells. The toxic effect of PCBs could be attenuated by an antioxidant tocopherol. PCBs induced condensed nuclear chromosome in ovarian cells and caused cell exfoliation and breakdown within initial hours of treatment. After 24 h, the estrogenic effect of PCBs began to exhibit and the survived germ cells manifested proliferation. Inhibition of the estrogenic effect of PCBs by tamoxifen led to increased toxicity on germ cells and somatic cells. These results indicate that PCBs exposure may interfere with ovarian germ cell proliferation and cause reproductive disorder via both toxic and estrogenic actions in embryonic chickens.