Karen A. Kidd

Collapse of a fish population after exposure to a synthetic estrogen

Municipal wastewaters are a complex mixture containing estrogens and estrogen mimics that are known to affect the reproductive health of wild fishes. Male fishes downstream of some wastewater outfalls produce vitellogenin (VTG) (a protein normally synthesized by females during oocyte maturation) and early-stage eggs in their testes, and this feminization has been attributed to the presence of estrogenic substances such as natural estrogens [estrone or 17β-estradiol (E2)], the synthetic estrogen used in birth-control pills [17α-ethynylestradiol (EE2)], or weaker estrogen mimics such as nonylphenol in the water. Despite widespread evidence that male fishes are being feminized, it is not known whether these low-level, chronic exposures adversely impact the sustainability of wild populations. We conducted a 7-year, whole-lake experiment at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada, and showed that chronic exposure of fathead minnow (Pimephales promelas) to low concentrations (5–6 ng·L−1) of the potent 17α-ethynylestradiol led to feminization of males through the production of vitellogenin mRNA and protein, impacts on gonadal development as evidenced by intersex in males and altered oogenesis in females, and, ultimately, a near extinction of this species from the lake. Our observations demonstrate that the concentrations of estrogens and their mimics observed in freshwaters can impact the sustainability of wild fish populations.

Science and policy on endocrine disrupters must not be mixed: a reply to a “common sense” intervention by toxicology journal editors

The “common sense” intervention by toxicology journal editors regarding proposed European Union endocrine disrupter regulations ignores scientific evidence and well-established principles of chemical risk assessment. In this commentary, endocrine disrupter experts express their concerns about a recently published, and is in our considered opinion inaccurate and factually incorrect, editorial that has appeared in several journals in toxicology. Some of the shortcomings of the editorial are discussed in detail. We call for a better founded scientific debate which may help to overcome a polarisation of views detrimental to reaching a consensus about scientific foundations for endocrine disrupter regulation in the EU.

The influence of trophic level as measured by δ15N on mercury concentrations in freshwater organisms

The relationship between mercury (Hg) concentrations in freshwater biota and trophic position, as defined by stable nitrogen isotope ratios (δ15N), was examined in 6 lakes in northwestern Ontario. The heavier isotope of nitrogen (15N) increases an average of 3 parts per thousand (‰) from prey to predator and is used as a measure of an organisms trophic position. Dorsal muscle from lake trout, burbot, walleye, northern pike, white sucker, lake cisco, lake whitefish, and yellow perch was analyzed for Hg and δ15N using flameless atomic absorption and mass spectrometry respectively. Within each lake, log Hg was significantly related to δ15N (r2 ranged from 0.47 to 0.91,P<0.01). For four species, yellow perch, northern pike, lake cisco, and lake trout, log Hg was positively related to δ15N (r2 ranged from 0.37 to 0.47,P≤0.09) across all lakes. We also used δ15N measurements (assuming a 3‰ shift between an organism and its diet) and the developed within-lake regression equations to calculate a prey Hg for each individual fish. These food Hg values were then used to predict predator Hg using Norstromet als bioenergetics model. Predicted results were strongly correlated to measured Hg concentrations (r=0.91,P<0.001), indicating that δ15N has potential to be used in modeling.

Biomagnification of Mercury in Aquatic Food Webs: A Worldwide Meta-Analysis

The slope of the simple linear regression between log10 transformed mercury (Hg) concentration and stable nitrogen isotope values (δ(15)N), hereafter called trophic magnification slope (TMS), from several trophic levels in a food web can represent the overall degree of Hg biomagnification. We compiled data from 69 studies that determined total Hg (THg) or methyl Hg (MeHg) TMS values in 205 aquatic food webs worldwide. Hg TMS values were compared against physicochemical and biological factors hypothesized to affect Hg biomagnification in aquatic systems. Food webs ranged across 1.7 ± 0.7 (mean ± SD) and 1.8 ± 0.8 trophic levels (calculated using δ(15)N from baseline to top predator) for THg and MeHg, respectively. The average trophic level (based on δ(15)N) of the upper-trophic-level organisms in the food web was 3.7 ± 0.8 and 3.8 ± 0.8 for THg and MeHg food webs, respectively. For MeHg, the mean TMS value was 0.24 ± 0.08 but varied from 0.08 to 0.53 and was, on average, 1.5 times higher than that for THg with a mean of 0.16 ± 0.11 (range: -0.19 to 0.48). Both THg and MeHg TMS values were significantly and positively correlated with latitude. TMS values in freshwater sites increased with dissolved organic carbon and decreased with total phosphorus and atmospheric Hg deposition. Results suggest that Hg biomagnification through food webs is highest in cold and low productivity systems; however, much of the among-system variability in TMS values remains unexplained. We identify critical data gaps and provide recommendations for future studies that would improve our understanding of global Hg biomagnification.

Spatial and temporal trends of contaminants in Canadian Arctic freshwater and terrestrial ecosystems: a review

The state of knowledge of contaminants in Canadian Arctic biota of the freshwater and terrestrial ecosystems has advanced enormously since the publication of the first major reviews by Lockhart et al. and Thomas et al. in The Science of the Total Environment in 1992. The most significant gains are new knowledge of spatial trends of organochlorines and heavy metal contaminants in terrestrial animals, such as caribou and mink, and in waterfowl, where no information was previously available. Spatial trends in freshwater fish have been broadened, especially in the Yukon, where contaminant measurements of, for example, organochlorines were previously non-existent. A review of contaminants data for fish from the Northwest Territories, Yukon and northern Quebec showed mercury as the one contaminant which consistently exceeds guideline limits for subsistence consumption or commercial sale. Lake trout and northern pike in the Canadian Shield lakes of the Northwest Territories and northern Quebec generally had the most elevated levels. Levels of other heavy metals were generally not elevated in fish. Toxaphene was the major organochlorine contaminant in all fish analyzed. The concentrations of organochlorine contaminants in fish appear to be a function not only of trophic level but of other aspects of the lake ecosystem. Among Arctic terrestrial mammals, PCBs and cadmium were the most prominent contaminants in the species analyzed. Relatively high levels (10-60 micrograms g-1) of cadmium were observed in kidney and liver of caribou from the Yukon, the Northwest Territories and northern Quebec, with concentrations in western herds being higher than in those from the east. For the organochlorine contaminants, a west to east increase in zigma PCBs, HCB and zigma HCH was found in caribou, probably as a result of the predominant west to east/north-east atmospheric circulation pattern which delivers these contaminants from industrialized regions of central and eastern North America to the Arctic via long-range atmospheric transport. Radiocesium contamination of lichens and caribou has continued to decrease. Significant contamination by PCBs and lead of soils and vascular plants was observed in the immediate vicinity and within a 20-km radius of DEW line sites in the Canadian Arctic. There was also evidence for transfer of PCBs from plants to lemmings. There was no evidence, however, that large mammals such as caribou living in the general area of the DEW line sites had elevated levels of PCBs. There is very limited temporal trend information for most contaminants in biota of Arctic terrestrial and freshwater environments.

Trophic magnification factors: Considerations of ecology, ecosystems, and study design

Recent reviews by researchers from academia, industry, and government have revealed that the criteria used by the Stockholm Convention on persistent organic pollutants under the United Nations Environment Programme are not always able to identify the actual bioaccumulative capacity of some substances, by use of chemical properties such as the octanol-water partitioning coefficient. Trophic magnification factors (TMFs) were suggested as a more reliable tool for bioaccumulation assessment of chemicals that have been in commerce long enough to be quantitatively measured in environmental samples. TMFs are increasingly used to quantify biomagnification and represent the average diet-to-consumer transfer of a chemical through food webs. They differ from biomagnification factors, which apply to individual species and can be highly variable between predator-prey combinations. The TMF is calculated from the slope of a regression between the chemical concentration and trophic level of organisms in the food web. The trophic level can be determined from stable N isotope ratios (δ(15) N). In this article, we give the background for the development of TMFs, identify and discuss impacts of ecosystem and ecological variables on their values, and discuss challenges and uncertainties associated with contaminant measurements and the use of δ(15) N for trophic level estimations. Recommendations are provided for experimental design, data treatment, and statistical analyses, including advice for users on reporting and interpreting TMF data. Interspecies intrinsic ecological and organismal properties such as thermoregulation, reproductive status, migration, and age, particularly among species at higher trophic levels with high contaminant concentrations, can influence the TMF (i.e., regression slope). Following recommendations herein for study design, empirical TMFs are likely to be useful for understanding the food web biomagnification potential of chemicals, where the target is to definitively identify if chemicals biomagnify (i.e., TMF > or < 1). TMFs may be less useful in species- and site-specific risk assessments, where the goal is to predict absolute contaminant concentrations in organisms in relation to threshold levels.

High Concentrations of Toxaphene in Fishes from a Subarctic Lake

Concentrations of toxaphene and other organochlorine compounds are high in fishes from subarctic Lake Laberge, Yukon Territory, Canada. Nitrogen isotope analyses of food chains and contaminant analyses of biota, water, and dated lake sediments show that the high concentrations of toxaphene in fishes from Laberge resulted entirely from the biomagnification of atmospheric inputs. A combination of low inputs of toxaphene from the atmosphere and transfer through an exceptionally long food chain has resulted in concentrations of toxaphene in fishes that are considered hazardous to human health.

Bioaccumulation of organochlorines through a remote freshwater food web in the Canadian Arctic

Abstract Persistent organochlorines (OCs) were measured in water, sediment and biota from a remote lake in the Canadian Arctic to examine the bioaccumulation of atmospherically deposited OCs through a high-latitude freshwater food web. All major OC groups (polychlorinated biphenyls [PCBs], dichlorodiphenyl trichloroethane and metabolites [DDT], chlordane [CHL]-related compounds, and hexachlorocyclohexane [HCH] isomers) were detectable at sub-ng liter −1 concentrations in lake water and at low ng g −1 levels (dry wt) in surface sediments. Estimates of air–water exchange using a two-film model suggested that lake waters were close to equilibrium with the atmosphere for αHCH, trans -nonachlor and p,p ′-DDE but that PCB congeners 52 and 153 were undergoing volatilization. Despite the relatively short open water season, gas absorption was found to be a major input pathway into the lake, when compared to estimated inputs from precipitation. Mean concentrations of ΣHCH, ΣDDT, ΣCHL and ΣPCB ranged from 1 to 10 ng g −1 wet wt in arctic char and from 2 to 82 ng g −1 in lake trout and were comparable to results from other lakes in the Canadian Arctic. Exceptionally high concentrations (six- to 10-fold higher than mean values) of these OCs were observed in a few lake trout and were explained by the larger size, longer lifespans and higher lipid contents of these individuals. Trophic interrelationships of food-web organisms were characterized using their tissue stable carbon and nitrogen isotope ratios. Through the food web, lipid-adjusted concentrations of αHCH, trans -nonachlor, p,p ′-DDE, and PCB congeners 52 and 153 in biota were significantly related to their trophic position as determined by measurements of tissue stable nitrogen isotope ratios. In addition, the slopes and coefficients of determination for these relations increased with the lipophilicity and recalcitrance of the OCs, demonstrating that the more lipophilic OCs bioaccumulated to a greater degree through this food web even after accounting for the effects of lipid.

Correlation between stable nitrogen isotope ratios and concentrations of organochlorines in biota from a freshwater food web

The relationship between total concentrations of hexachlorocyclohexane (sigma HCH), sigma DDT, and chlorinated bornanes (toxaphene, sigma CHB) and the trophic position of biota from a subarctic lake was investigated using stable isotope ratios of nitrogen (15N/14N). Zooplankton, benthic invertebrates, and forage and piscivorous fishes were analysed for 15N/14N and organochlorines using mass spectrometry and high resolution capillary gas chromatography (GC-ECD), respectively. The trophic relationships of the biota were clearly defined, with 15N/14N increasing an average of 3.3/1000 from prey species to predator. Mean concentrations of sigma HCH were lowest in chironomids (subfamily Chironominae, 0.2 ng/g wet wt.) and highest in burbot liver (Lota lota; 30.2 ng/g wet wt.). Mean concentrations of sigma DDT and sigma CHB ranges from 0.5 and 2.0 (ng/g wet wt.), respectively, in snails (Family Limnaeidae), to 3430 and 2820 (ng/g wet wt.) in burbot liver. Regression analyses indicated that both the wet and lipid weight concentrations of sigma HCH, sigma DDT, and sigma CHB in the biota from this food web were significantly related to trophic position, as defined by delta 15 N. Results from this study indicated that delta 15 N can be used to predict concentrations of organochlorines in freshwater biota.

Mercury Concentrations in the Food Web of Lake Malawi, East Africa

Little is known about the concentrations of mercury (Hg) and factors affecting this contaminant in tropical freshwater biota. Lake Malawi, an East African Rift Valley lake, is internationally renowned for having the highest diversity of fish species in the world, and the lake supports subsistence fisheries for the three riparian countries. In this study the concentrations of Hg in fish and invertebrates collected from the lake in 1996 and 1997 were examined, and tissue stable carbon (δ13C) and nitrogen (δ15N) isotopes were used to distinguish and contrast those consumers relying upon carbon fixed by either benthic or pelagic primary producers, and their trophic positioning. Concentrations of Hg were generally low (2 to 200 ng/g wet weight) in fish from Lake Malawi. In addition, pelagic fish contained significantly higher concentrations of Hg than the benthic species. As in temperate systems, log-transformed Hg concentrations were significantly predicted by δ15N and the highest concentrations of Hg were found in the largest fish within each species. The rate of Hg accumulation was not significantly different between the pelagic and benthic fishes but pelagic species had significantly higher Hg concentrations at a common weight and trophic position. The slope of the Hg-δ15N relationship in Lake Malawi was comparable to what has been found in temperate and arctic lakes, suggesting that Hg accumulation in freshwater food webs is independent of climatic factors and species composition.