Systemic Effects of Arctic Pollutants in Beluga Whales Indicated by CYP1A1 Expression

Cytochrome P450 1A1 (CYP1A1) is induced by exposure to polycyclic aromatic hydrocarbons (PAHs) and planar halogenated aromatic hydrocarbons (PHAHs) such as non-ortho polychlorinated biphenyls (PCBs). In this study, we examined CYP1A1 protein expression immunohistochemically in multiple organs of beluga whales from two locations in the Arctic and from the St. Lawrence estuary. These beluga populations have some of the lowest (Arctic sites) and highest (St. Lawrence estuary) concentrations of PCBs in blubber of all cetaceans. Samples from these populations might be expected to have different contaminant-induced responses, reflecting their different exposure histories. The pattern and extent of CYP1A1 staining in whales from all three locations were similar to those seen in animal models in which CYP1A has been highly induced, indicating a high-level expression in these whales. CYP1A1 induction has been related to toxic effects of PHAHs or PAHs in some species. In St. Lawrence beluga, the high level of CYP1A1 expression coupled with high levels of contaminants (including CYP1A1 substrates, e.g., PAH procarcinogens potentially activated by CYP1A1) indicates that CYP1A1 could be involved in the development of neoplastic lesions seen in the St. Lawrence beluga population. The systemic high-level expression of CYP1A1 in Arctic beluga suggests that effects of PAHs or PHAHs may be expected in Arctic populations, as well. The high-level expression of CYP1A1 in the Arctic beluga suggests that this species is highly sensitive to CYP1A1 induction by aryl hydrocarbon receptor agonists

Accumulation, depuration and hepatic mixed-function oxidase enzyme induction in juvenile rainbow trout and lake whitefish exposed to dietary 2,3,7,8-tetrachlorodibenzo-p-dioxin

Juvenile rainbow trout (Oncorhynchus mykiss) and lake whitefish (Coregonus clupeaformis) were exposed to three concentrations (40, 190, 400 pg g-1) of dietary 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin (TCDD) to compare bioaccumulation and hepatic monooxygenase enzyme (MO) induction. Fish were exposed for 30 days followed by a 180 day depuration phase. Differences in the accumulation and depuration of TCDD were found between rainbow trout and lake whitefish, despite similar body size and lipid content. Assimilation efficiencies of TCDD were greater in lake whitefish (66-76%) than rainbow trout (43-58%), but TCDD half lives were shorter in lake whitefish (32-39 days) than in rainbow trout (73-83 days). Biomagnification factors (BMF) ranged from 1.6 to 1.8 in rainbow trout and from 0.8 to 0.9 in lake whitefish, confirming the known potential for biomagnification of TCDD in aquatic food webs. Reverse phase HPLC showed that a majority of the radioactivity in the rainbow trout bile was TCDD, with minor amounts present as a hydroxylated TCDD and as a glucuronide conjugate. MO enzyme induction, measured by ethoxyresorufin-O-deethylase (EROD), was observed in the rainbow trout after 10 days of exposure to 400 pg g-1 TCDD, and in the lake whitefish after 5 days of exposure to 380 pg g-1 TCDD. The whole fish threshold concentration for EROD induction by TCDD ranged between 15 and 45 pg g-1 (wet weight) for both species. EROD activity returned to control levels 120 and 80 days after the cessation of the treatments in the rainbow trout and lake whitefish, respectively. Growth rates were significantly reduced in trout and whitefish at whole fish concentrations (wet weight) of 150 ± 4.6 and 85 ± 8.3 pg g-1, respectively. Histological effects of the TCDD were found in the spleen and liver of the rainbow trout which had whole fish concentrations (wet weight) of, 150 ± 4.6 pg g-1 and 72 ± 8.0 pg g-1 TCDD, respectively

(Table 1) Age, fork length, and tissue d15N and element concentration of arctic char (Salvelinus alpinus) from Lake Hazen

Arctic char (Salvelinus alpinus L.), the top predator in High Arctic lakes, often is used as a bioindicator of Hg contamination in Arctic aquatic ecosystems. The present study investigated effects of trophic position, size, and age of Arctic char in Lake Hazen, the largest lake in the Canadian High Arctic (81°50'N, 70°25'W), on Hg bioaccumulation. In addition, several essential (Se, K) and nonessential elements (Tl, Cs) in char muscle tissue were examined to compare their behavior to that of Hg. Trophic position of Arctic char was identified by stable isotope (d15N) signature. Temporal trends of Hg from seven sampling campaigns over a 16-year period (1990-2006) were investigated for the overall data and for one trophic class. Concentrations of Hg were not correlated with age but were positively related to fork length and trophic position. Large char with greater d15N signatures (>12 per mil) had larger Hg concentrations (0.09-1.63 µg/g wet wt) than small char with smaller d15N signatures (<12 per mil, 0.03-0.32 µg/g wet wt), indicating that Hg concentrations increased with trophic position. Nonessential Cs and Tl showed relationships to age, length, and trophic position similar to those of Hg, indicating their potential to bioaccumulate and biomagnify. Essential Se and K did not show these relationships. Concentrations of Hg were adjusted using d15N, leading to less within-year variability and a more consistent temporal trend. The d15N-adjusted trend showed no decline of Hg in Arctic char from Lake Hazen (1990-2006) in the overall data set and in the small morphotype. Trends for the same period before the adjustment were not significant for the overall data set, but a slight decrease was apparent in the small morphotype. The results confirm the need to consider trophic position and fish size when monitoring temporal trends of Hg, particularly for species with different morphotypes

Dietary accumulation and biochemical responses of juvenile rainbow trout (Oncorhynchus mykiss) to 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126)

Juvenile rainbow trout (Oncorhynchus mykiss) (initial weights 2-5 g) were exposed to three dietary concentrations (0, 12.4 and 126 ng g-1, wet weight) of a 14C-labelled 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126) for 30 days followed by 160 days of clean food. We assessed bioaccumulation, histology (liver and thyroid) and biochemical responses (liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and tocopherol) and muscle thyroid hormone levels) along with growth and survival. The half-life of PCB 126 in the rainbow trout ranged from 82 to 180 days while biomagnification factors (BMF) ranged from 2.5 to 4.1 providing further evidence that PCB 126 is among the most bioaccumulative PCB congeners. Toluene extractable 14C declined with time in the trout suggesting the possibility of some biotransformation and/or covalent bonding with biological macromolecules. The threshold for liver EROD induction by PCB 126 was approximately 0.1 ng g-1 (wet weight). EROD activities in the low- and high treatments were 9 and 44 times greater than control, respectively, and remained elevated throughout the experiment. EROD activity was correlated with whole body concentrations of PCB 126 although there was evidence of EROD activity suppression in the highly exposed fish. Liver didehydroretinoids and tocopherol concentrations were depressed by the high PCB 126 dose after 30 days exposure. Initially, muscle concentrations of thyroxine (T4) and triiodo-L-thyronine (T3) declined as the fish grew during the experiment, and exposure to PCB 126 accelerated the growth related decline. More information is needed to assess the functional significance of the reduced muscular stores of thyroid hormones. Despite the changes in liver EROD, liver vitamins and muscle thyroid hormones, liver and thyroid histology in trout examined after 30 days exposure and growth parameters were unaffected by PCB 126. This indicates that the functional competences of the physiological factors associated with growth were maintained under the experimental conditions. Copyright © 2002