Mercury Accumulation, and the Mercury-PCB-Sex Interaction, in Lake Whitefish (Coregonus clupeaformis)

Charles Madenjian, Mark Ebener, David Krabbenhoft
2016 Environments  
We determined whole-fish Hg concentrations of 26 female and 34 male adult lake whitefish (Coregonus clupeaformis) from northern Lake Huron captured during November 2010. Subsampling from these 60 fish, Hg concentration was also determined in both somatic tissue and ovaries (n = 5), while methylmercury (MeHg) concentration was determined in whole fish (n = 18). Bioenergetics modeling was used to assess the growth dilution effect on the difference in Hg concentrations between the sexes. Mean
more » ... he sexes. Mean whole-fish Hg concentration in females (59.9 ng/g) was not significantly different from mean whole-fish Hg concentration in males (54.4 ng/g). MeHg accounted for 91% of the mercury found in the lake whitefish. Bioenergetics modeling results indicated that the growth dilution effect did not contribute to the difference in Hg concentrations between the sexes. We estimated that females increased in Hg concentration by 17.9%, on average, immediately after spawning due to release of eggs. Using polychlorinated biphenyl (PCB) data for the same 60 lake whitefish from a previous study, we detected a significant interaction between sex and contaminant type (Hg or PCBs), which was attributable to males being significantly higher in PCB concentration than females. Males may be eliminating Hg at a faster rate than females. Environments 2016, 3, 7 2 of 16 By way of atmospheric emissions and transport, mercury has become a globally dispersed pollutant [6] . Because mercury can biomagnify in food webs, top predators, including humans, tend to exhibit elevated mercury concentrations. Mercury has been ranked as one of the ten chemicals of major public health concern in the world [7] . Mercury contamination is more damaging to the brain of fetal humans than to the brain of adult humans [8] [9] [10] [11] . Mercury can interfere with normal brain development by inhibiting the division and migration of neuronal cells in the brain of a human fetus. In addition, recent research has shown a link between mercury exposure and subclinical autoimmunity among reproductive-age women [12] . Consumption of contaminated fish is the predominant source of mercury exposure to humans and fish-eating wildlife, and consequently mercury contamination in fish is of special concern [9,13]. To develop fish consumption advisories and to assess risk to humans and wildlife consuming contaminated fish, determinations of mercury concentrations in fish are of vital importance [9, [14] [15] [16] [17] [18] . In Lake Huron, the biogeochemical cycling of mercury is currently dominated by air-water exchange processes [19, 20] . Water column concentrations of total mercury (Hg) are relatively low, typically averaging less than 1 ng/L. Moreover, based on analysis of sediment core samples and determinations of Hg concentrations in the surficial sediments, Marvin et al. [21] concluded that the current degree of mercury contamination in Lake Huron sediments does not represent a significant degree of anthropogenic enrichment, because present-day Hg concentrations in the surficial sediments averaged only 0.04 µg/g. In fact, Lake Huron had the lowest sediment Hg concentrations of all five Laurentian Great Lakes. In contrast, Hg concentrations in the water of Clear Lake, a highly contaminated lake in California (USA), ranged from 2 to 8 ng/L, and sediment Hg concentrations in this lake ranged from 0.50 to 83 µg/g [22] . An interesting pattern appears to be emerging with regard to the difference between the ratio of whole-fish Hg concentration in males to whole-fish Hg concentration in females and the ratio of whole-fish polychlorinated biphenyl (PCB) concentration in males to whole-fish PCB concentration in females [23] . Specifically, the ratio of Hg concentrations has been shown to be substantially lower than the ratio of PCB concentrations for a given population of teleost fish. This difference between the ratios is surprising, because both Hg and PCBs are considered reliable tracers of food consumption by fish [24, 25] . Given that nearly all of the Hg and PCB body burdens accumulated by fish are from dietary intake, we would have expected that the relative difference in Hg concentrations between the sexes is identical to the relative difference in PCB concentrations between the sexes. In several fish populations, including lake whitefish, PCB concentration in males has been shown to be greater than PCB concentration in females by 15%-45% [26] . For lake whitefish from northern Lake Huron, PCB concentration in males exceeded that in females by 34%, and this difference was statistically significant. The higher PCB concentration in males was attributed to a higher rate of energy expenditure in males, stemming from higher activity and a higher resting metabolic rate (or standard metabolic rate, SMR) in males. Because males expend energy at a higher rate than females, males consume food at a higher rate than females, which, in turn, leads to males accumulating PCBs at a higher rate than females. In lake trout (Salvelinus namaycush) from Lake Ontario, males were 22% greater in PCB concentration but only 8% greater in Hg concentration than females [27] . Male burbot (Lota lota) from Lake Erie and Great Slave Lake were 29% greater in PCB concentration than female burbot, whereas female burbot from these two lakes were 22% greater in Hg concentration than male burbot [23] . This lower value for the ratio of Hg concentration in males to Hg concentration in females compared with the ratio of PCB concentration in males to PCB concentration in females has been attributed to males eliminating Hg from their bodies at a faster rate than females, whereas long-term elimination rates for PCBs are negligible for both sexes. According to this explanation, Hg is ingested at a faster rate by males than by females, but Hg is also eliminated at a faster rate by males than by females. In contrast, PCBs are ingested at a faster rate by males than by females, but PCB long-term elimination rates do not vary meaningfully between the sexes because these rates are negligible for both sexes. Faster Hg-elimination rates in adult male northern pike (Esox lucius) compared with adult female northern Environments 2016, 3, 7 3 of 16
doi:10.3390/environments3010007 fatcat:r34th2fspve37pvampprhmx3pq