Ecotoxicology of mercury in burbot (Lota lota) from interior Alaska and insights towards human health

Abstract

Fish consumption has many health benefits, but exposure to contaminants, such as mercury (Hg), in fish tissue can be detrimental to human health. The Tanana River drainage, Alaska, USA supports the largest recreational harvest of burbot (Lota lota) in the state, yet information to evaluate the potential risks of consumption by humans is lacking. To narrow this knowledge gap, we sought to (i) quantify the concentrations of total Hg ([THg]) in burbot muscle and liver tissue and the ratio between the two tissues, (ii) assess the effect of age, length, and sex on [THg] in muscle and liver tissue, (iii) evaluate if [THg] in muscle tissue varied based on trophic information, and (iv) compare observed [THg] to consumption guidelines and statewide baseline data. The mean [THg] was 268.2 ng/g ww for muscle tissue and 62.3 ng/g ww for liver tissue. Both muscle [THg] and liver [THg] values were positively associated with fish length. Trophic information (δ¹⁵N and δ¹³C) was not significantly related to measured [THg] in burbot muscle, which is inconsistent with typical patterns of biomagnification observed in other fishes. All burbot sampled were within the established categories for consumption recommendations determined by the State of Alaska for women of childbearing age and children. Our results provide the necessary first step towards informed risk assessment of burbot consumption in the Tanana drainage and offer parallels to fisheries and consumers throughout the subarctic and Arctic region.

Keywords: Contaminants; Fish consumption; Food web ecology; Recreational fishing; Stable isotopes; Subsistence harvest.

Figure 1.

Map of the region of the Tanana River drainage, Alaska, USA sampled for burbot. The watershed boundary of the Tanana River drainage is bolded in black and the location of the focal map is identified by the purple polygon in the inset map of Alaska. The green star is the location of Fairbanks, Alaska (64.83, −147.84). Yellow dots represent sample locations from the seven water bodies monitored (n = number of burbot collected from each water body): Chena River (n = 18); Tanana River (3 sampling locations, n = 18); Pile Driver Slough (n = 3); Nenana River (n = 2); Healy Lake (n = 4); Middle Fork Chena River (n = 4); McManus Creek (tributary to the Chatanika River, n = 1).

Figure 3.

Linear regression of total mercury concentration ([THg]) and length in burbot muscle tissue (R² = 0.40, p<0.001) and burbot liver tissue (R² = 0.30, p<0.001) collected between 2018 and 2019 in the Tanana River drainage, Alaska. Bolded green line represents the mean predicted [THg] in burbot liver tissue and the green ribbon represents the 95% confidence interval; green circles represent the observational [THg] in sampled burbot liver tissue (n = 46). Bolded orange line represents the mean predicted [THg] in burbot muscle tissue and the orange ribbon represents the 95% confidence interval; orange triangles represent the observational [THg] in sampled burbot muscle tissue (n = 50). Dashed black line represents the State of Alaska Department of Health and Social Services (SOA DHSS) unlimited consumption advisory threshold of 200 ng/g ww for women of childbearing age and children. Dotted black line represents the upper limit of the SOA DHSS four meals per month consumption category (680 – 1360 ng/g ww).

Figure 4.

Mean bulk δ¹³C (‰) and δ¹⁵N (‰) stable isotope values in burbot muscle from sample locations in the Tanana River drainage, AK. Error bars represent ±SD.