National Institute for Minamata Disease, 4058-18 Hama, Minamata, Kumamoto, 867-0008, Japan.
National Institute for Minamata Disease, 4058-18 Hama, Minamata, Kumamoto, 867-0008, Japan; Hinokuni Benthos Laboratory, 2133-4 Sumiyoshi Cho, Uto, Kumamoto, 869-0401, Japan.
Environ Pollut. 2020 Jul;262:113982. doi: 10.1016/j.envpol.2020.113982. Epub 2020 Jan 19.
Marine animals often accumulate various harmful substances through the foods they ingest. The bioaccumulation levels of these harmful substances are affected by the degrees of pollution in the food and of biomagnification; however, which of these sources is more important is not well-investigated for mercury (Hg) bioaccumulation. Here we addressed this issue in fishes that inhabit the waters around Minamata Bay, located off the west coast of Kyushu Island in Kumamoto Prefecture, Japan. The total Hg concentration (hereafter [THg]) and carbon and nitrogen stable isotope ratios (δC and δN) were analyzed in the muscle tissue of 10 fish species, of which more than five individuals were caught by gillnet. Except one species, each was separated into two trophic groups with respective lower and higher δC values ranging from -17‰ to -16‰ and -15‰ to -14‰, which suggested that the fishes depended more on either phytoplankton- and microphytobenthos-derived foods (i.e., pelagic and benthic trophic pathways), respectively. Linear mixed effects models showed that the Hg levels were significantly associated with both δN and the differences in the trophic groups. [THg] increased with δN (i.e., indicative of higher trophic levels), but the slopes did not differ between the two trophic groups. [THg] was significantly higher in the group with higher δC values than in those with lower δC values. The effect size from marginal R squared (R) values showed that the variation in [THg] was strongly ascribed to the trophic group difference rather than δN. These results suggest that the substantial Hg bioaccumulation in the fishes of Minamata Bay is mainly an effect of ingesting the microphytobenthos-derived foods that contain Hg, and that the subsequent biomagnification is secondary.
海洋动物通过摄食积累各种有害物质。这些有害物质的生物积累水平受食物污染程度和生物放大程度的影响，但对于汞（Hg）的生物积累来说，这两个来源中哪一个更重要还没有得到很好的研究。在这里，我们研究了栖息在日本熊本县九州岛西海岸外的水俣湾周围水域的鱼类中的这一问题。分析了 10 种鱼类肌肉组织中的总汞浓度（以下简称[THg]）和碳氮稳定同位素比值（δC 和 δN），其中 5 种以上的鱼类是用刺网捕获的。除了一个物种外，每个物种都分为两个营养组，其 δC 值范围分别为-17‰至-16‰和-15‰至-14‰，这表明鱼类分别更多地依赖于浮游植物和微型底栖生物衍生的食物（即，浮游和底栖营养途径）。线性混合效应模型表明，Hg 水平与δN 和营养组差异均显著相关。[THg]随δN 增加（即指示更高的营养水平），但两个营养组的斜率没有差异。与δC 值较低的组相比，δC 值较高的组中[THg]显著更高。边缘 R 平方（R）值的效应大小表明，[THg]的变化主要归因于营养组的差异，而不是δN。这些结果表明，水俣湾鱼类中大量的 Hg 生物积累主要是由于摄入含有 Hg 的微型底栖生物衍生的食物所致，而随后的生物放大是次要的。
