Methylmercury Bioaccumulation in Deepest Ocean Fauna: Implications for Ocean Mercury Biotransport through Food Webs

Abstract

For many contaminants, the hadal zone (from 6000 to 11000 m depth) is potentially the least explored environment. In this work, we reveal the bioaccumulation of methylmercury (MeHg), a potent neurotoxin that can be substantially bioaccumulated within marine food webs, in amphipod fauna from the Mariana, Massau, and New Britain trenches. We identified high levels of mercury (Hg) and MeHg ranging in wet weight from 47 to 435 ng/g and from 3.8 to 61 ng/g, respectively, in amphipods from these trenches. Placing the MeHg level into a broader comparative context with previous values, we found that the MeHg level in this study is significantly higher than that from many other aquatic environments around the world. High MeHg levels are largely dependent on food availability, which is probably related to surface ocean production, terrestrial input, and MeHg bioaccumulation in marine food webs. Comparisons of the distribution and variation trends of MeHg levels based on fatty acid, radiocarbon (Δ14C), and stable carbon isotope (δ13C) analyses supported our hypothesis. Our study suggests that anthropogenic Hg inputs into surface oceans could be rapidly transported to the world’s deepest oceans through marine food webs and highlights that hadal trenches are not biological deserts.