A\nMeta-Analysis\nof Mercury Biomagnification in Freshwater\nPredatory Invertebrates: Community Diversity and Dietary Exposure\nDrive Variability

Accurate estimates\nof methylmercury (MeHg) exposure are\nvaluable\nto actionably assess risk and protect wildlife and human health. MeHg\ntrophic transfer is a critical driver of risk: MeHg is generally biomagnified\nby a factor of 8.3 ± 7.5 from one trophic level to the next,\naveraged across freshwater communities (mean ± standard deviation).\nThis variability can produce disparate risks even where basal MeHg\nconcentrations are similar. Taxonomy may be one driver of this variability:\nphysiologically diverse groups, like vertebrates and invertebrates,\nmay assimilate MeHg differently. To determine whether taxonomy affects\ntrophic transfer efficiency, we conducted a meta-analysis characterizing\npredatory invertebrate MeHg biomagnification. Our analyses estimated\nthat freshwater predatory invertebrates biomagnify MeHg by factors\nof 2.1 ± 0.2 to 4.3 ± 0.3, with a 98.9 ± 0.4% posterior\nprobability that factors are below 5 (mean ± standard error).\nWhen vertebrates or primary producers were included, a site’s\ntrophic magnification factor was 18.6 ± 6.2 to 54.1 ± 7.7%\nhigher than estimates for invertebrates alone. Biomagnification was\ninversely correlated to prey MeHg concentration and varied among systematic\nand functional groups. These data suggest that predatory invertebrates\nbiomagnify MeHg less efficiently than vertebrates and that a community’s\ndiversity and structure determine its biomagnification efficiency.\nIncorporating organismal variation in trophic transfer estimates may\nimprove the assessment, communication, and management of MeHg risk.