Ecological Traits of Fish for Mercury Biomonitoring: Insights from Compound-Specific Nitrogen and Stable Mercury Isotopes

Abstract

We coupled compound-specific isotopic analyses of nitrogen (N) in amino acids ((delta N-15(Glu), (delta N-15(Phe)) and mercury stable isotopes ((5202Hg, delta Hg-199) to quantify ecological traits governing the concentration, variability, and source of Hg in largemouth bass (LB) and pike gudgeon (PG) across four rivers, South Korea. PG displayed uniform Hg concentration (56-137 ng/g), trophic position (TPcorrected; 2.6-3.0, n = 9), and N isotopes in the source amino acid ((delta(15)NPhe; 7-13 parts per thousand), consistent with their specialist feeding on benthic insects. LB showed wide ranges in Hg concentration (45-693 ng/g), TPcorrected (2.8-3.8, n = 14), and (delta(15)NPhe (1.3-16 parts per thousand), reflecting their opportunistic feeding behavior. Hg sources assessed using Hg isotopes reveal low and uniform delta 199Hg in PG (0.20-0.49 parts per thousand), similar to delta 199Hg reported in sediments. LB displayed site-specific (5202Hg (-0.61 to -0.04 parts per thousand ) and delta 199Hg (0.53-1.09 parts per thousand). At the Yeongsan River, LB displayed elevated delta 199Hg and low (delta N-15(Phe), consistent with Hg and N sourced from the atmosphere. LB at the Geum River displayed low delta 199Hg and high (delta(15)NPhe, both similar to the isotope values of anthropogenic sources. Our results suggest that a specialist fish (PG) with consistent ecological traits and Hg concentration is an effective bioindicator species for Hg. When accounting for Hg sources, however, LB better captures site-specific Hg sources.