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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Ecotoxicology
Spatial and temporal trends of mercury and methylmercury in aquatic insects associated with historical gold mines in Northern California,
U. S. A.
J.T. May1, R.L. Hothem2, and C.N. Alpers1. 1U.S. Geological Survey, WRD, Sacramento, CA, U. S. A, 2U.S. Geological Survey, BRD, Dixon, CA, U. S. A
To prioritize abandoned gold mine sites for potential remediation, 430 samples of predatory aquatic insects were collected from 90 sites during 1999–2002 and analyzed for total mercury (THg) and methylmercury (MeHg). Taxa and quantities collected included Hemiptera (Gerridae, n = 129; Belostomatidae, n = 16), Coleoptera (Dytiscidae, n = 57), Plecoptera (Perlidae, n = 63), Megaloptera (Corydalidae, n = 57), and Odonata (Aeshnidae, n = 43; Cordulegastridae, n = 43; Gomphidae, n = 15; Libellulidae, n = 7). Sampling locations represented several habitat types (lentic, lotic, and wetland) and mining features (mine tunnels, ground sluices, and pit lakes). Eighteen sites sampled for three or more years were analyzed for annual variability. Methylmercury was variable within families, but was consistent amongst families from a given site, which indicated localized contamination. Ranges of MeHg (μg/g, wet weight) were: Gerridae (0.03–0.55), Belostomatidae (0.02–0.47), Dytiscidae (0.01–0.50), Perlidae (0.03–0.52), Corydalidae (0.02–0.39), and Odonata (0.01–1.61). The mean value of MeHg/THg was 0.87 (SD = 0.19; n = 254). Within taxa, annual variation in MeHg was related to habitat stability; intermittent habitats were more variable and permanent features had relatively consistent MeHg concentrations. Methylmercury in predatory insects served as a consistent criterion for helping to prioritize remediation projects.
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