Mercury, methylmercury and long-chain polyunsaturated fatty acids in selected fish species and comparison of approaches to risk-benefit analysis.

Fish (n = 281) of six species, caught in New Zealand waters, were analysed for total mercury (t-Hg), methylmercury (MeHg) and the long-chain polyunsaturated fatty acids, eicosapentanoic acid (EPA) and docosahexaenoic acid (DHA). Mean t-Hg and MeHg concentrations for the six species were in the range 0.06-0.53 mg/kg and 0.06-0.46 mg/kg, respectively. The mean proportion of t-Hg present as MeHg for the six species considered was in the range 83-93%. Positive associations were observed between t-Hg and MeHg content of fish and measures of fish size (length, weight), although the strength of the associations was species dependent. The mean EPA + DHA content of the six fish species varied in the range 2.0-20.5 mg/g. Two approaches were trialled to compare the risks, due to MeHg, and the benefits, due to EPA and DHA, from consumption of the six fish species. Both approaches identify that for these six fish species the benefits of normal patterns of fish consumption on offspring IQ largely outweigh the risks from MeHg.