Mercury and other heavy metals in trout of central North Island, New Zealand

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Abstract
Various organs of 111 specimens of rainbow trout Salmo gairdneri and 4 of brown trout Salmo trutta from various lakes and rivers in the central North Island were analysed for mercury, cadmium, copper, iron, manganese, and zinc. Except for mercury, none of the edible portions of any of the specimens had heavy metal concentrations likely to cause problems in public health. Mercury in the flesh of fish caught from Lakes Rotorua, Rotoiti, Rotomahana, and Maraetai averaged 1.3 μg.g‐1 and was well above the normally accepted maximum of 0.5 μg‐g‐1. The mercury levels in fish from Lake Maraetai (mean 1.40 μg.g‐ 1) were assumed to have been derived in part from a pulp and paper mill at Kinleith. High levels in other localities were presumed to be derived from adjacent geothermal areas. Acceptable daily consumptions of fish from various areas are recommended. In some areas (e.g., Lake Rotomahana), relatively small amounts (14 g of flesh) contain the acceptable daily intake of mercury, but because of lower mercury concentrations in smaller fish, the daily consumption can be increased if large fish are avoided.