Bioaccumulation and toxicology of nickel: implications for wild mammals and birds

The tissues of wild mammals and birds from uncontaminated environments generally contain from ~0.1 to 5 μg nickel∙g dry weight−1, whereas in Ni-polluted environments, tissues accumulate from -0.5 to 10 (mammals) and -0.5 to 80 (birds) μg nickel∙g dry weight−1. The highest concentrations in these ranges are usually associated with tissues directly exposed to the external environment (fur, feathers, skin). Bone frequently contains higher Ni concentrations than other internal tissues. Ni concentrations in the most commonly analysed internal organs (liver, kidneys) range from nondetectable to about 3 μg∙g dry weight−1, the kidneys often containing higher concentrations than the liver. There is some evidence that birds may tend to accumulate higher Ni burdens in polluted habitats than do mammals. For mammals, reduced growth and survival occur in response to chronic exposure to 500–2500 μg Ni∙g diet−1 (10–50 mg∙kg body weight−1∙d−1). Effects on reproduction and essential trace metal (especially iron) metabolism have been reported at levels as low as 5 μg∙g−1 in food or drinking water (0.2–0.4 mg∙kg body weight−1∙d−1), but these findings have not always been corroborated. Toxicological data on birds are more limited than those pertaining to mammals. Newly hatched chickens suffered reduced growth rates when fed ≥300 μg∙g diet−1, and chicks began to die when fed diets containing ≥500 μg∙g−1. In newly hatched mallard ducklings, chronic exposure to ≥800 μg∙g diet−1 resulted in ataxia, tremors, and significant mortality, whereas adult mallards fed 800 μg∙g−1 showed no evidence of systemic or reproductive toxicity. Tissue concentrations of Ni were not reliable indicators of potential toxicity in either mammals or birds, because significant effects, including mortality, frequently occurred in the absence of elevated tissue Ni concentrations. However, when there is evidence of elevated tissue Ni concentrations (>10 μg∙g−1 in the kidneys, and (or) >3 μg∙g−1 dry weight in the liver), Ni exposure sufficient to cause significant toxic effects should be suspected. Nickel has been reported in aquatic macrophytes and lower plants (but not in invertebrates or zooplankton) in the vicinity of Ni smelters in Canada in concentrations that approach or exceed dietary levels known to cause adverse effects in young animals. Sensitive species of wildlife ingesting this vegetation for considerable periods of time could experience Ni-related toxicity. In addition, wildlife food chains involving aquatic organisms (plants, invertebrates, fish) risk alterations in community structure in Ni-contaminated environments as Ni-sensitive taxa are eliminated or their abundance is reduced.Key words: nickel, toxicology, wildlife.