9 - Field studies on metal accumulation and effects in fish

Abstract

Metals have been present in the environment since the origin of our planet. Life has evolved in their presence, incorporating many of them in essential molecules and metabolic processes and developing protective mechanisms against both non-essential metals and excess essential metals. Anthropogenic metal contamination of terrestrial and aquatic systems dates as far back as the first traces of human civilization. However, it was not until the intense industrialization of the eighteenth century that severe environmental impacts of metal mining and smelting activities started to pose a serious threat to wildlife. Field research leading to environmental protection legislation first appeared for mercury and selenium, owing to their propensity to biomagnify and cause toxicity to the higher levels of food webs such as birds and humans. However, we have only recently started to reveal the mechanisms of metal accumulation and toxicity on fish and other wildlife for low-level, chronic exposure scenarios. In aquatic environments, fish accumulate metals via both aqueous and dietary routes. The effects of chronic metal exposure, typical of most metal-contaminated environments, are more subtle than, and greatly differ from, the effects of acute exposures. There is evidence of direct toxicity leading to bioenergetic consequences such as decreased growth rate and condition, as well as selective pressures reducing population genetic diversity. Direct metal toxicity at other trophic levels also induces indirect effects, both negative and positive, on fish populations. Because metal accumulation and toxicity in wild fish are affected by several biotic and abiotic factors, field modeling remains a challenge. Nevertheless, with the advancement of knowledge, reviewed in this chapter, on accumulation and effects of metals in wild fish, our capacity to protect fish and their habitat from anthropogenic metal contamination is fast improving.