Metals in Scandinavian Surface Waters: Effects of Acidification, Liming, and Potential Reacidification

Abstract

This article is a state-of-the-art review about such metals as Al, Fe, Mn, Cu, Zn, Cd, Pb, Cr, Ni, Hg, and As in surface waters. It focuses on natural and anthropogenic sources, chemical properties and levels, and toxicity mechanisms of these metals to aquatic organisms, primarily fish and invertebrates. Organisms living in almost anoxic, sulfide-rich evironments are not incorporated into this study. This information is then linked to a Nordic Lake Survey implemented in 1995 on major chemistry and metals in Scandinavian surface waters to scale the problems of metals in Swedish and Norwegian surface waters. Because many acidified Swedish and Norwegian lakes also are limed, we also assess the risk of remobilization of metals because these waters reacidify due to reduced liming activity. The concentrations and chemical properties of metals in lakes relative to the biological effect levels suggest that the potential risks associated to both current and potential reacidified status of limed waters decreases in the order Al >> Cd > Pb in Swedish and Norwegian lakes. Also Hg, because of the organometallic forms such as methylmercury (MeHg), might be of concern, because it biomagnifies in the food chain and subsequently of great importance for top predators, including human beings. However, other factors than pH, such as changes in organic matter load from the surrounding soils due to natural climatic variations, are much more important for the Hg load and thereby the Hg concentrations in lakes than pH. The risks associated with other metals such as Cu, Fe, Mn, Ni, and Zn are very low and have to be considered only occasionally, because high concentrations are very rare in Norwegian and Swedish lakes. Less than 2% of the lakes have concentrations ≥ the lowest biological risk levels quoted in the two countries. Because primarily As is present as anions in surface waters, this element differs significantly from the cationic metals. Only a few lakes have high As concentration in relation to critical levels in Sweden, and high As concentrations are mainly related to agricultural areas and consequently high pH waters.