What happens when an excess of metals enters freshwater ecosystems?
When the pH in water falls, metal solubility increases and the metal particles become more mobile. That is why metals are more toxic in soft waters. Metals can become ‘locked up’ in bottom sediments, where they remain for many years. Streams coming from draining mining areas are often very acidic and contain high concentrations of dissolved metals with little aquatic life. Both localized and dispersed metal pollution cause environmental damage because metals are non-biodegradable. Unlike some organic pesticides, metals cannot be broken down into less harmful components in the environment. Campbell and Stokes (1985) described two contrasting responses of an organism to a metal toxicity with declining pH: – If there is little change in speciation and the metal binding is weak at the biological surface, a decrease in pH will decrease owning to competition for binding sites from hydrogen ions. – Where there is a marked effect on speciation and strong binding of the metal at the biological
