Lakes and Watercourses

Metals
Introduction
Metals occur naturally in fresh water in low concentrations. Concentrations
in sediment and organisms are higher owing to a natural process of
accumulation. Concentrations vary depending on the geology and soil
types in the catchment area of the lake or watercourse. The water’s
acidity and content of organic matter etc also affect metal concentrations
so that a significant variation occurs even under natural conditions. In
small quantities, many metals perform vital biological functions.
Man has increased the quantities of metals in the environment.
Emissions to air and dispersal over large areas have caused concentrations
of some metals to rise generally in Swedish lakes and watercourses.
Moreover, emissions directly to water and other types of impact have, in
many instances, multiplied metal concentrations in the vicinity of
emission sources. Elevated metal concentrations are serious, since many
metals cause biological damage even at relatively low concentrations. A
deficiency of some metals may also cause adverse effects. Many metals
are essential to plants and animals. However, there is unlikely to be a
deficiency of metals in Swedish waters.
Damage caused by metals present in moderately elevated concentrations
occurs primarily in organisms towards the bottom of the food
chain, eg, phytoplankton and zooplankton. Fish reproduction is also
susceptible to effects caused by metals, as are fish fry in the early stages of
development. The lowest effect concentrations occur in connection with
long-term exposure (weeks or months). More acute effects occur at concentrations
some 3 – 10 times higher than those causing chronic effects.
Here, an assessment is made using the concentration of metals in
water, sediment, aquatic moss and/or fish.
Concentration of metals in water provide the best opportunity to assess
whether there is a risk of biological damage. Analyses of water also allow
calculation of transport of metals in watercourses and thus provide data
on which to assess the contributions made by different sources to the
pollution load on an aquatic area. Methods of taking samples and
analysing metals in water have been substantially improved over the last
decade. Concentrations of metals in water can now be determined with a
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