Lakes and Watercourses

very high degree of reliability and at a much lower cost than previously.
Analyses of metals in aquatic moss (Fontinalis antipyretica and F. dalecarlia)
can be used as an indirect measure of concentrations in water. Moss
growing locally as well as planted specimens can be used. Concentrations
in aquatic moss reflect metal concentrations in water over a lengthy
period (weeks) and are an effective means of surveying sources and the
size of contaminated areas and can also be used to gain an idea of the
level of pollution in the aquatic area. However, absorption of metals by
aquatic moss is not dependent merely on the concentration in water;
acidity, for example is another factor. This limits the utility of the
method, particularly in acidified waters.
Concentrations of metals in sediment provide a good picture of the
influx of metals into an aquatic area. Sampling procedures and analyses
are fairly simple and reliable and analyses of sediment are therefore
highly suitable for surveying the impact of metals, for example. By
analysing deeper sediment strata it is possible to extrapolate the time
trend for load backwards in time and to determine original metal concentrations
in the aquatic area.
Concentrations of mercury in fish mainly serve to provide a basis for
assessing the risks to humans of eating fish. Metal concentrations in fish
are also a useful means of evaluating the risk of damage to mammals and
birds whose diet mainly consists of fish.
Assessment of current conditions
TABLE 18.
CURRENT CONDITIONS: metals in water (µg/l)
Class Description Cu 1) Zn Cd Pb Cr Ni As
1 Very low conc. ≤ 0.5 ≤ 5 ≤ 0.01 ≤ 0.2 ≤ 0.3 ≤ 0.7 ≤ 0.4
2 Low conc. 0.5 – 3 5 – 20 0.01 – 0.1 0.2 – 1 0.3 – 5 0.7 – 15 0.4 – 5
3 Mod. high conc. 3 – 9 20 – 60 0.1 – 0.3 1 – 3 5 – 15 15 – 45 5 – 15
4 High conc. 9 – 45 60 – 300 0.3 – 1.5 3 – 15 15 – 75 45 – 225 15 – 75
5 Very high conc. >45 >300 >1.5 >15 >75 >225 >75
1) These values apply particularly to lakes and streams. Background concentrations are often higher in
larger watercourses; concentrations of up to 3 µg/l are not uncommon. The boundary between class
1 and 2 has been set on the basis of the 75th percentile for northern Swedish streams and lakes.
The following may be said of the risk of biological effects caused by
metals in concentrations corresponding to the various classes:
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