Lakes and Watercourses

of present concentrations in Sweden. The principles governing class
delineation for metals in sediment have also been used here.
TABLE 21.
CURRENT CONDITIONS: mercury in fish (1-kilo pike, Esox lucius,
muscle) (mg/kg ws)
Class Description Hg
1 Very low concentrations, naturally occurring ≤ 0.20
2 Low concentrations, usually elevated in comparison 0.20 – 0.50
with background 1)
3 Moderately high concentrations, elevated 0.50 – 0.75
in comparison with background
4 High concentrations 0.75 – 1.0
5 Very high concentrations > 1.0
1) Concentrations in this range may be natural in some oligotrophic forest
lakes
Concentrations of mercury in fish are generally greatly elevated these
days. Mean concentrations in one-kilo pike from lakes in various regions
of southern Sweden vary between 0.5 and 1.0 mg Hg/kg. Consequently,
the Swedish National Food Administration recommends that pregnant
women and those planning to become pregnant should not eat certain
species of fish, eg, perch (perca fluviatilis), pike (Esox lucius), burbot (Lota
lota), zander (pike-perch) (Stizostedion lucioperca) and eel (Anguilla
anguilla). Other people are recommended not to eat lake fish more than
once a week on average. Consumption should be further reduced if fish
contain more than 1 mg Hg/kg (National Food Administration 1992).
Variations in mercury levels between lakes in different regions and health
considerations have formed the basis for the above class boundaries.
Assessment of deviation from reference values
A somewhat modified classification system has been chosen here as
compared with that proposed in the background report on metals (in
Swedish). This is because the system used here is more consistent with
corresponding model criteria for groundwater, coastal water and
contaminated sites.
Classification is based on deviation from original, natural concentrations.
Class delineation is not related to biological effects. The following
applies to the respective classes:
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