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APPENDIX VIII
Monitoring data
Metals are a group of compounds for which relatively many reliable monitoring data in all
environmental compartments are present. Given the fact that the group of metals is limited to a
small number of compounds, for which usually sufficient monitoring data are available, risk
assessment may well be based on monitoring data. In general monitoring data are preferred over
model calculations. When interpreting the data, natural background concentrations, ambient
background concentrations and availability for uptake by biota need to be taken into account.
One should be aware that for the aquatic environment metal concentrations may sometimes be
reported as dissolved concentrations and sometimes as total concentrations. Dissolved
concentrations can be derived from total concentrations by means of the concentrations of
dissolved organic matter and suspended particulate matter and partition coefficients between
water and either organic or particulate matter. Since, as indicated before, risk assessment is to be
performed on the basis of availability, dissolved concentrations should preferably be used since
these indicate the bioavailable metal fraction in the aquatic environment.
For soils and sediments sufficient information is only rarely available from monitoring data to
directly determine the bioavailable metal fraction. By applying the appropriate Kp values,
estimates of the available metal concentrations can be obtained. PECs from calculations and
PECs from monitoring data can be compared. In cases where calculated PECs are below PECs
based on measured concentrations, natural background and ambient background concentrations
should be taken into consideration.
Effects assessment
Availability of data
Toxicity data are available for most metals in sufficient quantity, since there are few compounds,
and various toxicity data exist at least for the soluble metal salts. Most data are available for the
toxic effects of metals on aquatic organisms, to a lesser extent data are present for terrestrial and
sediment-dwelling organisms. Usually most data are based on total concentrations of the metals
under investigation. For essential metals deficiency data must be taken into account.
The data are available both on short and long-term tests, and are present for species from various
trophic levels. These data can be used for the effect assessment in all compartments following
the procedures for assessing the adequacy of data as presented in the main text (see Section 3.2).
However, some metal-specific criteria must be taken into account:
physico-chemical test conditions that define the metal speciation and bioavailability should be
relevant for field conditions: water hardness, pH, alkalinity, presence of complexing agents
(humic acids and EDTA);
content of metal already present in the test medium, especially for soils taken from the field and
natural waters. As metals are natural constituents of the biosphere these background
concentrations can influence the test results. However, it should be noted that the bioavailability
of the background concentration for soils is probably less than that of the “added” metal;
for essential metals organisms of a given habitat are conditioned to the natural concentration
range for essential elements. Within this range they can regulate their metal uptake in such a way
that their internal concentration is kept relatively stable (homeostasis). This implies that
organisms tested should originate and be cultivated within this optimal concentration range.
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