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Appendix VIII Environmental risk assessment for metals and metal
compounds
Introduction
APPENDIX VIII
This document gives a general outline on how to perform risk assessments for metals using the
methods that are available for risk assessment of new and existing organic chemicals as a starting
point. There are a number of fundamental differences between metals and organic chemicals that
must be taken into account when assessing the risks to man and the environment, e.g.:
• unlike most organic chemicals, metals, and a limited number of organometallo compounds
like methylmercury and methyltin, are a class of chemicals of natural origin. Consequently
natural background concentrations and the exposure due to these background concentrations
should be taken into account during risk assessment;
• the availability of metals for uptake by organisms under field conditions is limited, will vary
from site to site and is highly dependent on the speciation of the metal. Hence, it is of utmost
importance that both PEC and PNEC are based on similar levels of availability in both
exposure and effect assessment, taking the speciation into account;
• the same toxic form can originate from a variety of different substances, e.g. Zn 2+ from
ZnSO4, ZnCl2 etc. Therefore it is in general necessary to take into account all metal species
that are emitted to the environment which in the end lead to concentrations of the toxic
form.
Substantial levels of information are available regarding the fate and toxicity of metal ions
and this information will be examined to improve the assessment process. However, it is
recognised that many of the specific fate and toxicity extrapolations are either not appropriate
or need modification. The interaction of metal ions with the media in both the aquatic and
soil compartments may result in a high level of uncertainty regarding the true level of
bioavailablity of the toxic species necessary for a practical assessment.
Organo-metallic compounds are not explicitly covered by this procedure unless they act, through
their degradation products, as significant sources of the toxic metal ion. It is considered that these
organo-metallic compounds can generally be assessed as individual substances in accordance with
the procedures laid down in the main text (Chapter 3). When the emissions of these substances are
major contributors to the toxic metal ion concentration in either a local or regional environment,
they will be further assessed according to the procedures laid down in this document.
When describing the topics that need to be taken into consideration for the risk assessment of
metals, there is often a misunderstanding with regard to definitions of some of the key terms. In
this appendix the following definitions will be used for these key terms:
General
• total concentration of a metal: for terrestrial systems, the concentration of a metal that is
determined after complete destruction of the mineral matrix. For aqueous systems: the total
amount of metal present, including the fraction sorbed to particles and to dissolved organic
matter and the fraction in the mineral matrix;
• available fraction: the fraction of the metal that is extractable from the substrate with
chemical (e.g.: neutral salt, water extraction) or physical means (shaking, pore water
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