technical guidance documents - Institute for Health and Consumer ...
technical guidance documents - Institute for Health and Consumer ...
technical guidance documents - Institute for Health and Consumer ...
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APPENDIX VIII<br />
chemicals (see Section 2.3.4 of the main text). The same applies to the bioconcentration factors<br />
required: only experimentally determined values should be used (see Section 3.8 of the main text<br />
<strong>and</strong> Section 3.3 of this appendix). For soils, the Kp values to be used should, as far as possible,<br />
be derived <strong>for</strong> the soil type of interest. The soil usage should also be taken into account (<strong>for</strong><br />
instance cultivated versus non-cultivated soils) since this may be of importance <strong>for</strong> the most<br />
appropriate Kp values. Often volatilisation is to be ignored. In such cases, most of the metal<br />
present in the atmosphere is predominantly bound to aerosols which means that rates of dry <strong>and</strong><br />
wet deposition (in combination with the scavenging ratio) of atmospheric aerosols will suffice to<br />
quantify transport from the atmosphere. If biotrans<strong>for</strong>mation occurs this must be taken into<br />
account.<br />
More specific <strong>guidance</strong> on the use of regional fate models is given in Figure 1.<br />
In general, the mathematical descriptions of fate processes used in multimedia fate models are<br />
also applicable to local models.<br />
Background concentrations<br />
When assessing the exposure of man <strong>and</strong> ecosystems to metals previous releases into the<br />
environment need to be considered. In view of differences in bioavailability (see below) it is<br />
important to distinguish between ambient background concentrations <strong>and</strong> natural background<br />
concentrations. One should be aware that natural background concentrations within an<br />
environmental compartment may vary from site to site by several orders of magnitude. Also, due<br />
to natural dynamic processes like weathering, natural background concentrations may change<br />
over time. This means that it is impossible to attribute single values to natural background<br />
concentrations of specific metals within a certain compartment. It should be noted that under<br />
natural conditions in certain regions, clearly elevated natural background concentrations can be<br />
encountered. When assessing the natural background concentration within a certain area, these<br />
“outliers” should not be used or included in the calculation of the st<strong>and</strong>ard background<br />
concentrations as they would give a non-representative picture thereof.<br />
Several methods are available <strong>for</strong> determining background concentrations. Apart from the<br />
obvious method of measuring metal levels at selected sites considered to be undisturbed by<br />
human activities, additional methods include:<br />
Geochemical modelling: estimation methods on the basis of the contribution of weathering<br />
processes (erosion). This method is shown to be well applicable <strong>for</strong> assessing natural<br />
background concentration in aqueous systems (rivers).<br />
Assessment of metal concentrations in the deeper sediment layers, taking into account<br />
anthropogenic contributions <strong>and</strong> leaching to these layers.<br />
For surface water having ground water as its origin: assessment of the metal concentrations in<br />
the deeper ground water.<br />
For soils, ambient background concentrations can be calculated as described above (reference<br />
lines). Through this procedure the natural binding capacity of soils, making the metal more or<br />
less inert in the solid phase, is approximated. Application of this procedure to both laboratory<br />
toxicity data <strong>and</strong> to field soils is possible.<br />
For surface water extensive national monitoring programs exist <strong>for</strong> the follow-up of metals in the<br />
aquatic environment since most metals are considered in the EC Regulation 76/464 as list I<br />
(“black list”) or list II (“grey list”) substances. Extraction of representative natural background<br />
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