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MARINE RISK ASSESSMENT<br />

assumption. In practice this in<strong>for</strong>mation is often available <strong>for</strong> production <strong>and</strong>/or large processing<br />

sites. It may also be possible to assume the presence of connection to an STP <strong>for</strong> certain industry<br />

<strong>and</strong>/or use categories if appropriate justification about the general connection frequency to the<br />

STP <strong>for</strong> that specific industry is provided. For releases to municipal wastewater of substances<br />

that are used <strong>for</strong> private or public use (substances belonging to IC5 <strong>and</strong> IC6, Appendix I),<br />

however, it can be assumed that the degree of treatment in a biological STP corresponds to the<br />

inl<strong>and</strong> scenario (see Section 2.3.7.1).<br />

For discharges to a coastal zone, local dilution will be greater than in a freshwater river. First,<br />

initial dilution may occur if the density between the effluent <strong>and</strong> the saline receiving medium<br />

differs (Lewis, 1997). The initial dilution factor is usually around 10. Further dilution due to<br />

currents can also be assumed, particularly if the point of release is subject to tidal influences. In<br />

the Baltic or the Mediterranean sea, where there are almost no tidal influences compared to the<br />

Atlantic Ocean or the North Sea, only initial dilution may occur on calm days, but normally,<br />

further dilution due to currents is probable. Dilution factors of more than 500 have been<br />

determined from model simulations (based on current measurements) in the North Sea, 200 m<br />

away from the discharge point (e.g. Pedersen et al., 1994).<br />

A dilution factor <strong>for</strong> discharges to a coastal zone of 100 may then tentatively be assumed, which<br />

seems to be representative of a realistic worst case. The same estimation method as <strong>for</strong> inl<strong>and</strong><br />

exposure assessment can then be used to obtain the local concentration in seawater (Clocalseawater,<br />

see Section 2.3.8.3, equations 45-49).<br />

In certain circumstances, it may be possible to identify specific emission points which would<br />

allow the use of more precise in<strong>for</strong>mation regarding the available distribution <strong>and</strong> fate processes.<br />

Such “site-specific” assessments should only be used when it is known that all the emissions<br />

emanating from the particular point in the life-cycle, e.g. manufacture, arise from a limited<br />

number of specific <strong>and</strong> identifiable points. In these circumstances each specific point of release<br />

will need to be assessed individually. If it is not possible to make this judgement, then the default<br />

assumptions should be applied. In “site-specific” assessments, due account can be taken of the<br />

true dilution available to the given emission as well as the impact of degradation, volatilisation,<br />

etc. in the derivation of the PEC. Normally, only dilution <strong>and</strong> adsorption to suspended sediment<br />

need be considered but site-specific conditions may indicate that valid local distribution models<br />

can be used.<br />

For estuaries, which are influenced by currents <strong>and</strong> tidal movements, it is assumed as a first<br />

approach that they are covered by either the inl<strong>and</strong> or the marine risk assessment. Thus, no<br />

specific assessment is proposed.<br />

Then, the local concentration in seawater can be obtained with:<br />

142<br />

Clocal<br />

seawater<br />

=<br />

( 1+<br />

Kp<br />

susp<br />

Clocaleff<br />

-6<br />

• SUSPwater<br />

•10<br />

)<br />

•<br />

DILUTION<br />

(83)

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