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MARINE RISK ASSESSMENT
marine waters, relative to freshwaters (cf. Appendix XIV). There are also circumstances,
however, where the special conditions existing in a particular environment such as that existing
in the Baltic Sea, give rise to a reduced or limited species diversity and/or specific stresses such
as low or variable salinity. In such circumstances of low species diversity, adverse impacts in
individual species can have devastating impacts on the specialised ecosystem. Thus, while high
species diversity may lead to a wide sensitivity distribution, but also considerable functional
overlap, low species diversity may result in a lower sensitivity distribution but increase the
ecosystem function dependency on individual keystone species.
In both cases, the effects assessment must use, where possible, data relevant to the
environmental compartment that is considered. However, compared to the situation for
freshwaters, there are relatively few data on the effects of chemical substances on estuarine and
marine organisms. Therefore, in practice there will be situations where saltwater toxicity data are
needed for hazard/risk assessments, but may not be available. In these situations it may be
necessary to use freshwater data in lieu of data for estuarine/marine species (Schobben et al., 1994;
Karman et al., 1998). In using data on freshwater species to characterise the risk in the marine
waters, a clear understanding of the comparability of effects data generated on both types of species
is necessary. Furthermore, there is some evidence, e.g. for some metals, that species living in
brackish water are more susceptible because of the salinity (osmotic) stress they have to endure in
contrast to those of the same species living in truly marine conditions. Under these circumstances
the applicability of the toxicity data needs to be considered on a case-by-case basis.
4.3.1.2 Evaluation of data
It has been recognised for many years that there is a wider diversity of taxonomic groups
(particularly invertebrates) in saltwaters compared to freshwaters and that many groups are only
found in marine waters (see Russell and Yonge, 1928; Tait, 1978). Moss (1988) stated that
56 phyla were present in marine waters compared to 41 in freshwaters. No phyla are confined to
freshwaters only while 15 phyla are found only in marine waters. These differences are partly
due to the fact that multicellular animals originated in the seas and they have been well
populated since the earliest fossil records.
Nevertheless, an important part of any evaluation of data must involve an assessment of the
usefulness of the main body of freshwater ecotoxicity data in predicting effects in the marine
environment. Where such data can be used, the focus of further investigation can concentrate on
additional factors which specifically characterise the marine conditions. Studies conducted on
the comparability of sensitivity of freshwater and marine species have been hampered by the low
level of substances for which a comparable dataset has been available. Nevertheless where such
data are available, it has tended to show that there is no systematic bias in sensitivity where
comparable tests and endpoints are paired. A recent report which collated much of the available
data confirmed these findings (ECETOC, 2000). Based on the currently available data, it can be
concluded that:
• overall, the data reviewed and current marine risk assessment practice suggest a reasonable
correlation between the ecotoxicological responses of freshwater and saltwater biota - at
least for the usual aquatic taxa (i.e., fish, crustacea, algae). No marked difference in
sensitivity between freshwater and saltwater biota appears that systematically applies across
all three trophic levels considered;
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