The exact number and type of studies to be conducted for an appropriate eco-toxicological risk assessment depend on the use pattern (e.g. production volume, areas of use) and the environmental fate of the surfactants as determined by an exposure and fate modelling approach. Depending on the physico-chemical properties, different environmental compartments have to be considered. One key parameter in this context is the hydrophobicity (i.e. as indicated by the octanol/water partition coefficient) of the chemical under consideration.
Eco-toxicity studies are intended to determine the intrinsic hazard properties of a chemical, and are therefore conducted under standardised (artificial) laboratory conditions. Guidance with respect to the appropriate test methods for the different compartments (fresh water, marine water, sediments and soil) can be found in the EU Technical Guidance Documents.
Eco-toxiclogical studies, in simple terms, can be differentiated as being acute or chronic. While acute studies are short term, covering only a fraction of the target species life-span, chronic studies cover a considerable part of the life-span including critical phases like reproduction and embryonic development. While there is a trend to conduct more in-vitro studies, thus limiting the number of animals used for testing, the quality of the information needs to be maintained to conduct a valid risk assessment.
In general, the severity of the eco-toxicological effects observed will intensify, if the concentration of a chemical substance is increased (dose-response relationship). However, under real environmental conditions, a chemical substance in fresh- or sea water may be either freely available or bound to solid particles that are either free floating in the water column or sedimented to the ground. Depending on the target organism under survey, the actual bio-available concentration may be either lower (if the organism is active in the free water column) or higher (if a sediment dwelling organism is considered). Hence the bio-availability of a chemical substance needs to be evaluated and taken into account to conduct a proper eco-toxicological risk assessment1.
1 ECETOC Workshop Report Nr. 17 – Significance of bound residues in environmental risk assessment