Aquatic Ecotoxicology : a review

As a result of the scientific developments along with the revised data requirements of the new Regulation EC 1107/2009 on Plant protection Products, the aquatic ecotoxicology issue is being reviewed.

The attention was focused, especially, on the tiered risk assessment for the aquatic organisms living in the water column in the edge-of-field surface waters as ditches, streams and ponds which represent the surface water system next to a treated field.

The risk assessment for aquatic organisms is based on two components: the exposure assessment linked to time-related environmental concentrations and the effect assessment through the toxicity of such time-dependent concentrations on the ecosystem. The relevant endpoints resulting from these two evaluations are the Predicted Environmental Concentration (PEC) and the Regulatory Acceptable Concentration (RAC), both referred to the surface waters.

In order to carry out a suitable risk assessment, beyond the most sensitive species, the aquatic species living in the realistic exposure scenarios as well have to be considered. Such scenarios depend on the substance characteristics i.e. the mode of action, the persistence, the accumulation and the tendency to hydrolyze in water.

As for herbicidal substances and plant growth regulators, the toxicity standard test on Lemna spp. has to be carried out as representative specie of higher aquatic plants. Additional testing may be required by Member State competent authorities on rooted macrophyte according to the expected exposure scenario (root uptake from the sediment), Lemna spp. not enough sensitive to the specific toxic mode of action of the substance, higher terrestrial sensitiveness of dicots compared to terrestrial monocot species.

Myriophyllum spicatum, growing in a water-sediment system, is the more suited dicot specie to be tested additionally. The validation of the test guidelines for these higher aquatic plants is ongoing (draft versions are currently available) and soon the related endpoints could be used to improve the risk assessment.