Assessing the need for groundwater quality guidelines for pesticides using the species sensitivity distribution approach

The water quality needs of groundwater ecosystems are rarely considered. It is currently assumed that water quality guidelines for surface waters will also protect groundwater ecosystems and their fauna, but this assumption has not been tested. The aim of this study is to determine whether water quality guidelines specifically for groundwater ecosystems are needed and to provide a preliminary risk assessment for groundwater ecosystems in Australia. In the absence of sufficient toxicity data for true groundwater fauna, 48-96 h LC50 data for groundwater-dwelling invertebrate orders (e.g., Crustacea, Rotifera) are used as a surrogate and were compared, using Species Sensitivity Distribution (SSD) curves, to a full suite of surface taxa (including fish, insects, and algae). SSD curves were derived for a range of pesticides previously detected in Australian groundwaters and were fitted using the Burr Type III distribution. Significant differences in the sensitivities of surface and groundwater taxa to Atrazine and Chlorpyrifos were detected, indicating surface water quality guidelines are not always suitable to protect or best manage groundwater ecosystems. Water quality guideline values derived from the SSDs highlighted a significant threat of contamination to groundwater ecosystems from agricultural chemicals. Clearly water quality guidelines specifically for groundwater ecosystems are needed.