Applying the threshold approach in fish acute toxicity studies

The European plant protection product (PPP) regulation (EC Regulation 1107/2009) requires that companies provide information on the potential acute toxicity of their formulated products and the active ingredients to fish. A range of substance concentrations are usually tested in these studies. However, an alternative method is to apply a “threshold approach”. This approach means that an initial test is carried out in fish at one concentration, which is calculated based on the results of Daphnia and algae toxicity tests, and the full concentration response is only triggered if mortality is observed at this threshold concentration.

In 2010 we held a workshop with representatives from regulatory bodies across several EU member states, industry and academic researchers, to determine whether the threshold approach is appropriate for assessing acute toxicity in fish for the majority of PPP active substances. Our consensus recommendation, that the threshold approach should be applied for acute fish toxicity studies, was subsequently included within the recently published guidance that companies consult when developing a regulatory data package for PPPs in Europe [1]. However, there is no recommendation within the guidance on how the approach should be integrated into testing and assessment procedures.

We analysed internal company data from 185 PPPs for fish (Oncorhynchus mykiss), Daphnia magna and algae (Pseudokirchneriella subcapitata). This provided an evidence base which supports the reduction of the number of fish test groups required, through the application of a threshold approach.  Based on this evidence we developed a framework for applying the threshold approach which enables the number of fish used in these studies to be reduced by approximately 40%. In addition to reducing the number of fish being tested, the analysis suggests that the suffering of fish is also potentially reduced using the threshold approach, as high concentrations of active substances would not require testing by default.