High Throughput Adaptation of Standardised Ecotoxicological Tests for the model freshwater invertebrate Daphnia magna

Current environmental regulations require the standardised testing of chronic ecotoxicological endpoints as part of their approval processes. However, although such tests tend to be resource intensive, new high throughput methods have not been favoured to date due to their lack of standardisation. To address this, a high throughput experiment that captured the conditions specified in the standardised Organisation for Economic Co-operation and Development’s (OECD) Test Guideline 211 was carried out. Daphnids (>400) were individually exposed to five concentrations of each of four polar narcotic chemicals (3,4-dichloroaniline (DCA), 2,4,5-trichloroaniline (TCA), 1,2-dichlorobenzene (DCB), 3-nitroaniline (3NA)) and four chemicals that are nACHhR inhibitors (acetamiprid, clothianidin, nitenpyram, thiacloprid) for a period of 21 days. Growth and reproduction were measured every other day using a spheroid counter. Mortality in controls was low (<20%) throughout the study period meeting OECD validity criteria. However, average cumulative reproduction of 52 neonates per Daphnid in controls was slightly below the OECD reproduction validity criteria of 60 neonates per Daphnid. Despite variations in average observed size of the animals due to their position during measurement, results show a clear dose-response effect for growth and reproduction, enabling ECx to be calculated for all chemicals at any time point. The results of this experiment demonstrate a robust methodology that can generate a large volume of time sensitive data for chronic and acute endpoints, under conditions consistent with standard OECD test guidelines in a cost and time efficient manner.