Species Sensitivity Distribution of Dichlorvos in Surface Water Species

Abstract During the last years, dichlorvos has had an extremely high occurrence in monitoring campaigns, showing concentrations that would result in severe environmental impact. Environmental quality concentrations (EQC) for dichlorvos in surface waters vary by more than two orders of magnitude among different regulations. Regulatory EQC-values are based on toxicity data where species sensitivity distributions (SSDs) are mostly used as a basis. Hence, what makes the difference between the different national and regional EQC-values? And will they all protect the aquatic fauna? To investigate these questions, we constructed an SSD based on our laboratory data and compared this with SSDs based on literature data for technical and formulated products and species of different taxa. Finally, we compared the SSD-derived EQCs with a meta-study on monitored environmental concentrations to determined the EQC-exceedance. The following hypotheses were tested: (i) formulated dichlorvos will result in lower EQCs, as formulated products may include synergists; (ii) different taxon will have different sensitivities with arthropods being the most sensitive group; (iii) environmental concentration of dichlorvos represents a risk for aquatic organisms. As a result, experimental SSD defined a protective concentration of 6.5 ng L-1 for 5% of the species, which is in line with the European limit values, but one to two-fold lower than the limit values of the USA, China, and Argentina. The EQCs of three of the four regions included in this study are therefore not enough to protect the aquatic fauna.