Species sensitivity distribution of dichlorvos in surface water species

Abstract

Dichlorvos is an organophosphorus insecticide frequently detected in surface waters all around the world. From an evaluation of the environmental quality concentrations (EQC) for dichlorvos in surface waters adopted by different countries, it was observed a wide variability among them. This is despite regulatory EQC-values are typically based on toxicity data and species sensitivity distribution (SSD) in all the investigated regulatory frameworks, and therefore should be similar. Hence, what is the cause of the differences between national and regional EQC-values? And, which ones will protect the aquatic fauna? These hypotheses were proposed to explain differences among SSDs based on the choice of toxicity data: (i) EQC values obtained from technical presentation (pure dichlorvos) will be higher than the estimated from dichlorvos formulation (containing other substances to improve the efficiency of the active principle), as they may include synergists; (ii) different taxa will have different sensitivities; (iii) data produced under different experimental conditions will severely affect the SSD. Regarding their capacity to protect the aquatic fauna the hypotheses were; iv) environmental concentration of dichlorvos represents a risk for aquatic organisms; and v) not all EQC-values are protective for the aquatic fauna. These were tested through a meta-analysis of toxicity data enabling the construction of SSD’s across technical and formulated dichlorvos and species of several taxa, and across literature and experimental data produced under analogous conditions. Finally, the EQC elaborated were compared with a meta-study on monitored environmental concentrations. The study suggested that technical dichlorvos increased toxicity compared to formulated products up to two-fold for arthropods. Species phylogeny affected sensitivity, but the SSD derived values used for setting regulatory concentrations were remarkably robust to the inclusion/exclusion of less sensitive species. The SSD results from the literature and experimental data were similar in the case of technical dichlorvos results. The regional differences in EQC values therefore most likely stem from political considerations on how to use SSDs to derive EQCs rather than from differences in SSDs. The experimental SSD defined a protective concentration of 6.5 ng L− 1 for 5% of the species, which is according to the European EQC, but one to two-fold lower than the limit values of the US, China, and Argentina.