<![CDATA[In vitro inhibition of whole blood cholinesterase (WBChE) by the organophosphate insecticide dichlorvos has been used to assess sentinel animal species among ruminants. The aim of the study was to calculate the benchmark dose (BMD) as a sensitive indicator of WBChE inhibition caused by dichlorvos. The BMD sensitivity of WBChE of humans and ruminants (sheep, goats and cattle) was assessed after in vitro dichlorvos 10-min inhibition in the assay mixture. At concentrations of 0 (control), 0.25, 0.5, and 1 µM, dichlorvos significantly, but variably reduced enzyme activity across the four species with IC50 values of about 0.5 µM. These data were used to calculate BMD using the online tool BMDS Online Version: 25.1 software introduced by U.S. Environmental Protection Agency (US EPA). The exponential 3 curve fitting model was recommended by the tool. The resultant plots showed dose-response curves estimated by the model. The BMD levels in humans, sheep, goats and cattle were 0.181, 0.126, 0.343, 0.304 µM, respectively. The goodness-of-fit p-values ranged from 0.757 to 0.983 across the species, which were larger than the predetermined critical p-value of 0.1 used by the US EPA. The data showed that the BMD model appropriately described the observed dose-response pattern of WBChE inhibition by dichlorvos, and showed that this model was a better sensitivity indicator of enzyme inhibition s compared to IC50 determined earlier. Sheep-derived benchmark dose assessment defines this species as the most sensitive (sentinel) one among humans, goats and cattle, with regards to WBChE inhibition threshold. Refining the in vitro dichlorvos toxicity outcome with in vivo studies and risk assessment methods is needed, as this study highlights and further supports the potential of BMD modelling in evaluating health risks posed by OP insecticides.]]>
