Biological Monitoring of Diazinon Exposure Using Saliva in an Animal Model

Abstract

Alternative biological monitoring methods are currently being pursued to better quantify pesticide exposures. In this study, the feasibility of using saliva as a tool for measuring diazinon exposure was determined in an animal model. Male Spraque-Dawley rats were dosed with 1 or 10 mg/kg diazinon by bolus intravenous injection. Time-matched saliva and arterial blood samples were collected from 10 to 250 min post administration. Diazinon was distributed and eliminated rapidly in rats following intravenous (iv) bolus injection, according to a two-compartmental pharmacokinetic analysis. Salivary concentration of diazinon showed a strong correlation with plasma concentration of diazinon. The saliva/plasma (S/P) concentration ratio of diazinon was not affected by administered dose, sampling time, or salivary flow rate, suggesting that salivary excretion of diazinon in rats is fairly constant. Diazinon concentrations in saliva were consistently lower than those in arterial plasma. The mean S/P concentration ratios of diazinon were 0.16 and 0.13 for 1 and 10 mg/kg iv bolus doses, respectively. It is most likely that the incomplete transfer of diazinon from plasma to saliva is due to protein binding of diazinon in plasma. If the protein-unbound fraction of diazinon in plasma is used to calculate the S/P ratio, the S/P concentration ratio of diazinon is close to unity. The results from this study support the conclusion that diazinon salivary concentrations not only can be used to predict the plasma levels of diazinon in rats, but also reflect the unbound fraction of diazinon in plasma.