Acute oral LD50 and 30-day dietary subacute LC50 studies of 10 selected pesticides were evaluated in microtine rodents. As a means to developing new animal model systems, four species of microtine rodents including Microtus ochrogaster (MO), Microtus canicaudus (MC), Microtus pennsylvanicus (MP) and Microtus montanus (MM) voles were used. The acute LD50 (median lethal dose in mg/kg) in all four species and the subacute LC50 (median lethal concentration in ppm) in MO and MC voles were computed using probit analysis. The data from both the acute and the 30-day subacute studies revealed that MC voles were approximately twice as sensitive to these pesticides as MO voles. Based on the acute studies, the overall order of pesticide toxicity was as follows: parathion > methyl parathion > dieldrin > 2,4-D > 2,4,5-T > simazine propanil = PCNB = HCB = trifluralin. The general order of species sensitivity was as follows: MC> MP> MO>MM. No apparent sex differences were observed in MP, MO or MM voles. In MC voles, the female appeared to be two- to three-fold more sensitive to methyl parathion than the male. Based on the 30-day subacute LC50 studies, the overall order of pesticide toxicity is as follows: dieldrin> parathion> methyl parathion> HCB> 2,4,5-T> PCNS> propanil. Based on LD50 values the laboratory rodents appear to be more susceptible to 2,4-D, dieldrin, methyl parathion, parathion, propanil, and 2,4,5-T, equally susceptible to HCB, PCNB, and trifluralin, and less susceptible to simazine than the MC voles.

Prepared for the U.S. Environmental Protection Agency, Office of Research and Development, Corvallis Environmental Research Laboratory, under Contract no. 68-01-4915. Includes bibliographical references (pages 19-20).