Abstract
Development of an acute oral toxicity test with a terrestrial-phase amphibian was considered necessary to remove the uncertainty within the field of agrochemical risk assessments. The bullfrog (Lithobates catesbeianus) was selected for use as it is a representative of the family Ranidae and historically this species has been used as an amphibian test model species. Prior to definitive study, oral gavage methods were developed with fenthion and tetraethyl pyrophosphate (TEPP). Dimethoate and malathion were subsequently tested with both male and female juvenile bullfrogs in comprehensive acute oral LD50 studies. Juvenile bullfrogs were administered a single dose of test article via oral gavage of a single gelatin capsule of Dimethoate Technical (dimethoate) or neat liquid Fyfanon® Technical (synonym malathion), then returned to their respective aquaria and monitored for survival for 14 days. The primary end-point was mortality, whilst behavioral responses, food consumption, body weight and snout-vent length (SVL) were used to evaluate indications of sublethal toxicity (secondary endpoints). Acute oral LD50 (95% fiducial interval) for dimethoate were 1,459 (1,176–1,810) [males] and 1,528 (1,275–1,831) [females], and for malathion were 1,829 (1,480–2,259) [males] and 1,672 (1,280–2,183) [females] mg a.s./Kg bw, respectively. Based on the results of these studies, the methodology for the acute oral gavage administration of test items to terrestrial-phase amphibians was demonstrated as being a practical method of providing data for risk assessments. This article is protected by copyright. All rights reserved
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