The acute toxicity of agricultural surfactants to the tadpoles of four Australian and, two exotic frogs

Nonionic surfactants are frequently incorporated into pesticide formulation s, and are therefore a group of chemicals to which amphibians may be expose d in agricultural or urban landscapes. However, little is known about the e ffects of surfactant exposure in amphibians. Feeding stage tadpoles of Bufo marinus, Xenopus laevis and four species of Australian frogs (Crinia insig nifera, Heleioporus eyrei, Limnodynastes dorsalis and Litoria moorei) were exposed to nonylphenol ethoxylate (NPE) and alcohol alkoxylate in static-re newal acute toxicity tests. All species exhibited nonspecific narcosis foll owing exposure to both these surfactants. The 48-h EC50 values for NPE rang ed between 1.1 mg/l (mild narcosis) and 12.1 mg/l (full narcosis). The 48-h EC50 values for alcohol alkoxylate ranged between 5.3 mg/l (mild narcosis) and 25.4 mg/l (full narcosis). Replicate acute toxicity tests with B. mari nus exposed to NPE at 30 degreesC over 96 h indicated that the narcotic eff ects were not particularly time dependant. The mean 24, 48, 72, and 96-h EC 50 (mild narcosis) values were 3.6, 3.7, 3.5 and 3.5 mg/l, respectively. Th e mean 24, 48, 72 and 96-h EC50 (full narcosis) were 4.0, 4.1, 4.2 and 4.0, respectively. Acute toxicity tests with B. marinus exposed to NPE at 30 de greesC under conditions of low dissolved oxygen (0.8-2.3 mg/l) produced a t wo to threefold increase in toxicity. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.