Light-dependent toxicity of α-terthienyl and anthracene toward late embryonic stages of Rana pipiens

Alpha-terthienyl occurs naturally in Tagetes erecta and in many other planting species in the family Compositae. It is toxic to late embryonic stages of Rana pipiens in the presence of sunlight. Neither alpha -terthienyl alone in the dark nor a previously photolyzed solution of alpha -terthienyl has comparable activity. The LC sub(50) was 0.11 ppm with 30 min of exposure and 0.018 ppm with 2 hr of exposure to sunlight. Anthracene, a representative example of polycyclic aromatic hydrocarbons widely distributed in the environment, also showed similar phototoxicity, with an LC sub(50) of 0.065 ppm after 30 min of exposure and 0.025 ppm after 5 hr.