Toxicity of Azadirachta indica to freshwater snails and fish, with reference to the physicochemical factor effect on potency.

A preliminary crude screening of plants in Jos Metropolis showed that at a concentration of 100 mg/l-1 the stem bark extract of the Neem plant Azadirachta indica caused a 100 percent mortality when tested against three common snail intermediate host species, Biomphalaria pfeifferi, Bulinus truncatus, and Lymnaea natalensis after 24 hours exposure. Toxicity test with freeze-dried aqueous extract of the plant gave 96 hours LC50 values of 19.00 mg/l-1 (p > 0.05), 10.96 mg/l-1 (p > 0.05) and 15.13 mg/l-1 (p > 0.05) against B. pfeifferi, B. truncatus and L. natalensis, respectively. When a similar test was carried out on fish, Aphyosemon giardneri a 96 hour LC50 of 15.1 mg/l-1 was recorded. Extraction with alcohol, increase in temperature within the optimal range, increase in acidity of aquatic medium and cold storage improved the potency of the extract while boiling and room storage reduced it.