Brine shrimp toxicity of some plants used as traditional medicines in Kagera Region, north western Tanzania

Dichloromethane and/or ethanol extracts of 30 plants used as traditional medicines in Bukoba district, northwestern Tanzania were evaluated for brine shrimp toxicity. Among the 50 extracts tested, 32 extracts (64%) showed very low toxicity with LC₅₀ values above 100 μg/ml. Among these 12 (24%) which had LC₅₀ >500 μg /ml can be categorized as being practically non-toxic. Among the remaining extracts 19 (38%) which showed LC₅₀ >100 < 500 μg /ml are also considered to be non-toxic. Extracts that showed LC₅₀ results between 30-100 μg/ml have been categorized as mildly toxic; these include ethanol extracts of Lantana trifolia (LC₅₀ 32.3 μg/ml), Vernonia bradycalyx (LC₅₀ 33.9 μg/ml), Antiaris toxicaria (LC₅₀ 38.2 μg /ml) and Rubus rigidus (LC₅₀ 41.7 μg /ml) and the dichloromethane extracts of Gynura scandens (LC₅₀ 36.5 μg /ml) and Bridelia micrantha (LC₅₀ 32.0 μg /ml). The dichloromethane extracts of Picralima nitida (LC₅₀ 18.3 μg/ml) and Rubus rigidus (LC₅₀ 19.8 μg /ml), were only moderately toxic. Picralima nitida and Rubus rigidus extracts are only 1.1 and 1.2 less toxic than the standard drug, cyclophosphamide (LC₅₀ 16.3 μg /ml). In conclusion, the results indicate that among the 30 plants used as traditional medicines, 28 are safe for short term use. Picralima nitida and Rubus rigidus extracts are mildly toxic, but by comparison have a remote possibility to yield active anticancer compounds.