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