DAVIS, K.C.; RIPLEY, B.J.; SIMOVICH, M.A.: Acute Toxicity of Malathion and Round Up to the San Diego Fairy Shrimp Branchinecta sandiegonensis

Branchinecta sandiegonensis is an endangered fairy shrimp (Anostraca) that lives in Southern California vernal pools. Contaminants such as the insecticide malathion and the herbicide Round Up are commonly sprayed in San Diego for fruit fly and weed control. While these contaminate pools, there is little documented information on their toxicity. In order to assess the risk due to toxic effects of malathion and Round Up, we determined the LD₅₀ of each chemical for B. sandiegonensis in 24 hour toxicity assays using standard EPA protocols. These tests were done using juvenile shrimp between 24-48 hours old. We also determined the LD₅₀ of malathion and Round Up for Ceriodaphnia dubia at the same age to determine if this, a commonly used assay organism (which co-occurs in pools with B. sandiegonensis) could be used as a surrogate in future toxicity testing. Ceriodaphnia dubia was four orders of magnitude more sensitive than B. sandiegonensis in the LD₅₀ for malathion. However, C. dubia are less than one order of magnitude more sensitive for Round Up. This toxicity information will be helpful in developing conservation plans for vernal pools.