N.P. Gola and W.J. Muller (South Africa)
Deltamethrin, pesticides, shrimp, Caridina nilotica, and toxicity
Due to the rapid growth in agriculture and industry, organisms face a wide range of environmental challenges. Such challenges include exposure of non-target organisms to pesticide residues. Deltamethrin has a broad-spectrum control and is considered the most powerful of the synthetic pyrethroids. Caridina nilotica is the most common indigenous freshwater shrimp in Southern Africa and its biological and life history has been studied. This study was aimed at assessing the acute effects of deltamethrin on different age groups, neonates (<7 days old), juveniles (>7days and < 20 days old) and adults (>40 days old), of C. nilotica. The chosen concentration range of deltamethrin (0.0005µg/l- 0.1µg/l) was much lower than the common application range of dips and sprays (0.005 – 0.075g/l). The mean LC50 values were as follows 0.006µg/l (neonates), 0.003µg/l (juveniles) and 0.011µg/l (adults). The observed effects of deltamethrin on the organisms of all age groups were uncoordinated movement, erratic swimming and immobility. Mortality generally increased in response to increasing deltamethrin concentration in all experiments. Juvenile shrimp seemed to be slightly more sensitive to deltamethrin than other age groups. High control mortalities showed shrimp neonates to be more sensitive to handling and experimental conditions than the other age groups.
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