Study of toxicity of pesticides using luminescent bacteria Photobacterium phosphoreum

The relative toxicity (expressed as 5-min EC50 value - the concentration of chemical which reduces the light output of bacteria by 50% after contact for 5 minutes) of 13 pesticides (e.g., 2,4-dichlorophenoxyacetic acid, atrazine, coumarin, glyphosate, paraquat, pentachlorophenol, lindane, malathion) and 14 solvents was evaluated using Biotox(TM) test that is based on reconstituted freeze-dried viable Photobacterium phosphoreum. The most toxic of the 13 pesticides analyzed using Biotox(TM) was pentachlorophenol (5-min EC50=0.55 mg/L) and the less toxic was paraquat (5-min EC50=14800 mg/L). The 5-min EC50 data for Biotox(TM) were compared to the respective data for Microtox(TM) test (also based on freeze-dried P. phosphoreum) and rodent oral LD50 values. For Biotox(TM) vs Microtox(TM) the log-log correlation coefficients for the whole data set (pesticides+solvents, pesticides, solvents) were 0.78, 0.37 and 0.95, respectively. The less toxic solvents to Biotox(TM) were ethylene glycol, DMSO, methanol, ethanol, acetone and acetonitrile and, therefore, these solvents could be used for increasing the solubility of lipophilic compounds, e.g., for testing the toxicity of pesticides. In order to analyze toxic effects of pesticides in complex mixtures the EC50 values of pentachlorophenol, coumarin and glyphosate as pure substances and in their mixtures were compared. the toxic effects of the above-mentioned pesticides in their mixtures were not additive. Copyright (C) 1996 IAWQ.