Toxicity of Some Pesticides, Heavy Metals and Their Mixtures to Vibrio fischeri Bacteria and Daphnia magna: Comparative Study

Abstract

The present study was conducted to evaluate the sensitivity of the Vibrio fischeri bioluminescence inhibition test (Microtox^® assay), and the standard acute Daphnia magna test; using 3 heavy metals, 3 organic pesticides, and their mixtures. In Daphnia tests, either at 24h or 30 min exposure times, the pattern of toxicity order for heavy metals was Cu ˃ Cd ˃ Pb. Chlorpyrifos-methyl was the highest toxic at 24h, while Triazophos was the highest toxic at 30 min exposure times. In the Microtox^® test at 5 min exposure time, the estimated EC50 values were 4.20, 4.53 and 6.60 mg/L for Cu, Cd and Pb, respectively. At the same exposure time, the EC50 values of Triazophos, Chlorpyrifos-Me and Profenofos accounted to 1.76, 3.36 and 4.12 mg/L, respectively. Similar order of toxicity was obtained when tests were conducted at 15 min exposure time. The paired mixtures of pesticides, as well as the mixtures of Cu + Cd and Pb + Cd, showed potentiation effects, while the mixture of Cu + Pb showed additive effect against D. magna. The tertiary mixtures of the pesticides or the heavy metals reacted antagonistically. In the Microtox^® assay, the heavy metal mixtures reacted antagonistically, while pesticide mixtures showed synergism. It was concluded that both Daphnia and Microtox^® tests showed similar pattern of sensitivity to the single toxicants, but dissimilar pattern to the heavy metal mixtures. On the other side, using shorter exposure time (ca. 30 min) with Daphnia bioassay may enable us to held reliable comparisons with Microtox^® results.