Effect of humic acids on toxicity of DDT and chlorpyrifos to freshwater and estuarine invertebrates

Abstract

The effects of dissolved humic acids (HAs) on the acute toxicities of the organophosphate pesticide chlorpyrifos and the organochlorine pesticide 4,4'-dichlorodiphenyltrichloroethane (DDT) were assessed by using freshwater crustaceans (Ceriodaphnia dubia) and saltwater crustaceans (Americamysis bahia). The effects of filtered Aldrich HAs (10-100 mg/L) on organism mortality were determined. Humic acids had no effect on mortality of A. bahia for either pesticide at a salinity of 20 parts per thousand, but greatly reduced the mortality of C. dubia for both pesticides in freshwater (0 parts per thousand). In the latter case, the effect was proportional to the HA concentration. The difference in toxicity mitigation as a function of salinity is believed to be due to conformational changes in the HA molecules, which impact pesticide-HA binding, rather than to organismal effects.

Differences in response of two model estuarine crustaceans after lethal and sublethal exposures to chlorpyrifos

“…[16] The freshwater tropical shrimp, Neocaridina denticulata sinensis, was much less sensitive to chlorpyrifos with a 24-h LC50 of 1103 µg L −1 and a 96-h LC50 of 457 µg L −1 . [17] For mysids, A. bahia published chlorpyrifos toxicity values have ranged from a 24-h LC50 of 0.326 µg L −1 for 4-day old mysids [18] to a 96-h LC50 of 0.035 µg L −1 for 24-h old mysids. [19] The western European species, Neomysis integer, was less sensitive with a chlorpyrifos 96-h LC50 of 0.13 µg L −1 for adults and 0.19 µg L −1 for 24-h old mysids.…”

Structural effects of the bioavailable fraction of pesticides in soil: Suitability of elutriate testing

“…The cholinesterase inhibitor chlorpyrifos has already shown high acute toxicity to D. magna with recorded 48 h-immobilisation EC 50 values or LC 50 values ranging 0.74-1 g L −1 following standardised bioassays using waterborne chemical solutions [47,48]. Moreover, the organic matter content, which should be considered in tests with elutriates, has already been shown to reduce the acute toxicity of chlorpyrifos to freshwater crustaceans [49]. Considering these records, the acute toxicity found for soil D8 can hardly be explained.…”

Soil and Water Pollution Monitoring, Protection and Remediation

“…All pesticides are characterized by high toxicity to biota (Choudhry, 1983;Draber et al, 1991). A whole number of publications are devoted to examination of pesticide toxicity in the presence of HS (Stewart, 1984;Day, 1991;Oikari et al, 1992;Genevini et al, 1994;Steinberg et al, 1994;Freidig et al, 1997;Gensemer et al, 1998;Koukal et al, 2003;Mézin and Hale, 2003). However, there is a substantial disparity in the reported findings.…”