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.

The unbound portion of dissolved hydrophobic environmental contaminants generally is presumed to be the most bioavailable to aquatic organisms. The effects of differing concentrations of Aldrich humic acid (HA) and salinity on the freely dissolved fraction of chlorpyrifos (CPF) and 4,4'-dichlorodiphenyltrichloroethane (DDT) in water were assessed through their relative uptake by solid-phase microextraction (SPME). This extraction method has been recently suggested as a valuable biomimetic tool. Increasing salinity (0-20 parts per thousand [parts per thousand]) alone had no effect on the uptake of DDT by the SPME fiber, but generally enhanced the SPME uptake of the more water soluble CPE Solid-phase microextraction uptake of DDT was decreased at an HA concentration of 10 mg/L, but 100 mg/L was required to decrease CPF uptake. Binding of CPF and DDT by HA was greatly reduced by the presence of salt at 5 to 20 parts per thousand. The extent of the HA and salinity effects appeared to be pesticide-dependent. These factors may ultimately impact the contaminant's environmental fate, transport, and bioavailability, for example, in estuarine situations.

Secretion of mucus by epidermal goblet cells protects fish against many biological, physical, and chemical insults encountered in the environment. This study monitored changes in hemoglobin concentration in epidermal mucus and in the density, diameter, and mucus quality of epidermal goblet cells in the mummichog, Fundulus heteroclitus, following exposure to creosote‐contaminated sediment from the Elizabeth River, Virginia, USA. Fish were exposed for 13 d in flow‐through aquaria to either uncontaminated (US) or contaminated (CS) sediments and were sampled periodically. The condition index was lower and the mortality rate and the occurrence of epidermal lesions were higher in CS‐exposed fish than in US‐exposed fish. Hemoglobin contents in epidermal mucus from the former group were significantly higher than from the latter. Significant reductions in both size and density of goblet cells in CS‐exposed fish suggested a mucus secretion rate exceeding its production rate. Significant changes in mucin types between treatments did not occur until day 13 and are not believed to be directly related to the creosote present in the contaminated sediment. These results all indicate that exposure to creosote‐contaminated sediment had a profound and deleterious effect on fish health.

Abstract-Secretion of mucus by epidermal goblet cells protects fish against many biological, physical, and chemical insults encountered in the environment. This study monitored changes in hemoglobin concentration in epidermal mucus and in the density, diameter, and mucus quality of epidermal goblet cells in the mummichog, Fundulus heteroclitus, following exposure to creosotecontaminated sediment from the Elizabeth River, Virginia, USA. Fish were exposed for 13 d in flow-through aquaria to either uncontaminated (US) or contaminated (CS) sediments and were sampled periodically. The condition index was lower and the mortality rate and the occurrence of epidermal lesions were higher in CS-exposed fish than in US-exposed fish. Hemoglobin contents in epidermal mucus from the former group were significantly higher than from the latter. Significant reductions in both size and density of goblet cells in CS-exposed fish suggested a mucus secretion rate exceeding its production rate. Significant changes in mucin types between treatments did not occur until day 13 and are not believed to be directly related to the creosote present in the contaminated sediment. These results all indicate that exposure to creosote-contaminated sediment had a profound and deleterious effect on fish health.

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