Combined effects of humic acids and salinity on solid‐phase microextraction of DDT and chlorpyrifos, an estimator of their bioavailability

Abstract

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.

Evaluating the impacts of some environmentally relevant factors on the availability of bisphenol A with negligible-depletion SPME

“…As the overall charge of humic acids at pH 7.0 is larger than that at pH 6.0, the binding of BPA to humic acids is relatively strong at pH 6.0 and thus the free fraction of BPA at pH 6.0 is lower than that at pH 7.0. Keeping the same humic acids concentrations and pH 7.0, the increase of sodium phosphate buffer from 5 mM to 125 mM resulted in higher freely dissolved fraction of BPA, i.e., the binding of BPA to humic acids was reduced with the increase of salinity, which is in agreement with early studies about nonpolar compounds (Schlautman and Morgan, 1993;Jones and Tiller, 1999;Mezin and Hale, 2004). Fig.…”

“…The environmental pH can affect the ionization of DOM (Jota and Hassett, 1991) and thus influence the binding of neutral hydrophobic compounds to DOM (Paolis and Kukkonen, 1997 ions used to control the ionic strength and the properties of DOM, the ionic strength or salinity can increase (Gauthier et al, 1986;Jota and Hassett, 1991;Brunk et al, 1997) or decrease (Schlautman and Morgan, 1993;Jones and Tiller, 1999) the association of DOM with polychlorinated biphenyls (PCBs) or polycyclic aromatic hydrocarbons (PAHs). By using negligible-depletion solid-phase microextraction (nd-SPME), a biomimetic tool, the combined effects of humic acids and salinity on the availability of 4,4 0 -dichlorodiphenyltrichloroethane (DDT) and chlorpyrifos pesticides were investigated, and it was reported that the binding of DDT and chlorpyrifos by humic acids was greatly reduced with the presence of salt (Mezin and Hale, 2004).…”

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

“…Similar results have been shown for pesticides, including DDT [11]. Concurrent research [14] assessed the freely dissolved fraction of the pesticides CPF and DDT in the presence of DOC at various salinities by using solid-phase microextraction. Results indicated that CPF and DDT sorption to Aldrich HA increased with increasing HA concentration.…”

“…When considering contaminant transport through different salinity regimes in the environment, this interaction could be important. The present research and its companion paper [14] point to the potential impact of the interaction of these factors in contaminant bioavailability and toxicity.…”

“…Mézin and Hale [14] showed that salinity strongly mitigated the association of the pesticides DDT and CPF to Aldrich HA. Because the association of contaminants to HAs has been shown to reduce toxicity, the role of varying salinity in the mitigation of the toxicities of pesticides by Aldrich HA was investigated further here by using the freshwater organism Ceriodaphnia dubia and the saltwater organism Americamysis bahia .…”