Impacts of Salinity on the Hydrolysis of Chlorpyrifos

The organophosphate insecticide, chlorpyrifos, was used as a probe to assess the individual effects of salinity and trace metals in seawater on its hydrolysis rate as their influence on organic chemicals remains poorly characterized. This investigation measured the hydrolytic degradation of chlorpyrifos to its transformation product, 3,5,6-trichloro-2-pyridinol (TCP), in five sterilized/buffered media: 25 parts per thousand (ppt) artificial seawater, 25 ppt sodium chloride (NaCl), 10 parts per billion (ppb) copper, 0.5 ppb copper, and buffered deionized water (0 ppt). Chlorpyrifos hydrolyzed 21, 62, and 13% faster in 25 ppt seawater, 10 ppb copper, and 0.5 ppb copper, respectively, and 40% slower in 25 ppt NaCl compared to 0 ppt. The formation of TCP in each medium was consistent with the observed degradation of chlorpyrifos. Trace amounts of copper at concentrations similar to those observed in freshwater environments and seawater accelerated the hydrolytic rate, while NaCl significantly inhibited it. This research illustrates the importance of considering the combined influences of trace metals as well as salinity when evaluating the environmental fate of hydrophobic organic compounds in aquatic ecosystems.