Transport and Photolysis of Pentachlorophenol in Soils Subject to Evaporating Water

Abstract

AbstractPentachlorophenol (PCP) was applied to loamy sand and sandy clay loam soils to determine the effect of upward evaporative flux on the rates of photolytic loss. Subirrigated soil columns were irradiated by ultraviolet lamps or sunlight to measure relative rates of photolytic loss under differing soil moisture regimes. Photolysis was initially rapid in loamy sand soil under near‐saturated flow conditions, with up to 55% more lost in light‐exposed treatments in 14 d as compared to dark controls. Rates of transport were slower in sandy clay loam soil, reflecting a soil sorption distribution coefficient of 10 mL/g, as compared to 0.4 mL/g in the loamy sand. Despite slower upward movement, similar amounts of photodegradation of PCP had occurred in the sandy clay loam soil after 14 d. Dropping the water table to the 15 or 25 cm depth resulted in unsaturated flow and increased losses to volatilization, with a much lower relative contribution of photodegradation over the course of the experiments. Up to 77% was lost from the loamy sand soil dark treatments during the 14‐day period, due to volatilization and irreversible sorption. Processes that translocate PCP into the sunlit surface zone under near‐saturated soil moisture conditions can be expected to enhance rates of photolytic loss while minimizing volatilization.