Influence of Temperature, Relative Humidity, and Soil Properties on the Soil–Air Partitioning of Semivolatile Pesticides: Laboratory Measurements and Predictive Models

Abstract

Soil–air partition coefficient (<i>K</i>_soil‑air) values are often employed to investigate the fate of organic contaminants in soils; however, these values have not been measured for many compounds of interest, including semivolatile current-use pesticides. Moreover, predictive equations for estimating <i>K</i>_soil‑air values for pesticides (other than the organochlorine pesticides) have not been robustly developed, due to a lack of measured data. In this work, a solid-phase fugacity meter was used to measure the <i>K</i>_soil‑air values of 22 semivolatile current- and historic-use pesticides and their degradation products. <i>K</i>_soil‑air values were determined for two soils (semiarid and volcanic) under a range of environmentally relevant temperature (10–30 °C) and relative humidity (30–100%) conditions, such that 943 <i>K</i>_soil‑air measurements were made. Measured values were used to derive a predictive equation for pesticide <i>K</i>_soil‑air values based on temperature, relative humidity, soil organic carbon content, and pesticide-specific octanol–air partition coefficients. Pesticide volatilization losses from soil, calculated with the newly derived <i>K</i>_soil‑air predictive equation and a previously described pesticide volatilization model, were compared to previous results and showed that the choice of <i>K</i>_soil‑air predictive equation mainly affected the more-volatile pesticides and that the way in which relative humidity was accounted for was the most critical difference