Influence
of Temperature, Relative Humidity, and Soil
Properties on the Soil–Air Partitioning of Semivolatile Pesticides:
Laboratory Measurements and Predictive Models
Soil–air partition
coefficient (<i>K</i><sub>soil‑air</sub>) 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><sub>soil‑air</sub> 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><sub>soil‑air</sub> values of 22 semivolatile current-
and historic-use pesticides and their degradation products. <i>K</i><sub>soil‑air</sub> 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><sub>soil‑air</sub> measurements were made. Measured values were used to derive a predictive
equation for pesticide <i>K</i><sub>soil‑air</sub> 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><sub>soil‑air</sub> predictive equation
and a previously described pesticide volatilization model, were compared
to previous results and showed that the choice of <i>K</i><sub>soil‑air</sub> predictive equation mainly affected the
more-volatile pesticides and that the way in which relative humidity
was accounted for was the most critical difference