Determination of octanol–air partition coefficients of organochlorine pesticides (OCPs) as a function of temperature: Application to air–soil exchange

Abstract

Octanol–air partition coefficients (KOA) for 7 organochlorine pesticides (OCPs) were determined as a function of temperature using the GC retention time method. Log KOA values at 25 °C ranged over two orders of magnitude, between 8.32 (chlorpyrifos) and 10.48 (methoxychlor). The determined KOA values were within a factor of 0.5 (endosulfan sulfate) to 7.9 (endrin aldehyde) for values calculated as the ratio of octanol–water partition coefficient to dimensionless Henry's law constant. The internal energies of phase transfer between octanol and air (ΔUOA) ranged between 71.8 and 95.4 kJ mol−1 and they were within the reported range for OCPs (55.8–105 kJ mol−1). Atmospheric and soil OCP concentrations were also measured in Izmir, Turkey, and data used to investigate the soil–air gas exchange. Net soil–air gas exchange fluxes of OCPs ranged from −0.01 (volatilization, cis-nonachlor) to 56.4 ng m−2 day−1 (deposition, chlorpyrifos) in winter, while in summer they ranged from −0.03 (trans-nonachlor) to 329 ng m−2 day−1 (endosulfan I). In both sampling periods, endosulfan I and II, trans-nonachlor, p,p′-DDD and p,p′-DDT were generally deposited to the soil while γ-HCH and heptachlor epoxide mostly volatilized. Fluxes of other OCPs were variable (volatilization or absorption) due to their largely fluctuating ambient air concentrations. Calculated dry deposition and recently measured wet deposition fluxes were used to estimate the relative importance of different mechanisms (i.e., dry deposition, wet deposition, gas absorption, and volatilization) to the local soil pollutant inventory. Generally, all mechanisms contributed significantly to the soil OCP inventory. Volatilization fluxes were generally much lower than the sum of input fluxes (dry deposition, wet deposition and gas absorption) for most of the OCPs indicating a net deposition to the soil.