Abstract
Semi-volatile organic contaminants (SOCs), such as certain pesticides and brominated flame retardants (BFRs), are distributed throughout the globe via local-scale and global-scale processes that are largely driven by temperature gradients. Given the potential for these contaminants to deposit into a variety of non-target, sensitive ecosystems where they can bioaccumulate and exert their toxic effects, it is essential that efforts are made to understand the processes and properties controlling their distribution so that more accurate predictions of their fate and behaviour can be made in the future.
Pesticide volatilisation and vapour drift are local-scale distribution processes that can have adverse effects on non-target ecosystems and human health. Four approaches to screen for pesticide volatilisation based on Fick’s Law of Diffusion were investigated. In each approach, vapour pressures or environmentally relevant partition coefficients were used to describe pesticide distribution in a bare agricultural soil system and to predict 24-h cumulative percentage volatilisation (CPV24h) losses. The multiphase partitioning approach based on soil-air (Ksoil-air) and water-air (Kwater-air) partition coefficients was found to most accurately predict measured volatilisation losses of pesticides reported in the literature. Predicted CPV24h losses were displayed on chemical space diagrams for sets of hypothetical Ksoil-air and Kwater-air combinations under different temperatures, relative humidity levels, and soil organic carbon contents. Using this visual screening technique, the pesticides and conditions under which the greatest volatilisation losses exist were easily identified.
Many environmental fate models use environmentally relevant partition coefficients to investigate the fate and distribution of SOCs in the environment. However, measured partition coefficient values are often unavailable in the literature and are instead estimated. In this study, a solid-phase fugacity meter was developed and validated to investigate the soil-air partitioning of pesticides. Ksoil-air values of selected current- and historic-use pesticides and degradation products were measured for two soils under different temperature and relative humidity combinations. Measurements were used to derive a predictive equation for pesticide Ksoil-air values based on temperature, relative humidity, the soil organic carbon content, and the pesticide-specific octanol-air partition coefficient.
Global-scale distribution processes, such as long-range atmospheric transport, result in the migration of SOCs towards the poles and deposition in remote environments far from where they are used or produced. High-volume air and water samplers were used to measure concentrations of BFRs, including a set of polybrominated diphenyl ethers (PBDEs) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), in the air and lake water at Toolik Lake, Arctic Alaska during the Northern Hemisphere summer of 2013. The BDE congeners associated with the penta-BDE commercial mixture (BDE-47, -99, and -100) were most frequently detected in air and at concentrations consistent with the ranges reported for other Arctic sites. Correlations with temperature suggest that volatilisation from local sources or re-emission from secondary sources were important for the lower-brominated BFRs during warmer periods, whereas cooler temperatures caused a shift in gas-particle distributions that favoured association with atmospheric particles. In lake water, only the high-brominated BFRs were detected in association with suspended particles.