APPLICATION OF PASSIVE SAMPLERS TO MONITOR REMEDIATION PROGRESS

Abstract

Passive samplers have been used as collection devices for measuring low concentrations of pollutants from air and water phases. Contaminant biouptake in benthic organisms and flux from contaminated sediments are controlled by the freely dissolved porewater chemical concentrations in sediment. The main challenges in measuring porewater concentrations of hydrophobic compounds such as PCBs and PAHs by direct extraction is the very low freely dissolved concentrations of these compounds and interference in the measurement from sorption to colloidal phases that are difficult to separate. Our recent work has explored the use of thin films of polyoxymethylene (POM) as equilibrium passive samplers to measure porewater concentrations of a range of toxic organic chemicals including PCBs, PAHs, dioxins, furans, and chlorinated pesticides in laboratory measurements and measurements conducted in the field. Using POM passive samplers we monitored changes in in-situ aqueous PCB concentrations over time at a pilot study site in a river where activated carbon was amended to sediment to reduce PCB bioavailability. Results of passive sampler monitoring in the field over four years indicated that amendment of activated carbon to sediments reduced porewater PCB concentration near the sediment surface to values lower than ambient concentrations in the overlying water. This finding reveals that amendment of strong sorbents may be effective in reversing the direction of chemical flux between contaminated sediment and overlying water locally during a pilot study. This talk will present an overview of the use of passive equilibrium samplers in laboratory assessment of aqueous equilibrium concentrations and use in the field to monitor changes in contaminant concentrations in the sediment porewater and overlying water.