R6 AM Plant Uptake of Organic Pollutants - Processes and Modeling
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in 324-326

(MAD-1117-841277) Background air component of vegetation/soil bioconcentration ratios.

Maddalena, R¹, Kulakow, P², ¹ Lawrence Berkeley National Laboratory, Berkeley, CA, USA² Kansas State University, Manhattan, KS, USA

ABSTRACT- Soil-to-plant biotransfer plays a critical role in assessing both human and ecological risks at phytoremediation sites and in establishing risk-based screening levels (RBSLs) at hydrocarbon impacted exploration and production sites. The plant/soil bioconcentration ratios (BCRs) that are used to estimate exposure concentrations are based on empirical relationships developed from measured chemical concentrations in plants and soil. However, these relationships do not explicitly account for the contribution of background air to measured concentrations in vegetation. As a result, measured plant/soil BCRs (and the resulting empirical models) likely overstate the contribution of soil to contaminant concentrations in vegetation. To explore this issue we combine two separate but related studies of Polycyclic Aromatic Hydrocarbon uptake into vegetation. Results from a controlled exposure chamber study using spiked soils provide details on direct (soil-plant) and indirect (soil-air-plant) uptake pathways while results from a cooperative phytoremediation field study yield relevant field measurements. Air-to-plant exchange is faster than soil-to-plant exchange such that air concentrations are the primary factor controlling the maximum attainable concentrations in the aboveground vegetation. The air-to-plant pathway also sets a limit on the concentrations in soil below which soil-to-plant transfers can no longer be reliably measured. We find that even low background atmospheric concentrations can affect our ability to reliably measure soil-to-plant BCRs, particularly for chemicals with high Koa. The contribution from air varies significantly across chemicals, which provides an opportunity to identify the primary factors that influence the fraction of chemical in vegetation that is attributable to air and subsequently that which is attributable to soil.

Key words: Plant uptake, Exposure modeling, Fate modeling, Koa