WP6 Emerging Pollutants
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(CON-1117-763143) Uptake of perchlorate by garden crops in perchlorate-impacted soil: Implications for risk assessment.

Conder, J¹, Haroun, L², Scofield, R², ¹ ENVIRON International Corporation, Irvine, CA, USA² ENVIRON International Corporation, Emeryville, CA, USA

ABSTRACT- Nearly all perchlorate uptake studies in garden crops have been conducted with plants grown in soil or water receiving multiple additions of perchlorate via irrigation with water containing perchlorate. Bioconcentration factor (BCF) values, based on concentration in plant tissue divided by concentration in water, are as high as 10,000. These values may be inappropriate for prediction of perchlorate uptake from perchlorate-impacted soils that do not receive additional inputs of perchlorate, as BCF values based on soil concentrations for inedible agricultural plants and native plants are 1-2 orders of magnitude lower. The differences in water-based and soil-based BCF values may be due to a number of factors, including lower availability in soils (especially at soil concentrations of less than 2-5 ppm) and the possible depletion of available perchlorate by plants from soil. For garden crops, the addition of organic matter amendments and fertilizer may also inhibit uptake and/or increase biodegradation, resulting in lower observed soil-based BCF values. BCF values vary by orders of magnitude among plant tissues, as perchlorate is accumulated in tissues that have high water permeation due to evapotranspirational flux. In general, differences in tissue-specific BCF values can be an order of magnitude or more, with Leaf BCF > Fruit BCF > Root BCF. Risk-based cleanup levels in soil can be below 40 ppb, the reporting limit using the standard analytical method, based on assumptions that water-based BCF values represent perchlorate uptake and consumers of garden produce consume only leaf produce. Risk-based cleanup levels for perchlorate in soil should be calculated using soil-based BCF values and dietary assumptions that consider consumption of representative dietary portions of leaf, fruit, and root produce.

Key words: bioconcentration, homegrown produce pathway, soil, perchlorate