The potential inhalation hazard posed by dioxin contaminated soil

Mathematical models and field data were used to estimate the airborne concentrations of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) vapor and particulates which could originate from soil containing 100 ppb TCDD. The model of Jury et al. (1983) and the box approach were used to predict the concentration of TCDD vapor from soil. The daily soil temperature was assumed to vary between 20 degrees C and 40 degrees C for six months of the year to account for diurnal warming and cooling of the soil. The depth of contamination was 50 mm. The model predicted average vapor flux rate for TCDD from soil for this temperature profile was 1.5 x 10(-14) mg/sec-cm2. The upper-bound estimates of the TCDD vapor concentration on-site at 40 degrees C and 20 degrees C were 2.5 pg/m3 and 1.8 pg/m3, respectively. Using a recently proposed unit risk value (URV) of 2.9 x 10(-6) (pg/m3)-1 [slope factor = 1.0 x 10(-14) (mg/kg-day)-1], the maximum plausible cancer risk is about 1 x 10(-5). If one accepts the EPA URV of 3.3 x 10(-5) (pg/m3)-1 (slope factor = 1.2 x 10(-13) (mg/kg-day)-1), then the risk is no greater than 1 x 10(4). A maximum TCDD vapor concentration of 0.21 pg/m3 was predicted 100 meters downwind (for summer days). The on-site concentration of TCDD in suspended particulate was estimated to be 1.4 pg/m3 (based on a TSP level of 0.07 mg/m3 from site soil). For persons exposed to vapors and particulates about 100 meters off-site, the exposure was about 10-fold less.(ABSTRACT TRUNCATED AT 250 WORDS)