UPTAKE AND PHOTODEGRADATION OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN SORBED TO GRASS FOLIAGE

Plant uptake rates were determined for vapor-phase 2,3,7,8-TCDD using grass foliage. The primary elimination mechanisms for 2,3,7,8-TCDD from grass, photodegradation and volatility, were measured in natural sunlight, filtered sunlight with reduced UV-B radiation, and in the dark. Rapid sorption of 2,3,7,8-TCDD vapor to grass resulted in an initial uptake rate constant of 1750 h-1. Photodegradation of 2,3,7,8-TCDD and volatility of 2,3,7,8-TCDD from the foliage back into the air were both significant elimination mechanisms. The photodegradation half-life of 2,3,7,8-TCDD sorbed to grass and exposed to natural sunlight was 44 h (k2 = 0.0156 h-1). The half-life resulting from volatility of 2,3,7,8-TCDD from the grass foliage was 128 h (k2 = 0.0054 h-1). A two-compartment uptake and clearance model was used to estimate a theoretical air-to-grass bioconcentration factor of 7.9 X 10(6) (v/v). The uptake and elimination rates and the bioconcentration factor for 2,3,7,8-TCDD and grass are compared to results reported for 1,2,3,4-TCDD and azalea (18). The rapid photodegradation of 2,3,7,8-TCDD sorbed to grass indicates this elimination mechanism should be considered when plant contamination from 2,3,7,8-TCDD is estimated.