POLYCHLORINATED BIPHENYL DESORPTION FROM LOW ORGANIC-CARBON SOILS - MEASUREMENT OF RATES IN SOIL-WATER SUSPENSIONS

The desorption of 13 PCB congeners from four soils has been investigat ed using the gas purge technique. The soils from PCB spill sites had b een in contact with Aroclor 1242/1254 mixtures for 3 or more years; th us, sorption equilibrium is presumed to have been obtained. Soils were ''engineered'' ground cover materials used at utility industry substa tions and consisted of fine rock chips and sand-silt-clay fractions wi th organic carbon < 0.2%. The congeners contained from three to five c hlorine atoms. Agreement of measured Henry's Law constants for the C-1 4-labeled congeners 24', 22'55' and 22'44'55' with literature values e stablished the proper function of the gas purge technique for measurem ent of congener release rates from soil-water suspensions. For all 13 congeners and all soils: 1) the labile fraction was typically 80 to 90 % of the total congener concentration, 2) the majority of the labile f raction was desorbed or released within 48 hours of contact with water , and 3) the release of the remaining nonlabile fraction persisted for over 6 months with complete release estimated to be 1 to 2 years. Rel ease rate constants, k(d), decreased with increasing chlorine number w ith typical values for labile and nonlabile fractions ranging from 1.4 to 0.5 d(-1) and 0.008 to 0.0006 d(-1), respectively. (C) 1997 Elsevi er Science Ltd.