Accumulation Kinetics and Equilibrium Partitioning Coefficients for Semivolatile Organic Pollutants in Forest Litter

Soils are important stores of environmentally cycling semivolatile organic contaminants (SVOCs) and represent relevant atmospheric secondary sources whenever environmental conditions favor re-emission. The exchange between air and soil is controlled by resistances posed by interfacial matrices such as the ubiquitously distributed vegetation litter. For the first time, this study focused on the experimental characterization of accumulation parameters for SVOCs in litter under real field conditions. The logarithm of the litter-air equilibrium partitioning coefficient ranged 6.8–8.9 and had a similar dependence on log<i>K</i>_OA as that of plant foliage and soil data. Uptake and release rates were also <i>K</i>_OA dependent with values (relevant for real environmental conditions) ranging 30,000–150,000 d^–1 and 0.0004–0.0134 d^–1, respectively. The overall mass transfer coefficient <i>v</i> controlling litter-air exchange (0.03–1.4 cm s^–1) was consistent with previously reported data of <i>v</i> for foliage in forest canopies after normalization on leaf area index. Obtained data suggest that litter holds the potential for influencing atmospheric fugacity in proximity to soil, likely affecting overall exchange of SVOCs between the soil reservoir and the atmosphere