ESTIMATING THE ATMOSPHERIC DEPOSITION OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS FROM SOILS

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) were studied in soils to determine if, and under what conditions, soil acts as a conservative matrix for the collection of atmospheric deposition. Studies of four soil cores showed that 80% of the PCDD/F load was contained in the top 15 cm of the core. Concentrations were highly correlated with organic carbon, indicating that sorption to organic carbon is the dominant mechanism. Study of two other cores did not exhibit this behavior due to low soil organic carbon and to heavy PCDD/F loading from the atmosphere. Soils and lake sediments were collected in similar geographic regions, and the soil-derived and lake sediment-derived PCDD/F fluxes were compared. The percent relative standard deviation of four soil-lake sediment pairs ranged from +/-1% to +/-26%, and the fluxes ranged from 180 to 990 ng m(-2) yr(-1). Comparison of homologue profiles also showed good agreement. Analysis of field duplicate soil samples gave percent relative standard deviations ranging from +/-5% to +/-59% with fluxes ranging from 2 to 470 ng m(-2) yr(-1). The results of this study suggest that soils can be used to estimate the deposition of PCDD/F from the atmosphere. This will allow us to easily expand the worldwide database of PCDD/F flux estimates.