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

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) were stud ied in soils to determine if, and under what conditions, soil acts as a conservative matrix for the collection of atmospheric deposition. St udies of four soil cores showed that 80% of the PCDD/F load was contai ned in the top 15 cm of the core. Concentrations were highly correlate d with organic carbon, indicating that sorption to organic carbon is t he dominant mechanism. Study of two other cores did not exhibit this b ehavior due to low soil organic carbon and to heavy PCDD/F loading fro m the atmosphere. Soils and lake sediments were collected in similar g eographic regions, and the soil-derived and lake sediment-derived PCDD /F fluxes were compared. The percent relative standard deviation of fo ur soil-lake sediment pairs ranged from +/-1% to +/-26%, and the fluxe s ranged from 180 to 990 ng m(-2) yr(-1). Comparison of homologue prof iles also showed good agreement. Analysis of field duplicate soil samp les 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.