Sampling bulk deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans

The suitability of a bulk deposition collector for quantifying the deposition of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) was investigated. It was found that the sampler -a glass funnel emptying into a bottle-collected almost exclusively PCDDs and PCDFs associated with sedimenting particles and wet deposition, with little contribution from dry gaseous deposition or impacting/diffusing particles when left exposed for one month. The long exposure period did not result in sampling artefacts as a result of volatilisation or photodegradation of the compounds on the collector surface. Indeed, efforts to conserve the sample on a daily basis by rinsing the funnel with solvent resulted in the generation of a new artefact caused by repeated removal of chemical that had adsorbed from the gas phase to the funnel surface. Experience gathered over 12 months of continuous sampling in Bayreuth indicated that when the sampler was rinsed monthly, artefacts were limited to about 10%, probably due to particle blow-out. The results indicate that the simple bulk deposition sampler is suitable for quantifying atmospheric deposition of these compounds to bare soil and in other situations where the dominant deposition mechanisms are particle sedimentation and wet deposition. (C) 1997 Elsevier Science Ltd.