Polychlorinated dibenzo-p-dioxin and furan (PCDD/F) uptake by pasture.

Uptake of airborne PCDD/Fs by a native pasture sward was studied. The concentrations of the less chlorinated PCDD/Fs (up to and including the Cl5DD/Fs) in pasture harvested on the same day after 2, 6, and 12 weeks exposure were the same, implying that air-pasture steady-state was reached within 2 weeks of exposure. The implications of these observations for the relative importance of input (atmospheric deposition, soil resuspension) and loss (photolysis, degradation, volatilization, cuticular shedding, and growth dilution) processes are discussed and inferences made about the controlling factors. The concentrations of the more chlorinated PCDD/Fs were more variable. We infer that they were influenced by wash-off of particle- and surface-bound chemical. Up to 4% of the Cl2-4DD/F and 4-13% of the Cl5-8DD/F loading on the pasture was estimated to have been supplied by adhering soil particles, with the remainder supplied by atmospheric deposition. Between 0.04 and 0.66 kg of each homologue group (excluding Cl2DFs) is estimated to be transferred annually from the atmosphere to pasture in the U.K.