Retention and mobility of atmospheric particle-associated organic pollutant PCDD/Fs and PAHs in maize leaves.

The fate of polychlorinated dibenzo-p-dioxins and dibenzofurans and polycyclic aromatic hydrocarbons deposited to maize leaves under ambient conditions was investigated, with focus on those compounds that are primarily associated with particles in the atmosphere. Leaf samples collected from mature maize plants over an 8-wk period were subjected to four extraction procedures: (1) rinsing with distilled water; (2) shaking in aqueous EDTA solution; (3) immersion in chloroform/methanol; (4) soxhlet extraction with toluene. Of the compounds deposited primarily in association with particles, > 20% of the total leaf contamination was present in the first two aqueous extracts, indicating that only a small portion of these substances was subject to ready erosion from the leaf surfaces. Some 50-60% of the chemical was present in the third extract, while 20-40% was found in the final extract. The chemical in the final extract was no longer associated with particles, since these had been removed with the first three extractions. This chemical must have desorbed from the particles with which it was originally deposited, and migrated through the epicuticular waxes. Model calculations indicated that 15-35% of the chemical in the third extract had also desorbed from the particles, and there was evidence that polychlorinated dibenzo-p-dioxins and dibenzofurans desorb more readily than polycyclic aromatic hydrocarbons. It is concluded that desorption of chemical from particles and subsequent transport through the cuticle is an important process determining plant accumulation of organic contaminants associated with atmospheric particles.