PARTITIONING OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS BETWEEN THE ATMOSPHERE AND CORN

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofu rans (PCDF) are lipophilic atmospheric contaminants that accumulate in vegetation, a process which may lead to the contamination of food. Th us, knowledge of PCDD/F accumulation in vegetation is crucial to evalu ating human exposure, in an effort to determine this accumulation mech anism, we analyzed matched atmosphere, corn kernel, and corn leaf samp les from a private farm in Felicity, OH. Corn is an important feed cro p in the United States; both corn kernels and corn leaves (silage) a r e widely used. PCDD/F concentrations were bel ow the detection limits (0.5-1 pg/g lipids) in the corn kernels. However, we found PCDD/F conc entrations of 510 +/- 75 fg/m(3), 1300 +/- 300 fg/m(3), and 4.2 +/- 1. 2 ng/g lipids in the atmospheric gas phase,atmospheric particle phase, and corn leaves, respectively. For each set of air and corn leaf samp les, we calculated corn leaf-atmosphere partition coefficients for bot h the atmospheric gas and particle phases, K-v,K-g and K-v,K-p respect ively. On the basis of plots of the natural logarithm of these partiti on coefficients versus the reciprocal of the average, atmospheric temp erature, we conclude that the partitioning of PCDD/F between the atmos phere and corn leaves is dependent on temperature. We calculated the e nthalpies of phase change between the vegetation and air for all PCDD/ F homologues; our values are comparable to literature values for polyc yclic aromatic hydrocarbons and polychlorinated biphenyls. The ratio o f K-v,K-p to K-v,K-g is a log-log function of the average vapor pressu re for each PCDD/F homologue, indicating that vapor pressure plays an important role in the partitioning of both the gas and particle phases to corn leaves.