THE DISTRIBUTION OF SEMIVOLATILE ORGANIC-COMPOUNDS IN CONIFER NEEDLESFOLLOWING GAS-PHASE CONTAMINATION

Spruce needles (Picea abies) which had been exposed for 6 hours to ele vated concentrations of gaseous SOC were immersed in dichloromethane f or up to 100 minutes. It was found that compounds with higher molecula r weights (PCBs, DDT and DDE) were completely removed from the needles after washing for several minutes. Large fractions of the compounds w ith lower molecular weight (chlorobenzenes and hexachlorocyclohexanes) could not be extracted by this method, even after immersion for 100 m inutes. These results are attributed to differences in the diffusion b ehavior of the two substance groups. For the SOC with higher molecular weights the cuticular lipids act both as a sink and as a diffusion ba rrier, whereas the SOC with lower molecular weight can readily penetra te into the interior of the needle. These results question contaminant models which assume that the leaf is a single, well mixed compartment . The solvent immersion extraction may be useful when employing needle s as biomonitors, possibly circumventing the problem of very slow kine tic behavior in the whole needle.