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

Spruce needles (Picea abies) which had been exposed for 6 hours to elevated concentrations of gaseous SOC were immersed in dichloromethane for up to 100 minutes. It was found that compounds with higher molecular weights (PCBs, DDT and DDE) were completely removed from the needles after washing for several minutes. Large fractions of the compounds with lower molecular weight (chlorobenzenes and hexachlorocyclohexanes) could not be extracted by this method, even after immersion for 100 minutes. These results are attributed to differences in the diffusion behavior of the two substance groups. For the SOC with higher molecular weights the cuticular lipids act both as a sink and as a diffusion barrier, whereas the SOC with lower molecular weight can readily penetrate 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 needles as biomonitors, possibly circumventing the problem of very slow kinetic behavior in the whole needle.