UPTAKE OF GASEOUS DDE IN SPRUCE NEEDLES

The accumulation and desorption of gaseous DDE in spruce needles was investigated in two chamber experiments using Picea omorika and in a third using Picea abies. The P. omorika needles were divided into two fractions for analysis: the soluble cuticular lipids and the remaining needle. The data were used to parameterize a one-compartment (complete needle) and a two-compartment (surface, reservoir) plant model. The one-compartment model performed poorly, whereas the uptake and clearance behavior of the complete needle was described very well with the two-compartment model. However, the two model compartments did not correspond to the two needle fractions that were analyzed for P. omorika. The validation of the P. abies model using environmental data was quite successful, whereas the validation of the P. omorika model gave poor results. It was concluded that chamber experiments are not sufficient for describing the air/plant exchange of contaminants for which the half-life of the exchange process with the slowest leaf compartment is longer than the length of the experiment. Furthermore, model validation is essential if the results of chamber experiments are to be extrapolated to environmental conditions.