UPTAKE OF GASEOUS DDE IN SPRUCE NEEDLES

The accumulation and desorption of gaseous DDE in spruce needles was i nvestigated in two chamber experiments using Picea omorika and in a th ird using Picea abies. The P. omorika needles were divided into two fr actions for analysis: the soluble cuticular lipids and the remaining n eedle. The data were used to parameterize a one-compartment (complete needle) and a two-compartment (surface, reservoir) plant model. The on e-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 corresp ond to the two needle fractions that were analyzed for P. omorika. The validation of the P. abies model using environmental data was quite s uccessful, whereas the validation of the P. omorika model gave poor re sults. It was concluded that chamber experiments are not sufficient fo r describing the air/plant exchange of contaminants for which the half -life of the exchange process with the slowest leaf compartment is lon ger than the length of the experiment. Furthermore, model validation i s essential if the results of chamber experiments are to be extrapolat ed to environmental conditions.