EXCHANGE OF AIRBORNE ORGANOPHOSPHORUS PESTICIDES WITH PINE NEEDLES

Organophosphate (OP) pesticide residues have been found in rain, snow, fog and air samples collected in the Sierra Nevada mountains. The fat e of these residues in this ecosystem is poorly understood. A major co mponent of the Sierra Nevada ecosystem is the varied plant biomass. in teraction between chemicals vapors and plant material has been demonst rated for various semivolatile organic compounds. This research addres ses the hypothesis that the extensive forests of the western slopes of the Sierra Nevada mountains, which lie in the predominant downwind di rection from the agricultural Central Valley of California, might serv e as sinks for airborne OPs. The main paths of vapor-leaf interaction are cuticular and stomatal. More specifically interactions may include sorption of residues to surface dust particles, or to the needle surf ace, solubilization in the cuticular wax of the needle, and penetratio n to the interior of the needle either by absorption th rough the stom ata or migration through the cuticle. Analytical methods, which can se parately assess surface, cuticle adsorbed, cuticle dissolved, and inte mal needle tissue residues, have been applied in two experimental situ ations. One involved measuring the vapor-needle distribution coefficie nt for several OPs exposed as vapors to pine branches in a laboratory chamber. A second, involving air and needle analyses for trees placed in, and downwind from a diazinon-treated orchard, provided outdoor dis tribution coefficients for comparison with chamber data. This paper ad dresses these two experimental situations, along with preliminary calc ulations of possible loading values for forests in the Sierra Nevadas. The results support the hypothesis that forests act as sinks for airb ome pesticide vapors.