Environ. Sci. Technol. 1990, 24, 353-357
Distribution of Several Organophosphorus Insecticides and Their Oxygen Analogues in a Foggy Atmosphere Dwlght E. Glotfelty,*vt Michael S. Majewski,t and James N. Selbert U S . Department of Agriculture, Agricultural Research Service, Environmental Chemistry Laboratory, Beltsville Agricultural Research Center, Beltsville, Maryland 20705, and Department of Environmental Toxicology, University of California, Davis, California 95616
We measured the distribution of four organophosphorus insecticides (diazinon, parathion, chlorpyrifos, and methidathion) between the droplet and air phases during six fog events. We also measured the distribution of their oxon transformation products, which result from the oxidative conversion of the parent organophoshorothioate to the corresponding organophosphate. We found up to 60 pg/L for the total of the four parent insecticides, and up to 75 pg/L for the total of their oxons in the fogwater. In agreement with earlier studies, nearly all the compounds exhibited aqueous-phase concentrations much higher than would be expected from measured vapor concentrations and Henry’s law. Even though high concentrations and high enrichments were found in the aqueous phase, for most of the compounds the largest proportion was present in the interstitial air phase, either as vapor or adsorbed to aerosol particles. Only very small amounts (8 pm through the large particle orifice of the device. Fog droplets of chlorpyrifos > paraoxon = parathion > methidathion. The EF varied between events, being small (EF = 1-10) for two events, intermediate (EF = 10-50) for two events, and large (EF up to 160) for the 1.12-13.86 event. The EF for all five compounds went up and down together from one event to another. The only compound that failed to
Environ. Sci. Technol. 1990,24,357-363
show an EF consistently greater than 1was methidathion. For this compound, KAWwas estimated from literature values of vapor pressure and solubility and may have been in error. Temperature effects play an important but poorly known role in the air/water distribution of pesticides and may reduce the measured EF by a factor of 2-4 in the present experiment. Even though there were high concentrations and high EF for the water phase, the largest proportion of all the compounds in all events was in the interstitial air phase, either vapor or adsorbed to aerosol particles. The distribution between air and droplet phases for each pesticide covered a broad range from one event to the next. The proportion associated with droplet-phase particles was small, averaging
