|Environmental Fate of Pesticides-79
Project Leader and Principal UC Investigators
D.G. Crosby,Dept. of Environmental Toxicology, UC Davis
As demonstrated by DrepamonŽ, molinate, and thiobencarb, laboratory
measurement of volatilization rates allow at least a rough estimate of the
relative field dissipation rates for these chemicals. DrepamonŽ was the
least persistent (most volatile) of the three. DrepamonŽ which remains in
water or mud is also rapidly degraded and remains as a highly water-soluble,
non-extractable product. As indicated by its close relative, molinate, these
herbicides can be expected to break down photochemically in the atmosphere
For nonvolatile pesticides such as Du-TerŽ and MCPA Amine, the action of sunlight assumes more direct importance in limiting their persistence. In addition to its photochemical degradation, Du-TerŽ reacts with other natural constituents of water. The rapid degradation of MCPA formulations in laboratory experiments is caused by both light-catalyzed oxidation and a new chemical condensation reaction, but the effects remain to be verified in the field.
A research project cooperatively funded with California Department of Food and Agriculture and involving the UCD departments of Environmental Toxicology and Botany began to yield highly useful information regarding the possible toxic impact of detectable airborne phenoxy herbicides (MCPA) on specific non-target crops such as almonds and pistachos. The chemical properties of MCP Amine formulations show them to be more "organic" than salt-like. They are rapidly degraded in sunlight to volatile products which would be expected to evaporate from spray droplets or leaf deposits. Extensive air and foliage sampling was conducted in Butte County during the 1979 spray season, and methods have been developed for trace analysis of MCPA and its degradation products. Preliminary results indicate that low levels of MCPA are detectable on orchard foliage immediately after spraying of adjacent rice fields, but none is found a little later in the year. Symptoms were observed on almond and pistachio trees placed in the path of a test MCPA application. As expected, the symptoms decreased as the trees were placed further from the direct pass of the aircraft. These symptoms will be correlated with leaf samples to see if a cause and effect relationship can be established. Ways to apply this important family of herbicides more efficiently and safely are being explored.
Scientists in the UCD Department of Environmental Toxicology, with support funds from the California Air Resources Board and the California Energy Commission, continued studies of the potential health hazards associated with particulate matter released from rice straw burning. As part of this research, studies were made to determine if the burning rice straw emissions contained products resulting from pesticides used in crop production. Although no Rice Research Funds were involved in this project, one Rice Research Board member and two other growers were cooperators in the field phases of the experiment.