|Fate of Pesticides 83
Project Leader and Principal UC Investigators
D.G. Crosby,Dept. of Environmental Toxicology, UC Davis
The primary purpose of this project is to provide information that will permit the use of rice pesticides without causing problems to the environment outside the target area. Specific objectives for 1983 were: (1) to identify, investigate, and model environmental factors which govern movement and chemical fate of rice pesticides, (2) to estimate the relative importance of such factors to the practical use of specific rice pesticides, and (3) to apply research results toward meeting regulatory requirements and improved management of rice pesticides.
Laboratory Rice Field Environmental Chamber
A laboratory rice field environmental chamber was developed in 1982 to make predictions and comparisons of the environmental fate of pesticides in rice fields. An improved model with more temperature flexibility and computer control was used successfully to predict molinate volatilization from a field application of Ordram l0G.
The weather during the 1983 field trial was very abnormal, and molinate dissipation differed significantly from that measured (and modeled) in 1982. The 1983 half-life was six days instead of two days, because of unusually low temperatures. The laboratory model environmental chamber predicted the dissipation curve with reasonable accuracy, based on volatility alone.
Analytical detection and measurement of molinate and thiobencarb in water has been greatly improved. At least 80 analyses can be conducted per day with over 98 percent recovery efficiency and one part per billion sensitivity. This method was used in other experiments during the year. Bolero and MCPA field applications in 1983 were monitored and will be modeled in the environmental chamber.
Effect of Atmospheric Ozone on Rice Herbicides
Ozone is a strong oxidant in the lower atmosphere. Initial evidence implicates ozone as a generator of natural field oxidants in water which may exert profound influence on pesticide persistence. Studies with ten other reagents indicate that herbicide degradation might be intentionally accelerated. Sodium hypochlorite, potassium persulfate, and titanium oxide (white paint pigment) provide the possibility of practical water treatment to lower residues in fields or drains.
Dissipation of Parathion Breakdown Products
The principal photodegradation product of parathion and methylparathion (p-nitrophenol) was found to be persistent in water. However, a corresponding phenol from a closelyrelated insecticide called fenitrothion was rapidly photo-oxidized, suggesting that it should be examined as a possible replacement for the parathions.
Parathion was rapidly degraded by rice field crayfish to p-nitrophenol which was excreted, leaving only very small parathion residues in the edible meat. This information is helpful in understanding residue dynamics in the crayfish which is increasingly harvested for human food.
Degradation of Molinate and Thiolcarbamates
The sulfoxides of molinate and thiobencarb are important degradation products. "Bolero sulfoxide" is suspected as contributing to ofd flavor in Sacramento city water, but analysis has been unsatisfactory. An extensive but unsuccessful search was made for a new chemical basis for the detection and measurement of molinate and thiobencarb sulfoxides. However, the preparation and purification of sulfoxide standards were improved.
Rice Station Well Water
Well water from the Rice Experiment Station at Biggs was analyzed from May through October for the principal rice pesticides and degradation products. None was detectable at the part-per-trillion level.
Rice Pesticide Data Bank
A comprehensive information file on MCPA is essentially complete, and compilation of the file on molinate is under way. The aim is to provide rapid access to technical information needed by research workers, farm advisors, and rice growers.