Impact of repeated pesticide applications on the binding and release of methyl 14C-monocrotophos and U-ring labelled 14C-carbaryl to soil matrices under field conditions.

The dissipation of (O-methyl-14C) monocrotophos and U-ring labelled 14C-carbaryl was monitored for over two years in absence and presence of other insecticides using in situ soil columns. The dissipation of 14C-monocrotophos from soil treated with methomyl and carbaryl showed a faster rate of downward movement than in a control column tagged with the labelled insecticide alone. The same trend was observed in experiments with 14C-carbaryl that dissipated more readily in soil treated with non-labelled monocrotophos and methomyl. In the presence of other insecticides the percentage of bound residues was generally lower than in control experiments. The bound residues at the top of the column are released at a low rate under conditions prevailing in the field. The overall time required for dissipation of 50% of monocrotophos and carbaryl (t50) as estimated from control experiment was approximately 20 and 24 weeks, respectively. The data indicate that repeated applications of pesticides might enhance the release of 14C-bound residues.

Decomposition of 14C-fenitrothion under the influence of UV and sunlight under tropical and subtropical conditions.

The decomposition of (14)C-fenitrothion on silica gel chromatoplates as well as in polar and non polar solvents under sunlight and ultraviolet light was investigated, Its stability to sunlight on leaf surfaces of bean plants and on different surfaces (such as glass, quartz and plastic) was also determined. The main photoproducts were identified as carboxyfenitrothion, fenitrooxon, carboxyfenitrooxon and 3-methyl-4-nitrophenol and a small amount 3-caboxy-4-nitrophenol and methyl parathion. The addition of carbaryl and deltamethrin insecticides slightly accelerated the photodecomposition of fenitrothion on silica gel plates and in solution.

Fate of 14C-chlorpyrifos in stored soybeans and its toxicological potential to mice.

Grains of soybeans were treated with [ethyl-1-4C]chlorpyrifos at a dose of 15 ppm and its triplet. During the 30-week storage period, the penetration and distribution of insecticide residues were studied. The amount of surface residues on stored soybeans, internal extractables and bound residues were determined. Surface residues were found to decrease with the increase in time of storage, whereas internal residues showed a gradual increase with time to reach 40-52% of applied dose after 30 weeks. Non-extractable residues showed a relatively slow but definite increase with time. The degradation products include, in addition to the parent insecticide which constitutes 50% of the total residues, the oxygen-analogue of chlorpyrifos, desethyl chlorpyrifos and 3,5,6-trichloropyridinol. Feeding mice for 90 days with a diet mixed with total internal chlorpyrifos residues in stored soybeans led to considerably inhibited plasma and red blood cells-cholinesterase activity by 78 and 46%, respectively, during the experimental period. Blood picture, liver and kidney function of treated mice were significantly affected during the feeding period.

Mineralization of 14C-ring labelled 2,4-D in Egyptian soils under aerobic and anaerobic conditions.

OBJECTIVES: To study the mineralization of 2,4-D in clay and clay loam Egyptian soils under subtropical conditions over a period of 90 d. METHODS: Using 14C-ring labelled pesticide, laboratory studies under aerobic and anaerobic conditions were conducted. 14C-activity in solutions was directly determined by liquid scintillation counting. Unextractable soil residues were determined by combustion. The nature of methanolic 14C-residues was determined by thin layer and high performance liquid chromatographic analysis. RESULTS: Under aerobic conditions 10%-14% of applied dose was mineralized during 90 d irrespective of soil type. The soil extractable pesticide residues decreased with time and the bound residues gradually increased. The highest binding capacity of about 26%-29% was observed in clay soil under aerobic conditions after 90 d. A good balance sheet was obtained and the percentage recovery was generally between 91% and 100%. CONCLUSION: The mineralization of 2,4-D in clay soil was higher than that in clay loam soil under anaerobic conditions. Under aerobic conditions, the soil type had no influence on mineralization capacity of 2,4-D during 90 d. The soil binding increased with time whereby the extractable 14C-residues simultaneously decreased. Chromatographic analysis of the methanol extractable 14C-residues of soils revealed the presence of 2,4-D as a main product together with 2,4-dichlorophenol.