** Evaluation in CCPR periodic review programme
RESIDUE AND ANALYTICAL ASPECTS
Thiram was originally evaluated in 1965 (toxicology) and 1967 (toxicology and residues) and is included in the dithiocarbamate group of compounds. It was evaluated at the present Meeting within the CCPR periodic review programme.
Thiram is a protective dithiocarbamate fungicide used as a foliar treatment on fruits, vegetables and ornamentals and as a seed treatment to control a number of fungal diseases. The Meeting was provided with information on registered uses on fruits, vegetables and other crops.
The Meeting received extensive information on the metabolism of thiram in rats, farm animals, apples, grapes, soya beans, cotton, wheat and sugar beet; environmental fate in soil and water/sediment systems, methods of residue analysis, the stability of residues in stored analytical samples, approved use patterns, supervised residue trials and the fate of residues during processing.
When animals are dosed with radiolabelled thiram much of the dose is eliminated as volatile CS2 and CO2. Dimethyldithiocarbamic acid, the initial product in animals, plants and soil, forms conjugates with natural products. The intermediate dimethyldithiocarbamoylalanine is converted to different metabolites in plants and animals.
The analytical methods for dithiocarbamates which rely on CS2 evolution may be used to determine thiram residues. Limits of determination for various commodities are usually 0.05-0.1 mg/kg (as CS2). An HPLC method specific for thiram is available for the determination of residues on crops.
Data were available on the stability of thiram residues on plums, and of thiram added to apple juice and pomace, during frozen storage.
The Meeting agreed that the definition of the residue of the dithiocarbamates should apply to thiram. For estimates of dietary intake the supervised trials median residue (STMR) will be expressed as thiram for comparison with the thiram ADI. For estimates of acute intake a residue such as an MRL, which is expressed in terms of CS2, must be multiplied by a factor of 1.58 for comparison with an acute reference dose expressed in terms of thiram.
The Meeting received data on thiram residues from supervised trials on apples, pears, peaches, plums, cherries, grapes, strawberries, dwarf French beans, French beans, Savoy cabbage, green peas, head lettuce, spinach and tomatoes. Thiram was determined by CS2 evolution methods or by HPLC, and in some trials by both methods.
Information on the fate of thiram during the processing of apples and grapes was made available to the Meeting. The thiram level in apple juice was about 30% of its level in the apples. In processing studies with grapes containing thiram residues of 1.2-4.3 mg/kg, thiram was below the LOD of 0.1 mg/kg in the wine as determined by the HPLC analytical method.
Monitoring data for dithiocarbamate residues in commodities in trade were provided from The Netherlands, Belgium and Denmark. Dithiocarbamates were detected in fewer than 15-20% of the samples of most commodities.
FURTHER WORK OR INFORMATION
Desirable
The rates of hydrolysis of thiram at various pH values should be clarified. Full copies of the reports of the studies should be made available for review.
