The Meeting considered the definition of thiram residues in terms of the crop metabolism studies, the supervised trials where residues had been determined by both a CS2 evolution method and an HPLC method, and the needs of enforcement agencies.
The metabolism studies suggest that thiram is the major part of the CS2-evolving residue, particularly when the residue is reasonably fresh and at the higher levels. Analyses of samples in supervised trials by the HPLC and CS2 methods are usually in good agreement, which also suggests that thiram itself is the main residue.
Thiram is different from the other dithiocarbamates because it can be determined by a specific method that measures the intact molecule and MRLs could be established for thiram separately. It would, however, be confusing for analysts and enforcement agencies interpreting analytical data for one compound to appear under two different residue definitions.
The 1995 JMPR (Report, Section 2.8.1), in explaining the current basis for the definition of residues in general, stated "Preferably no compound, metabolite or analyte should appear in more than one residue definition."
The Meeting agreed that thiram should be included in the definition of dithiocarbamate residues:
The MRLs refer to total dithiocarbamates, determined as CS
2 evolved during acid digestion and expressed as mg CS2/kg.
For dietary intake estimations the supervised trials median residue (STMR) will be expressed as thiram because estimated intakes need to be in terms of thiram itself for comparison with its ADI. For acute intake estimations a residue, such as an MRL, expressed in terms of CS2 must be multiplied by a molecular weight correction factor of 1.58 for comparison with its ADI.
