Ferbam was originally evaluated in 1965 (toxicology) and 1967 (toxicology and residues) and is included in the dithiocarbamate group of compounds. The compound was evaluated at the present Meeting within the CCPR Periodic Review Programme.
Ferbam is a broad-spectrum fungicide for the control of certain diseases in fruit trees, small fruits and berries, potatoes, ornamentals, conifers and tobacco.
The Meeting received information on the metabolism of ferbam in goats and sheep, methods of residue analysis, the stability of residues in stored analytical samples, approved use patterns, and supervised residue trials on mangoes.
When two lactating goats were dosed for 5 days with [thiocarbonyl-14C]ferbam at a rate equivalent to 220-250 ppm ferbam in the feed, the levels of 14C in the milk increased for the first 2 or 3 days of feeding and then reached a plateau. A large part of the administered 14C was not accounted for (59% and 62%). By analogy with the animal metabolism of thiram losses as CS2 and CO2 in expired air would be expected, but 14C in expired air was not measured. More of the 14C dose was in the faeces (25% and 32%) than in the urine (8.3% and 11.9%), tissues (2.7% and 5.6%) or milk (0.70% and 0.79%).
Levels of 14C were much higher in the liver (63 and 75 mg/kg ferbam equivalent) than in the kidneys (8.3 and 9.4 mg/kg), muscle (1.5 and 1.9 mg/kg), or fat (0.47-0.89 mg/kg). Most of the 14C in the milk and tissues was not extractable without protease treatment, which produced polar water-soluble compounds incorporating the 14C. Lactose and casein containing 14C were isolated from the milk.
In a sheep given a single dose of [3H]ferbam + [35S]ferbam and slaughtered 72 hours later for tissue collection more than 80% of the dosed 3H but only 23-24% of the 35S was excreted in the urine and faeces. This is consistent with the animal metabolism of thiram where 40-60% of the CS2 part of the molecule was eliminated as volatile compounds in exhaled air.
The level of 3H in the liver was much higher than in the other tissues, but the levels of 35S in the liver and kidneys were much the same. The level of 3H in the liver was much higher than that for 35S, demonstrating that the dithiocarbamic acid moiety had largely been degraded.
The analytical methods for ferbam residues are the same as those for other dithiocarbamates. They rely on acid hydrolysis to release CS2 which may then be measured by head-space gas chromatography or by spectrophotometry.
The head-space GLC methods used in the supervised trials on mangoes and the frozen storage stability studies on apples gave satisfactory recoveries of ferbam.
Ferbam residues were stable in macerated apples fortified at 1 mg/kg and stored at -20°C for 22 weeks.
Generally, the information on ferbam was quite limited. For a compound in the periodic review programme an adequate set of supporting studies is needed. Because of the absence of plant metabolism and environmental fate studies the Meeting would not have been able to recommend MRLs for dithiocarbamate residues from uses of ferbam even if adequate information on GAP and data from supervised trials had been available for some commodities.
Dithiocarbamate MRLs are derived from supervised trials on specific dithiocarbamate compounds according to the relevant GAP. The table of recommended MRLs for dithiocarbamates indicates the compound or compounds for which data have been evaluated and found to be adequate to support the recommended MRL. Because of the lack of critical supporting studies ferbam is not included in the list of dithiocarbamates with adequate data to support recommended MRLs for dithiocarbamates.
The Meeting recognised that for most dithiocarbamates there are no practical regulatory analytical methods to identify the compound producing dithiocarbamate residues in a food commodity. National governments, under approval and registration systems, may control which uses are permitted.
Ferbam residues found in the supervised trials were measured as evolved CS2 by the same methods as are used for the other dithiocarbamates. The Meeting agreed that ferbam would be included in the residue definition of the dithiocarbamates if adequate critical supporting studies become available.
The Meeting received data on residues of ferbam from two supervised trials on mangoes in the USA, but the data could not be evaluated because information on GAP for the use of ferbam on mangoes was not available.
Monitoring data for dithiocarbamate residues in commodities in trade are included in the monograph on thiram.
