RESIDUE AND ANALYTICAL ASPECTS
Captan was extensively reviewed in 1994 and recommendations were made for new and revised MRLs for a number of fruits, and for tomatoes. Information was made available to the present Meeting on GAP and supervised trials in the USA on apples, cherries, grapes, nectarines, pears, plums and strawberries. The residue data were evaluated together with the relevant data evaluated in 1994 to produce revised recommendations.
MRLs for captan are for residues defined as captan. Captan breaks down under some conditions to form THPI (1,2,3,6-tetrahydrophthalimide) and when a raw agricultural commodity is found to contain captan and THPI it is likely that some captan was converted to THPI during storage of the sample. In most cases the THPI residue is a negligible or minor part of the residue and its inclusion or exclusion makes little difference. The Meeting agreed that the definition of the residue for the estimation of STMR levels should also be captan alone.
Captan is registered for use on apples in the USA at 2.2-4.5 kg ai/ha with up to 36 kg ai/ha applied in a crop cycle, equivalent to 8 applications at the maximum rate. Harvest is permitted on the day of the final application. The decline of captan residues was measured in 7 trials on apples with sampling on at least 5 occasions after the final application. The median half-life of captan from the 7 trials was 11.9 days, which suggested that an increased number of applications would not influence the final residue levels because the contribution from applications more than 40-50 days before harvest would be negligible in comparison with that from the final application. A trial with only one application at the GAP rate was also included (captan residue 14 mg/kg on the day of application).
The residues from the US trials at GAP application rates (3.4-5.0 kg ai/ha) and PHI (0-1 days) but with 1-14 applications were 3.7, 4.0, 5.7, 6.1, 6.6, 14 and 16 mg/kg.
US GAP also permits a post-harvest spray or dip for apples at 0.15 kg ai/hl, which may be used in combination with the pre-harvest treatment. In 13 US trials reported in the 1994 evaluation where captan had been used before, after, or both before and after harvest, the captan residues were 0.86, 1.4, 1.5, 2.3, 3.3, 3.9, 4.0, 4.7, 4.9, 5.2, 5.5, 5.9 and 7.7 mg/kg.
Captan trials on apples in Argentina, Brazil, Canada, Japan and the UK were evaluated against the relevant GAP for these countries in 1994. The residues from 22 trials according to GAP were 0.005, 0.44, 0.68, 0.98, 1.0, 1.4, 2.5, 2.8, 2.9, 2.9, 3.5, 3.8, 4.1, 4.2, 4.2, 4.3, 4.4, 4.5, 4.5, 4.8, 7.2 and 13 mg/kg.
The residues in rank order (median underlined) from the total of 42 trials were 0.005. 0.44, 0.68, 0.86, 0.98, 1.0, 1.4, 1.4, 1.5, 2.3, 2.5, 2.8, 2.9, 2.9, 3.3, 3.5, 3.7, 3.8, 3.9, 4.0, 4.0, 4.1, 4.2, 4.2, 4.3, 4.4, 4.5, 4.5, 4.7, 4.8, 4.9, 5.2, 5.5, 5.7, 5.9, 6.1, 6.6, 7.2, 7.7, 13, 14 and 16 mg/kg.
The Meeting estimated a maximum residue level of 20 mg/kg for captan on apples to replace the 1994 recommendation of 10 mg/kg, and an STMR level of 4.05 mg/kg.
Information from US supervised trials on pears was made available but could not be evaluated because there was no corresponding GAP.
Captan may be applied in the USA at 2.2 kg ai/ha up to 7 times to cherries, which may be harvested on the day of the final application. It may also be used as a post-harvest spray or dip at a concentration of 0.15 kg ai/hl, and the two treatments may be used in combination. Details of 7 trials according to GAP were available to the Meeting. The captan residues were 2.4, 4.3, 5.5, 14, 20, 20 and 21 mg/kg. Two trials where the application rate was 1.1 kg ai/ha (half the label rate) should also be included because residues were 16 and 17 mg/kg. In most of the trials there was no explicit description of the sample for analysis (e.g. whole fruit + stems).
Ten US trials on cherries reported in 1994 included pre-harvest, post-harvest and combined applications according to GAP. The captan residues were 7.3, 10, 11, 14, 14, 15, 19, 23, 25 and 35 mg/kg.
In summary, the captan residues in rank order (median underlined) from the 19 trials on cherries were 2.4, 4.3, 5.5, 7.3, 10, 11, 14, 14, 14, 15, 16, 17, 19, 20, 20, 21, 23, 25 and 35 mg/kg.
The Meeting estimated a maximum residue level of 40 mg/kg for captan on cherries to replace the 1994 estimate of 20 mg/kg, and an STMR of 15 mg/kg.
Data from 11 US supervised trials on nectarines could not be evaluated because the trial conditions were not sufficiently close to GAP.
US GAP permits the use of captan on plums at 3.4 kg ai/ha with harvest on the day of the final application. The total application permitted per season is 30 kg ai/ha, which corresponds to 9 applications. Data from 2 US trials on plums were reported to the Meeting and the use pattern in one of them exactly complied with GAP while in the other the application rate was correct but there were 13 applications and the PHI was 2 days. The use pattern in the 3 trials reported in the 1994 monograph complied with US GAP. The captan residues in the 5 valid trials (median underlined) were 0.45, 0.60, 0.71, 5.6 and 7.9 mg/kg.
The Meeting concluded that the results suggest that a higher limit than the present draft MRL of 5 mg/kg is required, but the database is limited. The Meeting agreed not to estimate a revised maximum residue level, but to await the periodic review of captan in 1998 when complete information on GAP and residues resulting from supervised trials should be available.
In the USA captan may be applied to grapes at 1.1-2.2 kg ai/ha with no more than 13 kg ai/ha used in a growing season, equivalent to 6 applications at the higher rate. Harvest is permitted on the day of the last application. The conditions in 9 US trials closely matched the maximum conditions of US GAP. Seven of the trials were reported to the present Meeting and 2 had been reported in 1994. The residues in the 9 trials were 1.3, 3.5, 3.7, 6.4, 7.2, 7.4, 8.4, 11 and 22 mg/kg.
Trials on grapes in Argentina, France, Germany and Japan were evaluated in 1994. The residue was 0.74 mg/kg in an Argentinian trial according to Argentinian GAP (1.3 kg ai/ha, 3 applications, 25 days PHI). A French trial and 12 German trials were evaluated against French GAP (10 applications of 3.5 kg ai/ha with a PHI of 33 days). Pre-harvest intervals of 28-38 days in these trials were accepted. The residues in the 13 trials were 1.4, 1.7, 1.7, 1.9, 2.8, 3.0, 3.6, 4.4, 6.5, 7.0, 8.3, 9.8 and 15 mg/kg. In Japan captan may be sprayed 5 times on grapes at a concentration of 0.10 kg ai/hl, with harvest 14 days after the final application. The residues on grapes from 6 Japanese trials complying with GAP were 3.2, 5.8, 6.1, 6.1, 12 and 14 mg/kg.
In summary, the residues in rank order (median underlined) from the 29 trials were 0.74, 1.3, 1.4, 1.7, 1.7, 1.9, 2.8, 3.0, 3.2, 3.5, 3.6, 3.7, 4.4, 5.8, 6.1, 6.1, 6.4, 6.5, 7.0, 7.2, 7.4, 8.3, 8.4, 9.8, 11, 12, 14, 15 and 22 mg/kg.
The Meeting estimated a maximum residue level of 25 mg/kg for captan on grapes to replace the current draft MRL of 20 mg/kg, and an STMR of 6.1 mg/kg.
US GAP permits application rates for captan on strawberries of 1.7-3.4 kg ai/ha and a PHI of 0 days, with a total application for the growing season of 27 kg ai/ha, equivalent to 8 applications at the highest rate. Six US and one Canadian trial according to the US application rate and PHI were reported to the Meeting. The number of applications varied from one to 11 but apparently the number had little effect on the residue levels. The residues in the 7 trials were 3.4, 3.9, 5.8, 6.4, 7.3, 13 and 27 mg/kg.
Trials in the USA, Canada, Chile and Hungary were recorded in the 1994 evaluations. In nine US trials complying with US GAP the residues were 1.0, 2.6, 3.9, 4.4, 5.2, 7.7, 12, 13 and 15 mg/kg. The residue was 3.0 mg/kg in a Canadian trial according to Canadian GAP (3.4 kg ai/ha, PHI 2 days). Chilean GAP allows 2 applications of 3.2 kg ai/ha and a PHI of 2 days. In trials at this rate but with 1 application and a 3-day PHI the residues were 3.8, 4.2 and 4.8 mg/kg. The residue in a Hungarian trial according to GAP (1.3 kg ai/ha, 3 applications, 10-day PHI) was 0.93 mg/kg.
In summary, captan residues in strawberries from the 21 trials (median underlined) were 0.93, 1.0, 2.6, 3.0, 3.4, 3.8, 3.9, 3.9, 4.2, 4.4, 48, 5.2, 5.8, 6.4, 7.3, 7.7, 12, 13, 13, 15 and 27 mg/kg.
The Meeting estimated a maximum residue level of 30 mg/kg for captan on strawberries to replace the 1994 estimate of 15 mg/kg, and an STMR of 4.8 mg/kg.
Information was provided to the Meeting on the fate of captan during the processing of apples and grapes.
Details of the processes for producing juice and pomace from apples were very limited. Heating and cooking are very influential on the fate of captan but no information on these operations was provided. Calculated processing factors for the production of juice, wet pomace and dry pomace from apples were 0.30, 0.48 and 0.064 respectively.
More detailed studies were provided to the 1994 JMPR, and that Meeting concluded that captan is not present in processed commodities such as apple sauce, canned apple slices, apple jelly or canned juice because it is destroyed by cooking and heating.
The supervised trials median residues for the processed commodities (STMR-Ps) calculated from the processing factors and the STMR for apples (4.05 mg/kg) were apple juice (unheated) 1.2 mg/kg, apple juice (heated) 0 mg/kg, apple sauce 0 mg/kg and dry apple pomace 0.26 mg/kg.
The Meeting also used the processing factor to estimate a maximum residue level for dry apple pomace of 2 mg/kg after rounding (maximum residue level in apples 20 x processing factor 0.064).
The processing factors for captan in the production of grape products were highly variable from one experiment to another, probably reflecting the sensitivity of captan to degradation under some heating conditions. The processing factors (mean and range) from grape processing studies supplied to the current Meeting and to the 1994 JMPR were grapes to juice 1.2 (range 0.23-4.9), grapes to wet pomace 0.94 (range 0.19-1.4), grapes to dry pomace 0.67 (range 0.12-1.7) and grapes to raisins 1.66 (range 0.11-4.8).
The STMR-Ps calculated from the processing factors and the STMR for grapes (6.1 mg/kg) were grape juice 7.3 mg/kg, dry grape pomace 4.1 mg/kg and raisins 10.4 mg/kg.
The Meeting also used the processing factor for raisins to estimate a maximum residue level for dried grapes of 50 mg/kg after rounding (maximum residue level in grapes 25 mg/kg x processing factor 1.66).