Methamidophos was first evaluated in 1976, with further reviews of residue aspects in 1979, 1981, 1984, 1990 and 1994. The 1994 JMPR withdrew the previous recommendations for MRLs for broccoli, Brussels sprouts, head cabbages, cauliflower, citrus fruits, eggplant, melons except watermelon, peaches and tomato which had been held at Step 7B by the 1992 CCPR (ALINORM 93/24, para 119-123). The manufacturer indicated that information on GAP and residue data would be available to support new MRLs for these commodities. This information was provided to the Meeting, together with information on analytical methods and residues in food in commerce or at consumption.
Analytical methods
Samples from the supervised trials were analysed by GLC. Recoveries of both acephate and methamidophos were generally >70%, with limits of determination of 0.01-0.02 mg/kg.
These methods were considered suitable for use in supervised trials and for enforcement.
Stability of residues in stored analytical samples
Studies of the storage stability of acephate and methamidophos were carried out with vegetables, pulses, oilseed, animal products, cereals and grasses using samples which had been treated with acephate. The stability of methamidophos in the macerated or ground samples was not established by the results as most of the samples contained substantially higher residues of acephate than of methamidophos, and there may have been some conversion of acephate to methamidophos during storage.
Validity of data
In view of the difficulty of determining methamidophos caused by its high polarity, the Meeting did not evaluate trials which lacked data on analytical recoveries or in which recoveries were below 70%, trials without analysis of control samples and/or sample chromatograms, or trials with abnormally high control values and for which sample chromatograms were not supplied.
Supervised trials
Where data were available from applications of both methamidophos and acephate the results of trials with methamidophos are discussed first and the acephate trials are indicated by a sub-heading. Trials on citrus fruits and Brussels sprouts were with acephate only and are considered last.
Peaches. Four Italian trials with 0.6-0.68 kg ai/ha and a PHI of 21 days were according to GAP in France, Greece and/or Italy (0.38-0.68 kg ai/ha, 21 days PHI) and residues were 0.09-0.27 mg/kg. Five of the six Spanish trials (0.72-1.3 kg ai/ha, 28-35 days PHI) were according to Spanish GAP (0.75-1.1 kg ai/ha, 35 days PHI) with residues of <0.01-0.76 mg/kg. One of these, at 1.0 kg ai/ha, included a PHI of 21 days and was therefore comparable with Portuguese GAP (0.8-1.0 kg ai/ha, 21 days PHI). The residue was 0.27 mg/kg. The sixth Spanish trial was not according to Spanish GAP, but included conditions (0.6 kg ai/ha, 21 days PHI) which complied with GAP in France, Greece and Italy. The residue after 21 days was 0.09 mg/kg.
The residues in the 4 Italian trials carried out at maximum GAP were 0.09, 0.12, 0.16 and 0.27 mg/kg, and those in the five Spanish trials detailed above were 0.07, 0.09, 0.24, 0.27 and 0.76 mg/kg. The residues from the 9 trials in rank order (median underlined) were 0.07, 0.09, 0.09, 0.12, 0.16. 0.24, 0.27, 0.27 and 0.76 mg/kg.
The Meeting estimated a maximum residue level of 1 mg/kg and an STMR of 0.16 mg/kg for peaches, based on residues of methamidophos from the application of methamidophos.
Broccoli. Two Brazilian trials and one Canadian trial complied with their national GAP (Brazil 0.3-0.6 kg ai/ha, 0.06 kg ai/hl, 21 days PHI, Canada 0.53-1.1 kg ai/ha, 14 days PHI). The residues were <0.01 and 0.2 mg/kg in Brazil and 0.01 mg/kg in Canada.
Two Canadian (1972), one Mexican and nine American trials were also according to GAP (Mexico 0.6-0.9 kg ai/ha, 21 days PHI; USA 0.56-1.1 kg ai/ha, 14 or 21 days PHI). Residues were 0.13-0.41 mg/kg in Canada, 0.01-0.08 mg/kg in Mexico and 0.01-0.14 mg/kg in America. However information on analytical recoveries was lacking so the Meeting could not evaluate the trials.
Residues from the application of acephate. One Australian and two Japanese trials with acephate complied with GAP (Australia 0.98 kg ai/ha, 0.098 kg ai/hl, 14 days PHI; Japan 0.05 kg ai/hl, 14 days PHI). In the Australian trial the spray concentration of 0.21 kg ai/hl was higher than the GAP concentration but the dosage rate complied with GAP. The residues of methamidophos were <0.02-0.08 mg/kg and 0.017-0.566 mg/kg in Australia and Japan respectively. One Brazilian trial with acephate did not include data on methamidophos. Two French and two Spanish trials on acephate were reported but no information on GAP was available. An Italian trial did not comply with Italian GAP.
The Meeting could not estimate a maximum residue level.
Cabbages. One Brazilian trial complied with GAP (0.3-0.6 kg ai/ha, 0.06 kg ai/hl, 21 days PHI). The residue was 0.08 mg/kg.
Two German supervised trials with 0.36 kg ai/ha, 0-28 days PHI, and 3 applications were comparable with German GAP (0.36 kg ai/ha, 14 days PHI, 2 applications) except in the number of applications. The Meeting considered that the additional application would not have a significant effect on the results. The residues were 0.05 and 0.2 mg/kg.
The results of seven US trials submitted to the 1990 JMPR were rejected by the 1994 JMPR. The present Meeting found the trial conditions (1.1 kg ai/ha, 6 application, 21-35 days PHI) were comparable with current GAP (0.56-1.1 kg ai/ha, 35 days PHI) and could evaluate the data. The residues were <0.01 (5) and 0.01-0.03 mg/kg in six trials and 0.76-1.1 mg/kg in the seventh. The Meeting agreed not to consider the residues from the seventh trial since they seemed to be of a different population from others and because of difficulties encountered with the evaluation of data without the original studies.
Four trials in Germany were not evaluated in 1990 but the trial conditions (0.3 kg ai/ha, 2 application, 0-28 days PHI) were comparable with GAP (see above). The residues were <0.01, 0.01, 0.01 and 0.09 mg/kg at 14 days PHI.
One Argentinean and one Mexican trial were comparable with Brazilian or Mexican GAP but information on analytical recoveries was lacking so the Meeting could not evaluate the trials.
Residues from the application of acephate. Three of four French and two Japanese trials with acephate complied with their national GAP (France 0.075 kg ai/hl, 7 days PHI; Japan 0.025-0.05 kg ai/hl, 7 days PHI). The residues of methamidophos were 0.01 (2) and 0.09 mg/kg in France and 0.010 and 0.138 mg/kg in Japan.
One supervised trial on acephate in The Netherlands (0.75 kg ai/ha, 14 days PHI, 1 application) was within the limits of GAP (0.75 kg ai/ha, 14 days PHI, 6 applications) and the residues of methamidophos were 0.038-0.050 mg/kg.
The residues of methamidophos from its application according to maximum GAP were 0.08 mg/kg in Brazil, 0.01 (5) and 0.03 mg/kg in the USA and 0.01 (2), 0.01, 0.05, 0.09 and 0.2 mg/kg in Germany.
The residues of methamidophos from the application of acephate according to maximum GAP were 0.01 (2) and 0.09 mg/kg in France, 0.010 and 0.117 mg/kg in Japan and 0.05 mg/kg in The Netherlands.
The residues from 19 trials in rank order were <0.01 (7). 0.01 (4). 0.03, 0.05 (2), 0.08, 0.09 (2), 0.12 and 0.2 mg/kg.
The Meeting estimated a maximum residue level of 0.5 mg/kg and an STMR of 0.01 mg/kg, based on the residues of methamidophos from the use of acephate or methamidophos on cabbages.
Cauliflowers. Two Brazilian trials complied with GAP (0.3-0.6 kg ai/ha, 0.06 kg ai/hl, 21 days PHI). The residues were <0.01-0.5 mg/kg. Reports of three French trials were submitted without information on GAP.
Six supervised trials in Germany were reported to the 1981 JMPR. Reports of three were resubmitted to the present Meeting. The trial conditions (0.36 kg ai/ha, 2-3 applications, 0, 14, 21 and 28 days PHI) complied with GAP (0.36 kg ai/ha, 2 application, 21 days PHI). The residues were <0.01, <0.01 and 0.01 mg/kg (reported in the 1981 JMPR monograph) and <0.01, 0.01 and 0.04 mg/kg.
One supervised trial was carried out in Mexico, but there was no comparable GAP and recovery data were lacking. One American trial was reported to the Meeting and the conditions accorded with American GAP (0.56-1.1 kg ai/ha, 28 days PHI). The residue was 0.07 mg/kg, but again critical information, including recovery data, was lacking.
Residues from the application of acephate. One Australian and two Japanese supervised trials on acephate were according to national GAP (Australia 0.98 kg ai/ha, 0.098 kg ai/hl, 3 days PHI; Japan 0.05 kg ai/hl, 14 days PHI). In the Australian trial the spray concentration (0.24 kg ai/hl) was higher than the GAP concentration but the kg ai/ha rate complied with GAP. The residues of methamidophos were 0.05-0.20 mg/kg at PHIs of 3-7 days in Australia and 0.005-0.228 mg/kg at 14 days in Japan.
Five supervised trials in The Netherlands were according to GAP (0.75 kg ai/ha, 14 days PHI, 6 applications) except that there were only 1-4 applications, but it seems that the number of applications does not influence the residue significantly. The Meeting considered that the results were valid for the estimation of a maximum residue level and an STMR. The residues of methamidophos were <0.01-0.03 me/kg.
Four supervised trials in France and one in Germany were well conducted but the conditions were not comparable with any available GAP. One Brazilian trial with acephate did not include analyses for methamidophos.
The residues of the 2 Brazilian and 6 German trials with methamidophos at maximum GAP were <0.01 and 0.5 mg/kg, and 0.01(3), 0.01(2) and 0.04 mg/kg respectively. The residues of methamidophos from applications of acephate at maximum GAP were 0.2 mg/kg in Australia, 0.006 and 0.23 mg/kg in Japan and <0.01 (3), 0.03 and 0.018 in The Netherlands.
The residues from the 16 trials in rank order were 0.006, <0.01(7), 0.01(2). 0.018, 0.03, 0.04, 0.2, 0.23 and 0.5 mg/kg.
The Meeting estimated a maximum residue level of 0.5 mg/kg and an STMR of 0.01 mg/kg for residues of methamidophos in cauliflower arising from the use of acephate or methamidophos.
Melons. Two Spanish trials were reported without information on relevant GAP.
Two supervised trials in Mexico were reviewed in 1990. The trial conditions (0.6 kg ai/ha, 0, 3, 7/8, and 14 days PHI) complied with GAP (0.6-0.9 kg ai/ha, 7 days PHI) and the residues were 0.05 and 0.08 mg/kg in the whole fruit, 0.06 mg/kg in the pulp and 0.13 mg/kg in the peel. In another Mexican trial with the same conditions the residues were 0.23-1.63 mg/kg, but critical information including data on analytical recoveries was lacking.
A single supervised trial was carried out in Argentina, but there was no relevant GAP and critical information was again lacking.
The Meeting could not estimate a maximum residue level.
Egg plants. One Spanish, one Argentinean and three American trials were reported to the Meeting without information on relevant GAP.
Conditions in two Mexican trials were comparable to Mexican GAP (0.6-0.9 kg ai/ha, 14 days PHI) with residues of 0.28 and 0.95 mg/kg, but critical information was lacking.
The Meeting could not estimate a maximum residue level.
Tomatoes. An Australian trial was carried out at higher spray concentration (0.44 kg ai/hl) than GAP (0.029-0.11 kg ai/hl), but at a dose rate within the GAP range (0.32-1.2 kg ai/ha, 4 days PHI). The residues were 0.64-0.96 mg/kg at 3-5 days PHI.
Two Brazilian trials reflected GAP (0.3-0.6 kg ai/ha, 0.06 kg ai/hl, 21 days PHI) and the residues were <0.01 and 0.3 mg/kg. In one of them the residue at 14 days PHI was determined and this could be related to GAP in Chile and Ecuador where the PHI is 15 days. The residue was <0.01 mg/kg. Four French supervised trials were reported without information on GAP, but the conditions were comparable with GAP in Portugal (0.6-1.2 kg ai/ha, 21 days PHI). The residues were <0.02, 0.03-0.04, 0.05-0.06 and 0.07-0.08 mg/kg.
Twelve Spanish trials at 0.045-0.06 kg ai/hl, 7-8 days PHI, complied with Spanish GAP (0.05-0.075 kg ai/hl, 7 days PHI) but six of them showed abnormally high control values and were without sample chromatograms, so were not used for the estimation of a maximum residue level. The residues from the other 6 trials were <0.02 (2), 0.12, 0.14, 0.29 and 0.32 mg/kg.
Trials in Italy and Mexico were comparable with Greek and Mexican Gap respectively but critical information was lacking. One supervised trial in Turkey was reported to the Meeting without information on relevant GAP.
Residues from the application of acephate. One Australian, one Spanish and two Japanese supervised trials with acephate reflected national GAP (Australia 0.98 kg ai/ha, 0.098 kg ai/hl, 3 days PHI;
Japan 0.025-0.05 kg ai/hl, 1 days PHI; Spain 0.038-0.11 kg ai/hl, 14 days PHI). In the Australian trial the spray concentration (0.35 kg ai/hl) was high but the dose rate (kg ai/ha) accorded with GAP. The residues of methamidophos were 0.40 and 0.50 mg/kg in Australia and 0.03 mg/kg in Spain. In Japan the residues at 7 days (higher than at 1 and 3 days) were 0.072 and 0.106 mg/kg in one trial and 0.085 and 0.123 mg/kg in the other.
Seventeen French supervised trials with acephate were reported to the Meeting with no information on GAP, but four of them (0.62-0.83 kg ai/ha, 13-15 days PHI, 1-3 applications) could be related to Polish GAP (0.75 kg ai/ha, 14 days PHI, 1 application), since it seems that the number of application does not significantly affect the residue level. Furthermore these four and six other trials (0.03-0.075 kg ai/hl, 13-15 days PHI) were according to Spanish GAP (0.038-0.11 kg ai/hl, 14 days PHI). The residues of methamidophos at 13-21 days ranged from <0.02 mg/kg to 0.44 mg/kg.
The residues of methamidophos from its use at maximum GAP were 0.96 mg/kg in Australia, <0.01 and 0.3 mg/kg in Brazil, <0.02 and 0.08 mg/kg in France (according to Portuguese GAP) and 0.12, 0.14, 0.29 and 0.32 mg/kg in Spain.
The residues of methamidophos from the use of acephate at maximum GAP were 0.5 mg/kg in Australia, 0.089 and 0.104 mg/kg in Japan, 0.03 mg/kg in Spain, and 0.04, 0.06, 0.16 and 0.16 mg/kg in France.
The residues from the 17 trials in rank order were <0.01, <0.02. 0.03, 0.04, 0.06, 0.08, 0.089, 0.104, 0.12. 0.14, 0.16, 0.16, 0.29, 0.3, 0.32, 0.5 and 0.96 mg/kg.
The Meeting estimated a maximum residue level of 1 mg/kg and an STMR level of 0.12 mg/kg, based on the residues of methamidophos from the uses of acephate or methamidophos on tomatoes.
Residues of methamidophos in citrus fruits and Brussels sprouts resulting from the application of acephate
Citrus Fruits. Six supervised trials, two on Satsuma mandarins, two on Natsudaidai, one on Kabosu (sour orange) and one on Yuzu (lemons and limes), were carried out with acephate applied according to GAP in Japan. (0.025-0.05 kg ai/hl, 30 days PHI) The residues of methamidophos were 0.07 and 0.11 mg/kg in Satsuma mandarins, 0.06 and 0.33 mg/kg in Natsudaidai, 0.031 mg/kg in Kabosu and 0.044 mg/kg in Yuzu.
A single New Zealand residue trial with acephate on mandarins complied with GAP (0.075 kg ai/hl, 14 days PHI) and the residue of methamidophos was 0.29 mg/kg.
A trial in Greece with acephate on oranges reported without information on GAP, but the conditions (0.031 kg ai/ha, 20 days PHI) were comparable with Italian GAP (0.024-0.036 kg ai/hl, 21 days PHI). The residue of methamidophos was 0.05 mg/kg.
Since the Meeting was unable to estimate a maximum residue level for acephate in citrus fruits it could not estimate the maximum residue level of methamidophos arising from the use of acephate.
Brussels sprouts. Two Australian supervised trials with acephate were considered to be comparable with Australian GAP (0.98 kg ai/ha, 0.098 kg ai/hl, 3 days PHI) since the dose rate was 0.98 kg ai/ha although the spray concentration was high (0.21 kg ai/hl). The residues of methamidophos were 0.05-1.0 mg/kg. One of two US trials with acephate complied with US GAP (0.56-1.1 kg ai/ha, 14 days PHI). The residues of methamidophos on the trimmed heads were 0.01 and 0.02 mg/kg.
The results did not require any change of the existing CXL for Brussels sprouts (1 mg/kg).
Processing studies
Peaches. The concentration factors from 2 trials were 0.73 and 0.56 for washed fruit, 0.91 and 0.44 for juice, 0.91 and 0.33 for jam, and 0.82 and 0.22 for preserve. The mean concentration factors were respectively 0.65, 0.68, 0.62 and 0.52. The Meeting estimated STMR-P levels of 0.10, 0.11, 0.10 and 0.08 mg/kg for washed fruit, juice, jam and preserve by calculation from the STMR for peaches (0.16 mg/kg) and the mean concentration factors.
In cooking studies on tomatoes, cabbages and broccoli, 30 minutes boiling had no measurable effect on the levels of methamidophos residues.
Monitoring data
In monitoring in The Netherlands a total of 8681 samples of peaches, nectarines, grapes, strawberries, tomatoes, sweet peppers, cucumbers, lettuce, celery and beans were analysed for methamidophos during 1991-1994. Detection frequencies ranged from 0.07% for strawberries to 4.2% for nectarines and the highest mean residue was 0.02 mg/kg, found in peaches and lettuce.
Market basket surveys
Market basket surveys for methamidophos were carried out at 24 locations in the USA in 1984 and 1985. Methamidophos was found in samples of 7 of 62 of collected commodities. The highest residue was 0.26 mg/kg in a sample of green sweet peppers.
