R-residue and analytical aspects
** Evaluated within the Periodic Review Programme of the Codex Committee on Pesticide Residues
RESIDUE AND ANALYTICAL ASPECTS
Methamidophos was evaluated initially in 1976 for residues and toxicology and the latest evaluation for residues was in 1997. It was identified as a priority compound under the Periodic Review Programme of the 29th Session of the CCPR for review by the 2002 JMPR (ALINORM 97/24A). At the 31st Session of the CCPR, the Committee noted that an acute RfD would be established by the 2000 JMPR, but this was finally established only at the 2002 Meeting. The present Meeting received information on methamidophos metabolism and environmental fate, methods of residue analysis, freezer storage stability, national registered use patterns, supervised residue trials, farm animal feeding studies, fate of residues in processing and national MRLs. Some information on GAP, national MRLs and residue trials was reported by the governments of Australia, Germany and The Netherlands.
The 2002 JMPR established an ADI and acute RfD for methamidophos of 0-0.004 mg/kg bw and 0.01 mg/kg bw respectively.
Methamidophos is a broad-spectrum organophosphorus insecticide with uses on many crops. It is also formed as a metabolite of the insecticide acephate.
The following abbreviations are used for the metabolites discussed below.
DMPT = O,S-dimethyl O-hydrogen phosphorothioate
SMPAA = O-S-methyl O-hydrogen phosphoramidothioate
Animal metabolism
The Meeting received reports of studies of methamidophos metabolism in lactating goats and laying hens.
Methamidophos is rapidly metabolized and was not identified as a component of the residue in ruminant (goat) kidney, liver, muscle or fat and only at low levels in milk. In laying hens low levels of methamidophos were detected in liver and eggs.
In three lactating goat metabolism studies with [S-methyl-14C]methamidophos daily doses were administered in one, two or three parts and the interval between the last dose and slaughter ranged from 3 h to 11 days. Generally, methamidophos accounted for <3% of the 14C in milk with the majority of radioactivity incorporated into lactose, proteins/amino acids and triglycerides. In tissues, most of the 14C was incorporated into natural products: proteins, and amino acids in kidney, liver and muscle and triglycerides in fat. Methamidophos was not detected in any tissues and only low levels of the metabolites DMPT and SMPAA were detected in kidney but not in other tissues or milk.
In laying hens administered [S-methyl-14C]methamidophos, the parent compound was identified as a minor component of the 14C residues in liver (<1%) and represented <7% of the 14C residue in egg white and yolk. Natural products (lipids, proteins and amino acids) accounted for most of the 14C with only trace amounts of the metabolites SMPAA and DMPT.
Plant metabolism
The Meeting received reports of metabolism studies of methamidophos in tissue cultures of sweet potatoes and tobacco, glasshouse-grown bean, cabbage, lettuce and tomato plants and outdoor-grown lettuce, potato and tobacco plants.
Radioactivity in glasshouse-grown cabbage and tomato plants was mostly associated with natural products, mainly lipids, pigments and amino acids, although trace amounts of the metabolite DMPT were detected. Most of the residue on exposed foliage of tomato and lettuce plants was methamidophos. Methamidophos is systemic.
Comprehensive studies of the nature of the residue followed the foliar application of [S-methyl-14C]methamidophos to lettuce and potato plants. Most of the 14C residue in lettuce leaves harvested 21 days after application was methamidophos (about 66%). A minor metabolite, a conjugate of S-methyl phosphorothiolate, was detected at <2% of the 14C with the remainder associated with natural products, principally sugars and starch.
Radioactivity in potato tubers harvested 14 days after the last of four foliar sprays with [S-methyl-14C]methamidophos was essentially accounted for by incorporation into starch and other natural products; methamidophos represented only 0.2% of the total radioactive residue.
In a comparison of the decline of radioactive and methamidophos residues in field- and glasshouse-grown tobacco plants, methamidophos was also the major component of the 14C residue in glasshouse tobacco leaves. The decline in methamidophos residues was more rapid in the field (half-life 5 days) than in the glasshouse (half-life 15 days).
In both animals and plants, methamidophos undergoes hydrolysis of the ester and thioester moieties, liberating small carbon fragments to the general metabolic pool for incorporation into natural products. The main identified residue component is methamidophos per se.
Environmental fate in soil
Information was provided on the soil adsorption of methamidophos and its fate during soil photolysis, aerobic and anaerobic soil degradation, the column leaching of aged residues and field dissipation.
Methamidophos degradation on soil surfaces by photolysis occurred with a half-life of about 60 h. The major product was SMPAA with small amounts of DMPT also observed.
The half-lives of methamidophos in soil under aerobic test conditions were estimated to be £6 days in the laboratory and £3 days in the field. Degradation occurred by hydrolysis of ester and amino groups to form SMPAA and DMPT. The principal mechanism of degradation appears to be microbial metabolism.
Methamidophos and DMPT are only very weakly adsorbed by soils and can be classified as mobile. The rate of degradation both in the laboratory and in the field is such that residues are not expected to persist at detectable levels for more than a few days. Methamidophos is not persistent.
Environmental fate in water-sediment systems
The Meeting received information on the sterile aqueous hydrolysis of methamidophos and its fate in water-sediment systems.
Methamidophos is stable to hydrolysis at low pH but is readily degraded at neutral and high pH (half-life 27 and 3.2 days at pH 7 and 9 respectively).
The half-life for the degradation of methamidophos in the water-sediment systems was estimated to be 4-6 days.
In summary, chemical hydrolysis is only expected to occur in waters having high pH values. Indirect photochemical transformation of methamidophos is expected to occur but is considered to be only a minor route of degradation. Biodegradation in the aquatic environments is expected to be rapid, so that methamidophos is not expected to persist in the environment.
Analytical methods
Samples in field trials were analysed for methamidophos by solvent extraction (ethyl acetate, acetone/water and in the case of oily crops and animal commodities acetonitrile/hexane), clean-up by solvent partition and/or silica gel or gel permeation chromatography, and determination by gas chromatography with a thermionic detector. A typical LOQ was 0.01 mg/kg.
Stability of pesticide residues in stored analytical samples
The Meeting received information on the stability of methamidophos in various commodities under freezer storage (-20°C). Residues were stable in or on the following commodities (storage period, in parentheses): broccoli (9 months); lettuce (2 months); cabbage (8 months); cauliflower (6 months); Brussels sprouts (5 months); celery, peppers, peanut forage (26 months); sorghum grain (6 months); sorghum forage (10 months); rape seed, potato tubers, granules and dry peel, tomato fruit, purée and dry pomace (24 months); bovine milk, meat and fat, eggs (3 months) and poultry liver and heart/gizzard (2 months).
Methamidophos residues were not stable in cattle liver, with only 26% of the residues remaining after 3 months frozen storage.
Definition of the residue
Methamidophos is the principal residue in crops. Significant residues of methamidophos and metabolites were not observed in animal commodities. The Meeting agreed that the residue should be defined as methamidophos.
The log Pow of -0.8 and the animal metabolism and feeding studies suggest that methamidophos should not be described as fat-soluble.
Definition of methamidophos residue (for compliance with MRLs and for estimation of dietary intake):
methamidophos.
The definition applies to plant and animal commodities. Methamidophos residues may arise from the use of methamidophos and/or acephate.
Supervised trials
Supervised trials were reported for the use of methamidophos on broccoli, cabbage, cauliflower, cotton seed, fodder beet, maize, nectarines, peaches, peppers (including chili peppers), potatoes, soya beans, sugar beet and tomatoes.
Trials data or relevant GAP were not reported for the following crops with current CXLs: alfalfa forage, green (2 mg/kg), head lettuce, (1 mg/kg), and tree tomato (0.01 mg/kg). The Meeting agreed to recommend withdrawal of the CXLs for these commodities.
In cases where maximum residue levels have been estimated for acephate, it is also necessary to ensure that the resulting methamidophos residues are covered by a maximum residue level estimate for methamidophos. Residues of methamidophos arising from the use of acephate and derived from the same trials as were used to estimate the maximum residue, STMR and HR levels for acephate are reported below.
Citrus fruits
Methamidophos residues arising from the use of acephate on mandarins were 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.08, 0.09, 0.09, 0.13, 0.14, 0.15, 0.25 and 0.26 mg/kg. The Meeting estimated a maximum residue level, STMR and HR for methamidophos in mandarins of 0.5, 0.085 and 0.26 mg/kg, all based on whole fruit as insufficient information was available to estimate residues in the edible portion.
Pome fruits
Methamidophos residues in apples and pears from the use of acephate (n=13) were <0.1, <0.1, 0.03, 0.03, 0.04, 0.04, 0.06, 0.06, 0.13, 0.14, 0.16, 0.22 and 0.28 mg/kg. The Meeting estimated a maximum residue level, STMR and HR for methamidophos in pome fruits of 0.5, 0.06 and 0.28 mg/kg.
Stone fruits
Methamidophos trials on nectarines were conducted in Italy (GAP for peaches 0.03-0.06 kg ai/hl, maximum 2 sprays, PHI 35 days) and Portugal (GAP for peaches 0.6 kg ai/ha, 0.06 kg ai/hl, maximum 1 spray, PHI 35 days). No trials matched GAP as either the application rates were too low or samples were not collected after an appropriate interval.
Data reported from supervised trials on peaches in France (GAP 0.05 kg ai/hl, PHI 14-21 days), Italy, Portugal and Spain (GAP 0.05-0.08 kg ai/hl, PHI petal fall + 10 days). The trials in France and Spain did not match GAP in these countries. The Meeting decided to evaluate the trials in Spain according to the GAP of Italy and Portugal.
Four trials in Italy approximated Italian GAP with methamidophos residues of 0.04, 0.06, 0.11 and 0.13 mg/kg, all on a pulp basis (calculated whole fruit residues 0.04, 0.05, 0.11 and 0.12 mg/kg) 28 days after application at 0.05-0.06 kg ai/hl. A further six trials in Spain matched GAP in Italy and/or Portugal and showed residues of 0.01, 0.02, 0.03, 0.04, 0.09 and 0.15 mg/kg.
The residues in peaches from trials with methamidophos according to GAP were 0.01, 0.02, 0.03, 0.04, 0.04, 0.05, 0.09, 0.11, 0.12 and 0.15 mg/kg. Residues of methamidophos in peaches arising from the use of acephate according to Greek GAP were 0.09, 0.1, 0.16, 0.22, 0.28 and 0.35 mg/kg, and since this use gave higher residues than the use of methamidophos, the Meeting used the acephate data to estimate a maximum residue level, STMR and HR.
The Meeting also considered that the residues of methamidophos on peaches and nectarines treated at the same rate would be similar and noted that GAP for the use of acephate in Greece was for stone fruit which includes both peaches and nectarines. The Meeting estimated a maximum residue level, STMR and HR for peaches and nectarines of 0.5, 0.19 and 0.35 mg/kg and recommended withdrawal of the draft MRL of 1 mg/kg for peach.
Brassica vegetables
Trials reported from Belgium (no GAP), Canada (GAP 0.53-1.1 kg ai/ha, PHI 7 days for cauliflower, 14 days for broccoli), Germany (GAP 0.36 kg ai/ha, PHI 21 days), and the UK (no GAP) on broccoli and cauliflower.
No trials on broccoli matched GAP. Residues in eight trials on cauliflower from Germany approximating GAP in that country were <0.01 (5), 0.01 (2) and 0.04 mg/kg while the residue of methamidophos in one trial in Canada approximating Canadian GAP was 0.08 mg/kg.
The residues in trials according to GAP in Canada and Germany appeared to be from different populations and could not be combined for estimating a maximum residue level. Residues in cauliflower complying with GAP in Germany in rank order, median underlined, were <0.01 (5), 0.01 (2) and 0.04 mg/kg.
Residues of methamidophos in broccoli and cauliflower from the use of acephate (n=14) were <0.01(5), 0.01, 0.01, 0.03, 0.03, 0.08, 0.09, 0.1, 0.2 and 0.33 mg/kg, giving a higher maximum residue level than the trials with methamidophos. The Meeting used the acephate data to estimate a maximum residue level, STMR and HR for methamidophos in flowerhead brassicas of 0.5 mg/kg, 0.02 mg/kg and 0.33 mg/kg respectively. The estimated maximum residue level of 0.5 mg/kg is recommended to replace the existing CXL of 0.5 mg/kg for cauliflower.
Trials on head cabbage were reported from Canada (GAP 0.53-1.1 kg ai/ha, PHI 7 days) and Germany (GAP 0.36 kg ai/ha, PHI 14 days).
Residues in head cabbage in three trials in Canada approximating GAP in that country were 0.04, 0.60 and 0.62 mg/kg. Residues in eight trials on head cabbage in Germany approximating German GAP were <0.01 (2), 0.01, 0.03, 0.04, 0.07, 0.09 and 0.20 mg/kg.
The residues evaluated according to the GAP of Canada and Germany appeared to be from the same population and could be combined to estimate a maximum residue level. The residues in rank order, median underlined (n=11) were <0.01 (2), 0.01, 0.03, 0.04, 0.04, 0.07, 0.09, 0.20, 0.60 and 0.62 mg/kg.
The Meeting estimated a maximum residue level, STMR and HR for methamidophos in head cabbages of 1 mg/kg, 0.04 mg/kg and 0.62 mg/kg respectively. The maximum residue level of 1 mg/kg is recommended to replace the existing CXL of 0.5 mg/kg.
Tomatoes. Trials on tomatoes with methamidophos were reported from Brazil (no GAP), France (no GAP), Germany (no GAP), Greece (GAP 0.6-0.9 kg ai/ha, PHI 21 days), Italy (no GAP), Mexico (GAP 0.6-0.9 kg ai/ha, PHI 7 days), Spain (no GAP), Turkey (no GAP) and the USA (GAP 0.84-1.1 kg ai/ha, maximum 5.6 kg ai/ha/season, PHI 7 days).
Methamidophos residues in 18 trials in the USA matching GAP ± 30% in rank order, median underlined, were 0.05, 0.08, 0.12, 0.14, 0.14, 0.16, 0.22, 0.24, 0.26, 0.31, 0.36, 0.36, 0.42, 0.56, 0.86, 1.3, 1.4 and 1.5 mg/kg.
The Meeting estimated a maximum residue level, STMR and HR for methamidophos in tomatoes of 2 mg/kg, 0.285 mg/kg and 1.5 mg/kg respectively. The maximum residue level is recommended to replace the draft MRL of 1 mg/kg for tomato.
Peppers. In Mexico methamidophos is registered for use on peppers at 0.6-0.9 kg ai/ha with harvest permitted 14 days after the last application. In five trials in the USA matching those conditions methamidophos residues on sweet peppers were 0.04, 0.07, 0.22, 0.38 and 0.95 mg/kg.
Methamidophos residues in peppers from the use of acephate (n=9) were 0.05, 0.22, 0.24, 0.25, 0.25, 0.29, 0.34, 0.35 and 1.6 mg/kg. As the acephate trial showed higher residues the Meeting used the acephate data to estimate a maximum residue level, STMR and HR for methamidophos in peppers of 2, 0.25 and 1.6 mg/kg. The maximum residue level is recommended to replace the existing CXLs for chili peppers of 2 mg/kg and sweet peppers of 1 mg/kg.
Common beans. Residues of methamidophos in beans, except broad bean and soya bean, from the use of acephate in rank order, median underlined (n=8) were 0.01, 0.04, 0.15, 0.15, 0.19, 0.34, 0.45 and 0.54 mg/kg
The Meeting estimated a maximum residue level, STMR and HR for methamidophos in beans, except broad bean and soya bean, of 1, 0.17 and 0.54 mg/kg respectively.
Soya beans. Field trials were reported from Brazil (GAP 0.15-0.5 kg ai/ha, PHI 23 days). Residues in four trials approximating GAP were <0.01, <0.01, <0.04 and <0.04 mg/kg.
The Meeting decided that four trials were not sufficient to recommend a maximum residue level for such an important crop. However, the Meeting noted that in an additional four trials conducted at twice the maximum application rate, residues were all below the LOQ (<0.01, <0.01, <0.04, <0.04 mg/kg). Those trials were considered as support for the trials complying with GAP.
Residues of methamidophos in soya beans from the use of acephate in rank order, median underlined (n=7) were <0.01, <0.01, <0.01, <0.01, 0.02, 0.06 and 0.06 mg/kg. The Meeting noted that the residues from the use of acephate would lead to the higher estimates for a maximum residue level, STMR and HR for methamidophos in soya beans and estimated values of 0.1, 0.01 and 0.06 mg/kg respectively. The maximum residue level is recommended to replace the existing CXL of 0.05 mg/kg for soya bean (dry).
Potatoes. Field trials were reported from Canada (GAP 0.9-1.1 kg ai/ha, PHI 14 days), France (no GAP), Germany (GAP 0.5-0.6 kg ai/ha, PHI 14 days), Greece (GAP 0.045-0.09 kg ai/hl, PHI 21 days), Italy (GAP 0.57 kg ai/ha, PHI 21 days), Spain (no GAP) and the USA (GAP 0.84-1.1 kg ai/ha, maximum 4.5 kg ai/ha, PHI 14 days). The Meeting decided to evaluate the trials conducted in Spain against the GAP of Italy.
Twenty-nine trials in Germany matched GAP in that country with residues in potatoes of <0.01 (25), 0.01, 0.01, 0.02 and 0.02 mg/kg. In two trials in Greece according to GAP, residues in potatoes were <0.01 mg/kg at 21 and 22 days after application, and were also <0.01 mg/kg in two trials in Italy according to GAP, and in four trials in Spain approximating the GAP of Greece.
In 3 trials in Canada matching GAP methamidophos residues in potatoes were all <0.01 mg/kg. In 23 trials in the USA matching GAP from that country the residues were <0.01 (5) and <0.05 (18) mg/kg.
The Meeting considered that to estimate a maximum residue level the trials could be considered to come from the same population. Residues in rank order, median underlined, were <0.01 (41), 0.01 (2), 0.02 (2) and <0.05 (18) mg/kg.
The Meeting estimated a maximum residue level, STMR and HR for methamidophos in potatoes of 0.05, 0.01 and 0.02 mg/kg respectively. The estimated maximum residue level of 0.05 mg/kg confirms the existing CXL.
Sugar beet. Field trials on sugar and fodder beet were reported from France (no GAP), Germany (GAP 0.36-0.48 kg ai/ha, PHI 28 days), Greece (no GAP), Italy (GAP 0.4-0.57 kg ai/ha, PHI 21 days) and Spain (no GAP). The Meeting evaluated the trials in France against the GAP of Germany.
Two trials in France and three in Germany matched GAP in Germany with residues in sugar beet roots (only 4 results at GAP PHI) of <0.01 (3) and 0.01 mg/kg, and in tops of 0.9, 1.4, 1.5, 2.3 and 6.1 mg/kg. In six trials in Germany according to GAP, residues in fodder beet were all <0.01 mg/kg at 28 days after application and in tops 0.49, 0.54, 2.1, 2.8, 2.9 and 3.1 mg/kg. The Meeting agreed to combine the trials results for sugar and fodder beet to give a combined data set of <0.01 (9) and 0.01 mg/kg and estimated a maximum residue level, STMR and HR for methamidophos in sugar and fodder beet of 0.02, 0.01 and 0.01 mg/kg respectively. The maximum residue level of 0.02 mg/kg for sugar beet is recommended to replace the existing CXL of 0.05 mg/kg.
Residues in beet leaves or tops on a fresh weight basis from the combined trials approximating GAP and arranged in rank order, median underlined, were 0.49, 0.54, 0.9, 1.4, 1.5, 2.1, 2.3, 2.8, 2.9, 3.1 and 6.1 mg/kg. Allowing for an average dry weight of 23%, the Meeting estimated a maximum residue level, an STMR and HR for methamidophos in sugar and fodder beet leaves or tops of 30, 9.1 and 26.5 mg/kg respectively on a dry weight basis. The estimate of a maximum residue level of 30 mg/kg for sugar beet leaves or tops is recommended to replace the existing CXL of 1 mg/kg.
Globe artichokes. Methamidophos residues in globe artichokes from the use of acephate (n=4) were 0.02, 0.02, 0.04 and 0.08 mg/kg. The Meeting estimated a maximum residue level, STMR and HR for methamidophos in globe artichokes of 0.2, 0.03 and 0.08 mg/kg.
Maize. Field trials were reported from Germany (4 trials: no GAP), Greece (4 trials: GAP 0.6-0.8 kg ai/ha, PHI 21 days) and Spain (4 trials: GAP 0.05-0.08 kg ai/hl, PHI 35 days).
A single trial in Spain approximated GAP ± 25% for that country with residues of <0.01 mg/kg in both the cob and grain. The Meeting agreed that the available data were insufficient to estimate a maximum residue level.
Cotton seed. Trials on cotton in Brazil (GAP 0.21-1.2 kg ai/ha, PHI 21 days), India (no GAP) and the USA (GAP 0.11-1.12 kg ai/ha, PHI 50 days) were reported to the Meeting.
In one trial in Brazil, with 21 days PHI methamidophos residues in cotton seed were below the LOQ (0.01 mg/kg).
In 15 US trials matching the GAP of the USA residues in fuzzy seed in rank order, median underlined, were <0.01 (9), 0.01, 0.05, 0.06, 0.06, 0.09 and 0.16 mg/kg.
The Meeting decided that the Brazilian trial could be combined with the USA trials to estimate a maximum residue level, HR and STMR. Residues in cotton seed in rank order, median underlined, were <0.01 (11), 0.01, 0.05, 0.06, 0.06, 0.09 and 0.16 mg/kg.
Residues in cotton gin trash were 0.1, 0.2, 0.2, 0.35, 0.69, 0.85, 0.9, 1.5, 4.3 and 7.7 mg/kg.
The Meeting estimated a maximum residue level, STMR and HR for methamidophos in cotton seed of 0.2, 0.01 and 0.16 mg/kg respectively. The maximum residue level of 0.2 mg/kg for cotton seed is recommended to replace the existing CXL of 0.1 mg/kg.
Processing
Processing studies with methamidophos on apples, peaches, tomatoes, potatoes, soya beans, sugar beet and cotton seed were reported, together with a range of studies on the effects of washing, cooking or dehydration on residues in brassica vegetables, tomatoes, peppers and potatoes.
Two studies on peaches investigated residues in home-prepared jam as well as simulated commercially produced preserve and juice. With initial residue levels of 0.1 mg/kg, processing factors were estimated for washed peaches (0.75), jam (0.62), juice (0.33) and preserve (0.52).
The transfer of residues from field-treated raw tomatoes to juice, purée, paste and pomace, as well as the effect of canning on incurred residues, was investigated using simulated commercial practices. The Meeting estimated average processing factors for processed tomato commodities of: 0.74 for juice, 0.84 for purée, 0.8 for wet pomace and 3.8 for dry pomace.
The Meeting derived processing factors of 13.5 for soya bean hulls, 1.6 for soya bean meal and 0.75 for soya bean flakes, based on a processing study in which soya beans treated with methamidophos in a field trial in the USA, containing initial residues of 0.08 mg/kg methamidophos, were processed using procedures that simulated commercial practice. No residues were detectable in any of the oil fractions or in the soapstock.
The Meeting estimated a maximum residue level, HR and STMR for methamidophos in soya beans to accommodate methamidophos residues arising from the use of acephate. As some acephate may be converted to methamidophos on processing, the relevant processing factors for the estimation of residues in crude soya bean oil (<0.5) and animal feed commodities (2.0 for soya bean meal and 4.5 for soya bean hulls) were based on the acephate processing study.
One processing study with sugar beet was reported in which sugar beet roots from a field trial in the USA, containing 0.05 mg/kg methamidophos, were processed into juice, pulp, molasses and sugar. The Meeting noted that no residues were detectable in any of the fractions analysed.
Cotton seed from a residue trial in the USA in which fivefold rates of methamidophos were applied, was processed in a way that simulated commercial practice. Initial residues in the cotton seed were 0.74 mg/kg and no residues were detectable in the crude or refined oil, or the soapstock. Residues were found in the meal and hulls, and the Meeting estimated processing factors of 0.014 for cotton seed oil (crude), 0.58 for cotton meal and 0.76 for cotton hulls.
Farm animal dietary burden
The Meeting estimated the dietary burdens of methamidophos residues for livestock using the diets in Appendix IX of the FAO Manual. The calculation from MRLs or HRs in feed provides the feed levels suitable for estimating animal commodity maximum residue levels, while the calculation from feed STMRs is suitable for the estimation of animal commodity STMRs.
Maximum burden
|
Commodity |
MRL or HR |
Group |
% DM |
MRL ÷ DM |
Chosen diets, % |
Residue contribution, mg/kg |
||||
|
Beef |
Dairy |
Poultry |
Beef |
Dairy |
Poultry |
|||||
|
Apple pomace, wet |
0.28×1.35 = 0.378 |
AB |
40 |
0.945 |
|
|
|
|
|
|
|
Potato culls |
0.02 |
VR |
20 |
0.1 |
|
|
|
|
|
|
|
Potato processed waste |
0.02 |
AB |
15 |
0.13 |
|
|
|
|
|
|
|
Beet, fodder tops |
6.1 |
AV |
23 |
26.5 |
20 |
10 |
|
5.3 |
2.65 |
|
|
Cotton seed |
0.16 |
SO |
88 |
0.18 |
25 |
25 |
|
0.045 |
0.045 |
|
|
Cotton gin by-products |
7.7 |
AM |
90 |
8.56 |
|
|
|
|
|
|
|
Cotton meal |
0.16×0.58 = 0.093 |
- |
89 |
0.104 |
|
|
20 |
|
|
0.0208 |
|
Cotton hulls |
0.16×0.76 = 0.122 |
AM |
90 |
0.135 |
|
|
|
|
|
|
|
Soya bean seed |
0.06 |
VD |
89 |
0.067 |
|
|
20 |
|
|
0.0134 |
|
Soya bean meal |
0.06×2.0 = 0.12 |
AL |
92 |
0.13 |
|
|
|
|
|
|
|
Soya bean hulls |
0.06×4.5 = 0.27 |
AL |
90 |
0.3 |
|
|
|
|
|
|
|
TOTAL |
|
|
|
|
45 |
35 |
40 |
5.3 |
2.7 |
0.0342 |
STMR burden
|
Commodity |
STMR |
Group |
% DM |
STMR ÷ DM |
Chosen diets, % |
Residue contribution, mg/kg |
||||
|
Beef |
Dairy |
Poultry |
Beef |
Dairy |
Poultry |
|||||
|
Apple pomace, wet |
0.06×1.35 = 0.081 |
AB |
40 |
0.2025 |
|
|
|
|
|
|
|
Potato culls |
0.01 |
VR |
20 |
0.05 |
|
|
|
|
|
|
|
Potato processed waste |
0.01 |
AB |
15 |
0.067 |
|
|
|
|
|
|
|
Beet, fodder tops |
2.1 |
AV |
23 |
9.1 |
20 |
10 |
|
1.82 |
0.91 |
|
|
Cotton seed |
0.01 |
SO |
88 |
0.011 |
25 |
25 |
|
0.00275 |
0.00275 |
|
|
Cotton gin by-products |
0.77 |
AM |
90 |
0.86 |
|
|
|
|
|
|
|
Cotton meal |
0.01×0.58 = 0.0058 |
- |
89 |
0.0065 |
|
|
20 |
|
|
0.0013 |
|
Cotton hulls |
0.01×0.76=0.0076 |
AM |
90 |
0.008 |
|
|
|
|
|
|
|
Soya bean seed |
0.01 |
VD |
89 |
0.0122 |
|
|
20 |
|
|
0.0024 |
|
Soya bean meal |
0.01×2 = 0.02 |
AL |
92 |
0.022 |
|
|
|
|
|
|
|
Soya bean hulls |
0.01×4.5= 0.045 |
AL |
90 |
0.05 |
|
|
|
|
|
|
|
TOTAL |
|
|
|
|
45 |
35 |
40 |
1.82 |
0.91 |
0.0037 |
The methamidophos dietary burdens for estimating animal commodity maximum residue levels and STMRs (residue levels in animal feeds expressed on dry weight) are beef cattle 5.3 and 1.8 ppm, dairy cattle 2.7 and 0.91 ppm and poultry 0.034 and 0.0037 ppm.
Farm animal feeding studies
The Meeting received information on the residue levels arising in animal tissues and milk when dairy cows were dosed with methamidophos for 28 days at the equivalent of 0.2, 1.0 and 5.0 ppm in the diet. Residues in tissues were all <0.01 mg/kg. Owing to the interval between sample collection and analysis, liver residues were estimated to be <0.07 mg/kg from the rate of decomposition of residues in liver during frozen storage and the storage period. In a supplementary study residues in liver after dosing for 30 days at 10 and 20 ppm in the diet were <0.01 mg/kg for the 10 ppm dose group and up to 0.03 mg/kg for the 20 ppm dose group. Residues in milk were a maximum of 0.021 mg/kg from the 5 ppm feeding level.
The Meeting also received information on the residue levels arising in tissues and eggs when laying hens were dosed with methamidophos for 28 days at the equivalent of 2, 6 and 20 ppm in the diet. Residues in composite tissue and egg samples were highest in eggs. Transfer factors based on average residues in tissues and eggs from the 20 ppm feeding level were 0.0001, 0.00015, 0.0002, 0.0009, 0.0011, 0.002 and 0.006 for fat, liver, kidney, skin, heart/gizzard, muscle and eggs respectively.
Maximum residue levels and STMRs in animal commodities
The maximum dietary burdens for beef and dairy cattle are 5.3 and 2.7 ppm respectively, so the levels of residues in tissues and milk can be obtained from the highest residues in tissues and the mean residue in milk at the 5 ppm feeding level (10 ppm for liver) and by noting the results of the metabolism study on lactating goats. The maximum residues expected in tissues are <0.01 mg/kg and the mean residue in milk is 0.011 mg/kg.
The Meeting estimated maximum residue levels in meat (from mammals other than marine mammals) of 0.01* mg/kg; in edible offal (mammalian) of 0.01 (*) mg/kg, and in milks of 0.02 mg/kg. These are recommended to replace the existing CXLs of 0.01 (*) mg/kg for cattle fat, cattle meat, goat meat, goat fat, sheep meat, sheep fat and milks.
The STMR dietary burdens for beef and dairy cattle are 1.8 and 0.91 ppm respectively. The estimated STMRs are meat (from mammals other than marine mammals) <0.01 mg/kg, fat (from mammals other than marine mammals) <0.01 mg/kg, edible offal (mammalian) <0.01 mg/kg and milks <0.01 mg/kg.
The highest individual tissue residue from the relevant feeding group was used in conjunction with the highest residue dietary burden to calculate the highest likely residue level in the animal commodity.
|
Dietary burden (ppm)1 |
Methamidophos residues, mg/kg3 |
|||||||||
|
Milk |
Fat |
Muscle |
Liver4 |
Kidney |
||||||
|
mean |
high |
mean |
high |
mean |
high |
mean |
high |
mean |
||
|
MRL beef |
(5.3) |
|
(<0.01) |
|
(<0.01) |
|
(<0.01) |
|
(<0.01) |
|
|
MRL dairy |
(2.7) |
(0.011) |
|
|
|
|
|
|
|
|
|
STMR beef |
(1.8) |
|
|
(<0.01) |
|
(<0.01) |
|
(<0.01) |
|
(<0.01) |
|
STMR dairy |
(0.91) |
(<0.01) |
|
|
|
|
|
|
|
|
1 Values in parentheses are the estimated dietary burdens
2 Values in square brackets are the actual feeding levels in the feeding study
3 Residue values in parentheses in italics are interpolated from the dietary burden, feeding levels in the feeding study and the residues found in the feeding study. High is the highest individual tissue residue in the relevant feeding group. Mean is the mean tissue or milk residue in the relevant feeding group.
4 The dietary level for liver in the feeding study was 10 ppm for the estimation of both the maximum residue level and the STMR
The maximum dietary burden for poultry is 0.034 ppm. The levels of residues in tissues and eggs are all expected to be <0.01 mg/kg at this level.
The Meeting estimated maximum residue levels of 0.01 (*) mg/kg for poultry meat, poultry offal and eggs.
As no residues are expected at the maximum feeding level in poultry, the STMRs for poultry meat, edible offal and eggs are estimated to be zero.
DIETARY RISK ASSESSMENT
Long-term intake
The evaluation of methamidophos has resulted in recommendations for maximum residue levels and STMRs for raw and processed commodities. Consumption data were available for 17 food commodities and were used in the dietary intake calculation. The results are shown in Annex 3.
The International Estimated Daily Intakes for the 5 GEMS/Food regional diets based on STMRs were in the range 0-10% of the maximum ADI of 0.004 mg/kg bw (Annex 3). The Meeting concluded that the long-term intake of residues of methamidophos from uses that have been considered by the JMPR is unlikely to present a public health concern.
Short-term intake
The international estimated short-term intake (IESTI) of methamidophos was calculated for the food commodities (and their processed fractions) for which HRs arising from the use of methamidophos and acephate were estimated and for which consumption data were available. The results are shown in Annex 4.
The IESTI varied from 0 to 150% of the acute RfD (0.01 mg/kg bw) for the general population and from 0 to 410% of the acute RfD for children aged 6 years and below. The short-term intakes for cabbage, sweet peppers and tomatoes were 120% to 150% of the acute RfD for the general population. For children 6 years and below, short-tem intakes of between 110% and 410% of the acute RfD for broccoli, cauliflower, apples, sweet peppers, cabbages and tomatoes. The information provided to the Meeting precluded a conclusion that the acute dietary intake for these commodities would be below the acute RfD.
The Meeting concluded that the short-term intake of residues of methamidophos arising from the uses of methamidophos that have been considered by the JMPR is unlikely to present a public health concern, with the exception of cabbage (head) and tomatoes.
