TOXICOLOGY
Glyphosate was evaluated toxicologically by the 1986 JMPR, which allocated an ADI of 0-0.3 mg/kg bw.
The primary degradation product of glyphosate in plants, soil, and water, is aminomethylphosphonic acid (AMPA), whose chemical structure is very similar to that of glyphosate. AMPA itself has no commercial use. On the basis of the low residual levels of AMPA in crops which are susceptible to glyphosate the 1986 Joint Meeting concluded that AMPA could be omitted from the definition of the residue when considering recommendations for MRLs, but recent supervised trials on the application of glyphosate to crops genetically modified to be glyphosate-resistant have shown that AMPA can be the main residue. As residues of AMPA may therefore be of toxicological concern, the compound was evaluated by the present Meeting.
After oral administration of AMPA to rats, 20% of the dose was absorbed and excreted unmetabolized in the urine within 120 h (17% of the dose within 24 h), and 73% of the dose was eliminated in the faeces. Only 0.07% of the dose was excreted as expired carbon dioxide within 24 h, and 0.06% was recovered from tissues after 120 h. Minor amounts (1-6 m g/kg) were found in tissues after 120 h.
AMPA is slightly hazardous to rats given a single oral dose, with an LD50 of 8300 mg/kg bw.
In a 90-day study of toxicity, rats received AMPA in the diet at 0, 400, 1200, or 4800 mg/kg bw per day. A significant, dose-related decrease in body-weight gain was seen in males at the two highest doses and in females at the highest dose. The two highest doses also resulted in significantly increased lactate dehydrogenase activity, whereas aspartate aminotransferase activity and cholesterol levels were significantly increased only at the highest dose. Urinalysis showed a significant decrease in urinary pH and increased amounts of calcium oxalate crystals in the urine of animals at the highest dose. Dose-related irritation of the mucosal and submucosal layers of the urinary tract, corresponding to hyperplasia of the urinary bladder, was seen in rats at 1200 and 4800 mg/kg bw per day, the effect being more marked in males than in females. In addition, epithelial hyperplasia in the renal pelvis was observed at the highest dose. The NOAEL was 400 mg/kg bw per day.
In a 90-day study of toxicity in dogs receiving AMPA at 0, 10, 30, 100, or 300 mg/kg bw per day in gelatin capsules, no statistically significant treatment-related changes were observed. The NOAEL was thus the highest dose, 300 mg/kg bw per day. It should be noted that in a one-month range-finding study with groups of only two male and two female dogs, changes in some haematological parameters (e.g. decreased haemoglobin and PCVs, decreased erythrocyte counts) were seen in animals at 300 or 1000 mg/kg bw per day. These effects were not reproduced in the 90-day study.
No indication of genotoxic activity was seen in studies of gene mutation in bacteria, of DNA repair in bacteria and mammalian cells in vitro, or of micronucleus formation in vivo. No assays for gene mutation were performed in mammalian cells in vitro, but the structural similarity of AMPA to glyphosate and the negative results of genotoxicity assays of glyphosate, including one for gene mutation in mammalian cells in vitro, indicate that such an assay with AMPA would be redundant.
In a study of developmental toxicity, rats received AMPA at 0, 150, 400, or 1000 mg/kg bw per day in corn oil by gavage. Dose-related increases in the incidences of soft stools, mucoid faeces, and hair loss were seen in dams at the two higher doses. Dams at the highest dose also had short periods of decreased body-weight gain and food consumption. Fetal body weight was decreased at 1000 mg/kg bw per day. No teratogenic effects were observed. Dams at 150 mg/kg bw per day also had an increased incidence of soft stools; however in the absence of any associated effects, such as hair loss or mucoid faeces, the Meeting considered this dose to be the NOAEL for maternal toxicity. The NOAEL for developmental toxicity was 400 mg/kg bw per day.
AMPA did not induce dermal or ocular irritation in rabbits.
No long-term study of the toxicity or carcinogenicity of AMPA has been carried out, but in the more recent of two such studies with technical-grade glyphosate in rats at dietary levels of 0.2, 0.8, or 2%, the AMPA content of the test compound was given, namely 0.68%. At the highest dose of 2% glyphosate in the diet, females showed decreased body-weight gain and males showed an increased incidence of degenerative lenticular changes. The NOAEL for technical-grade glyphosate was 0.8% in the diet, corresponding to 400 mg/kg bw per day for glyphosate and 2.7 mg/kg bw per day for AMPA. No increase in tumour incidence was seen in this study (as evaluated by the International Programme on Chemical Safety (IPCS)1).
No multigeneration study of the reproductive toxicity of AMPA has been reported, but in a recent two-generation study in rats with technical-grade glyphosate at dietary levels of 0.2, 1, or 3%, the test compound contained 0.61% AMPA. At the highest dose, soft stools, decreased parental body weights, slightly decreased litter sizes, and decreased pup weights were observed. The NOAEL was 1% in the diet, corresponding to 740 mg/kg bw per day glyphosate and 4.5 mg/kg bw per day AMPA (as evaluated by IPCS1).
1WHO (1994) Glyphosate (Environmental Health Criteria 159), Geneva
Glyphosate and AMPA have very similar chemical structures. Studies of the metabolism of glyphosate in experimental animals indicate that essentially none is biotransformed into AMPA. Toxicological data on the metabolite are therefore essential for risk assessment. The Meeting compared the toxicity profile of AMPA with that of glyphosate and concluded that the major targets of the toxicity of AMPA had been investigated. The results showed little toxicity. The Meeting concluded that the two compounds have similar toxicological profiles and considered that a full database on AMPA is unnecessary. AMPA was considered to be of no greater toxicological concern than its parent compound. The Meeting established a group ADI for AMPA alone or in combination with glyphosate of 0-0.3 mg/kg bw on the basis of the 26-month study of toxicity in rats fed technical-grade glyphosate, using a safety factor of 100 (see 1986 JMPR report and toxicological evaluations, FAO/WHO, 1986d, 1987a).
Since the last JMPR evaluation for toxicity in 1986, new data have become available on glyphosate, some of which are evaluated in EHC 159. The Meeting therefore recommended that glyphosate be re-evaluated by the JMPR.
A toxicological monograph on AMPA was prepared.
TOXICOLOGICAL EVALUATION
Levels that cause no toxic effect
AMPA
|
Rat: |
400 mg/kg bw per day (90-day study of toxicity) |
|
|
150 mg/kg bw per day (maternal toxicity in a study of developmental toxicity) |
|
|
400 mg/kg bw per day (fetal toxicity in a study of developmental toxicity) |
|
| |
|
Dog: |
300 mg/kg bw per day (highest dose in 90-day study of toxicity) |
Glyphosate (from 1986 JMPR)
|
Mouse: |
0.5% in the diet, equal to 814 mg/kg bw per day (two-year study of toxicity and carcinogenicity) |
|
| |
|
Rat: |
31 mg/kg bw per day (26-month study of toxicity and carcinogenicity) |
|
| |
|
Dog: |
500 mg/kg bw per day (one-year study of toxicity) |
Estimate of acceptable daily intake for humans
0-0.3 mg/kg bw (sum of glyphosate and AMPA)
Toxicological criteria for setting guidance values for dietary and non-dietary exposure to aminomethylphosphonic acid (AMPA)
|
Human exposure |
Relevant route, study type, species |
Results/remarks |
|
Short-term (1-7 days) |
Oral toxicity, rat |
LD50 = 8300 mg/kg bw |
|
Skin irritation, rabbit |
Not irritating |
|
|
Eye irritation, rabbit |
Not irritating |
|
|
Skin sensitization |
No data |
|
|
Medium-term (1-26 weeks) |
Repeated oral, 90 days, toxicity, rat |
NOAEL = 400 mg/kg bw per day: urinary tract changes |
|
NOAEL = 150 mg/kg bw per day: maternal toxicity |
||
|
Repeated oral, developmental toxicity, rat |
NOAEL = 400 mg/kg bw per day: developmental toxicity. |
|
|
Repeated oral, reproductive toxicity |
No data |
|
|
Long-term (> 1 year) |
Repeated oral, toxicity |
No data |
RESIDUE AND ANALYTICAL ASPECTS
Glyphosate was first evaluated in 1986, and residue aspects were reviewed in 1987, 1988 and 1994. Maximum residue levels were estimated for kiwifruit and a range of vegetables, cereals, oilseeds and animal products.
The 1997 JMPR was requested to evaluate the new uses of glyphosate on cotton, maize and sorghum according to GAP. These new uses are (1) pre-harvest topical applications and (2) in-crop applications to cotton and maize crops which have been genetically modified to be resistant to glyphosate. Relevant data on metabolism and residue trials were submitted to the Meeting.
Genetic modification of crops
Glyphosate binds to and blocks the activity of 5-enolpyruvoyl-shikimate-3-phosphate synthase (EPSPS), an enzyme of the aromatic amino acid biosynthetic pathway. Glyphosate inhibition of EPSPS prevents the plant from synthesizing the aromatic amino acids essential for protein production, Glyphosate-resistant EPSPS is derived from Agrobacterium sp. strain CP4 (CP4 EPSPS), and has been used to develop glyphosate-resistant (i.e. glyphosate-tolerant) crops.
While CP4 EPSPS has been successful in providing glyphosate resistance in cotton, its activity alone has been insufficient to ensure adequate resistance in other crops. In maize, a second mechanism has been developed to ensure sufficient levels of crop resistance to allow applications of glyphosate at rates necessary for effective weed control. The second mechanism is glyphosate inactivation, which effectively reduces cellular levels of glyphosate by converting it to aminomethylphosphonic acid (AMPA). The enzyme responsible for glyphosate inactivation is glyphosate oxidoreductase (gox). The gene encoding gox was isolated from a naturally-occurring bacterium, Achromobacter sp., and has been modified to optimize its expression in plants.
Plant metabolism
Numerous plant metabolism studies with vegetable, orchard tree, nut tree and pasture crops were reported to the 1986 JMPR. The 1986 Meeting concluded that glyphosate applied to the soil was absorbed very slightly or not at all by the crops examined and its conversion to AMPA, the primary metabolite, was not observed.
However, hydroponic administration allows sufficient uptake of glyphosate to elucidate its metabolism in plants. Metabolic studies with glyphosate in hydroponically-grown maize, wheat, cotton and soya beans have shown the conversion of glyphosate to AMPA and further degradation in plant tissues.
Metabolic studies in plants that have been genetically modified to be resistant to glyphosate show that the metabolism is the same as in susceptible plants. Glyphosate is metabolized to AMPA, which is either non-selectively bound to natural plant constituents, further degraded to one-carbon fragments that are incorporated into natural products, or conjugated with naturally-occurring organic acids to give trace-level metabolites. The metabolites are the same in resistant and susceptible crops but their relative distribution depends on the speed and extent of conversion to AMPA.
Methods of residue analysis
Glyphosate and its major metabolite AMPA can be determined by GLC or HPLC after derivatization. In the GLC method evaluated by the 1986 JMPR, clean-up on anion exchange, cation exchange and carbon columns is followed by trifluoroacetylation and methylation. The limit of determination was 0.05 mg/kg in cotton seed and hay and recoveries of glyphosate and AMPA respectively at 0.05-0.4 mg/kg fortification levels were 66.3-89.4% and 66.0-84.9% in cotton hay, and 56.7-74.8% and 63.4-93.2% in cotton seed.
HPLC methods were discussed in the 1986 and 1994 monographs. The preferred method employs two-column switched HPLC with a post-column reactor. The limit of determination was 0.05 mg/kg in all commodities and mean recoveries were 77-88% for glyphosate and 78-90% for AMPA.
Residues of AMPA in or on crops and definition of the residue
The Meeting received data on supervised trials on maize into which the gox gene had been introduced, which showed that residue levels of AMPA were much higher than those in normal crops.
The Meeting agreed to recommend two MRLs for residues in maize, one as glyphosate to accommodate uses on glyphosate-susceptible crops and the other as AMPA to accommodate uses on glyphosate-resistant crops. A violation would occur if either MRL were exceeded.
The current definition of the residue is "glyphosate" because residues of AMPA in crops are usually very low or undetectable, except in soya beans.
The Meeting agreed that the definition of the residue for estimations of dietary intake should include AMPA but the definition for enforcement purposes for all commodities, including genetically modified crops, should remain as "glyphosate" for the following reasons.
1. Already many commodities have CXLs based on the residue defined as glyphosate. All existing CXLs would have to be reviewed if the definition of the residue were changed.2. It is not thought appropriate to establish a separate definition of the residue for maize.
3. The existing definition of the residue has already been incorporated into many national regulations, and a change of the definition would be likely to cause difficulties in international harmonization.
The Meeting also noted the significant residue levels of AMPA that occurred in soya beans, and recommended that their significance should be evaluated in a future periodic review even though they are not believed to pose any risk to consumers.
Supervised trials
In the following text the sum of glyphosate + AMPA expressed as glyphosate is referred to as "total glyphosate". The total glyphosate residue was evaluated to estimate STMRs for the assessment of dietary intake.
Cotton. Twelve supervised trials were carried out on glyphosate-susceptible cotton in the USA with pre-harvest application at 3.4 kg ai/ha. US GAP allows pre-emergence (crop) application (including pre-plant or at-planting applications), post-directed application (post-crop-emergence, directed at weeds), spot treatment and pre-harvest application at 4.2 kg ai/ha as the maximum for each treatment. The total application is restricted to 6.7 kg ai/ha per year.
Six of the trials were with pre-emergence and post-emergence applications before a pre-harvest application. The pre-emergence application rate (6.7 kg ai/ha) and the total applied (10-26 kg ai/ha) exceeded the GAP limits, but the Meeting concluded that these trials were comparable with GAP because the rate of the pre-harvest application (3.4 kg ai/ha), which should be most influential on the residue in the harvested crops, was within the GAP rate of 4.2 kg ai/ha and the studies of plant metabolism indicated that the uptake of glyphosate from soil would be negligible. The other six trials with only one pre-harvest application at 3.4 kg ai/ha were according to GAP.
Sixteen supervised trials, with three different application patterns in each, were carried out on glyphosate-resistant cotton in the USA with 4 or 5 applications which included pre-emergent, post-emergent, post-directed and pre-harvest treatments. Eleven trials were with genotype 1445 cotton and five with genotype 1698 cotton but these have the same basic genetic structure and would be expected to show no differences in glyphosate metabolism.
All the application patterns slightly exceeded US GAP: post-emergence (trials: 0.84-1.26 kg ai/ha, GAP: 0.84 kg ai/ha), post-directed (trials: 1.26 kg ai/ha, GAP: 0.84 kg ai/ha), and total application (trials 7.56-8.8 kg ai/ha, GAP: 6.7 kg ai/ha), but the Meeting again concluded that the trials complied with GAP because the most influential final applications were compatible with GAP and earlier applications would be unlikely to have much effect on the residues.
In susceptible cotton seed the residues of glyphosate were 0.54-5.9 mg/kg at 5-9 days and 0.15-3.6 mg/kg at 10-14 days, and those of AMPA were <0.05-0.20 mg/kg at 5-14 days. The residues of total glyphosate were 0.62-6.0 mg/kg at 5-9 days and 0.23-3.7 mg/kg at 10-14 days, and of total glyphosate after maximum GAP treatments 0.62, 0.71, 2.4, 2.8, 3.0 and 6.0 mg/kg.
In resistant cotton seed the residues of glyphosate were 0.13-5.0 mg/kg at 6-9 days and 0.30-0.50 mg/kg at 17 days, and those of AMPA were <0.05-0.21 mg/kg at 7-9 days. The residues of total glyphosate were 0.21-5.2 mg/kg at 6-9 days and 0.38-0.58 mg/kg at 17 days. Those of total glyphosate after maximum GAP treatments were 0.21, 0.30, 0.42, 0.49, 0.51 (2), 0.52, 0.54, 0.55, 0.66, 0.68, 0.73, 0.75, 0.77 (2), 1.1 (2), 1.3, 1.4, 1.5, 1.8, 1.9, 2.1 (2), 2.2, 2.3, 2.5, 2.6 (3), 2.8, 2.9 (2), 3.2, 3.5, 3.7, 3.8, 4.2 (2), 4.4, 4.7 and 5.2 mg/kg.
Since the differences between both the median and maximum total glyphosate residues in resistant and susceptible crops were not significant, the Meeting based the STMR on the combined residues from the two sets of trials.
The total glyphosate residues from the 48 individual trials which complied with GAP (six on susceptible cotton and 42 on resistant cotton) in rank order (median underlined) were 0.21, 0.30, 0.42, 0.49, 0.51 (2), 0.52, 0.54, 0.55, 0.62, 0.66, 0.68, 0.71, 0.73, 0.75, 0.77 (2), 1.1 (2), 1.3, 1.4, 1.5, 1.8, 1.9, 2.1 (2), 2.2, 2.3, 2.4, 2.5, 2.6 (3), 2.8 (2), 2.9 (2), 3.0, 3.2, 3.5, 3.7, 3.8, 4.2 (2), 4.4, 4.7, 5.2 and 6.0 mg/kg.
The Meeting estimated an STMR level of 2.0 mg/kg total glyphosate. Taking into account the residues of glyphosate alone in susceptible (0.54-5.9 mg/kg) and resistant (0.13-5.0 mg/kg) crops, the Meeting estimated a maximum residue level of 10 mg/kg glyphosate and recommended the withdrawal of the CXL of 0.5 mg/kg.
The residues of glyphosate in the hay from susceptible cotton were 3.8-33 mg/kg at 5-9 days and 6.3-84 mg/kg at 10-14 days, and those of AMPA were 0.10-0.46 mg/kg at 5-14 days. The residues of total glyphosate were 4.1-33 mg/kg at 5-9 days and 6.4-85 mg/kg at 10-14 days.
The glyphosate residues (3.8-84 mg/kg) were below the existing CXL for the straw and fodder (dry) of cereal grains (100 mg/kg), although cotton hay is not classified within this group of commodities. The Meeting agreed not to recommend an MRL for cotton hay in view of its insignificance in international trade.
The residues of glyphosate in the gin by-product from resistant cotton were 3.7-84 mg/kg at 6-9 days and 0.79-2.2 mg/kg at 17 days, and those of AMPA were <0.05-0.84 mg/kg at 6-9 days and <0.05 mg/kg at 17 days. The residues of total glyphosate were 3.8-85 mg/kg at 6-9 days and 0.87-2.3 mg/kg at 17 days.
The Meeting did not recommend an MRL because the commodity does not figure in international trade.
Maize. Twelve supervised trials on susceptible maize and 66 on resistant maize were carried out in the USA. The 12 trials were with one pre-harvest application (2.5 kg ai/ha). US GAP allows pre-emergence application (0.32-4.2 kg ai/ha), spot treatment (0.32-4.2 kg ai/ha) and pre-harvest application (2.5 kg ai/ha for ground, 0.84 kg ai/ha for aerial) but the Meeting considered that the trials were effectively compatible with the maximum GAP application because the residue from pre-emergence application would be expected to be negligible and spot treatment should not affect crops if carried out according to GAP.
The 66 trials on resistant maize were with 2 to 4 applications which included pre-emergent, post-emergent and pre-harvest applications; 22 of the trials were according to maximum GAP.
Grain. The residues of glyphosate, AMPA and total glyphosate in the susceptible maize were 0.05-0.54 mg/kg, 0.05-0.13 mg/kg and 0.13-0.62 mg/kg respectively at 6-7 days. The residues of total glyphosate after maximum GAP treatments were 0.13 (5), 0.13, 0.14, 0.19, 0.23, 0.25, 0.27 and 0.62 mg/kg.
The residues of glyphosate, AMPA and total glyphosate in the resistant maize were 0.05-0.34 mg/kg, 0.05-1.4 mg/kg and 0.13-2.2 mg/kg respectively at 6-8 days. The residues of total glyphosate after maximum GAP treatments were <0.13 (2), 0.22 (2), 0.23, 0.26, 0.37, 0.38 (2), 0.41, 0.42, 0.51 (2), 0.52, 0.54 (2), 0.60, 0.67, 0.78, 1.0, 1.6 and 2.2 mg/kg.
Since the total glyphosate residues in the susceptible and resistant maize clearly belonged to difference populations, the Meeting estimated an STMR of 0.47 mg/kg total glyphosate, based on the residues in the resistant maize.
On the basis of the residues of glyphosate in susceptible (<0.05-0.54 mg/kg) and resistant (<0.05-0.34 mg/kg) maize, the Meeting recommended an MRL of 1 mg/kg for glyphosate to replace the existing CXL (0.1* mg/kg). The Meeting also estimated a maximum residue level of 2 mg/kg for AMPA in maize on the basis of the residues of AMPA found in resistant maize (<0.05-1.4 mg/kg).
Fodder. The residues of glyphosate, AMPA and total glyphosate in the susceptible maize fodder were 3.7-92 mg/kg, 0.09-0.81 mg/kg and 3.8-93 mg/kg respectively at 6-7 days. The corresponding residues in the fodder from resistant maize were 1.8-41 mg/kg, <0.05-4.7 mg/kg and 2.0-48 mg/kg respectively at 6-8 days. The residues in both susceptible and resistant maize fodder were below the existing CXL for the straw and fodder (dry) of cereal grains (100 mg/kg).
The Meeting estimated a maximum residue level of 5 mg/kg for AMPA in maize fodder from the residues in fodder from resistant maize (<0.05-4.7 mg/kg).
Forage. According to GAP, the forage of susceptible crops should be cut before the pre-harvest application of glyphosate, whereas the forage of resistant crops can be cut after the application before harvest. Trials to determine residues in forage were therefore restricted to resistant maize.
The residues of glyphosate, AMPA and total glyphosate in the maize forage were <0.05-0.52 mg/kg, 0.06-1.1 mg/kg and 0.18-1.9 mg/kg respectively after 48-65 days. Those of total glyphosate from maximum GAP treatments were 0.18, 0.23, 0.26, 0.35, 0.55, 0.61, 0.64, 0.81, 0.86, 0.92, 1.0 (2), 1.1, 1.8 and 1.9 mg/kg.
The Meeting estimated maximum residue levels of 1 mg/kg glyphosate and 2 mg/kg AMPA, which are recommended for use as MRLs, and an STMR of 0.81 mg/kg total glyphosate.
Sorghum (pre-harvest applications to susceptible plants). Eight supervised trials were carried out in the USA with one pre-harvest application at 1.7 kg ai/ha. US GAP allows pre-emergence application at 0.32-4.2 kg ai/ha, spot treatment at 0.32-4.2 kg ai/ha and pre-harvest application at 1.7 kg ai/ha. For the reasons given above, the Meeting considered the trials to be compatible with maximum GAP.
Grain. The residues of glyphosate, AMPA and total glyphosate were 1.4-13, <0.05-0.22 and 1.6-13 mg/kg respectively after 6-8 days. Those of total glyphosate in rank order were 1.6, 1.8, 1.9, 5.4, 6.2, 6.6 and 13(2) mg/kg.
The Meeting recommended an MRL of 20 mg/kg for glyphosate to replace the existing CXL (0.1* mg/kg), and an STMR of 5.8 mg/kg for total glyphosate.
Fodder and hay. Residue data said to be on sorghum hay were submitted, but the Meeting concluded that the commodity analysed in the trial should be classified as sorghum fodder.
The residues of glyphosate, AMPA and total glyphosate in fodder were 2.9-33, <0.05-0.41 and 3.0-34 mg/kg respectively at 6-8 days. The corresponding residues in "hay" were 3.1-37, <0.05-0.45 and 3.2-37 mg/kg at 10-15 days.
The glyphosate residues in both fodder (2.9-33 mg/kg) and hay (3.1-37 mg/kg) were below the existing CXL for the straw and fodder (dry) of cereal grains (100 mg/kg).
Processing
Cotton. Although only one study was available the Meeting agreed to calculate STMR-Ps because the processing adequately simulated industrial practice.
Processing factors from cotton seed to delinted cotton seed, cotton kernels, cotton hulls and cotton meal were 0.19, 0.084, 0.34 and 0.12 respectively. They were 0.034 for processing to crude cotton seed oil, cotton soapstock, refined cotton seed oil and bleached-deodorized cotton seed oil.
The Meeting estimated maximum residue levels of 0.05* mg/kg for crude and edible cotton seed oil, and STMR-Ps of 0.38, 0.17, 0.68 and 0.24 mg/kg for delinted cotton seed, cotton kernels, cotton hulls and cotton meal respectively, by calculation from the cotton seed STMR of 2.0 mg/kg.
Maize. Residues of glyphosate and AMPA were determined in the processed commodities but the residue of glyphosate in the raw grain was below the LOD, although AMPA was detected. Information on the conversion of glyphosate to AMPA during the processing was not available. The Meeting could not use the data to estimate STMR-Ps.
Sorghum. The mean processing factors were 4.7, 1.2, 0.36, 4.7 and 0.49 from sorghum to bran, clean grain, flour, grain dust and grits (medium) respectively and <0.028 or <0.11 for processing to germ and starch.
The Meeting estimated STMR-Ps of 0 for sorghum germ and starch because they contained negligible residues of glyphosate and AMPA individually, and 27, 7.0, 2.1, 27 and 2.8 mg/kg for bran, clean grain, flour, grain dust and grits (medium) respectively, by calculation from the sorghum STMR (5.8 mg/kg).
FURTHER WORK OR INFORMATION
Desirable
Processing studies with both susceptible and resistant maize in which the raw grain contains measurable residues of both glyphosate and AMPA.
