Residue aspects of aldicarb were last evaluated in 1994 within the CCPR periodic review programme. A temporary MRL of 0.5 mg/kg was recommended for potato pending the submission of data on supervised trials according to current use patterns. The previous estimate of a maximum residue level for banana was withdrawn owing to a change in the use pattern.
Extensive new information was provided on residues deriving from the currently recommended uses on bananas and potatoes, and on the revised GAP for potatoes in the USA. The Meeting was informed about ongoing trial programmes for refining use patterns on bananas and expanding the use permit for potatoes within the USA, where the use of compound is authorised at present only in Florida and the Northwest States.
The new GAP for bananas allows a maximum of two applications at a rate of 2 g ai/plant each season with a 180-day PHI. The new US GAP for potatoes specifies positive-displacement application equipment, a single application at a maximum rate of 3.36 kg ai/ha, and the exclusion of in-furrow irrigation. PHIs are 100 days for Florida and 150 days for Northwest States.
The trials were with granular formulations of aldicarb. The samples were mainly analysed by HPLC methods which determined aldicarb, its sulfoxide and its sulfone individually. In some cases the residues were oxidized to, and determined as, the sulfone by GLC. The typical limit of determination was about 0.01-0.02 mg/kg for each residue component. The residues are reported in the monograph and appraisal as the total carbamate residue expressed as aldicarb sulfone, which can be converted to the parent aldicarb by multiplying by 0.856.
In trials with bananas, aldicarb was applied to the soil at the recommended maximum rate of 2 g ai/plant, corresponding to 3.6-4 kg ai/ha. Samples were taken from 3 to >360 days after the last application. Aldicarb residues were determined in composite samples consisting of 7-12 fingers or in individual fingers. The average residue ranges found in whole bananas were 0.23-0.5 mg/kg at 45 and 75 days, 0.02-0.4 mg/kg at 87 and 124 days, and 0.04 mg/kg at 150 days.
The residues were determined in the peel and pulp separately and calculated for the whole fruit in 14 trials. There was little difference between the residues in whole fruit and pulp, the average ratio of whole fruit to pulp residues being 1.19.
The residues were determined only in the pulp in most of the samples, at PHIs much shorter than the recommended 180 days. In 6 samples the residues in the pulp were between 0.02 and 0.04 mg/kg at PHIs of about 150 days and longer. Of these 6 trials, one or two applications (GAP) were made at five occasions resulting in maximum, median and mean residues of 0.04 mg/kg, 0.03 mg/kg and 0.029 mg/kg, respectively.
The main residue was aldicarb sulfoxide. Aldicarb was not detected in any of the samples and the sulfone in only a few. The sulfoxide/sulfone ratio ranged from 3 to 23 in those samples where both residues were present in detectable concentrations.
Taking into consideration the slow decline of residues, the factor for the conversion of aldicarb sulfone to the parent compound according to the residue definition, and the factor of 1.2 for the ratio of the residues in the whole fruit to those in the pulp, the Meeting concluded that a maximum residue level of 0.05 mg/kg expressed as aldicarb would be likely to cover residues from applications in accord with GAP. However, since residues were reported in the whole commodity in only a single trial which complied with GAP, the Meeting considered the data from GAP applications insufficient to recommend an MRL.
A number of trials on potatoes were reported from 14 countries. The residues were mainly aldicarb sulfoxide.
In supervised trials representing national GAP except in the USA and South Africa, the total residue expressed as aldicarb sulfone ranged from 0.005 mg/kg to 0.7 mg/kg with a median of 0.03 mg/kg. Of the total of 94 trials the highest residues measured in rank order were 0.21, 0.23, 0.25, 0.26, 0.3, 0.35, 0.4, 0.4, 0.46 and 0.7 mg/kg. The 95th and 98th percentiles were 0.25 and 0.4 mg/kg respectively.
Twenty-nine trials were reported from South Africa in a summarized form without sufficient details of trial conditions or analytical methods. Aldicarb was applied once or twice at rates from 3.75 to 7.5 kg ai/ha, and PHIs were from 38 to 125 days. Eight of the 29 trials were in accordance with GAP for food and feed potatoes (1 application with 2.55-5.25 kg ai/ha and 120 days PHI). Residues in composite samples from these trials ranged from 0.01 to 1.12 mg/kg. Although the residue levels fit well into the distribution of residues in Spanish trials (0.02-0.7 mg/kg), taking into account the higher rate (5.25 kg ai/ha compared to 1.5 kg ai/ha in the Spanish trials), the Meeting was not able to evaluate the trials because essential details were not reported.
In most of the reported US trials the nominal application rate was the maximum recommended 3.36 kg ai/ha. Treatment was either with positive-displacement application (PDA) equipment according to the new GAP requirement or with the traditional gravity-flow applicator (GFA).
Residues were measured in a very large number of individual potato tubers to determine the effects of the mode of application, method of irrigation, and climatic conditions on the magnitude and distribution of the residues. The residues in individual potatoes extended over wide ranges and their relative frequency distributions were not normal, in accord with previous findings with other crop-pesticide combinations. In order to estimate maximum residue levels, 100 composite random samples of 12 tubers each were drawn from the selected primary sample populations with replacement, according to a computer programme.
The relative frequency distributions of composite samples taken from a single site were close to normal. The average residues found in composite samples and the average of the residues in the primary samples (field site residues) were very similar.
In the case of trials according to US GAP the between-field variance (square of the standard deviation) of the maximum residues in the composite samples (Vbf = 0.000488) was about 2.4 times the average within-field variance (Vwf = 0.00021). The between-field coefficient of variation of the residues was found to be 40%, while the combined between- and within-field CV was 48%. When all US trials complying with GAP were taken into consideration (either with field site residues or with maximum composite residues) the Vbf/Vwf ratio was >10. Consequently the within-field variation has little or no effect on the overall coefficient of variation of residues, and the calculated average residues obtained from the analysis of large numbers of primary samples (79-100 from an experimental site) or the average of smaller numbers of primary samples (>12 equal to one composite sample) can be used to estimate maximum residue levels.
Following single applications at planting or at emergence with commercial ground equipment and at PHIs above 139 days, in-furrow irrigation in 6 trials resulted in higher residues (average 0.18 mg/kg; range 0.025-0.316 mg/kg) than overhead irrigation (average 0.048 mg/kg; range 0.01-0.077 mg/kg) in four trials. The between-field coefficients of variation of the average residues were very similar: 66% and 69% respectively.
Eight field trials were conducted in 6 States of the USA to determine the variability of residues within fields and within plants. One hundred potato tubers and ten potato plants were selected from each field. The average within-plant and within-field coefficients of variation were 49.9% and 60.7% respectively. The between-field coefficient of variation was 87.4%. At trial sites where the PHIs complied with GAP, the field site residues ranged from 0.02 mg/kg to 0.09 mg/kg and the maximum residues in composite samples were from 0.03 to 0.15 mg/kg.
Seventeen field trials were conducted in twelve States of the USA to determine the distribution of residues in centre-row and end-row areas. The average residues in the centre and end parts of the rows were 0.094 and 0.12 mg/kg respectively. Twelve of a total of 918 tubers contained residues above 1 mg/kg with a maximum of 3.13 mg/kg. All of these tubers were taken from the end sections of the rows. The 95th percentiles for the centre and end parts of rows were 0.34 and 0.52 mg/kg respectively.
Positive-displacement application (PDA) equipment and the conventional gravity-flow applicator (GFA) were used in sixteen trials to compare the variability and magnitude of residues in potato tubers grown in the 6 m end-sections with rows to the residues in mid-row tubers. Following PDA treatment according to the field site residues in mid-row and end-row samples ranged from <0.02 to 0.18 and 0.02 to 0.23 mg/kg respectively. The averages of the field site residues found in mid-row and end-row sections of the experimental sites (0.065 and 0.052 mg/kg) did not differ significantly. The average residue in end-row samples from GFA treatments (0.234 mg/kg) was significantly higher than that found following PDA treatments, while the mid-row samples were not analyzed. The between-field variation (CV %) of the average residues from mid-row and end-row sections following PDA and GFA treatments did not differ significantly and were 78.2%, 115% and 109% respectively. The highest 10 residues found in individual potato tubers in trials according to US GAP including end-of-row sections were 1.2, 1.2, 1.12, 0.61, 0.51, 0.32, 0.31, 0.29, 0.26 and 0.25 mg/kg.
To estimate a maximum residue level the Meeting took into consideration all of the 87 residues measured in composite field samples and the averages of residues measured in individual potatoes from trials which complied with relevant national GAP, but excluded the summarized data from the South African trials and the results of the trials from The Netherlands (where GAP is limited to seed and starch potatoes).
To estimate the STMR level only those samples were considered which were taken within ±30% of the GAP PHI and which had been treated by applications at rates within the range GAP to GAP +30%. The residue values considered in reverse rank order were 0.7, 0.43, 0.4, 0.4, 0.35, 0.3, 0.3, 0.25, 0.25, 0.24, 0.23, 0.23, 0.1-0.18 (6), 0.09, 0.09, 0.053-0.08 (7), 0.03-0.048 (5) and 0.03 (5) mg/kg. The same residues were considered for the estimation of a maximum residue level: these gave a 98th percentile value between 0.4 and 0.43 mg/kg.
On the basis of the results the Meeting confirmed its previously estimated maximum residue level (no longer temporary), of 0.5 mg/kg for potato, and estimated an STMR level of 0.09 mg/kg expressed as aldicarb sulfone (0.077 mg/kg expressed as aldicarb).
The Meeting examined the relationship between the average and maximum residues found in individual potato tubers at sites treated according to the US GAP rate and PHI, including both PDA and GFA treatments to reflect the current world-wide uses. For acute risk assessment the residues found at the end-of- row sections were also included in the data base. Taking into consideration the populations consisting of >80 residues determined in individual potatoes which provided an estimate for 95% of the residues with 98-99% confidence, the linear regression of the data resulted in a regression equation of
Rmax = 13.25Rav - 0.46 (eq. 1)
with a correlation coefficient of 0.904, which indicates an acceptable correlation. Consequently, the maximum residues in individual tubers in a treated field may be expected on average to be in the range of 13-14 times the average residue found at the site. It should be noted that higher values may occasionally occur.
When only the residues arising from PDA treatment according to current US GAP were taken into account the linear regression equation was
Rmax = 5.5Rav + 0.06 (eq.2)
with a correlation coefficient of 0.79.
The Meeting noted that the data points available for estimating maximum residues arising from PDA treatments were limited and rather scattered, and the correlation between the average and maximum residues was poor. The results were of some interest however, and underline the importance of considering the effect of different use patterns individually first, and pooling only residues from similar populations. The results may otherwise be distorted and unrealistic. The Meeting therefore decided to present both estimates.
On the basis of equation 1 and the estimated maximum residue level (0.5 mg/kg) the estimated maximum residue in individual potatoes is 6.2 mg aldicarb/kg. When the 98th percentile residue value (between 0.4 and 0.43 mg/kg as aldicarb sulfone or 0.415 x 0.856 mg/kg as aldicarb) which was obtained from all field trials which were in accordance with GAP is used, the calculated maximum residue in individual potato tubers is 4.2 mg/kg.
However, if only the residues arising from PDA treatments according to new US GAP are taken into account, with a maximum field site residue of 0.2 mg/kg, the maximum residue in individual potatoes (see equation 2) would be 0.94 mg aldicarb/kg.
Under normal commercial storage conditions the mean total residues calculated as sulfone after 0, 1 and 6 months storage were 0.45, 0.44 and 0.30 mg/kg respectively.
Three replicate potato samples were processed by treatments closely resembling commercial procedures. A portion of deep-frozen French fries were further cooked in hot oil for 1.5 min under conditions similar to those used in fast-food restaurants. The average decrease of the total carbamate residue level was 3.2% in potato flakes, 27% in chips, 55.5% in processed fries, 41.7% in cooked fries and 41% in wet peel. After drying, the residue level in the peel increased to 65.3% of that in the fresh potato owing to the loss of moisture.
The effects of baking and microwave cooking were studied on additional potato samples. The residues decreased by 35.7% and 16.1% respectively.
