RESIDUE AND ANALYTICAL ASPECTS
Chlorothalonil is a non-systemic protectant fungicide. It was first evaluated for residues in 1974 and has been reviewed several times since, most recently as a periodic review in 1993. The 1993 JMPR required additional residue data from supervised trials on different types of melons, residue data on grapes treated according to GAP in Australia and animal transfer studies.
At the 27th (1995) Session of the CCPR the manufacturers indicated that they would provide information on GAP and residue data to the 1997 JMPR for some crops. The representative of the EU was invited to submit residue trials data and information on GAP for the use of chlorothalonil on tomatoes to the JMPR, to support extrapolation and to establish an MRL for peppers (ALINORM 95/24A, paras 107-111). The 1996 CCPR was informed that additional data would be provided for peaches, and decided to keep the MRL for peach at Step 7B.
The fate of residues has been studied with [14C] chlorothalonil in lactating goats, laying hens and in vitro in bovine tissues.
Lactating goats. In goats dosed at a level equivalent to 3 ppm in the daily diet, the total radioactive residue (TRR, calculated as chlorothalonil equivalents) in milk and meat were extremely low with residues of 0.009 mg/kg in the milk and 0.004 mg/kg in the meat. The organs with the highest TRR were the liver and kidney which averaged 0.08 mg/kg and 0.22 mg/kg respectively, the residues being complex mixtures. The 4-hydroxy metabolite, SDS-3701 (4-hydroxy-2,5,6-trichloroisophthalonitrile) was identified in milk, liver and kidney. The metabolite was quantified in a group at 30 ppm at levels up to 0.05 mg/kg in the milk and liver and 0.08 mg/kg in the kidneys. The other major components of the residue that could be characterized were conjugates of chlorothalonil with glutathione. There were no detectable residues of the parent compound in the milk or tissues.
In similar metabolism and transfer studies with SDS-3701 this compound was the only terminal residue. After doses equivalent to 0.2 ppm it was found in muscle and fat at 0.01 to 0.02 mg/kg, in heart at 0.04 to 0.05 mg/kg, in liver at 0.07 mg/kg, in milk at 0.09 to 0.15 mg/kg and in kidney at 0.17 to 0.26 mg/kg.
Poultry. Laying hens were dosed once daily at levels equivalent to 2, 6 or 20 ppm of chlorothalonil in the diet for 21 days. The TRR was calculated as chlorothalonil equivalents. No radioactivity (<0.04 mg/kg) was detectable in egg whites at the 2 or 6 ppm levels at any sampling interval. The high dose yolks showed a maximum total radioactivity of 0.047 mg/kg from day 13 of dosing. Since no activity was detectable in the egg whites, the residues in whole eggs would be <50% of those in the yolks. Analysis of the tissues revealed the only detectable TRR to be present in the liver. The maximum TRR of 0.098 mg/kg was present in the livers of the mid-dose group within 6 hours after the final dose (2 ppm dose <0.04 mg/kg; 20 ppm dose 0.05 mg/kg).
Similar metabolism and transfer studies were conducted with SDS-3701 at dose levels equivalent to 0.1, 0.3 and 1 ppm. The TRR were calculated as SDS-3701 equivalents. No radioactivity (<0.04 mg/kg as SDS-3701) was detectable in egg whites at any dose level. In egg yolks the TRR in the low-dose group reached a plateau at approximately 0.04 mg/kg on day 21. The TRR in the mid- and high-dose yolks reached plateaus of 0.12 mg/kg at day 21 and 0.42 mg/kg at day 16 respectively. The residue in the egg yolks was shown to be unchanged SDS-3701. No activity was detectable in the fat or cardiac tissue of the low-dose group. The cardiac tissue from the mid- and high-dose groups showed maximum activities of 0.055 mg/kg and 0.15 mg/kg. The low-dose livers contained maximum residues of 0.06 mg/kg within 6 hours after the final dose. The highest TRR levels in the mid- and high-dose livers were 0.27 and 0.78 mg/kg respectively.
Studies of in vitro reactions of chlorothalonil with ruminant tissue systems as well as freezer storage stability studies with meat tissues and milk demonstrated that chlorothalonil was not stable in these substrates. It reacts extremely rapidly with components of bovine tissue homogenates with a maximum half-life of 1 minute, giving rise to polar metabolites and bound residues.
A multi-residue analytical method is used for the determination of chlorothalonil in fatty and non-fatty foods by gas chromatography with electron-capture or ion trap detection, with an LOD of 0.01 mg/kg and recoveries of 89-104%.
Chlorothalonil residues are lost quite rapidly at room temperature during such sample preparation as the comminution of fruits and vegetables (e.g. 95% loss from lettuce and 80% from broccoli), but subsequent losses were minimal during storage in the freezer. The losses have important implications, as analytical results could seriously underestimate chlorothalonil residues. The Meeting wishes to draw the attention of enforcement and monitoring laboratories to the need for sample preparation to be carried out under frozen conditions and followed by immediate extraction. The manufacturer confirmed that the data on residues in the samples from supervised trials evaluated by the present Meeting were valid because the samples were kept frozen throughout sample preparation.
Definition of the residue for animal products. Because the metabolite SDS-3701 is considered to be of toxicological importance, the Meeting recommended its inclusion in the definition of the residue for the risk assessment of residues in products of animal origin.
Definition of the residue in animal products for compliance with MRLs: chlorothalonil.
Definition of the residue in animal products for risk assessment: sum of chlorothalonil and 4-hydroxy-2,5,6-trichloroisophthalonitrile, expressed as chlorothalonil.
Chlorothalonil is not fat-soluble (log Pow = 2.87).
Supervised residue trials gave the following results.
Citrus fruits. The use of chlorothalonil is registered in Spain (2 x 1.25 kg ai/ha, PHI 28 days). Whole fruits were analysed in six Spanish trials (one on mandarins, five on oranges). After two applications of 1.25 kg ai/ha the residues of chlorothalonil at 26-28 days ranged from 0.26 to 1.9 mg/kg. No information was received on residues in the pulp.
The Meeting concluded that the residue data were insufficient to estimate a maximum residue level for a major crop and confirmed the recommendation of the 1993 JMPR to withdraw the CXL.
Peaches. Chlorothalonil is registered in Italy and Spain (4 x 1.5 kg ai/ha). The Italian PHI is 14 days, and in Spain the last treatment should be not later than nut size of the fruit (PHI about 60 days).
Six residue trials were carried out in Italy and Spain at the GAP application rate (4 x 1.5 kg ai/ha), but the PHI was three weeks. The residues ranged from 0.54 to 1.4 mg/kg.
In six Italian trials with 3 applications of 1.25-1.5 kg ai/ha, the last with the fruit at nut size (PHI 64 or 66 days) the residues were <0.01 (5) and 0.04 mg/kg, and four Spanish trials (3 or 4 x 1.25-1.5 kg ai/ha) showed residues of 0.01 (82 days), 0.01 (69 days), 0.03 (87 days) and 0.15 (87 days) mg/kg. As one of the results at 87 days is higher than the Italian residues at 66 days, all these results should be included in the assessment. All the residues in the ten trials carried out in Italy and Spain (with PHIs of 64, 66, 69, 82 and 87 days) in rank order were <0.01 (6), 0.01, 0.03, 0.04 and 0.15 mg/kg.
The JMPR was informed that the reported residues were in the fruit without stone, not calculated for the whole commodity, and that the pulp represented 95% of the total weight. The Meeting concluded that a reduction in the residue values by 5% was not significant and did not recalculate the results.
The Meeting estimated a supervised trials median residue level of 0.01 mg/kg, and a maximum residue level of 0.2 mg/kg, based on Spanish GAP, to replace the draft MRL for peach (1 mg/kg) recommended by the 1993 JMPR.
Grapes. The 1993 JMPR listed as desirable additional residue data on grapes treated according to GAP in Australia (multiple treatments of 1.3-1.65 kg ai/ha, 0.12-0.15 kg ai/hl). The PHIs are 7 days for table grapes and 14 days for wine grapes.
Two trials according to GAP were reported to the 1983 and 1993 Meetings. In the first trial (7 x 0.11 kg ai/hl) residues were 8.6 mg/kg after 10 days. In the second (6 x 0.13 kg ai/hl) they were 0.6 mg/kg after 7 days and 2.9 mg/kg after 18 days.
In the five Australian trials reported to the current Meeting, grapes were treated 1 -4 times at rates of 1.9-4.6 kg ai/ha. In two of them, residues of chlorothalonil were 4.8 and 5.2 mg/kg in two samples taken 7 days after a single treatment of 1.9-2.25 kg ai/ha (0.125-0.15 kg ai/hl). In the other trials, samples were taken from 60 to 96 days after the last treatment. Thus the trials were with fewer treatments or longer PHIs than the recommended GAP.
The Meeting agreed that the Australian residue data suggest the need for a higher MRL, but the data were not sufficient to support a recommendation to replace the current CXL (0.5 mg/kg).
Blackberries. Chlorothalonil is registered in the UK (4 x 2.5 kg ai/ha, 28-day PHI). One trial on blackberries in Sweden at the lower rate of 1 x 1.25 kg ai/ha was reported. No residues higher than the LOD of 0.01 mg/kg were found 7-28 days after treatment.
The Meeting noted that insufficient data were submitted and could not estimate a maximum residue level. The recommendation of the 1993 JMPR to withdraw the CXL was confirmed.
Currants. Chlorothalonil is registered in the UK (4 x 2.5 kg ai/ha, 28-day PHI). Six trials on black currants in the UK with 3 x 2.5 kg ai/ha, PHI 28 days, were reported. The chlorothalonil residues in rank order were 0.83, 0.94, 1.5, 1.9, 3.3 and 3.8 mg/kg.
The Meeting agreed to extrapolate from black to white and red currants and estimated a supervised trials median residue level of 1.7 mg/kg and a maximum residue level of 5 mg/kg for black, red and white currants.
Bananas. Registered uses exist with multiple treatments and PHIs of 1 or 0 days in Australia (1.1-2.16 kg ai/ha) and Latin America (aerial application, 0.88-1.63 kg ai/ha).
Two Australian trials on unbagged bananas reported to the 1993 JMPR were according to Australian GAP (10 x 1.1 or 2.2 kg ai/ha, 1-day PHI) and resulted in residues of 0.6 and 2.0 mg/kg.
In three of the four Latin American trials evaluated by the 1993 JMPR the residues were below 0.01 mg/kg; it was not stated whether the bananas were bagged or unbagged. In the fourth trial on unbagged fruit carried out in Costa Rica in 1985 (10 x 1.75 kg ai/ha, aerial application) the maximum residue in 6 field samples was 0.12 mg/kg 6 days after treatment.
Six Latin American supervised trials carried out in 1993 according to GAP (10-15 x 1.7 kg ai/ha, aerial application) were reported to the present Meeting. Samples of bagged bananas taken on the day of treatment showed residues below the LOD (<0.01 mg/kg).
On the basis of the residues in bagged bananas, the Meeting estimated an STMR of 0 and a maximum residue level of 0.01* mg/kg as a practical limit of determination.
Broccoli. Chlorothalonil is registered in the UK (2 x 1.5 kg ai/ha, 7-day PHI) and in the USA (1.7 kg ai/ha, 7-day PHI, number of treatments not specified). The Meeting re-evaluated the two US residue trials according to GAP reported to the 1993 JMPR (4 or 8 x 1.3 kg ai/ha, PHI 7 days) and reviewed two new trials (2 x 1.5 kg ai/ha, PHI 7 days).
The residues from the four trials show a median value of 2.25 mg/kg (rank order 1.5, 2.2, 2.3 and 2.6 mg/kg).
The Meeting estimated a supervised trials median residue level of 2.25 mg/kg and a maximum residue level of 5 mg/kg for broccoli.
Gherkins. The residues in four plot samples from one indoor Dutch trial were 0.64-1.1 mg/kg (median 0.78 mg/kg) three days after one treatment with 2.2 kg ai/ha.
As there were too few treatments to comply with Dutch GAP, which specifies 3-5 applications of 0.75-2.25 kg ai/ha, the Meeting could not estimate a maximum residue level.
Peppers. In response to a referral from the 1995 CCPR, the Meeting agreed that an extrapolation from tomatoes to peppers was inappropriate because of the large difference in the surface-to-weight ratio.
Chlorothalonil is registered in Australia, where multiple treatments of 1.3-1.65 kg ai/ha with a PHI of one day are recommended. In Latin America, multiple treatments of 1.8 kg ai/ha and a PHI of seven days are registered.
A total of 15 residue trials were carried out on bell peppers. Eight trials were conducted in Australia with 6 to 8 applications at 1.65-3.3 kg ai/ha, but samples were taken at the 1-day PHI in only two of them. The residues of chlorothalonil one day after treatment with 1.65 kg ai/ha were 0.43 and 5.3 mg/kg. Residues of 0.04 mg/kg were found in one Brazilian trial (3 x 1.75 kg ai/ha) 7 days after treatment. The residues in five trials carried out in 1996 (7-12 x 1.74-1.92 kg ai/ha) in Mexico, Honduras, Chile and Costa Rica 7 days after treatment were 0.05, 1.4, 1.6, 4.1 and 5.4 mg/kg. These were of the same order as the Australian residues and support the conclusion that a maximum residue level higher than 5 mg/kg is appropriate. All the results in rank order were 0.04, 0.05, 0.43, 1.4. 1.6, 4.1, 5.3 and 5.4 mg/kg (median 1.5 mg/kg).
The Meeting estimated a supervised trials median residue level of 1.5 mg/kg and a maximum residue level of 7 mg/kg for sweet peppers.
Mushrooms. Results of four field trials and one indoor trial reflecting Dutch GAP for cultivated mushrooms were reported by The Netherlands. The maximum residue was 0.78 mg/kg seven days after two treatments with 22 kg ai/ha.
The data were insufficient to estimate a maximum residue level.
Sweet corn (corn-on-the-cob). Registered uses of chlorothalonil exist in Australia (multiple treatments, 1.3-1.65 kg ai/ha, 1-day PHI) and the USA (multiple ground or aerial treatments, 0.7-1.6 kg ai/ha, 14-day PHI).
Four trials were carried out in the USA with 8 x 1.3 kg ai/ha. No residues above the LOD of 0.01 mg/kg were found in the cobs or the grain 14 days after treatment. Forage samples from three of the trials showed residues from 8.2 to 58 mg/kg at day 14. The difference between the residue levels In the cobs and the forage shows that surface residues of chlorothalonil would not be expected to translocate into the grain.
The Meeting estimated a supervised trials median residue level of 0.01 mg/kg and a maximum residue level of 0.01* mg/kg as a practical limit of determination.
Beans (dry). Chlorothalonil is registered in the UK with 2 x 1.5 kg ai/ha, and in the USA with multiple treatments of 1.2-1.75 kg ai/ha. The last treatment should be at end of flowering.
Residues from 24 trials with treatments near UK GAP (2 x 1.5 -1.8 kg ai/ha) at 49-71 days after treatment ranged from <0.01 to 0.1 mg/kg.
Chlorothalonil residues in trials according to US GAP (2-6 x 1.2-1.8 kg ai/ha) were <0.04 (2), 0.04 and 0.05 mg/kg at 40 to 43 days after treatment.
Combining the UK and US data gave residues in rank order of 0.01 (10), 0.02 (7), <0.04 (2), 0.04 (2), 0.05, 0.06, 0.07, 0.08 and 0.1 (3) mg/kg. The Meeting estimated a supervised trials median residue level of 0.02 mg/kg.
The Meeting also estimated a maximum residue level of 0.2 mg/kg for beans (dry), and confirmed the recommendation of the 1993 JMPR to withdraw the CXL for lima bean (dry).
Celeriac. A single trial in The Netherlands approximated Dutch GAP of 3-5 x 1.88 kg ai/ha, PHI 28 days. The maximum residue in four field samples was 2.8 mg/kg 28 days after two treatments with 1.8 kg ai/ha.
The data were insufficient to estimate a maximum residue level.
Wheat. Four field samples were taken in each of two trials in The Netherlands at 1 x 1.2 kg ai/ha with a 41-day PHI which approximated Dutch GAP of one treatment at 1 kg ai/ha and a PHI of 42 days.
The residues in the straw ranged from 0.03 to 4.1 mg/kg. No change of the current CXL of 20 mg/kg is proposed. The highest residue in the grain was 0.12 mg/kg. The Meeting agreed that the data suggested that a higher MRL than the current CXL of 0.1 mg/kg was needed, but the two trials were not sufficient to support a new recommendation.
Fresh herbs. Chlorothalonil is registered for outdoor use in the Netherlands an parsley and celery leaves (3-5 x 1.87 kg ai/ha, 28-day PHI). One trial on parsley, one on celeriac leaves and two on celery leaves (3-4 x 1.8-1.9 kg ai/ha, PHI 27-28 days) were reported. The maximum residues of the four replicates from each trial in rank order were 0.13, 1.6, 2.3 and 2.4 mg/kg.
The Meeting estimated supervised trials median residue levels of 1.95 mg/kg and maximum residue levels of 3 mg/kg for parsley and celery leaves (fresh).
Determination of metabolites and impurities in plants. Samples of selected crops were analysed for the metabolite 4-hydroxy-2,5,6-trichloroisophthalonitrile (SDS-3701), and the technical impurities hexachlorobenzene (HCB) and pentachlorobenzonitrile (PCBN). In sweet peppers the highest residue of SDS-3701 was 0.04 mg/kg. SDS-3701 and HCB residues in bananas and sweet corn cobs were below the LODs of 0.01 and 0.00025 mg/kg respectively. SDS-3701, HCB and PCBN were not detected in dry beans (<0.03, <0.004 and <0.01 mg/kg respectively).
Animal products. Animal metabolism and transfer studies with [14C] chlorothalonil on lactating goats and laying hens showed very little or no transfer of the pesticide from animal feed to milk, fat, tissues or eggs. Chlorothalonil per se absorbed from the gastrointestinal tract would be very short-lived and could not be transmitted as a residue to food items such as meat, liver, milk or edible offal.
Animal transfer studies on cattle were carried out for 28 days at levels of 1.5 ppm chlorothalonil plus 0.1 ppm SDS-3701, 3 ppm chlorothalonil plus 0.2 ppm SDS-3701, 9 ppm chlorothalonil plus 0.6 ppm SDS-3701 and 30 ppm chlorothalonil plus 2 ppm SDS-3701, to represent potential dietary levels of residues in livestock feeds. The median residue levels of chlorothalonil in such feed items as sugar beet and cereal straw found in supervised trials reported to the 1993 JMPR demonstrate that a level of 3 ppm chlorothalonil plus 0.2 ppm SDS-3701 should be realistic for residues in potential feed items and appropriate for estimating the transfer of chlorothalonil to animal products. The residues of the metabolite SDS-3701 were 0.1 mg/kg in milk (reaching a plateau after day 9), 0.02 mg/kg in muscle, 0.04 mg/kg in liver and 0.28 mg/kg in kidney at the end of the study (day 28).
Since the full details of the studies were not reported, the Meeting could not estimate maximum residue levels for animal products.
Data on residues of chlorothalonil in foods in commerce in 1995 were reported from The Netherlands. Of 4282 samples analysed, 4228 (98.7%) were without residues (<0.01 mg/kg). Residues above the Dutch MRLs were found in 14 samples (0.33 %).
FURTHER WORK OR INFORMATION
1. Additional residue data on table grapes and sweet corn treated according to GAP in Australia.
2. Additional residue data from supervised trials on different types of melons (from 1993).