PESTICIDE RESIDUES IN FOOD - 1983 Sponsored jointly by FAO and WHO EVALUATIONS 1983 Data and recommendations of the joint meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues Geneva, 5 - 14 December 1983 Food and Agriculture Organization of the United Nations Rome 1985 BROMIDE ION RESIDUES Explanation Residues of bromide ion in food commodities and in diets were last evaluated by the 1981 Meeting.1 The occurrence of bromide in crops grown in soils treated with methyl bromide is recognized as a potential major contribution to bromide in the diet. A report on bromide ion residues in crops grown in the United Kingdom following soil fumigation with methyl bromide was made available to the Meeting. Extensive data from supervised trials and from surveys of commercial crops were received (UK 1983). RESIDUES IN FOOD AND THEIR EVALUATION USE PATTERN Bromine is widely distributed in the environment as inorganic bromide. The bromide content of United Kingdom soils normally does not exceed 5 mg/kg bromide ion, although coastal soils may attain levels of 100 mg/kg. Surface waters normally do not exceed 1 mg/l, but bromide levels in rain-water are variable, possibly due to pollution factors. Background inorganic bromide levels in fresh fruit and vegetables can generally be expected to be below 10 mg/kg fresh weight. Natural bromide levels are added to by industrial pollution and the agricultural use of chemicals. One of the largest uses of bromine is in the manufacture of ethylene dibromide, the bulk of which is utilized as a lead scavenger petrol. Amounts of bromine entering the environment from this use cannot readily be estimated. The largest agricultural source of bromine in soil within the United Kingdom is probably derived from the use of bromomethane (methyl bromide) as a soil fumigant. Bromomethane is applied to soil under protection or in the open for control of nematodes and other pests, weeds and micro-organisms. Bromomethane is now applied to the soil in glasshouses, at intervals that may be as short as one year, by releasing the gas from several points at soil level beneath a sealing sheet of plastic, usually polyethylene, the edges of which are buried in the soil, which is then compacted. The purpose of the sheet is to try to maintain the bromomethane vapour at a sufficiently high concentration to kill target organisms. The soil remains covered for a period that will allow bromomethane to penetrate the soil and act. When the sheeting is removed, any remaining gas escapes into the atmosphere. Under glass, the gas is usually introduced beneath the sheet from perforated lay-flat polyethylene tubing connected to a thermal vaporizer, which is coupled to a cylinder of bromomethane (capacity 35-150 kg). In open fields, liquid bromomethane is injected at an appropriate depth from hollow tines by an applicator, which simultaneously lays polyethylene sheeting to seal the soil. Bromomethane is currently applied at rates of 50-125 g/m2, the amount being dependent on an agreement between the grower and fumigator. Application, in the United Kingdom, is made by trained and licensed contractors because of the high toxicity of bromomethane gas to humans and other mammals. When the gas is in contact with the soil various processes occur, e.g. physical adsorption, chemisorption, solution in the soil water, chemical reaction and decomposition. The precise form in which bromine, derived from bromomethane, exists in soil is not easy to determine. Many workers have demonstrated the presence of increased bromide ion levels in plants grown on bromomethane-treated soil that could be related to pre-cropping fumigation. Data presented below show that the highest levels have been found in leafy vegetables. RESIDUES RESULTING FROM SUPERVISED TRIALS In order to assess the uptake of bromide ion by crops a level open air plot (clay-loam, 12 percent organic matter) was fumigated with bromomethane at 100 g/m2 and left covered for five days. Three days after the end of fumigation the fumigated plot and an adjacent untreated plot were marked off into micro-plots 1.25 m × 1.25 m. The plots were then planted with crops, at commercial densities, for the next 18 months. A summary of the results is presented in Table 1. Lettuce harvested approximately 12 weeks after fumigation contained between 146 and 458 mg/kg bromide ion/lettuce (fresh weight) with a mean value of 305; controls ranged from 3 to 7 with a mean value of 4. Lettuce planted one year after fumigation contained approximately seven times the background level. Spring cabbage harvested 10 months after fumigation contained 93 to 182 (mean value 127) mg/kg bromide ion/cabbage (fresh weight); for 'January King' cabbage harvested 18 months after fumigation, the range was 73 to 139 (mean value 106). The cabbage controls ranged from 3 to 9 mg/kg bromide ion. Tomatoes During 1981 a study was made to investigate the uptake of bromide ion by tomato fruit from plants grown under protection on soil previously treated with bromomethane. For the purpose of this study seven holdings were selected for intensive investigation. 1 See Annex 2 for FAO and WHO documentation. Table 1 Bromide Ion Residues in Soil (Preplanting) and in Various Crops After Growth on an Unprotected Plot1 Type No. of Soil bromide at planting Crop bromide at harvest Crop Planting Harvesting of plots (mg/kg dry weight) (mg/kg fresh weight) date date sample sampled Range Mean Range Mean Lettuce July 1977 Sept. 1977 Control 4 8 - 11 10 3 - 7 4 var. 'Avondefiance' Treated 11 25 - 82 49 146 - 458 305 (3 wk old plants) July 1978 Sept. 1978 Control 2 16 - 18 17 2 - 3 3 Treated 7 18 - 27 22 15 - 26 22 Spring July 1977 May 1978 Control 4 8 - 12 10 3 - 8 5 Cabbage Treated 6 47 - 65 52 93 - 182 127 (seed) July 1978 Jan. 1979 Control 2 14 - 21 18 18 - 23 21 Treated 6 15 - 23 21 78 - 193 123 Cabbage July 1978 Jan. 1979 Control 2 14 - 21 18 8 - 9 9 'January King' Treated 6 15 - 23 21 73 - 139 106 (seed) Radish July 1977 Aug. 1977 Control 1 11 64 (seed) Treated 2 41 681 - 901 791 Cress July 1977 Aug. 1977 Control 1 11 6 (seed) Treated 1 52 1947 Mustard July 1977 Aug. 1977 Control 1 11 63 (seed) Treated 1 52 1353 1 Fumigated with bromethane at 100 g/m2 in July 1977. Where possible the fruit from each truss of three selected and labelled plants on each holding were sampled and analysed for bromide ion content. The analytical results are presented in Table 2. For the six holdings treated with bromomethane in 1980/81 throughout the major part of the season (even up to 21st truss in the case of one plant), the bromide ion levels exceeded 30 mg/kg tomato fruit (fresh weight). The overall mean value was 57 mg/kg for all samples from the six sites. The highest residue found was 326 mg/kg from the site with an organic soil (organic matter content in excess of 50 percent). Although the soil fumigation took place over a year prior to planting, no sample from this site was below 98 mg/kg and the mean value was 170 mg/kg. Tomato fruits taken from the seventh site, fumigated in October 1979, were all found to contain less than 30 mg/kg. Lettuce The conventional recommendation for reducing soil bromide ion levels has been to leach with large amounts of water. This technique is reputed to be more successful in the Netherlands than in the United Kingdom. Initial work has indicated that not all the bromide in soil is freely extractable with water and that the bound bromide in a soil is directly proportional to the organic matter content. The organic constituents of a soil seem likely to provide, on decomposition, a reservoir from which soluble bromide may be released. The effects of current cultural regimes where bromomethane is used annually are important in the accumulation of bromide in soil. During 1980 a supervised trial to investigate the effect of leaching following soil fumigation with bromomethane was carried out. In order to obtain results from different soil types, the trial was conducted on greenhouse soils with different textures and with different histories of bromomethane fumigation (but all had been fumigated recently). Within a greenhouse, five plots of equal size were marked off and differential irrigation was applied by blanking off the appropriate irrigation nozzles. In practice, all the required water could not be applied in one application and it was necessary to irrigate over several days. It was possible to apply 400 mm of water to four of the six sites by limiting daily applications to about 50 mm. However, the treated plots were small and were surrounded by unirrigated areas. Excellent drainage would be needed if similar quantities were to be applied to large commercial glasshouses. Even then, planting conditions would probably remain difficult for a considerable time. A summary of the data is presented in Table 3. Soil residues at sites A and B were low and did not respond to leaching. On the other sites, there was a positive but diminishing response to increasing rates of leaching. The very high residues at site F were probably due to the high organic matter (51 percent) and the previous history of fumigation; the prefumigation soil residue here was higher than the postfumigation level on any other site. Table 2 Bromide Ion in Tomato Fruits Grown on Soil Previously Fumigated with Bromomethane Dates of Rates of Date of soil fumigation application planting Truss Number (g/m2) tomato (mg/kg bromide ion/tomato fresh weight) crop 1 2 3 4 5 6 7 8 9 10 Each October 75 55 55 60 - - - 42 49 34 35 1973-1980 31 30 24 27 - 18 19 15 - 12 (8 fumigations) 13 17 - - - 20 18 16 14 15 Each October 75 71 55 79 64 64 66 69 68 57 47 1977-1980 58 55 51 47 46 45 - - 35 32 (4 fumigations) 46 61 66 56 69 - 51 38 42 40 Prior to 100 149 130 119 187 167 194 tomato crops 137 125 188 161 242 128 326 1977-1980 100 119 98 113 120 117 (4 fumigations) April 1977, 1980, 1981 (3 fumigations) 100 15-4-81 44 38 34 35 46 33 46 55 36 55 67 58 61 54 30 36 27 33 43 16 40 Nov. 1977 & 1978 100 27-2-81 34 37 55 63 - - 20 - - 30 Dec. 1980 13 18 28 46 - - 46 - - 22 (3 fumigations) 22 31 38 34 - - 44 - - 33 Nov. 1978 & 1980 100 26-2-81 32 45 47 56 41 38 52 52 46 34 (2 fumigations) 36 51 53 40 43 44 38 44 40 29 36 43 49 44 35 36 45 34 33 36 Oct. 1978 & 1979 75 15-4-81 - - - - 22 15 20 11 14 8 (2 fumigations) ca. - - - - 16 22 17 14 10 11 - - - - - 6 5 5 6 6 Table 2a (con't) Dates of Truss Number soil fumigation (mg/kg bromide ion/tomato fresh weight) Plant Site 11 12 13 14 15 16 17 18 19 20 21 22 23 24 mean mean Each October 25 28 31 28 28 39 1973-1980 10 9 13 10 - 18 (8 fumigations) 13 26 - - - 17 25 Each October 40 30 21 26 - - 54 1977-1980 32 41 - 33 31 28 41 (4 fumigations) 27 28 23 - 20 18 42 46 Prior to 158 tomato crops 187 1977-1980 111 152 (4 fumigations) April 1977, 1980, 1981 (3 fumigations) 39 55 32 42 Nov. 1977 & 1978 - 31 - - 22 19 23 24 - 24 20 31 Dec. 1980 - 26 - - 13 42 13 12 - 12 13 23 (3 fumigations) - 42 - - 61 44 36 34 - 40 39 38 31 Nov. 1978 & 1980 27 25 20 16 17 15 12 19 22 20 19 20 21 25 30 (2 fumigations) 31 36 28 29 24 25 21 19 16 14 15 20 - - 32 29 28 32 19 18 14 11 11 10 9 15 10 10 26 29 Oct. 1978 & 1979 14 15 (2 fumigations) 6 14 6 6 12 Table 3 Bromide Ion in Lettuce Grown on Soil Previously Fumigated with Bromomethane plus Leaching Site Soil Organic Rates of previous 1979 Planting First texture1 matter bromomethane application date harvest (%) application (g/m2) date date 1975 1976 1977 1978 1979 A FSL 4 75 75 100 5-11-79 23-11-79 25-02-80 B SL 12 75 75 12-09-79 1-12-79 6-12-79 C SL 13 100 100 100 6-09-79 5-10-79 10-12-79 D SL 75 75 26-10-79 9-01-80 15-04-80 E SL 8 75 75 75 75 75 3-11-79 3-12-79 1-04-80 F3 LP 51 75 100 100 100 100 17-10-79 26-10-79 24-01-80 Table 3a (con't) Site Water application rates (mm) 0 100 200 300 400 Bromide residue mg/kg2 S L S L S L S L S L A 52 81 42 102 28 92 24 150 21 142 B 63 62 44 70 47 232 40 93 42 114 C 214 307 170 215 116 98 98 157 107 117 D 86 765 46 427 32 392 30 284 28 250 E 77 676 63 335 59 328 77 164 67 134 F3 383 1958 226 1534 294 1001 - - - - Mean Sites 98 378 73 230 56 228 54 170 53 151 A-E 1 FSL = fine sandy loam; SL = sandy loam; LP -- loamy peat. 2 S = dry weight for soils; L -- fresh weight for lettuce. 3 At F, the leaching treatments were applied after planting the lettuce crop. RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION Lettuce Samples of lettuce were collected direct from growers in England and Wales from November 1977 to April 1978. Data were recorded, when samples were taken, of the most recent bromomethane application (rate and date) and 57 samples were analysed for bromide content. The results are tabulated in Table 4 and indicate that 67 percent of the samples exceeded 100 mg bromide ion/kg in lettuce (fresh weight). From October 1979 to September 1980 samples of protected lettuce (unspecified varieties, grown under polyethylene tunnels or in glasshouses) were collected from a wide selection of holdings in England and Wales, with a bias towards those on which bromomethane had been used for soil sterilization during any of the preceding six years. When each sample was collected, a questionnaire was completed to record bromomethane treatment data, cropping and cultural details. A total of 828 samples were analysed from 470 individual holdings. Of these samples, 684 were grown on soil fumigated with bromomethane during 1974-1980 and 144 on soil that had not been treated. Table 4 indicates that, of the 684 samples taken from crops grown on treated soil, 71 percent exceeded 100 mg/kg bromide ion/lettuce (fresh weight), approximately 30 percent contained more than 500 mg/kg, 12 percent more than 1 000 mg/kg and 2 percent exceeded more than 2 000 mg/kg. The mean residue for the first crops of lettuce planted within three months of soil treatment with bromomethane was found to be in excess of 700 mg/kg bromide ion/lettuce (fresh weight). Of the lettuce grown on soil not treated with bromomethane, 86 percent of the samples contained less than 10 mg/kg. Examination of the data indicates some of the factors that may influence bromide ion levels in crops. The effect of the interval between the last fumigation of the soil with bromomethane and planting the sampled crop on bromide ion residues is shown in Table 5a, for the study as a whole, and in Table 5b for crops grown on soil that had been treated once. These data indicate that there is a decline in the bromide ion residue level with increasing interval between fumigation and planting out. Even where the soil has only received a single application it appears to be in excess of three years before the bromide levels return close to the background level. In Table 6 (a and b) data relating the number of bromomethane fumigations to glasshouse soils and residues in the sampled lettuce crops are presented. These data show that the high extremes were independent of the number of bromomethane fumigations but the means increased over the range of one to three applications. Table 4 Bromide Ion in Lettuce Grown on Soil Previously Fumigated with Bromomethane bromide ion/lettuce fresh weight (mg/kg) Survey date Total No. of samples 0-50 51-100 101-200 201-500 501-1000 1001-2000 2001-3000 Analysed No. % No. % No. % No. % No. % No. % No. % 11/77 - 4/781 57 9 16 10 18 12 21 20 35 5 9 1 2 0 0 10/79 - 9/802 684 135 20 64 9 111 16 174 25 117 17 68 10 15 2 10/79 - 9/803 144 143 944 0.7 0 0 0 0 0 0 0 0 0 0 0 1 From bromomethane-fumigated soil. 2 From soil fumigated with bromomethane since 1974 (1 to 7 applications). 3 From soil fumigated with bromomethane prior to 1974, or not at all. 4 Of the 143 samples in the 0-5 range, 124 (86 percent) were in the range 0-10. Table 5a Bromide Ion in Lettuce Versus Interval Between Last Soil Fumigation and Planting1 Interval (weeks) between last fumigation and planting sampled crop 0-4 5-8 9-16 17-24 25-32 33-40 41-48 49-56 57-64 65-72 73-80 81-88 89-96 No. of 236 29 60 58 47 40 24 44 18 17 12 13 6 samples *224 Mean 722 751 429 520 228 218 133 126 120 107 121 119 24 *642 Range 15 34 4 4 1 20 4 1 1 3 8 2 1 to to to to to to to to to to to to to 2589 2506 1543 2735 973 786 417 742 397 338 643 898 39 *1936 Table 5a1 (con't) Interval (weeks) between last fumigation and planting sampled crop 97-104 105-112 113-120 121-128 129-136 137-144 145-156 No. of 23 7 5 2 4 2 3 samples Mean 106 83 30 67 4 2 8 Range 4 7 1 25 1 1 5 to to to to to to to 302 250 77 108 8 2 13 Table 5b Bromide Ion in Lettuce Versus Interval Between One Soil Fumigation and Planting1 Interval (weeks) between last fumigation and planting sampled crop 0-4 5-8 9-16 17-24 25-32 33-40 41-48 49-56 57-64 65-72 73-80 81-88 89-96 No. of 47 4 17 19 17 19 6 14 10 8 6 8 6 samples *45 Mean 585 354 216 443 220 203 185 64 84 141 32 40 17 *498 Range 50 128 26 4 31 20 4 1 1 3 8 2 1 to to to to to to to to to to to to to 2589 522 458 2735 973 761 365 382 319 338 100 213 39 *2107 Table 5b1 (con't) Interval (weeks) between last fumigation and planting sampled crop 97-104 105-112 113-120 121-128 129-136 137-144 145-156 No. of 6 4 2 2 4 1 2 samples Mean 40 37 8 67 9 2 6 * Range 4 9 7 25 1 2 5 to to to to to to 97 74 9 108 8 7 1 mg/kg bromide ion/lettuce fresh weight. * Figures obtained after rejecting the top 5% of the bromide ion analytical results, in accordance with FAO practice. Table 6a Bromomethane Fumigations to Glasshouse Soils in Relation to Lettuce Crops Sampled Methyl bromide Total sampled lettuce crops Range bromide Mean bromide fumigations ion/lettuce ion/lettuce 1974-1980 October 1979 - July 1980 fresh weight fresh weight (No.) (No.) (%) (mg/kg) (mg/kg) 0 144 17.4 1-59 6 1 228 27.5 1-2735 243 2 138 16.7 1-2122 416 3 118 14.3 1-2506 537 4 40 4.8 1-1936 516 5 59 7.1 7-2580 682 6 92 11.1 5-2132 538 7 2 0.2 138-192 not specified 7 0.8 1-511 Totals 828 Table 6b Bromomethane Fumigations to Glasshouse Soils in Relation to Lettuce Crops sampled Methyl bromide Total sampled lettuce crops Range bromide Mean bromide fumigations ion/lettuce ion/lettuce 1974-1980 October 1979 - July 1980 fresh weight fresh weight (No.) (No.) (%) (mg/kg) (mg/kg) 0 137 16.5 1-22 5 1 217 26.2 1-801 171 2 131 15.8 1-1539 342 3 112 13.5 1-1549 457 4 38 4.6 1-1584 448 5 56 6.8 7-2017 593 6 87 10.5 1-1551 466 Totals 778 1 Top 5 percent of bromide ion analytical results rejected. Cucumbers Twenty-five commercial producers of protected cucumbers (with a total of 30 separate houses) within the three major growing regions of England were identified by the Agricultural Service. The selection of holdings was biased towards those on which bromomethane had been used during or since autumn 1980, generally at a rate of 100 g/m. Samples were collected during September and October 1981, each consisting of two individual cucumbers of an unspecified variety picked from adjacent plants. A questionnaire recording relevant treatment and cultural details was completed at the time of sampling. Twenty-five of the samples were taken from plants grown on soil that had been treated with bromomethane during or since autumn 1980. The five remaining samples were taken from crops either grown on soil treated earlier than 52 weeks prior to planting or the soil treatment data was uncertain. The mean interval between the most recent soil fumigation and planting was 28 weeks, the mean bromide ion level in cucumbers was 27 mg/kg on fresh weight with a range of 1 to 109 mg/kg (Table 7). There were insufficient samples to make any correlations between bromide ion residues, treatment data and cultural regimes. Celery Samples were obtained from 35 commercial producers of self- blanching celery (with a total of 38 separate houses) in the south of England. The selection of holdings was biased towards those on which bromomethane had been used during the previous two years, generally at a rate of 75 g/m2. Samples were collected during April to July 1982, each consisting of a single plant. A questionnaire recording relevant treatment and cultural details was completed at the time of sampling for each sample. The mean interval between the most recent fumigation and planting of the celery was 51 weeks (range 1 to 140) and the mean bromide ion level in the celery was 104 mg/kg, with a range of 2 to 521 mg/kg. The mean period between planting and harvesting the celery was approximately 12 weeks (Table 8). Various Crops From June 1981 to July 1982 a programme of surveillance of retail samples for bromide ion residues was maintained principally for lettuce, tomatoes, celery, cucumbers and mushrooms; cursory observations were made on other crops. With the exception of lettuce, celery, radish, tomatoes and eggplant, the mean levels were all less than 10 mg/kg. Means and ranges are tabulated in Table 9. Table 7 Bromide Ion in Cucumbers Grown on Soil Previously Fumigated with Bromomethane Crop grown Crop grown Interval between Growth Crop bromide direct in on straw most recent period at harvest soil fumigation and fresh weight planting (weeks) (weeks) (mg/kg) + 3 21 55 + 139 11 1 + 37 14 17 + 43 8 81 + 4 13 10 + 1 17 20 + 40 12 3 + 138 13 25 66 9 1 + 2 17 109 + 91 10 1 + 2 11 48 + 8 37 13 + 14 26 6 + 12 29 14 + 30 17 23 + 2 19 47 ? ? ? ? 5 + manure 3 16 12 + 48 27 6 + 3 11 39 + 3 11 73 + 16 29 1 + 3 8 56 + 37 14 14 + 4 21 17 + 3 24 13 + 30 17 1 + 26 28 1 + 2 10 102 Table 8 Bromide Ion in Celery Grown on Soil Previously Fumigated with Bromomethane Total fumigations Interval between Growth Residue bromide 1976-1982 most recent fumigation period ion/celery (7 years) and planting fresh weight (No.) (weeks) (days) (mg/kg) 3 52 89 14 5 23 82 87 1 126 82 4 3 74 89 27 6 23 82 359 3 22 91 180 2 23 82 50 2 140 74 2 6 30 46 209 3 78 83 208 1 82 93 97 2 1 58 3 1 1 64 158 1 48 90 179 1 18 80 66 1 4 62 6 1 78 93 10 1 18 73 294 1 78 87 521 2 44 74 31 1 40 65 44 1 58 72 75 3 22 81 77 4 22 73 367 1 104 85 120 1 26 103 31 2 52 76 6 2 16 83 370 2 30 87 146 1 87 105 17 3 26 92 41 1 91 90 7 1 82 71 5 1 39 89 40 2 78 68 9 1 30 68 26 1 30 96 54 1 48 82 13 Table 9 Bromide Ion in Various Crops Obtained from Retail Outlets1 Place of Range Mean Crop origin Samples bromide bromide (No.) ion/crop ion/crop fresh weight fresh weight (mg/kg) (mg/kg) Apple France 5 0.1 - 0.3 0.2 Avocado pear Not known 1 1 1 Banana Windward Islands 2 2 2 Bean, broad England 3 1 - 2 2 Bean, French Guernsey 1 1 1 Bean, runner England 2 1 1 Bean, sprouts England 3 1 1 Cabbage England 3 1 - 2 2 Celebres England 2 1 1 Carrot England 1 2 2 Cauliflower England 3 0.3 - 1 1 Chinese leaves England 3 1 - 2 1 Celery England 12 1 - 178 28 Celery Guernsey 1 9 9 Celery Israel 4 7 - 14 10 Celery Spain 16 2 - 8 4 Celery United States 1 4 4 Cucumber Canary Islands 15 0.3 - 10 3 Cucumber England 36 0.2 - 87 9 Cucumber Holland 7 0.1 - 14 7 Cucumber Spain 3 0.2 - 10 4 Eggplant Holland 4 2 - 23 11 Grapefruit Cyprus, Israel 4 0.1 - 0.4 0.3 (segments) S. Africa Green pepper Holland 7 0.4 - 5 2 Lettuce Belgium 1 5 5 Lettuce Cyprus 5 1 1 Lettuce England 69 1 - 241 15 Lettuce France 9 0.2 - 19 4 Lettuce Holland 26 2 - 57 21 Lettuce Israel 6 1 - 4 2 Lettuce Spain 11 0.4 - 4 2 Lettuce United States 12 0.1 - 2 1 Marrow England 2 1 - 2 1 Mushroom England 62 0.2 - 24 1 Onion Holland, Israel 3 0.4 - 1 1 Onion, spring England 3 2 - 4 3 Orange segments S. Africa, Spain 6 <0.1 - 0.4 0.2 Table 9 (con't) Place of Range Mean Crop origin Samples bromide bromide (No.) ion/crop ion/crop fresh weight fresh weight (mg/kg) (mg/kg) Pea England 4 1 - 3 2 Potato Cyprus, England 3 1 - 2 1 Radish England 18 0.2 - 3 1 Radish Holland 12 0.1 - 48 13 Radish Israel 2 5 5 Radish United States 1 1 1 Strawberry England 1 0.03 0.3 Tomato Canary Islands 8 1 - 5 4 Tomato England 33 1 - 70 13 Tomato Holland 14 1 - 39 11 Tomato Spain 15 1 - 7 3 Zucchini England 3 1 - 3 2 1 From June 1981 to July 1982. METHOD OF RESIDUE ANALYSIS The analytical data in this monograph addendum have been obtained by the following method, which is a combination and modification of published methods (Roughan et al. 1983). It involves drying and grinding the sample, digestion with alcoholic sodium hydroxide and ashing in a muffle furnace at 500°C (600°C for oily substrates such as tomato). The residue is taken up in 0.6N sulphuric acid and mixed with a solution of ethylene oxide in acetonitrile to form 2-bromoethanol. After drying, the 2-bromoethanol is determined by electron-capture gas chromatography using a column of 10 percent Carbowax 20M TPA on Chromosorb W-HP 80-100 mesh. The detector responds to give a straight line calibration from 0-10 mg of bromide as 2-bromoethanol. Sample solutions are diluted to bring them within the calibration range when 5 µl injections are used. The main recovery for dried vegetable substrates was found to be better than 97 percent for a wide range of bromide levels, which is equivalent to approximately 20 mg/kg to 1 000 mg/kg on a fresh weight basis. The method can be used to determine 0.1 mg/kg substrate fresh weight. APPRAISAL Data on bromide ion levels in lettuce, cabbage and tomatoes following supervised trials involving bromomethane fumigation of soil prior to planting are reviewed. Samples of lettuce planted on an open fumigated site immediately after fumigation and grown for approximately eight weeks before harvest contained 146 to 458 mg/kg bromide ion/fresh weight, with a mean of 305 mg/kg. First crops of spring cabbage and 'January King' cabbage planted immediately after fumigation contained mean bromide ion levels in excess of 100 mg/kg. Spring cabbage planted a year after fumigation contained bromide ion levels that were not significantly different from those determined in the first-year crops. Tomatoes grown under protection on seven sites with histories of repeated fumigation with bromomethane contained bromide ion levels ranging from 5 to 326 mg/kg. In general, there was no significant difference in bromide levels in fruit at the start and end of the season, although the data suggest a slight downward trend on one or two sites. The mean bromide ion level for the season's fruit from each site ranged from 25 to 152 mg/kg. The highest residues were associated with an organic soil. Lettuce grown under protection on six sites following recent fumigation with bromomethane ranged in mean bromide ion contents from 62 to 1 958 mg/kg. Excluding the mean value for the high end of the range, i.e. 1958 mg/kg, which was associated with a soil of high organic matter content, the overall mean was 378 mg/kg (bromide ion/fresh weight). On four of the sites, a positive but diminishing response to pre-planting leaching of the fumigated soil with water was observed. On two sites, the residues did not respond to leaching. Data from selected surveys of lettuce, cucumber and self- blanching celery from horticultural holdings with known soil treatments with bromomethane were received. From October 1979 to September 1980, 684 samples of lettuce, grown on soils with known histories of bromomethane fumigation, were analysed. The highest level from a single application was found to be in excess of 2 700 mg/kg (two previous crops had been grown on the site since fumigation). The mean residue for first crops of lettuce planted immediately following soil fumigation (many of the soils received applications in the preceding years) was estimated as being in excess of 700 mg/kg, omitting the top 5 percent of the analytical results reduced this figure to approximately 640 mg/kg. Lettuce sampled from soil with no history of bromomethane treatment generally contained less than 10 mg/kg. Decreasing bromide ion levels are associated with increasing interval between soil fumigation and planting. On some sites it may, however, be in excess of three years before the bromide ion levels approach the general background level. Late season cucumbers, planted after a mean interval of 28 weeks following soil fumigation with bromomethane (mostly at 100 g/m2), contained an average value for bromide ion of 27 mg/kg and a range of 1 to 109 mg/kg. Samples of celery grown on soil after a mean interval of 51 weeks following soil fumigation with bromomethane contained bromide ion levels ranging from 2 to 521 mg/kg, with a mean of 104 mg/kg. Data from monitoring studies of fresh fruit and vegetables obtained from retail outlets in the United Kingdom were also reviewed. With the exception of lettuce, cucumber, celery, radish, tomatoes and eggplant, which could be expected to be grown on bromomethane treated soil, the mean bromide ion levels were all less than 10 mg/kg. Bromide levels of the named crops were found to be within the ranges found in the selected studies. Bromide ion levels in first crops after fumigation often exceeded the maximum residue limit proposed by the Codex Alimentarius Commission (at Step 6) of 100 mg/kg for lettuce and cabbage. The meeting noted that the mean levels were all less than 10 mg/kg in a programme of surveillance in the United Kingdom of retail samples for bromide ion residues, with the exception of lettuce, celery, radish, tomatoes and eggplant. As the survey was carried out by determining the bromide residue in individual crop items, representative laboratory samples had to be composed before estimating the maximum residue levels. The minimum number of primary samples recommended by the Codex procedure was taken into account in the composition of samples. The residue figures reported were considered as random distributions, which enabled the formation of laboratory samples by combining 5-5 consecutive results. The average residue in each composite laboratory sample, consisting of 10 pieces of cucumber and 5 pieces of celery, was calculated. In the case of tomato, the site means were considered to be the residue levels in the laboratory sample. The residue content of laboratory samples was used for the estimation of maximum residue levels. RECOMMENDATIONS Residue data on cucumbers from selected surveys of 25 sites enabled the Meeting to estimate a maximum residue level of 50 mg/kg bromide ion in cucumbers. Further data on residues enabled the Meeting to estimate a maximum residue level in celery and tomatoes. The following levels were considered suitable for proposals as maximum residue limits: celery 300 mg/kg Tomatoes 75 mg/kg REFERENCES - RESIDUES Roughan, J.A., Roughan, P.A. & Wilkins, J.P.G. Modified gas - liquid 1983 chromatographic method for determining bromide/total bromine in foodstuffs and soils. Analyst, 108:742-747. U.K. Report on residues of bromide ion following soil fumigation with 1983 methyl bromide and data on supervised trials and surveys of commercial crops. Submitted to FAO by the Government of the United Kingdom. (Unpublished)
See Also: Toxicological Abbreviations Bromide ion (FAO/PL:1968/M/9/1) Bromide Ion (FAO/PL:1969/M/17/1) Bromide ion (Pesticide residues in food: 1981 evaluations) Bromide ion (Pesticide residues in food: 1988 evaluations Part II Toxicology)