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)