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    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 500C (600C 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 l 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)