Fruit Surface Residues of DDT and Parathion at Harvest M. M. BARNES, G. E. CARMAN, W. H. EWART, and F. A. GUNTHER
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University of California Citrus Experiment Station, Riverside, Calif.
Surface residues of DDT and parathion at various times during the season and at harvest were determined for apples, pears, peaches, oranges, and lemons. Low level surface residues of parathion on apples were not carried over into cider. Harvest residues on fresh fruit are distinguished from residues present in food at the time of consumption which are included under the designation ultimate residues.
W i t h reference to the surface deposits accruing from orchard application of insecticides, certain characteristics which enhance their value as implements i n the chemical control of many species of insects—physical persistency and chemical stability—may also be conducive to the contamination of the harvested fruits with potentially deleterious residues. Supplementary to the need for data on the acute and chronic toxicity of these i n secticides to man and domesticated animals is the requirement for information concerning the magnitudes of the deposits that are present on or in foodstuffs as harvest or ultimate residues following commercial usage. The widespread commercial use of D D T [ 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] and the potentialities of the more recently developed parathion (0,0-diethyl 0-pnitrophenyl thiophosphate) have placed emphasis on such investigations concerning these compounds. The Food and D r u g Administration has not as yet held hearings concerning the establishment of formal tolerances for D D T or parathion on fresh produce or i n processed foods. F o r apples and pears, an informal tolerance for D D T of 7 p.p.m. has been announced (3). [These hearings were i n progress at the time of publication.]
Scope, Definitions, and Methods This investigation is a portion of a general experimental program being carried out b y the University of California Citrus Experiment Station on the fate of insecticide residues (2) and methods of removing them (5). The discussion presented herein involves tree fruits and is largely restricted to a consideration of "surface residues." This term has been defined (5) to refer to residues present above the cuticle (extrasurface residues) and to deposits that may be incorporated i n the cuticle (cuticular residues). The quantities reported as surface residues are those present i n the solvent following standardized extraction procedures and include both extrasurface and cuticular residues. Little is known as to what extent insecticide residues may be redistributed through the epidermal layer i n the process of solvent extraction or stripping. While most of the data presented are representative of harvest residues on fresh fruit, some consideration is also given to residues present i n processed food. It is considered 112
AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
113
BARNES et α/.—FRUIT SURFACE RESIDUES OF DDT AND PARATHION AT HARVEST
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appropriate to refer to residues present i n food at the time of consumption as "ultimate residues" (5). D D T was determined b y the dehydrohalogenation method (4). Parathion analyses were made b y the magenta color reaction of Averell and Norris (1) as modified b y Gunther and B l i n n (6). Two compounds or degradation products thereof which may cause the development of interference colors i n the magenta color reaction may be encountered i n surface residues resulting from commercial spray or dust applications. The first of these, dicyclohexylamine dinitro-o-cyclohexylphenate, is i n widespread commercial use, whereas the second, a dinitrocaprylphenylcrotonate, is involved at present only i n experimental and semicommercial usage. Blank corrections were provided for all sets of analyses. Samples for estimates of surface residue parameters on apples and pears were taken from three trees selected for representative size and shape among those of the experimental orchard. E a c h of the three samples consisted of 30 fruits. Six fruits were taken from each of four tree quadrants composing three fourths of the tree height and six from the top one fourth of the tree. These samples were generally taken before and after the penulti mate and ultimate orchard applications and at harvest. Samples for analyses of cider were taken from juice expressed with a hydraulic cider press. Samples of fruit for pressing were selected at harvest from a series for which parallel analyses for surface and pulp residues were made. E a c h of the triplicated peach samples was constituted b y selecting three fruits from each of eight trees. Citrus varieties were sampled b y selecting one fruit from each quadrant of seven trees. Replicate samples were taken from other sets of seven trees. Sample routing and manipulation have been described (6, 7). Table I.
Surface Residues of DDT on Rome Beauty Apples at Harvest
Technical Compound , Lb./100 Gal.
No. of Applications
Interval, Days&
Fresh Weight, Entire Fruit, P.P.M.
1 0.5 0.5 0.5 0.5 1
3 4 4 5 6 6
75 50 50 40 40 60
1.0 1.5 0.3 2.0 3.8 5.2
0
As wettable powder containing 50% technical D D T . b Since final application.
a
Table II.
Surface Residues of DDT on Bartlett Pears at Harvest
Technical Compound", Lb./100 Gal.
No. of Applications
Interval, Days*>
Fresh Weight, Entire Fruit, P.P.M.
2 1 1 0.5 0.5 0.5 0.5
1 1 2 2 2 3 4
110 110 70 70 85 40 14
0.9 0.4 2.2 1.6 0.9 1.2 2.7
As wettable powder containing 50% technical D D T . b Since final application.
α
Results The amounts of surface deposits resulting from commercial and experimental applica tions of D D T and parathion were ascertained on apples, pears, peaches, oranges, and lemons. Applications were made with conventional high pressure spraying equipment, utilizing manually operated guns or semiautomatic booms, and with two types of air blast sprayers. Surface residues of D D T on apples resulting from experimental applications applied in schedules comparable to commercial usage ranged from less than 0.5 to 2.0 p.p.m. at harvest. Schedules of application involving higher spray concentrations and greater fre quency of application than are at present required i n commercial practice resulted i n most cases i n residues of less than 7 p.p.m. T y p i c a l harvest residues are presented i n Table I. AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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ADVANCES IN CHEMISTRY SERIES
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On pears, experimental applications of D D T applied in commercial schedules resulted in surface residues ranging from less than 0.5 to approximately 3 p.p.m. T y p i c a l harvest residues are shown i n Table I I . Intervals between application and sampling of apples retaining weathered surface residues of parathion ranged between 21 and 70 days. A t harvest, these residues were 0.05 p.p.m. or less, following each of 13 varied schedules of application (Table I I I ) . (These values are derived from samples containing an optimum amount of parathion for analytical precision.) Low level surface residues on apples were not carried over as u l t i mate residues i n cider (Table III). This fact supports the contention that there is close association of the parathion deposits with the waxlike coating of the fruit.
Table III. Technical Compound , Ounces/100 Gal.
Surface Residues of Parathion on Apples
0
Variety
Application
Interval, Days&
Fresh Weight, Entire Fruit, P.P.M. Pretreat- Posttreatment ment
Interval, Daysb
Fresh Weight, Entire Fruit, P.P.M. Surface Cider
Conventional Sprayer Rome Beauty
1 2 4 2 4 1
Delicious
2 2 4
3rd 4th 3rd 4th 3rd 4th 1st 1st 2nd 3rd 2nd 3rd 3rd 4th 2nd 3rd
21 25 21 25 21 25 27 36 27 36 27 36 27 36
0.02 0.01 0.04 0.02 0.09 0.09
0.01 0.01 0.02 0.01 0.03 0.02 0.09 0.05
0.3 0.3 0.4 0.4 1.3 1.0 0.5 1.2 0.5 0.3 0.8 0.6 1.4 0.6 2.2 0.9
41
0.02
c
41
0.02
c
41 70 70
0.05 Trace Trace c
0
c
29
0.01 c
29
o.'oi c
29
0.02'
00*
29
0.'05
00
