Absorption of DDT and Parathion by Fruits

Neither DDT nor parathion was found in the pulp of apples, pears, ... studies to determine the magnitude and location of D D T and parathion residues ...
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Absorption of DDT and Parathion by Fruits G. Ε. CARMAN, W. H. EWART, M. M. BARNES, and F. A. GUNTHER

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University of California Citrus Experiment Station, Riverside, Calif.

Commensurate with the need for information on the effectiveness of new organic insecticides has been the need for determining the magnitude and distribution of toxic residues on and in edible produce. Absorption of insecticide residues of DDT and parathion by fruit was investigated. Specific techniques for the physical separation of component fruit parts with minimization of sample contamination are described. DDT residues were analyzed by the dehydrohalogenation method. The magenta color reaction as modified by Gunther and Blinn was used for parathion residues. Results indicated the presence of DDT and parathion in the peel but not in the pulp of harvested citrus fruits. The relatively rapid penetration of the toxicants was followed by a slower loss with the retention of appreciable amounts over long periods of time. Neither DDT nor parathion was found in the pulp of apples, pears, or peaches following treatment with standard dosages in sequence applications. Spectrographic examination of transmission-wave­ length curves of the benzene extractives of DDT-treated and parathion-treated navel oranges in comparison with curves for parent compounds indicated definite shifts in absorption bands.

Although various workers (6, 18, 20, 21) have reported on the mammalian toxicity of l,l,l-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT) and 0,0-diethyl 0-p-nitrophenyl thiophosphate (parathion), more detailed studies with these toxicants are being conducted by numerous pharmacological groups because available information indicates that certain hazards may be associated with the use of these materials as economic poisons. In addi­ tion to the possible dangers from exposing personnel to these toxic materials in the course of handling or making insecticide applications, the retention of deposits on edible products or the accumulation of residues by translocation may be objectionable or hazardous. A s a means of clarifying the problems incident to this aspect of food contamination, agri­ cultural chemists and entomologists have recognized the desirability of projecting parallel studies to determine the magnitude and location of D D T and parathion residues on or in treated produce. In many instances the problem of surface contamination has been principally studied {8-6, 7-10, 16,17, 19, 22). However, early in the D D T studies on citrus fruits, it be­ came evident that appreciable amounts of this insecticide penetrated into certain compo­ nents of the peel. Following this disclosure, suitable techniques were investigated and an evaluation of the penetration of D D T and later of parathion into various kinds of fruit was undertaken. The studies reported herein consider for the most part the occurrence of penetration following the practical uses of these insecticides on specified crops and, to a limited ex­ tent, the ultimate fate of the penetrated compounds. They may additionally serve to indicate the nature of the problems which may be associated with other uses. The final interpretation of these results will be dependent on the fuller elaboration of pharmaco128

In AGRICULTURAL CONTROL CHEMICALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1950.



logical studies and on the subsequent clarification of the need for legal tolerances for resi­ dues of these specific toxicants or their degradation compounds on consumer products.

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Materials and Methods These studies were limited to work with navel and Valencia oranges, lemons, grape­ fruit, apples, pears, and peaches. Preliminary results have also been obtained with avo­ cados, grapes, olives, plums, and certain vegetable crops. Representative fruit samples were assembled from trees which had been treated with experimentally formulated technical grades of D D T and parathion or with commer­ cially available formulations of these toxicants. A l l insecticide applications were made with power equipment typical of that used i n commercial practice. As a means of mak­ ing direct comparisons and of assuring greater control over those variables, inherent i n field studies, most fruit samples were taken from test plots i n experimentally treated grove areas. The experimental groves were located i n Los Angeles, Orange, Riverside, San Ber­ nardino, San Diego, Tulare, and Ventura counties of California. Approximately eight pounds of fruit constituted each analytical sample (11, 14)', the number of fruits per sample varied from ten to thirty. Fruits were selected at random from within a peripheral band around the tree 3 to 6 feet above the ground. Individual samples were constituted with fruits from six to eight trees and replicate samples were taken from different groups of trees. I n some cases, samples of deciduous fruits were col­ lected from three trees and additionally involved a portion of fruit from the upper quarter of the tree. Duplicate, or more generally triplicate, samples were utilized for analyses. A l l fruits for penetration studies were collected i n paper bags, which were immediately stapled to ensure sample integrity. The sample preparations and quantitative estimations of residues were completed as soon after the fruits were sampled as proved practicable (14)· Standardized procedures were adopted with regard to sample preparation, recovery of toxicant, and chemical assay. I n order to determine the nature and magnitude of pene­ trated residues, i t was necessary to disassociate all extra-surface residues. The techniques originally developed to effect this separation and which were used i n most of the D D T penetration studies have been described b y Gunther (11). Certain modifications which have been developed subsequently i n connection with the parathion studies are described in detail below since this phase of penetration studies assumes singular importance (see also 14)Citrus Fruit Types. T h e method previously described (11) consisted essentially of scrubbing the fruits w i t h a w a r m 1 0 % trisodium phosphate solution, rinsing w i t h distilled water, h a l v i n g each fruit, a n d reaming the juice a n d pulp from each half with a power juicer. Pieces of pulp adhering to the insides of the individual hemispheres of peel were carefully scraped free and combined with the remainder of the pulp and juice. Independent analyses were then completed on the discrete peel and pulp-juice samples. Whenever desirable the flavedo and albedo components of the peel were separated with peeling tools, and each was pooled and analyzed. This method proved inadequate i n the parathion studies because of trace contami­ nations and the following procedure of sample preparation was adopted : Approximately 8 pounds of fruit were scrubbed manually i n warm 1 0 % trisodium phosphate solution. One hemisphere of peel was then removed from each fruit, using a household-type peeler. F r o m the pooled segments of peel a 1-pound subsample was used for processing. To obtain the pulp sample a circle of peel approximately 1.5 inches i n diameter was lifted from the center of the remaining hemisphere of peel on each fruit and a decontami­ nated N o . 15 cork borer with a serrated cutting edge was forced through the fruit antipodally i n such a manner as to avoid a l l flavedo peel. The albedo-bearing ends of each extracted plug of fruit pulp were carefully removed with the aid of a clean razor blade. After being pooled, a 1-pound subsample of the pulp was utilized for processing. The samples of citrus peel obtained b y either method may have contained trace amounts of extra-surface D D T residues as differentiated from subsurface or penetrated In AGRICULTURAL CONTROL CHEMICALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1950.


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residues (2, 18). Although difficult to establish experimentally the empirical evidence indicated that the washing of fruits with warm trisodium phosphate solution was nearly quantitative i n removing or degrading D D T extra-surface residues. The extra-surface residues of parathion shortly after application appear to be n i l ; the amounts obtained by stripping procedures apparently were extracted from the waxlike cuticle of fruits {2). I n the preparation of citrus pulp samples by this revised method the likelihood of contamination appeared to be eliminated providing the tools and work area were free of contaminants and the manipulations were carefully executed. However, the samples so prepared do not contain any of the pulp from the area immediately adjacent to the peel and to that extent are not totally representative. P o m e F r u i t Types. A s with citrus fruit types, the method of sample preparation was modified for the parathion studies. I n the earlier studies the D D T - t r e a t e d apples a n d pears were scrubbed i n a warm 1 0 % solution of trisodium phosphate, and all the peel was removed from the water-rinsed fruit with a household-type potato peeler. The pooled samples of peel and pulp were then processed independently to re­ cover the contained toxicant for subsequent estimation. I n the parathion studies and the more recent D D T studies, the fruits were split in half by cutting axially one third through the fruit with a broad-bladed knife and then twisting the blade to one side. The core and pulp, exclusive of the part touched by the knife blade, were carefully scraped out with sharpened melon bailers. As much of the pulp as possible was removed but in the event the skin was punctured the fruit was discarded and the scraping tools decontaminated. The pulp taken from the individual fruits of the sample was pooled for subsequent processing. Separate samples of fruit were used for surface residue estimations (12). Stone F r u i t Types. V e r y preliminary studies of D D T or parathion penetration into peach fruits were completed. T h e pulp samples were prepared b y immersing the intact fruits i n boiling water for 1 minute, slipping the skins off, rinsing thor­ oughly w i t h water and removing the seeds. Subsequent processing of the fruit components and extraction of the contained toxi­ cants have been described (11, 12, H, 15). Analyses for D D T residues have been made with the dehydrohalogenation method (11, 15). The magenta color reaction of Averell and Norris (1) as modified by Gunther and B l i n n (14) was used to analyze for parathion residues. Appropriate fruit blanks were run with each set of analyses. The results of all determinations are expressed as parts per million based on fresh weight of analyzed substrate. When dissection of fruits was involved i n the preparation of the samples, the values reported represent the parts per million of toxicant based on fresh weight of the indicated component only and not of the weight of the whole fruit. A s separated i n these studies the peel of most citrus fruits constitutes approximately one sixth the weight of the whole fruits.

Results The summarized data presented in Tables I to V I I indicate the nature of the results which have been obtained in certain of these studies. It is not intended that these be i n ­ terpreted as absolute values since cogent limitations exist not only i n the techniques of Table I.

Immediate Posttreatment Residues of DDT in Peel of Citrus Fruits (Sampled 48 hours after application)

Type Formulation

Technical Grade DDT/100 Gal., L b .

Wettable powder Kerosene solution Kerosene solution Light medium oil solution Light medium oil solution β

2.0 2.0 1.0 1.2 0.6

Navel oranges 5.6 13.9 3.9 17.1 11.8

Ρ.Ρ.ΜΛ D D T Valencia oranges 5.8 16.4 10.7 6.3 5.9

Based on fresh weight of peel only.

In AGRICULTURAL CONTROL CHEMICALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1950.

Eureka lemons 5.6 12.2 7.5 13.1 7.8


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sampling and sample preparation but also i n the methods of recovery by extraction and i n the quantitative procedures of estimation. For example, in these studies the over-all efficiency of the D D T dehydrohalogenation method from sampling through calculated results appears to be approximately 9 0 % whereas that for parathion is probably not more than 6 0 % (14, 15). On the other hand, the data may help to characterize the nature and extent of the problem imposed by the use of these or similar materials and to indicate the relative effects of some of the factors i n penetration phenomena. Consistent with the definition of terms adopted for the discussion in this series of papers of integral phases of the residue studies being conducted by the Division of E n t o ­ mology, University of California Citrus Experiment Station (2, 13-15), the following distinctions are noted: Residues may be specified as pretreatment, posttreatment, har­ vest, or ultimate. The latter refers to the residue on or i n foodstuffs, whether fresh or processed, at the time of consumption (2, 13). The location of residues with reference to fruit parts may be extra-surface (external to the cuticle) or subsurface. Subsurface residues may be differentiated with reference to actual location as cuticular residues or specified intracarp residues. Residues i n the cuticular layers or in any of the cellular structures or matrices are herein indicated as subsurface (penetrated) residues (2, 13). Citrus F r u i t s . T h e recovery of demonstrable amounts of D D T i n the peel of oranges and of lemons indicated the necessity for detailed studies w i t h regard to the effect of dosage, formulation, number of applications, method of application, fruit development at time of application, and other factors. W i t h i n the precision of the methods utilized D D T has never been recovered from the pulp portions of D D T - t r e a t e d citrus fruits. Results typical of the amounts found as subsurface D D T i n the composite peel of citrus fruits are collated in Tables I and I I . The infiltration of D D T into the peel was rapid, and it persisted there over long periods during the development and m a ­ turing of the fruits. The magnitude and distribution of penetrated D D T residues were influenced by the specific nature of the formulation applied. Dissection of orange and lemon peel into subsamples of flavedo (outer peel) and albedo (inner peel) showed in subse­ quent analyses that in all cases most or all the D D T was present i n the flavedo. I n a limited number of instances relatively small amounts of D D T were recovered i n the albedo tissues, particularly when the fruits were sprayed with D D T formulations involving large amounts of kerosene or heavier fractions of petroleum oils. Table II.

Harvest Residues of DDT in Peel of Citrus Fruits (Averages for all samples)

Spray Schedule , No. Applications 0

Valencia oranges 1 2 3 Navel oranges 1 2 3

Fruit Development at Time of Last Application Approaching maturity Intermediate Post blossom -P.P.M.6 D D T 11.3 10.7 4.7 4.7 7.3


16.7 22.0 25.3

5.3 13.3 12.7

25.3 36.7

All sprays were formulated by dissolving 2 pounds of technical grade D D T (8 grams D D T / 1 0 0 ml. solvent) in 3 gallons of kerosene-Velsicol AR-60 (95-5) and emulsifying the solution with 4 ounces of blood albumin spreader in 100 gallons of finished spray. b Based on fresh weight of peel only. α

The use of D D T at application rates indicated i n Table I I represents the maximum dosage that has been considered for commercial use on citrus. The largest current uses of D D T on citrus involve single applications at the rate of 0.75 pound of technical grade compound per 100 gallons of spray mixture. The amount of D D T found in the peel of oranges harvested from 2 to 7 months after treatment with these dosages has ranged from 0.6 to 4.6 p.p.m., fresh weight of peel. Varietal differences with regard to the amount of D D T present i n the peel of har­ vested fruits sprayed at different times during the development of the fruit suggest the In AGRICULTURAL CONTROL CHEMICALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1950.



possibility of determining i n subsequent investigations certain of those factors limiting the infiltration of D D T into fruit tissues (Table I I ) . Studies with parathion-treated citrus fruits have also shown no parathion to be present i n the endocarpal, or pulp segment, portions of the fruit (Tables I I I , I V , and V I ) . Since the magenta color reaction for parathion is extremely sensitive, i t is believed that even trace quantities are not present i n the pulp. The rapidity of the subsurface penetration of parathion into the peel of citrus fruits and the persistence of these residues i n the peel is demonstrated i n Tables I I I through V I I . Table III.

Posttreatment Residues of Parathion in Citrus

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(Sprayed with 4 pounds of 25% parathion wettable powder per 100 gallons water 4-26-48) - P . P . M . ParathionEureka Lemons Valencia Oranges Peel & Peel b Pulp Pulp

Sampled after, No. Days




1 2 4 8 10 14 17 53

12.4 9.8 9.1 6.2 4.4 2.9 2.7 3.0

15.9 11.8 10.5 8.9 5.1 4.6 2.8

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0


0.0 0.0 0.0 0.0 0.0 0.0

° Valencia oranges approaching maturity and lemons mature when sprayed. b Based on fresh weight of peel only. Based on fresh weight of entire fruit. c

Table IV.

Harvest Residues of Parathion in Valencia Oranges

Technical Grade Parathion/ 100 Gal.°, L b .

Time after Application, Days 140 170 P . P . M . Parathion


Peel 0.5 0.75 1.0 Pulp