PESTICIDE RESIDUES IN FOOD - 1984 Sponsored jointly by FAO and WHO EVALUATIONS 1984 The monographs 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 Rome, 24 September - 3 October 1984 Food and Agriculture Organization of the United Nations Rome 1985 DIPHENYLAMINE Explanation Diphenylamine (DPA) was evaluated in 1969, 1976, 1979 and 1982 1/. The 1982 meeting noted that biphenyl-4-ylamine (identified in the 1982 evaluation as p-biphenylamine), a known carcinogen, had been found in four of six samples of diphenylamine analysed for minor impurities. Information on the nature and level of the impurities in commercial DPA was therefore thought to be desirable. An extensive review of the uses, manufacture and properties of DPA was available to the present meeting. Information relevant to the uses of DPA in food production is evaluated in this monograph addendum. IDENTITY Purity of the commercial product Methods for the synthesis of DPA have been described by Kirk-Othmer (1968, 1978), Hoelscher and Chamberlain (1950, 1951) and Scott (1962). Diphenylamine of the quality used in early work on scald control in apples was produced by a chemical company in the USA. The standard they specified was 99.9% DPA minimum as a fine white powder of 52.9°C minimum melting point; 10 mg/kg maximum primary amines expressed as aniline; 20 mg/kg maximum lead; volatiles by vapour phase chromatography 0.5% and ash 0.01%. The method of manufacture was by the reaction of aniline in the vapour phase at 480°C and about seven atmospheres pressure over an activated alumina catalyst. The product vapours were cooled, condensed and subject to continuous distillation to remove most of the unreacted aniline and by-product ammonia. The crude DPA concentrate was then distilled batchwise to recover the remainder of the unreacted aniline and to separate DPA from the impurities. The cooled DPA in flake form was then dissolved in aqueous isopropanol and the solution purified with activated carbon. After filtration, the solution was cooled to cause the DPA to crystallise and the purified DPA was isolated by centrifugation. 1/ See Annex 2 for FAO and WHO documentation It appears to have been material of this quality that was referred to in the 1969 evaluation. The samples analysed by Safe et al. (1977) (see 1982 evaluation) were from six different sources, but it was not disclosed what they were, nor who made the chemicals. It is therefore not possible to say whether any of the samples referred to the grades of purity in use for apple scald control. Commercial purification of DPA It appears from the literature that it is possible to recognise five stages in the purification of DPA produced by the above process. "Stage 1 DPA" comes into existence when the aniline has been partly converted to DPA but is still in the vapour stage at 480°C. After cooling and release of ammonia gas the material is distilled to form "Stage 2 DPA". This would contain about 250 mg/kg or less of biphenyl-4-ylamine, more frequently referred to as 4-aminobiphenyl (4-ABP). This is again fractionally distilled to produce "stage 3 DPA" which is the "technical DPA" of general commerce. According to Kirby (Patent-date unknown) an orthophosphoric acid treatment of Stage 2 DPA would result in a twenty-fold reduction in impurity levels. If that factor is applied to the 250 mg/kg 4-ABP level of Stage 2 DPA, one could expect 12.5 mg/kg of 4-ABP in Stage 3 DPA. In fact sales and technical literature for commercial DPA claim a maximum level of 4-ABP of 20 mg/kg. Material of this grade is used in industry as an antioxidant in explosives, plastics, oils and greases etc. This "Stage 3 DPA" when recrystallised from alcohol with a carbon treatment might be expected to have its 4-ABP level reduced from about 20 to 2 mg/kg. Unpublished evidence to support this was seen in the late 1970s. This can be regarded as "Stage 4 DPA". In view of the publication by Safe et al. (1977), the Australian authorities obtained certificates of analysis of the DPA batches received from the manufacturer. The level of 4-ABP, confirmed by independent analysis, varied from about 0.8 mg/kg 4-ABP to just under 3 mg/kg. The DPA in all batches was from a supplier whose specification included one stage of recrystallization. It therefore appears that the original material of the 1960s could reasonably be expected to have contained about 2 mg/kg of 4-ABP if the means had been available then to determine it. In relation to the impurities in the diphenylamine on which previous JMPR evaluations were based, it became possible to establish the source of the material used by Coulston et al. (1971) in work cited by the 1976 JMPR. Subsequent analysis of DPA from the same source and with the same reference number showed a 4-ABP content of 0.4 mg/kg. The DPA was marketed as "American Chemical Society (ACS) Grade". In reply to enquiries, the manufacturers stated that they had had two suppliers of ACS DPA and that two stages of recrystallization were made routinely. The specification received did not include a statement of the 4-ABP content. The DPA with 2 recrystallizations may be called "Stage 5 material", and is believed to be the purest DPA available commercially; it would contain about 0.4 mg/kg 4-ABP and is likely to be similar to the material used in 1971 by Coulston et al. The characteristics of DPA corresponding to the five stages described above are summarized in Table 1. Table 1. Characteristics of DPA at various stages of purification Process Physical Colour Analysis 1st Vapour - DPA with gross amounts of 4-ABP, anilene and co-products. 2nd Flake or Yellow DPA with 250 mg/kg or less of 4-ABP, solid to brown aniline and co-products. 3rd Flake or DPA with 20 mg/kg or less of 4-ABP, and solid or White less than 1000 mg/kg of primary amines. crystals 4th Crystals Colourless DPA with about 2 mg/kg of 4-ABP and less to white than 10 mg/kg of primary amines. 5th Crystals Colourless DPA analytical standard containing to white about 0.4 mg/kg of 4-ABP 1st and 2nd Stage DPA is not normally encountered in commerce. 3rd Stage DPA is used as an intermediate for the synthesis of other chemicals. It is also an antioxidant used in the formulation of such products as oils, greases, plastics, explosives. 4th Stage DPA is the present standard of DPA used for apple scald control; some may be used in fragrances and cosmetics. 5th Stage DPA is used as an indicator and as a reagent in analysis. It is the grade marketed for analytical work. Similar to the grade used by Coulston et al. (1971). The nature and content of impurities other than 4-ABP in DPA are uncertain. Acridine, quinoline and indole are implicated in published literature. Safe et al. found cyclohexyl-anilines, as well as 2- and 4-aminobiphenyls. In the present context, it is the 4-ABP content that is of most concern. In the present circumstances, it seems possible to propose the following partial specification for diphenylamine (food grade): Appearance: white crystalline powder Purity: 99% minimum Impurities: aniline 5 mg/kg maximum biphenyl-2-ylamine20 mg/kg maximum (2-aminobiphenyl) biphenyl-4-ylamine1 mg/kg maximum (e-aminobiphenyl) Melting point: 52.5°C Manufacturers with whom this specification has been discussed believe that it would be possible and economically practical to comply with it. RESIDUES IN FOOD AND THEIR EVALUATION USE PATTERN Diphenylamine as an industrial chemical is used widely because of its antioxidant properties. Its main and almost only significant agricultural use is to control superficial scald in apples (see 1969 evaluation). Information provided by one of the major companies supplying DPA formulations for scald control indicates that the annual world-wide use for this purpose is about 85 tonnes. Application Both pre- and post-harvest treatments have been used, but the latter have been found more effective. In current practice (see also 1969 evaluation), harvested fruit are (a) dipped in aqueous suspension (500 to 3000 mg/l,) (b) sprayed in boxes, pallet loads, bins or conveyors (1000 to 2000 mg/l) boxes immersed in suspensions or emulsions, or (c) individual apples wrapped in impregnated paper (1 to 2 mg/wrap). During the 1970s the techniques of spraying (rain) or drenching (waterfall) treatments together with 20-bushel bin dunking have been accepted as the most cost-efficient. Particular attention is now paid to time of exposure to the chemical suspension, to the temperature of the fruit and to the subsequent drying of the chemical film as these all determine the peak value of chemical residues. Most treated fruit are held in storage for 80 to 200 days or more before marketing. Early harvesting and longer storage periods are conducive to scald. Holmes et al.(1981) determined the lowest effective DPA concentrations as influenced by harvest date and storage time on Granny Smith apples in southern Victoria (Table 2). Table 2. Lowest Effective DPA Concentration in relation to harvest date and storage time Harvest Date Removal Date from Store September 2 October 12 November 22 Lowest effective dip concentration, mg/l April 7 2400 2400 2400 April 14 600 2400 2400 April 21 600 600 2400 April 28 600 600 2400 May 5 0 600 600 If dipping was delayed on early-picked fruit it was found that not even 2000 mg/l was effective. Present recommendations are therefore not to delay dipping by more than four weeks if Granny Smith are harvested early (mid-April). Diphenylamine may be used in conjunction with cooled storage in atmospheres where the carbon dioxide concentration is controlled. Scott et al. (1962) showed that under such conditions Granny Smith apples could be stored for at least seven months. There was better retention of green colour, reduced rots and senescent blotch, freedom from core flush, firmer fruit as measured by penetrometer tests, and better customer acceptance as judged by organoleptic panels. The highest quality was evident when 5% carbon dioxide and 2.5% oxygen were combined with the DPA. Diphenylamine may be used in conjunction with calcium salts, added to control bitter pit of apples. Ginsberg et al. (1976) in South Africa have reviewed the data available to 1976 on the combined use of DPA and either calcium chloride or calcium nitrate. Lee et al (1984)showed that the addition of 3% calcium chloride to the DPA dip bath did not influence the level of DPA deposited on apples, nor did the addition of surfactant spreaders. This is no doubt true of current commercial formulations but it is certainly not true for formulations used in the 1960s and early 1970s. Diphenylamine is also used in combination with fungicides to control fungal rots, and in multi-formulation dips containing DPA, calcium salts, fungicides and waxes. Factors affecting the use and efficacy of the latter have been discussed by Little et al. (Little, 1977a,b; 1984. Little et al., 1980a,b; 1981a,b; 1984. Little and Peggie,(1984). Recommendations and registrations Recommendations are noted in Table 3. Some of them may no longer be current practice. Formulations Currently available formulations for use world-wide consist of 7 xylene-based emulsifiable concentrates, 1 wettable powder, 1 wax coating, 1 soluble concentrate and 3 sources of impregnated paper wraps. It is now common practice to use DPA, calcium and fungicides as a single post-harvest treatment, but each is presented as a separate formulation and the grower combines them as a tank-mix. Since the N-hydrogen of DPA is easily replaced and any nitrous acid present will form N-nitrosodiphenylamine, calcium nitrate salts are not advisable in the tank mix in case nitrite might be a contaminant. Other agricultural uses of diphenylamine Stem cavity browning and brown core of McIntosh apples were controlled by DPA, but only in conjunction with controlled atmosphere storage (Lougheed et al.(1978). Wills and Scott (1982) controlled soft scald on Jonathan apples with a mixture of DPA, a vegetable oil and "Tween 80". The use of DPA as a pre-treatment to prevent phytotoxicity to apples from methyl bromide fumigation (Sproul et al.1976) is the subject of a patent application (McLachlan et al.1983). Rahman (1980) has suggested the use of DPA on pineapples to extend the time of marketing of the fruit. Dalton & Nel (1982) have treated sunburn on South African Granny Smith apples. There seems the possibility that soft scald may also be controlled on the Jonathan variety (Wills et al. 1981), but may cause damage by initiating low-temperature breakdown in the core of the apples (Wills & Scott, 1973). DPA has been used in photodegradable formulations of DDT (Parmar, 1976), and to degrade DDT deposits in sunlight (Ivie & Casida, 1971). It can stabilize ethylene thiuram monosulphide fungicide formulations, (Yamaguchi, 1972). It has also been suggested for use to protect rice against thiocarbamate herbicides but this use has not been developed yet (Takematzu, 1976). Table 3. Recommended applications of diphenylamine to apples Method of Application Diphenylamine Ethoxyquin Ref. Australia Tree spray 300 to 400 g/100 l -- Hall 1972 3000 to 4000 ppm Dip or spray 100 to 250 g/100 l 200 to 500 g/100 l after harvest 1000 to 2500 ppm 2000 to 5000ppm Wrap, plain 31 mg/m2 76 mg/m2 Wrap, oiled 23 mg/m2 54.62 mg/m2 Tray packs 300 mg per tray 1500 mg per tray In cell-packs 50-80 mg/kg in cell 4000 mg per carton dividers and layer of 20 kg fruit pads South Africa Dip or drench 2000-2500 mg/l -- Eksteen, 1980 USA Precautions Pre-harvest spray 22 kg a.i./ha Spray once only, Thomson,1981 to run-off not above 27°C Harvest within 36h Post-harvest dip 2000 mg a.i./l Dip only between or spray (30 sec.) 10 and 32°C, preferably between 15 and 27°C Treat fruit once only Wax emulsion 5000 mg a.i./l spray or roller treatment The use of DPA as a bird repellant is recorded (Thomson, 1981), and it has been used to stabilize carotene in alfalfa meal (Thompson, 1950). It has been superseded in a number of minor pesticidal applications by other compounds. RESIDUES RESULTING FROM SUPERVISED TRIALS A wide range of residue levels has been reported during the last 25 years. There are reports showing up to 19 mg/kg on whole fruit or about 50 to 150 mg/kg on the peel just after dipping in 1000 to 1500 mg/l DPA (Hall and Scott, 1961), whilst others show maxima of about 0.2 mg/kg in the flesh and 5 mg/kg on the skin (Huelin, 1968). At least two factors contributing to the wide range can be identified: (1) it is not always clear whether skin, flesh, or whole apple was analysed; (2) methods of analysis have changed, and it must be accepted that later work is likely to be more reliable. Residues resulting from supervised trials were reviewed in the 1969, 1976 and 1979 evaluations, the latter including extensive information on the effects of a variety of factors on residues resulting from post-harvest treatments. In trials since 1979 Lee et al.(1984) showed that the nature and quality of the commercial formulation influenced the magnitude of the deposit of DPA on the fruit. In one trial with three commercial formulations from different sources the deposit on identical Granny Smith apples dipped for 60 sec. in a bath containing 2000 mg/l DPA ranged from 1.5 to 3.0 mg/kg. (two formulations deposited 1.5 mg/kg) when the temperature of the bath and fruit was 13°C. Lee et al.(1980) also reported that when the DPA bath was at 35°C, DPA residues on apples were higher than when bath temperatures were between 5°C and 21°C. No significant differences were found between 13° and 22°C, but residues were significantly lower at 4°C. Odental et al.(1981) tested residue levels after using the waterfall and rain systems of applying DPA to Granny Smith apples. Fruit picked at optimum harvest time were treated at 2500 mg/l at a rate of 3000 and 2000 litres per minute for 25 and 60 seconds respectively in 20-bushel bins. The fruit were stored at 0.5°C and sampled after 30 days from the top, middle and bottom layers. The residues in the three layers were 4.5, 5.2 and 5.3 mg/kg (waterfall) and 3.6, 5.7 and 5.9 mg/kg (rain system) respectively. DPA uptake differed little between powder and emulsion formulations and the addition of 1000 mg/l thiabendazole or benomyl made little difference. These levels compare well with the immersing of bins in dip reported earlier (Hanekom et al. 1976). Little and his colleagues at Knoxfield, Australia, between 1979 and 1984, examined the effect on the DPA residue of including calcium and fungicides in the treatments. They also examined dip time and temperature effects on residues. The DPA was applied 'on line' ("rain" in South Africa) and by drench ("waterfall" in South Africa). A xylene-based emulsifiable concentrate and a non-hydrocarbon-solvent- based preparation were compared. There were direct relationships between DPA residues and time in the dip, temperature of the fruit and dip, and concentration of the DPA. There were indications that stickers used with the calcium and possibly the added calcium itself and fungicides also affected residue levels. The residues recorded in the reports are expressed as mg/kg in the skin. If reduced by a factor of 8 to convert to mg/kg whole fruit, it can be seen that residues equivalent to about 11 mg/kg on the whole fruit were found only at the highest fruit temperature (40°C), longest dip time (100 secs), in a xylene-based formulation (at 4000 mg/l), with sampling shortly after dipping and with calcium and stickers. With the current standard recommendations for dipping (see "Use pattern" above), the MRL of 5 mg/kg would not be exceeded. An examination of the ongoing records of the monitoring of DPA residue levels on export fruit from Australia for 1983 shows no cause for concern in that respect (Little, 1979; Little et al. 1984; Snelson, 1984). FATE OF RESIDUES Information on the fate of residues in storage was reviewed in 1969, 1976 and 1979. Losses on peeling are indicated in the 1976 and 1979 evaluations. The following additional information has been received. In Cooking Pennwalt (1982) in two series of trials in France and the USA, showed that 70-95 percent of the residue present in whole raw apples was lost when the apples were baked for 30 minutes at 180°C. Cored apples had a lower residue after baking than fruit with the core intact. The loss during baking was greatest in apples that were in store at 0°C for 2 weeks prior to baking, but the reason for this was not determined. RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION Data from the USA (Pennwalt, 1984) provided evidence that the application of DPA to apples in commercial packing houses results in residues, at the time of treatment, which are within the MRL recommended by the JMPR (5 mg/kg). During 1983, 87 samples of apples were received from more than 40 packing houses through the USA. These represented 5 varieties treated over a period of 5 months. Analyses were performed with 3-8 days of treatment. The results are shown in Table 4. Table 4. Residues of diphenylamine in apples in packing houses in the USA (Pennwalt 1984) High 6.60 mg/kg Low 0.10 mg/kg Average 1.62 mg/kg Standard duration 1.01 mg/kg Range, mg/kg Number % >5 1 1.1 4-5 2 2.3 3-4 6 6.9 2-3 11 12.6 1-2 49 56.3 0.5-1 14 16.1 >0.5 4 4.6 87 100.0 METHODS OF RESIDUE ANALYSIS Several analytical methods have been published since the 1979 evaluation. Waefler et al. (1972) described a rapid method sensitive to 0.05 mg/kg. Samples are extracted under alkaline conditions with ethyl acetate and analysed by capillary gas chromatography on a persilylated OV-73 column with flame ionization detection. In Australia, Luke and Cossens (1980) extracted apple peel with acetonitrile and cleaned up the extract by hydrochloride formation. Determination was by GLC with a Hall electroconductivity detector. Using 12.5g peel, a limit of determination of 0.05 mg/kg was reached. The detector in use now is modified. The method is rapid and consequently suitable for the large-scale monitoring of Australian export apples. In England, Allen and Hall published two methods: the first involved formation of the fluorobutryl derivative of DPA after clean-up and the second steam distillation of the DPA and direct determination. The former method used electron-capture GLC and the latter a nitrogen-sensitive termionic detector. The latter method after correction for recovery losses gave residue levels about one third higher (Allen & Hall, 1980). Results obtained by both methods have been reported (Johnson et al. 1980). Allen and Hall speak of a possible binding of the DPA to the apple during the storage period and suggest that possibly one method released the DPA and the other did not. They recommend the use of Veith and Kiwis steam-distillation and solvent-extraction apparatus with the direct method of determination because of the higher results. Little and his colleagues have also used the latter method in experiments described in an unpublished paper (Little et al. 1984). A development of an earlier dip-side test originated by J.B. Watkins of the Trout Food Preservation Research Laboratories, Brisbane, is described by Little et al. (1981). It is a rapid and reliable method based on the formation of a blue oxidation product of diphenylbenzidine. This can be compared with standard preparations at a wavelength of 650 nm. Diachenko (1979) described a procedure sensitive to 20 µg/kg (ppb) to determine industrial amines in fish. The tissue is digested in aqueous sodium hydroxide and extracted with benzene. After washing in acid, the extract is cleaned by gel-permeation chromatography and quantitated using nitrogen-selective GLC. This method can separate DPA from other diarylamines. Laub and Woller (1976) described a method of volatilizing material by heating in a micro-oven and passing the volatiles on to a thin-layer plate via a nitrogen stream, where they are adsorbed and separated by TLC. DPA, biphenyl and e-phenylphenol were shown to be detected in citrus and banana peels. NATIONAL MAXIMUM RESIDUE LIMITS The following national MRLs have been reported. It should be noted that not all countries publish MRLs routinely and the absence of an MRL does not necessarily mean that DPA-treated fruit would be barred entry to the country concerned. Table 5. National MRLs effective March 1984 Country MRL, mg/kg Apples Pears UK 10 10 USA 10 - Canada 10 - Fed. Rep. Germany 3 - Denmark - - Finland 5 - Hungary 10 - Israel 10 - Kenya 10 - Norway 10 - Sweden 3 - Table 5 (continued) Country MRL, mg/kg Apples Pears Belgium 3 3 Eire 3 3 France 3 - South Africa 10 - Netherlands 3 3 Australia 10* 7 New Zealand 10 - Hong Kong Permitted Philippines Permitted Iran Permitted Malaysia Permitted Brazil Approval anticipated Italy Approval anticipated * Proposal to lower to 5 mg/kg. In some countries a zero MRL exists for milk and meat. The first country to register the use of DPA was the USA which in 1962 allowed its use on apples with a tolerance of 10 mg/kg. There is a zero tolerance for milk and meat. The Codex Alimentarius MRL is 5 mg/kg. OCCURRENCE OF DPA IN UNTREATED FOOD AND THE ENVIRONMENT DPA has been identified in baked potato, buckwheat flour, tomato, green tea, salted fish and dried plums. (Coleman et al. 1981); Yajima et al. 1983; Chung et al. 1983; Nose et al. 1971; Fahmy et al. 1983; Moutounet et al. 1975. So far as can be ascertained from the literature it has not been found in apple volatile compounds. Although early work showed blank control apple levels as high as 0.9 mg/kg apparent DPA (USDA, 1961), more recent analyses with specific detectors have not detected DPA in control samples. (Allen & Hall et al. 1980; Luke & Cossens, 1980). Both in Austria and in Sweden, DPA has been recorded as a component of the smoke of tobacco (Klus & Kohn, 1977; Peterson et al. 1980). It was discovered in the volatiles of exogenous origin from the human oral cavity (Kostelc et al. 1981). The sources were stated to be water and cosmetics. Veith et al. (1979) have measured the uptake and bioconcentration factor of DPA in fish. This is of concern if river pollution occurs where DPA is manufactured. DPA has a bioconcentration factor of 30 (cf DDT, 29400) and potentiation 0.1 (cf DDT, 580). Schafer et al. (1983) have reported on the acute oral toxicity, repellency and hazard potential of DPA amongst 197 other chemicals to one or more species of wild and domestic birds. The LD 50 was found to be greater than 101 mg/kg. Briggs included DPA in a study of factors which determine transport of a pollutant by water and its possible bioconcentration factor. (Briggs, 1981). APPRAISAL An extensive review of all aspects of the use of diphenylamine in agriculture was available to the meeting. In view of certain toxicological issues, attention was given to the various methods of synthesising and purifying diphenylamine to produce a quality which is suitable and acceptable for the treatment of apples and pears as a means of preventing the development of superficial scald. A proposal is made for a specification for such a pure (food grade) diphenylamine. This specification has been discussed with the several manufacturers concerned with the production of diphenylamine formulations for treating apples and pears, who believe it would be possible and economically practical to comply with such a specification and thereby ensure that there were no grounds for concern over the safety of such treatments to consumers of treated fruit. The importance of diphenylamine in preventing superficial scald of pome fruit, which has serious economic and logistical effects on the storage, marketing and distribution of high quality fruit, is noted. The importance of harvest date and fruit maturity in relation to the effectiveness of diphenylamine is confirmed. Recent developments have provided practical means of simultaneously controlling other fruit storage diseases. These demand the availability of high quality diphenylamine formulations. A study of the extensive data on residues of diphenylamine in fruit confirms that the MRL recommended by the 1979 meeting (5 mg/kg) is adequate to cover the residues resulting from the effective use of modern commercial diphenylamine formulations. This is further confirmed by monitoring studies in Australia and the USA. A number of developments in analytical techniques in recent years have improved the simplicity, accuracy and versatility of methods which are suitable for regulatory purposes. The advantage of analysing only the peel is confirmed but it is stressed that the results must be expressed on the basis of the whole fruit. It appears that if diphenylamine occurs naturally in apples, the level is too low to present any practical problems in enforcing the recommended MRL. Some observations are made about the occurrence of diphenylamine in untreated food and the environment. The meeting confirms that the MRL previously proposed is appropriate. It recommends that only purified grade diphenylamine be used in the formulation of preparations for the treatment of apples and pears. This grade should meet the following specification. Appearance: white crystalline powder Purity: 99.9% minimum Impurities: aniline 5 mg/kg max. biphenyl-2-ylamine (2-aminobiphenyl) 20 mg/kg max. biphenyl-4-ylamine (4-aminobiphenyl) 1 mg/kg max. Melting point: 52.5°C REFERENCES Allen, J.G. and Hall, K.J. Methods for the determination of 1980 diphenylamine residues in apples. J. Agr. Food Chem. 28: 225-228. Briggs, G.G. 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Holmes, R.J. Showell, L. and Tozer, N. Victorian Dept. of Agriculture, 1981 Biennial Research Report. pp 39-40. Huelin, F.E. Superficial scald, a functional disorder of stored 1968 apples. III Concentration of diphenylamine in the fruit after treatment. J. Sci.Food Agric. 19 (6): 294-6. Ivie, G.W. and Casida, J.E. DPA will degrade DDT in sunlight. J. Agri. 1971 Food Chem. 19: 405-409. Johnson, D.S., Allen, J.G. and Warman, T.M. Post harvest application of diphenylamine and ethoxyquin for the control of superficial scald on Bramley's seedling apples. J.Sci. Food Agric. 31 (11: 1189-94. (C.A. 94:11598j). Kirby, K.D. DPA purification using ortho phosphoric acid. Australian Patent 253616. German offen 1161567. British Patent 910 130. Kirk-Othmer. Synthesis of DPA. Encyclopaedia of Chemical Technology, 1968 2nd Ed. Vol.7, Diarylamines. Monograph page 41. Kirk-Othmer. Production figures for DPA. Encyclopaedia of Chemical 1978 Technology 3rd Edition. Vol 2. page 331 (Monograph). 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See Also: Toxicological Abbreviations Diphenylamine (ICSC) Diphenylamine (FAO/PL:1969/M/17/1) Diphenylamine (Pesticide residues in food: 1976 evaluations) Diphenylamine (Pesticide residues in food: 1979 evaluations) Diphenylamine (Pesticide residues in food: 1982 evaluations) Diphenylamine (Pesticide residues in food: 1984 evaluations)