PESTICIDE RESIDUES IN FOOD - 1984
Sponsored jointly by FAO and WHO
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
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
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
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
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
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.
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,
4th Stage DPA is the present standard of DPA used for apple
scald control; some may be used in fragrances and
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
biphenyl-4-ylamine1 mg/kg maximum
Melting point: 52.5°C
Manufacturers with whom this specification has been discussed
believe that it would be possible and economically practical to comply
RESIDUES IN FOOD AND THEIR EVALUATION
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.
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
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
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.
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
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.
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
Dip or drench 2000-2500 mg/l -- Eksteen, 1980
Pre-harvest spray 22 kg a.i./ha Spray once only, Thomson,1981
to run-off not above 27°C
Post-harvest dip 2000 mg a.i./l Dip only between
or spray (30 sec.) 10 and 32°C,
15 and 27°C
Treat fruit once
Wax emulsion 5000 mg a.i./l
spray or roller
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;
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
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
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. 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
METHODS OF RESIDUE ANALYSIS
Several analytical methods have been published since the 1979
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
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.
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
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
Belgium 3 3
Eire 3 3
France 3 -
South Africa 10 -
Netherlands 3 3
Australia 10* 7
New Zealand 10 -
Hong Kong 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).
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
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
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
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
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