PESTICIDE RESIDUES IN FOOD - 1979
Sponsored jointly by FAO and WHO
Joint meeting of the
FAO Panel of Experts on Pesticide Residues
in Food and the Environment
WHO Expert Group on Pesticide Residues
Geneva, 3-12 December 1979
Diphenylamine was first evaluated in 1969 when an ADI was allocated
and a MRL for apples. In 1976 additional toxicological and residue
data from Australia and the Netherlands were received and the meeting
confirmed the ADI and recommended that, unless countries had a need to
maintain the MRL for apples at 10 mg/kg, it should be reduced to 5
Residue data have been generated in Australia and additional
information has been obtained from USA and the open scientific
literature to permit the meeting to further evaluate the MRL.
RESIDUES IN FOOD AND THEIR EVALUATION
Since the evaluation in 1976 indicated that residues on apples are
generally less than 2 mg/kg, the data considered in 1969 have been
re-evaluated with a view to seeking an explanation for the higher MRL
proposed on that occasion. The difference can be explained by the
1. The concentration of diphenylamine dip solutions used over recent
years is substantially less than those used in experiments in the late
2. The quality and stability of the formulation has an important
bearing on the amount of diphenylamine deposited on fruit from dips
and sprays. The quality of diphenylamine emulsion and wettable powder
formulations has been improved considerably with a result that they
give more uniform and lower deposits.
3. All of the residue data reported by Harvey and Clark (1959) and
apparently much of that reported by Bruce (1958) used as a basis for
the evaluation in 1969, refer to residues in the peel rather than the
whole fruit. These and later studies have usually shown that the
concentration is much higher in the peel than in the whole fruit.
Importance of formulation and stability of dips
Denmead et al (1961) used a diphenylamine emulsion which was
homogenised by passing five times through a colloid mill until a
uniform globule size was achieved; most globules being between 1 and 4
microns diameter, with very few exceeding 5 microns. It was noted
that without homogenisation less uniform emulsions with much larger
globules were formed and that these coarse emulsions gradually broke
down during their passage through the spray equipment. Diphenylamine
uptake was found to be negatively correlated with globule size and
until fine uniform emulsions were formed, it was not possible to
obtain reproducible uptake of diphenylamine.
During drenching operations the diphenylamine concentration in the dip
gradually fell as a result of uptake of diphenylamine by apples and
dilution of the emulsions by water introduced on the wet apples. The
concentration of the bath before and after treatment differed by as
much as 30 percent.
Gorman and Row (1977) investigated the properties of two different
commercial diphenylamine formulations and showed that emulsion
breakdown was accompanied by phytotoxicity due to the uneven and
excessive deposition of diphenylamine on the skin of fruit. The
practice of combining calcium chloride with diphenylamine dips to
control bitter pit as well as superficial scald can result in rapid
breaking of the emulsion. The spraying operation, which greatly
increased aeration, also resulted in the rapid breaking of the
diphenylamine emulsion. The quality of the water used for diluting
the emulsion also had a distinct bearing on its stability.
Gorman and Rowe (1977) also showed that stable formulations give a
lower deposit on apples and consequently are not as effective in
controlling superficial scald. This can be overcome by increasing the
concentration in the dip bath. In dipping tests, one preparation
yielded initial deposits three to six times higher than the more
stable preparation applied at the same concentration for the same
time. The unstable emulsion tended to give a much higher deposit when
the dip time was increased from 60 to 180 seconds. The residual
deposit from the stable preparation was not significantly affected by
the dipping times.
Little et al (1977) drew attention to the effect of additives (calcium
chloride, benomyl and on fruit susceptibility to phytotoxic damage.
Calcium chloride benomyl caused the active ingredient to be stripped
out rapidly onto the fruit.
Denmead et al (1961) used a standard diphenylamine solution in oil,
emulsified with water to prepare a range of concentrations from 0.05%
to 0.3%. These were used to dip two varieties of apples. The uptake
of diphenylamine was measured by analyzing the fruit. Hanekom et al
(1976) demonstrated the effect of immersion time and diphenylamine
concentration on the uptake of diphenylamine by Granny Smith apples.
This could be readily correlated to the percentage reduction of
superficial scald. Their results are summarised in Table 1 (see also
comment under "Residues resulting from Supervised trials, Cornell
Table 1. Effect of immersion time and DPA concentration on the uptake
of DPA (ppm) by Granny Smith apples (Percentage superficial scald
given in brackets)
Immersion time (sec.) DPA concentration (ppm)
600 1200 1800
30 0.7 (91) 1.7 (83) 1.6 (78)
75 1.4 (80) 1.7 (95) 2.4 (77)
120 1.8 (74) 2.5 (71) 3.5 (4)
LSD (P = 0.05) Immersion time × DPA concentration = 0.6
Picking stage = 150 days
Fruit Temperature = 20°C
Temp. of immersion solution = 20°C
Hanekom at al (1976)
Hanekom et al (1976) investigated the effect of fruit temperature and
temperature of immersion solution on the uptake of diphenylamine by
Granny Smith apples and showed that this was readily correlated with
percentage superficial scald. Optimum results were obtained when the
immersion solution was at 40°C and the fruit temperature between 10°C
and 20°C. Their results are given in Table 2. The higher
temperatures lead to higher deposits on the fruit.
Table 2. Effect of immersion solution and fruit temperatures on the
uptake of DPA by Granny Smith apples (Percentage superficial scald
given in brackets)
Temp. of immersion Fruit temperature (°C)
solution (°C) -0,5 10 20
20 1.0 (91) 1.0 (100) 2.4 (89)
30 1.8 (85) 1.4 (84) 2.6 (50)
40 3.2 (30) 3.8 (0) 3.6 (2)
LSD (P = 0.05) Immersion solution × fruit temperature = 0.7
DPA concentration of immersion solution = 1 200 ppm
Picking stage = 150 days
Immersion time = 75 sec.
Hanekom et al (1976)
Effect of variety
The diphenylamine uptake was measured for a number of varieties of
apples in studies by Denmead et al (1961). A 0.2 percent emulsion of
diphenylamine was applied as a drench for one minute and the uptake
was determined by analyzing the fruit. The results are given in Table
Table 3. Variation of DPA uptake with variety
Worcester Pearmain 14.5
Cox's Orange Pippin 6.8
Ballarat (1) 4.0
Ballarat (2) 1.6
Granny Smith (1) 1.0
Granny Smith (2) 0.76
Denmead et al (1961)
Effect of size of fruit on uptake of diphenylamine
Since superficial scald and diphenylamine uptake are both surface
phenomena, some investigators have expressed the diphenylamine
concentration as mg/cm2 rather than as mg/kg, though the former
figure is not suitable for expressing residue concentration. The
surface area of apples was obtained by assuming them to be spheres and
applying the surface to volume relationship of a sphere (Denmead et al
1961). When the concentration of diphenylamine expressed as mg/cm2
and mg/kg on 8 apples of different weights were plotted against
surface area and weight respectively, it was apparent that the
diphenylamine concentration expressed as mg/kg was negatively
correlated with the weight of individual apples whereas when expressed
as mg/cm2 it was independent of surface area. For an apple weighing
180 g with a volume of 220 ml for example, the values of diphenylamine
uptake expressed as either mg/kg or mg/cm2 were numerically equal.
For larger apples the mg/kg figure became progressively smaller than
the mg/cm2 and conversely for smaller apples.
Rate of loss on storage
Hall et al (1961) showed that the concentration of diphenylamine on
apples fell greatly during storage. The concentration in the skin at
the end of seven months was only about 1/30th of that in the skin at
the time of treatment. The concentration in the whole apple fell by a
Table 4 (Denmead et al, 1961) sets out the initial and final
diphenylamine concentrations on three varieties of apples held in cold
storage. By measuring diphenylamine concentration at intervals during
storage, the rate of loss was obtained for a sample of Doughtery
apples. When the concentrations were plotted against storage times
for four samples of different initial concentrations, the rate of loss
was found to be almost constant and independent of the amount applied
to the apple.
Table 4. Loss of DPA from apples during storage
Storage Before storage After storage
Variety period Co-efficient
days p.p.m. of variation % p.p.m.
Granny Smith 199 ) 15.6 18 1.0
) 11.0 22 0.9
) 4.5 11 0.4
) 1.8 14 0.3
Ballarat 207 ) 6.7 11 0.5
) 4.6 16 0.3
) 1.4 22 0.2
Dougherty 172 ) 12.4 9 1.1
) 4.8 8 0.5
) 1.4 11 0.3
Denmead et al (1961)
Distribution on fruit
With the exception of Ginsburg (1962) all authors appear to agree that
the bulk of the residue is located in the natural wax on the fruit
with over 90% occurring in the peelings.
Harvey and Clark (1959) report that irrespective of variety, method of
treatment or concentration of diphenylamine applied, over 95% of the
diphenylamine is distributed in the peeling even after the fruit has
been in cool storage for lengthy periods.
Hanekom et al (1976) studied the percentile distribution of
diphenylamine in different fractions of the fruit after different
storage periods. Whilst there was a tendency for apples, in which
superficial scald was completely controlled, to have significantly
more in the cuticle wax layer, all fruit had from 52-77% in the wax
layer with as little as 1.3 to 5.6% in the hypodermis. This is
important as the diphenylamine is mainly restricted to parts of the
fruit where superficial scald initiates and develops, and therefore
the treatment is specifically effective at the site where it is most
Hall et al (1961) reported diphenylamine was practically confined to
the peel irrespective of the level and method of treatment or the time
in storage. These observations were borne out in recent studies in
Australia (Luke 1978, Gorman and Rowe, 1977). However, Ginsburg
(1962) using the methods of Harvey (1958) found that the amount of
diphenylamine remaining on the surface was negligible and the amount
found in the pulp was always much higher than in the skin except in
one instance. The one difference in technique was that most reports
in the literature are for studies carried out on apples immediately
after cold storage, whilst the work reported by Ginsburg was done
after the apples had been held at room temperature (15-20°C) for one
Luke (1978), reporting the results of analysis of approximately 50
different samples, treated both with dips and paper wraps, from many
parts of Australia, showed that diphenylamine does not penetrate
beyond 2-4 mm from the peel surface and that the residue levels in
peel are similar to those reported by Harvey and Clark (1959).
RESIDUES RESULTING FROM SUPERVISED TRIALS
The work of Harvey and Clark (1959) reviewed by the meeting in 1969
refers entirely to levels of residues found in peelings and pulp and
nowhere in the paper is any attempt made to report or calculate these
on the whole fruit basis. (But this fact is not clear in the 1969
monographs.) Luke (1978) reviewed the data in the light of Australian
experience, and calculated the approximate level in using his own
experience of the ratio of skin to whole fruit. He found the
diphenylamine residue level on whole fruit for the data reported by
Harvey and Clark to range from less than 0.1 mg/kg to 0.4 mg/kg.
Bruce et al (1958) found 3.23 to 3.64 mg/kg diphenylamine residue
immediately after use of a 1000 mg/l bath and 1.59 to 1.77 mg/kg after
5 months storage.
Hall et al (1961) have published the results of extensive trials which
encompass most of the variables likely to be encountered in practice.
With the exception of residues determined in fruit one day after
dipping, all values recorded for whole fruit were 1 mg/kg or less.
The high values recorded immediately after treatment decreased to
about 2 percent of the original level during the time the fruit was in
The USDA (1961) reported studies carried out in Wenatchee, Washington,
in which the effect of four variations of treatment and storage times
were examined. Residues on the surface and in the pulp were
determined separately. Results are given in Table 5. The total
diphenylamine residue ranged from 5 mg/kg immediately after dipping to
0.5 mg/kg after storage for nine months. The pulp contained a higher
fraction of the total residue in the samples which had been stored for
two months (58%) or nine months (52 to 83%) than was the case one day
after dipping (18%). The colorimetric procedure (Bruce et al 1958)
used in these investigations gave a high apparent value in untreated
Cornell University (1962), reporting trials carried out in 1961 at
Ithaca, N.Y., showed that the nature and stability of the formulation
was critical in determining the level and uniformity of diphenylamine
deposits on apples. The report points to unsatisfactory results
obtained with alcoholic solutions due to the deposition of crystals of
diphenylamine in the dipping bath. When satisfactory wettable powder
formulations were used the deposit, determined immediately after
treatment, remained generally below 3 mg/kg irrespective of the
concentration of diphenylamine in the dip bath (Table 6 and 7) or
whether the treatment was carried out immediately after harvest or
after a period in cold storage (Table 8).
All of the data reported by Ginsburg (1962) are for fruit which has
been held in cold storage for an extended period and then for one week
at room temperature (15°C to 20°C) prior to analysis. The
diphenylamine residue level on whole fruit at the end of this storage
in all cases was well below 1 mg/kg, usually below 0.2 mg/kg.
Gorman and Rowe (1977) report that laboratory dipping trials with
different formulations produced residues of the order of 2 mg/kg to 4
mg/kg on the day of treatment, but that these had fallen, to less than
1 mg/kg after 14 to 28 days in cool storage. Unstable formulations
used at high dip concentrations gave rise to residues which after 21
days in storage at minus 0.5°C ranged up to 2.5 mg/kg.
Hanekom et al (1976) report the level of residues in whole apples,
four days after immersion for various periods in diphenylamine
emulsions at several concentrations. The highest concentrations and
longest time gave rise to residues of the order of 3.5 mg/kg, though
this concentration fell to approximately half during ten week storage.
Sproul and Sivyer (1976) investigated the use of diphenylamine dips,
prior to fumigation with methyl bromide, to prevent phytotoxic damage
from the fumigation. They showed that fruit dipped in diphenylamine
baths containing 250 mg/L to 1,000 mg/L were completely free of any
injury following fumigation. The residues in such fruit ranged from
0.6 mg/kg to 1.9 mg/kg after three weeks in cold storage. Rippon
(1977) reported the results of one trial in which apples were treated
in baths containing 1,000 mg/L and 1,250 mg/L of diphenylamine. The
residues resulting from such treatment ranged from 0.36 mg/kg to 0.86
mg/kg on the whole fruit.
Table 5. Diphenylamine Residues on Apples following Different Treatments and Storage Times
Treatment Storage Variety Diphenylamine Residues
Time Value Surface Pulp Total
Number 2 2 0
None None Delicious Range 0.02-0.03 0.23-0.29 -
Mean 0.03 0.26 0.29+
Number 5 2 0
None None Winesap Range 0.01-0.07 0.28 -
Mean 0.03 0.28 0.31+
Number 4 4 2
1000 ppm 1 day Winesap Range 4.2-5.1 0.9-1.0 -
(42% WWP) Mean 4.3 0.9 5.2
Number 4 4 1
1000 ppm 2 mo. Winesap Range 1.5-1.7 1.8-2.4 -
(42% W) Mean 1.6 2.2 3.8
Number 4 3 1
1000 ppm 9 mo. Delicious Range 0.16-0.20 0.40-0.42 -
(42% WWP) Mean 0.18 0.40 0.48
Number 4 4 1
1000 ppm 9 mo. Delicious Range 0.23-0.27 0.24-0.29 -
(50% Emul) Mean 0.25 0.26 0.51
* Total residue in these instances was calculated by addition of amount found on surface and pulp.
Table 6. Effect of Formulation on Diphenylamine residues on single,
whole McIntosh apples resulting from Dipping. (Residues immediately
after Treatment but treated after storage)
DPA applied Formulation DPA residues
1000 alcohol 1.7
1000 alcohol 2.2
2000 alcohol 17.6
1000 42% DW* 2.1
1000 42% DW 0.8
2000 42% DW 1.1
2000 42% DW 0.4
3000 42% DW 3.3
2000 84% DW 2.3
2000 84% DW 1.8
3000 84% DW 1.6
* DW = dry wettable. (See Cornell, 1962). Analytical method of
Bruce et al, (1958).
Table 7. Effect of Formulation on Diphenylamine Residues on 20 Apple
Samples of whole McIntosh Apples resulting from Dipping. (Residues
immediately after treatment)
Actual DPA residues
DPA applied Formulation Avg. of two samples
1000 alcohol 3.0
2000 alcohol 5.6
3000 alcohol 6.0
1000 84% DW 0.6
1000 84% DW
2000 84% DW 1.8
2000 84% DW
3000 84% DW 2.1
3000 84% DW
See Cornell, 1962. Bruce et al (1958).
Table 8. Diphenylamine Residues on Whole Apples with Dry Wettable formulation (Residues Immediately
after treatment* at Harvest time).
Analytical Actual Active Variety DPA residues (avg. of 2
Method DPA Ingredient corrected for control
applied, ppm % ppm
Bruce et al (1958) 2000 42 Cortland 3.0
" " 2000 42 "
Harvey et al (1959) 2000 42 " 2.7
" " 2000 83 R.I. Greening 1.9
" " 2000 83 "
" " 2000 83 " 1.4
" " 2000 83 "
" " 1000 83 McIntosh 1.6
" " 1000 83 "
" " 1000 83 Cortland 2.2
" " 1000 83 "
" " 2000 83 " 3.9
" " 2000 83 "
By Crate Sprays
Bruce et al (1958) 2000 42 Cortland 8.5
" " 2000 42
Harvey et al (1959) 1000 83 McIntosh 2.3
" " 1000 83 "
" " 1000 83 Cortland 2.3
" " 1000 83 "
" " 2000 83 " 4.7
" " 2000 83 "
Harvey et al (1959) 1000 83 McIntosh 2.0
" " 1000 83 "
" " 1000 83 Cortland 3.0
" " 1000 83 "
Apples frozen in sealed poly bags until time of analysed. First box dipped in 1 gallon of 2000 ppm
DPA. 16th box dipped in 1 gallon of 2000 ppm DPA. Recoveries 70 -95%
Allen et al (1979) reporting on-going studies in the United Kingdom
indicated that the deposit on Bramley apples increased with increasing
dip concentration (Table 9). The initial concentration deposited from
the unusually high dip concentration of 1,000 mg/L was 6 mg/cm2
(approximately 6 mg/kg).
Table 9. Effect of dip concentration of residue deposit
Dip concentration Mean initial deposit (S D)
(ppm) (µg cm2)
500 1.32 (0.25)
1000 2.27 (0.42)
2000 3.62 (0.89)
4000 6.01 (1.26)
The levels after 5 months' storage were less than 0.25 µg cm2 and
after nine months storage, less than 0.01 µg cm2, from all
concentrations of dip solution.
For Bramley apples, an amount per unit area (µg cm2) is approximately
equal to the whole fruit concentration (ppm or mg/kg). Further work
is in progress to determine if deposits or efficacy vary between two
commercial formulations of DPA when applied in the laboratory.
Similar work, with one of these formulations, was carried out under
commercial conditions on farms in 1977, and is being repeated in 1978.
Preliminary work suggests that problems may arise if DPA dip solution
is mixed with certain other chemicals.
Extensive investigations carried out in Australia over three years
(Snelson, 1979) in which apples from 88 packing houses were analyzed
for diphenylamine residues, reveal that only 1% of the samples
contained residues above 3 mg/kg when examined after approximately 8
weeks in cold storage. The distribution of residues is indicated in
Table 10. It will be noted that 86% of the residues in whole fruit
are at levels below 1 mg/kg. 99% of the samples contained less than 3
mg/kg, notwithstanding the fact that in some samples the peel
contained more than 20 mg/kg of diphenylamine.
Table 10. Distribution of Diphenylamine Residues in Australian Apples
PEEL WHOLE FRUIT
Range of Range of
Residue No. of % residue No. of %
Levels samples Levels samples
1.0 10 11 0.1 8 9
1.1 - 2.0 14 16 0.1-0.5 46 52
2.1 - 5.0 27 31 0.51-1.0 22 25
5.1 -10.0 28 31 1.1-2.0 7 6
10.1-20.0 5 6 2.1-3.0 5 6
20 4 5 3.0 1 1
Total 88 100 88 100
METHODS OF RESIDUE ANALYSIS
No new information has become available on improved analytical
techniques. The Ad Hoc Working Group on Methods of Analysis of the
Codex Committee on Pesticide Residues has recommended that the method
published in Pesticides Analytical Manual, Volume 2, US Food and Drug
Administration, Washington DC, USA (1977) is suitable for regulatory
purposes and should be used for the determination of phenylamine
residues on apples. It should be recognized that since the bulk of
the residue is in the peel, it is not necessary to process the whole
fruit. The peel may be removed and processed for analysis so long as
the ratio of peel to whole fruit is determined on each sample. The
considerably higher concentration in the peel greatly facilitates the
cleanup and quantitation steps.
NATIONAL RESIDUE LIMITS REPORTED TO THE MEETING
The meeting was made aware that national governments had proclaimed
the following maximum residue limits:
Federal Republic of Germany 3
United Kingdom 3
Following the recommendations of the 1976 Meeting and a request from
CCPR, the available data on residues on apples has been reviewed and
the results of additional surveys and trials have been made available.
Although some results from supervised trials made in 1961 suggest that
residues could reach levels of the order of 10 mg/kg, later data
suggest that, in some cases, the higher and variable residue levels
obtained at that time were due to the use of formulations which have
since been replaced by preparations which do not separate in dip
The meeting was aware that following normal treatment in packing
houses, the residue level in some treated apples could exceed 5 mg/kg
for a few days, but this is of little practical consequence since
treated fruit is usually not presented for sale immediately.
Treatment is normally only applied to fruit going into cold storage
and even minimum storage results in a significant decline of
diphenylamine residues from the skin surface. At room temperature,
the surface deposit disappears in a few days.
The meeting agreed that there is little justification for retaining
the maximum residue limit at the value of 10 mg/kg established in
1969. Available information indicates that a MRL of 5 mg/kg is
adequate to deal with residues in apples in commerce, resulting from
typical levels and methods of treatment especially if the period
between application and release into trade is 21 days or more.
Use patterns and application practices appear to have changed since
the early 60's when the data considered at the 1969 meeting were
generated. The meeting requested further information on current
practices and residues resulting therefrom from countries where higher
MRLs have been established.
The meeting recommends that the existing maximum residue limit of 10
mg/kg for diphenylamine on apples should be lowered to 5 mg/kg.
FURTHER WORK OR INFORMATION
Information on current practices, formulations, use patterns and
selective surveys of residues in crops known to have been treated
under practical circumstances.
Allen, J.G., Hall, K. L., Martin, S., Sharples, R.O. and Johnson, D.S.
Diphenylamine for scald control. Rep. E. Mathing Res. Sta. for 1978.
Bruce, R.B., Howard, J.W. and Zink, J.B. - Determination of
diphenylamine residues on apples. J. Agr. Food Chem. 6: 597-600.
Denmead, C.F., Vere-Jones, N.W. and Atkinson, J.D. - A commercial
method of controlling apple scald with diphenylamine emulsions. J.
Hort. Sci. 36: 73-84.
Cornell University - Diphenylamine residues on apples. Information
supplied to US Food and Drug Administration February 26, 1962.
Ginsberg, L. - Superficial scald and its control on South African
apples. The Deciduous Fruitgrower Feb. 1962 pp. 34-41.
Gorman, R.C. and Rowe, N.B. - Investigation into the preparation,
stability and effectiveness of apple dipping emulsions of
diphenylamine. Report to Pesticides Co-ordinator August 1977 from
Western Australian Government Chemical Laboratory.
Hall, E.G., Scott, K.J. and Cook, G.C. - Control of superficial scald
on Granny Smith apples with diphenylamine. Aust. J. Agric. Res 12 (5):
Hanekom, A.N., Scheepers, J.L. and DeVilliers, J.F. - Factors
influencing the uptake of diphenylamine by apple fruit. The Deciduous
Fruitgrower, October 1976 pp. 402-411.
Hardisty, S.E. - Bitter pit control could save export Granny Smith
apples. J. Agric. W.A. p. 28-30.
Harvey, Helen and Clark, P.J. - Diphenylamine residues on apples. NZ
J. Sci. 2: 266-72.
Little, C.R. - Post-harvest treatment for pome fruit - some practical
implications. Proceedings of Fruit and Vegetable Post-Harvest
Research Workshop, Glenelg, South Australia, Sept. 1977 pp. 140-145,
CSIRO Canberra, Australia.
Luke, B. - Diphenylamine residues on apples. Report to Australian
Government Analyst, 28 July 1978.
Rippon, L.E. - Pesticide residues in fruit resulting from post harvest
treatments: Proceedings - Fruit and Vegetable post-harvest Research
Workshop, Glenelg, South Australia, September 1977. CSIRO, Canberra,
Snelson, J.T. - Diphenylamine residues in apples. Report from Dept. of
Primary Industry, Canberra, 12 October 1976.
Sproul, A.N. and Sivyer, M. - Residues resulting from the use of
diphenylamine to reduce injury from methyl bromide. Report to Fresh
Fruit Disinfestation Committee from Western Australian Department of
Sproul, A.N., O'Loughlin, J.B., Terands, A., and Hardisty, S. - The
use of diphenylamine to protect apples from methyl bromide injury.
Aust. J. Agric. Res., 27, 541-5.
USDA - Determination of diphenylamine residue in apples. Report by the
Handling, Storage and Transport Investigations Unit, Agricultural
Marketing Service, U.S. Department of Agriculture, Wenatatchec,
Washington (September 1961) to US Food and Drug Administration.