PESTICIDE RESIDUES IN FOOD - 1997
Sponsored jointly by FAO and WHO
with the support of the International Programme
on Chemical Safety (IPCS)
TOXICOLOGICAL AND ENVIRONMENTAL
EVALUATIONS 1994
Joint meeting of the
FAO Panel of Experts on Pesticide Residues
in Food and the Environment
and the
WHO Core Assessment Group
Lyon 22 September - 1 October 1997
The summaries and evaluations contained in this book are, in most
cases, based on unpublished proprietary data submitted for the purpose
of the JMPR assessment. A registration authority should not grant a
registration on the basis of an evaluation unless it has first
received authorization for such use from the owner who submitted the
data for JMPR review or has received the data on which the summaries
are based, either from the owner of the data or from a second party
that has obtained permission from the owner of the data for this
purpose.
PHOSALONE (addendum)
First draft prepared by
T.C. Marrs
Medical Toxicology and Environmental Health
Department of Health, London, United Kingdom
Explanation
Evaluation for acceptable daily intake
Long-term toxicity and carcinogenicity
Comments
Toxicological evaluation
References
Explanation
Phosalone was evaluated toxicologically by the 1972 JMPR (Annex
1, reference 18), when an ADI of 0-0.006 mg/kg bw was established; it
was re-evaluated in 1993 (Annex 1, reference 68), when an ADI of
0-0.001 mg/kg bw was established on the basis of the lowest dose
tested (5 ppm), equal to 0.2 mg/kg bw per day, in a two-year study in
rats, with a safety factor of 200 because of concern about the
possibly significant occurrence of testicular atrophy and reduction in
testicular weight. More information on this study was supplied for
consideration at the present Meeting.
Evaluation for acceptable daily intake
Long-term toxicity and carcinogenicity
A study was completed by Barker and Sortwell in 1993 in which
groups of 50 Sprague-Dawley CD rats of each sex were given phosalone
(purity, 94.5%) in the diet for two years. Volume 1 of the study was
evaluated at the 1993 meeting (Annex 1, reference 68). The entire
report became available, with an addendum containing a review of the
testicular pathology. Phosalone was administered in the diet at
concentrations of 0, 5, 50, or 1000 ppm, the highest dietary
concentration being reduced to 500 ppm at week 27. These
concentrations were equal to 0, 0.2, 1.8, or 20 mg/kg bw per day for
males and 0, 0.2, 2.5, or 31 mg/kg bw per day for females, on the
basis of consumption from week 27 until the end of the study.
Satellite groups of 15 rats of each sex at each dose except the high
dose, which contained 25 animals, were killed at 52 weeks.
Phosalone did not affect mortality; in fact, the rate was lower
in the group at the high dose, especially among males, than in the
other groups. The clinical effects were mainly confined to rats at the
high dose, which showed hypersensitivity, abnormal posture, and poor
grooming; females at this dose also had a marked impairment in
body-weight gain during the first 26 weeks, and the effect was seen to
a lesser extent in males. Body weight recovered after the dose of
phosalone was reduced. Depression of plasma and erythrocyte
cholinesterase activity was found in rats at the highest dietary
concentration and to a lesser degree in those at 50 ppm at various
times throughout the study. Biologically significant depression of
brain acetylcholinesterase activity was found only at the highest dose
(see Table 1). No evidence of tumorigenesis was found. Some
treatment-related changes were seen in the adrenals, consisting of
enlargement and foamy change in the zona glomerulosa in animals at the
high dose at the interim kill and vacuolation of adrenal cortical
cells at the terminal kill.
Statistically significant atrophy of the testes was seen in rats
at the high and intermediate doses. Moreover, there appeared to be a
dose-response relationship in the prevalence of testicular atrophy:
2/27, 3/34, 8/30, and 12/42 in survivors at the time of terminal kill.
A dose-response relationship was seen even when only the incidence of
'marked' testicular atrophy was considered: 1/27, 3/34, 6/30, 10/42;
however, the incidence in each group was not statistically
significantly greater than that in the controls, when only those
animals surviving to the terminal kill were considered. At the highest
doses, the findings were significant when decedents were included; in
view of the bias that could be introduced as a result of longer
survival in this group resulting from the inclusion of decedents, the
use of the figures for animals killed at the end of the study is more
appropriate. Thus, it can be concluded that no clear dose-response
relationship was demonstrated. No evaluation was made of whether the
atrophy was bilateral or unilateral at this stage.
The slides were re-examined by a consultant who concluded that
the apparent dose-response relationship was largely a product of
increased survival of animals at the high dose, although this is
clearly not the case when only data on survivors are considered. The
data could be interpreted as showing a trend for bilateral or
unilateral testicular atrophy, but the consultant argued that
bilateral atrophy is a more reliable indicator of treatment-related
change than unilateral atrophy. On this basis, there was no clear
dose-response relationship (Table 2; Isaacs, 1995). The number of
animals used was slightly different because of the inclusion of those
that died in week 106 of the study but were analysed as part of the
terminal kill.
The findings were re-examined at the laboratory which originally
performed the study (Barker, 1996; Table 3). The incidences of
unilateral or bilateral testicular atrophy in the survivors to
termination were 26% in controls, 24% at the low dose, 40% at the
intermediate dose, and 40% at the high dose; these percentages were
stated to be within the background range in the laboratory. The
incidences of bilateral atrophy only in the survivors to termination
of the bioassay were 7% in controls, 3% at the low dose, 7% at the
intermediate dose, and 12% at the high dose. Since testicular atrophy
in the rat is commonly an age-related phenomenon, the prevalence of
lesions in animals killed at termination is the appropriate variable;
an exception would be analysis of the data in an age-to-occurrence
fashion. This was not the case.
Table 1. Erythrocyte and brain acetylcholinesterase activity (% concurrent controls) in rats given
phosalone in the diet for two years
Dose Erythrocytes Brain
(ppm) (week 105/6)
Week 13 Week 26 Week 52 Week 78 Week 104
Male
5 101 70 120 99 101 98
50 77 58 < 93 61 98 92
1000/500 < 35 < 36 < 45 < 24 34 27
Female
5 107 118 100 103 105 147
50 68 67 52 < 65 78 140
1000/500 < 40 < 42 < 33 43 37 40
Table 2. Testicular lesions in decedents (D) and terminally-killed animals
(T) in rats given phosalone in the diet for two years (Isaacs, 1995)
Dose (ppm)
0 5 50 1000/500
D T D T D T D T
No. of animals 21 29 16 34 20 30 7 43
Lesion
Unilateral atrophy 1 5 1 6 4 11 1 10
Bilateral atrophy 4 2 4 4 4 3 1 8
Total atrophy 5 7 5 10 8 14 2 18
Table 3. Testicular lesions in decedents (D) and terminally-killed animals
(T) in rats given phosalone in the diet for two years (Barker, 1996)
Dose (ppm)
0 5 50 1000/500
D T D T D T D T
No. of animals 23 27 16 34 20 30 8 42
Lesion
Reduced spermiogeuesis 0 0 1 1 1 2 0 1
Unilateral atrophy 3 5 1 7 6 10 1 12
Bilateral atrophy 2 2 3 1 3 2 1 5
Total atroplxy 5 7 4 8 9 12 2 17
Testicular weight was reduced in these groups at the terminal but
not the interim kill, the mean testicular weights being 5.03 g in
controls, 4.66 g at the low dose, 4.51 g at the intermediate dose, and
4.22 g at the high dose. These reductions were statistically
significant at the high and intermediate doses. Nonetheless, these
values were stated to be within the range in historical controls at
the institution where the study was performed.
If it is assumed that only bilateral testicular atrophy is
toxicologically significant, the incidence figures of neither Isaacs
(1995) nor Barker (1996) show any clear dose-response relationship
(see Table 4). Furthermore, there appeared to be no effects of
treatment in the testes examined at 52 weeks. The first long-term
studies in rats evaluated by the 1993 JMPR showed no evidence of
testicular effects. The Meeting was satisfied that no
treatment-related testicular effects had been induced. Accordingly,
the Meeting concluded that the NOAEL was 50 ppm, equal to 1.8 mg/kg bw
per day, on the basis of inhibition of brain acetylcholinesterase
activity at the highest dose.
No data from the other studies reviewed in 1993 support a
specific treatment-related effect on the testis.
Comments
Dietary concentrations of 0, 5, 50, or 1000 ppm phosalone were
administered to rats for two years, the highest dose being reduced to
500 ppm later in the study. Significant depression of brain
acetylcholinesterase activity was found only at the highest
concentration. There was a statistically significant increase in the
prevalence of testicular atrophy, a reduction in testicular weights in
animals at both the high and intermediate doses, and a dose-response
relationship across all groups for both effects. All testicular
weights were within the range in historical controls at the institute
where the study was performed. The slides were re-examined by a
consultant, who argued that the apparent dose-response relationship
for testicular atrophy was largely a product of increased survival
among the rats at the highest dose. Furthermore, it was argued that
bilateral atrophy is a more reliable indicator of treatment-related
change than unilateral atrophy; on this basis, there was no clear
dose-response relationship. The findings were also re-examined at the
laboratory where the study was originally performed; no clear
dose-response relationship was found. In view of the fact that neither
an earlier long-term study in rats nor studies in mice and dogs gave
evidence of changes in the male reproductive system, the Meeting
considered the NOAEL to be 50 ppm, equal to 1.8 mg/kg bw per day, on
the basis of inhibition of brain acetylcholinesterase activity at the
highest dose.
The rat remained the most sensitive species examined, and on the
basis of the NOAEL of 1.8 mg/kg bw per day in the above study the
Meeting established an ADI of 0-0.02 mg/kg bw, using a safety factor
of 100.
Table 4. Incidence of bilateral testicular atrophy (%) in rats given phosalone in the diet
for two years, according to Isaacs (1995) and Barker (1996)
Reference Dose (ppm)
0 5 50 1000/500
No. % No. % No. % No. %
Isaacs (1995) 2/29 7 4/34 12 3/30 10 7/43 16
Barker (1996) 2/27 7 1/34 3 2/30 7 5/42 12
Toxicological evaluation
Levels that cause no toxic effect
Mouse: 150 ppm, equal to 23 mg/kg bw per day (two-year study
of toxicity and carcinogenicity)
Rat: 50 ppm, equal to 1.8 mg/kg bw per day (two-year study
of toxicity and carcinogenicity)
50 ppm, equivalent to 2.5 mg/kg bw per day
(multigeneration study of reproductive toxicity)
Rabbit: 10 mg/kg bw per day (study of developmental toxicity)
Dog: 200 ppm, equivalent to 5 mg/kg bw per day (several
studies)
Estimate of acceptable daily intake for humans
0-0.02 mg/kg bw
Studies that would provide information useful for continued
evaluation of the compound
Observations in humans
References
Barker, M.H. (1996) Report amendment RPN375/930643 dated 14 June 1996
to: Barker, M.H. & Sortwell, R.J. (1993) Unpublished study. Phosalone
(11974 RP). Potential tumorigenic and toxic effects in prolonged
dietary administration to rats. Huntingdon Research Centre Ltd,
Huntingdon, Cambridgeshire, United Kingdom. Submitted to WHO by
Rhone-Poulenc, United Kingdom.
Barker, M.H. & Sortwell, R.J. (1993) Unpublished study. Phosalone
(11974 RP). Potential tumorigenic and toxic effects in prolonged
dietary administration to rat. Huntingdon Research Centre Ltd,
Huntingdon, Cambridgeshire, United Kingdom. Submitted to WHO by
Rhone-Poulenc, United Kingdom.
Isaacs, K.R. (1995) Unpublished report. Evaluation of the testes from
study RNP/375 (Project No. K94/001). Submitted to WHO by Rhone
Poulenc, Research Triangle Park, North Carolina, USA.
See Also:
Toxicological Abbreviations
Phosalone (ICSC)
Phosalone (WHO Pesticide Residues Series 2)
Phosalone (WHO Pesticide Residues Series 5)
Phosalone (Pesticide residues in food: 1976 evaluations)
Phosalone (Pesticide residues in food: 1993 evaluations Part II Toxicology)
Phosalone (JMPR Evaluations 2001 Part II Toxicological)