2-PHENYLPHENOL AND ITS SODIUM SALT
EXPLANATION
First draft prepared by Professor C.L. Berry,
London Hospital Medical College, United Kingdom
2-Phenylphenol (OPP, o-phenylphenol) and its sodium salt (SOPP)
were previously reviewed by the Joint Meeting in 1969, 1983, 1985, and
1989 (FAO/WHO 1970ab, 1984, 1986ac, and 1989b. A temporary ADI was
allocated in 1983, which was extended in 1985 and 1989.
EVALUATION FOR ACCEPTABLE INTAKE
Toxicological studies
Reproduction study
One hundred forty male and 140 female albino Sprague-Dawley rats,
nine weeks old at the start of the study, were divided into four dose
groups of 35 rats/sex/group, and fed 0, 40, 140 or 490 mg/kg bw/day of
technical grade OPP (99.4 - 99.5% pure) administered in the diet in 1%
corn oil (actual doses were 25, 125, and 460 mg/kg bw/day based on
analysis of the diet consumed). Adjustment of dosage during the pre-
mating period was made according to body weight changes. During
lactation adjustments in dose were made to avoid overdosing the pups
but this was later considered unnecessary. A number of animals were
removed from the study in order to examine the heritability of
hypotrichosis (two high dose F1 females and 12 F2a pups). Parents
(F0) for the F1 generation were randomly assigned to dosage groups.
For F1 parents the genealogy of the F1b pups was checked to prevent
the mating of litter mates. For the production of the F2 generation,
a total of 132 male and 134 female F1b pups were randomly selected
using one or more pups/sex/litter as parents (F1) and divided into 35
pairs of rats per dose group except for the controls which had 27
males and 29 females. Estrus cycles were studied by vaginal smears.
The animals were examined daily and routine observations of birth
statistics and pup weights were made and culling to eight pups was
performed where necessary. Standard observations with the addition of
extensive examination of the histology of the urinary tract were
carried out when the animals were sacrificed.
There were no treatment related effects on clinical signs,
gestational or lactation body weight gain or any of the reproductive
variables examined. Histological examinations of the adults and pups
revealed no significant changes in the reproductive tracts.
The following changes were observed:
1. There was a treatment related decrease in body weight in the
high dose F0 and F1 animals which was not clearly related
to decreased food consumption.
2. There was a significant decrease in weight in the high dose
F1b, F2a, and F2b pups at 14 and/or 21 days during
lactation, an effect not seen in the first week of post-
natal life. This indicated that development had not been
disturbed.
A no reproductive effect level of 490 mg/kg bw/day was set.
Relative renal weight was increased in a dose related manner in the
absence of other organ weight changes, in high dose F0 and F1 males.
The incidence of calculi in the urinary tract was increased in male
rats in the 140 and 490 mg/kg bw/day groups. Transitional cell
hyperplasia occurred in the urinary bladder. The report defines this
change as "an area (focal or diffuse) of at least three to four cells
thick (of cuboidal cells) in an inflated bladder" where normal
bladders had a cell thickness of one or two flattened cells. These
changes were quantified by simple morphometry which indicated a
compound related effect in the bladder in 140 and 490 mg/kg F0 males
and females and in the 490 mg/kg F1 males. Neoplasms of the urinary
tract were found in 4 rats, 1 bladder and 1 ureteric tumour in the 140
mg/kg group and 2 bladder tumours in the 490 mg/kg group. The NOAEL
for these effects was 40 mg/kg bw/day (Eigenberg, 1989).
Special studies on interactive effects
(ascorbic acid, saccharin and hippuric acid)
Male F344 rats were given OPP or SOPP at 2% in feed for a period
of 24 weeks. Groups of treated animals also received ascorbic acid
(AS) sodium ascorbate (SA) acid saccharin (SAC), sodium saccharin
(SSAC), hippuric acid (HI) or sodium hippurate (SHI) at 5% in the
feed (20 animals/group). Urinary sodium concentration was increased
in all animals receiving sodium salts in the diet and in SOPP treated
animals. The pH value of the urine increased after SOPP, SA and SSAC
and urine osmolarity was decreased by SOPP, SA and SHI. OPP decreased
osmolarity but did not affect urinary pH or sodium concentrations.
Histopathologically, the bladders showed epithelial thickening (4-8
cell epithelial thickness) at 8, 16, and 24 weeks after SOPP and
papillary and nodular changes at 16 and 24 weeks. Treatment with
other sodium salts provoked "slight to moderate" hyperplasia at 8 and
16 weeks but no papillary or nodular changes; these changes had
regressed by 24 weeks. A combination of raised urinary pH and sodium
acted as promoting agents for SOPP; SHI raised urinary sodium but not
pH and was without effect (Fukushima et al., 1986).
An essentially similar study was done in male F344 rats (31
animals/group) using NaHCO3 to raise the urinary pH and NH4C1 to
lower it. Both OPP and SOPP were examined (at 1.25% and 2% in the
diet respectively). Changes were seen in all 4 groups and can be
summarized as follows: hyperplasia of the bladder epithelium occurred
with OPP, OPP, and bicarbonate and SOPP. SOPP with NH4C1 had no
significant effect. Tumours were significantly increased after OPP
(12/31), SOPP (22/31) and OPP plus NaHCO3 (20/31). Only 3 tumours
were seen in 31 rats after SOPP and NH4C1. The oncogenic effects of
OPP were promoted in alkaline urine and those of SOPP were inhibited
in acid urine (Fujii et al., 1987).
COMMENTS
Previous concerns about 2-phenylphenol and its sodium salt have
focused on the urothelial carcinogenicity of the compound in the rat.
The many carcinogenicity and metabolic studies now available have
provided data which are reassuring with regard to this effect.
The ADI was based on the study in rats in which a clear no-effect
level for proliferative effects in the urothelium was observed.
Because the rat is clearly an extremely sensitive species for this
effect, a hundred-fold safety factor was considered to be appropriate.
The available data now make previous requirements for additional
information unnecessary. No further carcinogenicity/ long-term
toxicity studies in rats are needed and metabolic studies in other
species are of less significance than the qualitative and quantitative
monitoring data of the urinary excretion of 2-phenylphenol and its
metabolites by those regularly exposed to 2-phenylphenol or sodium 2-
phenylphenate.
There were no significant findings in the rat reproduction study
apart from the urothelial lesions. The ADI was established on the
basis of the NOAEL in the rat long-term study.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 40 ppm in the diet (equivalent to 2 mg/kg bw/day)
Dog: 300 mg/kg bw/day
Estimate of acceptable daily intake for humans
0 - 0.02 mg/kg bw
Studies which will provide information valuable in
the continued evaluation of the compound
Further observations in humans.
REFERENCES
Eigenberg, D.A. (1989). Two-Generation dietary reproduction study in
rats using Orthophenylphenol. Unpublished report number 85-671-02
from Health, Environment and Safety, Corporate Toxicology Department,
Mobay Corporation. Submitted to WHO by Bayer AG, Leverkusen, Germany.
Fukushima, S., Shibata, M.A., Kurata, Y., Tamano, S., and Masui, T.
(1986). Changes in the urine and scanning electron microscopically
observed appearance of the rat bladder following treatment with tumour
promoters. Jpn. J. Cancer Res. 77:1074-1082.
Fujii, T., Nakamura, K., and Hiraga, K. (1987). Effects of pH on the
carcinogenicity of o-phenylphenate in the rat urinary bladder. Fd.
Chem. Toxic. 25:259-362.