Toxicological Evaluation and Limit Values for Nonylphenol, Nonylphenol Ethoxylates, Tricresyl, Phosphates and Benzoic Acid

7. Evaluation

A study in humans involving two volunteers provides evidence that nonylphenol is rapidly absorbed from the gastrointestinal tract in humans. Also, the fact that only a small proportion of the dose was recovered in faeces within 56 hours suggests that almost complete absorption of a dose had occurred. Following oral administration, most of the nonylphenol was present in the blood as glucuronide or sulphate conjugates, in contrast to the findings for intravenous administration where similar proportions of unconjugated and conjugated nonylphenol were detected; these findings are indicative of extensive first pass metabolism. First pass metabolism does not occur when the route of exposure is inhalation. Therefore, an inhalatory dose of NP may be more toxic than the same dose administered orally.

No data have been found which describe the health effects of NP or NPEs in humans after oral ingestion or exposure via inhalation.

The systemic toxicity of NP and NPE by inhalation is unknown. Data from a mouse study suggest that NP can cause mild sensory irritation to the respiratory tract at high exposure levels. At a vapour concentration of 267 mg/m³ there was no effect.

The acute oral toxicity of NP and NPE is low.

NP has not been tested for mutagenicity in a study of good quality. No data regarding the carcinogenicity of NP have been found. NPEs with 9 or 30 ethylene oxide units were negative in the Ames test. Two-year feeding studies showed no tumourigenic effects of NPEs with 4 or 9 ethylene oxide units, however, the studies did not include a sufficient number of test animals and are for this reason inconclusive.

Nonylphenol

A 28-day study NOAEL of 100 mg/kg b.w./day for NP, and a 90-day study NOAEL of 50 mg/kg b.w./day for NP have been determined in studies of good quality. The results of the 28-day study and the 90-day study are in agreement with each other. In a multigeneration study, also of good quality, increased incidence of renal tubular degeneration and/or dilatation were found. There was no dose level without effect. It is difficult to decide for certain whether or not the kidney effect was related to treatment because these changes were not seen in the 90-day study, which was conducted using the same strain of rats, and because a dose-dependent trend was not apparent in all generations/sexes. The lack of concordance between the studies cannot be explained on the basis of a slightly longer exposure period in the multigeneration study because kidney effects were seen in the F3 generation which were exposed for only 8 weeks, nor solely on the basis of in utero and neonatal exposure because the effect also occurred in the F0 generation. Giving special emphasis to the fact that the increased incidence occurred consistently across all four generations in the multigeneration study, it is considered that this cannot be dismissed as background variation. The F3 generation showed the highest incidence of kidney changes, indicating that the effect may become more pronounced after exposure during several generations. Consequently, the conclusion has been drawn from this study that there is a LOEL for repeated exposure of 15 mg/kg/day, based on histopathological changes in the kidneys. Since renal tubular degeneration and/or dilatation are common findings in untreated rats, and as they were not accompanied by other related signs or symptoms in the affected rats, they are not considered signs of severe toxicity by the rapporteur.

Alkyl phenols, including NP, have been shown in laboratory studies to mimic the effects of oestrogen in vitro and in vivo.
NP has been found positive in the uterotrophic response assay in immature Wistar-derived rats, in immature Sprague-Dawley rats, and in ovariectomised Sprague-Dawley rats. Although the uterotrophic assay is a standard assay for oestrogenic effect, the significance to human health of oestrogenic effects in this assay has not been established.
In the 28-day study, and especially the 90-day study of NP, rather extensive examinations of sexual organs were performed. Sexual organ morphology, oestrous cycle pattern, and sperm quality were studied and were found to be unaffected by treatment. Absolute ovary weight was found to be slightly decreased in the highest dose group. The relative ovary weight was not reduced, and histopathological changes of the ovary were not found. Other targets which may be affected by oestrogen (haemoglobin, red blood cell count, pituitary gland, mammary gland, endometrium) were not affected by NP in this study. It is therefore concluded that, although NP may possess oestrogenic activity, it did not affect endpoints commonly associated with oestrogenic activity at the highest dose used in this study, which was high enough to cause general toxicity in the rats.

However, the results of the three-generation study indicate that effects on male and female reproductive parameters may occur at dose levels above 15 mg/kg/day. In females, accelerated sexual maturation, increased oestrous cycle length and reduced ovarian weights were found, while males exhibited a reduced number of spermatids. The effects were found in one or more of the three filial generations.

NOAEL for NP

In conclusion, for NP a LOAEL of 15 mg/kg/day is set, based on the reproductive/developmental effects seen in the oral three-generation study. This dose level is also a LOEL for the kidney effects also identified in this study.

Nonylphenol ethoxylate

For NPEs, a number of 90-day studies in rats and dogs exist. The studies are all rather old (reports dated 1959-1965) and probably do not fulfil present standards. Histopathology apparently has only been performed in the highest dose groups, and therefore it is not possible to evaluate the toxicological significance of increased organ weights of other dose groups. For this reason, a change in organ weight was regarded as an adverse effect in the absence of histopathological data. NOAELs ranging between 40 and 160 mg/kg/day in rats for NPEs with 4-15 ethylene oxide units have been found. In dogs, 90-day NOELs of 40 mg/kg/day were found for NPEs with 4, 6, 9, 15, and 20 ethylene oxide units. For NPEs with ethylene oxide chains of 20 or 30, NOAELs of 1000 ->5000 mg/kg/day were found in rats. In dogs, the NOAEL for NPE with 30 ethylene oxide units was >1000 mg/kg/day. NPE with 40 ethylene oxide units had a NOAEL of 300 mg/kg/day in rats. NPE effects included retarded growth and increased liver weight, for some compounds necrosis of liver cells.
In dogs, similar effects have been found. Dose-response relations seem comparable. However, in the dog a specific toxic effect of certain NPEs on the heart has been found, related to ethoxylene oxide chain lengths of 15, 17.5, and 20 (but not NPEs with chains outside this range). The cardiac effect is focal myocardial necrosis, sometimes lethal. A dose of 1000 mg/kg/day reliably induced cardiotoxicity. Microscopic changes in the myocardium were found even at a dose of 40 mg/kg/day for NPE with 20 ethylene oxide units. The NOAEL for cardiotoxicity in the dog is not known, nor is the mechanism. Guinea pigs also seem to develop this type of lesion, while cats, rats, and rabbits do not. It is not known whether humans are sensitive to the cardiotoxic effect of NPEs with ethoxylene oxide chain lengths of 15, 17.5, and 20.

NPEs with 4 or 9 ethoxylene oxide units have been administered orally to rats and dogs for periods of 2 years. Effects included reduced weight gain, and increased relative liver weight, while no increased frequency of tumours was reported. However, the studies were not properly designed to evaluate carcinogenic effects. In the dog studies, the group size was very small, and the 2-year dose period did not cover the whole lifetime for this species, which is at least 7-8 years. In the rat studies, the number of animals examined in detail for tumour occurrence was far too small to allow any conclusions. In rats and dogs, the 2-year chronic toxicity NOAEL for NPE with 4 ethoxylene oxide units was 40 mg/kg/day, while NPE with 9 ethoxylene oxide units did not cause any effects in rats in highest dose administered, 270 mg/kg/day. In dogs, the 2-year NOAEL for NPE with 9 ethoxylene oxide units was 88 mg/kg/day.

NOAEL for NPE

In conclusion, an oral NOAEL of 40 mg/kg/day for NPEs with ethylene oxide chain lengths shorter than 15 and between 21-40 can be set. This NOAEL covers the most toxic NPEs among the group tested (Table 6).

For NPEs with ethylene chain lengths between 15 and 20 a NOAEL cannot be determined from the available data. The LOAEL for cardiotoxicity in the dog is 40 mg/kg

For the purpose of setting a limit value covering all NPEs a LOAEL of 40 mg/kg/day is set.