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International Agency for Research on Cancer (IARC) - Summaries & Evaluations

DI(2-ETHYLHEXYL) PHTHALATE
(Group 3)

For definition of Groups, see Preamble Evaluation.

VOL.: 77 (2000) (p. 41)

CAS No.: 117-81-7
Chem. Abstr. Name: 1,2-Benzenedicarboxylic acid, bis(2-ethylhexyl) ester

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Di(2-ethylhexyl) phthalate is a liquid of low volatility, widely used as a plasticizer in flexible poly(vinyl chloride) products at concentrations of up to 40%, as well as in a number of other minor applications. Occupational exposure occurs mainly by inhalation as an aerosol during its manufacture and its use as a plasticizer in poly(vinyl chloride) product manufacturing plants, at concentrations usually below 1 mg/m3.

Di(2-ethylhexyl) phthalate is ubiquitous in the general environment as a result of its widespread use in poly(vinyl chloride) products. It is found in ambient air at levels usually below 100 ng/m3. The highest levels of di(2-ethylhexyl) phthalate in foods are found in milk products, meat and fish and in other products with a high fat content, where concentrations up to 10 mg/kg have been reported. The leaching of di(2-ethylhexyl) phthalate from flexible plastics used in medical devices, such as during dialysis and transfusion, can result in large direct exposures.

5.2 Human carcinogenicity data

One small study of workers in a di(2-ethylhexyl) phthalate production plant did not show any excess of cancer mortality. However, this study did not have adequate power to detect a potential excess risk.

5.3 Animal carcinogenicity data

Di(2-ethylhexyl) phthalate was tested for carcinogenicity by oral administration in the diet in two experiments in mice and six experiments in rats. Hepatocellular tumours were produced consistently in both species.

In a number of initiation/promotion studies in strains of mice susceptible to liver carcinogenesis, administration of di(2-ethylhexyl) phthalate following administration with known carcinogens enhanced the incidences of hepatocellular preneoplastic foci, adenomas and carcinomas. In a number of similar studies in rats and in one study in hamsters, in general, no promoting activity of di(2-ethylhexyl) phthalate was demonstrated. No initiating activity of di(2-ethylhexyl) phthalate was found in the liver of mice or rats. In two N-nitrosamine-initiation target organ models in rats, one showed enhancement of renal tubule tumours by di(2-ethylhexyl) phthalate, whereas the other showed no promotion of urinary bladder tumours.

5.4 Other relevant data

The absorption and disposition of di(2-ethylhexyl) phthalate has been investigated extensively in humans and laboratory animals. In all species studied, the compound underwent rapid metabolism, with the urine and faeces being the major routes of excretion. Following oral administration, the bulk of a di(2-ethylhexyl) phthalate dose was absorbed as the monoester, mono(2-ethylhexyl) phthalate. This ester is also formed by esterases in the body following intravenous administration and is subject to extensive oxidative metabolism by the cytochrome P450 system.

The peroxisome-proliferating effects of di(2-ethylhexyl) phthalate in susceptible species (e.g., rats and mice) have primarily been related to mono(2-ethylhexyl) phthalate and two other specific metabolites. However, while species differences have been observed in the absorption and disposition of di(2-ethylhexyl) phthalate, they do not provide an explanation for the species differences in hepatic peroxisome-proliferating activity.

The literature on potential toxic effects of di(2-ethylhexyl) phthalate following human exposure is limited. Taken together, the data indicate that di(2-ethylhexyl) phthalate does not cause observable toxicity following oral and intravenous exposure, but do not contribute information relevant to the evaluation of human carcinogenicity.

A considerable amount of information on the hepatic effects of orally administered di(2-ethylhexyl) phthalate indicates that it causes hepatic peroxisome proliferation (ultrastructural effects and enzyme induction), hepatomegaly and increased replicative DNA synthesis in rats and mice. At a lower magnitude in Syrian hamsters, enzyme induction and hepatomegaly have been observed (ultrastructural effects and replicative DNA synthesis have not been evaluated). Guinea-pigs, marmosets and cynomolgus monkeys evaluated under the same or similar experimental conditions did not exhibit peroxisome proliferation responses. Studies of di(2-ethylhexyl) phthalate metabolites in primary rat, mouse and, to a lesser extent, Syrian hamster hepatocyte cultures in vitro elicited markers of peroxisome proliferation, while the same or similar experimental conditions did not elicit markers of peroxisome proliferation in primary cultures of either guinea-pig, rabbit, dog, cynomolgus monkey, marmoset or, most notably, human hepatocytes.

Hepatic peroxisome proliferation depends on a nuclear receptor, PPARa, to mediate these responses in mice, based on lack of response to peroxisome proliferators in PPARa-deficient mice. In one study with another peroxisome proliferator, WY-14,643, carcinogenesis was shown to be dependent on the same receptor. Oral administration of di(2-ethylhexyl) phthalate failed to elicit markers of peroxisome proliferation in PPARa-deficient mice, while the same treatment elicited this response in normal mice. Metabolites of di(2-ethylhexyl) phthalate caused activation of PPARa-mediated gene expression in mammalian cell co-transfection assays. Differences between responsive rodents and humans in various aspects of PPARa-mediated regulation of gene expression are consistent with the lack of activity of di(2-ethylhexyl) phthalate metabolites in hepatocyte cultures from 12 people studied to date.

No data on reproductive and developmental effects in humans were available.

Oral exposure of rats and mice to di(2-ethylhexyl) phthalate during organogenesis caused malformations and fetal death. A study in knock-out mice suggested that the developmental effects are not PPARa-mediated.

Irreversible testicular damage has been observed in male rat pups exposed prenatally and during suckling via maternal exposure to drinking water containing the compound.

Oral exposure of adult rats and mice caused effects on fertility in males and females and serious effects on the testicles. Young animals were much more sensitive to gonadal effects than adults and in some cases, the onset of occurrence of the testicular effects was earlier in young animals. Dose-dependent testicular effects were seen in young rats exposed to di(2-ethylhexyl) phthalate in the diet.

In one study using small groups of adult marmosets, oral exposure did not cause testicular toxicity at doses higher than those producing testicular effects in adult rats.

The Sertoli cells in the testes appear to be the main target of the testicular toxicity. Proposed mechanistic hypotheses relate to reduced testicular zinc levels, altered hormonal status, altered metabolic function and altered follicle-stimulating hormone reactivity.

Di(2-ethylhexyl) phthalate has been studied extensively for its genotoxic effects in a wide range of test systems, both in vitro and in vivo. The majority of these studies did not reveal any activity. No mutagenic activity was observed in bacteria. In fungi, all but two studies failed to show any evidence of recombinational events or mutation. A single study in yeast for aneuploidy was positive. Low levels of mutation were induced in Drosophila melanogaster in somatic cells in some studies, but no germ-cell mutations or DNA damage were induced in these insects. In cultured mammalian cells, no primary DNA damage, mutation, sister chromatid exchange or chromosomal aberrations were induced (except in a single study for DNA strand breakage), whereas transformation of cells was induced in a number of different systems.

In vivo, neither covalent binding to DNA nor DNA strand breakage was induced in several studies on rat liver, and unscheduled DNA synthesis was not induced in the liver of either rats or mice. Gene mutations were not induced in the liver of dosed mice in a single study and there was no evidence for induction of chromosomal aberrations in mice or rats. Aberrations were induced, however, in the embryos of dosed pregnant Syrian hamsters. Dominant lethal effects were reported to be induced in male mice, but re-evaluation of these data did not confirm this conclusion.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of di(2-ethylhexyl) phthalate.

There is sufficient evidence in experimental animals for the carcinogenicity of di(2-ethylhexyl) phthalate.

Overall evaluation

Di(2-ethylhexyl) phthalate is not classifiable as to its carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.

In making its overall evaluation of the carcinogenicity to humans of di(2-ethylhexyl) phthalate, the Working Group took into consideration that (a) di(2-ethylhexyl) phthalate produces liver tumours in rats and mice by a non-DNA-reactive mechanism involving peroxisome proliferation; (b) peroxisome proliferation and hepatocellular proliferation have been demonstrated under the conditions of the carcinogenicity studies of di(2-ethylhexyl) phthalate in rats and mice; and (c) peroxisome proliferation has not been documented in human hepatocyte cultures exposed to di(2-ethylhexyl) phthalate nor in the liver of exposed non-human primates. Therefore, the mechanism by which di(2-ethylhexyl) phthalate increases the incidence of hepatocellular tumours in rats and mice is not relevant to humans.

Previous evaluations: Vol. 29 (1982); Suppl. 7 (1987) (p. 62) (Group 2B)

Synonyms:


Last updated: 21 August 2000





















    See Also:
       Toxicological Abbreviations
       Di(2-ethylhexyl) phthalate (ICSC)
       Di(2-Ethylhexyl) Phthalate (IARC Summary & Evaluation, Volume 29, 1982)