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Evaluation of the health risk to animals playing with phthalate containing toys

3 Toxicity

• 3.1 Critical effects of DEHP
  • 3.1.1 Studies in dogs
• 3.2 Critical effects of DINP
  • 3.2.1 Studies in dogs
• 3.3 NOAEL or LOAEL of DEHP and DINP
• 3.4 Relevance of effects observed in rats for effects in dogs
  • 3.4.1 DEHP
  • 3.4.2 DINP

Within the EU, specific programs on risk assessment for new and existing chemicals are on going. For both DEHP and DINP individual Risk Assessment Reports have been produced and agreed.

The adverse effects of the individual phthalates will only be summarized shortly and the no observed adverse effect levels (NOAEL) used in the present risk assessment will be in concordance with the NOAELs presented in the agreed reports. The Risk Assessment Reports are published at http://ecb.jrc.it/existing-chemicals/.

Most studies regarding the toxicological effect of DEHP and DINP are made in rats and NOAELs for DINP and DEHP have been established based on studies in rats. However, few studies in dogs have been reported and these studies will be described shortly.

3.1 Critical effects of DEHP

The effects of DEHP on testis, development of the reproductive system, fertility and kidney (repeated dose toxicity) are considered to be the critical effects.

Severe and irreversible testicular injury was induced in rats exposed to low oral doses of DEHP in a three generation reproductive toxicity study by Wolfe et al. (2003 – quoted in DEHP 2001) with a NOAEL of 4.9 mg/kg b.w./day.

The testes injury was much more severe in the F₁ and F₂ generation than in F₀. Also severe developmental effects were observed in mice in the absence of maternal toxicity with a NOAEL of 20 mg/kg b.w./day.

Effects on male fertility have been observed in mice and rats. In mice, DEHP adversely affected the number of fertile matings. In a continuous breeding study in mice, an oral NOAEL of 20 mg/kg b.w./day was identified for fertility (Lamb et al, 1987 – quoted in DEHP 2001). In rats, the oral NOAEL for body weight, testis, epididymis, and prostate weights and for endocrine and gonadal effects in male rats was considered to be 69 mg/kg b.w. per day in a 60 day study (Agarwal et al. 1986 – quoted in DEHP 2001).

The NOAEL for kidney toxicity is considered to be 500 ppm DEHP in the diet (corresponding to 28.9 mg/kg b.w./day in the males and 36.1 mg/kg/day in the females) derived from a 2-year study in rats and based on increased absolute and relative kidney weight in both sexes at the next higher dose level (2500 ppm) (Moore 1996 – quoted in DEHP 2001).

Based on all available studies, an overall oral NOAEL of 4.9 mg/kg b.w./day for developmental toxicity is established for DEHP. The NOAEL is derived from the three-generation study in rats (Wolfe et al. (2003) – quoted in DEHP 2001) and it is based on small male reproductive organs (testis, epididymes and seminal vesicles) and testis atrophy.

3.1.1 Studies in dogs

The effects of DEHP have been studied in groups of dogs (2 of each sex) receiving 59 mg DEHP /kg b.w./day in gelatine capsules 5 times weekly for one year. No significant differences were observed between treated and control dogs in several parameters: mortality, body weight gain, blood counts and gross and microscopic examination of several organs and tissues (e.g. liver, kidney, spleen, adrenal and ovary or testes) (Union Carbide 1951 – quoted in DEHP 2001).

3.2 Critical effects of DINP

The effects of DINP on the liver and kidney (repeated dose toxicity) are considered to be the critical effects. Testicular toxicity is also observed. However, DINP seems to be less potent in inducing hormonal and testicular effects than DEHP.

Effects on the liver consisting of hepatic biochemical changes (increased ALT, AST) and of increased liver weights in both sexes (absolute and relative liver weights) concurrently with histopathological findings have been observed in rats with a NOAEL of 88 mg/kg b.w./day being established from a 2-year study (Aristech 1994 – quoted in DINP 2001). This NOAEL is established for liver effects, which are not related to peroxisome proliferation.

For effects on the kidney, a NOAEL of 88 mg/kg b.w./day can be established from the same study based on increased kidney weights in both sexes (absolute and relative kidney weights) at higher dose levels.

For testicular effects (decreased testicular weight without histological changes), a NOAEL of 276 mg/kg b.w./day can be derived from a 2-year mouse study (Aristech Chemical Corporation – quoted in DINP 2001).

Based on the available studies, an overall oral NOAEL of 88 mg/kg b.w./day is established for DINP. The NOAEL is derived from the chronic study (2 years) in rats for effects on the liver and kidneys. This NOAEL also covers the reproductive effects of DINP as they were seen at higher doses e.g. a NOAEL of 276 mg/kg b.w./day for testicular effects (DINP 2001).

3.2.1 Studies in dogs

The effect of DINP has been studied in beagle dogs in a 13 week feeding study. Groups of dogs (4 of each sex) were fed approximately 37, 160 and 2000 mg DINP/kg/day. As an indication of liver damage, a slight to moderate elevation of serum glutamic oxaloacetic transaminase (SGOT or ALT) was observed at week 4 at all doses in both sexes (no statistical data available) and the effect showed dose-dependent relationship in females. These biochemical changes were associated with an increase of absolute and relative liver weights from 160 mg/kg b.w./day as well as liver histopathology at highest dose. At the highest dose, changes in relative and absolute weight of kidney and spleen were also observed. No NOAEL can be identified in this dog study. Instead, a LO(A)EL of 37 mg/kg b.w./day based on an increase in SGOT (ALT) is identified. However, according to DINP (2001), there was absence of statistical data and inconsistency between tables and text which weakens the relevance of this study (Hazleton et al. 1971 – quoted in DINP 2001).

3.3 NOAEL or LOAEL of DEHP and DINP

The critical effect(s) identified for each phthalate as well as the NOAEL (or LOAEL in the case where a NOAEL has not been identified) have been compiled in Table 4.

Table 4. NOAELs (or LOAELs) for DEHP and DINP

(DEHP 2001 and DINP 2001)

3.4 Relevance of effects observed in rats for effects in dogs

3.4.1 DEHP

Differences in DEHP-induced toxicity between rats and dogs and cats can be caused by e.g. toxicokinetic differences between species. MEHP is believed to be the active metabolite of DEHP and therefore knowledge about the ability of a species to form MEHP is crucial when considering the relevance of the DEHP-induced testicular effects observed in rats to e.g. dogs.

In one study, the toxicokinetics of DEHP in rats and dogs have been compared. DEHP were administrated in the diet in doses of 50 mg/kg b.w./day for 21-28 days before a single dose of ¹⁴C-labelled DEHP. The distribution and excretion of the radioactivity were analysed. The fraction of radioactivity excreted in faeces and urine was relatively similar in rats and dogs with faecal excretion as predominant. The excretion was virtually complete in 4 days. However, the elimination was slightly more prolonged in dogs compared to rats. There were 4 radioactive metabolites in rat urine and 3 in the dog urine. Metabolites in dog urine were indistinguishable from those in the rat urine. In both rats and dogs, one of the metabolites present in bile was indistinguishable from MEHP. Substantial radioactivity was found in both rats and dogs in the gastro-intestinal tract. In remaining organs the highest level of radioactivity was found in the liver of rats and in bile samples from dogs (Ikeda et al. 1980).

The possible role of other metabolites in the testicular toxicity of DEHP is not fully elucidated and therefore the importance of species differences in the formation of other metabolites is not known. Other parameters e.g. altered zinc homeostatsis or protein-content in diet also seems to influence the susceptibility to the toxic effects (DEHP 2001), but no data are available with regard to these differences between rats and dogs.

The limited toxicokinetic data in dogs, indicate that MEHP is formed following exposure to DEHP and that metabolism of DEHP are relatively similar between rats and dogs. Therefore, DEHP induced effects on testes and reproductive functions in rats are also considered relevant for dogs and cats.

3.4.2 DINP

Although limited reported, the toxicity study in dogs reveals effects on the liver at lower doses than the rat study used to establish the overall NOAEL. Therefore it is obvious that the effects on liver in rats are also relevant to dogs. No data is available for cats, but it will be assumed that the observed effects in rats and dogs also are relevant to cats.

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Version 1.0 August 2006, © Danish Environmental Protection Agency