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Appendices 1-18 to: Report on the Health Effects of Selected Pesticide Coformulants

 43   Animal toxicity

43.1   Single dose toxicity

43.1.1   Inhalation

Twenty rats were exposed for 6.5 seconds/minute for an hour to an aerosol antiperspirant containing 16-20% isopropyl myristate at a nominal concentration of 33-41 mg/l. During exposure all rats exhibited lethargy, and slight muscle and eye discharge. No deaths occurred, and no evidence of systemic toxicity was found at necropsy or during the 14-day post-exposure observation period. (Hazleton Laboratories 1978 – quoted from BIBRA 1988 and CIR 1982).

Groups of 6 rats served as controls or were exposed for four 15-minute periods each separated by 5-minute fresh air periods to an aerosol antiperspirant containing 4.7% isopropyl myristate at a nominal concentration of 9.7 mg/l. No deaths occurred and no significant differences were found between control and exposed rats during exposure or at necropsy. (CTFA 1974 – quoted from BIBRA 1988 and CIR 1982).

43.1.2   Oral intake

The oral LD₅₀-value of undiluted isopropyl myristate has been reported to be higher than 13700 mg/kg b.w. for rats (4 studies) and from 42400 to higher than 85000 mg/kg b.w. for mice (2 studies) (Anon 1953, Avon 1971, Inolex 1975, Kolmar Research Center 1972, Lebarco Laboratories 1973, Platcow & Voss 1954 – all quoted from BIBRA 1988 and CIR 1982).

43.1.3   Dermal contact

43.1.3.1     Acute toxicity

The dermal LD₅₀-value of undiluted isopropyl myristate has been reported to be higher than 5000 mg/kg b.w. for rabbits (1 study) (Moreno 1974 – quoted from BIBRA 1988 and CIR 1982).

In rabbits exposed dermally to a single dose of 7600 mg/kg b.w. of isopropyl myristate experienced no overt toxic symptoms or significant haematological changes occurred. Urinary analysis revealed no evidence of metabolic disturbance or kidney damage. (Anon 1953 – quoted from BIBRA 1988).

No deaths or abnormalities at autopsy were reported in a study where 6 guinea pigs were dosed dermally (with an antiperspirant) with about 1000 mg/kg b.w. of isopropyl myristate (CTFA 1972 – quoted from BIBRA 1988 and CIR 1982). 

43.1.3.2     Skin irritation

The Draize primary skin irritation test or a slight modification of it was used in rabbits to evaluate undiluted isopropyl myristate in 5 studies and four product formulations containing the ester in 5 studies. Isopropyl myristate caused no to minimal irritation. (Avon 1974, 1976, 1977, Bio/dynamics 1978, CFTA 1972, 1978, Consumer Product Testing 1978, Inolex 1975, Leberco Laboratories 1973, MB Research Laboratories 1974 – all quoted from CIR 1982).

Isopropyl myristate was slightly irritating in one of the rabbit tests, which was performed according to OECD-guideline 404 and following the principles of GLP (ECETOC 1995 – quoted from Bagley et al. 1996 and IUCLID 2000).

43.1.4   Other routes

43.1.4.1     Eye irritation

The Draize rabbit eye irritation test or a modification of it was used to evaluate undiluted isopropyl myristate in more than 10 separate studies and four product formulations containing the ester in 4 studies. No or minimal irritation generally followed a single application of the undiluted material or the product formulations (Avon 1972a, b, c, 1976, 1977, Bio/dynamics 1978, CFTA 1972, 1978, Guillot et al. 1977, Kolmar Research Center 1967, Leberco Laboratories 1973, Platcow & Voss 1954, Weil & Scala 1971 – all quoted from BIBRA 1988 and/or CIR 1982; Ohno et al. 1999), although in one study slight corneal opacity was reported in a minority of rabbits (Guillot et al. 1982 – quoted from BIBRA 1988).

43.2   Repeated dose toxicity

43.2.1   Inhalation

Two groups of twenty guinea pigs were exposed for an hour three times a day, seven days a week for 4 (half of the animals) or 13 (the other half of the animals) weeks to an aerosol antiperspirant containing 16-20% isopropyl myristate. Test groups were exposed to mean isopropyl myristate concentrations of 10-13 or 36-45 mg/m³. A control group of 40 guinea pigs were exposed to air. One female guinea pig died for unknown causes. Both absolute and relative lung weights increased in the exposed animals but no histological changes were found. The organs examined were not specified. (Bio/dynamics 1979 – quoted from BIBRA 1988, CIR 1982 and IUCLID 2000).

Four groups of nine cynomolgus monkeys were exposed for an hour three times a day, seven days a week for 13 weeks to an aerosol antiperspirant containing 16-20% isopropyl myristate. Test groups were exposed to isopropyl myristate concentrations of about 0.95, 1.5, 6.0 or 6.7 mg/m³. A control group of 9 monkeys were exposed to air. During the study, the treated monkeys wheezed and coughed and two of the monkeys exposed to about 1.5 mg/m³ of isopropyl myristate developed nosebleeds. Lung function tests after 6 and 13 weeks were normal, as were the results of haematology, blood chemistry and urinalysis. No gross lesions were seen at necropsy, and organ weights were unaffected by treatment. Histological examinations revealed a dose-related accumulation of macrophages within the alveolar and bronchiolar walls of the lungs of treated monkeys. (Hazleton Laboratories 1978 – quoted from BIBRA 1988, CIR 1982 and IUCLID 2000).

Groups of 12 female CD rats and of 12 female hamsters were exposed by whole body inhalation to aerosols of a diluted complex fragrance mixture at 0 or 50 mg/m³ (aerodynamic mean diameter = 1.4 mm) for 4 hours per day, 5 days per week for 13 weeks. The fragrance mixture consisted of approximately 200 ingredients with close to one-half of the ingredients present at a level of 1% or more. The animals were exposed to isopropyl myristate at a maximal concentration of 0.16 mg/m³. No toxicological significant effects were observed on survival, behaviour, body weights, organ weights, haematology, clinical chemistry, gross pathology, or histopathology. (Fukayama et al. 1999).

43.2.2   Oral intake

Groups of 50 rats were fed 2.5, 5, or 10% of isopropyl myristate (equal to about 2000, 3700 or 7900 mg/kg b.w. per day) in their diet for up to 16 weeks. Histopathological examinations revealed no damage to any organs or tissues at any dose. At the highest dose, the liver weight and the blood levels of two liver enzymes were increased. In addition the males had increased spleen, small intestine and kidney weights, and in both sexes the proportion of neutrophilic leucocytes was increased. At the mid-dose only transient changes in some of the organ weights (spleen, liver, small intestine) were observed. (Gaunt et al. 1972 – quoted from BIBRA 1988 and IUCLID 2000).

Groups of Wistar rats were given 0, 100, 500 or 1000 mg/kg b.w. per day of isopropyl myristate by gavage once a day, 5 days per week for 28 days. No mortality, symptoms of intoxication, or substance-related injury of organs were recorded. Histologically, a reversible hyperplasia of the forestomach mucosa was observed in all test groups including the negative control group indicating local irritating effects of the olive oil carrier. (Henkel KgaA – quoted from IUCLID 2000).

43.2.3     Dermal contact

43.2.3.1   Systemic toxicity

Rabbits had dermal applications of 5100 mg/kg b.w. of isopropyl myristate daily for 20 days. Skin inflammation, liver damage (mild cloudy swelling), and leucocytosis were observed. No changes were found in the kidneys, testes, or spinal cord. (Anon 1953 – quoted from BIBRA 1988 and IUCLID 2000).

Groups of 10 rabbits were dosed for five days a week for 4 weeks on abraded skin of their back with either distilled water or 320-400 mg/kg b.w. of isopropyl myristate from an aerosol antiperspirant containing 16-20% of the chemical. None of the animals died and no changes considered to be related to the product were seen in general behaviour, body weights, or haematological studies. See also section 4.2.3.2 Local effects regarding local dermal effects. (IRDC 1978 – quoted from BIBRA 1988, CIR 1982, and IUCLID 2000).

Groups of 6 rabbits either remained untreated or were dosed for five days a week for a total of 21 dermal applications with 730-800 mg/kg b.w. of isopropyl myristate from an aerosol antiperspirant containing 43-47% of the chemical. One of the dosed animals died from causes thought to be unrelated to treatment. No significant pathological changes were discovered at necropsy other than local skin damage – see also section 4.2.3.2 Local effects for more details. (CFTA 1972 – quoted from BIBRA 1988 and CIR 1982).

43.2.3.2   Local effects

A 0.5 ml (425 mg) sample of undiluted isopropyl myristate was applied for three consecutive days to a 2 inch² area of clipped skin on a total of 42 rabbits (7 studies). Isopropyl myristate was moderately to severely irritating under the conditions of the study as evidenced by the occurrence of oedema, severe erythema, drying, cracking, and scaling. No further details were given. (Avon 1970, 1971a, b, c, 1972a, b, c – all quoted from CIR 1982).

New Zealand white rabbits or Albino Spartan mice had daily dermal applications of undiluted isopropyl myristate for up to 14 or 28 days, respectively. Erythema, lichenification and fissure formation occurred at the application site. Microscopically, the treated skin of exposed animals showed acanthosis, parakeratosis, hyperkeratosis, focal erosion, and focal haemorrhage. In mice, the skin lesions tended to regress during continued treatment while the lesions in rabbits regressed slowly after cessation of treatment. No further details were given.  (Fitzgerald et al.  1968 – quoted from CIR 1982 and IUCLID 2000).

Groups of 10 rabbits were dosed for five days a week for 4 weeks on their abraded back with either distilled water or 320-400 mg/kg b.w. of isopropyl myristate from an aerosol antiperspirant containing 16-20% of the chemical. Moderate to severe erythema, desquamation, slight coriaceousness, moderate fissuring, and atonia occurred at the application site. Microscopically, the treated skin of all exposed rabbits showed marked to severe acanthosis and hyperkeratosis with varying degrees of parakeratosis and mixed inflammatory cell infiltration. No further details were given. (IRDC 1978 – quoted from CIR 1982).

Groups of 6 rabbits either remained untreated or were dosed for five days a week for a total of 21 dermal applications with 730-800 mg/kg b.w. of isopropyl myristate from an aerosol antiperspirant containing 43-47% of the chemical. Signs of product-related changes in the skin included erythema, oedema, drying, cracking, and fissuring. No further details were given. (CFTA 1972 – quoted from CIR 1982).

White albino rabbits, which had 1, 5 or 100% of isopropyl myristate in propylene glycol applied to the ears twice daily 5 days a week for 2 weeks developed significant comedones formation even at the lowest concentration (Fulton et al. 1976 – quoted from BIBRA 1988 and IUCLID 2000).

43.2.3.3   Skin sensitisation

In 2 guinea pig sensitisation tests with 2 or 10 animals, respectively, isopropyl myristate suspended at 0.1% in physiologic saline showed no evidence of a sensitisation potential (Inolex 1975, Platcow & Voss 1954 – both quoted from CIR 1982). 

Isopropyl myristate was found to be weakly positive for skin sensitisation in the local lymph node assay (LLNA) in mice. In this assay, groups of 5 female CBA/J mice were treated once a day for 3 consecutive days on the dorsum of both ears with 25 ml of 25, 50 or 100% of isopropyl myristate in acetone/olive oil (4:1) or with vehicle alone. Five days after the initial treatment, all mice were injected intravenously via the tail vein with marked methylthymidine. The incorporation of methylthymidine in the cells of the draining auricular lymph nodes was determined. It is generally taken as a measure for the lymphocyte proliferation provoked by sensitising chemicals during the induction phase. The authors are suggesting that the positive result might be a false-positive response since a) isopropyl myristate is not expected based on structure to be a skin sensitiser, b) it has been reported that some irritants can produce a positive response in LLNA and isopropyl myristate is known to be a skin irritant at high concentrations, c) and isopropyl myristate was only weakly positive at the highest concentration tested. (Ryan et al. 2000).

43.2.4   Other routes

43.2.4.1   Eye irritation

Applications of isopropyl myristate to the eyes of rabbits daily for 3 consecutive days apparently caused no irritation (Avon 1970, 1971a – all quoted from BIBRA 1988 and CIR 1982) or slight irritation that had vanished after 7 days (Avon 1971b – quoted from BIBRA 1988 and CIR 1982).

43.3   Toxicity to reproduction

Twenty Swiss albino mice (housed one male and one female per cage) had 0.1 ml of 1% isopropyl myristate (equivalent to 42.5-56.6 mg/kg b.w.) in acetone applied to the skin once weekly for 18 months. No abnormalities were found in litters, which were examined grossly. (Giles & Byron 1968 – quoted from BIBRA 1988 and IUCLID 2000).

43.4   Mutagenic and genotoxic effects

Isopropyl myristate tested negative in an Ames test with 5 strains of Salmonella typhimurium (TA 98, TA 100, TA 1535, TA 1537 and TA 1538) both with and without metabolic activation (Blevins & Tayler 1982 – quoted from BIBRA 1988 and IUCLID 2000).

43.5   Carcinogenic effects

In a lifetime study, groups of 50 female Swiss mice were given skin applications from the age of 7 weeks on their backs of 0.02 ml of 10, 50 or 100% isopropyl myristate (equivalent to 85, 425 or 850 mg/kg b.w.) in acetone twice a week. Control groups consisted of 135 untreated animals (negative), 50 treated with acetone (negative), and 50 treated with 7,12-dimethylbenzanthrancene (positive). Two benign skin tumours remote from the site of application developed in exposed mice. Internal tumours (including lymphomas, lung adenomas, liver haemangiomas and thymomas) were also found. However, no significant differences were observed between exposed or negative control animals in the incidence of skin or internal tumours. (Stenbäck & Shubik 1974 – quoted from BIBRA 1988, CIR 1982 and IUCLID 2000).

No skin tumours were found when 0.1 ml of a 1% solution of isopropyl myristate (equivalent to 42.5-56.6 mg/kg b.w.) in acetone was applied once a week to the clipped skin of 20 Swiss albino mice for 18 weeks. Acetone was used as a negative control and 9,10-dimethyl-1,2-benzanthracene as a positive control. Five mice escaped and 4 died before the end of the study in the exposed group. (Giles & Byron 1968 – quoted from BIBRA 1988, CIR 1982 and IUCLID 2000).

In a lifetime study, groups of 5 New Zealand white rabbits were given skin applications on the interior left ear from the age of 8 weeks of 0.02 ml of 10, 50 or100% isopropyl myristate (equivalent to 0.85, 4.25 or 8.5 mg/kg b.w.) in acetone twice a week. No tumours of the skin or internal organs developed. (Stenbäck 1977 – quoted from BIBRA 1988 and IUCLID 2000).

A 50% solution of isopropyl myristate (in ethanol according to BIBRA and IUCLID but in isopropyl alcohol according to CIR) significantly accelerated the carcinogenic activity of 0.15% benzo[a]pyrene (known skin carcinogen) on the skin of mice (Horton et al. 1966 – quoted from BIBRA 1988, CIR 1982 and IUCLID 2000).

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