Reproductive toxicity evaluation of methylethyl ketoxime by gavage in CD rats

[Indoor air guide values for 2-butanone oxime. Communication from the Ad-hoc Working Group on Indoor Guide Values of the Indoor Air Hygiene Commission and the States' Supreme Health Authorities]

The German Working Group on Indoor Guidelines of the Indoor Air Hygiene Committee and of the Supreme State Health Authorities is issuing indoor air guide values to protect public health. No reliable human studies are available for health evaluation of 2-butanone oxime in indoor air. In a well documented chronic inhalation animal study with rats and mice assessed as reliable, degenerative changes in the olfactory epithelium were observed, which led to a dose related increased incidence and severity, especially in mice. Using a benchmark approach the Working Group assessed a BMD10 of 13.8 mg 2-butanone oxime/m(3) for continuous exposure for the endpoint degeneration of the olfactory epithelium. For interspecies differences a reduced factor of 1 was applied due to the same susceptibility of rodents than human for this endpoint. By applying a factor of 10 for interindividual variability, and a factor of 2 to account for the higher respiratory rate of children compared to adults, a health hazard guide value (RW II) of 0.06 mg 2-butanone oxime/m(3) indoor air is obtained. A precautionary guide value of 0.02 mg 2-butanone oxime/m(3) indoor air is recommended.

Oxime silanes: structure/toxicity relationships

Acute and repeated oral and dermal rat toxicology studies of standard designs were conducted on four methyl ethyl ketoxime (MEKO) silanes and four methyl isobutyl ketoxime (MIBKO) silanes. Each compound contained either MEKO or MIBKO groups (but not both) and either a single methyl, vinyl, or phenyl group (trifunctional oxime silane), two methyl groups or a methyl and vinyl group (difunctional oxime silane), or no nonoxime group (tetrafunctional oxime silane) attached to the central silicon atom. All compounds caused transient narcosis and anemia, with oral exposure associated with the hydrolyzed oxime groups. Difunctional oxime silanes, containing both a methyl and a vinyl group, caused degeneration of the seminiferous tubules of the testes following oral administration. Serial testicular histopathology indicated the effect originated at the level of the spermatocyte, resulting in a wave of cellular depletion of later maturation stages of spermatogenesis. Spermatogenesis gradually recovered but function was not evaluated. Tetrafunctional oxime silanes, trifunctional oxime silanes, including those containing a single methyl or vinyl group, or difunctional oxime silane containing two methyl groups did not affect the testes, indicating that both a methyl and vinyl group needs to be present on the oxime silane molecule for testicular toxicity. The testicular toxicity appears to be associated with the methyl/vinyl silane portion and not the oxime portion of the oxime silane molecule. With the exception of the methyl/vinyl difunctional oxime silanes, the silane portion of oxime silanes does not appear to contribute any significant toxicity to these compounds.

Developmental toxicity studies of methyl ethyl ketoxime (MEKO) in rats and rabbits

The developmental toxicity of methyl ethyl ketoxime (MEKO), an industrial antioxidant used primarily as an antiskinning agent in alkyd paint, was investigated in rats and rabbits. Following preliminary dose range finding studies, groups of 25 pregnant rats or 18 pregnant rabbits were dosed by gavage with aqueous solutions of MEKO at 0, 60, 200, or 600 mg/kg (rats) or 0, 8, 14, 24, or 40 mg/kg (rabbits) on gestation days 6-15 or 6-18, respectively. In rats, dose-dependent clinical signs of maternal toxicity including reduced body weight gains were noted at 200 and 600 mg/kg. At 60 mg/kg and above enlarged spleens were observed at necropsy. The preliminary study found methemoglobin formation and reticulocytosis indicative of anemia at these dose levels. No treatment-related gestational effects, malformations or developmental variations were observed in the rats. In rabbits, 3 females aborted and 8 females were found dead at 40 mg/kg between gestation days 11 and 24. Clinical signs of maternal toxicity were present in surviving doses at this dose level. Body weight gains were reduced at 24 and 40 mg/kg. The preliminary study indicated maternal hematological effects in the rabbits similar to the rats at dose levels as low as 10 mg/kg. MEKO was not considered to have produced any treatment-related gestational effects, malformations or developmental variations in the rabbit at dose levels at or below 24 mg/kg. Because of excessive maternal mortality and abortions at the 40 mg/kg dose level, only 6 rabbits produced litters. The severe maternal toxicity and limited number of litters precluded a full assessment of developmental toxicity at 40 mg/kg. Nonetheless, MEKO did not appear to be teratogenic to the rabbit at this dose level.

Disposition of methyl ethyl ketoxime in the rat after oral, intravenous and dermal administration

1. The disposition of 14C-methyl ethyl ketoxime (MEKO) was determined in the male F344 rat following oral, intravenous (i.v.) and dermal administration. 2. Oral doses of 2.7, 27 and 270 mg/kg were primarily excreted as CO2 (71-49%) in decreasing percentage as the dose increased. Excretion in urine (13-26%) and as volatiles (5-18%) increased as the dose increased. Five to 6% of the dose remained in the major tissues after 72 h. 3. An i.v. dose of 2.7 mg/kg was also principally excreted as CO2 (48.8%) with excretion in urine and as expired volatiles accounting for 21.4 and 11.4%, respectively. About 7% of the administered radioactivity remained in the tissues after 72 h. 4. Following dermal administration, 13 and 26% of a 2.7 and 270 mg/kg dose, respectively, were absorbed. Volatilization from the dose site prior to placement in the metabolism cage may account for the low absorption. 5. MEKO was biotransformed to at least five polar metabolites that could only be partially resolved by anion exchange chromatography. Incubation with glucuronidase, but not sulphatase, changed the urinary metabolic profile. Methyl ethyl ketone was a major component in the volatiles.