Mineral oil saturated hydrocarbons (MOSH) in female Fischer 344 rats; accumulation of wax components; implications for risk assessment

Abstract

Female Fischer 344 rats were exposed to three MOSH mixtures: oils largely below and above C₂₅ (S-C25 and L-C25) and a 1:1 mixture of L-C25 with a wax; doses of 400, 1000 and 4000mg/kg feed were administered during 120days. MOSH were determined by on-line HPLC-GC-FID in liver, spleen, adipose tissue and the carcass. The composition of the hydrocarbons accumulated in the tissues was further analyzed by comprehensive two-dimensional GC (GC×GC). MOSH in the mass range of C_26-30 were more strongly accumulated than those between C_20-25, which does not support the present classification of MOSH differentiating at n-C₂₅ for risk assessment. Compared to the total of the MOSH, n-alkanes and n-alkyl monocyclic naphthenes were generally enriched in adipose tissue. In liver and spleen, n-alkanes up to C₂₅ were eliminated, but strongly accumulated at around C₃₀. Based on this profile, poor solubility and the melting points, it is hypothesized that crystallization protects these wax components against metabolism and elimination. In the liver, relative retention of n-alkanes decreased again beyond C₃₀, accentuated at high exposure, suggesting reduced absorption. Compared to the animal data, accumulation of n-alkanes from food sources, such as apples, into human tissues seems low, perhaps because of low absorption due to their presence in crystalline form. A series of dominant isoalkanes, accumulated in all tissues analyzed, was characterized, though without proposing a structure. Implications on present regulation of white mineral oil products are discussed.

Keywords: Class I mineral oils; Crystallization of waxes; Granulomas; Mineral waxes; Naphthenes; n-Alkanes.