Residual Oils (Petroleum), Solvent-Refined

Residual oils (petroleum), solvent-refined (CAS 64742-01-4) are a class of heavy petroleum base oils produced by solvent refining of petroleum residua. They serve as the heavy carrier base in industrial greases, anti-seize compounds, and high-temperature lubricants, providing paste body and lubrication before the carrier volatilizes during service.

This fraction is classified by IARC as a Group 1 carcinogen based on evidence of skin cancer in industrial workers who experienced repeated, prolonged dermal exposure to untreated or mildly treated mineral oils over decades. Solvent-refined residual oils are lower-risk than untreated oils but retain the Prop 65 cancer listing in California.

In paste anti-seize applications (occasional fastener service), the acute exposure pathway is limited skin contact. The Prop 65 disclosure is a regulatory requirement reflecting the fraction's classification, not an indication of acute hazard under typical home-mechanic use.

Regulatory status: UNRESOLVED, flag left as-is

This ingredient was one of 7 flagged by a catalog-wide screen for prop65_listed: true entries whose CAS number does not appear directly in data/prop65/oehha-list.json. For this one, the direct CAS check comes back negative, but the underlying regulatory question is genuinely unsettled, and the flag is deliberately being left at true rather than corrected, for the following reasons:

• CAS 64742-01-4 does not appear directly on the OEHHA list. OEHHA's relevant listing is a category entry, "Soots, tars, and mineral oils (untreated and mildly treated oils and used engine oils)" (cancer, listed 1987-02-27), which carries no CAS number of its own and is defined by treatment level rather than by a specific CAS.
• The published IARC/NTP literature on this category draws a real distinction by degree of refining: "mildly" solvent-refined oils are classified Group 1 carcinogenic, while "severely" solvent-refined oils show no evidence of carcinogenicity in the same evaluations. CAS 64742-01-4's own name, "Residual oils (petroleum), solvent-refined," does not specify which side of that mild/severe line it falls on, and this pass was not able to find an authoritative CAS-to-treatment-level cross-reference that resolves it.
• This is the sole Prop 65 driver for one live product: content/products/loctite/loctite-299175-anti-seize/index.md resolves prop65_warning: true citing "residual oils petroleum, solvent-refined" as its only stated basis, with no independent Amazon-posted or second-ingredient arm found in the product file. Flipping this flag to false would change that product's published Prop 65 value, which is exactly the case the audit instructions say to stop on rather than resolve unilaterally.

What would settle this: a proper CAS-level cross-reference between the CAS Registry's petroleum-stream nomenclature (which distinguishes "solvent-refined," "solvent-dewaxed," "hydrotreated," and so on) and the specific mild-vs-severe treatment classification IARC/NTP use for the "untreated and mildly treated" mineral oils listing, for example via the API's petroleum-substance categorization or a specialist Prop 65 compliance reference, applied specifically to CAS 64742-01-4. Absent that, this flag stays true on the honest-unresolved principle: an unconfirmed true that turns out wrong is a legal-exposure bug, but so is an unconfirmed false that removes a real warning from a live product, and the second failure mode is the one with a concrete product depending on it here.

Sources

• OEHHA Proposition 65 list cross-check: data/prop65/oehha-list.json (986 entries, published 2025-12-05), no direct match for CAS 64742-01-4. Category listing "Soots, tars, and mineral oils (untreated and mildly treated oils and used engine oils)" present (cancer, listed 1987-02-27, no CAS assigned).
• IARC mineral-oils monograph summary and NTP Report on Carcinogens profile for "Mineral Oils: Untreated and Mildly Treated" (15th edition), consulted for the mild-vs-severe refining distinction; neither source, as consulted in this pass, resolves CAS 64742-01-4 to one side or the other.
• This entry is left genuinely unresolved rather than corrected. Do not treat the "no direct CAS match" screening signal as a verdict for this ingredient without redoing this research with a real petroleum-stream classification reference.