Naphthalene

Naphthalene (CAS 91-20-3) is the simplest polycyclic aromatic hydrocarbon — two fused benzene rings — historically known as the active in classic mothballs. In petroleum-solvent degreasers it is a trace contaminant (under 1%) of the heavy-aromatic-naphtha solvent cut, not an intentional ingredient. The petroleum refining process cannot economically eliminate it without changing the solvent properties of the parent cut, so it persists in heavy-aromatic distillates as a residual constituent.

It is the regulatory anchor for the Prop 65 cancer warning on the Engine Brite EB1 label: California listed naphthalene as a carcinogen on April 19, 2002 (CRT designation). It is also a CERCLA hazardous substance, a SARA 313 TRI-reportable chemical, and a Clean Air Act Hazardous Air Pollutant. ACGIH carries a skin designation, meaning dermal absorption is a meaningful exposure route in addition to inhalation. The Prop 65 cancer warning on consumer aerosols containing this solvent fraction is driven by naphthalene, not by the bulk petroleum distillate.

For users: the Prop 65 warning on petroleum-solvent engine degreasers is a real chemistry-based call, not generic California-label noise. The naphthalene exposure is small per use, but the classification is based on a recognized carcinogenic endpoint.