Toluene

Toluene (methylbenzene) is an aromatic hydrocarbon solvent widely used in carburetor and throttle-body cleaners as a co-solvent with acetone — its strong solvent power against varnish, gum, and resinous fuel deposits is hard to replicate with VOC-exempt alternatives. It is also a Prop 65–listed substance (developmental toxicity) and a federal Hazardous Air Pollutant under Clean Air Act Section 112.

In aerosol carb cleaner formulations, toluene typically appears at less than 10% of formula weight, but its presence drives the Prop 65 warning label and contributes the H361d (suspected reproductive toxicant) and H373 (target organ toxicity – repeated exposure, central nervous system) classifications even at modest concentrations. The chronic effects of toluene exposure are well-documented in occupational medicine; brief consumer use of an aerosol product applied outdoors poses meaningfully lower risk than the SDS hazard codes might suggest in isolation, but the ingredient is the chemistry reason a Prop 65 warning is required regardless of use case.

Aquatically toxic with rapid biodegradation in aerobic surface water but poor degradation in anaerobic groundwater. Listed under SARA 313 Toxic Chemicals — release reporting required for certain facilities.