Introduction
Organic solvents are carbon-based liquids that dissolve other substances and evaporate readily at room temperature. They are used in paints and varnishes, adhesives, degreasing and cleaning, printing, rubber and pharmaceutical manufacture, and in laboratories. This topic covers their toxic effects on workers, the principles of occupational risk assessment for solvent exposure, and the preventive measures that protect workers.
Definition and main groups
Organic solvents are volatile organic compounds that are lipophilic, so they dissolve fats and cross cell membranes easily. The main occupational groups are:
- Aromatic hydrocarbons: benzene, toluene, xylene, styrene.
- Aliphatic hydrocarbons: n-hexane, white spirit, petrol fractions.
- Halogenated hydrocarbons: trichloroethylene, perchloroethylene, dichloromethane, carbon tetrachloride.
- Alcohols, ketones and esters: methanol, ethanol, acetone, ethyl acetate.
- Glycol ethers and carbon disulfide, which have their own specific toxicity profiles.
Routes of exposure and toxicokinetics
The main route is inhalation of vapour. Solvents are absorbed rapidly through the alveoli because of their high lipid solubility. Skin absorption is significant, especially with liquid contact, and some solvents permeate common gloves. Ingestion is rare and usually results from contaminated hands or food. After absorption, solvents distribute to fatty tissues and to the brain, which explains their depressant effect on the central nervous system. Many are metabolised in the liver by cytochrome P450 enzymes, and some metabolites are more toxic than the parent compound, for example benzene to phenol and hydroquinone, n-hexane to 2,5-hexanedione, methanol to formaldehyde and formic acid, and trichloroethylene to trichloroacetic acid. Uptake rises with physical workload, high air temperature, poor ventilation and alcohol intake.