Creosote — distilled from coal tar — is one of the most effective wood preservatives ever developed, and its distinctive dark brown colour and tarry smell are familiar from fence posts, garden sleepers, and telegraph poles. It contains a complex mixture of polycyclic aromatic hydrocarbons (PAHs), including potent carcinogens such as benzo[a]pyrene and chrysene, as well as phenolic compounds and heterocyclic aromatics. Coal tar creosote has been banned for consumer use in the UK and EU since 2003, but millions of garden railway sleepers, fence posts, and structures treated before 2003 remain in UK gardens, and illegal or non-compliant products continue to be sold. Garden enthusiasts who touch or work near old creosote-treated wood are receiving ongoing PAH exposure.
Where it's found
Old railway sleepers used as garden edging, raised bed borders, and decorative landscaping features — these are often pre-2003 creosote-treated items that remain in widespread use. Creosote-treated fence posts and panels. Preservative-treated telegraph poles reused in gardens. Old sheds and outbuildings treated with creosote before 2003. Some "wood preserver" products still available in the UK contain coal tar components below regulatory thresholds but above background PAH levels. Post-2003 alternatives use copper-based or triazole preservatives that carry different but overlapping toxicological concerns.
Routes of exposure
Dermal absorption from touching, leaning against, or working with creosote-treated wood — particularly in warm weather when the wood is warm and residual creosote becomes more fluid and transferable. Children sitting or playing on creosote-treated sleepers receive sustained skin contact exposure. Inhalation of PAH vapours volatilising from warm treated wood. Soil contamination adjacent to creosote-treated structures provides ongoing dermal and incidental ingestion exposure. Vegetables grown in raised beds edged with old creosote sleepers absorb PAHs from soil contamination.
Health concerns
Creosote is classified as a probable human carcinogen (IARC Group 2A). Benzo[a]pyrene, the marker compound for carcinogenic PAH mixtures, is a Group 1 confirmed human carcinogen. PAHs from creosote are genotoxic — they form covalent DNA adducts following metabolic activation by CYP1A1 and CYP1B1 enzymes. Occupational exposure to creosote in wood preservation and railway industries is causally associated with scrotal cancer, skin cancer, and lung cancer. Consumer garden exposure is at lower levels but is often chronic over decades. The phenolic components of creosote are also skin sensitisers and irritants.
Evidence
PAH carcinogenicity including from creosote is established. Occupational creosote exposure causing skin and scrotal cancer was among the earliest recognised occupational cancers (Percivall Pott's 1775 description of chimney sweep scrotal cancer involved coal tar PAH exposure). The cancer risk from garden-level creosote exposure — handling old sleepers, touching treated wood — is lower magnitude than occupational exposure but biologically plausible given the same chemical mechanisms. IARC Group 2A classification reflects limited direct human evidence at non-occupational doses but sufficient animal and mechanistic evidence.
Who's most at risk
Children who play on or near creosote-treated railway sleepers and garden structures, receiving sustained skin contact exposure during play. Gardeners who regularly handle creosote-treated wood without gloves. DIY enthusiasts cutting or sanding old treated wood, generating PAH-contaminated dust. People growing edible vegetables in raised beds edged with creosote-treated timber.
Regulatory status
RegulationCoal tar creosote is banned for consumer use in UK and EU under the Biocidal Products Regulation (BPR) and predecessor Biocidal Products Directive. Sale and supply to the public has been prohibited since 2003. However, existing treated structures are not required to be removed, creating ongoing exposure from legacy materials. Benzo[a]pyrene is restricted in consumer products under UK REACH and CLP. Trading Standards prosecute illegal sales of creosote products, but the market for legacy railway sleepers remains active and their PAH content is not regulated.
How to reduce your exposure
Remove old creosote-treated railway sleepers from vegetable growing areas and replace with untreated hardwood, stone, or brick alternatives. Do not use creosote-treated wood as raised bed edging — PAHs leach from the wood into soil and are absorbed by root vegetables and leafy greens. Wear gloves when handling any old dark-brown creosote-treated wood. Do not sand, cut, or burn creosote-treated timber — sanding generates PAH dust, burning generates PAH combustion products. If you suspect a treated wood source, wipe a cloth across it: creosote-treated wood leaves brown tarry residue.
The nutrition connection
Cruciferous vegetables (broccoli, Brussels sprouts, cabbage, kale) are the most consistently evidence-backed dietary strategy for supporting PAH detoxification. Their glucosinolate breakdown products (sulforaphane, indole-3-carbinol) induce phase I CYP1A1 enzymes that metabolise benzo[a]pyrene and simultaneously induce phase II conjugation enzymes (GSTs) that detoxify the reactive metabolites — the net effect is accelerated clearance of PAH-DNA adducts. Dietary fibre reduces gut transit time and may reduce enterohepatic recirculation of PAH metabolites. Antioxidants (vitamins C, E, carotenoids) protect against the oxidative stress component of PAH toxicity.