Diuron is a persistent herbicide used in path, patio, and driveway weedkiller products — it kills weeds by blocking photosystem II in plants and remains active in soil for months, providing the "long-lasting" weed prevention claimed on product labels. Diuron is the active ingredient in products including Pathclear, Weedol Path & Patio, and several driveway weed prevention treatments. It is one of the most commonly detected herbicides in UK water courses and drinking water catchments — its persistence in soil and its mobility in water mean that garden applications on paths and patios are regularly washed into drains and eventually into rivers. Diuron is classified as a priority hazardous substance under the Water Framework Directive for exactly this reason.
Where it's found
Consumer path and patio weedkiller products — "long-lasting" or "total weedkiller" products for hard-standing areas almost universally contain diuron as their persistent active ingredient. Pathclear (Scotts) is the leading UK brand. Path clear products combining glyphosate (fast-acting) with diuron (residual) are widely sold. Agricultural use on non-crop areas, railway embankments, and amenity land. Professional driveway and car park maintenance treatments. Historic use in some vine and tree crop protection.
Routes of exposure
Dermal contact during application without gloves and long sleeves. Inhalation of diuron dust when handling concentrated granular products. Children and pets walking on treated paths and patios and then transferring residues indoors via shoes and paws — diuron's persistence means treated surfaces remain contaminated for months. Dietary exposure via diuron residues in food and drinking water — diuron is detected in UK tap water in agricultural and urban catchment areas. Incidental oral ingestion by children who touch treated path surfaces and then hands-to-mouth.
Health concerns
Diuron is classified as a possible human carcinogen (IARC Group 2B) based on animal studies showing bladder tumours. It is also a suspected endocrine disruptor — in vitro evidence shows oestrogenic activity and effects on thyroid hormone signalling. The primary environmental concern is its persistence and water contamination: diuron metabolites (3,4-DCA — 3,4-dichloroaniline) are potentially more toxic than the parent compound, are mutagenic in some assays, and accumulate in aquatic sediments. 3,4-DCA is toxic to aquatic organisms, amphibians, and earthworms. Drinking water contamination with diuron and its metabolites is a significant water utility management challenge in UK agricultural and suburban catchments.
Evidence
Diuron bladder carcinogenicity in rodents is established in animal studies, forming the basis for IARC Group 2B classification. Human epidemiological evidence is limited — no definitive human carcinogenicity study is available specifically for diuron. The endocrine disrupting properties are documented in vitro. Environmental data on diuron water contamination from garden use are robust — the UK Drinking Water Inspectorate and Environment Agency monitor diuron regularly and find it at concentrations requiring water treatment intervention in some catchments.
Who's most at risk
Children who play on diuron-treated paths and patios and who have high hand-to-mouth transfer rates. People applying products without appropriate PPE. People eating homegrown vegetables in soil receiving diuron contamination via irrigation or runoff. Communities whose drinking water is sourced from surface water catchments with heavy residential herbicide use.
Regulatory status
RegulationDiuron is approved for amateur use in the UK and EU under plant protection product and biocidal product regulations for path and non-crop weed control. It is designated as a priority hazardous substance under the Water Framework Directive due to its ubiquitous water contamination. EU and UK Maximum Residue Limits apply in food. The UK Drinking Water Quality Regulator sets individual pesticide limits in drinking water (0.1 µg/L per compound). Diuron has been under renewal review — its future regulatory status in the EU is uncertain given its hazard profile, though UK post-Brexit regulation may diverge.
How to reduce your exposure
For path and patio weed prevention without diuron: flame weeding (propane torch or infrared weeder) is highly effective on patios and drives. Boiling water kills surface weeds instantly. Path sand containing horticultural iron sulphate inhibits weed germination. Polymeric jointing sand for paving reduces weed establishment. Physical weed fabric under gravel reduces need for chemical control. Regular brushing and pressure washing is preventive maintenance that reduces weed establishment between chemical treatments.
The nutrition connection
Diuron's endocrine disrupting thyroid activity makes iodine and selenium nutrition relevant, as described for other thyroid-active herbicides. The bladder carcinogenicity concern from diuron and its metabolites is mechanistically relevant to hydration — adequate water intake dilutes bladder carcinogen concentrations and reduces contact time with urothelial cells. Folate supports DNA repair mechanisms relevant to chemical carcinogen exposure. Dietary fibre from vegetables and wholegrains supports beneficial gut bacteria that metabolise herbicide residues before they reach systemic circulation.