Trifluralin
(endorsed 2011)
Guideline
Based on human health concerns, trifluralin in drinking water should not exceed 0.09 mg/L.
Related chemicals
Trifluralin (trifluraline)(CAS 1582-09-8) belongs to the dinitroaniline class of chemicals. Other pesticides in this class include oryzalin and pendimethalin (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, trifluralin would not be a health concern unless the concentration exceeded 0.09 mg/L. Minor excursions above this level would need to occur over a significant period to be a health concern, as the health-based guideline is based on long-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Trifluralin is a pre-emergent herbicide for the control of ryegrass, wireweed, and yellow burr weeds in cereal, legume, herb, and vegetable crops, and for the control of garden weeds in domestic settings.
There are registered products containing trifluralin in Australia. The products are intended for professional and home garden use. Use patterns include application to soil by ground boom spray in agricultural settings and by hand-held spray for home gardens. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to trifluralin and its metabolites are the use of home garden weedkiller products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of trifluralin may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
Trifluralin has low solubility in water and generally is not detected in surface water. It is unlikely to leach into groundwater supplies, given its low solubility and strong soil adsorption (Health Canada 1989). Trifluralin has been detected very occasionally in drinking water supplies in Australia at concentrations well below the health-based guideline value. It was reported above 1 µg/L in 0.2% of the samples taken in the Murray-Darling Basin (NSW 1998/99 data) (NSW Department of Primary Industries 2005).
In the USA, trifluralin was found in 172 of 2047 surface water samples and in 1 of 507 groundwater samples analysed, but was not found in 229 drinking-water supplies analysed in Italy (WHO 1996). It was detected at low concentrations (ng/L) in raw drinking water samples and in 1 of 91 groundwater samples (41 µg/L) in Canada (Health Canada 1989).
Treatment of drinking water
Trifluralin is efficiently removed (100% effectiveness) by conventional treatment using alum, sedimentation and filtration. In addition, it may be removed from drinking water by reverse osmosis, granular activated carbon and air stripping (Health Canada 1989, Ormad et al. 2008).
Measurement
Trifluralin can be analysed in water by solvent extraction or by solid phase extraction. Quantification is performed by gas chromatography with electron capture detection (GC-ECD); gas chromatography with mass spectrometry (GC-MS) or liquid chromatography (LC) with ultraviolet detection. The limit of detection (LOD) is 0.01µg/L (Van Hoof et al. 2001, Carabias-Martinez et al. 2003). Direct injection liquid chromatography–mass spectrometry or online solid phase microextraction liquid chromatography with mass spectrometry can achieve a lower LOD. The GC-ECD-GCMS United States Environmental Protection Agency method 3510/8080 can achieve a LOD of 0.1 µg/L (Queensland Government 2007).
History of the health values
The current acceptable daily intake (ADI) for trifluralin is 0.02 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 2.5 mg/kg bw/day from a 2-generation study in rats. The NOEL is based on decreased foetal and parental weights. The ADI incorporates a safety factor of 100, and was established in 1991.
The previous health value was 0.05 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Trifluralin is poorly absorbed via the gastrointestinal tract and the majority is excreted unchanged in the faeces. Absorbed trifluralin is eliminated as metabolites in urine within three days. The primary metabolites are dealkylated and hydrogenated compounds.
Acute effects: Trifluralin has low acute oral and dermal toxicity. It has some potential for skin sensitisation.
Short-term effects: In a 3-month dietary study in rats born from mothers pre-treated with oral doses of trifluralin, bodyweights were decreased and relative liver weights were increased at 100 mg/kg bw/day. In a 4-month dietary study in rats, effects on the kidney were seen at the lowest dose, 20 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies in rats reported liver weight changes and tissue irritation in the kidney at 33.5 mg/kg bw/day.
Carcinogenicity: Kidney tumours were noted in rats at high dose levels as a result of persistent tissue irritation. This effect was not considered relevant to humans at the normal low levels of exposure.
Genotoxicity: Trifluralin is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: In three reproduction studies in rats (2-3 generations), there was reduced fertility and reduced neonatal viability at dose levels above 2.5 mg/kg bw/day. In developmental studies in rats and rabbits, there was no evidence of effects on foetal development. The NOEL of 2.5 mg/kg bw/day is the basis for the ADI.
Poisons Schedule: Trifluralin is considered not to require control by scheduling due to its low toxicity and is therefore in Appendix B of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010). Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.09 mg/L for trifluralin was determined as follows:
where:
2.5 mg/kg bw/day is the NOEL based on a 2-generation reproduction study in rats.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the conservative assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
100 is the safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
The World Health Organization has a Guideline value of 0.02 mg/L for trifluralin (WHO 2004).
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety.
Carabias-Martinez R, Garcia-Hermida C, Rodriguez-Gonzalo E, Soriano-Bravo FE, Hernandez-Mendez J (2003). Determination of herbicides, including thermally labile phenylureas, by solid-phase microextraction and gas chromatography-mass spectrometry. Journal of Chromatography A, 1002(1-2):1-12.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
Health Canada (1989) Guidelines for Canadian Drinking Water Quality – Technical Documents: Trifluralin. Available at https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-trifluralin.html
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
NSW Department of Primary Industries (2005). Impacts of urban and rural development. Available at https://www.dpi.nsw.gov.au/fishing/habitat/threats/urban
Ormad MP, Miguel N, Claver A, Matesanz JM, Ovelleiro JL (2008). Pesticides removal in the process of drinking water production. Chemosphere, 71(1): 97-106.
Queensland Government (2007). Water Monitoring Data Collection Standards, WMO010, Natural Resources and Water.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
Van Hoof F, Van Wiele P, Bruchet A, Schmitz I, Bobeldiji I, Sacher F, Ventura F, Marti I, Morecos Do Monte MH, Sa Da Costa M (2001). Multiresidue determination of pesticides in drinking and related waters by gas chromatography/mass spectrometry after solid-phase extraction: interlaboratory study. Journal of AOAC International, 84(5):1420-9.
WHO (World Health Organization) (1996). Trifluralin in Drinking-water. WHO, Geneva, Switzerland.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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