Norflurazon
(endorsed 2011)
Guideline
Based on human health concerns, norflurazon in drinking water should not exceed 0.05 mg/L.
Related chemicals
Norflurazon (CAS 27314-13-2) belongs to the pyridazinone class of chemicals. Another pesticide in this class is maleic hydrazide (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, norflurazon would not be a health concern unless the concentration exceeded 0.05 mg/L. Excursions above this level over a short to medium term are of concern as the health-based guideline is based on effects observed in a 3-month study.
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: Norflurazon is a pre-emergent herbicide for the control of annual grasses, broad-leaf and perennial weeds in agricultural crops.
There is at least one registered product containing norflurazon in Australia. Norflurazon products are intended for professional use and are available as a concentrated solution that is diluted and applied by aerial and ground spray to soil. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to norflurazon and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of norflurazon may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Reported values in Australian waters
No data were found on the occurrence of norflurazon in Australian waters. Norflurazon has been detected in several wells in Florida, USA, at levels approaching or in some cases exceeding 0.03 mg/L (the US Health Advisory Level) (USEPA 1996).
Treatment of drinking water
No specific data on the treatment of norflurazon in drinking water have been identified.
Measurement
Norflurazon can be analysed by gas chromatography with a nitrogen–phosphorous specific detector (USEPA Method 645).
History of the health values
The current acceptable daily intake (ADI) for norflurazon is 0.02 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1.5 mg/kg bw/day from a medium-term dietary study in dogs. The NOEL is based on increased liver weights. The ADI incorporates a safety factor of 100 and was first established in 1984.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Norflurazon is readily and extensively absorbed via the gastrointestinal tract in rats. It is extensively metabolised, and is rapidly excreted in urine and faeces, with excretion being complete by 4 days.
Acute effects: Norflurazon has low acute oral and dermal toxicity. It is not a skin sensitiser in guinea pigs.
Short-term effects: In short-term (21-day) dietary studies in rats, there was increased testis and kidney weight without accompanying histopathological changes at 100 mg/kg bw/day and above.
In medium-term dietary studies in rats, increased kidney weight without accompanying changes in histopathology was reported at a dose level of 127 mg/kg bw/day. In medium-term dietary studies in dogs, increased liver weight was reported at 10 mg/kg bw/day, with a NOEL of 1.5 mg/kg bw/day. This NOEL is the basis for the current ADI.
Long-term effects: Long-term dietary studies in mice and rats reported decreased bodyweight and food consumption and significant changes in relative organ weights. The overall NOEL was 18 mg/kg bw/day in rats.
Carcinogenicity: Based on long-term studies in mice and rats, there is no evidence of carcinogenicity for norflurazon.
Genotoxicity: Norflurazon is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 3-generation reproduction study in rats and a developmental toxicity study in rabbits did not produce any evidence of effects on reproductive parameters or foetal development.
Poisons Schedule: Norflurazon is considered not to require control by scheduling due to its low toxicity and is therefore included 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 0.05 mg/L for chemical was determined as follows:
where:
1.5 mg/kg bw/day is the NOEL based on a medium-term (3-month) dietary study in rats.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the 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.
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.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (1996). RED Factsheet – Norflurazon. EPA-738-F-96-012 July 1996. Office of Prevention, Pesticides and Toxic Substances, USEPA.
USEPA Method 645. The determination of certain amine pesticides and lethane in municipal and industrial wastewater. United States Environmental Protection Agency.
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