Oryzalin
(endorsed 2011)
Guideline
Based on human health concerns, oryzalin in drinking water should not exceed 0.4 mg/L.
Related chemicals
Oryzalin (CAS 19044-88-3) belongs to the dinitroaniline class of chemicals. Other pesticides in this class include butralin and pendimethalin (Tomlin 2006).
Human risk statement
There are currently insufficient data on which to base a human health risk statement.
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: Oryzalin is a herbicide used for the pre-emergent control of certain annual grasses and broad-leaf weeds in non-bearing and bearing fruit and nut orchards, vineyards, nursery stock, ornamentals and amenity plantings. In addition, it is used for the pre-emergent control of annual ryegrass, phalaris, wireweed (hogweed) and deadnettle in wheat, barley and canola.
There are registered products containing oryzalin in Australia. The products are intended for professional use and are available as a granular formulation, suspension concentrates or emulsifiable concentrates. The concentrates are diluted and applied by ground boom, hand spray or overhead irrigation, and the granules spread by hand or mechanical spreader. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to oryzalin is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of oryzalin 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
No occurrence data for oryzalin in Australian waters could be found. In the USA, the highest predicted concentration of oryzalin in surface and groundwater was 90 and 0.9 µg/L, respectively (USEPA 2004). The highest measured concentration in surface and groundwater was 1.9 and 0.018 µg/L, respectively, while concentrations of oryzalin in US drinking water samples ranged from 0.01 to 0.07 µg/L (USEPA 2004).
Treatment of drinking water
No data on drinking water treatment removal efficiency were found for oryzalin.
Measurement
Oryzalin in water can be measured by high performance liquid chromatography, with a method detection limit of 0.14 µg/L (USGS 2006).
History of the health values
The current acceptable daily intake (ADI) for oryzalin is 0.1 mg per kg body weight (mg/kg bw), based on a no-observed-effect level (NOEL) of 12 mg/kg bw/day established in 1982. It is assumed this incorporates a safety factor of 100. The basis of this ADI cannot be traced with current records, although, according to available United States reports, it is probably based on a NOEL of 12 mg/kg bw/day from a long-term rat study.
The previous health value was 0.3 mg/L (NHMRC and NRMMC 2004).
Health considerations
No evaluation report on the toxicity of oryzalin is currently available from the Office of Chemical Safety and Environmental Health (OCSEH).
Metabolism: No studies have been evaluated in Australia.
Short-term/long-term effects: No studies have been evaluated in Australia.
Carcinogenicity: No studies have been evaluated in Australia. Oryzalin has not been evaluated by International Agency for Research in Cancer.
Genotoxicity: No studies have been evaluated in Australia.
Reproductive and developmental effects: No studies have been evaluated in Australia.
Poisons Schedule: Oryzalin is not scheduled in 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 0.4 mg/L for oryzalin was determined as follows:
where:
12 mg/kg bw/day is the NOEL on which the existing ADI was based; however further details are unknown.
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 assumed to be the safety factor applied to the ADI, which is a safety factor typically applied to a NOEL derived from animal studies. The safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation. This is consistent with US reports.
References
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.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (2004). Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Oryzalin. EPA 738-R-04-009. USEPA.
USGS (United States Geological Survey) (2006). Pesticides in the Nation’s Streams and Ground Water, 1992–2001. National Water Quality Assessment Program, USGS.
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