Carfentrazone-ethyl
(endorsed 2011)
Guideline
Based on human health concerns, carfentrazone-ethyl in drinking water should not exceed 0.1 mg/L.
Related chemicals
Carfentrazone-ethyl (CAS 128639-02-1) belongs to the triazolinone class of chemicals. Another pesticide in this class is amicarbazone (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, carfentrazone-ethyl would not be a health concern unless the concentration exceeded 0.1 mg/L. 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: Carfentrazone-ethyl is a herbicide used alone, or in combination with other herbicides, for the control of certain broad-leaf weeds prior to establishment of a variety of crops including winter cereals, pyrethrum, fruit trees, nuts, cotton and grapevines. It is also used to control weeds in commercial and industrial settings, in public areas, and around agricultural buildings and yards. In addition, carfentrazone-ethyl is used to control aquatic weeds in rice and for desuckering grapevines.
There are registered products that contain carfentrazone-ethyl in Australia. These products are dry flowables, emulsifiable concentrates or micro-encapsulated formulations, and are intended for professional use. They are most commonly applied by broadcast methods (boom spray). Back-pack hand spray is also used, with aerial application recommended for some products for cotton desiccation only. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to carfentrazone-ethyl is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of carfentrazone-ethyl may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater. In addition, carfentrazone-ethyl can also be applied directly into water bays of rice crops.
Typical values in Australian drinking water
No reports of carfentrazone-ethyl in Australian drinking waters have been identified.
Treatment of drinking water
No reports of the treatment of carfentrazone-ethyl in drinking water have been identified. However, it has been reported that carfentrazone-ethyl is rapidly converted to carfentrazone-chloropropionic acid and then gradually degraded under aerobic aquatic conditions (Elmarakby et al. 2001).
Measurement
Solid-phase extraction (SPE) and gas chromatography with electron-capture detection has been used for sensitive, simple, and reliable analysis of carfentrazone-ethyl residues in water. Recent research has demonstrated that the use of multiwalled carbon nanotubes as a SPE adsorbent for analysis of carfentrazone-ethyl can achieve a limit of quantitation of 0.03 mg/L (Dong et al. 2009).
History of the health values
The current acceptable daily intake (ADI) for carfentrazone-ethyl is 0.03 mg per kg body weight (mg/kg bw), based on a no-observed-effect level (NOEL) of 3 mg/kg bw/day from a long-term (2-year) study in rats. The NOEL is based on red fluorescence seen in the female liver at the next highest dose of 12 mg/kg bw/day. The ADI incorporates a safety factor of 100 and was established in 1998.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Carfentrazone-ethyl is readily absorbed via the gastrointestinal tract in mice and rats. It is extensively metabolised, the main metabolites being carfentrazone-ethyl-chloropropionic acid and 3-hydroxymethyl-carfentrazone-ethyl-chloropropionic acid. Most of the administered dose is excreted as metabolites in the urine within 24 hours.
Acute effects: Carfentrazone-ethyl has low acute oral and dermal toxicity. It is not a skin sensitiser in guinea pigs.
Short-term effects: Repeat-dose studies indicate that the primary targets for carfentrazone-ethyl toxicity are the red blood cells (RBC) and the liver. In 28-day and 90-day dietary studies in mice, rats and dogs, effects were noted on blood parameters at very high dose levels only (in excess of 500 mg/kg bw/day).
Long-term effects: An 80-week dietary study in mice reported some reduction in RBCs at the lowest dose tested (10 mg/kg bw/day), and more significant effects (reduced packed cell volume and haemoglobin, increased mean corpuscular volume at 100 mg/kg bw/day. In long-term dietary studies in rats, there was a slight increase in urinary porphyrins, together with red fluorescence in the liver, correlating to porphyrin deposits, at 12 mg/kg bw/day. The lowest NOEL was 3 mg/kg bw/day in the rat study and this is the basis for the current ADI. A 52-week oral study in dogs showed an increased level of urinary porphyrins from 150 mg/kg bw/day.
Carcinogenicity: Based on long-term exposure studies in mice, rats and dogs, there is no evidence of carcinogenicity for carfentrazone-ethyl.
Genotoxicity: Carfentrazone-ethyl 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 developmental studies in rats and rabbits did not produce any evidence of effects on reproductive performance or on foetal development at below maternotoxic dose levels.
Poisons Schedule: Carfentrazone-ethyl 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 0.1 mg/L for carfentrazone-ethyl was determined as follows:
where:
3 mg/kg bw/day is the NOEL based on a long-term (2-year) 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.
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.
Dong MF, Ma YQ, Liu FM, Qian CF, Han LJ, Jiang SR (2009). Use of multiwalled carbon nanotubes as a SPE adsorbent for analysis of carfentrazone-ethyl in water. Chromatographia, 69(1-2):73-77.
Elmarakby SA, Supplee D, Cook R (2001). Degradation of [C-14]carfentrazone-ethyl under aerobic aquatic conditions. Journal of Agricultural and Food Chemistry, 49(11):5285-5293.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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