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The health concerns associated with naphthalophos have not been fully evaluated and therefore a health value for naphthalophos in drinking water cannot be set.
Naphthalophos belongs to the organophosphate class of chemicals. There are many other pesticides in this class, which includes acephate, chlorfenvinphos, diazinon and profenofos.
HUMAN RISK STATEMENT
There are currently insufficient data on which to base a human 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.
Uses: Naphthalophos is a parasiticide for the control of organophosphate-susceptible gastrointestinal roundworms in sheep and lambs.
There are 11 registered products that contain naphthalophos. Products containing naphthalophos are intended for professional use and are administered orally to sheep and lambs using drench guns. Products are typically diluted in water in original packaging before being transferred into the backpack reservoir of a drenching gun.
Exposure sources: The main source of public exposure to naphthalophos and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
The veterinary use of naphthalophos provides some potential for contamination of drinking water through the washing of equipment near dams, streams or watercourses.
TYPICAL VALUES IN AUSTRALIAN DRINKING WATER
No data on occurrence of naphthalophos in water could be found.
TREATMENT OF DRINKING WATER
No information on efficiency of drinking water treatment to remove naphthalophos could be found.
No method to measure naphthalophos in water could be found.
HISTORY OF THE HEALTH VALUES
The current acceptable daily intake (ADI) for naphthalophos is 0.0001 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.25 mg/kg bw/day. The ADI incorporates a safety factor of 2500 and was established in 1971. The toxicological endpoint used to establish this ADI is unknown. The reason for such a large safety factor is also unknown, although it is likely to be due to the limited toxicological database for naphthalophos.
An Australian Drinking Water Guidelines health value has not been previously established.
Metabolism: There are no metabolic or kinetic studies available for naphthalophos.
Acute effects: Naphthalophos has moderate acute oral toxicity in rats and mice and moderate dermal toxicity in rats. No other acute toxicity data are available for naphthalophos.
A quantitative evaluation of the dermal absorption of naphthalophos is not available. However the moderate acute dermal toxicity in rats suggests that it is well absorbed dermally.
Short-term and long-term effects, carcinogenicity, genotoxicity, reproductive and developmental effects: No repeat-dose studies, or developmental or reproductive studies have been evaluated in Australia. Therefore the potential toxicity from exposure to naphthalophos cannot be adequately determined. There are no short-term studies available for naphthalophos. However, as an organophosphate compound, there is potential for cumulative anti-cholinesterase toxicity through repeated minor exposure.
Naphthalophos is in Schedule 6 or 7 of the Standard for the Uniform Scheduling of Drugs and Poisons depending on its concentration (SUSDP 2008).
DERIVATION OF THE HEALTH-BASED GUIDELINE
Due to its current status as a chemical under review in Australia, a health-based guideline value for naphthalophos in drinking water is not recommended at this stage.
Office of Chemical Safety (2003). Toxicology report on naphthalophos (2003/05143, 2003/0142).
Office of Chemical Safety (2007). Toxicology report on naphthalaphos (2007/024914).
SUSDP (Standard for the Uniform Scheduling of Drugs and Poisons) (2008). National Drugs and Poisons Scheduling Committee (NDPSC), Australian Government.