Drinking water guidelines—pesticides

The current (2011) Australian Drinking Water Guidelines (ADWG) were prepared by the National Health and Medical Research Council (NHMRC) and National Resource Management Ministerial Council (NRMMC). They contain:

  • information about a wide range of chemical and microbiological contaminants that could potentially find their way into drinking water
  • information about management of drinking water systems
  • water monitoring.

The ADWGs provide the authoritative Australian reference for use within Australia’s administrative and legislative framework to ensure the accountability of drinking water suppliers (as managers) and of state and territory health authorities (as auditors of the safety of water supplies). However, these guidelines are not mandatory nor legally enforceable.

The 2011 ADWGs contain ‘health-based guideline’ values for over 200 pesticides. These and the guideline values in previous versions of the ADWGs were set by the NHMRC and the NRMMC. The establishment of drinking water guidelines is not the APVMA’s responsibility and they are not our standards.

1. The APVMA’s role

We are responsible for assessing all agricultural chemical products, which include classes of products such as insecticides, herbicides, fungicides, nematicides, rodenticides, and miticides, intended for sale and use in Australia. Prior to an approval of an active constituent used in an agricultural chemical product, a large amount of data related to public health, workplace health and safety, and environmental safety is assessed. The toxicology data relating to public and workplace health and safety are evaluated by the Office of Chemical Safety (OCS) within the Australian Government Department of Health, on our behalf. The OCS then provides advice to us about the degree of hazard of the active constituent under consideration, and the acceptability of proposed uses for products containing the active constituent (with respect to public health and workplace safety). The OCS also makes recommendations for first-aid and safety directions to go on product labels.

2. Health-based guideline values for pesticides

Using data supplied by the APVMA as well as other publicly-available data, the OCS, under contract to the NHMRC and the NRMMC, established the health-based guideline values for the pesticides listed in the 2011 ADWG, and drafted the accompanying pesticide factsheets.

The definition of a health-based guideline value is:

the concentration or measure of a water quality characteristic that, based on present knowledge, does not result in any significant risk to the health of the consumer over a lifetime of consumption.

The health-based guideline values for pesticides are derived from the acceptable daily intake (ADI) for each pesticide and are generally set at 10 per cent of this value; they assume an adult body weight of 70 kilograms and a daily water consumption of two litres. The accompanying text in the ADWG states that ‘the health values are very conservative, and include a range of safety factors, which always err on the side of safety’.

Pesticides should not be found in water supplies above safe levels (as indicated by these health-based guideline levels) and if they are, investigations must be undertaken to determine how they came to be there. These investigations should then be followed by corrective action aimed at preventing the contamination of drinking water supplies by pesticides.

In earlier versions of the ADWG (for example, the 2004 version), two guideline values were set for each of the limited number of pesticides included in the ADWG. Pesticides that were not approved for use in water or water catchment areas were given a so-called ‘guideline value’ (or ‘action level’) set at or about the practical analytical detection limit for the particular chemical. If a pesticide was detected at or above the guideline value, it was recommended that relevant control authorities should determine the source and stop further contamination. While exceeding the guideline value did not mean that there was any risk to public health, it indicated that an undesirable contamination of drinking water had occurred.

A second guideline called the ‘health value’ was also established. As with the current health-based guideline value, for most pesticides the health value was set at about 10 per cent of the ADI, and assumed an adult weight of 70 kilograms and a daily water consumption of two litres. Both these ADI-derived values are used by health authorities in managing and communicating the health risks associated with inadvertent pesticide exposure, due to a spill or misuse.

The 2011 ADWG has replaced the guideline value and the health value with a single health-based guideline value. This revised approach has been adopted for two reasons:

  • analytical detection limits are constantly decreasing as a result of ongoing technological advancements—this means that a guideline based on a detection limit would also need to be continuously revised downward, which is impractical
  • the desirability of a scientifically and methodologically consistent approach to setting guidelines across all chemicals.

This change in guideline setting for pesticides has no impact on the general philosophy regarding the management of pesticides in 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.

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