This review will address:
• The basis for establishing an Acceptable Daily Intake (ADI), which usually drives the derivation of guideline values
• Assumptions about body weight, water intake and the exposure proportion attributable to drinking water used in the derivation of guideline values
• Differences in the risk assessment approach for chemicals whose toxicity exhibits threshold and non-threshold characteristics
• Reasons why guidelines set under different regulatory regimes may differ numerically, and the basis for the hierarchy recommended in Australian risk assessment guidance documents
• An approach to managing chemicals for which the available toxicity data are absent or too incomplete to allow derivation of health-based guideline levels using conventional methodology
Risk assessment methodology used in setting standards
Three key references describe the basic risk assessment methodology which is used to establish chemical drinking water guideline values.
1. Australian Drinking Water Guidelines (2004)
2. enHealth Council Guidelines for Assessing Human Health Risks from Environmental Hazards (2004)
3. Research Report 11: A Guide to Hazard Identification & Risk Assessment for Drinking Water Supplies (2004) CRC for Water Quality & Treatment Chapter 6 of the Australian Drinking Water Guidelines (ADWG) outlines the general approach to setting drinking water guidelines for inorganic chemicals, organic chemicals and pesticides, while
Part 5 includes Fact Sheets for individual chemicals, which include general descriptive information, typical levels found in Australian drinking water, and values for recommended guideline levels and the basis for their derivation. The guideline values are intended to represent a concentration which would not be a health concern unless exceeded over a prolonged period of time.
They are based on estimates of likely health risks associated with a lifetime of exposure, and incorporate conservative safety factors and assumptions. Therefore, they should not be considered to represent a black-andwhite dividing line between safe and unsafe consumption.