2. General considerations.(EVALUATION OF CERTAIN FOOD CONTAMINANTS)(Conference notes)

The tasks before the Committee were:

--to elaborate further principles for evaluating the safety of food contaminants (section 2); and

--to undertake toxicological evaluations of certain food contaminants (section 3, and Annex 2).

2.1 The formulation of advice on compounds that are both genotoxic and carcinogenic

The Committee has established procedures for determining health-based guidance values, such as the acceptable daily intake (ADI) or provisional tolerable weekly intake (PTWI), for chemicals that produce adverse effects that are thought to show a threshold in their dose--response relationships. Compounds that are both genotoxic and carcinogenic may show non-linear dose--response relationships, but the no-observed-effect level (NOEL) in a study of carcinogenicity represents the limit of detection in that bioassay, rather than an estimate of a possible threshold. Therefore the Committee does not establish health-based guidance values for compounds that are genotoxic and carcinogenic using the NOEL and safety (uncertainty) factors. In the absence of evidence on the influence of non-linearity on the incidence of cancer at low levels of exposure, the advice given previously by the Committee for compounds that are both genotoxic and carcinogenic has been that intakes should be reduced to as low as reasonably achievable (ALARA). Such advice is of limited value, because it does not take into account either human exposure or carcinogenic potency, and has not allowed risk managers to prioritize different contaminants or to target risk management actions. In addition, ever-increasing analytical sensitivity means that the number of chemicals with both genotoxic and carcinogenic potential detected in food will increase.

The Committee at its present meeting considered a number of compounds for which genotoxicity and carcinogenicity are important issues. The Committee was aware of a number of recent developments relevant to the risk assessment of such compounds, including:

--a WHO workshop that developed a strategy for dose--response assessment and the formulation of advice (1);

--discussions within the European Food Safety Authority about a margin of exposure (MOE) that would indicate the level of priority for risk management action (2); and

--Australian recommendations for genotoxic and carcinogenic soil contaminants regarding a guideline dose that would be protective of human health based on a modified benchmark dose and the application of uncertainty factors to allow for …