Carcinogen risk assessment. Can we harmonise?

Harmonisation of risk assessment (RA) is one of the priorities for sound chemical management set by Chapter 19, Agenda 21 of the United Nations Conference on the Environment and Development (UNCED) 1992 Earth Summit. The benefits of harmonisation are self evident and include transportability and consistency of RA outcomes, transparency and efficiency of process, and credible science. The outcomes of carcinogen RA are a description or classification of the carcinogenic hazard, the conditions under which cancers may be induced, and an estimate of a dose or exposure which poses a minimal, or otherwise defined, risk in exposed human populations. Weight-of-evidence based systems which classify carcinogenic hazards are part of, but do not substitute for, the risk assessment process. Carcinogen RA is based on assessment of appropriate toxicological and exposure data sets, which may have much in common. However, national policy frameworks can differ to the extent that RA outcomes may be quite different for the same chemical(s). Historically, differences in science policy have been greater for cancer RA compared to other toxic endpoints, with a tendency to differentiate cancer RA on the basis of presumed mechanism (i.e. genotoxic or non-genotoxic) and relevance to humans (some carcinogenic responses in animals may be considered not relevant for human RA). Significant strides towards harmonisation are being made, with reassessment of some national policies and participation in international harmonisation programmes, such as the ones being managed by the International Programme for Chemical Safety (IPCS). Alternative approaches to quantitative carcinogen RA are being considered which are more amenable to harmonisation, and one such approach being developed in Australia in connection with contaminated sites will be discussed.