The United States Environmental Protection Agency, USEPA, has, since 1991, been engaged in a comprehensive reassessment of dioxin science, which it hopes to complete this year. Last June, the USEPA published two chapters of its proposed report for the purpose of scientific peer review. In so doing, it cautioned that the material concerned should not be cited as the agency's final assessment of dioxin risks, and stated that the question of using the outcome of the reassessment for regulatory purposes does not arise until the review procedure is completed.
The USEPA now characterises the most toxic dioxin compound as a human carcinogen, and proposes to re-evaluate upwards its own 1994 assessment of cancer risk attributable to dioxins. However, the International Agency for Research on Cancer, an agency of the World Health Organisation, has since 1997 classed the relevant dioxin compound as a known human carcinogen. WHO guidelines for tolerable daily intake of and recommendations for dioxins, from 1998, take this classification into account. The USEPA considers that its draft findings are supportive of the WHO position.
Clearly, because of the potential toxic effects of exposure to dioxins, their emission must, where possible, be strictly controlled and minimised, to ensure exposure does not exceed relevant guidelines and standards. In licensing incineration facilities in Ireland, the Environmental Protection Agency already applies a flue gas emission limit value for dioxins of 0.1 nanograms, that is, one ten thousand millionth of a gram, per cubic metre of gas emitted. This extremely stringent standard will shortly be adopted by the EU generally, under the proposed Council directive on the incineration of waste. By comparison, dioxin emission standards issued by the USEPA last year, which will only apply to US hazardous waste incinerators from 2002, are between two and four times higher.
