Toxic substances list: Dibenzo-para-dioxin

Dibenzo-para-dioxins have a chemical structure consisting of two benzene rings attached to a six carbon ring with the first and fourth carbon replaced by an oxygen atom. It is typically referred to as a family of organic compounds that have the ability to substitute one of their hydrogen atoms with another atom such as chlorine. This particular ability of dibenzofurans and dibenzo-para-dioxins can allow them to be precursors to Polychlorinated Dibenzofurans and Polychlorinated Dibenzodioxins. The Ministers of the Environment and of Health Canada have concluded that polychlorinated dibenzodioxins and polychlorinated dibenzofurans may enter the environment in quantities which have immediate and long-term harmful effects on the environment, and which constitute a danger in Canada to human health. These substances are therefore considered "toxic" as defined under Sections 11(a) and 11(c) of the Canadian Environmental Protection Act, 1988.

Pulp and paper mills use defoamer additives to manage properties of process water. Defoamer additives can be manufactured from oils which could contain dibenzofurans and dibenzo-para-dioxins. When used in a pulp and paper mills having a chlorine bleaching process, the dibenzofurans and dibenzo-para-dioxins contained in a defoamer can react with chlorine to form the polychlorinated dioxins and furans which were assessed as toxic under the Priority Substances List 1. The Pulp and Paper Mill Defoamer and Wood Chips Regulations require that these defoamers, containing dibenzofurans and dibenzo-para-dioxins, used by pulp and paper mills utilizing a chlorine bleaching process be limited to a maximum concentration of 10 ppb (parts per billion) of Dibenzo-para-dioxins and 40 ppb of Dibenzofurans.

CAS (Chemical Abstract Service) registry number: 262-12-4

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