The zero discharge concept sparked intense debate about what zero means and whether to stringently manage substances or stop using them regardless of the adequacy of controls. While this debate was never resolved, other concepts have emerged that provide meaningful assistance to managing chemicals responsibly.

The United Nations Conference on Environment and Development (UNCED) agreed on a broad range of tools for toxic chemicals management. Phasing out or banning chemicals was seen as the option for chemicals posing "unreasonable and otherwise unmanageable risks." This confirmed the science-based approach of risk assessment and risk management in the responsible use of chemicals, and defined a standard for when bans or phase-outs are appropriate -- something the zero discharge concept never achieved. UNCED also reaffirmed the focus on persistent and toxic chemicals, but added a third criterion: bioaccumulation.

Meanwhile, the Canadian Accelerated Reduction and Elimination of Toxics (ARET), a multi-stakeholder consensus process, identified 117 priority substances using toxicity, persistence and bioaccumulation criteria. It targeted emission reductions of 90 percent for substances meeting all three criteria and 50 percent for other substances on the list by the year 2000. The first ARET report, expected soon, should show significant achievement by industry. While ARET has moved significantly beyond zero discharge in establishing benchmarks and motivating strong industry responses for environmental improvement, it owes a debt to the related idea that we should prioritize attention on persistent toxic chemicals.

Zero discharge is a remarkably succinct and rich statement of the ecological conscience of the Great Lakes region. It focuses on avoiding the generation, use or production of toxic substances, not controlling them after the fact and at the end of the pipe. It means, as the International Joint Commission has wisely recognized, that the use of precursor chemicals like chlorine should be "sunsetted" when and where feasible. It includes as a corollary the concept of "reverse onus" -- those who would profit from dumping their wastes into public air or water resources bear the burden of demonstrating a lack of harm.

As is true of all ethical principles, zero discharge sets a high standard. Our failure to achieve it quickly or easily should not diminish our resolve. Compare, in this regard, zero discharge to equal justice under law, another core ethical principle in both the United States and Canada. In both nations, few would claim the job is done or the principle achieved. But nor would many give up just because the work is harder and the road longer than anticipated.