The Trail Smelter arbitration occupies a strange place in international environmental law. It forms part of the canon of the discipline – indeed, it is generally regarded as a foundational case – and reference to it is ubiquitous. Yet there is little agreement on how its holding should be interpreted and applied, and its persuasive value is often called into question. Trail Smelter cannot be reconciled with international rules of state responsibility, and the principle for which it appears to stand, namely, that states can be liable for transboundary environmental damage in the absence of a breach of an international obligation, holds very dubious status in international law. International environmental disputes are very rarely litigated; instead, states have invested their efforts in the creation of often very elaborate legal and policy regimes, many of which contain their own internal mechanisms for implementation, compliance, and enforcement. These considerations tend to lead one to the conclusion that international environmental law has moved beyond the Trail Smelter arbitration.
Regardless of these difficulties, the influence of the case on subsequent developments in international environmental law is not far to seek. Principle 21 of the Stockholm Declaration, which has itself taken on almost mythical proportions, is generally regarded as a reflection or restatement of the Trail Smelter holding, and the case has been relied on heavily in the work of the International Law Commission (ILC) concerning liability for harm caused by acts not prohibited by international law.