In the Trail Smelter case, the international principle that was established in the tribunal ruling was Trans-Boundary Harm.
The Trail Smelter case refers to a transboundary pollution case which involved the federal governments of both Canada and the United States. In the case United States sued Canada for damages and demanded an injunction for air pollution in the state of Washington, by the Trail Smelter, a Canadian corporation. Consequently, the case contributed to the establishment of the harm principle in the environmental law of transboundary pollution. Trans-boundary harm principle stated the requirement that states should preclude activities on their territory which causes significant harm or damage to the environment of another state or areas beyond national control.
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