Friday, the first traces of the plume of radioactive gas from the damaged Japanese reactors were reported to reach California. The cornerstone of international environmental law is often said to be the “prevention principle,” which says that states have “the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States.” Does that mean that the transboundary radiation has put Japan in violation of international law?
In a word, No.
Although the quoted language, from the 1992 Rio Declaration, sounds as if any transboundary damage would violate international law, almost no one interprets the prevention principle so strictly. To be an obligation under customary international law, the principle would have to reflect states’ customary practice, and states don’t prevent all transboundary pollution. Last year, in a case between Argentina and Uruguay, the International Court of Justice characterized the principle this way: “A State is . . . obliged to use all the means at its disposal in order to avoid activities which take place in its territory, or in any area under its jurisdiction, causing significant damage to the environment of another State.”
So the ICJ believes that a state is only required to prevent “significant” transboundary harm. That seems more likely to reflect state practice, although you might question whether states comply even with this lower standard, given the amount of transboundary pollution that still occurs. If the ICJ is right, Japan hasn’t failed to comply with the principle, since the radiation that has crossed the Atlantic is at low levels not expected to cause any significant harm. Even at higher levels, the transboundary radiation wouldn’t violate international law as long as Japan has done all it can to prevent it from occurring – a condition that the regulatory failures described in Rebecca’s post below may call into question. (Whether or not Japan has complied with the prevention principle, international law may impose liability for transboundary harm, but that’s an issue for another post.)
The obligation to prevent harm isn’t the only relevant international obligation, though. It’s also generally thought that states facing environmental emergencies with potential transboundary effects have an obligation to notify their neighbors and keep them informed. In this latter respect, Japan may be more open to criticism, for issuing general statements that do not provide other countries much detail about the problem. On Thursday, China urged Japan to be more forthcoming, a message that will likely grow louder as fears of radiation increase among the people of China and other nearby countries.