Any significant adverse effect on the environment resulting from human activity, the physical origin of which is situated wholly or in part within an area under the jurisdiction of another State. (Source: draft based on UNECE definition of transboundary effect/MMA)

Environmental impacts and threats that do not respect national borders (such as use of transboundary waters, long-range air-pollution, industrial accidents), impacts that requests consultation between (presumably) effected countries (Draft based on UNECE re. transboundary context of conventions)