According to my personal knowledge (talking wit colleagues who participated), Japan and China is doing cleanup works together in china (post world war 2 abandoned weapons). However, they do not open much of the research works and findings to the public due to sensitivity of the findings.
Similarly, US is doing cleanup works in Vietnam. (US Congressional Research Service (CRS)).
https://www.hsdl.org/?abstract&did=818860
Moreover, there is a US unit in Afghanistan for Environmental protection (the unit is attached to US military). I think there are similar units in other US-war involved countries. (so basically the unit is operated under US Defense (probably their website should have more details.