To add to that, Chernobyl disaster and the subsequent coverup attempt clearly showed that Glasnost lacked actual substance. It was the one of the main reasons behind lifting the censorship regime (since the 1987 the press was essentially free to write about anything, and did so), and a major contributor to allowing competing factions inside the party. Nemtsov in particular became a prominent figure after his Chernobyl-related activism.

However, claiming that environmentalists took down the whole Union is downright silly. Yes, the fears of the crumbling infra and coverups, Chernobyl nuclear disaster, Spitak earthquake, and Ufa train disaster dominated the media of the late USSR (and especially Armenia, due to the Spitak earthquake), but that was only a small factor, the reasons were much more fundamental.