The funny thing is I never really questioned this idea, mostly because I knew clams are very sensitive to water quality, and also the biomonitoring is a thing. Though I do wonder if it had been a made up article that it might have spurred someone to try it out at some point,(reply>), I think such a thing was even tested by the US army decades ago, even back in WWII, like torpedo dolphins and such stuff. But that may really be made-up.,(reply>), Doubtful.  I think some marine biologist somewhere proposed it. It’s not that much of a stretch of logic. Once you consider canaries used in coal mines, it becomes an example of what is possible.