perchlorate
Safe level of perchlorate in water is 1/10th as much as prior thought
https://www.hopkinsmedicine.org/news/newsroom/news-releases/research-story-tip-something-in-the-water-environmental-pollutant-may-be-more-hazardous-than-previously-thought https://www.nature.com/articles/s41594-020-0417-5