When you mention thresholds you also have to say that they are not medical but administrative. For many substances medical, desirable, values are zero. For exam

When you mention thresholds you also have to say that they are not medical but administrative. For many substances medical, desirable, values are zero. For example, lead: "There is no safe threshold for lead exposure" https://pubmed.ncbi.nlm.nih.gov/27837574/ https://pubmed.ncbi.nlm.nih.gov/27837574/ There simply is no feasible way to have "zero" of pretty much anything today though. The molecules are out there and there time flows only in one direction. So thresholds simply mean that above that is when something can be done about it. If environmental levels rise thresholds would have to rise too because what can you do if it's everywhere? No use having the option to sue someone, including government, when it's out of there hands. Things like mercury or lead in the environment are global (even higher levels can be found in the arctic -- https://cordis.europa.eu/article/id/122855-a-better-understanding-of-the-high-levels-of-mercury-pollution-in-the-arctic-tundra https://cordis.europa.eu/article/id/122855-a-better-understa...). So for better or worse, life on this planet will have to adapt. There will only be action on the edges, when it gets so bad that it cannot be ignored. All the many small long term effects can't even be properly studied, because what do you compare with when it's everywhere and it's impossible to isolate only one or few chemicals' effects? . So, in summary, citing thresholds in a medical discussion is pretty much just a distraction at best. It's for discussions about what to do, or what can you do (legally). The values of the thresholds don't easily or directly translate to "it's safe". Of course they are taken into consideration when threshold levels are set, but only as one factor.