Average human body temperature declining?

https://phys.org/news/2020-10-decline-average-body-temperature-healthy.html

The above article talks about how the average human body temperature, among healthy adults, in at least certain areas of the world, is declining. They have some hypotheses about why this is the case. I have my own. Here it is:

I hypothesize that the increased mercury in the environment is responsible. Mercury is known to lower body temperature, and we do know that there is more mercury in the environment than there used to be. Similar neurotoxins may also play a part.

mercury_
body_temperature