I am not daft enough to think this is just Texas, i know its everywhere, but this is where i live dagnabit..LoL I wanna blame Monsanto...and Isis...and Donald Trump. I cant ever remember as a kid, the need to worry about if the fish Dad and caught was safe. Huh..maybe i should have been.. I dunno, i think i will just steer clear of the lakes on the "list", its not like we have a shortage in Texas!
When we were kids (I'm an old guy) the technology to detect such things in such extremely low concentrations did not exist. A lot of what is in the water got there naturally, some did not.
Bottom line is that just because you can detect something (say radiation from Fukushima) does not mean that it is bad for you.
Mercury, a lot of it, comes from the timber industry's past when they used methyl mercury as a log preservative.
PCB's mostly come from old transformers and dioxin from burning trash and from chemical plants.
You probly got worse things to worry about in your drinking water, arsenic, radon, and a ton of other things.