Yeah, a lot of people tell me I have scary eyes.
-Blast

Blast, what's the situation with the heavy metal contamination? How is it so pervasive? What is the source? Any chance that heavy metals can concentrate in plants taking in the water? (to say nothing of higher trophic levels...)

Darn it! Water's heavy enough without adding heavy metal to it....

I would also like more background on the heavy metal issue.

I know there are many places in the world where natural (geological) arsenic is a major health issue. Exacerbated, unfortunately, by well-intentioned well drilling programs.

I also recall Colin Fletcher mentioning desert springs that might be poisonous due to heavy metals.

I suppose that for me (and many of us) the primary concern is methyl-mercury (fat-soluble) in aquatic animals (i.e., tasty fish). But that's a more complicated situation.

Anyway, details would be most welcome.

Texas actually used to be a large iron mining state. A lot of the soil is still very red from iron oxide, especially up in the part of the state where this trail is located. With iron you often get assorted other heavy metals including mercury.
-Blast