Lead.
"Due to insufficient water treatment, lead leached from water pipes into the drinking water, exposing over 100,000 residents to elevated lead levels."
Iguanas have spines along their backs to help protect them from predators. They also have a bunch of extra skin below their necks called a dewlap. This dewlap helps them to regulate their temperature, which is helpful as they are cold-blooded and their bodies don't control their body temperature automatically.
