Arsenic: It has long been known that arsenic, if ingested in very high levels, is deadly. However, lower levels of exposure are also harmful and can cause nausea, vomiting, and diarrhea; anemia and decreased production of the white, infection-fighting blood cells; abnormal heart rhythms; blood vessel damage; numbness in the hands and feet; partial paralysis; and decreased vision, even blindness. Repeated low levels of exposure over an extended period of time can produce effects similar to a one-time high level of exposure, and chronic exposure to low levels can cause skin cancer. Arsenic has also been linked to cancers of the lung, bladder, kidney, liver and prostate.
Contaminated drinking water is a primary route of arsenic exposure. Exposure from birth may increase urinary cancer risk much later in life, suggesting that people whose drinking water is contaminated by arsenic from coal ash should be monitored long-term for this cancer, even if they stop drinking the contaminated water.
I know a lot of environmental advocates who are energetic as all get-out, but lacking somewhat in the details. Energy is important, but you need some basic factual tools at your disposal if you want to persuade others the danger is real. Understanding the toxics involved and their deleterious effect on our health is likely the best tool you could wield in that effort: