Upon learning they had been exposed for a decade to an unapproved chemical in their drinking water, many residents of a small South Carolina town were frightened about how that might have affected their health.

The S.C. Department of Health and Environmental Control, which is charged with protecting state drinking water supplies, had not stopped the city of Denmark from using the unauthorized chemical.

That caused federal regulators to step in, and the city was ordered to quit injecting the chemical into a public drinking water well.