Arsenic occurs naturally, and Michigan is one of a handful of states with unusually high arsenic concentrations in groundwater.
Arsenic was also used in insecticides for many years and it's still being used in some weed killers.
David Heath is a senior reporter at the Center for Public Integrity, and he investigated why a health assessment on arsenic from the U.S. Environmental Protection Agency has been delayed.
Why does this health assessment matter?
Heath said when the EPA first wants to determine how dangerous a toxic chemical is, they first do the science. These assessments can take a long time and the arsenic assessment has been going on for more than a decade.
"It's not until they have done the science to figure out exactly how dangerous a chemical is that they can really take action on it," Heath said. "So it really does come down to 'this is how they protect your health.'"
A single member of Congress, Rep. Mike Simpson, R-Idaho, was able to intentionally delay the EPA's health assessment for years.
Heath wanted to know why.
He pored through documents he had already collected and traced campaign contributions, but when asked directly, Rep. Simpson said he was concerned about whether the EPA's science was good. He also cited concerns about how much it would cost water companies to meet new EPA standards.
A ban under scrutiny
In 2001, the EPA set a new standard for arsenic, and all water companies had to meet that standard by 2006.
"Typically they met it well below that standard, so that if there were a new standard a lot of companies that already made these changes probably wouldn't have to do it again," said Heath.
Heath interviewed an executive at a pesticide company that sells a weed killer with arsenic in it.
"Their product was slated to be banned at the end of last year… so they had been aggressively criticizing the EPA’s science, trying to delay any new regulations that would come from it," said Heath.
The delay from Simpson forced the EPA to lift the ban on this weed killer and it remains on the market.
"It had quite a huge financial impact on this company," said Heath.
What the delay means in Michigan
In the U.S., city water systems must meet the federal limit for arsenic, but if you're on a private well, there are no limits that have been set.
According to Heath, states rely on the EPA for guidance on how toxic certain chemicals are because they don't have the resources to do the analysis themselves. Michigan had to do a lot to meet the 2001 standard change.
"But the attitude, I think, was that once they did that, that was sort of the end of it. Until the EPA comes out with its new findings, I don't think you're going to see the state of Michigan really doing a whole lot," Heath said.
Here's a timeline of how the government has handled the issue of arsenic in drinking water (see below or click here):
To see our entire series on arsenic in Michigan, go to our page, Michigan's Silent Poison.
And you can go here to find out more about testing your drinking water well for arsenic.
*This story was reported in partnership with David Heath from the Center for Public Integrity and produced as part of a collaboration among the Center for Public Integrity, The Center for Investigative Reporting and Michigan Radio. It was featured on Reveal, a new program from The Center for Investigative Reporting and PRX.