‘Dark Waters’ star Mark Ruffalo on true story behind one of the biggest cover-ups

Lawyer Rob Bilott battled chemical giant DuPont over PFOA toxins.
8:13 | 11/26/19

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Transcript for ‘Dark Waters’ star Mark Ruffalo on true story behind one of the biggest cover-ups
Reporter: Actor and activist Mark Ruffalo is waging a new battle on capitol hill. These chemicals don't respect political boundaries. Reporter: He's sounding the alarm about so-called forever chemicals, manmade substances that don't break down in the environment. They are found in every one of you. Reporter: His new movie "Dark waters" exposes how toxic they can be and how common. Du pont is knowingly poisoning 70,000 local residents for the last 40 years. Who is paying for this failure to act? It's people like bucky Bailey, who's here today. I was originally born with just one nostril. Limited vision in my right eye. Reporter: Bucky Bailey's mother worked in the du pont chemical plant in 1980 in parkersville, West Virginia making teflon. The non-stick surface for pots and pans. What bucky's mother didn't know at the time was that she was exposed to a chemical known as pfoa. She was working directly with the chemical while she was pregnant with me. Reporter: Which has now proven to be linked to cancer. The doctors, they were just completely scared. They said don't get your hopes up, he won't make it through the night. Reporter: And I can't imagine what it must have been like for your mom to hear that and see that. Two of the seven women, nearly 30% gave birth to babies that had the exact facial deformity that's your company already knew about. We're done here. Reporter: "Dark waters" tells the true story of Robert bilott, the underdog lawyer who took on the industrial giant du pont chemical on behalf of people like bucky. I am a corporate defense attorney. Reporter: Ruffalo plays the real-life lawyer who started out defending chemical companies, only to switch sides and file lawsuits against du pont. We were dealing with something that was not just affecting one family and one farmer and animals on one piece of property. But when I saw that this was a chemical that was in the entire community's water supply and in the blood of the entire country but nobody knew that. Reporter: It was 1998 when West Virginia farmer Wilbur tenant asked Robert bilott for help. Something was killing his cattle. They started dying about 20, 30 minutes ago. Reporter: He made these videos showing runoff from a landfill owned by the du pont chemical plant, one of the largest employers in his town of parkersburg. You saw these animals with tumors, with black teeth wasting away, and they're standing in white sudsy foaming water. And you could see it coming out of a landfill. I mean, to me at least it was pretty obvious, there was a problem here. How many did you lose? 190. 190 cows. You tell me nothing's wrong Reporter: As seen in the movie bilott sued du pont and in the process uncovered decades' worth of evidence that the chemical giant knew the pfoas in teflon and other products was toxic. I kept rereading and reading it over again thinking this really can't be what I'm reading. Reporter: What was the ultimate truth he uncovered in those boxes? That du pont had knowingly poisoned us. They knew. And they went ahead and did it anyway. Reporter: According to bilott and the EPA, du pont's internal documents reveal that the company failed to disclose its dangerous effects in all the years the company was marketing teflon. Let me ask you the old watergate question, which is what did du pont know and when did they know it? They knew it was causing cancer in animals by the 1980s. They knew it was in the drinking water of the community by the 1980s. And they'd even set their own internal standards of what's safe. Even though the government regulators didn't know about it. Reporter: The lawsuit on behalf of Wilbur tenant alleges du pont was dumping toxic chemicals. Contaminating his water supply. Killing hundreds of his cattle. Tenant ultimately settled with du pont and the company admitted no wrongdoing. In a statement to ABC news du pont says "Nothing is more important than the safety of our employees and the communities in which we operate. Unfortunately, this movie misrepresents things that happened years ago, including our history, our values and science. In some cases the film depicts wholly imagined events." We should want to nail du pont. All of us should. Reporter: Tim Robbins, who plays Ruffalo's boss, understands the moisture's potential impact. It really is up to us to make films like, this to spread information, to hold people accountable that are polluting our environment and making our people ill. Isn't that lovely? Reporter: Knowing du pont had polluted the groundwater bilott sued the chemical maker over and over to expose the truth. Bilott launched a class action lawsuit after telling the EPA in 2001 that du pont continues to release an essentially unregulated confirmed animal carcinogen into the air, land, and water. Making many residents of parkersburg, West Virginia sick. As depicted in the movie, the lawsuit grew to 70,000 people, who for years had been wondering what was causing the health problems all around them. Bilott's epic legal battles chronicled in his new book "Exposure" helped focus worldwide attention to the wide variety of pfoas all around us. Well, it coats the pots you cook with so the food doesn't stick. It protects the carpet your baby crawls on. You may also have it in your winter jacket, your skin lotion, even your makeup. We're talking about teflon. Reporter: Without admitting wrongdoing du pont settled the class action lawsuit for $70 million, part of which funded a scientific study that eventually found a probable link between pfoas and diseases like testicular cancer, kidney cancer, and thyroid disease. And you said your mom is now suffering illnesses herself. She is. She has thyroid disease, which is linked to the chemical -- Jimmy: Exposure. Chemical exposure, yes. Reporter: Initially bucky was part of the class action lawsuit but dropped out after his birth defect couldn't be linked. It hasn't stopped him from becoming a fierce advocate. I don't want money. I want peace of mind. I want other people to have hope and faith that they can take a shower, they can take a drink of water around their water source and it be clean water. Now I know what products and what products don't have it, and I'm still learning. I'm not going to put myself or my kids in waterproof clothing that has pfoa in it. Reporter: In a statement to ABC news, du pont says they do not make the chemicals in question and agree that further action needs to be taken. They add they are eliminating the use of all pfas-based firefighting foams and support innovative pfas remediation technologies. Taking on du pont and exposing the danger of forever chemicals has been Robert bilott's life work. At the end of the movie it says after 20 years that you're still fighting. Mm-hmm. Reporter: What does that mean? Well, we still have people in that community that are getting diagnosed with cancer. And it's being found in drinking water all over the country. New communities are waking up almost every day to learn this is in our water and may have been there for a long time. Reporter: Du pont eventually settled over 3,000 lawsuits related to pfoas, paying out over $670 million. Once again, without admitting wrongdoing. Bucky Bailey, who has a cameo in the film, has endured over 40 reconstructive surgeries on his face. Happy birthday to daddy now 38, he's the father of two beautiful children. It's interesting to see just how it has shaped my life as a father of a 3-year-old and a 7-month-old now, just wanting the best for them and wanting them to have success. Reporter: What's the overall message that audiences would walk away from having seen the movie? Even one individual standing up could make a change. And "Dark waters" is in theaters now.

This transcript has been automatically generated and may not be 100% accurate.

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