The Environmental Protection Agency's Inspector General will investigate research conducted at UNC-Chapel Hill.
The medical testing first came under scrutiny in September, when the American Tradition Institute Environmental Law Center filed a lawsuit against the EPA for on-going experiments at the EPA's Human Studies facility in Chapel Hill. The lawsuit alleges EPA researchers took diesel exhaust and piped it into the lungs of unknowing patients.
"It's a recognition by EPA's Inspector General that there's something seriously wrong that warrants investigation at this North Carolina laboratory, where there is what I consider to be illegal human testing," said Steve Milloy, a public health advocate with the American Tradition Institute Environmental Law Center.
"We've got Congress looking into this, the EPA Inspector General, our lawsuit, another lawsuit coming. The walls are closing in on this rogue research operation that EPA is running in North Carolina."
The lawsuit that alleges the EPA exposed unhealthy patients to high levels of PM2.5, a toxic substance found in diesel exhaust, in experiments that began roughly six years ago.
The EPA has previously stated that the toxins are deadly and can cause cancer.
The EPA declined to offer a comment Monday about the Inspector General's announcement and continues to maintain that all studies conducted by EPA are independently evaluated for safety and ethics.