Data Omission in Key EPA Insecticide Study Shows Need for Reviewing Industry Studies

“This has huge public health implications,” said Sheppard. “This study was the basis of policy for over 15 years and because it concluded that the ‘no observed adverse effect level’ was more than twice as high as it should have been, the standard was a lot less protective than it should have been.”

In the new study, UW researchers stated: “Such an omission of valid data without justification is a form of data falsification that violates all standard codes of ethical research practice and is classified as outright research misconduct. It is tragic that an omission of valid data from the analysis of the Coulston study may have adversely impacted public health.”

Sheppard pointed out two other critical problems with this study that made its results more susceptible to producing a higher level of “safe” exposure.

In short, because of how the Coulston study was designed, investigators were not able to compare the test results of the three groups treated with different doses of chlorpyrifos within the same analysis. “This meant that their original analysis was much less powerful than it could have been if it had put all the dose groups together in one analysis,” Sheppard said.

Secondly, Sheppard points out, better statistical methods and software tools became available in the 1980s — well within the window when the EPA was using the Coulston study to set acceptable exposure limits for chlorpyrifos — and those would have shown that the study did not find a “safe” level of exposure. These ‘longitudinal data analysis’ tools allow a more direct assessment of how accumulation of the chemical would affect the body’s chemistry over time, while also being able to accommodate the poor study design.

Had the Coulston data been put through the more modern technique, as was done by the UW researchers in their new study, EPA’s reviewers would have seen that chlorpyrifos’ effect on the body’s chemistry accumulated over time and that the study had not discovered the “no observed adverse effect level” used by regulators to set safe levels of exposure.

Why the 1972 Coulston study was not thoroughly examined even as the maturing EPA began reviewing these kinds of studies more rigorously through its inaugural 2006 Human Studies Review Board is a mystery, said co-author Richard Fenske, emeritus professor in the UW School of Public Health’s Department of Environmental & Occupational Health Sciences.

But when the EPA formally set out to review human-subject studies like the Coulston study, the maker of chlorpyrifos (Dow) specifically removed the study from that process, said Fenske, who was a member of that initial review board.

“You can speculate why they did,” said Fenske, “but they formally asked the Human Studies Review Board not to review this study and so it was never reviewed.”

Fenske, whose decades-long work involving insecticides includes a 1990 study of chlorpyrifos residue left behind after an in-home spray treatment (finding the treatment could expose children to unsafe levels of the chemical), said that while the Coulston study could be old news now, “it is a cautionary tale that data being submitted for pesticide registration may not have undergone proper review, and that could be happening today.”

Sheppard added that “at a minimum,” studies funded by companies developing a chemical that’s under study must be opened to outside scrutiny. “I’m not sure industry should be doing these studies at all. I don’t think the fox should be guarding the hen house.”