A U.S. senator is demanding answers after news broke that Scott Pruitt, head of the Environmental Protection Agency (EPA), met privately with the CEO of Dow Chemical in March — just weeks before Pruitt rejected a petition to ban the company's pesticide. SEE ALSO: Trump might pick a non-scientist to be USDA's 'chief scientist' Chlorpyrifos  — which is sprayed on U.S. crops like corn, wheat, and strawberries — can potentially cause impaired brain function in children and lead to acute poisoning of farm workers, according to the EPA's own scientists. Dow Chemical says the science is inconclusive. In a June 29 letter,  Sen. Tom Udall (D-N.M.), the ranking member on the Senate Appropriations subcommittee that oversees the EPA's budget, asked Pruitt to explain why he found other studies to be "more robust" than that of his own agency, especially in light of the chemical's potential risks. An activist protests outside of the Harvard Club where EPA Administrator Scott Pruitt was scheduled to speak on June 20, 2017 in New York City. Pruitt abruptly canceled his appearance.Image: Drew Angerer/Getty ImagesUdall sent the letter a day after the Associated Press reported that Pruitt met with Dow CEO Andrew Liveris on March 9, which was 20 days before Pruitt rejected a petition filed by two national environmental groups asking the EPA to ban all uses of chlorpyrifos. Pruitt and Liveris met for about 30 minutes at a hotel in Houston, according to records obtained by the AP through several Freedom of Information Act requests. Both men were there to speak at a major energy industry conference.  Weeks after their meeting, on March 29, Pruitt upheld agricultural use of the chemical, citing the need for "regulatory certainty" and "sound science in decision-making." EPA spokeswoman Liz Bowman said Pruitt was "briefly introduced" to Liveris at the conference but that the two men did "not discuss chlorpyrifos," the AP reported. Donald Trump, then president-elect, introduces Dow CEO Andrew N. Liveris.Image: Drew Angerer/Getty ImagesPruitt's decision reversed the former Obama administration's finding that the 52-year-old pesticide is potentially too risky to keep spraying on our crops.  EPA scientists reached that conclusion last year after extensively reviewing studies that pointed to the pesticide's potential health problems, including learning and memory declines in people who are exposed through drinking water and other sources.  One of those studies, by Columbia University researchers, found that children exposed to effects of chlorpyrifos in the womb had persistent "disturbances" in their brains throughout childhood. The EPA banned the chemical for most household settings in 2000, after finding the pesticide — used in common products like Raid sprays and Black Flag ant killer — posed an "unacceptable" health risk, particularly to children. Yet about 40,000 farms in the U.S. still use the chemical on about 50 different food crops. A woman harvests strawberries.Image: FAROOQ KHAN/EPA/REX/ShutterstockIn 2007, the Natural Resources Defense Council and the Pesticide Action Network petitioned the EPA to ban food uses of chlorpyrifos. Later, they sued the agency to compel a ruling on their petition. After the Obama administration proposed a ban in 2015, a court order compelled the agency to issue a final rule by March this year. That forced Pruitt to make a decision, and he acted in Dow's favor. According to the EPA's website, the agency will "continue to review the science addressing neurodevelopmental effects and complete our assessment by October 1, 2022." Disturbing. Which is more important to Pruitt—Dow Chemical or children’s health? EPA must act now to ban Chlorpyrifos. https://t.co/Y8A7pgnISX — Tom Udall (@SenatorTomUdall) June 27, 2017 Sen. Udall urged the EPA to act immediately to stop use of chlorpyrifos, writing: "Delay will only result in additional and unnecessary exposures by farm workers and children who continue to have chlorpyrifos experimented on them while the rest of the scientific community has determined there is reasonable cause for danger." WATCH: How to turn your kitchen into a tiny produce farm