In this Feb. 5, 2019, photo, a student waits for a bus outside the abandoned John C. Clark Elementary and Middle School in Hartford, Conn. The school was closed in 2015 after toxic PCBs were found during a renovation. Many students in the neighborhood now must travel long distances to get to other schools. (AP Photo/Martha Irvine)

In this Sept. 12, 2019, photo, Cynthia Yost, who used to teach at the Sky Valley Education Center in Monroe, Wash., poses for a photo in Mercer Island, Wash. Yost was among teachers who sent pieces of carpet and classroom air filters to a lab that found elevated levels of PCBs, toxic chemicals used as coolant in old fluorescent light ballasts. (AP Photo/Ted S. Warren)

In this Oct. 9, 2019, photo, people walk near an entrance to the Sky Valley Education Center in Monroe, Wash. A lawsuit filed on behalf of several families and teachers claims that officials failed to adequately respond to PCBs, or polychlorinated biphenyls, in the school. (AP Photo/Ted S. Warren)

In this Jan. 4, 2019, photo, a toxicology team gathers samples inside the Sky Valley Education Center school in Monroe, Wash. The samples were tested for PCBs, or polychlorinated biphenyls, as well as dioxins and furans. A lawsuit filed on behalf of several families and teachers claims that officials failed to adequately respond to PCBs, or polychlorinated biphenyls, in the school. (AP Photo/Ted S. Warren)

In this Feb. 4, 2019, photo, Steven Harris, a grandfather and former city council member, looks inside the abandoned John C. Clark Elementary and Middle School in Hartford, Conn. The school was closed in 2015 after toxic PCBs were found during a renovation. It is one of several Hartford public schools built during the era when PCBs were commonly used in school construction in caulk, floor adhesive and certain types of fluorescent light ballasts. (AP Photo/Martha Irvine)

This combination of images from April 28, 2014, and July 15, 2016, respectively, and provided by teacher Cynthia Yost, shows black residue from a failed fluorescent light ballast, left, and a carpet sample from the Sky Valley Education Center in Monroe, Wash. Teachers at the public K-12 school took samples from their rooms and had them tested for toxic polychlorinated biphenyls, or PCBs. The teachers claim that several samples, including air filters, had elevated levels of PCBs, which were used in building materials and fluorescent light ballasts until the chemicals were banned in the late 1970s. (Cynthia Yost via AP)

In this Oct. 9, 2019, photo, Donya Grant, second from left, poses for a photo with her children, Rowyn, 11, left, Mabry, 8, center, Hadley, 16, second from right, and Kemper, 14, right, in their home in Monroe, Wash. The family joined a lawsuit against the Monroe School District and others, alleging that the district failed to adequately respond to PCBs, or polychlorinated biphenyls, at the Sky Valley Education Center, a K-12 public school. Grant has homeschooled her children since they left Sky Valley in 2016 for health reasons that they believe were related to the toxic chemicals. (AP Photo/Ted S. Warren)

In this Oct. 9, 2019, photo, Donya Grant, center, works on a homeschool lesson with her son Kemper, 14, as her daughter Rowyn, 11, works at right, at their home in Monroe, Wash. The family joined a lawsuit against the Monroe School District and others, alleging that the district failed to adequately respond to PCBs, or polychlorinated biphenyls, at the Sky Valley Education Center, a K-12 public school. Grant has homeschooled her children since they left Sky Valley in 2016 for health reasons that they believe were related to the toxic chemicals. (AP Photo/Ted S. Warren)

In this Sept. 3, 2019, photo, University of Iowa civil and environmental engineering professor Keri Hornbuckle poses for a photo in a university lab in Iowa City, Iowa. “There is a good reason PCBs were banned,” she said. (AP Photo/Charlie Neibergall)

In this Aug. 21, 2019 photo, Stacy Mullen-Deland, right, a former Spanish teacher at Sky Valley Education Center, and husband Eric eat dinner in their home in Snohomish, Wash. Mullen-Deland says she and her children have dealt with numerous ailments since they spent time at the school, including migraines, thyroid problems and learning and neurological issues. She and her husband are part of a lawsuit filed against the school district, the local health department and Monsanto, the maker polychlorinated biphenyls, or PCBs, which several families believe have made them sick. (AP Photo/Ted S. Warren)

In this June 13, 2019, photo, Stacy Mullen-Deland, a former Spanish teacher at Sky Valley Education Center, pauses during an interview at her home in Snohomish, Wash. Mullen-Deland says she and her children have dealt with numerous ailments since they spent time at the school, including migraines, thyroid problems and learning and neurological issues. She and her husband are part of a lawsuit filed against the school district, the local health department and Monsanto, the maker polychlorinated biphenyls, or PCBs, which several families believe have made them sick. (AP Photo/Ted S. Warren)

In this Feb. 5, 2019, photo, documents and an image of an old fluorescent light ballast sit on a table at the U.S. Environmental Protection Agency Region 2 headquarters in New York. The agency and a lawsuit from parents prompted the replacement of hundreds of thousands of PCB-containing light ballasts in New York City Public Schools. (AP Photo/Martha Irvine)

This July 5, 2017, image provided by Malibu Surfside News shows the demolition of the former Malibu Middle School in California. The school was torn down after testing found high levels of PCBs, which were used in some caulk, floor adhesive and in fluorescent light ballasts until the chemicals were banned in the late 1970s over fears that they could cause cancer. (Barbara Burke/Malibu Surfside News via AP)