More than 100 organizations and 800 individuals, including 350.org founder Bill McKibben and celebrity activists Mark Ruffalo, Shailene Woodley, and Josh Fox, have penned an open letter to Pennsylvania Governor Tom Wolf demanding an investigation into whether or not the increasing cases of rare cancer in the state are linked to shale gas development.

The letter, prompted by the Pittsburgh Post-Gazette series “Human toll: Risk and exposure in the gas lands”, will be delivered to the governor and State Health Department Secretary Dr. Rachel Levine.

The Post-Gazette has documented 67 cases of childhood and young adult cancers in four counties – Washington, Greene, Fayette, and Westmoreland – where fracking operations are active. 46 of these cases are children and at least 27 cases are Ewing sarcoma, a rare form of bone cancer. The reports also confirmed 13 deaths of children and young adults from cancer since 2008.

The four counties being studied overlie the Marcellus and Utica Shales and are the center of the gas drilling and fracking development. Nearly 12,000 wells have been drilled in the four countries since 2004, with more projects being approved every year.

Hydraulic fracturing, or fracking, uses water, sand, and chemicals injected deep underground to free oil and natural gas from rock formations. Studies on the toxic chemicals using in drilling and fracking suggest a connection to many different types of cancers. Many of the chemicals are known carcinogens and pose a significant risk to children and other at-risk populations. Several studies have also linked gas drilling and fracking to low birth weight, birth defects, asthma and respiratory issues, and other health problems.

“This ongoing public health crisis calls for immediate action. The Editorial Board of the Pittsburgh Post-Gazette recently called on state officials to conduct an investigation into the childhood cancer cases. We also call on you to direct your Department of Health to begin a formal investigation into the cause of these childhood cancer cases and to stop issuing permits for drilling and fracking in the state while this investigation commences,” concludes the letter.

A state health department review of some of the cases of Ewing sarcoma was not able to designate them as a “cancer cluster” and the shale industry vigorously denies any link between human health decline and air and water pollution that results as byproducts of oil and gas operations.

Raina Ripple, director of the Southwest Pennsylvania Environmental Health Project, believes that there are significant questions that need to be answered on the spike in cancer rates. What is new in the last five or 10 years that could have triggered this?” Ms. Ripple said. “Many in the community are quick to seize on legacy causes like radioactive waste but something has changed. The indices of childhood cancer are out of whack. And what’s changed, what’s new, is the shale gas industry.”

Read the entire letter and see the list of all signing individuals and organizations here.