Health Concerns Mount in East Palestine Weeks After Ohio Train Derailment

“There are hundreds of chemicals that could be at play at this point, and we absolutely have the tools in academia to test for most all of them,” said Dr. Kari Nadeau, the head of the environmental health department at Harvard, who studies the toxicological effects of smoke in air pollution, including burning plastics. But Congress allows the E.P.A. to monitor for only a limited list of contaminants in the environment, and even with approval, the bureaucratic process of validating and deploying each of the assays could take years.

Instead, air monitors are hanging on stop signs and trees — wrapped in plastic bags to protect them from rain, an impediment that Dr. Nadeau called “concerning.”

Another key force that is often overlooked in toxin surveillance: gravity. Even once the air and surface resources appear to be clear, chemicals tend to seep downward into soil and deep municipal water sources, even some that have previously tested safe, toxicologists say. And as water sources become diluted over time, toxin levels could simply fall below regulation thresholds, giving a false sense of purity.

“With toxicology, it’s both the dose and the passage of time” that matter, said Dr. Nadeau, who also practices medicine and treats children with sensitivities. “We are only as good as our assays.”

The Mascher family has been a fixture in East Palestine since Mr. Mascher’s great-great-grandfather opened a jewelry store in 1876 on Market Street, down by where Gorby’s sandwiches and an antique shop are now, and later became mayor. The granddaughters are eighth-generation residents. But on the night they returned from the evacuation, they also became an illustration of a painful reality: When trauma strikes, not everyone can flee.

When Vivian, Ms. Glavan’s 8-year-old, broke out in new rashes, she turned her car around. Her household has since moved to Homeworth, Ohio, about 30 miles west.

“You know I can’t bring them back there, Dad,” Ms. Glavan said to Mr. Mascher over the phone. He nodded silently.