EAST PALESTINE, Ohio — When a team came by the morning of Valentine’s Day to test the air quality in Maggie Guglielmo’s store a few blocks from where a freight train carrying hazardous chemicals derailed this month, the smell was undeniable.

“The air monitoring team left within 10 minutes due to the unpleasant/overwhelming odor,” the team of government and private environmental experts wrote in its report, describing a “super glue/pool/fruity-like odor.” But there was no detection of significant amounts of vinyl chloride, a colorless gas carried by the train, or other toxic chemicals.

Ms. Guglielmo, 67, was not satisfied. Instead, she paid $900 for an independent contractor to analyze the air in the store, Wristbands America, and was planning to pay to test her inventory of silicone bands. The sickly, plastic smell still lingers inside and clings to the creek, Sulphur Run, a few feet from her door.

“I’m not going to take that chance” of doing nothing, Ms. Guglielmo said, though she acknowledged the extra analysis could be a luxury for others. “Not everybody has money sitting around to do these kinds of tests.”

Reflecting the fundamental mistrust residents have in the railroad company Norfolk Southern and the government, Ms. Guglielmo is one of several people who live in the region who are seeking independent tests or are looking for ways to conduct their own.

State and federal officials have said repeatedly that they have yet to detect dangerous levels of chemicals in the air or municipal water, citing preliminary data from hundreds of homes in the town of roughly 4,700 people. Teams of experts from top environmental and health agencies have been fanning out across the region to test whether chemicals carried by the Norfolk Southern train or burned off days after the derailment have contaminated the air or water.

But Ms. Guglielmo and others, particularly on the outskirts of East Palestine near where the train collided, continue to report a lingering stench of chemicals in some parts of town and have found little comfort in the assurances in light of the rashes and headaches they have experienced.

Residents are also deeply suspicious of Norfolk Southern conducting its tests in tandem with government agencies and have questioned whether the tests are accounting for the creation of other chemicals when officials decided to burn the cargo of a car on the brink of explosion. The news, which arrived days after the derailment and the controlled burn, that the train had been carrying additional chemicals, further fueled their mistrust.

The threat of possible long-term exposure to the chemical cocktail released into the air and water, coupled with a deep fear that the town and its neighboring villages will be forgotten in the coming months, has also left many residents feeling as if they are on their own to prove that it is safe to remain or return through means that include paying out of pocket for their own tests. Some have become novice chemists, rattling off the names and effects of chemical compounds that had no meaning to them two weeks ago.

It is unclear, however, whether commercial tests outside of the government’s efforts will address the mushrooming pile of unanswered questions.

“Consumer testing does exist, but it is expensive — it’s not going to test for everything,” said Sydney Evans, a science analyst with the Environmental Working Group, a climate advocacy organization. Asked about doing home tests on wells, she warned that some may not pick up trace amounts of all the volatile organic compounds in the water, and that the legal limits for some contaminants released by the derailment are higher than some researchers consider safe.

Officials with the Ohio Environmental Protection Agency did not immediately respond to emails seeking comment.

“We are working closely with Ohio environmental and health agencies on the long-term plan to protect the environment and the community,” Alan Shaw, the president and chief executive of Norfolk Southern, said in a statement after visiting East Palestine this weekend. He noted that, after meeting with local officials, it was clear “they are frustrated by the amount of misinformation circulating about their community and are eager to show that the air and water are safe.”

Connor Spielmaker, a spokesman for the company, confirmed that it had contracted an independent environmental firm to collaborate with federal staff and conduct testing. According to the Environmental Protection Agency, it had screened 525 homes for air quality as of Saturday and had sampled the municipal water in town, with no concerning levels of contaminants. The E.P.A. had also tested 48 wells, mostly in Ohio, and found them safe.

Gov. Mike DeWine, speaking at a news conference on Friday, defended the veracity of tests, though he acknowledged that there was “nothing wrong with healthy skepticism.” Still, he added, “We believe the testing is accurate.”

He also said that the state would continue to test air and water in East Palestine until health experts determined the danger has passed, promising that “we are going to stay there until we are not needed.”

The federal government has also expanded its outreach in the area. The Biden administration dispatched staff members from the U.S. Environmental Protection Agency to East Palestine. And at Mr. DeWine’s request, the Department of Health and Human Services and Centers for Disease Control and Prevention will set up a clinic on Monday for residents in the area with medical concerns.

The Agency for Toxic Substances and Disease Registry, an arm of the federal government’s health department, will also launch an investigation assessing chemical exposure in the area. The most recent such assessment was done last year in Hawaii, after gasoline- and diesel-range hydrocarbons were discovered in a well overseen by the Navy.

A key Senate committee is expected to hold a hearing soon, examining the toll on the environment and on public health in the region. Ohio’s senators — Sherrod Brown, a Democrat, and J.D. Vance, a Republican — sent a joint letter on Saturday calling on the state and national E.P.A.s to test the air for dioxins, toxic pollutants that could have formed after vinyl chloride was burned in the train’s cargo.

Erin Brockovich, the environmental activist who has successfully challenged companies on the spread of toxic pollutants, is set to appear in East Palestine on Thursday for a town meeting, a day after former President Donald J. Trump visits.

Along streets in East Palestine, where shamrocks and dangling red-and-pink hearts were replacing winter holiday decorations on porches and front yards, officials have tied air filters to stop signs and street signs, wrapping them in plastic bags. Cases of bottled waters are piled in the parking lots of local businesses as volunteers and police officers haul them into passing cars.

Officials have encouraged families with private wells to keep drinking bottled water until their water has been tested. But scheduling those tests has been challenging as demand continues to grow, especially as neighboring communities wonder about the consequences of their proximity to the derailment and to the plume of smoke that followed.

At an emotional town meeting Wednesday, Linda Murphy, 49, confronted officials about the challenges she faced getting the water in her private well tested and whether it was safe to drink. Some private companies had turned her away, in part because they said they did not have the specialized tests needed to examine the chemicals on the train.

Four days later, a team arrived at her house. But when she and her husband pulled the filter out of their system Sunday morning as requested ahead of the visit, it smelled just like the chemicals that hung over Leslie Run, the creek near their home where hundreds of fish and frogs were found dead days after the derailment.

Her family is now prepared to renew their push for independent testing, regardless of the results of the E.P.A. tests.

“It’s a little worrisome,” said DJ Yokley, 38, whose broadcasting company is housed near the derailment next door to Ms. Guglielmo’s wristband company. The tests in his store did not detect any significant hazardous chemicals, but he was still weighing additional tests.

“That’s just another added expense,” he said, adding that thousands of dollars of equipment had been sitting in his store and might have been contaminated. “If you go into a marshmallow factory and there’s a mustard plant right beside it, then your marshmallows are going to taste like mustard. That’s exactly what’s happening.”

Even if they were not as concerned as they were in the immediate days after the derailment, other families said they were seeking their own tests with the future health of their land and families in mind.

Ryan Cresanto, 44, said his family had bought tests for the water on their land a few miles outside of East Palestine to establish a baseline for the current water quality. That will allow them to catch any possible changes to the chemical makeup — and do so independently of the railroad company, which he does not trust.

“We’d rather pay out of pocket,” Mr. Cresanto said.

Zolan Kanno-Youngs, Coral Davenport, James C. McKinley Jr. and Carlo Wolff contributed reporting.