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WASHINGTON — The two-week-old shutdown has halted one of the federal government’s most important public health activities, the inspections of chemical factories, power plants, oil refineries, water treatment plants, and thousands of other industrial sites for pollution violations.

The Environmental Protection Agency has furloughed most of its roughly 600 pollution inspectors and other workers who monitor compliance with environmental laws. Those scientists, engineers and analysts are responsible for detecting violations that endanger human health, as they did, for example during an August 2018 airborne inspection that found that oil and gas fields in Karnes County, Tex., were leaking illegal levels of chemicals into the atmosphere, in violation of the Clean Air Act.

While the inspection personnel represent a relatively small proportion of the E.P.A.’s total of about 15,000 workers, their absence increases the chances that, either by design or by accident, companies might emit illegal levels of contaminants into the air or water without detection, for weeks on end, according to people familiar with the E.P.A. inspections.

“There are plants that discharge wastewater into streams and rivers, places that store hazardous chemicals in containers that could leak — we show up and test these places to see if they’re meeting pollution laws,” said Garth Connor, a furloughed E.P.A. inspector based in Philadelphia who has been off the job since Monday. “Now there’s nobody out there to check if they’re complying.”