WASHINGTON – The Agriculture Department is reviewing research that shows new bacteria-killing chemicals used in chicken slaughterhouses may be masking the presence of salmonella and other pathogens that remain on the birds that consumers buy, according to records and interviews.

Academic researchers agree that the chemicals could be overwhelming an antiquated testing process. Several of the scientists have been enlisted by the USDA’s food safety experts to help resolve the matter.

The issue came to the department’s attention this spring after chemical companies pointed to academic research that shows there could be a problem and told the USDA that further study was needed.

“This is a valid concern,” said Catherine Cutter, chairwoman of Penn State University’s Food Safety Impact Group, whose scientific work was referenced in materials chemical companies provided to the USDA.

The new controversy comes as the number and strength of chemicals used on poultry-processing lines is increasing as plants scramble to meet new USDA demands to slash pathogens.

Some experts say the rising tide of chemicals may be causing unanticipated side effects. Some USDA inspectors said they believe such chemicals can contribute to a host of medical problems, including respiratory ailments and persistent skin rashes, The Washington Post reported in April.

The Occupational Safety and Health Administration is conducting a follow-up investigation into a New York poultry plant where one inspector, who was profiled in the Post story, died after his lungs bled out in 2011.

The latest allegations — that the stronger chemicals are undermining testing — are spurring disputes among rival companies competing to sell their products to chicken processors. The companies say their competitors are the ones tripping up the tests.

At issue in the latest allegations is the testing procedure the USDA requires. As the chicken moves down the processing line, the bird is sprayed and bathed in an average of three to four different chemicals. To check that most bacteria have been killed, occasional test birds are pulled off the line and tossed into plastic bags filled with a solution that collects any remaining pathogens. That solution is sent to a lab for testing, which occurs about 24 hours later. Meanwhile, the bird is placed back on the line and ultimately packaged, shipped and sold.

Scientists say in order for tests to be accurate, it is critical that the pathogen-killing chemicals are quickly neutralized by the solution — something that routinely occurred with the older, weaker anti-bacterial chemicals. If the chemicals continue to kill bacteria, they indicate the birds are safer to eat than they actually are.

Several chemical companies — which all have a financial stake in the issue — were present at a June briefing on the matter with USDA officials. The department’s food safety experts asked for the briefing this spring, after the chemical companies raised concerns.

Jon Howarth, a scientist and vice president of EnviroTech Chemical, who took part in the meeting, said some of the newer chemicals are not deactivated in the solution.

The company’s scientists put together a lengthy PowerPoint presentation that cited research from a USDA scientist and several university scientists that they believe backed up their assertions about the new chemicals.

“Is it any wonder that the USDA-FSIS data shows the slaughter plants are doing well?” said one of the PowerPoint slides. Over the past few years, poultry plants have cut salmonella rates in half, according to USDA test data.

The reduction in salmonella rates has raised suspicions about the tests among USDA inspectors, a union representative said. “I don’t really know if the new treatments are working or if it’s giving us all false hope,” said David Hosmer, president of the Southwest Council of Food Inspection Locals.

Howarth, who was a main presenter at the briefing said, “Food is safer; just not as safe as the tests are showing.”

He added that he believes the problem with the testing explains why the number of people getting sick from salmonella in poultry has not dropped in recent years even though the tests results have improved.

The chemical that came in for the greatest scrutiny at the USDA briefing meeting was Cetylpryridinium chloride (CPC) ,which is supplied to poultry plants by Safe Foods, an Arkansas company. Over the past three years, CPC has become the finishing rinse of choice in about 30 percent of poultry plants nationwide.

Officials of Safe Foods, which is a competitor to Howarth’s company, California-based Enviro Tech, were not at the meeting.

Enviro Tech recently posted a YouTube video showing a laboratory experiment that the company says proves CPC is not neutralized if not adequately rinsed when the test sample is taken and therefore produces false test results, sometimes called a “false negative” or “false kill.” It makes no mention of Safe Foods. However, within hours of the video’s posting, a Safe Foods’ attorney threatened the company with a cease and desist order, saying the video includes “inaccurate and misleading information.”

In an interview, Safe Foods chief executive Rush Deacon, who wasn’t at the USDA briefing, dismissed criticism of his product as “pot shots” from competitors. “We did our own tests to make sure we are giving a real kill and they showed we are,” he said.

Deacon said his scientists believe the older acid-based solutions, like the ones Enviro Tech makes, are more likely to produce false test results, but only if “testing protocols are not followed.” Such protocols would include properly neutralizing the chemicals.

Besides CPC, other chemicals getting a closer look from USDA include formulas containing high levels of peracetic acid (PAA) and acidified sodium chlorite. Their use has become commonplace over the past few years in nearly all of the nation’s poultry slaughterhouses, scientists and experts in the poultry chemical industry said

Scott Russell, an international expert on poultry processing and a professor of poultry science at the University of Georgia, was a presenter at the USDA briefing and now plans to work with the department and other researchers to identify ways to ensure all chemicals are neutralized prior to testing.

“This could be happening,” Russell said. “There is variance in the data that doesn’t make sense. Further investigation is needed.”