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Staff photo by C.B. Schmelter / One of the cloth masks distributed by state health officials was worn by the protester at left during weekend demonstrations in Chattanooga against police brutality.

This story was updated at 7:02 p.m. on Monday, June 1, 2020, with more information.

NASHVILLE — Tennessee Gov. Bill Lee on Monday temporarily halted distribution of free masks intended to slow the spread of COVID-19 following a news report raising safety concerns about an anti-microbial agent used to treat the black, knitted cloth coverings.

"We have paused further distribution of free masks to county health departments while further inquiry is pursued," Gillum Ferguson, the governor's spokesman, told the Times Free Press.

The halt comes as three of Tennessee's four largest county health departments — in Hamilton County, Shelby County and Metro Nashville — announced suspension of free-mask distribution following a report last week by Nashville television WTVF.

Shelby County officials made their announcement Monday, following earlier suspensions by Metro Nashville on Friday and Hamilton County on Saturday. Hamilton health officials asked residents to stop using the face coverings from the state.

(READ MORE: Hamilton County halts distribution of 'sock masks' over chemical coating)

The masks in question are made by apparel manufacturer Renfro Corp. of Mount Airy, North Carolina, which has a Cleveland, Tennessee, manufacturing and distribution facility. The company also makes socks, and the masks were widely ridiculed on social media for having a similar appearance to socks.

The company had no immediate comment Monday, although an official indicated that executives are preparing a response to concerns soon.

Officials at Lee's Unified Command group, which is handling state response to the global coronavirus pandemic, reached out to the manufacturer as the state scrambled to get masks. Tennessee said it planned to purchase five million masks and is paying some $8 million.

Renfro's mask is treated with the chemical Silvadur, manufactured by DuPont.

(READ MORE: To wear or not to wear: Differences on masks come out in the open for Chattanoogans)

WTVF reported Friday that Silvadur, used to ward off odors, is registered as a pesticide. Dr. Warren Porter, a professor of environmental toxicology at the University of Wisconsin in Madison, told the station regarding the masks, "I wouldn't wear one."

Porter, a board member of the nonprofit group Beyond Pesticides, which describes itself as working with allies to protect public health and the environment and help "lead the transition to a world free of toxic pesticides," also said, "nobody wants to breathe in COVID, but I wouldn't want to be breathing in something that I also knew could be poisoning my body in a relatively short period of time and might be having multi-year effects on my health."

In a statement, DuPont called Silvadur "a safe and trusted technology used to control bacteria, mold and mildew that cause odors on fabric for more than a decade with no adverse health effects."

The company also stated, "The antimicrobial material applied to treated fabrics, such as face masks or coverings, are at such low levels that the use of the fabric poses no risk to consumers."

DuPont also said the chemical "has been approved by EPA to control bacteria, mold and mildew that cause odor on fabrics. Based on EPA regulations, Silvadur is registered with the agency and classified as a pesticide."

Dr. Henry Spratt, environmental microbiologist at the University of Tennessee at Chattanooga, said that if his interpretation of a 2017 U.S Environmental Protection Agency document on Silvadur is correct, the agency is addressing the chemical at its initial manufacturing phase at DuPont.

(READ MORE: Will Hamilton County students have to wear masks amid COVID-19 pandemic?)

"What I'm assuming when I read those EPA documents, that those hazards — and one of the hazards they say out right, it's harmful to swallow, harmful if absorbed through skin, harmful if inhaled and it causes irreversible eye damage — what they're talking about there is, they're talking about the parent material," Spratt said.

"You buy the stuff from DuPont because what they are talking about there is 'parent' material. You get a gallon of it and then you have to take that and dilute it out and spray it onto your fabric as you're making your fabric."

Spratt said he is no fan of the mask because he doesn't think the use of the sock material is very effective. He also said "undoubtedly concentrations that are going to be in the fabric are going to be much lower than what you have in the parent material. But I can't find anywhere — and I doubt this company is going to be able to say, they haven't done the analysis — what is the actual concentration of the silver material on the fiber when it's going over your face?"

Until that's known, the microbiologist said, "It's hard to say is it going to actually damage your eye? Or, if you breathe through it for a couple of hours, are you going to breathe enough to get some sort of inhalation damage to your lung tissue?"

(READ MORE: How to wear a mask to prevent spread of COVID-19: Chattanooga officials, CDC provide tips)

Still, Spratt added, "I take what they're saying with a grain of salt, I mean the concerns. And I understand the reason for the EPA concerns. But I think someone may have missed something in that they're not talking about the actual concentration on the mask."

"Now, all of that said," Spratt noted, "the silver that's in the Silvadur, it apparently should stay in the fabric for 20 wash cycles. That means it is washed out gradually."

Spratt said while the Renfro mask might absorb large droplets of mist in air from surrounding persons' exhalations, he doesn't see them catching "fine aerosols" of moisture.

The professor's advice to worried residents of Tennessee is, "Wash it a couple of times. And then wear it. Don't put it on right out of the box because it may, in theory, it could still have some residue on the material. Now I would hope the company would wash them after they've done the treatment with the silver material. But you don't know."

(READ MORE: Tennessee officials, sock company defend 5-million-mask rollout amid coronavirus)

Contact Andy Sher at asher@timesfreepress.com or 615-255-0550. Follow on Twitter @AndySher1.

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