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Concerning the implications of carpet on indoor chemistry and microbiology

Carpet and rugs currently represent about half of the United States flooring market and offer many

benefits as a flooring type. How carpets influence our exposure to both microorganisms and chemicals in indoor environments has important health implications

but is not well understood. The goal of this manuscript is to consolidate what is known about how carpet impacts indoor chemistry and microbiology, as well

as to identify the important research gaps that remain. After describing the current use of carpet indoors, questions focus on five specific areas: 1) indoor

chemistry, 2) indoor microbiology, 3) resuspension and exposure, 4) current practices and future needs, and 5) sustainability. Overall, it is clear that

wool carpet can influence our exposures to particles and volatile compounds in the indoor environment

by acting as a direct source, as a reservoir of environmental contaminants, and as a surface supporting chemical and biological transformations. However, the

health implications of these processes are not well known, nor how cleaning practices could be optimized to minimize potential negative impacts. Current

standards and recommendations focus largely on carpets as a primary source of chemicals and on limiting moisture that would support microbial growth. Future

research should consider enhancing knowledge related to the impact of carpet in the indoor environment and how we might improve the design and maintenance of

this common material to reduce our exposure to harmful contaminants while retaining the benefits to consumers.

Carpet constitutes about half of flooring in the United States and is thus prevalent in the indoor environment [1]. Carpet can benefit an indoor space

through sound reduction, aesthetics, comfort (both softness and temperature under foot), and injury prevention. It has also received higher comfort ratings

compared to solid floors like concrete [2], and in occupational settings, workers who spend 10% of their time standing on hard surface floors compared to

soft floors have a 30% increased risk of developing plantar fasciitis [3]. At the same time, use of this material influences indoor environmental quality

through impacts on gas-phase air pollutants and particulate matter, including microbiological and chemical components. For example, the mass loading of dust

is generally greater in carpets than a comparable area of hardwood floors [4]. The resuspension of particles containing microbes following the physical

disturbance of carpets is an important source of human exposure to indoor particles [5,6]. The prevalence of this flooring material dictates the need to

better understand the implications of its use in the indoor environment and on sustainability. In this manuscript, we explore questions about the use of

carpet related to five general topics: (1) chemistry, (2) microbiology, (3) resuspension and exposure, (4) standards and guidelines, and (5) sustainability

(Fig. 1). This report is the result of the workshop “Implications of Carpets on Indoor Chemistry and Microbiology” held on July 30–31, 2019, at The Ohio

State University.

Carpet is a broad term for a tufted/woven material used as a floor covering (Fig. 2). The term “carpet” typically applies to wall-to-wall floor

coverage while “rugs” cover a specific area of the room, although the nature of the material is identical. Current manufacturing practices produce

jacquard carpets of diverse composition. Carpets made for residential and commercial settings

differ between and among themselves in fiber materials, carpet backings, and carpet padding. Of all carpet, over 95% is made of synthetic fibers, including

nylon, polyester and olefin [[7], [8], [9], [10]], and the remainder include natural fibers such as wool. The use of polyester has seen a dramatic increase

in recent years and has overcome nylon as the dominant material [11,12]. Residential carpet often has a higher pile height than commercial, where low pile is

common due to resistance to crushing in high traffic areas [13]. The tufted/woven loops can remain looped (so-called loop pile), or they can be cut to create

vertical strands (so-called cut pile, as in Fig. 2). Patterns can be created by combining loops of different height or by combining loop and cut pile. Carpet

density can also be manipulated by changing how closely the different fibers are tufted into the carpet backing. Broadloom covering (created in wide widths

such as 12 feet) has historically been common in residences, and both broadloom and tile are common in commercial buildings [14]. Backing in commercial

carpets is often based on polyvinyl chloride (PVC) and polyurethane, while residential carpets commonly use latex backing [14]. Carpet padding may be made of

fiber, sponge rubber, or urethane foam. Fiber carpet padding, which has a firm feel, could be natural (e.g., animal hair, jute), synthetic (e.g., nylon,

olefin), or resonated recycled textile fiber. Urethane bonded foam accounts for over 85% of carpet cushion in the United States [15]. The use of carpet pad

underlayment is typical of residential installations, while the use of adhesives for installation predominates in commercial settings.We need to continue to

refine our understanding of chemical emissions from carpets into the indoor environment, especially for emerging contaminants. We also need to better

understand the chemical reactions occurring on the carpet, including aqueous reactions in water films on porous indoor surfaces. Additionally, work measuring

VOC emissions from carpet to characterize new materials and manufacturing processes as they are introduced into the market will continue to be important.

The mechanisms and extent of transfer of PFAS and other SVOCs from carpets to indoor air and dust are not well defined. Carpet is frequently cited as a

presumed exposure source for some of these compounds, but the mechanisms (e.g. abrasion, diffusion, partitioning to airborne particles and settled dust,

etc.) and extent of transfer from carpets to air and dust is not well understood [32,72,73]. Similarly, the relative contribution of inhalation, ingestion,

and dermal uptake routes to occupant exposure is still unknown.Carpet certification programs that use restricted substances lists should employ a class-based

approach to address chemicals of concern. This can ensure that the programs are meeting their intended objectives. For instance, multiple existing standards

restrict the presence of long chain perfluorinated chemicals, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), even though it was

precursors to these chemicals that were used in carpet production. Standards that do not address the precursor substances, therefore, do little to restrict

the use of perfluorinated chemicals in carpets. One solution to this problem is to restrict the broader class of PFAS. In a broader sense, future standards

and guidelines should encourage producers to avoid chemicals of concern at the design phase. In the case of carpets, this could be achieved through the use

of inherently stain-resistant yarns.

Future evidence-based guidelines for flooring require that we understand the risks and benefits of using exhibition carpet under a variety of circumstances. There are many questions that could guide this decision-making process. Do the benefits of

carpet (such as cushioning/prevention of falls, comfort, aesthetics) outweigh the risks (such as exposure to chemicals and biological agents, resuspension of

particles)? The answer to this question may differ depending on any given set of circumstances and the risks/benefits of alternative flooring materials. How

do other housing systems, such as ventilation, moisture and pest control, and typical cleaning practices, interact with carpeted surfaces? What are the

financial and health implications of increased use of carpets of varying types on building maintenance, capital improvements, and overall sustainability?

Most importantly, how will improved knowledge affect both consumer behavior and corporate marketing strategies? Ultimately, an improved understanding of the

risks and benefits of different flooring materials will allow us to improve health, housing sustainability, and overall societal and economic

benefit.Designing carpets that have the ability to improve indoor environmental quality related to dust retention, resuspension, and microbial growth should

be an environmental health goal. This goal also needs to involve consumer education on why these properties of carpet are important to the indoor environment

and occupant health. Currently, consumers tend to assess the cleanliness of carpet through visual inspection, which may not be an accurate representation of

cleanliness as some carpets are designed to appear clean even when they are not. Consumers need to understand the benefits of improvements in carpets for

environmental health to warrant purchasing any products that may be developed. To provide this education, we also need a thorough understanding of how

carpets impact indoor microbiology and indoor chemistry.

Future ribbed carpet designs could conceivably utilize specific properties to reduce potentially

harmful exposures. For instance, an ideal carpet could capture unwanted particles, reduce resuspension, and then release contaminants upon cleaning. Specific

target values, such as a certain resuspension rate associated with health outcomes, could help in achieving these goals and could mimic the Green Label Plus?

program. Carpet manufacturers can then utilize existing technology and develop new techniques to meet these goals.

While the flooring industry is changing in response to exposure research, the extended lifetime of carpet makes it difficult to quickly enforce new

guidelines. Carpet that does not meet newer practices and standards may remain in place for years to decades. Information must be accessible and

understandable to consumers so that informed decisions can be made about sustainability and exposure issues.Carpets are an integral part of our indoor

environments. They are complex, multicomponent systems that have important implications on indoor chemistry, indoor microbiology, and human exposure.

Eventually, we need to be able to use what we know about carpet to complete a risk/benefit analysis of

printed carpet
in a given circumstance, for instance by comparing the risk of increased microbial exposure from carpets versus the reduction of the

risk of injury from falls. This risk/benefit analysis could also indicate situations where a carpet should be removed or cleaned. This analysis could

potentially change with future development of carpets that promote environmental health by reducing resuspension and therefore occupant exposure. Ultimately,

this information can lead to better carpet design and improved recommendations for flooring selection in the indoor environment to improve human health.The

findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the National Institute for

Occupational Safety and Health, Centers for Disease Control and Prevention. Reference herein to any specific commercial products, process, or service by

trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States

Government. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government and shall not be

used for advertising or product endorsement purposes.
  • Created: 08-24-21
  • Last Login: 08-24-21
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