Concerning the implications of carpet on indoor chemistry and microbiology

Concerning the implications of carpet on indoor chemistry and microbiology
Posted by rtyu1yu on 2021/08/24
Concerning the implications of carpet on indoor chemistry and microbiology

    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.


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