Microfibers generated from the laundering of cotton, rayon and polyester based fabrics and their aquatic biodegradation

Abstract

The effect of fiber type (cotton, polyester, and rayon), temperature, and use of detergent on the number of microfibers released during laundering of knitted fabrics were studied during accelerated laboratory washing (Launder-Ometer) and home laundering experiments. Polyester and cellulose-based fabrics all shed significant amounts of microfibers and shedding levels were increased with higher water temperature and detergent use. Cellulose-based fabrics released more microfibers (0.2–4 mg/g fabric) during accelerated laundering than polyester (0.1–1 mg/g fabric). Using well-controlled aquatic biodegradation experiments it was shown that cotton and rayon microfibers are expected to degrade in natural aquatic aerobic environments whereas polyester microfibers are expected to persist in the environment for long periods of time.

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Marine Pollution Bulletin
journal homepage: www.elsevier.com/locate/marpolbul
Microfibers generated from the laundering of cotton, rayon and polyester
based fabrics and their aquatic biodegradation
Marielis C. Zambrano
a
, Joel J. Pawlak
a
, Jesse Daystar
b,d
, Mary Ankeny
b
, Jay J. Cheng
c
,
Richard A. Venditti
a,⁎
a
Department of Forest Biomaterials, College of Natural Resources, North Carolina State University, Raleigh, NC 27695-8005, United States
b
Cotton Incorporated, Cary, NC 27513, United States
c
Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC 27695-7625, United States
d
Nicholas School of the Environment, Duke University, Durham, NC 27708, United States
ARTICLE INFO
Keywords:
Microplastics
Microfibers
Laundering
Biodegradation
Textiles
Aquatic environments
ABSTRACT
The effect of fiber type (cotton, polyester, and rayon), temperature, and use of detergent on the number of
microfibers released during laundering of knitted fabrics were studied during accelerated laboratory washing
(Launder-Ometer) and home laundering experiments. Polyester and cellulose-based fabrics all shed significant
amounts of microfibers and shedding levels were increased with higher water temperature and detergent use.
Cellulose-based fabrics released more microfibers (0.2–4 mg/g fabric) during accelerated laundering than
polyester (0.1–1 mg/g fabric). Using well-controlled aquatic biodegradation experiments it was shown that
cotton and rayon microfibers are expected to degrade in natural aquatic aerobic environments whereas polyester
microfibers are expected to persist in the environment for long periods of time.
1. Introduction
In the last 60 years, the production of resin and fibers has increased
significantly from two million metric tons (Mt) in 1950 to around 380
Mt. in 2015 (Geyer et al., 2017;Plastics Europe, 2017;Statista, n.d.).
Geyer et al. (2017) estimated that 8300 Mt. of plastics have been pro-
duced up to 2015 generating approximately 6300 Mt. of plastic waste
from which 9% have been recycled, 12% incinerated, and 79% accu-
mulated in landfills and natural environments. The accumulation of
plastics in the environment is a subject of concern for industries, gov-
ernments, and communities (Rochman et al., 2013;Thevenon et al.,
2011;Thompson et al., 2010), especially in water sources (Thompson
et al., 2004).
The presence of plastics in water bodies can be the origin of dif-
ferent problems such as aesthetic issues, entanglement and suffocation
of marine animals in plastic nets, plastic ingestion by the fauna, ad-
sorption of pollutants and pathogens in plastics particles and trans-
portation in the ecosystems (Moore, 2008;Thevenon et al., 2011).
Plastics found in the environment may be classified according to
their size and source. Macroplastics are big pieces (> 5 mm) generated
from poor waste management strategies. Particles below 5 mm in size
are commonly called microplastics (Boucher and Friot, 2017;Eriksen
et al., 2014;Moore, 2008;Thevenon et al., 2011;Wagner et al., 2014).
In general, microplastics are classified into two forms. Primary micro-
plastics are discharged to the environment at the micro size; these can
be plastics manufactured in the micro size such as scrubbing agents or
pellets, or particles produced from the abrasion during wear and use of
plastic goods such as tires and synthetic textiles (Boucher and Friot,
2017). Secondary microplastics are produced from the fragmentation of
mismanaged plastic waste in the environment (Boucher and Friot,
2017). Nevertheless, there is no consensus about the microplastics de-
finition in the scientific community. After a comprehensive review of
reported methods for describing and identifying microplastics, Frias
and Nash (2019) proposed a new definition of microplastics that con-
siders their physical and chemical properties, size, and origin: “Micro-
plastics are any synthetic solid particle or polymeric matrix, with regular or
irregular shape and with size ranging from 1 μm to 5 mm, of either primary
or secondary manufacturing origin, which are insoluble in water”. In that
study nanoplastics were considered < 1 μm.
Microplastics are floating in the world's oceans, rivers, lakes, and
are depositing in sediments (Browne et al., 2011;Eriksen et al., 2014;
GESAMP, 2015;Miller et al., 2017;Thompson et al., 2010;Wagner
et al., 2014). It has been estimated that a minimum of 5.25 trillion
plastic particles weighing about 270,000 tons are floating in the world's
oceans and 93% of these plastics particles are in the micro size range
(Eriksen et al., 2014). This represents ~ 0.1% of the world's plastic
https://doi.org/10.1016/j.marpolbul.2019.02.062
Received 8 November 2018; Received in revised form 25 February 2019; Accepted 26 February 2019
⁎
Corresponding author.
E-mail address: richardv@ncsu.edu (R.A. Venditti).
Marine Pollution Bulletin 142 (2019) 394–407
0025-326X/ Published by Elsevier Ltd.
T

annual production (Eriksen et al., 2014).
Available studies have demonstrated that marine fauna is suscep-
tible to microplastics ingestion (Thevenon et al., 2011;Wagner et al.,
2014). The presence of anthropogenic debris in seafood for human
consumption has been observed (Miranda and de Carvalho-Souza,
2016;Rochman et al., 2015). There is also evidence of microplastic
ingestion by humans (Schwabl, 2018). Microplastics have been ob-
served even in commercial food-grade salts (Kim et al., 2018). Conse-
quently, microplastic pollution is raising concerns regarding human
health.
Even though the microplastics are relatively inert, due their large
surface-to-volume ratio and chemical composition, they can adsorb
pollutants and pathogens and transfer them via ingestion to other
trophic levels, even to humans through the food chain (Egbeocha et al.,
2018;GESAMP, 2015;Rummel et al., 2017;Wagner et al., 2014;Wang
et al., 2018). It has been shown that microplastics sampled from dif-
ferent environments adsorbed toxic compounds such as polychlorinated
biphenyls (PCB), dichloro diphenyl trichloroethane (DTT), hexa-
chlorocyclohexane (HCH), polycyclic aromatic hydrocarbons (PAHs),
polybrominated diphenyl ethers (PBDE), hexabromocyclododecane
(HBCD), heavy metals, nonylphenols (NP), and perfluoroalkyl sub-
stances (Akhbarizadeh et al., 2017;Chen et al., 2018;Holmes et al.,
2014;Llorca et al., 2014;Mato et al., 2001;Vedolin et al., 2018;Wang
et al., 2018). Several studies indicated that microplastics and macro-
plastic debris distributed at various concentrations in aquatic ecosys-
tems around the world affect the growth, development, behavior, re-
production, and mortality of aquatic animals (Chae and An, 2017).
However, other authors consider that at environmentally relevant
concentrations, microplastics have not been shown to have harmful
effects to aquatic fauna and do not represent a significant exposure
route for toxic chemical compared to prey consumption in aquatic birds
or organisms (Burton, 2017;Henry et al., 2019).
There are many different sources of primary microplastics and one
of the main challenges is to prevent the generation and leakage of these
particles to the environment from their origin (Boucher and Friot, 2017;
GESAMP, 2015). Although wastewater treatment plants (WWTPs) have
shown good efficiency in microplastic removal, they are not designed
for that purpose (Lares et al., 2018;Magnusson and Norén, 2014;
Talvitie et al., 2015). Microplastics, mainly particles and fibers smaller
than 100 μm, have been observed in wastewater effluents at low con-
centration (Browne et al., 2011;Lares et al., 2018;Magnusson and
Norén, 2014;McCormick et al., 2014;Mintenig et al., 2017;Talvitie
et al., 2015, 2017a, 2017b;Wolffet al., 2018). However, the large
volumes of effluents discharged every day to the water bodies and the
use of sewage sludge (where most of the microplastics are retained) as
soil amendment/fertilizer represent an important source of micro-
plastics introduced into the environment (Lares et al., 2018;Mintenig
et al., 2017;Nizzetto et al., 2016;Talvitie et al., 2017b). These mi-
croplastics are found mainly in the fiber-like form in some effluents
(Lares et al., 2018;Mason et al., 2016;Mintenig et al., 2017;Talvitie
et al., 2015, 2017a, 2017b). These fibers are predominantly made of
polyester, and more specifically, polyethylene terephthalate (PET)
(Lares et al., 2018;Mintenig et al., 2017;Talvitie et al., 2017a;Wolff
et al., 2018;Ziajahromi et al., 2017). Nevertheless, some studies also
indicate that cellulose-based fibers are present in the wastewater ef-
fluents (Lares et al., 2018;Talvitie et al., 2017b, 2015; Ziajahromi et al.,
2017).
All of these fibers are common in the textile industry and it is be-
lieved that they enter the WWTPs from the effluent of the washing
machines (Browne et al., 2011;McCormick et al., 2014;Thompson
et al., 2010). In addition, in less developed countries, it is common to
discharge home laundering effluents directly into the environment
(Boucher and Friot, 2017).
The International Union for Conservation of Nature (IUCN)
(Boucher and Friot, 2017), estimated that between 0.8 and 2.5 Mt./year
of primary microplastics are released into the ocean. From this, it is
estimated that 35% are micro-size fibers released from textiles during
laundering (Boucher and Friot, 2017). Fibers at the micro-size are
commonly named microfibers by the environmental science commu-
nity. Microfibers could be made of synthetic polymers, in that case, they
will also be microplastics. Natural fibers also represent a large pro-
portion of the textile industry and the fate of these microfibers are
largely unknown in published literature (Henry et al., 2019;Ladewig
et al., 2015;Mishra et al., 2019;Salvador Cesa et al., 2017). The term
“microfiber”is also used in the textile industry to refer to fabrics made
of fine polyester or polyamines fibers, < 1 denier (mass in grams of
9000 m) and a fiber cross-section smaller than 10 μm(Henry et al.,
2019;Salvador Cesa et al., 2017). To avoid confusion in this study, the
term microfiber will refer exclusively to the synthetic, artificial, and
natural fibers (< 5 mm) released from fabrics during laundering.
Several studies have quantified the number of microfibers released
during home laundering, however, there is lack of standardization in
the methods used and the metrics that are needed to incorporate a re-
liable value in environmental sustainability assessments (Henry et al.,
2019;Salvador Cesa et al., 2017).
Browne et al. (2011) observed that polyester garments (blankets,
fleeces, and shirts) can shed > 1900 fibers per wash. All garments re-
leased > 100 fibers per liter of effluent, with > 180% more from
fleeces than other construction types. Carney Almroth et al. (2018)
reported, using a laboratory scale washing machine, that fleece and
microfleece synthetic fabrics shed the greatest amount of fibers, up to
7360 fibers m
−2
L
−1
in one wash, indicating that the fabric construc-
tion plays a major role in the shedding ability of fabrics. Likewise,
Napper and Thompson (2016) observed that 6 kg of synthetic material
fabrics (polyester, polyester-cotton blend, and acrylic fabrics) could
release about 140,000 to 700,000 fibers per wash in commercial home
laundering washing machines. Another study showed that the re-
covered microfiber mass per garment tested, jackets or sweaters made
of polyester fleece or nylon shell with nonwoven polyester insulation,
ranged from approximately 0 to 2 g, exceeding 0.3% of the unwashed
garment mass (Hartline et al., 2016).
Hernandez et al. (2017) showed in their study of polyester fabrics
that the use of detergent during home laundering is the aspect that has
the greatest effect on the generation of microfibers. Approximately 75%
more microfibers were released when using detergent regardless of type
(liquid, powder, or surfactant) and dosage, 0.025 vs 0.1 mg fibers/g
textile washed, without and with detergent, respectively (Hernandez
et al., 2017). De Falco et al. (2018) observed a similar tendency with
polyester and polypropylene woven and knitted fabrics. The use of
detergents promoted an increase of microfibers released from fabrics
during laundering; in this case, the powder detergent induced more
microfiber shedding than the liquid one in domestic washing and, in
general, products for industrial washing have a higher impact than
domestic washing detergents (De Falco et al., 2018).
De Falco et al. (2018) saw a 35% decrease in microfiber shedding
when using a softener. Nevertheless, the influence of temperature and
softener use in the microfiber generation have been less consistent and
significant between studies than the effect of detergent use (De Falco
et al., 2018;Hernandez et al., 2017;Napper and Thompson, 2016;Pirc
et al., 2016).
When comparing washing machine types, it was observed that top-
load machines shed more fiber mass than front-load machines (Hartline
et al., 2016). Additionally, Hartline et al. (2016) reported that me-
chanically aged-fabrics release more fibers than new fabrics. Never-
theless, sequential washing experiments have shown that the number of
microfibers released during laundering is generally reduced with in-
creased washing cycles until reaching a constant level (Carney Almroth
et al., 2018;Napper and Thompson, 2016;Pirc et al., 2016;Sillanpää
and Sainio, 2017).
To our knowledge, there has been only one study that investigates
the effect of the type of polymer yarn material used in textiles with the
same fabric constructions. However, natural fibers were not included in
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
395

this study, only synthetic fibers such as polyester, acrylic, and nylon
were compared (Carney Almroth et al., 2018). In most research, the use
of different fabric constructions and/or textile goods studied does not
allow a fair comparison of the fiber polymer composition effect on
microfiber generation.
Sillanpää and Sainio (2017) reported the mass, 0.12 to 0.33% w/w
per mass of fabric washed, and number, 2.1 × 10
5
to 1.3 × 10
7
fibers
per kg of fabric washed, of microfibers released during sequential home
laundering washing cycles of polyester and cotton fabrics of different
constructions. The results of this study indicate that cotton fabrics have
a higher tendency than polyester fabrics to shed fibers during washing,
however, the differences in fabric constructions make it difficult to
derive a final conclusion from this data (Sillanpää and Sainio, 2017).
In the research reported herein of fabric shedding during laun-
dering, different fiber polymer materials were studied all with the same
knit construction. Accelerated laboratory laundering and home laun-
dering experiments were performed and the shed microfiber quantity
and characteristics were determined. Polyester and cotton knitted fab-
rics were evaluated since they represent the greatest portion of the
global fiber production for natural and synthetic fibers, respectively
(Mills, 2011). As well, a rayon knitted fabric was included in this study
as a representation of the regenerated cellulosic fibers in the market. In
addition, methods to predict fiber shedding based on fabric and yarn
mechanical properties are proposed and evaluated herein.
Another important dimension to the laundering microfiber issue is
their fate in the environment. Surprisingly, little is known about the
biodegradation of textile fibers in aquatic environments. Most de-
gradation studies have been focused on biodegradable and synthetic
polymers intended for packaging applications in composting environ-
ments (Eubeler et al., 2009, 2010;Karamanlioglu and Robson, 2013;
Lešinský et al., 2005;Lucas et al., 2008;Pagga et al., 1996;Starnecker
and Menner, 1996). There have been no studies on aquatic biode-
gradation of textile fibers known to the authors of this study. In addi-
tion, there is an emerging concern about the role of natural and arti-
ficial fibers on the distribution of chemical pollutants in aquatic
environments (Ladewig et al., 2015). Therefore, this research includes a
study of the aquatic biodegradation of the yarns of the major textile
fibers, cotton, polyester, rayon, and polyester-cotton blends as a
starting point to differentiate the effect of fiber polymeric material on
the fate of the microfibers in aquatic environments.
2. Materials and methods
2.1. Fabrics and yarns
Four interlock fabrics without finishing were manufactured by
Cotton Incorporated to perform the laundering experiments; the spun
yarns contained 100% cotton, 100% rayon, 100% polyester, and 50%/
50% polyester/cotton (Table S1). The weft knitted interlock construc-
tion was made on a 24-cut circular knitting machine (24 needles/in.).
Spun yarns from staple fibers with a size of 40/1 Ne (English Cotton
Count, 40 ×840 yards of one single yarn weight 1 pound) were used to
knit the fabrics (Table S2). As pre-treatment, all fabrics were scoured to
remove impurities from the fibers such as wax, fats, pectin, proteins,
and organic acids, and improve their wettability. Additionally, fabrics
containing cotton were also bleached. These fabrics were dyed with
different colors to assess cross-contamination. The spun yarns cut in
1 cm length were used in the biodegradation experiments. These yarns
were pre-treated as were the fabrics and did not contain finishes or
dyes.
2.2. Accelerated laundering experiments
2.2.1. Washing protocol
The behavior of the fabrics during laundering was studied at dif-
ferent conditions using the AATCC (American Association of Textile
Chemist and Colorists) standard SDL Atlas Launder-Ometer (South
Carolina, USA) with metal canisters of 550 mL capacity. The fabrics
were cut in square pieces of size 4in × 4in using an ATOM Swing Arm
Clicker Presses model SE20C (Italy). The edges were secured using the
1150 MDA Serger Machine Brand Bernina (Thurgau, Switzerland) with
white 100% polyester yarn brand Excell to avoid errors by the excessive
release of microfibers through the edges of the fabrics, these edges were
approximately 12% of the total sample weight. Each piece of fabric
weighed approximately 2–3 g. A cleaning cycle was performed on the
fabric pieces. In each metal canister 25 metals balls (6 mm of diameter),
150 ml of deionized (DI) water and the fabric sample were added. The
cleaning cycle of the fabric was done for 16 min at the temperature of
interest. The cleaning wash is a very important step in this procedure; it
allows the removal of fibers and impurities present in the fabrics from
the manufacturing process.
Cold (25 °C) and warm (44 °C) laundering experiments were con-
ducted with deionized (DI) water and detergent solution (AATCC
Monograph 6-2016, 2017). According to the conditions studied, 25
metals balls (6 mm diameter), 150 ml of DI water or detergent solution
and the fabric sample were added to a 550 ml metal canister and
tumbled for 16 min. The detergent solution was prepared with 1. 47 g of
the 2003 AATCC Standard Reference Liquid Laundry Detergent with
optical brightener (AATCC Monograph 2-2005, 2017) dissolved in one
liter of DI water (AATCC Test Method 135-2015, 2017). For each
condition and fabric type, eight to ten canisters were prepared for the
Launder-Ometer. In addition, a canister with the cleaning agent and the
metal balls but with no fabric was used as a blank during the filtrate
analysis.
2.2.2. Laundering filtrate analysis
After the washing protocol, all the liquid (150 mL) inside each
canister was recovered in individual glass bottles of 16 oz. capacity,
eight to ten replicates were collected for each fabric type and condition.
The mass of microfibers released during laundering was recovered by
filtration using Whatman glass microfiber filter papers grade GF/C,
47 mm and 1.2 μm particle retention, whereas the quantification of
individual fibers and their length and width distributions were obtained
with the HiRes Fiber Quality Analyzer (FQA), OpTest Equipment Inc.
(Ontario, Canada). These analyses were also made on the liquid col-
lected from the canisters without fabrics used in each condition as
blanks to account for the potential influence of the washing agent and
the background variability.
2.2.3. Statistics
The effect of temperature and use of detergent on the microfiber
generation during laundering was evaluated with a linear mixed model
using SAS 9.4 and Excel 2016. This model assumes data non-linearity
and assesses if the effect of fabric type, temperature, and use of de-
tergent influence the microfibers generation at a significant level
α= 0.05. The details of this model are described in the Supplementary
material (S 1.1.4).
2.3. Home laundering experiments
2.3.1. Washing/drying protocol
The Whirlpool Washing Machine Model WTW57005WO (Michigan,
USA) with temperature control system Quick Temp SDL ATLAS (South
Carolina, USA) and the Dryer Whirlpool Model WED57005WO
(Michigan, USA) were cleaned carefully prior to performing this pro-
tocol (Supplementary material section S 1.2.1). The fabrics were cut to
obtain samples of 4 lb. (1.8 kg), representative of a large load in a home
laundering washing machine (AATCC Test Method 135-2015, 2017).
The samples were weighed using an OHAUS Champ bench scale (New
Jersey, United States). In addition, the edges of the fabric were secured
using the 1150 MDA Serger Machine Brand Bernina (Thurgau, Swit-
zerland) with white 100% polyester yarn brand Excell to avoid errors
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
396

by the excessive release of microfibers through the edges of the fabrics.
As a first step, each sample was washed with tap water using the normal
wash load setting to remove the loose fibers and impurities from the
manufacturing process and storage.
Before starting the washing cycle, a circular nylon mesh filtering
screen of 20 μm Sefar 03–20/14 of 24 cm of diameter was secured at the
discharge pipe of the washing machine to collect the microfibers gen-
erated during the laundering process. The temperature control system
was configured to have 115 °F (46 °C) during the washing cycle and
80 °F (27 °C) during the rinsing cycle. Once the washing cycle was
completed, the fabric sample was transferred to the drying machine.
The drying process was set at high temperature (heavy load) for 60 min.
After the first cycle of washing and drying was completed, the
procedure was repeated two more times with the same fabric to study
how subsequent washings influence the microfibers generation.
Samples collected during washing on the nylon mesh were re-dispersed
in water prior to further analysis. The nylon mesh was washed five
times with 100 mL of DI water to remove the fibers retained and this
water was collected in a clean glass beaker (1 L). A new nylon mesh was
used in each washing cycle to avoid cross-contamination. The re-dis-
persed sample was filtered through a Whatman glass microfiber filter
paper grade GF/C (47 mm and 1.2 μm particle retention) and the filter
paper was dried at 105 °C overnight and weighed.
2.4. Correlations between microfiber shedding and physical testing of yarns
and fabrics
The tensile properties of yarns used to knit the fabrics were mea-
sured by the single-strand method (ASTM D2256/D2256M −10, 2015)
in the dry and wet states. The tensile tester MTS Q Test 5 (Minnesota,
USA) was used to perform the test in 1 Grab 10 in. GL mode. The yarns
were conditioned for 24 h prior to testing under the standard atmo-
sphere for textile testing (70 ± 2 °F and 65 ± 2% relative humidity)
and the dry tests were performed in the same environment. For the wet
state tests, the samples were submerged for 5 min in DI water and
loaded immediately in the tensile tester. For the dry state, 15 strands
were tested of each yarn sample; and for the wet state, only 10 strands
of each yarn sample were evaluated. The initial speed of the machine
was adjusted between samples and conditions to achieve a breaking
time of 20 ± 3 s during the experiments (Table S5). The Maxi-Mar-
tindale Abrasion tester from James H. Heal and Co. Ltd. (Halifax, UK)
was used to measure the abrasion resistance of the fabrics used for the
laundering experiments following the Martindale Abrasion Tester
Method (ASTM D4966 −12, 1992). Three replicates of each fabric
were prepared, circular specimens of 1.5 in (38 mm). Standard wool
abrasion fabric was used as an abrasion agent applying a pressure of
9 KPa and 20,000 rubs. The fabrics were conditioned for 24 h prior to
testing under standard atmosphere for textile testing (70 ± 2 °F and
65 ± 2% relative humidity) and the test was performed under the
same environment. The mass loss of the fabric after the abrasion test
was obtained by weighing the sample before and after the test using the
balance Voyager Pro OHAUS, precision = 0.1 mg (New Jersey, United
States).
2.4.1. Statistics
SAS 9.4 and Excel 2016 software versions were used to assess the
differences in breaking load between the types of yarns, in wet and dry
state, and in abrasion resistance between the types of fabrics at a sig-
nificant level α= 0.05. Pair comparisons between the types of yarns
were made using PROC ANOVA and PROC GLM within conditions (dry
and wet state). The PROC MIXED procedure was used to analyze the
fabric abrasion resistance data based on a linear mixed model taking as
fixed the effect of the type of fabric tested. There is a significant dif-
ference between compared variables when the p-value obtained from
the tests is < 0.05.
2.5. Aquatic biodegradation of yarns
The aquatic biodegradation of the spun yarns was assessed by
measuring the oxygen demand of the yarns in a closed respirometer
using as inoculum aerobic microorganisms in the activated sludge from
the Neuse River WWTP in Raleigh, NC (ISO 14851:1999, 2005). The
activated sludge was added to the flasks within 72 h after collection.
The concentration of suspended solids in the activated sludge was
measured (ISO 11923: 1997, 1997) and the inoculum was added to the
flasks to achieve a concentration of 30 mg of solids per liter of testing
medium to simulate biodegradation in natural environments. For the
preparation of each flask, a magnetic stirrer bar was inserted in each
bottle with the appropriate amounts of test medium and inoculum to
have 400 mL of testing medium in each flask. The standard test medium
(nutrients) for the ISO 14851 was used.
The level of biodegradation was determined by comparing the
oxygen uptake (Ou) with the theoretical oxygen demand (ThOD) of the
spun yarns. Microcrystalline Cellulose (MCC), 20 μm powder from
Aldrich Chemistry, was used as reference material to check the in-
oculum activity during the test.
After measurement and adjustment of the pH to 7, the flasks were
aerated using aquarium pumps to achieve oxygen saturation in the
medium for 15 min at the beginning of the experiment and after each
measurement. The dissolved oxygen (DO) concentration after satura-
tion was measured. The DO in the medium was measured with an Orion
Star™A123 Dissolved Oxygen Portable Meter (Thermo Fisher Scientific,
Massachusetts, USA) and the pH meter Accumet XL150 from Fisher
Scientific (New Hampshire, USA). The DO meter was calibrated prior
measurments with moisture saturated air (100% Relative Humidity)
and the pH meter was calibrated using buffer solutions (pH 4, 7, and
10) from Fisher Chemicals (New Hampshire, USA). The flasks were
closed tightly, incubated in a water bath at a constant temperature
(25 °C) and stirred at 300rpm. The test medium was allowed one week
of incubation to let the microorganisms use the organic matter already
present in the activated sludge and allow the stabilization of the in-
oculum to the test medium. After this incubation period, the test ma-
terials (spun yarns and MCC) were added to each flask.
Every week, or more frequently depending on oxygen depletion
rates, the concentration of DO in each flask was measured and the pH
adjusted to 7. The flasks were then aerated to saturate the test medium
with oxygen and maintain the aerobic environment for the biode-
gradation process. After saturation, the DO in each flask was measured.
This procedure was performed to account for the oxygen consumption
during the course of the experiment.
Based on the standard method, this test should be considered valid if
the degree of biodegradation of the reference material is > 60% and the
biological oxygen demand (BOD) of the blank did not exceed 60 mg/L
at the end of the test (ISO 14851:1999, 2005).
Several samples were collected at the end of the experiment. The
liquid portion was separated from the solids remaining by filtration
using Whatman glass microfiber filter papers grade GF/C (47 mm and
1.2 μm particle retention). The liquid portion was used to measure the
nitrification interferences to account for the oxygen consumed by ni-
trification reactions. In the solid portion, scanning electron microscope
(SEM) images were taken and elemental analysis and Fourier-transform
infrared spectroscopy (FTIR) were performed and compared with the
same analyses on test materials before the biodegradation experiment.
2.5.1. Statistics
SAS 9.4 and Excel 2016 software versions were used to assess the
differences in biodegradation between the types of yarns. Pair com-
parisons between the types of yarns were made using a non-parametric
model for ANOVA (Wilcoxon Model) with a significance level α= 0.05.
There is a significant difference between the variables compared when
the p-value obtained from the test is < 0.05.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
397

3. Results and discussion
3.1. Microfibers generation during accelerated laundering at small scale
3.1.1. Effect of fabric material
All fabric types released significant amounts of microfibers, with
rayon, cotton, and polyester/cotton fabrics of the same knit construc-
tion releasing significantly more microfibers during accelerated
washing than polyester fabrics (Fig. 1). Similar behavior was observed
by Sillanpää and Sainio (2017) in domestic washing, after 5 sequential
washes, cotton fabrics released up to 1.0 × 10
6
fibers per kg of fabric
washed whereas polyester fabrics shed up to 5.0 × 10
5
fibers per kg of
fabric washed.
The result reported here for the microfibers released during ac-
celerated laundering of blended knitted fabric (50%/50% polyester/
cotton) versus 100% polyester knitted fabric is different than the be-
havior described by Napper and Thompson (2016). They showed that
65% polyester/35% cotton jumper fabrics released significantly fewer
fibers than polyester and acrylic jumper fabrics. These jumper fabrics
were not all made in the same way as they were purchased from
commercial retailers and were not specified as the same brands. This
suggests that the influence in fabric and yarn construction and pro-
portion of the components of the blend play a major role in the mi-
crofibers generation during laundering and should not be generalized.
The generation of microfibers with length between 25 and 200 μm had
the same or higher number magnitude than the microfibers released
from the fabrics during laundering with length > 200 μm, at the con-
ditions of this study (data shown in Fig. S10).
The influence of fabric structure was also reported elsewhere
(Carney Almroth et al., 2018;De Falco et al., 2018). Carney Almroth
et al. (2018) observed that polyester fleece fabrics shed significantly
more fibers than knit fabrics (polyester, nylon, and acrylic), about 1200
and 9 fibers per 100 cm
2
of fabric, respectively. Whereas, De Falco et al.
(2018) noted the highest release of microfibers from woven polyester
with respect to knit polyester and woven polypropylene.
3.1.2. Effect of detergent use
The effect of the washing solution on the mass of microfibers re-
leased during accelerated laundering is also presented in Fig. 1. All
materials at 25 °C and at 44 °C showed an increased mass of microfibers
released during the laundering with detergent. There was a statistically
significant increase (p-value < 0.05) in the microfibers mass released
when the detergent solution was used as a washing agent for all fabric
types at 44 °C (Fig. S9, A). For cotton, rayon, and polyester/cotton
fabrics, the increase in microfibers generated by the presence of de-
tergent during accelerated laundering was statistically significant (p-
value < 0.05) also at 25 °C (Fig. S9, B).
Similarly, the data obtained using the FQA (Fig. 2) shows the same
tendency as the gravimetric measurements, the number of microfibers
released during laundering are increased with detergent and this in-
crease is statistically significant (p-value < 0.05) for all but the rayon
fabric (Fig. 2, A). Generally, the main influence of the detergent in the
washing solution is attributed to the generation of microfibers with
25–200 μm in length, which outnumber, from a count basis, the mi-
crofibers with length > 200 μm, Fig. 2.
In fact, several options have been proposed to reduce the number of
microfibers released into the effluent wash water, such as The GUPP-
YFRIEND washing bag, the Coral ball, and filters that retain the fibers
for later disposal (Cora Ball, n.d.;Environmental Enhancements, 2019;
Filtrol, n.d.;Guppyfriend, n.d.). Nevertheless, our results show that
there is an important portion of microfibers with a size below 200 μm
that cannot be addressed by these trapping mechanisms.
McIlwraith et al. (2019) showed that the Lint LUV-R filter that can
be installed at the effluent pipe of the washing machine can capture
87% of the fibers released by a 100% polyester fleece blanket during
washing and the Coral ball only trapped 26%. The fibers lost in the
effluent water were also measured. After using the Coral ball, the length
of the fibers did not change significantly compared to the length of the
fibers collected from the effluent with no mitigation strategy
(1.5 ± 0.5 mm). However, this was not the case when the Lint LUV-R
filter was used; the length of the fibers decreased significantly to
0.4 ± 0.1 mm, since these mechanisms cannot trap fibers smaller than
Fig. 1. Distribution of the mass of microfibers generated during accelerated laundering per mass of fabric washed at different conditions; washing with detergent
(WD), washing without detergent (WOD), and different temperatures. The different types of fabrics are shown in different colors: purple for cotton, pink for polyester,
green for rayon, and orange for the polyester/cotton blend. The length of the box represents the interquartile range (IQR, the range between the 25th and 75th
percentiles), the mean is represented by a square and the median by a horizontal line in the box, and the vertical lines (whiskers) represent the range within 1.5 IQR.
(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
398

their pore size, in this case, 150 μm(McIlwraith et al., 2019).
According to these results, it can be concluded that the presence of
surfactant assists the mobilization process of the broken/loose fibers
from the fabric to the washing solution, also reported in previous stu-
dies made with polyester and acrylic fabrics during home laundering
(Carney Almroth et al., 2018;Hernandez et al., 2017).
3.1.3. Effect of temperature
The effect of temperature on the microfibers generation in the
presence of detergent solution and in deionized water is reported in
Fig. 1. The mass of microfibers released from the fabrics during laun-
dering increased at a higher temperature for all types of fabrics,
nevertheless, the difference was only statistically significant for cotton
(p-value < 0.05) (Fig. S9, C and D).
The FQA results were similar to the gravimetric analysis (Fig. 2). In
all cases, the total number of microfibers released using detergent so-
lution or DI water increased with higher temperature. These increases
were not found to be statistically significant at p-value < 0.05 in some
cases (Fig. 2, B). Uncertainty on the effect of temperature on the mi-
crofiber generation during laundering has been reported, even at ex-
tended washing times (Hernandez et al., 2017;Napper and Thompson,
2016).
In general, the swelling action of water on cellulose-based fibers
increases with temperature. The water acts as a plasticizer, lubricating
and softening the amorphous regions of the cellulose fibers by the
disruption of the hydrogen bonds between the cellulose chains. This
causes a reduction in the glass transition temperature of the amorphous
regions and a decrease in mechanical properties such as stiffness and
resiliency in regenerated fibers such as rayon (Bryant and Walter,
1959). Essentially the increase of temperature promotes the swelling of
cellulosic fibers, and as a consequence, the textile structure, generating
free space for the mobilization of the broken fibers from the fabric
construction. The swollen fabric structure generates expanded material
expected to enhance fuzz formation due to the shear forces during
washing. Polyester does not swell in water as much as cellulosic fibers
and its relatively lower changes in microfiber generation at higher
temperatures are in agreement with this (Bryant and Walter, 1959).
3.1.4. Fiber size distribution
The size distribution of the released microfibers collected was
measured using the FQA. The FQA only measures the size distribution
of fibers with length > 200 μm. The length distribution of the micro-
fibers with length > 200 μm at 44 °C without detergent is presented in
Fig. 3. Very few microfibers > 2.5 mm were detected. The length dis-
tribution of microfibers released by rayon fabrics was broader than the
other fabrics tested. Cotton, polyester, and the blended (polyester/
cotton) fabrics released a greater proportion of shorter microfibers than
did the rayon.
The width or diameter of the microfibers released is different de-
pending on the fabric material. Cotton and rayon microfibers are
thicker than polyester microfibers, Fig. 4. The width distribution of the
microfibers generated from polyester/cotton blended fabrics during
laundering is bimodal as expected when the two types of microfibers
are both being released in the washing solution. Similar size distribu-
tions were observed in the microfibers recovered from laundering of
Fig. 2. Number of microfibers generated during accelerated laundering per
mass of fabric washed. A - Effect of detergent use on the generation of micro-
fibers at 44 °C. B - Effect of temperature on the generation of microfibers,
without detergent (WOD). Error bars represent the standard error (N = 4, ex-
cept for Polyester at 25 °C with N = 5). Significant differences are indicated by
* (p < 0.05).
Fig. 3. Fiber Length Distribution of microfibers (T = 44 °C, without detergent).
The normalized values are presented based on the percentage of total micro-
fibers counted by the FQA within the size range, 2000 to 19,000 microfibers
measured per sample. The vertical dotted lines indicate the FQA detection limit
for fiber length.
Fig. 4. Fiber Width Distribution (T = 44 °C, without detergent). The normal-
ized values are presented based on the percentage of total microfibers counted
by the FQA within the size range, 1000 to 15,000 microfibers measured per
sample. The vertical dotted lines indicate the FQA detection limit for fiber
length.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
399

fabrics at different temperatures, with or without detergent.
3.2. Microfibers generation during home laundering
In agreement with the accelerated laundering experiments, all fab-
rics released microfibers with fabrics made of cellulose-based fibers
(cotton and rayon) releasing more microfibers than polyester during
laundering for all of the three cycles in series, Fig. 5.
There was a consistent decrease in the number of microfibers re-
leased with increasing washing cycles, but there was still very sig-
nificant amounts of microfibers being released during the third cycle.
This is in agreement with other studies showing the number of micro-
fibers released during laundering is generally reduced with increased
cycles until reaching a constant amount (Carney Almroth et al., 2018;
Napper and Thompson, 2016;Pirc et al., 2016;Sillanpää and Sainio,
2017).
In the accelerated laundering experiments, more microfibers were
generated per weight of fabric washed than in the home laundering
experiments as a result of the more intense mechanical action of the
metal balls; approximately forty times more mass was shed. There is
general agreement between the accelerated and home laundering ex-
periments for the relative amounts of microfibers shed for the different
fabrics with a correlation coefficient of 0.8 (Fig. S19, Supplementary
material). Thus, accelerated laboratory laundering can be used as a
method to assess the relative difference in shedding capacity of fabrics
in a simple, well-controlled way without the burdensome, labor-in-
tensive efforts involved in using the home washing machine that is
poorly suited for quantitative analysis. Home laundering machines
utilize large quantities of water and have complex washing compart-
ments and inlet and outlet piping and valves that make accurate re-
covery of microfibers difficult. In addition, the accelerated laundering
experiments provide larger quantities of microfibers than home laun-
dering that are easier to capture and measure gravimetrically.
Regarding the size of the microfibers (length > 200 μm), in the
home laundering experiments, longer microfibers were obtained than in
the accelerated laundering experiments, in agreement with the hy-
pothesis that the lower intensity action during home laundering
washing does not break offas many small microfibers (Fig. 6). In ad-
dition, for both the accelerated and home laundering experiments,
rayon fabrics generated longer microfibers, followed by cotton, polye-
ster/cotton, and polyester, respectively. In addition, SEM images
showed that the shedded fibers were approximately the same width as
the original fibers in the yarns in the fabrics prior to washing for both
accelerated and home laundering washing (Figs. S20 and S21).
3.3. Predictive tests for the microfibers generation during laundering
Certainly, microfiber generation during laundering involves many
factors such as fabric type and geometry (woven, knit, or nonwoven),
yarn type (twist, evenness, hairiness, and number of fibers), processing
history (spinning, knitting or weaving, scouring, bleaching, dyeing,
finishing, and drying processes), and physicochemical properties of the
fibers (Hernandez et al., 2017).
In this study, all the above-mentioned variables were the same ex-
cept the physicochemical properties of the fibers in the yarns, thus, to
understand why some knitted fabrics released more microfibers than
others, the microfiber generation process during laundering was com-
pared using the schematic model for pilling formation of fabrics. This
process is composed of several steps: fuzz formation (a fiber with a
loose end extending out of the fabric), swelling, fibrillation, pill for-
mation (entanglement of the fibers), and pill wear off(Geology, 1966;
Okubayashi et al., 2005;Okubayashi and Bechtold, 2005). In this case,
it is proposed that the shedding capacity of the fabrics depends mainly
on the fuzz formation step and how easy these fibers are broken by the
mechanical action of the washing machine before forming the pill
(Fig. 7). The breakage of the staple fibers is the main contribution to
microfiber formation and release. In this study, most shed microfibers
were < 2 mm long (Figs. 3 and 6) whereas the staple fibers are much
longer. Generally, natural staple fibers are classified as short staple fi-
bers (length between 25 and 60 mm) and long staple fibers (length >
60 mm) (Elhawary, 2015). For cotton fibers, the US Cotton Fiber Chart
2017/2018 reported the length for US cotton fibers ranging from 1.11
in (28.19 mm) to 1.17 in (29.72 mm) (Cotton Incorporated, n.d.). Ad-
ditionally, synthetic or semi-synthetic fibers are generally uniformly cut
in lengths higher than 32 mm for staple fiber applications (Barnet, n.d.).
The fuzz formation step depends on the friction, shape, thickness,
stiffness, and abrasion resistance of the fibers (Geology, 1966;
Okubayashi et al., 2005;Okubayashi and Bechtold, 2005). Therefore, to
assess how easy the fuzz forms and the fibers break, some mechanical
properties were evaluated: the abrasion resistance of the fabrics and the
tensile breaking load and hairiness of the same yarn types used to
construct these fabrics.
The tensile breaking load of the yarns is presented in Table 1 for the
dry and wet states. Polyester, which does not swell significantly in
water, showed similar breaking loads for both the wet and dry states.
The polyester yarns presented significantly higher breaking load com-
pared to the other yarns, explaining to some extent why polyester
fabrics released fewer microfibers than the other fabrics studied.
In contrast to polyester, rayon and cotton yarns had different be-
haviors in the dry and wet states. In the wet state, rayon yarns were
Fig. 5. Mass of microfibers generated during home laundering after subsequent
washing per mass of fabric washed. The same fabric sample (N = 1) was wa-
shed and dried three times. Fig. 6. Mean length of microfibers (> 200 μm) released during home laun-
dering and accelerated laundering (T = 44 °C, with detergent). The mean va-
lues are presented based on the number of fibers measured by the FQA, 2000 to
5000 microfibers per sample. Error bars represent a 95% confidence level.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
400

weaker while cotton yarns were stronger compared against the re-
spective dry yarns. In fact, cotton fibers have higher crystallinity and
molecular weight than rayon fibers. The cellulose chains in the non-
crystalline regions of the cotton fibers tend to rearrange and orient if a
force is applied increasing their tensile strength (Hajime et al., 2000).
Additionally, the crystallites in the cotton in the wet state are
maintained as a reinforcing component. In rayon, there is a lower
crystallinity and thus a lower wet strength of the yarns. According to
the results of the tensile tests, cotton yarns were significantly stronger
than rayon yarns when wet. However, the microfibers generation of the
cotton and rayon fabrics were similar and not predicted by differences
in the tensile strength results.
Other parameters to consider are the hairiness and evenness of the
yarns which are critical measurements for the quality of the yarn and
also affect the microfiber generation during laundering. The char-
acteristics of the yarns used in this study are presented in Table S2
(Supplementary material). They have similar yarn count and twist; the
main differences are due to their strength properties, discussed above,
and their evenness and hairiness.
Evenness is a measure of how uniform the yarn is in terms of mass
and cross-section variation per unit length (ASTM D1425/
D1425M—14, 2014;Hasler and Honegger, 1954;Slater, 1986;Soares
et al., 2008). Higher coefficient of variation percents are an indication
of uneveness, poor appearance and quality and lower yarn strength. In
this case, the yarn samples have similar evenness except for the 50/50
polyester/cotton yarn that has a higher coefficient of variation.
Moreover, hairiness is a measurement of the amount of free fibers
loops and ends protruding from the yarn surface at a certain distance.
High hairiness affects the appearance of textiles products and increases
the surface friction of yarn and fabrics and their pilling tendency,
therefore, it can affect the microfibers generation during laundering
(Barella, 1957, 1983;Krupincová and Meloun, 2013;Majumdar, 2010;
Manich and Barella, 1997;Yuvaraj and Nayar, 2012). The hairiness
depends on several factors such as the twisting levels and the diameter
Fig. 7. Proposed mechanism for the microfibers release during laundering from fabrics and yarns made of polyester fibers (blue dashed line, left) and cellulosic fibers
(green solid line, right). The loose fibers (fuzz) come out of the textile structure during wear and use (FUZZ FORMATION). Then, these fibers are broken in the
washing cycle by the mechanical action of the washing machine, FIBER BREAKING. In the presence of water and detergent, cellulosic fibers swell (SWELLING), due
to the mechanical action of the washing cycle these fibers could also be fibrillated (FIBRILLATION) and broken (FIBER BREAKING). Adapted from Okubayashi et al.,
2005 and Okubayashi and Bechtold, 2005. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Table 1
Breaking Load of Spun Yarns measured by the single-strand method (ASTM D2256/D2256M −10, 2015).
Sample Break load (N) Strain at break (%)
Dry state
N=15
Wet state
N=10
Dry state
N=15
Wet state
N=10
Mean Std Dev Mean Std Dev Mean Std Dev Mean Std Dev
Cotton yarns dry state 1.8053 0.1655 2.2742 0.1912 5.6944 0.554 8.6700 0.7837
Polyester yarns dry state 4.3364 0.3176 4.4316 0.1800 10.7539 0.5252 10.5975 0.6643
Polyester/cotton yarns dry state 2.2028 0.1414 2.2804 0.2320 13.1837 0.9946 14.1328 0.9308
Rayon yarns dry state 1.7077 0.1113 0.9884 0.1097 15.3462 1.1053 15.3316 1.7243
SD –Standard Deviation.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
401

of the yarn, and the rigidity, elongation, tenacity, and length of the
fibers (Barella, 1957, 1983;Majumdar, 2010).
The hairiness measurement also provides an indication of which
yarns have more tendency to form fuzz on the surface. The Zweigle
Hairiness parameter indicates the number of fibers protruding 3 mm or
more from the yarn surface in 100 m of yarn (Krupincová and Meloun,
2013). The hairiness of the yarns used to knit the fabrics in this study is
presented in Fig. 8. In decreasing order, 100% cotton spun yarn has
higher hairiness followed by 100% polyester spun yarns, 100% rayon
spun yarns, and 50/50 polyester/cotton spun yarns. In general terms, it
can be said that the similarity in microfibers generation between rayon
and cotton fibers may be related to the high hairiness of cotton and low
tensile strength of rayon yarns. Polyester yarns have relatively similar
hairiness to rayon but the fibers are much stronger, which does not
generate a large number of microfibers during laundering. In the case of
50/50 polyester/cotton, the hairiness is low but the variation in even-
ness is considerably high which can lead to poor abrasion resistance.
Moreover, the abrasion resistance of the knitted fabrics was studied
using the Martindale Abrasion Tester. The weight loss of the fabrics was
determined after 20,000 cycles of the wool abrasion fabric scraping the
surface of the fabrics, reflecting the resistance of the fabric to shed mass
under the mechanical action of the washing and drying cycles. The
results presented in Table 2 show that rayon knitted fabrics are less
resistant to abrasion followed by cotton, polyester/cotton and polyester
knitted fabrics with a significant difference between them.
The breaking load of the yarns and the abrasion resistance of the
fabrics in this study correlate with the number of microfibers released
during laundering (Figs. 9 and 10). These correlations exist for all
conditions but at different levels (Figs. S22 and S23).
In summary, it is expected that fabrics with higher abrasion re-
sistance, low hairiness, and higher yarn breaking strength would have a
lower tendency to form fuzz and/or release microfibers during the
mechanical action of washing.
3.4. Aquatic biodegradation of yarns
The aquatic biodegradability of the microfibers shed in the en-
vironment via home laundering provides a good indication of their
persistence in the environment. The aquatic biodegradability was stu-
died following the ISO standard method for ultimate aerobic biode-
gradability of plastic materials in aqueous mediums (ISO 14851:1999,
Zweigle Hairiness
2108
A – 100 % Cotton Spun Yarn
Zweigle Hairiness
1641
B – 100 % Polyester Spun Yarn
Zweigle Hairiness
1529
C – 100 % Rayon Spun Yarn
Zweigle Hairiness
952
C – 50/50 Polyester/Cotton Spun Yarn
Fig. 8. Selected optical microscope images of the spun yarns. The Zweigle hairiness data for each yarn is indicated.
Table 2
Abrasion resistance of knitted fabrics measured as the weight loss of the fabrics
by the action of the Martindale Abrasion Tester (ASTM D4966 −12, 1992).
Sample Weight loss SD
Rayon knitted fabrics 5.63% 0.28
Cotton knitted fabrics 3.34% 0.22
Polyester/cotton knitted fabrics 1.63% 0.12
Polyester knitted fabrics 0.11% 0.13
SD –Standard Deviation, N = 3.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
402

2005) using the yarns used to knit the fabrics and a low concentration
of activated sludge solids to simulate natural aquatic environments. The
yarns have fibers with similar width to the shedded microfibers during
laundering and as such are reasonable materials to evaluate for relative
biodegradability. The percentage of biodegradation was measured
comparing the oxygen uptake of the system with the theoretical oxygen
demand ThOD calculated according to the total organic carbon in each
sample. The nitrification interferences during the experiments were not
significant compared to the oxygen consumption due to biodegradation
of the polymeric materials studied. At the end of the experiment, the
reference material (microcrystalline cellulose) reached 84% degrada-
tion (Fig. 11) indicating the inoculum was working and the BOD of the
blank was 12 mg/L, it did not exceed 60 mg/L, as required by a valid
experiment (ISO 14851:1999, 2005).
The biodegradation curves of the materials over the 243 days are
shown in Fig. 11. Only the polyester material had fully reached the
plateau phase; the other materials including the microcrystalline cel-
lulose were continuing to consume oxygen, albeit a slow rate towards
the end of the experiment (Fig. 11). The percentage of biodegradation
after the 243 days, subtracting the nitrification interferences (oxygen
consumed in nitrification reactions), was 75.90 ± 12.35% for cotton
yarns, 62.21 ± 13.29% for rayon yarns, 39.76 ± 3.52% for 50/50
Polyester/Cotton Yarns, and 4.05 ± 0.75% for polyester yarns. The
results are as expected, the cellulose-based materials are a readily
available source of carbon for the microorganisms. The polyester, on
the other hand, being hydrophobic and non-sugar based is not degraded
by the microorganisms (Li et al., 2010).
There is no pass/fail criteria for aquatic biodegradability in the ISO
method 14851 and it is generally understood that there does not exist a
clear biodegradability threshold to certify a material as biodegradable
in aquatic and marine environments (European Bioplastics, 2018).
Nevertheless, the tests were performed under valid conditions based on
the method criteria, 60% of degradation in the biodegradable reference
material (microcrystalline cellulose) and < 60 mg/L of oxygen con-
sumption occurred at the end of the test (ISO 14851:1999, 2005).
The withdrawn standard for non-floating biodegradable plastics in
the marine environment (ASTM D7081-05, 2005) specified that to
consider a plastic product biodegradable in marine environments >
30% of the organic carbon must be converted to carbon dioxide (CO
2
)
within 180 days at 30 °C with satisfactory disintegration after 12 weeks
and 90% of biodegradation in an active environment such as com-
posting. However, until now there is no replacement for this standard
clarifying these requirements but clearly in this experiment for all
materials, except for polyester, > 30% of the carbon was converted to
Fig. 9. Mass of microfibers generated during accelerated laundering (T = 25 °C, without detergent) vs A - Breaking Load of Yarns in Wet State and B - Weight Loss of
the fabrics after 20,000 cycles in the Martindale abrasion tester. Mean values are shown for all the variables.
Fig. 10. Mass of microfibers generated during accelerated laundering (T = 25 °C, with detergent) vs A - Breaking Load of Yarns in Wet State and B - Weight Loss of
the fabrics after 20,000 cycles in the Martindale abrasion tester. Mean values are shown for all the variables.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
403

CO
2
(Fig. 11).
With respect to the biodegradation of cellulosic fibers, rayon is ex-
pected to have a higher biodegradability than cotton due to the dif-
ferences in crystallinity, orientation and moisture regain of these fibers;
rayon has lower crystallinity and higher moisture regain than cotton
due to the antiparallel configuration of cellulose II within the rayon
fiber structure (Battista, 1950;Howsman, 1949;Niu et al., 2012;Park
et al., 2004)
.
The amorphous regions are easier to degrade, chemically
and enzymatically than crystalline regions in polymeric materials
(Mochizuki and Hirami, 1997). Nevertheless, in this study, the differ-
ence in the biodegradation percentage between the three types of cel-
lulosic materials was not significant. In the cellulosic samples, the
variability of the data could be related to the changes in the levels of
oxygen in the flasks that affect the behavior of the microorganisms. The
oxygen supply was not constant during the experiment, every week or
as needed the bottles were saturated with oxygen for 15 min using an
aquarium pump and air stones to diffuse the air in the test medium to
reach around 8 mg/L of dissolved oxygen. The differences in the oxygen
levels represent the oxygen consumed during the biodegradation pro-
cess to convert the organic carbon to CO
2.
The curves in Fig. 11 indicate that polyester and polyester/cotton
yarns had reached more of a plateau than did microcrystalline cellulose,
rayon, and cotton. In addition, 50/50 polyester/cotton yarns reached a
plateau phase at about 40% of biodegradation, as would be expected
from a weighted average of the polyester and cotton degradation re-
sults. As expected, only the cotton in the blend degraded during the
experiment, confirmed by FTIR (section S 2.4.4, Supplementary mate-
rial).
Polyester yarns did not degrade under the test conditions. The
biodegradation of polyester and cotton fabrics have also been tested
under the action of natural soil under aerobic laboratory controlled
conditions and a large scale composting facility (Li et al., 2010). After
90 days in natural soil, cotton fabrics without finishing agents achieved
around 23% of biodegradation and polyester fabrics only 13% (Li et al.,
2010). In composting, the cotton fabrics weight loss was 55% and
polyester fabrics only 20% in 90 days (Li et al., 2010). Moreover, the
normal microbial communities in the environment do not attach to
polyester (Bajpai et al., 2011). It has been shown that bacterial ad-
herence in polyester fabrics was low compared to cotton and polyester/
cotton blended fabrics (Bajpai et al., 2011). In addition, polyester is less
susceptible to fragmentation of the structure by hydrolysis due to its
high hydrophobicity and low moisture regain (Fuzek, 1985;Li et al.,
2010).
Herein, cotton spun yarns were completely disintegrated during
biodegradation. The rayon sample showed evidence of some partially
degraded small fibers in the suspension at the end of the experiment. In
the case of polyester, the yarns did not undergo significant changes. The
50/50 cotton/polyester blended yarn shows no intact cotton fibers after
biodegradation, in agreement with the FTIR results. Images of the re-
sidual solids and initial yarns are shown in the Supplementary material
(Figs. S29 and S30).
Despite the variation in the biodegradation data, these results are in
line with the behavior expected, that cellulose-based fibers are biode-
gradable. Cellulose-based fabrics release more microfibers in laun-
dering but they degrade readily in aerobic aquatic environments. More
research is needed to understand the flow of microfibers and improve
the removal efficiency in the WWTPs.
3.5. Environmental implications of microfibers from laundering
The efficiency of WWTPs in microplastics removal has been re-
ported to be higher than 98% (Lares et al., 2018;Magnusson and Norén,
2014;Talvitie et al., 2015). The microplastics are mainly retained in the
sewage sludge, nevertheless, most of these results were reported with
microplastics > 250 μm being analyzed (Lares et al., 2018;Magnusson
and Norén, 2014), only Talvitie et al. (2015) evaluated particles and
fibers > 20 μm in size.
Most of the microplastics (particles and fibers) are removed in pri-
mary and secondary treatment (clarification, sedimentation, and
aerobic bioreactors or activated sludge treatment) (Talvitie et al.,
2017b, 2015). Traditional tertiary treatments such as gravity sand fil-
ters, or biological filtration are very efficient to further remove mi-
croplastics after secondary treatment (Carr et al., 2016;Mintenig et al.,
2017;Talvitie et al., 2017b, 2015). In addition, advanced technologies
such as membrane bioreactors (0.4 μm pore size), rapid sand filters,
dissolved air flotation, and disc filters as tertiary treatments have the
potential to trap up to 99.9% of the microplastics escaping the sec-
ondary treatment (Lares et al., 2018;Talvitie et al., 2017a). Never-
theless, WWTPs are not designed to capture microplastics and these
advanced technologies are still not implemented in most of the pro-
cesses.
Without a doubt, WWTPs are a route for microplastics entering
aquatic environments. Despite the high removal efficiency, the high
volume of effluents discharged constantly to aquatic environments
Fig. 11. Biodegradation curves of the textile yarns used to knit the fabrics used for the laundering experiments. The percentage of biodegradation is based on the
oxygen uptake versus the theoretical oxygen demand. The error bars represent the standard error (n = 3 for all materials, except MCC with n = 1).
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
404

contribute significantly to the microplastic pollution problem. Talvitie
et al. (2017b) estimated, on average, 1.97 × 10
8
“microlitter”particles
per day are discharged into the Baltic Sea from wastewater effluent.
Taking into consideration the annual discharges of 12 WWTPs in Lower
Saxony (Germany), Mintenig et al. (2017) predicted a total discharge of
9×10
7
to 4 × 10
9
microplastics (particles and fibers) per WWTP an-
nually. In the US, Mason et al. (2016) estimated that the daily dis-
charges from a municipal WWTP ranged from around 50,000 up to
nearly 15 million particles. Likewise, Lares et al. (2018) forecasted that
approximately 1.0 × 10
7
and 4.6 × 10
8
microplastics were discharged
daily with the final effluent and digested sludge from the Kenklaver-
onniemi WWTP (Finland), respectively. These numbers vary depending
on the location, type of effluents, demand and capacity, the population
in the area, weather conditions, and type of treatment. In addition,
there is a lack of standardization on the methods used to collect and
identify these microplastics from the different points in the wastewater
treatment process that could cause over or underestimation of these
values. Another problem that needs to be considered is the transfer of
microplastics to agricultural soils by the use of WWTPs sludge as fer-
tilizer. In Europe, it was estimated that 63,000–430,000 tons of mi-
croplastics are applied to farmlands per year (Nizzetto et al., 2016). The
consequences in agricultural sustainability and human health of this
activity are also not well understood (Nizzetto et al., 2016).
In some wastewater effluents, microfibers represent an important
proportion of the microplastics found in the wastewater effluents (Lares
et al., 2018;Mason et al., 2016;Mintenig et al., 2017;Talvitie et al.,
2015, 2017a, 2017b). In general, it has been reported that these mi-
crofibers are predominantly made of polyester, and more specifically,
polyethylene terephthalate (PET) (Lares et al., 2018;Mintenig et al.,
2017;Talvitie et al., 2017a;Wolffet al., 2018;Ziajahromi et al., 2017).
In most of the WWTP assessments on microplastics, the removal
efficiency of cellulose-based fibers has been ignored. However, cellu-
lose-based fibers have been observed in the effluents of WWTPs (Lares
et al., 2018;Talvitie et al., 2017b, 2015; Ziajahromi et al., 2017).
Talvitie et al. (2017b) found that 30% of the microlitter collected from
the wastewater effluent was fibers and from that 66% was comprised of
cellulose-based fibers and 33% of the fibers were polyester fibers (PET).
Moreover, in this study, we observed that around 50% of the mi-
crofibers released during laundering were below 200 μmin size in all
the fabric types evaluated and that these particles still have the po-
tential to escape the wastewater treatment process. The smallest size
fractions are the most common microplastics (particles and fibers) ob-
served in the effluents of the WWTPs (10 μm–100 μm) (Mintenig et al.,
2017;Talvitie et al., 2017a, 2017b;Wolffet al., 2018). Nevertheless,
another study that analyzes larger microplastics (> 250 μm), including
fibers, also reported that > 50% of the microplastic recovered in the
effluents were smaller than 1 mm (Lares et al., 2018). In addition, Wolff
et al. (2018) reported that the microfibers recovered from the WWTP
effluents ranged between 100 μm and 1000 μm in length similar to the
results herein (Fig. 4).
Similarly, many studies that have been focused on the ecotoxicity of
micro and nanoplastics in marine and freshwater ecosystems overlap
with the size of the microfibers observed in our study, nevertheless
cellulose-based fibers were generally not considered (Chae and An,
2017). These studies observed various effects on the growth, develop-
ment, behavior, reproduction, and mortality of aquatic animals (Chae
and An, 2017). However, there is a lot of uncertainty about the sig-
nificance of these toxicity studies due to (1) the differences between
simulated lab conditions and environmentally relevant concentrations
of micro and nanoplastics, (2) the unknown long-term effects of these
small plastics on aquatic organisms, and (3) the possible effects on
human health from trophic transfer of micro and nanoplastics through
the food chain (Burton, 2017;Chae and An, 2017). Kosuth et al. (2018)
estimated that the average person ingests 5,800 synthetic particles,
such as synthetic microfibers, a year from tap water, beer, and sea salt
alone. However, only one study examined microplastics in stool
samples (Schwabl, 2018) with particles between 50 and 500 μm in size
observed in all the samples evaluated, 18 to 172 particles per 10 g of
stool. No fibers were reported, however, the microplastics were mainly
comprised of polypropylene (62.8%) and polyethylene terephthalate
(17%) (Schwabl, 2018).
The sorption mechanisms between microplastics/microfibers and
chemicals are controlled by the physical-chemical properties of the
materials, the nature of chemicals, temperature, and solution chemistry
(pH, salinity, etc.) (Wang et al., 2018). Synthetic microfibers such as
polyester being low surface energy materials will interact more strongly
with non-polar organic chemicals in a stronger way than will cellulose-
based microfibers. Natural based fibers have distinct surface chemis-
tries and have a different role in the environment; they may adsorb
different chemicals than do synthetic fibers (Grancaric et al., 2005). It is
therefore important to study microfibers throughout their life cycle,
including both the generation and environmental fate of these mate-
rials.
4. Conclusions
The shedding mechanism of microfibers from textiles and their
biodegradability are fundamental to understand how to reduce the
presence of these fibers in aquatic environments. In summary, all fiber
types released significant amounts of microfibers during laundering,
however, cellulose-based fabrics released more microfibers than
polyester with the same fabric structures. The fiber and yarn physico-
chemical properties play a major role in the microfiber generation.
Fabrics with higher abrasion resistance, low hairiness, and higher yarn
breaking strength have a lower tendency to form fuzz and/or release
microfibers during the mechanical action of washing. From the laun-
dering parameters studied, the use of detergent increases the generation
of microfibers, the surfactant promotes the mobilization process of fi-
bers from the fabric to the washing solution. In general, accelerated
laundering experiments results correlated with home laundering ex-
periments but accelerated laundering experiments were easier to con-
trol and had better sensitivity and repeatability. Despite the fact that
the cellulose-based fabrics shed more microfibers than the polyester
fabric, cotton and rayon fibers degrade in aquatic conditions whereas
polyester fibers do not and are expected to persist in the environment
for a long time. More research is needed to understand the fate of textile
microfibers and their additives in the environment.
Notes
The authors declare no competing financial interest.
Acknowledgments
Cotton Incorporated (United States) and the Cotton Research and
Development Corporation (Australia) financially supported this re-
search. We would like to thank Suzanne Holmes and Angela Massengill
from the Product Evaluation Laboratory and Tony Evans from the Color
Services Laboratory at Cotton Incorporated for their support with
training and equipment for the laundering experiments and mechanical
testing of yarns and fabrics. In addition, Harry Frost (University of
Surrey, UK) took the optical microscope images to complement the
hairiness data measurements. Moreover, the Neuse River Wastewater
Treatment Plant in Raleigh, NC, USA contributed with the activated
sludge used as a source of microorganisms for the biodegradation ex-
periments. Finally, Heather Starkey (NC State University) provided
support for the statistical analysis.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.marpolbul.2019.02.062.
M.C. Zambrano, et al. Marine Pollution Bulletin 142 (2019) 394–407
405

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