Workers exposure to synthetic textiles microfibers

. The textile industry is one of the most polluting sectors, its contribution to the growing contamination with microfibers being of recent interest. Microfibers are an important part of microplastics, a real problem in our society. Textiles are dominated by synthetic fibres, generating microfibres as environmental contaminants. Exposure may also occur in the workplace, but fewer studies address this topic. Although synthetic microfibres toxicity is not fully understood, is accepted that their dimensions can influence health effects. This study analysed the length and diameter of 201 airborne polyester fibres sampled in the working environment of a textile factory. Phase contrast microscopic analysis was performed using NIOSH method 7400. Three size categories were considered for the length: small (≤ 10 µm), medium (10 - 100 µm) and large (≥ 100 µm). Four diameter categories: thin (≤ 1 µm), medium (≤ 2 µm) and thick (≤ 3 µm) were defined. Diameters over 3 microns were considered elongated microplastics. Results show that most of the fibres (93%) were less than 100 µ long (20.1% being less than 10 µ) and the fibres with 1µ diameter were predominant (42.8%) Such fibres may reach into the bronchial tree and even further, where they may cause health problems.


Introduction
The attention currently paid to microplastics -MP (plastic particles that are less than 5 mm in size) is a consequence of their extensive pollution, not only from industry but also from private sources.Many consumer goods are made of plastics that end up as waste.The textile industry has one of the highest impacts on the environment.Considering a global life cycle, in Europe, the textile sector had the fourth-highest impact on the environment and climate change in 2020.At the same time, this sector is the third biggest employer worldwide [1].The consumption of textiles in the EU 27 for 2010-2020 was estimated at several million tonnes per annum [1].The textile industry is dominated by synthetic fibres [2] that pollute even before becoming wastes, for example when various textile objects are cleaned in household washing machines [3].
Studies consider microfibers included in microplastics, in some cases fibres being the most numerous MPs [3,4].Exposure of humans to microplastics/ microfibers occurs directly, from the environment or through various consumer goods, like food.Exposure to airborne microplastics occurs both indoors and outdoors.Some studies [4,5,6] show that the concentration of microfibers in the indoor air is higher than that in the outdoor air.Many of these microfibers are synthetic or mixed fibers, with polyesters being among the most encountered ones [6,7].The size of microplastics may vary considerably between several microns and several thousand microns in the longest dimension.One study for indoor and outdoor airborne MPs measured the longest dimension between 2.40 and 2181.48 μm [7].The same study reported that, while 11.72% of all MPs were longer than 100 μm, 21.24% were less than 10 μm long.About the same size for length was found in another study for outdoor fibers [8].
The Romanian legislation [9] defines respirable fibers, regardless of their nature, as having a length >5µm, a diameter <3µm and an aspect ratio 3:1.Other sources also use such definition for asbestos and recommend it for other fibers, like glass fibers [10].Such dimensional criteria correspond to the fibers considered to involve greater health risks since they are more likely to penetrate the alveolar level of the lungs.However other dimensions are also recommended, like a length-to-width ratio equal to or greater than 5:1 [9] or ≤ 3.5µm in diameter & ≥ 10μm in length [11].It is generally acknowledged that dimensions influence to a great extent the behaviour of fibers, in general, and their toxicology.
There are studies that question the general opinion that only the smallest particles can reach deep into the lungs [9].The smallest particles may be indeed more likely to penetrate deep in the lungs but a faction of larger fibers may also reach and deposit into the lungs [12,13].There are also studies that have found fibers over 130 μm in length in lung tissues including malignant specimens [14].
The effects of inhaled synthetic microfibers is not yet known.Their dimensions influence their behaviour and the points they reach once they enter the organism.Their composition may also influence their effects since fibers are likely to carry dyes, mordants and other additives used for textiles.Various metals have been detected in clothes made of natural or synthetic fibers [15], including chromium, cadmium, lead nickel which are generally known for their potential to impair health.Some studies' results show that plastic microfibers may contribute to lung cancers [14], others show that such fibers, in particular nylon, can inhibit the repair of the cells coating the airways [16] but there are also studies that have shown toxicological effects on parameters such as oxidative stress (17), mitochondrial dysfunction (18) and genotoxicity (19).A study [20] showed the beginning of interstitial lung disease in the case of polypropylene flocking workers.Exposure to polystyrene and polypropylene microplastics may lead to pulmonary inflammation in mice [21].Another study on mice showed that the expression of inflammatory proteins (TGF-β and TNF-α) increased in the lung tissue, depending on the concentration [22].
Studies on exposure to microplastics and microfibers in the workplace are rather scarce.Occupational exposure to microfibers was studied mostly as regards asbestos or other several mineral fibers, natural or man made (e.g., glass fibers).Recent studies concerning exposure to microfibers used various types of sampling filters to collect polyamide and polypropylene in the workplace.These studies did not focus [23,24] on dimensional details, however, they provide the overall range of the fibers dimensions.The optical microscopy for Polyamide measurement of the collected fibers detected diameters of the fibre between 1-3 μm of these, 10 fibers had a length of less than 10 μm long [23].For polypropylene, the results show that the fiber diameters were between 1-3 μm and of these only 3 had a length of less than 10 μm [24].

Methods and materials
In this paper, the term micro fibers refer to fibers that have dimensions below one millimetre.The term is not used to designate the material identified by this trade name.
The airborne fibers were collected in the workplace of a textile factory during the waving of a polyester fabric using non-dyed 0.5 mm PES yarn.The fibers collection and their analysis were done according to NIOSH method 7400: 2019 "Asbestos and other fibers by PCM" [16].Active sampling was performed using a Gilian GilAir Plus air sampler with a conductive cowl on cassette.The fibers were collected using mixed cellulose ester filters, with 25mm diameter and 0.8 microns porosity.A number of 3 samples were taken in the proximity of the weaving machine, corresponding to the respiratory level of the operator.The medium air volume for the samples was 12.2 litres.
PES clothing was avoided during the sampling and analysis of the filters.
The study aimed at characterizing the main dimensions of the fibres: length and diameter.Three categories were defined for each of the studied dimensions.For the length, the categories were: small (≤ 10 µm), medium (10 -100 µm) and large (≥ 100 µm).For diameters, the categories were: thin (≤ 1 µm), medium (>1, ≤ 2 µm) and thick (>2, ≤ 3 µm) categories were defined.Diameters over 3 microns were considered elongated microplastics.The method does not allow to see fibers with a diameter smaller than 1 µm.
The sampled filters were transferred onto microscope slides and treated with triacetin (glycerol triacetate) for transparentisation and a more stable mounting.The samples covered with 25x25mm glass slides were analysed by phase contrast microscopy using a 10x ocular and a 50x phase objective.A Walton-Beckett reticule with a circular field of 100μm diameter (area = 0.00785 mm²) was used for fiber counting and measurement.Additionally, the samples were analysed and photographed using polarized light with a green filter.
A total number of 174 reticular fields in multiple focal planes were analysed.All fibers included (partially or totally) in the analysed reticular fields were counted and measured.

Results and discussions
A total number of 201 fibers were identified, measured and compared against the aspect criterion for respirable fibers used by the Romanian legislation [9] and by the NIOS 7400 method [10] i.e. 1:3 diameter to length ratio.A number of 194 fibers met the fiber criterion.
The fibers aspect was clear, with neat contours.On the filter, most of them were straight (especially the short and medium ones, but also some of the long fibers) or slightly curved.The longer ones had more intricate shapes as seen in Figure 1(a-d).As far as the length is concerned the most numerous fibers were those in the medium category (10 -100 µ), followed by the short ones, as seen in Table 1.Fibers with diameters smaller or equal to 1 µm were the most numerous while no fiber with a diameter bigger than 4 µm was identified, as seen in Table 2.As seen in Figure 2, most of the fibers were those in the medium categories both for the length (≤ 10 µm) and the diameter (>1, ≤ 2 µm).A share of 20.9 % of the fibres was ≤ 10 µm long with diameters ≤ 1 µm.

Fig. 2. Diameters of polyester fibres per length category
The results show that most of the airborne fibers collected while waving a polyester textile fabric had dimensions that allow them to penetrate into the bronchial tree and possibly even further.The most numerous categories of fibres had diameters small enough (>1, ≤ 2 µm) to enter deep into the lungs, down to the alveolar area.Their length (≤ 10 µm) would also allow them to get deep into the lungs while being problematic to clean.Most of the longer fibres (≥100 µm) had diameters ≤ 3 µm and although they are less likely to be respirable, such a situation is not totally excluded.Some studies show that fibers about 120-135 µm long were found deep in the lungs [9], such fibers being also identified in malignant lung tissues.
Considering the size of the fibers found in this study as well as their persistence it may be assumed they can contribute to the risks of occupational diseases.With the textile sector being one of the biggest employers [1] the potential risks to workers' health is even more concerning.

Conclusions
There is not much research regarding occupational exposure to microfibers.This study shows that such exposure is important because most of the fibres identified have dimensional characteristics that allow them to penetrate the lower parts of the respiratory system.Most of these fibers meet the diameter-to-length ratio of 1:3 criterion recommended by EU and USA authorities for fibers that are most relevant for human health.Moreover, most of these fibers also have a diameter of no more than 3 microns which makes them contributors to thoracic contamination.Exposure such as that indicated by the results of this study warns against the possibility of health effects even if the toxicological profile of microplastics/ microfibers still needs further research.
This research is carried out within the project:" Understanding exposure and toxicity of Micro-and Nano-Plastic contaminants in humans, POLYRISK" -Horizon 2020, Call: H2020-SC1-BHC-2018-2020" (Better Health and care, economic growth and sustainable health systems).

Fig. 1 .
Fig. 1.Polyester fibers were photographed with a camera connected to a trinocular polarised light microscope (green filter), and magnified 500 times.Fig 1.a) short, straight fiber; b) long straight fibres, c) loop long fiber, d) curved medium fiber Caption of the Figure 1.

Table 1 .
The number and percentage of fibers per lenght category.

Table 2 .
The number and percentage of fibers per diameter category