The impact of fabric conditioning products and lint filter pore size on airborne microfiber pollution arising from tumble drying

Abstract

Vented tumble dryers release moist warm air from the drying process to the external environment, usually through pipework linking the appliance to a vent in an exterior wall. Although such dryers contain a lint filter to remove fibers from this air stream, recent reports suggest that this process is incomplete, leading to microfibers being released in the ducted warm air and subsequently polluting the external environment. Microfiber release from wash loads comprising 10 100% cotton and 10 100% polyester T-shirts (total load mass ratio 48% cotton, 52% polyester) was measured at different stages of the washing and drying process to compare the quantities of fibers released ‘down the drain’, collected in the dryer lint filter, and released to air from the tumble dryer. Testing under both European and North American washing conditions found that the quantities of microfibers released to air during tumble drying were significant and comparable to levels released ‘down the drain’ during washing. Use of conventional rinse-added liquid fabric conditioner increased microfiber accumulation on the dryer lint filter, with reduced release from the dryer exhaust observed at the highest fabric conditioner dose tested (21.6% and 14.2% reduction under North American and European conditions, respectively). Conventional liquid fabric conditioner did not significantly impact microfiber release from the washing machine, in line with previous studies. A fabric conditioner specially designed for anti-wrinkle performance reduced microfiber release from the dryer exhaust at all levels tested (by 17.6–35.6%, depending on dose), apparently by increasing the efficiency of microfiber accumulation in the lint filter. Tumble dryer sheets were also found to cause a reduction in microfiber release from the dryer exhaust (by 14.1–34.9%, depending on the dose/product), likely driven by collection of liberated fibers on the sheet during the drying process. The use of both antiwrinkle liquid fabric conditioner and dryer sheet enabled a 44.9% reduction in microfiber emissions from the dryer exhaust. In all studies, the fiber mass collected on the lint filter or emitted from the dryer exhaust was richer in cotton fibers (range 83.4–96.3% on the lint filter, 93.0–99.8% from the dryer exhaust) than the wash load composition (48% cotton). Moreover, fibers collected by the lint filter contained a higher proportion of polyester than emissions from the dryer exhaust (range 3.7–16.6% on the lint filter, 0.2–7.0% from the dryer exhaust). There is significant variation in the porosity of lint filters among installed vented tumble dryers. Single-variable testing of the impact of lint filter design concluded that reducing screen pore size significantly reduces airborne microfiber release during tumble drying; a reduction in lint filter pore size from 0.2 mm2 to 0.04 mm2 reduced release by 34.8%. As some lint filters have pore sizes of around 1 mm2, there is enormous scope to reduce microfiber release from dryers though improved lint filter design. However, it is suggested that a step-change in appliance design away from vented dryers to only fully-sealed condenser dryers might be necessary to eliminate the contribution of tumble drying to airborne microfiber pollution.

A Review of the Origins of Microplastics arriving at Wastewater Treatment Plants

“…They detected that 1000 g of cotton textiles can release an average of 42,000 fibres, whereas the PES ones up to 55,330 fibres during 15 min of use, concluding that the PES textiles can produce more microfibres than the cotton ones. In contrast, the results presented by Lant et al, (2022) found that the fibres collected in both lint filter and the mesh adhered to the dryer exhaust were mostly cotton. They highlighted the importance of the pore size of the lint filter, as they discovered that changing from 100 µm to 40 µm reduces up to 35% the release of fibres through the exhaust.…”

“…The concerns related to tumble dryers mainly focus on microfibre pollution in air and terrestrial environments, and the consequent human exposure to these airborne microplastics. The drying of clothes is typically done in three ways: 1) Outdoors, by hanging the textiles on a clothesline, 2) Indoors, without any mechanical intervention, using for example drying racks or, 3) Indoors, by using a tumble dryer (Lant et al, 2022). There are three types of tumble dryers: vented tumble dryers, condenser dryers and those with combined washing and drying functions.…”

“…The second type, the condenser dryer, is a sealed system that condenses the moisture from clothes and the water collected is emptied by the consumer or automatically drained away. Some combined washer/dryer appliances, however, do not have a lint filter, meaning that the accumulated fibres are released to the drainage pipe (Lant et al, 2022). The latter two types of tumble dryers could be a potential source for microplastic pollution to wastewater, as they rely on the disposal of collected debris to the drainage system.…”

“…Investigating if the temperature applied, clothing load or the spin-dry rate of the dryer are factors contributing to the shedding of fibres, regardless of the laundry products used, would also be of merit. Apart from testing PES and cotton textiles, more experiments involving mixed laundry loads of clothes (Lant et al, 2022) or with different percentage of fabrics should be undertaken. As laundry activities are very common, it is crucial to understand consumer behaviours and habits behind laundry activities.…”

Prevalence and characterisation of microfibres along the Kenyan and Tanzanian coast

“…A 2021 report showed that in the last two decades, global fibre production has increased from 58 million tonnes in 2000 to 109 million tonnes in 2020 (Textile Exchange, 2021). Microfibres are released from clothing during laundering (De Falco et al, 2019Lant et al, 2020), drying (Kapp and Miller, 2020;Lant et al, 2022) and normal wear (De Falco et al, 2020;Sheridan et al, 2020). These eventually end up in the air (Dris et al, 2017), on land (Zubris and Richards, 2005) and in aquatic environments mainly through wastewater treatment plants, run offs and atmospheric deposition (Browne, 2015).…”