Contamination and removal efficiency of microplastics and synthetic fibres in a conventional drinking water treatment plant in Geneva, Switzerland

Although it is known that freshwater resources are contaminated with microplastics (MPs), still limited information is known about the efficiency of large drinking water treatment plants (DWTP) to remove microplastics. Moreover, reported concentrations of MPs in drinking water variates from some units to thousands of units per litre and the sampling volumes used for MPs analysis are generally heterogeneous and limited. The present study evaluates the removal of MPs and synthetic fibres in the main DWTP of Geneva, Switzerland, by considering large sampling volumes at different time intervals. Furthermore, contrary to other studies, this DWTP does not count with a clarification process before sand filtration and coagulated water is sent directly to sand filtration. In this study a distinction is made between microplastics as fragments, films, pellets, and synthetic fibres. Raw water and effluents of each filtering mass (sand and activated carbon filtration) are analysed for the presence of MPs and synthetic fibres with sizes ≥63 μm using infrared spectroscopy. Concentrations of MPs in raw water range from 25.7 to 55.6 MPs/m³ and in treated water from 0 to 4 MPs/m³, respectively. Results show that 70 % of MPs are retained during sand filtration and total removal is equal to 97 % in treated water after activated carbon filtration. Concentration of identified synthetic fibres is low (average value of 2 synthetic fibres/m³) and constant in all steps of water treatment. Chemical composition of microplastics and synthetic fibres is found more heterogeneous in raw water than after sand filtration and activated carbon filtration, indicating the persistence of some types of plastics (like polyethylene and polyethylene terephthalate) in water treatment processes. Heterogeneities in MP concentrations are observed from one sampling campaign to another, indicating significant variations of MP concentrations in raw water.

Examining the release of synthetic microfibres to the environment via two major pathways: Atmospheric deposition and treated wastewater effluent

Research on the discharge of synthetic microfibres to aquatic environments has typically focused on laundering, where fibres can be discharged via wastewater effluent. However emerging research suggests that microfibres generated during the wear of textiles in normal use could present a major, additional, pathway for microfibre pollution to the environment. This study aimed to quantify and compare the quantities of microfibre entering the marine environment via both these pathways; wastewater discharge and atmospheric deposition. Areas of high and low population density were also evaluated. Samples were collected in and around two British cities (Bristol and Plymouth) both of which are located on tidal waters. Fibres originating from the atmosphere were deposited at an average rate of 81.6 fibres m² d^-1 across urban and rural areas. Treated wastewater effluent contained on an average 0.03 synthetic fibres L^-1. Based on our results we predict ~20,000-500,000 microfibres could be discharged per day from the Wastewater Treatment Plants studied. When the two pathways were compared. Atmospheric deposition of synthetic microfibres appeared the dominant pathway, releasing fibres at a rate several orders of magnitude greater than via treated wastewater effluent. Potential options to reduce the release of microfibres to the environment are discussed and we conclude that intervention at the textile design stage presents the most effective approach. In order to guide policy intervention to inform the Plastics Treaty UNEA 5.2, future work should focus on understanding which permutations of textile design have the greatest influence fibre shedding, during both everyday use and laundering.

Controlling factors of microplastic fibre settling through a water column

Microplastic fibres are the most abundant microplastics in waterways worldwide. The settling of fibres is distinct from other particles because of their aspect ratio and shape. In this paper, we test the hypothesis that length, curliness, and settling orientation control the settling velocity of microplastic fibres in a suite of laboratory experiments. Using a Particle Tracking Velocimetry method, we measured the settling velocity of 683 polyester microplastic fibres of 1 to 4 mm in length. Experimental findings support our hypothesis that for microplastic fibre longer than 1 mm, changing settling orientation from horizontal to vertical can increase 1.7 times the settling velocity. Fibre curliness can significantly reduce the settling velocity, where a curly fibre 1.3 times longer than a straight fibre can settle 1.75 times slower. In contrast, short microplastic fibres (less than 1 mm) mostly settle horizontally, and their settling velocity is unaffected by curliness. The drag force exerting on settling microplastic fibres was analysed, and the sphere-equivalent diameter was found to be a good representation of microplastic fibre size to predict the drag coefficient. Measured settling velocity ranges between 0.1 and 0.55 mm/s and exhibits a slight increase with the increasing length of the fibres. This low-velocity range raises concerns that microplastic fibres can favour biological flocculation, form clustered aggregates with microorganisms, feed aquatic organisms and cause bioaccumulation at higher trophic levels.

Potential microplastic release from the maritime industry: Abrasion of rope

While land-based sources of plastic pollution have gained increasing attention in recent years, ocean-based sources have been less well studied. The aim of this study was to compare a variety of ropes (differing in age, wear surface and material) to quantify and characterise the production of microplastic during use. This was achieved by simulating, in laboratory and field experiments, rope hauling activity which is typically performed on board maritime vessels, such as fishing boats. Microplastic generation was quantified by collecting fragments that were released as a consequence of abrasion. Notably, we show that microplastic fragments generated from rope wear during use were characteristically irregular in shape, rather than fibrous such as those assigned to synthetic rope by previous studies. Therefore, we suggest that some of the plastic fragments found in the marine environment may have been falsely attributed to land-based sources but have in fact arisen form the abrasion of rope. Our research found that new and one-year old polypropylene rope released significantly fewer microplastic fragments (14 ± 3 and 22 ± 5) and less microplastic mass (11 ± 2 and 12 ± 3 μg) per metre hauled compared to ropes of two (720 ± 51, 247 ± 18 μg) or ten (767 ± 55, 1052 ± 75 μg) years of age. We show that a substantial amount of microplastic contamination is likely to directly enter the marine environment due to in situ rope abrasion and that rope age is an important factor influencing microplastic release. Our research suggests the need for standards on rope maintenance, replacement, and recycling along with innovation in synthetic rope design with the aim to reduce microplastic emission.

Antimony release from polyester textiles by artificial sweat solutions: A call for a standardized procedure

Polyester fibres are usually contaminated by antimony because of its use as a catalyst in the production of polyethylene terephthalate and as a flame retardant synergist in a variety of new and recycled polymers. The present study determined the release of antimony (at total concentrations ranging from about 125 to 470 μg g^-1) from polyester textile samples designed to be in contact with human skin using standard artificial sweat solutions (ISO 105-E04 and EN 1811). The study also examined the role of different experimental parameters on the release of the metalloid. Overall, and using the default parameters, between about 0.05 and 2% of total antimony (or 0.1-1 μg g^-1) was mobilized into artificial sweat. A reduction in time (from 24 to 12 h) and temperature (from 37 to 20 or 4 °C) and an increase in pH (from 5.5 to 7) resulted in a decline in antimony mobilization from textiles, while altering textile mass to solution volume and the presence of lactate had little impact on the results. Removal of a filtration step increased antimony mobilization but this was attributed to artefacts associated with release from microfibres during extract storage and analysis. In general, antimony mobilization was sufficiently repeatable using either EN 1811 or ISO 105-E04 but the latter is recommended for an assessment of antimony mobilization and potential exposure because its pH is closer to that of human sweat. Since the first fraction of either extractions mobilized the greatest quantity of antimony, exposure can be minimized by washing articles before use.

Assessment of bullet holes through the analysis of mushroom-shaped morphology in synthetic fibres: analysis of six cases

Textiles damage analysis is a very valuable tool in forensic investigations. However, to date, very little research has been carried out to understand the impact of bullet causing damages to clothing. According to the review of the most recent scientific papers, the frictional heating and crushing action of a bullet passing through synthetic fibres cause a unique transformation in their ends called mushroom-shaped morphology. In this study, the textile remains of six individuals executed during the first decade of the Chilean military dictatorship period (1973-1990) were analysed. The purpose was to examine their clothing in order to describe the fibre defects in the bullet holes. The fibres were directly observed using two different models of stereomicroscopy (MZ16A and EZ4D, Leica Microsystem Ltd., Wetzlar, Germany) and through a combination of transmitted, oblique and co-axial illumination (with Leica DFC500 Digital Camera), at × 230 and at a resolution of up to 840 Lp/mm. The mushroom-shaped morphology, along with rupturing of yarns, fibrillation or splitting of fibres, was observed in the bullet holes. Although the mushroom-shaped is a useful pattern for bullet hole identification in synthetic fibres, further research needs to be performed for developing a sounder interpretational framework of this type of forensic evidence.

Occurrence, Fate and Fluxes of Plastics and Microplastics in Terrestrial and Freshwater Ecosystems

Plastics and microplastics are nowadays ubiquitously found in the environment. This has raised concerns on possible adverse effects for human health and the environment. To date, extensive information exists on their occurrence in the marine environment. However, information on their different sources and their transport within and across different freshwater and terrestrial ecosystems is still limited. Therefore, we assessed the current knowledge regarding the industrial sources of plastics and microplastics, their environmental pathways and load rates and their occurrence and fate in different environmental compartments, thereby highlighting important data gaps which are needed to better describe their global environmental cycle and exposure. This study shows that the quantitative assessment of the contribution of the different major sources of plastics, microplastics and nanoplastics to aquatic and terrestrial ecosystems is challenged by some data limitations. While the presence of microplastics in wastewater and freshwater is relatively well studied, data on sediments and especially soil ecosystems are too limited. Moreover, the overall occurrence of large-sized plastics, the patterns of microplastic and nanoplastic formation from them, the presence and deposition of plastic particles from the atmosphere and the fluxes of all kinds of plastics from soils towards aquatic environments (e.g. by surface water runoff, soil infiltration) are still poorly understood. Finally, this study discusses several research areas that need urgent development in order to better understand the potential ecological risks of plastic pollution and provides some recommendations to better manage and control plastic and microplastic inputs into the environment.

Use of estuarine resources by top predator fishes. How do ecological patterns affect rates of contamination by microplastics?

This study assessed the seasonal patterns of habitat utilization, feeding ecology and microplastic contamination in different ontogenetic phases of sympatric snooks (Centropomus undecimalis and C. mexicanus) inhabiting a tropical estuary. More than 50% of snooks, in all ontogenetic phases, ingested microplastics (1.5 ± 0.1 and 1.4 ± 0.1 particles ind^-1). Juveniles migrated to nursery grounds in the upper estuary, during the early dry (C. undecimalis 6.5 ± 2.8 ind^-1) (p < 0.01) and early rainy seasons (C. mexicanus 4.1 ± 1.9 ind^-1). There, they fed mostly on invertebrates (Polychaeta) (p < 0.01), and became contaminated by microplastics (C. undecimalis: 0.8 ± 0.4 particles ind^-1; C. mexicanus: 1.7 ± 0.5 particles ind^-1). Sub-adults of both species forage principally in the estuarine habitats after shifting their diet from invertebrates (shrimps) in the upper reaches (1806.4 ± 1729.6 mg ind^-1) to pelagic fishes (R. bahiensis) in seaward habitats (2507.7 ± 1758.4 mg ind^-1). During feeding continues the contamination by microplastics (3.1 ± 0.8 part. ind^-1). Adults use the adjacent coastal as feeding and spawning grounds during the rainy season. In this phase, snooks are mostly piscivorous (R. bahiensis: up to 5303.8 ± 3213.4 mg ind^-1), but also ingest penaeid shrimp as complementary item (up to 175.9 ± 156.7). Microplastics contamination rates increased towards the adult phase, with maximum contamination coinciding with peaks of fish ingestion, suggesting trophic transfer of microplastics. The lower estuary and adjacent coastal zone were important contamination sites, especially during the rainy season (up to 3.1 ± 0.8 part. ind^-1) (p < 0.01), when fishery activities is intense and river basin runoff increases. Consequently, the availability of microplastics is higher during this time of year in the lower portion of the estuary. Snooks had similar prey preferences, but the use of different habitats along the life cycle of each species avoids overlaps in estuarine use and minimizes competition.

Microfibres from apparel and home textiles: Prospects for including microplastics in environmental sustainability assessment

Textiles release fibres to the environment during production, use, and at end-of-life disposal. Approximately two-thirds of all textile items are now synthetic, dominated by petroleum-based organic polymers such as polyester, polyamide and acrylic. Plastic microfibres (<5 mm) and nanofibres (<100 nm) have been identified in ecosystems in all regions of the globe and have been estimated to comprise up to 35% of primary microplastics in marine environments, a major proportion of microplastics on coastal shorelines and to persist for decades in soils treated with sludge from waste water treatment plants. In this paper we present a critical review of factors affecting the release from fabrics of microfibres, and of the risks for impacts on ecological systems and potentially on human health. This review is used as a basis for exploring the potential to include a metric for microplastic pollution in tools that have been developed to quantify the environmental performance of apparel and home textiles. We conclude that the simple metric of mass or number of microfibres released combined with data on their persistence in the environment, could provide a useful interim mid-point indicator in sustainability assessment tools to support monitoring and mitigation strategies for microplastic pollution. Identified priority research areas include: (1) Standardised analytical methods for textile microfibres and nanofibres; (2) Ecotoxicological studies using environmentally realistic concentrations; (3) Studies tracking the fate of microplastics in complex food webs; and (4) Refined indicators for microfibre impacts in apparel and home textile sustainability assessment tools.

Wastewater treatment plants as a pathway for microplastics: Development of a new approach to sample wastewater-based microplastics

Wastewater effluent is expected to be a pathway for microplastics to enter the aquatic environment, with microbeads from cosmetic products and polymer fibres from clothes likely to enter wastewater treatment plants (WWTP). To date, few studies have quantified microplastics in wastewater. Moreover, the lack of a standardized and applicable method to identify microplastics in complex samples, such as wastewater, has limited the accurate assessment of microplastics and may lead to an incorrect estimation. This study aimed to develop a validated method to sample and process microplastics from wastewater effluent and to apply the developed method to quantify and characterise wastewater-based microplastics in effluent from three WWTPs that use primary, secondary and tertiary treatment processes. We applied a high-volume sampling device that fractionated microplastics in situ and an efficient sample processing procedure to improve the sampling of microplastics in wastewater and to minimize the false detection of non-plastic particles. The sampling device captured between 92% and 99% of polystyrene microplastics using 25 μm-500 μm mesh screens in laboratory tests. Microplastic type, size and suspected origin in all studied WWTPs, along with the removal efficiency during the secondary and tertiary treatment stages, was investigated. Suspected microplastics were characterised using Fourier Transform Infrared spectroscopy, with between 22 and 90% of the suspected microplastics found to be non-plastic particles. An average of 0.28, 0.48 and 1.54 microplastics per litre of final effluent was found in tertiary, secondary and primary treated effluent, respectively. This study suggests that although low concentrations of microplastics are detected in wastewater effluent, WWTPs still have the potential to act as a pathway to release microplastics given the large volumes of effluent discharged to the aquatic environment. This study focused on a single sampling campaign, with long-term monitoring recommended to further characterise microplastics in wastewater.

Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging

The global presence of microplastic (MP) in aquatic ecosystems has been shown by various studies. However, neither MP concentrations nor their sources or sinks are completely known. Waste water treatment plants (WWTPs) are considered as significant point sources discharging MP to the environment. This study investigated MP in the effluents of 12 WWTPs in Lower Saxony, Germany. Samples were purified by a plastic-preserving enzymatic-oxidative procedure and subsequent density separation using a zinc chloride solution. For analysis, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FT-IR) and focal plane array (FPA)-based transmission micro-FT-IR imaging were applied. This allowed the identification of polymers of all MP down to a size of 20 μm. In all effluents MP was found with quantities ranging from 0 to 5 × 10¹ m^-3 MP > 500 μm and 1 × 10¹ to 9 × 10³ m^-3 MP < 500 μm. By far, polyethylene was the most frequent polymer type in both size classes. Quantities of synthetic fibres ranged from 9 × 10¹ to 1 × 10³ m^-3 and were predominantly made of polyester. Considering the annual effluxes of tested WWTPs, total discharges of 9 × 10⁷ to 4 × 10⁹ MP particles and fibres per WWTP could be expected. Interestingly, one tertiary WWTP had an additionally installed post-filtration that reduced the total MP discharge by 97%. Furthermore, the sewage sludge of six WWTPs was examined and the existence of MP, predominantly polyethylene, revealed. Our findings suggest that WWTPs could be a sink but also a source of MP and thus can be considered to play an important role for environmental MP pollution.

A quantitative analysis of microplastic pollution along the south-eastern coastline of South Africa

The extent of microplastic pollution (<5mm) in the southern hemisphere, particularly southern Africa, is largely unknown. This study aimed to evaluate microplastic pollution along the south-eastern coastline of South Africa, looking at whether bays are characterised by higher microplastic densities than open stretches of coastline in both beach sediment and surf-zone water. Microplastic (mean ± standard error) densities in the beach sediment ranged between 688.9 ± 348.2 and 3308 ± 1449 particles · m(-2), while those in the water column varied between 257.9 ± 53.36 and 1215 ± 276.7 particles · m(-3). With few exceptions there were no significant spatial patterns in either the sediment or water column microplastic densities; with little differences in density between bays and the open coast (P>0.05). These data indicate that the presence of microplastics were not associated with proximity to land-based sources or population density, but rather is governed by water circulation.