Point-source tracking of microplastics in sewerage systems. Finding the culprit.

Prior microplastic (MP) research has focused more on the efficiency of removal techniques within wastewater treatment plants (WWTP), with comparatively less emphasis placed on identifying and understanding the sources of MPs. In this study, the presence of MP in wastewater from various sources and their associated WWTPs was investigated. Utilising focal plane array micro Fourier Transform Infrared spectroscopy (FPA-µFTIR), the chemical composition, size distribution, and mass of MPs were quantified. Notably, wastewater generated from an industrial laundry facility exhibited the highest MP concentration of 6900 counts L-1 or 716 µg L-1. Domestic sewage contained MP levels (1534 counts L-1; 158 µg L-1) similar to those at the WWTPs (1640 counts L-1; 114 µg L-1). Polyester was identified as a significant component in most of the sources, predominantly originating from the shedding of fibres during textile washing. Additionally, a post-processing software was employed to compare two methods for fibre identification: aspect ratio and elongation ratio. These findings underscore the potential environmental impact of domestic activities and laundry washing on wastewater MP content.

Treating wastewater for microplastics to a level on par with nearby marine waters.

Retention of microplastics (MPs) at the third largest wastewater treatment plant (WWTP) in Sweden was investigated. The plant is one of the most modern and advanced of its kind, with rapid sand filter for tertiary treatment in combination with mechanical, biological, and chemical treatment. It achieved a significantly high treatment efficiency, which brought the MP concentration in its discharge on par with concentrations measured in marine waters of the same region. This novel data shows that properly designed modern WWTPs can reduce the MP content of sewage down to background levels measured in the receiving aquatic environment. Opposite to current understanding of the retention of MP by WWTPs, a modern and well-designed WWTP does not have to be a significant point source for MP. MPs were quantified at all major treatment steps, including digester inlet and outlet sludge. MPs sized 10-500 µm were analyzed by a focal plane array based micro-Fourier transform infrared (FPA-µFTIR) microscopy, a hyperspectral imaging technique, while MPs above 500 µm were analyzed by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Mass was estimated from the hyperspectral images for MPs <500 µm and from microscope images >500 µm. The overall treatment efficiency was in terms of MP counts 99.98 %, with a daily input of 6.42 × 1010 and output of 1.04 × 107 particles. The mass removal efficiency was 99.99 %. The mechanical part of the treatment, the pre-treatment, and primary stages, reduced both the MP counts and mass by approximately 71 %. The combined biological treatment, secondary settling, and final polishing with rapid sand filtration removed nearly all the remaining 29 %. MPs became successively smaller as they passed the different treatment steps. The digester inlet received 1.04 × 1011 MPs daily, while it discharged 9.96 × 1010 MPs, causing a small but not significant decrease in MP counts, with a corresponding MP mass reduction of 9.56 %.

Microplastics in the Indian and South Atlantic oceans translocate to gills, digestive glands, and muscle of the chokka squid Loligo reynaudii.

Comparative microplastic (MP) data for cephalopods between oceans is scarce. Our aim was to quantify, characterise, and compare MPs in gills, digestive gland, and mantle of chokka squid from the South Atlantic Ocean (SAO) and Indian Ocean (IO) off the coast of South Africa. South African squid had more MPs compared with other studies (means = 2.0 and 0.4 in SAO and IO squid mantle, respectively). Blue fibres were dominant. Identifiable MPs were polyethylene. Despite IO water having higher MP concentrations than the SAO, SAO squid had higher MP concentrations. Dilution by growth is the likely reason for the lower MP concentrations. Fibres were shorter in SAO than IO squid. However, we could not explain why fibre and mantle lengths from both oceans were positively correlated. Squid may not be the best indicator of marine MPs. The characteristics of MPs in squid can be used to track stocks and migrations.

Do drinking water plants retain microplastics? An exploratory study using Raman micro-spectroscopy.

The retainment of microplastics (MPs) down to 1 µm by a Danish drinking water plant fed with groundwater was quantified using Raman micro-spectroscopy (µRaman). The inlet and outlet were sampled in parallel triplicates over five consecutive days of normal activity. For each triplicate, approximately 1 m3 of drinking water was filtered with a custom-made device employing 1 µm steel filters. The MP abundance was expressed as MP counts per liter (N/L) and MP mass per liter (pg/L), the latter being estimated from the morphological parameters provided by the µRaman analysis. Hence the treated water held on average 1.4 MP counts/L, corresponding to 4 pg/L. The raw water entering the sand filters held a higher MP abundance, and the overall efficiency of the treatment was 43.2% in terms of MP counts and 75.1% in terms of MP mass. The reason for the difference between count-based and mass-based efficiencies was that 1-5 µm MP were retained to a significantly lower degree than larger ones. Above 10 µm, 79.6% of all MPs were retained by the filters, while the efficiency was only 41.1% below 5 µm. The MP retainment was highly variable between measurements, showing an overall decreasing tendency over the investigated period. Therefore, the plastic elements of the plant (valves, sealing components, etc.) likely released small-sized MPs due to the mechanical stress experienced during the treatment. The sub-micron fraction (0.45-1 µm) of the samples was also qualitatively explored, showing that nanoplastics (NPs) were present and that at least part hereof could be detected by µRaman.

Nanoplastic production procedure for scientific purposes: PP, PVC, PE-LD, PE-HD, and PS.

Studies on the environmental impact of nanoplastics face challenges in plastic analysis and a scarcity of nanoplastic materials necessary for the development of analytical techniques and experiments on biota impact. Here we provide detailed procedures for obtaining nanoparticles suspended in water for the most commonly used polymers: Polypropylene (PP), Polyvinylchloride (PVC), Low- and High-Density Polyethylene (PE-LD, PE-HD), and Polystyrene (PS). We dissolved larger size material to reprecipitate nanoparticles. For all plastic types, we obtained nanoparticles with a size between 50 and 300 nm, and a mainly spherical morphology. We verified that no irreversible agglomeration or coalescence of the particles occurred after 5 days of storage. The concentrations obtained in the final carrier solution were of the order of 109 particles mL-1. To prevent the persistence of reagents in the final carrier solution, a filtration step was implemented at the end of the process. The method proved unsuitable for Polyethylene Terephthalate (PET).

Abundance and distribution of microplastics in surface waters of the Kattegat/ Skagerrak (Denmark).

Microplastics (MPs) are ubiquitous pollutants in the ocean, and there is a general concern about their persistence and potential effects on marine ecosystems. We still know little about the smaller size-fraction of marine MPs (MPs <300 µm), which are not collected with standard nets for MPs monitoring (e.g., Manta net). This study aims to determine the concentration, composition, and size distribution of MPs down to 10 µm in the Kattegat/Skagerrak area. Surface water samples were collected at fourteen stations using a plastic-free pump-filter device (UFO sampler) in October 2020. The samples were treated with an enzymatic-oxidative method and analyzed using FPA-µFTIR imaging. MPs concentrations ranged between 11 and 87 MP m-3, with 88% of the MPs being smaller than 300 µm. The most abundant shape of MPs were fragments (56%), and polyester, polypropylene, and polyethylene were the dominant synthetic polymer types. The concentration of MPs shows a significant positive correlation to the seawater density. Furthermore, there was a tendency towards higher MPs concentrations in the Northern and the Southern parts of the study area. The concentration of MPs collected with the UFO sampler was several orders of magnitude higher than those commonly found in samples collected with the Manta net due to the dominance of MP smaller size fractions. Despite the multiple potential sources of MPs in the study area, the level of MPs pollution in the surface waters was low compared (<100 MP m-3) to other regions. The concentrations of MPs found in the studied surface waters were six orders of magnitude lower than those causing negative effects on pelagic organisms based on laboratory exposure studies, thus is not expected to cause any impact on the pelagic food web.

A complete mass balance for plastics in a wastewater treatment plant - Macroplastics contributes more than microplastics.

A complete plastic particle mass balance was established at Sweden's second-largest wastewater treatment plant. It comprised material collected at its two bar screens, a 20 mm and a 2 mm one, in the influent water after the 20 mm screen, the effluent water, and the digested sludge. Macro- and microplastics above 500 µm were analysed individually applying ATR-FTIR, while microplastics of 10-500 µm were analysed by µFTIR imaging with automated particle recognition. Masses of plastics >500 µm were determined by weighting, while the mass of the smaller microplastics was estimated from the imaging. The total plastic load on the plant was 202.2 kg d-1, of which the two screens retained 73%. The remaining plastic mass was found in the sludge (13.6%) and the effluent (0.4%). The missing 12.7% could be caused by sampling and measuring uncertainties and potentially also fragmentation below the size detection limit of the analytical approach, or by degradation. The bar screens furthermore retained plastics smaller than the screen size, indicating that this material should be taken into account also when solely looking at smaller particles. The overall treatment efficiency of the plant was high: 99.6% considering both macro- and microplastics, and 98.8% considering only microplastics <500 µm.

Drinking plastics? - Quantification and qualification of microplastics in drinking water distribution systems by µFTIR and Py-GCMS.

While it seems indisputable that potable water contains microplastics (MP), the actual concentrations are much debated and reported numbers vary many orders of magnitude. It is difficult to pinpoint the cause of these differences, but it might be variation between waters, variation between quantification methods, and that some studies did not live up to rigorous analytical standards. Despite the urgent need to understand human exposure by drinking water, there is a lack of trustable methods generating reliable data. Essentially, proper MP assessment requires that quality assurance is in place and demonstrated, that an adequate volume of drinking water is assessed, and that differences in analytical methods are understood. This study presents a systematic and robust approach where MP down to 6.6 µm were assessed in potable water distribution systems in terms of quantity, size, shape, and material. For the first time, sub-samples were analysed by two of the most validated and complementary analytical techniques: µFTIR imaging and Py-GCMS. Both methods successfully determined low contents in drinking water. However, µFTIR and Py-GCMS identified different polymer types in samples with overall low MP content. With increasing concentration of a given polymer type, the values determined by the techniques became more comparable. Most detected MPs were smaller than 150 µm, and 32% were smaller than 20 µm. Our results indicate a potential annual uptake of less than one MP per person, suggesting that drinking potable water produced at a high-performance drinking water treatment plant represents a low risk for human health.