Microplastics pollution in different aquatic environments and biota: A review of recent studies

Microplastics (MPs) are generated from plastic and have negative impact to our environment due to high level of fragmentation. They can be originated from various sources in different forms such as fragment, fiber, foam and so on. For detection of MPs, many techniques have been developed with different functions such as microscopic observation, density separation, Raman and FTIR analysis. Besides, due to ingestion of MPs by wide range of marine species, research on the effect of this pollution on biota as well as human is vital. Therefore, we comprehensively reviewed the occurrence and distribution of MPs pollution in both marine and freshwater environments, including rivers, lakes and wastewater treatment plants (WWTPs). For future studies, we propose the development of new techniques for sampling MPs in aquatic environments and biota and recommend more research regarding MPs release by WWTPs.

S. Rezania, J. Park, M. F. Md Din and al., Marine Pollution Bulletin, Volume 133, August 2018, Pages 191-208

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Application of an enzyme digestion method reveals microlitter in Mytilus trossulus at a wastewater discharge area

The ingestion of microlitter by blue mussels (450) was studied at a wastewater recipient area in the Baltic Sea. The mussel soft tissues were digested using enzymatic detergents and the detected litter particles characterized with FT-IR imaging spectroscopy. Microlitter concentration in seawater and WWTP effluent were also measured. Microlitter was found in 66% of the mussels. Mussels from the WWTP recipient had higher microlitter content compared to those collected at the reference site. Plastics made up 8% of all the analysed microlitter particles. The dominating litter types were fibres (~90% of all microlitter), 42% of which were cotton, 17% linen, 17% viscose and 4% polyester. The risk of airborne contamination during laboratory work was lowered when mussels were digested with their shells on instead of dissecting them first. The approach was found applicable and gentle to both non-synthetic and synthetic materials including fragile fibres.

Saana Railo, Julia Talvitie, Outi Setälä and al., Marine Pollution Bulletin, Volume 130, May 2018,  Pages 206–214

The article

Removal of Microbeads from Wastewater Using Electrocoagulation

The need for better microplastic removal from wastewater streams is clear, to prevent potential harm the microplastic may cause to the marine life. This paper aims to investigate the efficacy of electrocoagulation (EC), a well-known and established process, in the unexplored context of microplastic removal from wastewater streams. This premise was investigated using artificial wastewater containing polyethylene microbeads of different concentrations. The wastewater was then tested in a 1 L stirred-tank batch reactor. The effects of the wastewater characteristics (initial pH, NaCl concentration, and current density) on removal efficiency were studied. Microbead removal efficiencies in excess of 90% were observed in all experiments, thus suggesting that EC is an effective method of removing microplastic contaminants from wastewater streams. Electrocoagulation was found to be effective with removal efficiencies in excess of 90%, over pH values ranging from 3 to 10. The optimum removal efficiency of 99.24% was found at a pH of 7.5. An economic evaluation of the reactor operating costs revealed that the optimum NaCl concentration in the reactor is between 0 and 2 g/L, mainly due to the reduced energy requirements linked to higher water conductivity. In regard to the current density, the specific mass removal rate (kg/kWh) was the highest for the lowest tested current density of 11 A/m2, indicating that low current density is more energy efficient for microbead removal.

William Perren, Arkadiusz Wojtasik, and Qiong Cai, CS Omega, 2018, 3 (3), pp 3357–3364, March 20, 2018

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Danish study finds understanding of microplastics ‘extremely defective’

The research, carried out by the Danish Technological Institute with environmental consultancy group COWI, looked at existing techniques for measuring microplastics, to see how challenges in sampling, sample treatment and analyses could be used to develop new methods.

In order to tackle and quantify the problem, a standardised analytical method needs to be developed to measure the smallest particles, their report says.

It found that the most commonly used analysis method – light microscopy – is unable to analyse particles smaller than 100μm, or determine microplastic types.

The report identifies the “great differences” in the types and size of microplastics being discharged from wastewater treatment plants. The problem is that analysis is often only able to focus on larger particles, it says. (…) (chemicalwatch.com, 16/01/2018)

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Micro- and Nanoplastic Pollution of Freshwater and Wastewater Treatment Systems

Plastic waste is a widespread and persistent global challenge with negative impacts on the environment, economy, human health and aesthetics. Plastic pollution has been a focus of environmental research over the past few decades, particularly in relation to macroplastics that are easily visible by the naked eye. More recently, smaller plastic waste at the micro- and nanoscale has become of increasing concern, resulting in extensive investment in research to advance knowledge on the sources, distribution, fate and impact of these materials in aquatic systems. However, owing to their small sizes and a lack of unified methods, adequate quantitative and qualitative assessment has been difficult. Furthermore, most of the microplastic surveys available to date have focussed in the marine environment while scarce knowledge exists of freshwater systems. Because the majority of marine debris originates on land, the role of wastewater treatment systems and natural fluvial vectors in delivering these emerging contaminants to the environment should be explored. Considering fundamental aspects pertaining to microplastic sources, distribution, mobility and degradation in these systems is crucial for developing effective control measures and strategies to mitigate the discharge of these particles to the sea.

Reina M. Blair, Susan Waldron, Vernon Phoenix, Caroline Gauchotte-Lindsay, Environmental Science and Pollution Research, 07 June 2017, pp 1–7

The article

Freshwater’s macro microplastic problem

Like in the oceans, the bulk of the pollution in rivers and lakes is not in the form of plastic bottles and other large pieces, but tiny pieces called microplastics that would be hard to spot. “Three quarters of what we take out of the Great Lakes are less than a millimeter in size,” she says. “It’s basically the size of a period of a sentence.” These plastics are concerning to scientists because they are being ingested by a variety of aquatic organisms. (…) (pbs.org, 11/05/2017)

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How well is microlitter purified from wastewater? – A detailed study on the stepwise removal of microlitter in a tertiary level wastewater treatment plant

Wastewater treatment plants (WWTPs) can offer a solution to reduce the point source input of microlitter and microplastics into the environment. To evaluate the contributing processes for microlitter removal, the removal of microlitter from wastewater during different treatment steps of mechanical, chemical and biological treatment (activated sludge) and biologically active filter (BAF) in a large (population equivalent 800 000) advanced WWTP was examined. Most of the microlitter was removed already during the pre-treatment and activated sludge treatment further decreased the microlitter concentration. The overall retention capacity of studied WWTP was over 99% and was achieved after secondary treatment. However, despite of the high removal performance, even an advanced WWTP may constitute a considerable source of microlitter and microplastics into the aquatic environment given the large volumes of effluent discharged constantly. The microlitter content of excess sludge, dried sludge and reject water were also examined. According to the balance analyses, approximately 20% of the microlitter removed from the process is recycled back with the reject water, whereas 80% of the microlitter is contained in the dried sludge. The study also looked at easy microlitter sampling protocol with automated composite samplers for possible future monitoring purposes.

Julia Talvitie, Anna Mikola, Outi Setälä, Mari Heinonen, Arto Koistinen, Water Research, Volume 109, 1 February 2017, Pages 164–172

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