Microplastics in seawater and zooplankton: A case study from Terengganu estuary and offshore waters, Malaysia

Pervasive occurrence of microplastics in Hudson-Raritan estuary zooplankton

Microplastics (MP) are considered emerging contaminants in the water environment, and there is an interest in understanding their entry into the food web. As a growing body of literature demonstrates the ingestion of MP by zooplankton in controlled laboratory studies, few data are available demonstrating in situ observations of MP in zooplankton. A field survey was performed to collect zooplankton in the highly urbanized Hudson-Raritan estuary. Following washing, sorting by species, and enumeration, three dominant species of copepods (Acartia tonsa, Paracalanus crassirostris and Centropages typicus) were digested. MP were filter concentrated and characterized by size, morphology, and color via microscopy and polymer type by micro-FTIR imaging and/or Raman spectroscopy. MP were observed in all extracts performed on the three copepod species with averages ranging from 0.30 to 0.82 MP individual^-1. Polyethylene and polypropylene were the dominant polymer types observed and fragments and beads the most commonly observed morphologies for MP. These data were used to estimate the flux of MP through zooplankton based on gut turnover times, which we compare to estimates of MP entering this environment though the local waterways. The estimated fluxes were sufficiently large, indicating that ingestion by zooplankton is a major sink of MP in the size range subject to zooplankton feeding in surface estuarine waters.

Microplastics in copepods reflects the manmade flow restrictions in the Kochi backwaters, along the southwest coast of India

This baseline study on microplastics (MPs) in calanoid copepods in the Kochi backwaters (KBW), India's largest estuary system on the west coast, focuses on (a) the spatiotemporal variations of MPs with the seasonal hydrography setting, and (b) how man-made flow restrictions of a large saltwater barrage contribute to MPs in copepods and their potential to transfer to higher trophic levels. This study found that MPs in copepods in the KBW ranged from av. 0.01 ± 0.014 to 0.11 ± 0.03 no./ind. seasonally. When the saltwater barrage shutters were fully/partially closed during the Pre-monsoon/Northeast Monsoon, MPs in copepods were considerably larger (av. 0.11 ± 0.03 no./ind., and av. 0.075 ± 0.02 no./ind., respectively) as compared to the Southwest Monsoon (av. 0.03 ± 0.01 no./ind.), when the barrage shutters were fully open. This shows the potential of man-made flow restrictions to increase the bioconcentration of MPs in copepods and their possible transfer to higher trophic levels through the food chain, adding to the region's previous discovery that much higher trophic level resources are polluted with a high concentration of MPs.

Distribution and characteristics of microplastics in beach sand near the outlet of a major reservoir in north Mississippi, USA

Plastic debris both affects and is affected by the beaches it accumulates on. Most studies of microplastics (MPs) in beach sand are focused on coastal beaches or beaches of large lakes near population centers. Here, we assessed MP pollution at a sandy beach near the outlet of a major flood control reservoir (Sardis Lake) in a relatively unpopulated area in north Mississippi, USA, focusing on two prominent wrack zones and areas in-between. Putative MPs were isolated by density separation and matrix digestion, and then examined using stereomicroscopy, with a subset of samples additionally analyzed by μ-FTIR. MP abundance (particles/kg ± 1 standard error (SE), n = 15) averaged of 590 ± 360, with 950 ± 100 in the lower wrack zone, 540 ± 40 in the upper wrack zone, and 270 ± 30 in areas between; these differences were statistically significant (p < 0.01). The MPs generally had similar size and shape characteristics across sites. The majority were fibers (64%), followed by fragments (23%), beads (7%) and films (6%), with a slightly greater proportion of fibers in the wrack zones compared to areas in-between. The number of MPs rose dramatically with decreasing size. Beads were only found in the < 500 μm size fraction. Clear and blue were the predominant colors for all MPs. A total of 29 different types of polymers were detected, with more than half of the particles being composed of polyethylene and polyamide, followed by poly(methyl methacrylate), polyethylene terephthalate, polycarbonate, polypropylene, and others; although this distribution varied some depending on size fraction and location. Because there are no major wastewater discharges into Sardis Lake, the source of the MPs is likely degradation of carelessly discarded plastic, as well as atmospheric fallout. Overall, we found that MP concentrations were highest in the wrack zones and influenced by rates and duration of discharge from the reservoir. Thus, like coastal beaches, wrack zones on freshwater beaches along or downstream of reservoirs accumulate both macro- and micro-plastics and are prime locations for plastic cleanup. Finally, we show that MPs made from naturally weathered LDPE plastic film are prone to fragmentation during pretreatment procedures, which may result in its overestimation.

Ingestion of polyethylene microspheres occur only in presence of prey in the jellyfish Aurelia aurita

Microplastic ingestion was studied in A. aurita, a bloom-forming, circumglobal medusa. Here, we determined whether factors such as the concentration of polyethylene microspheres (75-90 μm) or the absence/presence of prey affect the ingestion, duration of microspheres in the gastrovascular cavity (time of presence), and retention time. The presence of polyethylene microspheres' was determined by exposing medusae during 480 min to three different treatments (5000, 10,000, 20,000 particles L^-1), and was checked every 10 min to ascertain whether they had incorporated any. Preliminary results show that microsphere ingestion occurred only in the presence of prey (⁓294 Artemia nauplii L^-1). The time of presence of microbeads in A. aurita increased (103, 177, and 227 min), with increasing microplastic concentration, and the microbeads were egested within 150 min. This study initiates the understanding of the potential implications that arise of the encounter between jellyfish and microplastic agglomerates, and with perspectives for future research.

Nutritional-status dependent effects of microplastics on activity and expression of alkaline phosphatase and alpha-amylase in Brachionus rotundiformis

Tissue-nonspecific alkaline phosphatase (ALPL) and alpha-amylase (AMY) are essential in the immune and digestive systems, respectively. Microplastics (MPs) pose a risk to zooplankton which may be in a state of feeding, starvation, or subsequent refeeding. However, molecular characterization of both enzymes and the regulated mechanisms affected by nutritional statuses and MPs remain unclear in zooplankton. In the present study, four full-length genes encoding ALPL and two genes encoding AMY were cloned and characterized from an isolated marine rotifer, Brachionus rotundiformis, including alplA, alplB, alplC, alplD, amy2a, and amy2al. AMY activity and expression of amy2a and amy2al were reduced by starvation and recovered after refeeding compared with feeding. ALPL activity remained unchanged among different statuses, while alplA, alplB and alplD were down-regulated by starvation and refeeding compared with feeding. ALPL activity was not affected by exposure to 10, 100 and 1000 μg/L MPs in rotifers subjected to feeding, starvation and refeeding, whereas AMY activity was significantly enhanced by 1000 μg/L MPs in rotifers subjected to refeeding. Gene expression of the tested genes, except amy2a, was significantly responsive to MPs, especially in the feeding rotifers, depending on MPs concentrations and nutritional statuses. Two-way ANOVA confirmed that these changes were strongly associated with the interaction between MPs concentrations and nutritional statuses. The present study is the first to demonstrate a nutritional status-dependent impact of MPs on immune and digestive responses, and provides more sensitive molecular biomarkers for assessing MPs toxicity using the species as model animals.

Microplastic ingestion and egestion by copepods in the Black Sea

Ingestion and egestion of microplastics by copepods in the Black Sea was assessed for the first time. Composition and concentration of microplastics in the water column was also evaluated. Samples were collected from three stations (river mouth, coastal and open water) in the Southeastern Black Sea over the course of one year. Microplastic concentration in the water column ranged between 0.12 and 7.62 mp·m^-3 (mean 2.04 ± 1.05 mp·m^-3) with significantly higher concentrations in the river mouth. The most common types of microplastics were fibres, followed by films and fragments. A total of 11 colours of microplastics were found, being blue the most common colour. Analysis of 1126 C. euxinus and 1065 A. clausi, resulted in 26 and 9 microplastics being detected, respectively. This resulted in a microplastic ingestion of 0.024 ± 0.020 mp. Calanus^-1 and 0.008 ± 0.006 mp. Acartia^-1. Analysis of 351 faecal pellets, resulted 4 microplastics being found. The average size of ingested microplastics was greater in C. euxinus (0.100 mm ± 0.153 mm) than in A. clausi (0.062 mm ± 0.056 mm). Size of ingested microplastics was in the size range of natural preys of these copepods. Fragments were the most common type of ingested microplastics, followed by films and fibres. The colour of ingested particles was black, blue and red. Our results show that the copepods and the pelagic environment of the Black Sea are contaminated by microplastics. Critical functions of zooplankton in this degraded ecosystem are under risk and zooplankton are likely to act as a vector for the transfer of microplastics and associated toxic chemicals to upper trophic levels including humans in the Black Sea.

Effects of polystyrene microplastic on the growth and volatile halocarbons release of microalgae Phaeodactylum tricornutum

Volatile halocarbons (VHCs) are trace greenhouse gases that can damage the ozone layer. Trihalomethanes are one of the most common VHCs and play an important role in global climate change. Due to their steadily increasing abundance, microplastics pollutants have attracted growing concern from scientists. However, their impacts on the growth of marine microalgae and the release of VHCs remain unknown. The influence of polystyrene microplastic (PS, 0.1 μm) at different concentrations (25-200 mg/L) on the growth of P. tricornutum and their release of trihalomethanes were studied over 96 h. The results showed that PS can inhibit P. tricornutum growth. At 200 mg/L PS, cell growth, chlorophyll a concentration and photosynthetic efficiency of P. tricornutum were inhibited by 53.53%, 25.45% and 12.50%, respectively. PS concentrations of 25-50 mg/L promoted the release of the three trihalomethanes by P. tricornutum during the 96 h culture as a response to oxidative stress. However, 100-200 mg/L PS severely altered the physiological state of the P. tricornutum cells after 48 h, which reduced the release of trihalomethanes. Our study also demonstrated that the production and release of trihalomethanes served as a protective mechanism against oxidative stress and the toxic effects caused by PS.

Microplastic pollution in surface seawater and beach sand from the shore of Rayong province, Thailand: Distribution, characterization, and ecological risk assessment

The distribution, characteristics, and ecological risk of microplastics in beach sand and seawater samples collected along the shore of Rayong province, Thailand, were investigated in this study. The average microplastics abundance in beach sand and seawater was 338.89 ± 264.94 particles/kg d.w. and 1781.48 ± 1598.36 particles/m³, respectively. Beach sand and seawater had the most yellow-brown particles and transparent microfibers, respectively. The most common microplastics (100-500 μm) and polyethylene were found. In beach sand, the potential ecological risk (RI) is classified as minor, while in seawater, it is classified as medium. The PLI_zone in beach sand and seawater was Hazard Level II and Hazard Level IV, respectively. Despite their apparent proximity, the non-correlation between risk levels in beach sand and seawater may be due to polymer type variations influenced by the different land-based and sea-based sources.

Challenges and opportunities in bioremediation of micro-nano plastics: A review

Rising level of micro-nano plastics (MNPs) in the natural ecosystem adversely impact the health of the environment and living organisms globally. MNPs enter in to the agro-ecosystem, flora and fauna, and human body via trophic transfer, ingestion and inhalation, resulting impediment in blood vessel, infertility, and abnormal behaviors. Therefore, it becomes indispensable to apply a novel approach to remediate MNPs from natural environment. Amongst the several prevailing technologies of MNPs remediation, microbial remediation is considered as greener technology. Microbial degradation of plastics is typically influenced by several biotic as well as abiotic factors, such as enzymatic mechanisms, substrates and co-substrates concentration, temperature, pH, oxidative stress, etc. Therefore, it is pivotal to recognize the key pathways adopted by microbes to utilize plastic fragments as a sole carbon source for the growth and development. In this context, this review critically discussed the role of various microbes and their enzymatic mechanisms involved in biodegradation of MNPs in wastewater (WW) stream, municipal sludge, municipal solid waste (MSW), and composting starting with biological and toxicological impacts of MNPs. Moreover, this review comprehensively discussed the deployment of various MNPs remediation technologies, such as enzymatic, advanced molecular, and bio-membrane technologies in fostering the bioremediation of MNPs from various environmental compartments along with their pros and cons and prospects for future research.

Occurrence, potential sources and ecological risk estimation of microplastic towards coastal and estuarine zones in Malaysia

Extensive global plastic production has led to microplastic (MP) pollution of marine ecosystems. This study analysed the abundance of MPs in the surface water of tropical coastal and estuarine zones in Malaysia affected by rapid urbanisation and intense human activity. It also estimated the risk posed by MPs to the marine environment. Mean MP abundance ranged from 2.10 to 6.80 particles/L. Fourier-transform infrared spectroscopic analysis found that the MP polymers were dominated by cellophane (54%), followed by polyester (33%) and polyethylene (2%). The risk posed by MPs was estimated with the risk quotient (RQ) method which found no potential ecological risk to both coastal and estuarine areas (RQ < 1). This study will serve as a baseline for future monitoring of MP pollution of marine water to assess the impact of heavily urbanised coastal and estuarine zones.

Microplastics in zooplankton in the eastern Arabian Sea: The threats they pose to fish and corals favoured by coastal currents

The baseline study of Microplastics (MPs) in zooplankton (copepods, chaetognaths, decapods, and fish larvae) from six different zones along India's west coast (off Kanyakumari/Cape Comorin, Kochi, Mangalore, Goa, Mumbai, and Okha) in the Eastern Arabian Sea (EAS) is presented here with their vast ecosystem impacts. This investigation revealed that zooplankton in all six zones accumulated MPs pellets (52.14%), fibres (28.40%), films (10.51%), and fragments (8.95%). The highest average retention of MPs (MPs/individual) was found in fish larvae (av. 0.57 ± 0.18) while copepods had the lowest (av. 0.03 ± 0.01). The presence of low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate was confirmed by Raman Spectra of MPs. The MPs in zooplankton found in this study (av. 22 ± 7 pieces/m³) were nearly 2-fold greater than those found in some of the world's most densely populated areas. It is shown that the strong southerly coastal currents could advect the MPs contaminated water mass too far away, having the potential to affect the fish and corals.

Concentration of microplastics in bivalves of the environment: a systematic review

The aim of this review was to identify the current knowledge regarding the concentration of microplastics in bivalves in the marine, estuarine, and freshwater environments. For this purpose, researches were conducted from September 2020 to February 2021 in the Scopus, Web of Science, and Google scholar databases, following a meticulous selection of articles. To comprehensively understand the selected articles, an extensive review was carried out in order to identify the methodologies employed, sampling sites, species evaluated, characteristics of the microplastics (concentrations, shapes, sizes, and polymers) and their relationship with the concentration of this particles in the environment. A total of 93 articles were selected, with an exponential growth in the number of articles from April 2014 to February 2021. Worldwide, 80 articles were realized in the Northern Hemisphere and thirteen in the Southern Hemisphere. The samplings of organisms were carried out in 36 countries, besides one in Antarctica. The concentration of microplastics were studied in 70 species, with mussels Mytilus spp. and the oysters Crassostrea spp. being the main genus studied. Due to the different methodologies used to digest the tissues of organisms and identify microplastics and species, it is difficult to make comparisons between the results of different studies. In addition, data on the concentrations of microplastics in the environment, as well as their composition and characteristics, are needed, enabling the verification of relationships with the concentrations identified in organisms, which does not occur in most studies. Thus, we suggest an increase in the number of studies to be realized in the southern hemisphere, future studies use the same methodology of digestion, the polymer identification of microplastics and samplings of the surrounding environment, enabling a greater comparison between studies.

Removal of microplastics from wastewater through electrocoagulation-electroflotation and membrane filtration processes

Wastewater treatment plants (WWTPs) are one of the major vectors of microplastics (MPs) pollution for the recipient water bodies. Therefore, the recovery of MPs from WWTPs is extremely important for decreasing their accumulation and impact in aquatic systems. In this present study, the electrocoagulation-electroflotation (EC/EF) and membrane filtration processes were investigated in removing MPs from wastewaters. The effectiveness of different electrode combinations (Fe-Al and Al-Fe), current density (10-20 A/m²), pH (4.0-10.0) and operating times (0-120 min) on the removal of two different polymer particles in water were investigated to obtain maximum treatment efficiency. The effect of pressure (1-3 bar) on membrane filtration removal efficiency was also investigated. The maximum removal efficiencies were obtained as 100% for both polymer types with electrode combination of Al-Fe, initial pH of 7, current density of 20 A/m² and reaction time of 10 min. The membrane filtration method also displayed a 100% removal efficiency. In addition, these laboratory-scale results were compared with the one-year average data of a plant treating with real-scale membranes. The results indicated that the proposed processes supplied maximum removal efficiency (100%) compared to conventional secondary and tertiary treatment methods (2-81.6%) in the removal of microplastics.

Disparities in Methods Used to Determine Microplastics in the Aquatic Environment: A Review of Legislation, Sampling Process and Instrumental Analysis

Plastic particles smaller than 5 mm, i.e., microplastics, have been detected in a number of environments. The number of studies on microplastics in marine environments, fresh water, wastewater, the atmosphere, and the human body are increasing along with a rise in the amounts of plastic materials introduced into the environment every year, all contributing to a range of health and environmental issues. Although the use of primary microplastics has been gradually reduced by recent legislation in many countries, new knowledge and data on these problems are needed to understand the overall lifecycle of secondary microplastics in particular. The aim of this review is to provide unified information on the pathways of microplastics into the environment, their degradation, and related legislation, with a special focus on the methods of their sampling, determination, and instrumental analysis. To deal with the health and environmental issues associated with the abundance of microplastics in the environment, researchers should focus on agreeing on a uniform methodology to determine the gravity of the problem through obtaining comparable data, thus leading to new and stricter legislation enforcing more sustainable plastic production and recycling, and hopefully contributing to reversing the trend of high amounts of microplastics worldwide.