Increasing microplastics pollution: An emerging vector for potentially pathogenic bacteria in the environment.

Particles with the largest dimension of less than 5 mm, also termed as microplastics (MPs), gained a lot of scientific and media attention in the last decade. MPs in the environment are of importance because of their potential for further fragmentation, accumulation, and impact on biota in the terres-trial and water environments. MPs research is challenging due to their diversity in size, shape, and chemical structure. For research purposes, MP particles can be purchased, but in terms of chemical structure, they properties might not correspond to the ones of MPs, found in the environment. Com-pared to purchased MPs, plastic products in the environment can contain different additives, despite being the same polymer type as purchased MPs. Therefore, for environmental studies preparation of MP particles from plastic products is preferable. In this contribution two methods for laboratory preparation of MP particles, different sizes and polymer types, are presented. Method using ultra-sound probe was found to be suitable for obtaining polyester fibres from thin sewing thread, while cryogenic milling was found to be preferable method for MPs preparation from larger and thicker plastic particles. In this way, MPs of other types of plastic (polyethylene terephthalate, polystyrene, polyvinyl chloride, polypropylene) were prepared from beforehand manually cut plastic particles, originating from everyday plastic products. Keywords: Miroplastics; Cryomilling; Separation; Challenges of preparation; Surface topology

Microplastics (MPs) are smaller plastics that have become prevalent in aquatic environments. Previous studies have reported MP occurrence in the gastrointestinal tracts of shrimp species collected from public markets and shrimp farms. There are reports that biofilm communities, including potentially pathogenic bacteria, can adhere to the MP surfaces. MPs, when ingested, pose significant health and economic risks, including potential exposure to Vibrio parahaemolyticus (Vp) – a prominent shrimp pathogen found in high concentrations on MP surfaces – increasing disease risks in shrimp and potentially entering the human food chain. In this study, the shrimp Litopenaeus vannamei from a shrimp farm and different wet markets in Bulacan, the Philippines, were tested for MP contamination and the attachment and colonization of Vp to MP surfaces and tested in vitro. The isolated MPs underwent chemical digestion and floatation separation, followed by imaging with a stereomicroscope and characterization based on their morphological features. The isolated putative MPs are frequently observed in fragments of irregular shape. Attenuated total reflectance–Fourier transform infrared spectroscopy results validated that only L. vannamei from Hagonoy and Meycauayan wet markets acquired MPs that exhibited characteristic absorption bands corresponding to the C-H stretching vibrations typical of polyethylene (PE) based plastics. A set of pristine PE-based plastics – one with a smoother surface (PE1) and one with a rougher surface (PE2) – were observed for the attachment of Vp. Scanning electron microscopy images confirmed the attachment of Vp on these MP surfaces and revealed that the colonization could be seen as early as 1 h of incubation. PE2 resulted in a higher abundance of adhered bacteria than PE1, suggesting that surface roughness plays a role in bacterial colonization on MP. However, this observed difference was not statistically significant, suggesting that other parameters such as temperature, pH, salinity, and nutrient availability should also be considered. This study shows that shrimps from the sampling sites are contaminated with MPs, and that PE-based MPs can be colonization sites for Vp.

Microplastic pollution in sediments of urban rainwater drainage system

Exploring the vertical transport of microplastics in subsurface environments: Lab-scale experiments and field evidence

The threat of plastic waste in the environment has evoked rising concern over the past decades. While these versatile and incredibly popular polymer materials undoubtedly fulfil unprecedented services, their extreme durability and alleged toxicity represent major downsides, once in the environment. As plastics break down into smaller microplastics (MP) they evidently pollute almost every thinkable habitat on the globe today. While an estimated 5–12 million tons of plastic end up in the oceans every year, rivers are important pathways, carrying an annual freight of 0.41–4 million tons downstream. The Rhine River, one of Europe’s main streams and one of the World’s busiest waterways, reportedly holds substantial amounts of MP in its near-surface waters and sediments. However, little is known about potential MP sources, seasonal dynamics and the MP pollution of benthic sediments of this major river. In my dissertation I address three pivotal knowledge gaps about MP in the Rhine River and investigate a new type of method to safely and efficiently separate MP from surrounding environmental sample matrices. The surface water MP pollution of the Rhine River was earlier characterised by the distinct appearance of vast amounts (~60%) of rigid polystyrene microbeads of unknown origin and former purpose. In a sustained investigation of a defined river stretch in the Lower Rhine downstream Cologne, we managed to narrow down the entry region of these pollutants and close-to-certainly unveil the particle’s former purpose as ion-exchange resin beads used in diverse fluid purification applications. As more data on MP in rivers emerges, an interesting gap opens: empirical field studies tend to generate temporally restricted snapshot data while modellers, laudably seeking the bigger picture, are confronted with enormous uncertainties in their results. In a bid to reduce this void we embarked on a quadruplicate surface water MP observation in the Rhine catchment during 2016–2017. The investigation included three nival discharge regime tributaries and the Rhine in Switzerland as well as a pluvial Rhine River section towards the German-Dutch border. It became evident that despite a coherent increasing MP concentration gradient downstream, reflecting average discharge and catchment size, overall variability in environmental MP data was large. This hampers clear-cut estimations about concentration fluctuations but at the same time reinforces the theory of high MP seasonal pollution fluxes in the European winter months, when Rhine discharge is highest. Seeking to contribute to the very scarce knowledge of MP and benthic sediment interaction in large dynamic rivers, we took a diving bell and a dredging vessel to the riverbed at two previously identified surface MP hotspots at the German Middle and Lower Rhine. Due to expected water turbulence and flow velocity, substantial settling of MP in such stretches is not necessarily anticipated. Interestingly, it showed that even the Rhine riverbed is not spared from vast MP pollution. The applied research technology allowed for reliable detection of MP down to particle sizes of 11 μm and yielded strongly varying concentrations of 260–11,000 MP kg^–1, with a strongly skewed size class distribution towards the smallest MP particles. Experience showed us that environmental sample preparation for MP research can be a tedious and resource-intensive enterprise – including health and environmental hazards. Instead of attacking the unwanted portions in a sample (e.g. biogenic residue to isolate MP), a more efficient approach is to select the MP specifically. We refined a proposed lipophilicity-based separation technique and broadened its scope by successfully testing it to four different types of environmental matrices. This one-for-all approach may present a promising means for quicker, cheap, safe and efficient MP data compilation. The method was successfully applied for the seasonal surface MP investigation presented in this dissertation.

Microplastics (MPs) can enter plants through the foliar pathway and are potential hazards to ecosystems and human health. However, studies related to the molecular mechanisms underlying the impact of foliar exposure to differently charged MPs to leafy vegetables are limited. Because the surfaces of MPs in the environment are often charged, we explored the uptake pathways, accumulation concentration of MPs, physiological responses, and molecular mechanisms of lettuce foliarly exposed to MPs carrying positive (MP+) and negative charges (MP-). MPs largely accumulated in the lettuce leaves, and stomatal uptake and cuticle entry could be the main pathways for MPs to get inside lettuce leaves. More MP+ entered lettuce leaves and induced physiological, transcriptomic, and metabolomic changes, including a decrease in biomass and photosynthetic pigments, an increase in reactive oxygen species and antioxidant activities, a differential expression of genes, and a change of metabolite profiles. In particular, MP+ caused the upregulation of circadian rhythm-related genes, and this may play a major role in the greater physiological toxicity of MP+ to lettuce, compared to MP-. These findings provide direct evidence that MPs can enter plant leaves following foliar exposure and a molecular-scale perspective on the response of leafy vegetables to differently charged MPs.

The distribution, characteristics and ecological risks of microplastics in the mangroves of Southern China

The presence of microplastics (MPs) along with agrochemicals is being widely reported from lakes, ponds, and rivers. Microplastic (MP) in association with agrochemicals could have synergistic or antagonistic effects on non-target aquatic organisms and pose ecological risks. The present study explored the combined effects of MP, the insecticide chlorpyrifos (CPF) and MP preconditioned with CPF (MP^CPF) on two cladocerans, Ceriodaphnia cornuta, and Echinisca triserialis in short-term and long-term laboratory bioassay tests. The experimental protocol included an acute bioassay at five different concentrations of MP (25, 40, 100, 200, and 500 particles mL-1), CPF (0.01, 0.05, 0.1, 0.5, and 1 µgL-1) and MP^CPF. Whereas, CPF (0.01 µg L-1), MP (25 particles mL-1), and MP^CPF in 0.01 µg L-1 of CPF were selected for the chronic bioassay. Upon exposure to CPF, C. cornuta and E. triserialis displayed a dose-dependent mortality pattern with a 48 h LC50 value of 0.06 µgL-1. No mortality was observed in the MP only treatment, but when MPs were preconditioned with CPF, the 48 h LC50 value was 0.02 µgL-1. Chronic exposure to MP, CPF, or MP^CPF resulted in reduced survival and reproductive output in both the cladocerans. However, C. cornuta was more vulnerable than E. triserialis. A significant delay in age at first reproduction and shorter generation time were observed in the presence of MP^CPF, suggesting MP-mediated enhanced toxicity of CPF, wherein CPF could have accumulated onto the MP surface, thus, intensifying its toxicity. The enhanced toxicity of organic pollutants by MPs in aquatic environments especially in pelagic organisms is a matter of concern.

Microplastic contamination in seafood: Comparison between fresh and canned samples

When microplastics meet microalgae: Unveiling the dynamic formation of aggregates and their impact on toxicity and environmental health.

Microplastics (MP) are widely distributed in the marine environment, and are generally defined as plastic particles lesser than 5 mm in size. These MPs can be ingested by various aquatic organisms, including oysters and subsequently transferred to the higher trophic levels. The primary objective of this study was to determine the quantity and types of MPs in cultured oyster (Crassostrea madrasensis) and, in surface-water and sediment samples from three culture sites located in Kalpitiya lagoon. This study extensively paid attention to the effect of depuration process on removing microplastics from oysters. Six out of twelveoyster samples from each site were subjected to a sixteen-hour depuration period. Both depurated and non-depurated oysters were acid digested and filtered to extract MP particles. Sediment samples from the culture sites were density separated by air venting through a super saturated calcium chloride solution. Water samples were filtered over a 63 μm mesh and treated with 30% H2O2. Extracted MP particles from oysters, sediment and surface-water were observed under a stereo microscope and size eligible MP particles were confirmed using FT-IR spectrometer. Microplastic concentration of non-depurated oysters was 4.0±2.4 particles per individual oyster. In depurated oysters average MP concentration was 1.1±0.6 MP particles per individual oyster. Bottom sediment samples from oyster culture sites had the highest concentrations of microplastics, which was an average of 24.5±4.2 MP particles per 1 kg of sediment dry weight and water samples with an average concentration of 7.4±1.3 MP particles per 1 L of lagoon water. Among observed MP types, fibers (74.3%) were the most common typeof MPs. Depuration of oysters successfully removed 72.5%. of MPs. This study reveals that, an average portion of non-depurated oysters (250 g wet weight or 12 oysters) contains approximately 50 MP particles to which the consumer will be exposed. Continuation of investigations on microplastics in different edible aquatic speciesare required to have a comprehensive understanding of this potential human health risk. Keywords: Microplastics, Crassostrea madrasensis, Oysters, Depuration, Kalpitiya lagoon

Advanced oxidation processes for microplastics degradation: A recent trend

Microplastic concentrations and risk assessment in water, sediment and invertebrates from Simon's Town, South Africa

Microplastics (MPs) are ubiquitous environmental contaminants that can serve as transport vehicles for pathogens, potentially spreading them into human settlements and posing a public health threat. In recent years, concerns have been raised about the potential hazardous effects of these “pathogenic hitchhikers” on human health. This review paper presents foundational information on pathogenic hitchhikers associated with MPs, based on a review of the literature published in scientific journals from 2000 to 2021. We used search engines such as Google Scholar and Mendeley to retrieve publications during those inclusive years. Over the past two decades, we identified only 57 published articles on human pathogenic microorganisms associated with MPs, underscoring this area of research as relatively novel and emerging. For the reviewed articles, the common polymer types associated with pathogens were polyethylene and polypropylene, while Vibrio spp. were the most commonly reported human pathogens present on MP surfaces. Albeit small in scale, these studies provide incontrovertible proof that MPs can act as vectors for disease spread and pose a threat to the ecosystem. Significant gaps, nonetheless, remain, particularly concerning their harmful effects on humans and other macro-organisms that may inadvertently ingest MPs harboring these ‘hitchhikers’. Addressing these gaps in future research is thus warranted to comprehensively understand the ecological roles and health risks posed by these hazardous contaminants on MPs and for informing relevant policy decisions.

Microplastics: A review of analytical methods, occurrence and characteristics in food, and potential toxicities to biota