Assessing Microplastic Pollution in Four Mile Run, an Urban Stream in Northern Virginia

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.

Costs of Meeting Water Quality Goals under Climate Change in Urbanizing Watersheds: The Case of Difficult Run, Virginia

Microplastic reorganization in urban river before and after rainfall

Microplastics in sediments from urban and suburban rivers: Influence of sediment properties

Most studies that address microplastic (MP) ingestion by fish are conducted in marine environments; however, freshwater ecosystems such as rivers and streams are also important sources of these particles in coastal areas. Considering that increasing urbanization surrounding watersheds increases the sources of plastic pollution and that fish feeding behavior may influence the probability of ingestion of these particles, the aim of this study was to evaluate the ingestion of MP by fish of different feeding habits in urbanized and non-urbanized streams. The fish were captured in ten streams in Southern Brazil and the stomach contents of 294 individuals belonging to 13 species were analyzed. Individuals of ten species ingested MP of fiber type. From a generalized linear mixed model, we observed that the urbanized streams and the omnivorous habit showed a positive correlation with MP intake. Our results suggest that both types of streams present MP, but this pollutant is probably more prominent in heavily urbanized sites, which may represent important sources of MP for larger systems along the river basin. This evidences the importance of preserving riparian areas of small order streams as a means to reduce MP inputs into these ecosystems.

Comparative analysis of microplastic organization and pollution risk before and after thawing in an urban river in Beijing, China

Distribution characteristics of microplastics in urban rivers in Chengdu city: The influence of land-use type and population and related suggestions

Seasonal influence on pollution index and risk of multiple compositions of microplastics in an urban river

This paper focuses on the Harbin section of the Songhua River in the cold region of northern China. The occurrence characteristics and pollution level of microplastics (MPs) are explored in both the ice and water of urban inland rivers and estuaries during the ice-covered periods. The abundance of MPs in Majiagou ice averaged 324.4 ± 261.5 particles/L, and the abundance of MPs in Songhua ice averaged 65.0 ± 68.2 particles/L. In the water with different depths of Songhua, the MP abundance ranged from 1.0 ± 0.7 particles/L to 12.9 ± 9.4 particles/L, with an average of 5.6 ± 7.6 particles/L. The amount of MPs in ice is about 11 times that in water, where ice formation is mainly responsible for the decline in the MP abundance in aquatic environments. The abundance of MPs in urban inland rivers gradually increased from south to north, while that in the mainstream of the Songhua River showed an increasing trend from east to west. Detected MPs were mainly fiber and white in shape and color, respectively, with a particle size < 0.5 mm. The extent of microplastics in ice is greater than that in water, and melting in the following spring will exacerbate the environmental impact. The results identified the discharge of domestic sewage as the main source of MPs in urban inland rivers. Polyethylene, polypropylene, and polyacrylonitrile were the main types of polymers. The results of the ecological risk assessment showed that the MP pollution in the Harbin section of the Songhua River reached moderate and severe pollution levels during the ice-covered periods. Its potential risk should receive more attention, and control should be strengthened.

Distribution and characteristics of microplastics in an urban river: The response to urban waste management

Microplastic pollution in sophisticated urban river systems: Combined influence of land-use types and physicochemical characteristics

The "plastisphere," comprising microbes associated with microplastics (MPs), may have substantial ecological impacts on riverine ecosystems. However, little is known about how the microbiomes associated with anthropogenic MPs compare with those associated with natural particles (NPs) in urban rivers with varying MP pollution levels. We therefore conducted a comparative analysis of the metagenomes associated with MPs and NPs (100-5000 μm) and river water (RW) across 10 urban river systems. Although we found similarities in taxonomic and functional compositions between the microbiomes associated with MPs and NPs, the plastisphere exhibited distinct associations with specialized taxa and life-history strategies. These unique traits enhanced the potential of the plastisphere for complex carbohydrate and plastic degradation, nitrate and nitric oxide reduction, and antibiotic resistance and virulence compared with the NP or RW microbiomes. Furthermore, MPs supported the sharing of unique microbes with the surrounding RW; these shared microbes possessed enhanced horizontal gene transfer capabilities and potentially could disperse traits of the plastisphere into the broader RW microbiomes. This study highlights the distinct ecological roles and shared microbes of the plastisphere, indicating that MP pollution may substantially and uniquely impact the function and health of riverine ecosystems.

Environmental fate of microplastics in an urban river: Spatial distribution and seasonal variation

Microplastics (MPs) have received a lot of attention since they were recognized as an emerging pollutant. Rivers transport 80 % of the land’s MPs to the oceans. With so many rivers in China, the problem of MPs pollution cannot be ignored. This paper collects data related to MPs in typical rivers in China, summarizes the sources of river MPs, and analyses the status of river MPs pollution and risk evaluation. The results show that riverine MPs mainly originate from sewage treatment plants, surface runoff, atmospheric deposition and plastic breakage. MPs abundance is closely related to population density, with urban rivers having higher MPs abundance than other regions. MPs less than 1 mm in size account for more than 60 % of most rivers. At present, the risk assessment of river MPs is mainly based on three methods, namely, the ecological risk index (PHI), the pollution load index (PLI) and the potential ecological risk index (PERI), and the results of the assessment are mostly low risk. There are differences in the results of the assessment models, which need to be applied jointly with each other for continuous improvement.

Spread performance and underlying mechanisms of pathogenic bacteria and antibiotic resistance genes adhered on microplastics in the sediments of different urban water bodies.