Taking the pulse of Mother Ganga – Identifying hotspots and hot moments of microplastic freshwater pollution at unprecedented scale

Besides the many technological benefits of living in the “plastic age”, the plethora of today’s plastic products, their unsustainable use and high durability cause severe pollution risks with major uncertainties regarding their environmental and human health risks which has understandably lead to considerable public health concerns. With microplastics research having previously focussed predominantly on marine ecosystems, the transport, fate, ecotoxicity and environmental and human health impacts of microplastics in freshwater systems are only poorly understood. Recent global estimates claim that the majority (>90 %) of plastics in the world’s oceans stem from the 10 top polluting rivers (Schmidt et al., 2017), all of which are in the developing world and have extremely dense urban populations along their banks, often with minimal waste management or processing whereby the rivers act as dumping sites. However, we are only starting to understand how hydro-meteorological conditions and fluvial dynamics control the fate and transport of plastics in rivers, including their hot-spots for accumulation, ageing and degradation behaviour under local temperature, UV and microbial conditions, and potential impacts on the local ecosystems and their service provision. Identification of accumulation and degradation hot-spots will lead to important opportunities for intervention and remediation, thereby reducing the pollution burden long term.

This project will therefore pioneer a large-scale analysis of microplastics (<5 mm size) in the waters and sediments of some of the largest Asian rivers, including the Red River (Vietnam), the Ganga (India, Bangladesh) and the Pearl River (China). Using the samples collected, an analysis of the influence of spatial and temporal variability in hydrodynamic forcing on the accumulation of microplastics of different sizes, shapes, densities etc. will be performed. The PhD project will develop cutting-edge flow weighted sampling techniques, including Langrangian stream and sediment sampling, to identify the magnitude of microplastics pollution in these rivers, under a range of different hydrodynamic conditions to reveal major drivers of microplastic transport and accumulation. This will be supplemented with development of new methods for joint water column + sediment sampling to link transport and sedimentation parts, and by complete characterisation of the microplastics collected from water and sediment samples, including size, shape, colour, density, biomolecules adsorbed and biofouling (i.e. colony forming assay and microbial metabolic assay), in order to correlate the nature of the accumulating microplastics with the different flow conditions.

Analysis of the ageing and degradation of the identified microplastics in water and sediments, simulating in the lab the local conditions (pH, ionic strength and composition, UV intensity and light/dark cycle) as well as the microbial conditions by extracting communities from the sediment samples and from the microplastics themselves. Controlled ageing experiments will be performed using the larger (~5mm) microplastic samples obtained, in order to develop understanding and models of microplastic degradation under different environmental condition. These data will be correlated with the size and shape distributions obtained from the sampling to assess whether the sampling is effectively capturing the range of sizes or whether the notoriously difficult to capture nano-scale microplastic fraction is being missed. Given the fact that particle number scales exponentially with decreasing size at constant mass, theoretical size distributions can be determined and compared to lab and field data.

This studentship is open to candidates with a first or upper second class Honours degree in environmental hydrology, environmental sciences, chemistry, natural sciences, geography, biology and related subjects. An MSc degree in any of these subjects is desirable, as well as an interest in research in overseas locations. The project requires a good understanding of hydrological flow and transport processes as well as environmental chemistry and sensing. Previous work with plastics or microplastics would be an advantage. Field work in India, Vietnam, and China will require extended travels and working in the field. The fieldwork will be supported by local supervisors and their teams, ensuring that all relevant health and safety provisions and sampling and on-site analysis equipment and support is available, as well as any necessary permissions for sampling.