Investigation and numerical modelling of microplastics in clean water treatment systems and a systematic review of the health effects of microplastics

The topic of microplastic (MP) pollution has been gaining considerable interest globally, with concern of their potential harm towards human health and the environment. MPs can be defined as small pieces of plastic which are <5mm. Over time, MPs accumulate within the natural environment. Much research has focused on the presence of MPs within the marine environment and the harmful effects on fish and other marine life. More recent research has begun to focus on MPs within wastewater treatment plants and tap and bottled water, with a recently published international study of tap water stating that 83% of tap water samples were found to be contaminated with MPs (The Lancet Planetary Health, 2017).
The quantity of MPs within drinking water treatment plants (DWTPs) is an area which is under-researched, with only a few studies attempting to quantify MPs in influent and effluent water. The movement of MPs through DWTPs is a novel area of interest, with no literature found which has reported on MP concentrations at numerous treatment stages. Therefore, there is no real understanding of the success rates of the individual treatment stages on MP removal. The main sources of polymers in clean water is also far from being understood and the potential impacts of MPs on human health are unknown. This information must be acquired to understand the urgency of developments to be made for the removal of MPs from the clean water system.

The main study aims are; - to develop a protocol for the sampling and analysis of MPs within the water supply system; to quantify the amount of MP present throughout the system and identify the potential sources of such polymers; to identify the main risks associated with MP presence in drinking water to gain a greater understanding of the need for MP removal.

This study is aligned to EPSRC's research area of 'water engineering.' The first stage of this project is to develop a sound sampling and testing methodology for the quantification and identification of MPs in clean water systems. The sampling methodology must be carefully designed, accounting for the potential effects of weather conditions, sampling depth, representativeness of sample size and numbers, potential contamination etc. Testing methodology will then be designed to isolate only the MPs from the sample. Finally, methods for the identification and characterisation of polymers will be adapted.

Stage two will be to carry out the methodology created in stage one, with samples taken at various stages of three individual DWTPs owned by NI Water. Further comparisons will be made to tap water from households provided by each treatment plant and bottled water. The sources of the treatment plants will differ (a river, lough and an upland source), for comparisons to me made relating to differing abstraction sources on MP quantities found.
Following sampling, each sample will be subjected to laboratory analysis, allowing for the quantification of MP numbers. The identification and characterisation of polymers found will be undertaken, providing important information to aid understanding of both; the sources of the MPs found, and the removal efficiency of the DWTP on different polymer types and shapes. Statistical analysis will review the significance of relationships between; MP number and treatment stage, MP types/quantities found and water sources etc.

The results found from the first two phases will help to inform the next steps of this project in more detail. Modelling of particle flow through the DWTP and design of an extraction method of MPs from the clean water system are expected to be important next steps. It is thought that biofilms and other contaminants, which adhere to MP particles due to the hydrophobic nature of polymers, may pose a significant risk to human health. The MPs collected will be assessed to try to gain a greater understanding of potential risks.