Micro and Nanoplastics in Wastewater Treatment Systems and Receiving Waters

Plastics are one of the most widespread materials that cause water pollution, reduce environmental status and are toxic to biofauna. Macroplastics have long been recognized as environmental pollutants posing threats to marine and terrestrial life(1), nevertheless, the importance of smaller fractions has only been recognised, within recent findings of plastic fragments at the micro- and nano-scale(2,3).These plastic fragments, between 5 mm and 1 nm in size(4) are derived from direct industrial, commercial or domestic waste (such as from beads in facial cleansers) or from decomposition of larger plastic debris. Their size renders then more easily absorbed or ingested and so their impact is frequently more acute than their macro-scale equivalents.

Due to their chemical composition there is little breakdown, and plastic debris has been accumulating in our aquatic systems. Recognition of this has led to recent investment in research projects (5) to understand source, distribution and fate of micro- and nanoplastics (hereafter termed mn-plastics) in the marine environment. However, this focus on the marine environment misses the crucial transmission vectors of fluvial and wastewater treatment systems. To explore this we must examine how a) fluvial systems transport, degrade and store mn-plastics? and b) waste water treatment systems degrade or capture mn-plastics.

Depending on the type of plastic debris and the nature of the agent in which given litter is present, variable processes control their destabilisation. These include uv photo-oxidative degradation, thermooxidative-, bio- or thermal degradation controlled by the action of temperature and physical aggregation, and binding onto biomass, in particular biofilms (present in natural and engineered systems).

As much of this material will come from industrial or domestic waste, the role of wastewater treatment plants in processing mn-plastics, and conversely the impact of these materials on water treatment plant efficacy, must be considered. Advancing understanding of this emergent water quality threat is the focus of this Hydro Nation scholarship. This scholar will create models which describe behavior of mn-plastics through both wastewater treatment and natural fluvial vectors, thus informing environmental risk assessment, policy and improved treatment.