Plastic and microplastic pollution is a global environmental and societal concern. While focus has been placed on assessing the direct impacts on biota, indirect ecological effects are unexplored. Following very recent (and unexpected) laboratory evidences of a considerable binding between metals and altered plastics, I hypothesize that such an interaction can be amplified in environmental conditions due to mechanical, UV and biological degradations during plastic ageing. Plastic can change the budget and cycling of nutrients, micronutrients and toxic metals in different environments (agricultural soils, sediments). If this holds, the implications for the ecosystem might be far-reaching. The mechanisms underpinning ions/metals- plastic interaction are still mostly unexplored. Through PLANET action, I will: i) conduct artificial plastic ageing experiment on selected polymers to create testing materials for following work; ii) characterize the alterations of plastic surface physicochemical properties, iii) run sorption tests with ions and metals in batch experiments under varying pH, salinity, redox potential to disentangle mechanisms, nature and energy of this interaction; iv) build a mathematical frame describing this interaction and its implications for ions/metals distribution in the environment; v) assess model predictions in sediments/water column microcosms to enable inference for ecological effects at different scales. I will work at the Norwegian Institute for Water Research, a top research centre for plastic pollution analysis and environmental modelling. The host owns advanced equipment and laboratory to enable the project. The supervisor is committed to provide training on several core and soft skills and give access to his scientific and stakeholder networks. This will largely benefit my career development. I will exploit these contacts for communication and dissemination towards concrete impacts in the scientific, policy and industrial sector.

In the UK 330 billion road miles are driven every year, generating particles of synthetic rubber as a consequence of friction between the tyre and the road surface. It has been estimated that tyre wear could account for 65% (18,000 tonnes annually) of all microplastics released to UK surface waters. However, these estimates are in stark disagreement with environmental data where polyethylene, polypropylene, polystyrene and PET are the main types of microplastics and on a global scale only around 1% of studies report finding any tyre particles at all. This contradiction is concerning because tyres contain a range of potentially hazardous chemicals which have been shown to cause harm to marine life. Tyre particles are challenging to identify from environmental samples and this might explain the discrepancies between modelling estimates and actual field sampling. In this proposal, we will use an approach that has been recently trialled by the team and has shown that very substantial quantities of tyre particles are indeed entering the sea via storm water, waste water and from airborne dust. This project will measure tyre particle concentrations at their points of entry to the marine environment and then describe their subsequent transport in the water column. We will measure concentrations in the water, sediment and marine life at increasing distances from the places where these particles enter the sea and construct and validate mathematical models to describe the dispersal of tyre particles in inshore waters. This information will then be used establish the potential for any associated risks to marine life at environmentally relevant concentrations. The proposal brings together the Universities of Plymouth, Exeter and Newcastle, together with Plymouth Marine Laboratory and an Advisory Group comprising 14 organisations including policy makers, tyre, automobile, plastics and water industries as well as academia and environmental charities (see letters of support). Our research team includes world-leading experts in microplastics, marine litter, environmental chemistry, coastal dynamics and ecotoxicology who have pioneered the field with numerous collaborative projects, jointly authored papers and awards for their work. Their previous research has had significant, broad impact influencing policy and industry on a global scale to help reduce plastic contamination in the environment. There has been considerable media attention on plastic pollution in recent years and this has translated into an urgent call for action by the public, policy makers and industry. However, current understanding of the most appropriate actions is less clear and reliable information on the relative importance and associated risks from various sources of microplastic, including tyre particles, is lacking. The outcomes of this research are therefore of critical importance to guide policy and industry intervention. The number of road vehicles is set to double by 2050 leading to increased particle emissions; however, there are interventions that could reduce the rate of tyre particle generation, hence the proposed research is both urgent and timely. The outcomes of this project will be widely disseminated via a dedicated Work Package on communication and impact, facilitated by an Impact Champion and the Advisory Group that has been specifically assembled for the project.

We estimate the microplastic (MP) input to agricultural lands from wastewater and sewage sludge reuse in Europe and North America to be comprehensively between 107,000 and 730,000 tonnes/year making the farm environment one of the major receptors and, possibly, environmental reservoirs of MPs. While it is widely acknowledged that microplastics in the ocean are a serious environmental problem, the alarming threats posed by MPs and associated contaminants accumulating in agricultural soils are almost entirely unknown. According to recent reports a large fraction of the MPs generated and used in industrialized countries may end up in municipal wastewater and sewage sludge. A sizeable fraction of wastewater and sewage sludge is reused in these countries in agricultural lands with no technology in place to remove MPs. This is especially alarming given the high concentrations of toxic compounds and endocrine disrupting substances that can be found in plastics. Effectively, wastewater reuse and sewage sludge application may be causing persistent, pernicious and so far unacknowledged contamination of agricultural land. In IMPASSE, we propose to develop and communicate the new understanding of MP behaviour, toxicology and impacts in agrosystems. Highlights from the project are: • Development of monitoring schemes to track the fluxes and impacts of MP in agrosystems from reuse of wastewater and sewage sludge, including: i) assessment of MPs inputs, loads and fate in 3 catchment case studies, and ii) ecotoxicology of MPs in agrosystems (i.e. accumulation in soil and freshwater organisms, implication for bioaccumulation of substances contained in MPs). • Analysis of risks posed to human health from the reuse of wastewater and sewage sludge in agriculture. Specifically, the implications for enrichment of MP-derived contaminants and metabolites in crop and milk from farmlands treated with sludge and wastewater. • Interactive stakeholder engagement (including risk communication and participatory definition of management and modelling scenarios) • Development of decision support tools (including catchment modelling of MP transport and analysis of economic and environmental implications of various mitigation scenarios). This part will focus on analysis of economic and environmental co-benefits and trade-offs associated with, e.g., introduction of new technology for wastewater/sludge processing, irrigation and drainage management, and soil amendment practices that minimize exposure to MPs. • Dissemination of scenario assessment results to farmers, stakeholder groups, scientists and regulators. IMPASSE will develop awareness about a new and potentially serious threat for farms and natural ecosystems. Alarmingly, this threat has passed, so far, unobserved. Our ultimate goal is to find solutions that safeguard agricultural sustainability, human and animal health, and circular economy goals.