Microplastics are a widespread form of plastic pollution. There is increasing evidence that they are a threat to human health and the environment. Microplastics in domestic and industrial wastewater become concentrated in sewage sludge during wastewater treatment processes. In 2020, water companies in England produced more than 800,000 tonnes of sewage sludge from urban wastewater. More than 90% of UK sewage sludge is spread on agricultural land as a fertilizer and soil conditioner. This provides a pathway for microplastics to enter the terrestrial environment. There is currently no UK legislation defining safe limits for microplastics in sludge and soils but future regulation is a possibility. There is currently no technology available to remove microplastics from wastewater treatment processes or the resulting sludge.
Safe limits for microplastics in treated sewage sludge, soils and water bodies should be identified. This will require a survey of the extent of microplastic pollution throughout the UK, including concentration, identity and characteristics of microplastics in each environmental reservoir, and understanding how microplastics affect different living organisms. Microbes or fungi that break down plastic could be added to existing wastewater treatment process to remove microplastics and prevent their release into the environment. Alternatively, only the active enzymes (rather than the live microorganisms) could be added to the process. Currently, only polyester microplastics (11% of the total microplastic burden) could be treated in this way. Different microorganisms would have to be discovered or developed to tackle other common microplastic polymers such as polypropylene or polyethylene.