(18)Recent scientific knowledge underpinning several Commission strategies, as set out in four communications from the Commission, namely that of 16 January 2018 entitled ‘A European Strategy for Plastics in a Circular Economy’, that of 11 March 2019 entitled ‘European Union Strategic Approach to Pharmaceuticals in the Environment’, that of 14 October 2020 entitled ‘Chemicals Strategy for Sustainability – Towards a Toxic-Free Environment’ and that of 12 May 2021 entitled ‘Pathway to a Healthy Planet for All – EU Action Plan: “Towards Zero Pollution for Air, Water and Soil”’, highlights the need to take action to address the issue of micropollutants, which are now routinely detected in all waters in the Union. Some of those micropollutants are hazardous for public health and the environment even in low concentrations, of micrograms per litre or below. While the primary, secondary and tertiary treatment already remove some micropollutants, an additional treatment, i.e. quaternary treatment, should be introduced in order to ensure that a large spectrum of the remaining micropollutants are removed from urban wastewater. Quaternary treatment should first focus on organic micropollutants, which represent a significant part of the pollution and for which removal technologies have already been designed. The quaternary treatment should be imposed on the basis of the precautionary principle, in combination with a risk-based approach. Therefore, all urban wastewater treatment plants of 150 000 p.e. and above should provide quaternary treatment, as those facilities represent a significant share of micropollutant discharges in the environment and the removal of micropollutants by urban wastewater treatment plants at such scale is cost-effective. For treatment plants of 150 000 p.e. and above, Member States should ensure the prioritisation of the required investments so that the facilities where the risks for the environment and human health are the highest are equipped without delay. For agglomerations of 10 000 p.e. and above, Member States should be required to apply quaternary treatment in areas identified as sensitive to pollution with micropollutants on the basis of clear criteria, which should be specified. Such areas should include locations where the discharge of treated urban wastewater to water bodies results in low dilution ratios, or where the receiving water bodies are used for the production of drinking water, for shellfish production or as bathing waters. Member States should be able not to apply quaternary treatment in those areas when a risk assessment shows that there is no potential danger from micropollutants to the environment or to human health. For all other types of water bodies in agglomerations of 10 000 p.e. and above, Member States should assess the risks that the discharge of micropollutants in urban wastewater poses for the environment or to public health on the basis of a standardised risk assessment and apply quaternary treatment only where needed according to the results of the risk assessment. Where there are several urban wastewater treatment plants in an agglomeration of 10 000 p.e. and above identified as sensitive to pollution with micropollutants, only those discharging into the area at risk should be required to apply quaternary treatment. In order to give Member States enough time to plan and deliver the necessary infrastructure, the requirement of quaternary treatment should progressively apply until 2045 with clear interim objectives.