A substance or a group of substances that may be harmful to the environment or to human health on account of its properties and of its introduction into the environment. Source: Protocol on Pollutant Release and Transfer Registers to the Convention on Access to Information, Public Participation in Decision-Making and Access to Justice in Environmental Matters (Kyiv Protocol), art. II (6)* * This term and definition is included in the glossary of key terms prepared for the work of the international negotiating committee to develop an international legally binding instrument on plastic pollution, including in the marine environment, under the category 'Terms not used in Environment Assembly resolution 5/14 that may be related to those used in the resolution and that have definitions adopted or endorsed by an intergovernmental process'. See UNEP/PP/INC.1/6.