Integration of production and use information into an exposure-based screening approach to rank chemicals of emerging Arctic concern for potential to be planetary boundary threats

Abstract

Planetary boundaries delimit a ‘safe operating space for humanity’ that should not be overstepped to maintain stable Holocene-like conditions on Earth. Some chemical pollutants have the potential to pose a planetary boundary threat to the functioning of vital Earth system processes as so-called ‘novel entities’. Recently, an exposure-based prioritization scheme was developed that uses model-estimated data on persistence and degree of mobility in air and water to identify and prioritise chemical substances that may be planetary boundary threats. As a case study, chemicals of emerging Arctic concern identified by the Arctic Monitoring and Assessment Programme (AMAP) were used to develop the scheme. The exposure-based prioritization scheme cannot address all scenarios for a chemical to pose an unknown planetary boundary threat, but it does allow for prioritization of chemicals according to environmental fate and exposure profiles. A key limitation of the scheme is that the quantity of chemical potentially released to the environment was not considered in the prioritization. Here, we use data on chemical production and use reported under the European chemicals regulation REACH, and an emission scoring system developed by the European Food Safety Authority (EFSA) to attempt to add information about estimated emissions to the exposure-based prioritization scheme. Using REACH data and the EFSA scoring system, we ranked the AMAP substances according to their potential for environmental release and combined that information with the previously reported exposure-based prioritization that considers persistence and long-range transport potential. Our method successfully assigned ‘high priority’ to known ozone-depleting substances (methyl chloride and dichloromethane) and identified chemicals of concern recently under consideration for nomination as persistent organic pollutants under the Stockholm Convention (octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane). The EFSA scoring system offers a useful starting point that provided useful additional information in the case study for chemicals of emerging Arctic concern, but lack of information to estimate potential releases of chemicals was a major limitation.