A set of planetary boundaries has been defined in the literature, delimiting a “safe operating space for humanity”. Many of the planetary boundaries that have so far been identified are determined by chemical agents. Other chemical pollution-related planetary boundaries likely exist, but are currently unknown.

This paper posits that a chemical poses an unknown planetary boundary threat if it simultaneously fulfills three conditions:

  1. it has an unknown disruptive effect on a vital Earth system process;
  2. the disruptive effect is not discovered until it is a problem at the global scale, and
  3. the effect is not readily reversible.

The authors outline scenarios in which chemicals could fulfill each of the three conditions, then use the scenarios as the basis to define chemical profiles that fit each scenario. The chemical profiles are defined in terms of the nature of the effect of the chemical and the nature of exposure of the environment to the chemical. Prioritization of chemicals in commerce against some of the profiles appears feasible, but there are considerable uncertainties and scientific challenges that must be addressed. Most challenging is prioritizing chemicals for their potential to have a currently unknown effect on a vital Earth system process.

The authors conclude that the most effective strategy currently available to identify chemicals that are planetary boundary threats is prioritization against profiles defined in terms of environmental exposure combined with monitoring and study of the biogeochemical processes that underlie vital Earth system processes to identify currently unknown disruptive effects.

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