Company operations can cause the release of a range of chemicals and particles. The emission of substances that are already abundant in nature, and of substances that nature can break down rapidly and without consequence, are not a concern.
Some substances are known to be toxic to people and organisms. Other substances may not seem immediately harmful, but if nature cannot break them down rapidly they may – through emission into air, land or water – systematically build up in the environment to dangerous levels.
Substances that have a higher potential to systematically build up in nature, and thus are of greatest concern, include those that are scarce in nature (e.g. trace metals such as cadmium), those that are persistent (e.g. CFCs), and those that are emitted in large volumes (e.g. NOx).
All such potentially harmful substances must be kept in tight closed loops, or not used in the first place. The context of this goal may vary from local (e.g. soil, rivers) to global (e.g. air, oceans) depending on the substance and mode of emission.