Yet, for several reasons, this 80:20 proportion is not as helpful as it might appear, says Dr Peter Kershaw, an independent consultant on marine environmental protection. For one thing, he says, you cannot apply it to every substance of concern, as they are released in different quantities in different regions and have different effects.
Another factor is the impact that chemicals have. While the global quantity of a particular chemical entering the ocean could be large, more damage might well be done in a particular area by a sea-based source of pollution—for example, the case in 2021 of a tanker carrying tons of nitric acid, other chemicals and plastic pellets that caught fire and sank off Sri Lanka.
The sources of marine chemical pollution, then, are varied and often complex. To try to make sense of them, The Invisible Wave breaks them down into six broad categories (which inevitably overlap to some degree):
- the chemicals industry
- other industries that use chemicals for their products and processes
- public use and legacy chemicals
- accidents and
- waste management and disposal