Sorbent materials effectively “sop up” oil and oily waste products. Some have the oil adhere to their external surfaces, and so are called ad-sorbents. Some absorb the oil into their structure, and are called ab-sorbents.
Irrespective of how they work, there are three types, depending on the materials from which they are made:
- Natural organic sorbents—these include peat moss, straw, hay, sawdust, ground corncobs, feathers, and other readily available carbon-based products. Mostly, these absorb the oil, can be wrung out and once used, will biodegrade or can be composted after use.
- Natural inorganic sorbents consist of clay, perlite, vermiculite, glass wool, sand, or volcanic ash. Mostly, these have the oil cling or adhere to their external surfaces, so it can be washed off and collected. They can be re-used before disposal. Although they do not decompose, oil adhered can biodegrade.
- Synthetic sorbents include synthetic polymers (plastics), such as polyurethane, polyethylene, and polypropylene, cross-linked polymers and rubber materials. These are very effective at collecting oil, can be re-used many times, and require careful disposal, like all contaminated plastics. They can create a microplastics pollution if not completely removed from the sea.
The decision to use sorbents must consider the net environmental benefit.
In 2001, AMSA commissioned the Centre for Ecological Impacts of Coastal Cities (University of Sydney) to review current literature and experience in the use of sorbents which naturally degrade in the environment. Such sorbents could potentially be deployed to contain the spread of oil, but then left in place to degrade naturally over time.
Logistics of retrieval may be difficult in a remote area, and some sensitive habitats may be damaged or have recovery reduced by disturbance during the retrieval process. In some circumstances though, this may be less damaging than allowing oil to spread uncontrollably.
This report— Properties of naturally-degrading sorbents for potential use in the cleanup of oil spills in sensitive and remove coastal habitats—provides a literature-based review of properties of different, naturally-occurring, biodegradable sorbent materials that could potentially be used in cleaning oiled foreshores.
The best types of sorbents were found to be those with great capacity for primary absorption of oil, particularly those formed from long fibres, such as wool, cotton and so forth. Wool-based sorbents have further merits.
They are natural, available on a sustainable basis and handling, storage and transport of wool are routine in many parts of Australia. Other possible sorbents with useful properties were also identified using a diverse set of criteria.
Such materials have been identified as potentially useful in the following situations:
- The remoteness of the incident and/or environmental features make it impractical or ineffective to contain and recover the oil at sea.
- When issues of environmental sensitivity make it inadvisable to use chemical dispersants.