TIP 14 - Sampling and Monitoring of Marine Oil Spills

Following a spill of oil, governments and other organisations often wish to know the extent of contamination of key resources or the impact of the incident on the marine environment. This information is important to determine if prompt action may be required to protect human health or sensitive resources. To facilitate decision-making, monitoring programmes may be undertaken, which will often involve surveys and the collection of samples of oil, water, sediment or biota for chemical analysis.

Documenting the extent of oil contamination through the use of aerial reconnaissance, boat- or shore-based surveys is usually undertaken as a first step in any monitoring programme. This enables the distribution and extent of the pollution to be identified and, for resources at risk, it may be possible to formulate response strategies for their protection. Delineating the extent of the contamination visually (Figure 1) will assist with the design of any monitoring programme and allow sampling stations within and outside the area affected to be identified according to the specific objectives of the monitoring.

The rationale for undertaking monitoring after an oil spill varies from incident to incident. Monitoring may not always be necessary, especially if the spill is small and resources are not at risk, or if the effects of the oil on a particular resource are well known.

Where monitoring has taken place, it has often been carried out with the following objectives, to:

• authenticate the origin of the oil pollution;
• establish the risk of transfer of contaminants to the human food chain;
• ascertain the effects of the pollution on commercial fish and shellfish to support decision-making regarding the need, or otherwise, to impose fishing restrictions;
• verify the cause and effect; that is, to establish whether or not any environmental effects observed are directly attributable to elevated oil concentrations arising from a particular pollution event;
• measure hydrocarbon concentrations in sediment or water to aid decision-making over the continuation or termination of the response;
• determine the decline of hydrocarbon concentrations in the marine environment and to monitor recovery;
• identify conditions appropriate for initiating and sustaining restoration measures;
• demonstrate that damage caused by a spill has been evaluated, that recovery is underway and that concentrations of oil in the marine environment are returning to background levels; 
• address monitoring requirements set out under applicable national regulations, such as standards for bathing waters.

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