August 27, 2025
ITOPF has published the 2025/26 edition of its Handbook, providing information on the different types of pollutants encountered at sea and the challenges, impacts, and response options associated with each.
Marine spills can involve a wide variety of substances beyond oil, including vegetable oils, chemicals, bulk cargoes, and plastics, each behaving differently in the marine environment and posing distinct risks. In its latest Handbook, ITOPF outlines the main categories of pollutants, their effects, and the approaches typically taken to manage them.
Vegetable oils
The carriage of vegetable oils, such as palm, canola and soybean oil, has increased in recent years. Although less toxic than hydrocarbon oils, spills of vegetable oils in the marine environment can prove problematic, nonetheless. In general, vegetable oils will behave similarly to hydrocarbon oils in the initial stage of a spill, in that they tend to float and spread on the surface of the water. However, vegetable oils are not very soluble in water; they do not undergo dispersion in the water column nor will they evaporate to any extent. Depending on their particular characteristics, they may form solid lumps or polymerise into floating rubbery strings.
Vegetable oils are comprised primarily of triacylglycerols or fatty acids and in their fresh state may be broken down by marine micro-organisms. This decomposition contributes to the rancid odours typical of these spills.
The primary environmental consequences of spills of vegetable oils are seen in relation to surface dwelling organisms where oil can lead to smothering, suffocation and starvation. Examples include oiling of bird plumage and animal fur, or oxygen depletion and asphyxiation.
The most appropriate response technique for vegetable oil spills is containment and recovery, such as using conventional booms combined with scoops, nets or grabs. Ideally, the floating lumps should be removed before they have chance to fragment, incorporate sediment and sink to the seabed or reach the shoreline. Dispersants formulated for use on hydrocarbon oils have been shown to have little or no effect on vegetable oils.
Chemicals
Spills of chemicals are less frequent than spills of oil. However, due to the wide variety of chemicals transported, their differing properties and fate in the marine environment, as well as potential effects on human health and safety, they can often prove to be a more complex challenge.
Chemicals can be categorised in a number of ways, for example whether they are a solid, liquid or gas when transported or spilled; whether they exhibit one or more of five hazards: flammable, explosive, toxic, corrosive or reactive; and whether they sink, dissolve, float or evaporate in water (or a combination of these processes), as illustrated above.
The effects of a spilled chemical will depend on a number of factors such as its toxicity, the quantities involved and the resulting concentrations in the environment. Even sub-lethal concentrations of hazardous chemicals can lead to long term impacts within the marine environment. For example, chemically-induced stress can reduce the overall ability of an organism to reproduce, grow, feed or otherwise function normally.
Some substances can persist for long periods in the marine environment once lost to sea, including heavy metals and some organic compounds. This can result in bio-accumulation, whereby the chemical builds up in tissue at a faster rate than it can be broken down. Sessile marine species that filter seawater for food, such as bivalve molluscs, are particularly vulnerable to this effect. Subsequent bio-magnification may also occur if the chemicals travel up the food chain and ultimately to humans.
Credit: ITOPF
The potential consequences of spills of hazardous chemicals mean that effective response planning is crucial. A response should be mounted only once a thorough safety assessment of the situation has been completed. A number of different models are available to predict how a substance will behave and its likely trajectory, as well as assessing fire, explosion and toxicity risks.
Response options for many chemicals are limited and monitoring, without necessarily undertaking an active response, must always be considered. If a response is required, responders should wear appropriate personal protective equipment (PPE). For gases and evaporators, techniques available include “knocking down” the vapour cloud or trying to stop or deflect it using water sprays. For dissolvers, acceleration of the natural processes of dispersion and dilution may be possible. Containment and recovery may be an option for some floating chemicals, depending on their flammability, whilst mechanical dredgers and pump/vacuum systems might be used to recover chemicals that have sunk to the seabed.
For all types of chemical spill, maintaining adequate health and safety for vessel crew, responders and the public is key. In a major casualty, the presence of spilled hazardous chemicals can affect the cleanup of spilled oil, requiring detailed risk assessments for all involved.
Coal
Although fairly infrequent, coal spills recently attended by ITOPF have typically occurred in sensitive tropical regions where reefs and fisheries are present. Common problems with large spills of coal include smothering and abrasion. The coal may sink, blocking light to seabed flora and fauna and restricting water circulation. Any fixed or slow moving benthic organisms, including corals, may be crushed or trapped and have limited access to food sources, potentially causing mortality. Negative impacts are exacerbated by high wave energy which can throw coal repeatedly against shoreline substrates causing physical damage through abrasion.
Small particles of coal (or fines) may remain suspended in the water column for some time and in calm waters coal ‘clouds’ can block light and reduce the photosynthetic ability of organisms. Mobile organisms will move to better light sources, but fixed organisms are vulnerable to starvation, with corals particularly at risk. Fines released close to mariculture facilities or water intakes can clog pumping equipment or affect stock.
The removal of large amounts of stranded coal can present logistical challenges in remote environments; manual recovery is usually required rather than reliance on mechanical resources due to access or availability issues. Furthermore, coal may become buried by subsequent tides and become difficult to remove, particularly in dynamic environments.
Storage of recovered coal should be managed with care. An awareness of the potential for self-combustion of stored coal is important. In areas of high rainfall, leachate should be managed to prevent contamination through runoff.
The above issues, particularly smothering, can apply equally to spills of other types of dry bulk cargoes, for example, iron and nickel ores, fertilisers, sulphur and cement.
Perishable & livestock cargoes
The loss of cargoes, such as foodstuffs and livestock, bring their own set of variables and challenges. Rotting or decomposing organic materials, for example, grain, thawing fish or rotting carcasses, can result in the generation of hydrogen sulphide gas which is particularly hazardous when allowed to accumulate in confined spaces as it is highly toxic and flammable.
Container ship losses
Container ship incidents are an area of increasing concern, not least the consequential loss of plastics into the marine environment. The recovery of containers is challenging in itself, but for breached containers, the sheer amount and variety of materials to recover – from packaged chemicals and foodstuffs to home electronics and textiles – often requires a lengthy response.
An understanding of the integrity of the container and the packaged contents inside may provide an indication of whether the containers are likely to remain intact, float or sink if lost overboard. The response actions, as with oil, will depend on the specific properties and characteristics of the materials in question. Larger floating solids can be corralled from boats using nets and then recovered using grabs. Sunken materials may require dive surveys, dredges or crane grabs.
Incidents can become particularly complex when non-oil cargoes mix with spilled oil. This can make the identification of hazardous materials amongst other cargoes more difficult and present challenges for the segregation of waste for disposal.
According to the World Shipping Council’s annual Containers Lost at Sea report, 576 containers were lost at sea in 2024.
Plastic pellets
A recent challenge for the shipping industry is the growing problem of plastic pellet spills.
Plastic pellets, also known as nurdles, are typically the size of a lentil and the building blocks for the manufacture of plastic goods. They are highly durable and are now found ubiquitously in the marine environment. Although considered inert in their original form, plastic pellets have the potential to be damaging to wildlife if ingested, through direct physical impacts or indirectly via the carriage of persistent organic pollutants.
Losses occur throughout the production and supply chain, with chronic losses typically stemming from land-based sources, while acute losses are the result of sudden, large-scale events, such as the accidental release of containers overboard during shipping incidents.
When released to sea, plastic pellets can spread over vast distances, and are extremely challenging to locate and remove. An early priority is to determine the source(s) of the pellets and, if possible, prevent further releases. The feasibility of mounting an at-sea response largely depends on whether the pellets remain in their packaging or become loose. If they stay intact, then response efforts at sea generally focus on source control, tracking, tracing and recovering the containers and/or packages. Once loose, pellets start to spread widely, in most circumstances the best course of action is to leave them to come ashore. In a port area or other situation where natural geography or artificial infrastructure limits their spread, then containment with booms and recovery with nets may be viable.
Credit: ITOPF
For shoreline clean-up, a rapid response, prioritising any stranded intact bags or the highest accumulations of pellets, is essential. The aim in the early stage of clean-up is to minimise the opportunity for pellets to remobilise or become buried by tidally transported sediments. Clean-up activities should be undertaken alongside continuous surveys and dynamic prioritisation.
Many of the plastic pellet response operations to date have relied heavily on low technology, manual recovery techniques, such as using shovels and buckets in conjunction with sieves or hand trommels. This is often the most effective clean-up option, as it is selective and reduces the amount of unpolluted material recovered. However, it is also labour intensive, involving sometimes hundreds of people over a wide geographic area for a protracted period. Means of mechanical recovery of plastic pellets are currently limited. They often involve adapting off-the-shelf tools and technology designed for oil spill response, such as vacuum systems, flushing or flooding systems, or heavy machinery. Due to lower selectivity, a secondary phase of separation may be necessary to avoid generating excessive volumes of waste.
Endpoints can be difficult to establish in plastic pellet cases, particularly in polluted areas. Comparing the level of residual contamination to background levels of plastic pollution (and the expectation of chronic strandings of pellets) is key to determining the appropriate level of clean-up work to be undertaken. Continuing labour-intensive shoreline cleaning operations to selectively remove small amounts of incident-related plastic pellets is likely to be unreasonable if the background level of plastic debris is high. Suitable endpoints should be agreed by all parties involved.
On a regulatory level, in April 2025, the Council of the EU and the European Parliament reached a provisional agreement on new regulations aimed at reducing plastic pellet losses.
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