Oil Spill Impact: Water Pollution Explained

Oil pollution is a pressing issue that affects marine life and human activity alike. Oil spills are a major contributor to this problem, with large quantities of oil being released into the sea by tankers, ships, pipelines, and other sources. The impact of oil spills is devastating for marine wildlife, including fish, birds, and sea otters, and can also ruin beaches and make seafood unsafe to eat. While cleanup efforts have been made, they often fall short of completely removing the oil and can sometimes cause additional harm. With oil drilling expected to continue, the threat of oil pollution in water persists, demanding ongoing attention and solutions.

Oil spills from tankers

In the 1970s, oil spills from tankers were common, with between 70 and 100 spills occurring annually. The quantity of oil spilled during this period was significant, often exceeding 300,000 tonnes per year. Since then, the number of spills has decreased by more than 90%, with no year in the last decade having more than eight oil spills. This reduction can be attributed to advancements in technology, improved safety measures, and a growing emphasis on oil spill prevention plans.

Despite this positive trend, oil spills from tankers remain a concern. In 2023, there were ten oil tanker spills worldwide, with nine incidents releasing less than 700 metric tons of oil. However, the Sanchi tanker collision in 2018 stands out as a particularly devastating event, resulting in the deaths of all crew members and the discharge of 113,000 metric tons of condensate into the East China Sea.

The impact of oil spills from tankers can be devastating for marine ecosystems. Oil spills can contaminate beaches, sediment, and water bodies, causing harm to marine wildlife. Oil can suffocate fish, impair the movement and insulation of birds and mammals, and block light from reaching photosynthetic plants in the water. The cleanup of oil spills is challenging, and even with advanced technology and trained personnel, it is nearly impossible to remove 100% of the spilled oil.

Additionally, it's important to note that oil spills from tankers are not the only source of oil pollution in water. Other sources include routine ship operations, such as the illegal discharge of bilge (a mixture of oil and water), and land-based runoff from pavement, industrial operations, and domestic oil use. These collective sources of oil pollution can discharge even more oil into the water than major oil spills from tankers.

Routine shipping

Oceans are polluted by oil routinely from shipping, run-offs, and dumping. While oil spills make up about 12% of the oil that enters the ocean, the rest comes from shipping travel, drains, and dumping.

One source of oil pollution from routine shipping is bilge pumping. Bilge is a mixture of oil and water. Each discharge is relatively small, but thousands of releases of bilge into the oceans add up to a large amount of oil pollution. It is illegal for ships to release bilge into ocean waters, so there are likely many bilge releases that go unnoticed.

Another source of oil pollution from routine shipping is the operational discharge of oily tank washings from tankers. This source of pollution is associated with the practice of filling the holding tanks with seawater ballast after the delivery of a load of petroleum or a refined product, and later discharging the oily bilge water into the sea as the ship travels to pick up its next load. The discharge typically contains a hydrocarbon residue that is equivalent to about 0.35% of the tanker's capacity (ranging from 0.1% for light refined oil to 1.5% for heavy bunker fuel). Beginning in the early 1970s, this operational source of oil pollution was substantially reduced by a simple change in the tank-cleaning procedure called the load-on-top (LOT) process. In the LOT process, the oily wash water is retained on board for some time as ballast, allowing most of the oil to separate from the seawater. The relatively clean seawater is then discharged, while the oily residue is combined with the next cargo. The LOT technique has a potential recovery efficiency of 99%, but in operational use, it is usually 90% or less, depending on how turbulent the sea is during the separation phase. As a result of the widespread (but not universal) adoption of LOT by tankers, oil pollution from this source was reduced from about 1.1 million tonnes/year in 1973 to 0.25 million tonnes in 1989.

The transportation and transfer of oil also increase the risk of oil spills. Up to 15 transfers may be required to transport oil from the source to its use, between ocean tankers, pipelines, trains, and tanker trucks. As the number of transfers increases, so does the risk of spilling the oil.

Run-offs

Motor oil leaked from vehicles or dumped by homeowners and commercial garages is a significant contributor to stormwater run-off. This run-off is precipitation that falls on roads and parking lots and eventually makes its way into local water bodies. These pollutants can include toxic substances like lead, benzene, zinc, or magnesium, as well as fertilizers, insecticides, plastic debris, cigarette butts, paints, solvents, sediments, and other hazardous waste.

Topsoil and natural vegetation can filter out many of these pollutants. However, the impermeable pavement that covers much of the surface where these pollutants originate allows them to flow directly into storm drains and then into streams, rivers, lakes, and the ocean. Here, the oil forms a thick sludge that can poison marine life. It can suffocate fish, get caught in the feathers of birds, and block light from reaching photosynthetic aquatic plants.

To reduce the impact of oil run-offs, individuals can take several measures. These include improving car maintenance to prevent and repair leaks, disposing of used motor oil and other automotive fluids at designated drop-off or recycling locations, and cutting back on fertilizers and pesticides in lawns or gardens. Additionally, permeable pavement, rain barrels, and rain gardens can be incorporated into landscaping projects to help filter contaminants before they reach storm sewers.

Dumping

Motor oil, or engine oil, is a type of lubricant used in vehicles to reduce friction and wear between moving parts. It contains various additives, including toxic substances like lead, benzene, zinc, and magnesium. When dumped, these toxic substances can contaminate water bodies, posing a significant threat to aquatic life and ecosystems.

One common form of oil dumping is the improper disposal of used motor oil. Individuals may dump used motor oil down drains or directly into waterways, unaware of the environmental consequences. Commercial garages and automotive repair shops may also contribute to this problem by improperly disposing of large quantities of used motor oil.

Additionally, oil dumping can occur during oil exploration and drilling activities. The process of drilling for oil can generate large amounts of waste, including drilling mud and dry cuttings, which may contain chemical additives, salts, metals, and hydrocarbons. These wastes are often dumped indiscriminately into waterways, drainage channels, or agricultural soils, leading to the contamination of water sources.

Furthermore, oil dumping can occur during oil transportation and storage. Oil spills from tankers, barges, or pipelines can result in large quantities of oil being released into water bodies, causing significant environmental damage. Oil spills can occur due to accidents, equipment failures, or even deliberate actions, such as sabotage or illegal dumping.

To mitigate the impacts of oil dumping, it is essential to promote proper waste management practices and raise awareness about the environmental consequences of improper oil disposal. Individuals can play a crucial role in reducing oil pollution by disposing of used motor oil at designated drop-off locations or recycling centres. Additionally, adopting more sustainable practices, such as reducing plastic consumption and properly disposing of chemical cleaners, can help minimise the impact on water bodies.

Bilge pumping

Oil pollution in water comes from a variety of sources, including natural ones. Oil can seep from the bottom of the ocean and from eroding sedimentary rocks. However, most oil pollution is a result of human activity, such as oil spills from large tankers, industrial and domestic runoff, and routine ship operations like bilge pumping.

Bilge is a mixture of oil and water that accumulates in the lowest part of a ship, known as the bilge well. A large ship can accumulate up to 8 metric tons of bilge water in just 24 hours of operation. This mixture needs to be pumped out periodically to maintain the stability of the ship and prevent hazards from oil vapours.

The process of bilge pumping can result in the discharge of oily bilge water into the ocean, which is a major source of marine pollution. Each discharge is relatively small, but thousands of releases from ships add up to a significant amount of oil pollution. This is difficult to measure as it is illegal, and so many bilge releases go unreported.

To prevent oil pollution from bilge pumping, there are several measures that can be taken. Firstly, bilge water should be passed through an oily water separator (OWS) to reduce the level of oil particles in the mixture. It is only permissible to discharge bilge water overboard when the ship is en route and the oil content is below 15 ppm. Additionally, marinas can offer bilge pumping services and provide oil/water filtration devices to ensure that oil and fuel are not released into the water. Boat owners can also use oil absorbent pads, install oil/water filters on their bilge discharge lines, and keep marine spill kits on board to quickly absorb and confine any spills.

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