Ships' Impact: Water Pollution And The Ocean's Future

The shipping industry has played a significant role in the development of the world economy, with the majority of international trade still being accomplished through shipping. However, ships have also been a major contributor to water pollution. From the release of ballast water filled with biological materials to the discharge of untreated sewage and oily wastewater, ships are filling the oceans with toxic pollutants, causing extensive ecological and economic damage to aquatic ecosystems. Noise and air pollution from ships further add to the problem, impacting marine life and human health. With the industry expected to grow, addressing water pollution from ships is crucial to protect marine environments and ensure sustainable trade practices.

Oil spills and ballast water discharge

Ballast water is essential for stabilising ships during travel. However, the discharge of ballast water can lead to the spread of invasive species, causing ecological and economic damage. Ballast water discharge often contains a variety of biological materials, including plants, animals, viruses, and bacteria, which can include non-native and exotic species. The introduction of these species into new ecosystems can have far-reaching consequences, as seen with the zebra mussel, which spread through ballast water discharge and cost the US economy billions of dollars.

The discharge of ballast water is governed by the Ballast Water Management Convention, which aims to minimise the spread of invasive species. However, the regulation of ballast water is complex, and current measures are often inadequate. The weight of ballast water also increases fuel consumption, contributing to air pollution and carbon emissions.

In addition to oil spills and ballast water discharge, cruise ships and other large vessels contribute to water pollution through sewage discharge, plastic waste, and greywater. Sewage from ships can be pumped directly into the ocean in most places, posing risks to public health and aquatic life. Plastic waste from ships entangles and is ingested by marine organisms, impacting their mobility, respiration, and feeding behaviours. Greywater, or wastewater from sinks, showers, galleys, and laundry, contains pollutants such as detergents, oils, metals, and organic compounds, further degrading marine ecosystems.

To address these issues, international organisations, national governments, and businesses must work together. While some efforts are being made, such as fines for illegal dumping, the cruise industry continues to grow, and the impact of water pollution on marine ecosystems remains significant.

Noise pollution

Sources of Ship Noise Pollution

The main sources of underwater noise from ships are the propeller, machinery, and the movement of the hull through the water. Propeller cavitation, a breakdown in water flow over the propeller blades, is a significant contributor to ship noise. It can be addressed through design changes to the propeller and hull or the use of devices that smooth water flow into the propeller. The engine also contributes to noise, and placing it on mounts can reduce noise transfer through the hull.

Other sources of ship noise include operating equipment such as echosounders used to measure water depth, and the simple act of the ship moving through the water. Slowing down can significantly reduce ship noise, with a 10% reduction in speed resulting in a 40% decrease in total sound energy.

Impact of Ship Noise Pollution

Underwater noise pollution has been shown to cause elevated stress in marine mammals, disrupting essential life functions such as feeding, navigation, and reproduction. It can also increase their anxiety levels, leading to relocation and difficulty in finding mates or food. Continuous noise from commercial shipping may have both short and long-term negative consequences on marine life, with potential impacts on species that are at risk of extinction, commercially important, or critical for ecosystem support.

The impact of ship noise pollution on human health has also been recognised. Continuous noise onboard ships can adversely affect the health and well-being of personnel, leading to the implementation of regulations to reduce on-board noise and protect individuals from hazardous noise levels.

Mitigation Efforts

Various initiatives and guidelines have been developed to address ship noise pollution, including the International Maritime Organization's (IMO) Guidelines for Reducing Underwater Noise from Commercial Ships, which provide advice on designing quieter ships and reducing noise from existing vessels. The IMO has also designated ""Particularly Sensitive Sea Areas" (PSSAs)" to protect vulnerable marine life from the impacts of underwater noise.

Other efforts include research projects, underwater listening stations to monitor noise levels and their effects on marine life, and incentives for quieter ships, such as reduced harbour dues. Additionally, the COVID-19 pandemic provided a unique opportunity to study the impact of reduced vessel traffic on underwater noise levels, with global shipping noise source energy decreasing by 6% during the pandemic.

Sewage and greywater

Greywater, on the other hand, refers to wastewater from sinks, showers, galleys, laundry, and cleaning activities aboard a ship. It can contain various pollutant substances, including fecal coliform bacteria, detergents, oil and grease, metals, organic compounds, petroleum hydrocarbons, nutrients, food waste, and even medical and dental waste. The accumulation of greywater can have a more significant impact on the marine environment due to its high concentration in oceanic waters.

The impact of sewage and greywater pollution from ships is not limited to ecological damage but also extends to economic and human health issues. For example, the discharge of ballast water, which is used to stabilise ships and often discharged in different regions, can contain non-native species that cause extensive ecological and economic harm to aquatic ecosystems and serious human health problems.

To address sewage and greywater pollution from ships, international regulations and initiatives have been introduced, such as the International Convention for the Control and Management of Ships' Ballast Water and Sediments. However, the current regulations are often considered inadequate, and the shipping industry's growth and impact on the environment continue to be a concern.

Overall, sewage and greywater pollution from ships have far-reaching consequences, and ongoing efforts are necessary to mitigate their impact on marine ecosystems and human health.

Air pollution

Diesel engines, commonly used in the freight industry, play a significant role in ship-sourced air pollution. The exhaust from these engines contains high levels of sulphur dioxide, nitrogen oxide, particulate matter, carbon monoxide, carbon dioxide, and hydrocarbons. The U.S. Environmental Protection Agency (EPA) has classified diesel exhaust as a likely human carcinogen, highlighting the serious health risks associated with exposure.

The impact of ship emissions is particularly pronounced in coastal areas, where maritime shipping traffic is on the rise globally. Studies have shown that shipping emissions can increase fine particulate matter (PM2.5) concentrations, posing risks to human health. For example, in eastern coastal regions of China, shipping emissions led to an increase of up to 5.2 µg m−3 in PM2.5 concentrations, which were carried as far as 900 km inland.

To address air pollution from ships, various strategies and technologies have been proposed. These include the use of scrubbers to reduce SO2 emissions, internal engine modifications to lower NOx production, and the implementation of emission control areas (ECAs) by the International Maritime Organization (IMO) to minimize NOx, SOx, and particulate matter emissions in designated areas. Additionally, speed reduction has been shown to effectively reduce fuel consumption and, consequently, air pollutant emissions.

While regulations and initiatives, such as the Green Shipping Corridor program, have made strides in mitigating ship-sourced air pollution, it remains a pressing issue. With the demand for seaborne trade projected to grow by almost 40% by 2050, the need for continued efforts to reduce air pollution from ships becomes increasingly crucial.

Plastic pollution

Plastic waste makes up 60-80% of marine debris, with single-use plastics accounting for 40% of the plastic produced annually. Ships are responsible for a large proportion of plastic pollution, with estimates ranging from 20-70% depending on the region. The majority of plastic pollution in the ocean is caused by littering and improper waste disposal, such as flushing wet wipes, cotton buds, and sanitary products down the toilet. Microfibres are also released into waterways when we wash our clothes. Once in the ocean, plastic waste is extremely difficult to retrieve, and it can take hundreds of years for it to degrade.

To address plastic pollution, some governments have taken steps to limit or ban the use of plastic bags, and new tools such as food waste biodigesters help separate non-plastics from organic waste during disposal. However, the best way to tackle the issue is to limit or eliminate our use of disposable plastics and increase the use of biodegradable resources.

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