Meghan Hodges
Marine pollution is a pressing issue, with billions of pounds of pollutants entering the ocean each year. These pollutants can be broadly categorized into two types: chemicals and trash. Chemical pollution includes nitrogen-phosphorus compounds from agriculture, sewage, and industrial runoff, as well as pesticides, pharmaceuticals, and heavy metals. Trash pollution includes plastic waste, microplastics, derelict fishing gear, and abandoned vessels. Land-based sources, such as littering, poor waste management, and industrial discharges, account for approximately 80% of ocean pollution, while the remaining comes from marine sources like shipping and waste disposal. Oil spills, while declining due to improved technologies, remain a significant contributor to ocean pollution. The accumulation of toxic chemicals in the marine environment poses a threat to marine life, human health, and economic structures worldwide.
| Characteristics | Values |
|---|---|
| Types of toxic materials | Microplastics, plastic waste, petroleum-based pollutants, toxic metals, manufactured chemicals, pharmaceuticals, pesticides, nitrogen, phosphorus, fertilizer, sewage, industrial waste, sewage sludge, radioactive waste, dredged material, nitrogen-phosphorus pollution, chemical pollution, heavy metals, antifoulants, personal care products, crude oil, alkylated PAHs, organometals, alkylated tin products, phenyltin compounds, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polynuclear aromatic hydrocarbons (PAHs), DDT, toxic sludge, solvents |
| Sources of toxic materials | Land-based sources (80% of ocean pollution), marine sources, littering, poor waste management practices, storm water discharge, extreme natural events, oil spills, accumulation of dispersed sources, agricultural runoff, urban and industrial runoff, maritime transportation, atmospheric pollution, runoff from land, rivers, drains, coastal activities, shipping, discharges from marine shipping, offshore industrial operations, waste disposal at sea |
| Impact of toxic materials on marine life | Harm or kill marine animals through ingestion or entanglement, threaten habitats, interfere with navigation safety, deplete oxygen levels in water, destroy coral reefs, impair shellfish development, increase toxicity of some pollutants, threaten marine mammals, seabirds, and fish, accumulate in large mid-ocean gyres, enter the tissues of marine organisms, increase frequency and severity of harmful algal blooms (HABs), bacterial pollution, and antimicrobial resistance, trigger poleward migration of dangerous pathogens, cause global declines in fish stocks, increase toxicity in the food chain |
| Impact of toxic materials on humans | Potential acute and (sub)chronic toxicity, carcinogenicity, developmental toxicity, economic impacts through losses in marine ecosystem services, potential health impacts through seafood contamination and ingestion of microplastics |
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What You'll Learn
Oil spills and petroleum products
Oil spills are a major contributor to ocean pollution, with thousands occurring in US waters each year. Oil is a fossil fuel formed over millions of years from the remains of ancient plants and animals. It is a critical resource for human activities, used to heat homes, generate electricity, and power economies. However, when oil spills into the ocean, it has detrimental effects on the marine environment and human activities.
Oil spills can occur anywhere oil is drilled, transported, or used. The most common causes are accidents involving tankers, barges, pipelines, refineries, drilling rigs, and storage facilities. Additionally, recreational boats can contribute to oil spills due to operational errors, unpreparedness, or human error. Oil spills can also result from the release of crude oil or refined petroleum products, such as gasoline, diesel fuel, and their by-products.
The environmental impact of oil spills is significant. Oil penetrates the plumage of birds and the fur of mammals, reducing their insulating ability and making them more vulnerable to temperature changes and less buoyant in the water. It harms sea creatures, including birds, sea mammals, fish, algae, and coral, and can make seafood unsafe for human consumption. Oil spills can also contaminate beaches, mangroves, and wetlands, disrupting ecosystems and recreational activities.
Oil spills release liquid petroleum hydrocarbons, which include toxic chemicals such as polynuclear aromatic hydrocarbons (PAHs) and alkylated PAHs. These compounds are generated during the incomplete combustion of organic materials and are naturally present in petroleum and oil products. PAHs can also be adsorbed by microplastics, further spreading toxicity in the marine environment.
The cleanup and recovery process after an oil spill is crucial but challenging. It involves scientific interventions to remove oil from the water and shorelines and to help the ocean recover. During this process, air pollutants such as nitric oxides and ozone from ships can be released, impacting air quality in coastal regions. Oil spills in the ocean have long-lasting consequences, and addressing them requires sound scientific knowledge and proactive measures.
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Industrial waste and sewage
Industrial Waste
Industrial waste includes liquid, solid, or semi-solid wastes from manufacturing or processing plants. In the 1970s, 17 million tons of industrial waste were legally dumped into the oceans, with acids, alkaline waste, scrap metals, waste from fish processing, and coal ash among the most common pollutants. While the dumping of industrial waste has decreased over the years, it still occurs illegally, and industrial operations continue to contribute to ocean pollution through discharges and runoff.
Sewage
Sewage refers to the sludge from the treatment of wastewater. If sewage sludge is not contaminated with oils, organic chemicals, or metals, it can be recycled as fertilizer. However, in the past, large quantities of sewage were dumped into the ocean, with a peak of 18 million tons in 1980. While this number has decreased, sewage remains a significant source of ocean pollution.
Toxic Materials in Industrial Waste and Sewage
Regulations and Treaties
Recognizing the detrimental effects of industrial waste and sewage dumping, international efforts have been made to regulate ocean pollution. The Marine Protection, Research, and Sanctuaries Act (MPRSA) in the United States regulates the transportation and disposition of materials in the ocean to protect human health and the marine environment. Additionally, the London Convention and its modern counterpart, the London Protocol, aim to protect the marine environment by prohibiting incineration at sea of industrial waste and sewage sludge.
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Plastic pollution and microplastics
Plastic is the most common type of marine debris found in the ocean and Great Lakes. Plastic debris can come in all shapes and sizes, but those less than 5mm in length are called "microplastics". These small plastic bits are formed when larger plastic debris degrades into smaller pieces.
Microplastics can also be intentionally designed to be small, such as microbeads, which are used in many health and beauty products. They pass unchanged through waterways into the ocean, where aquatic life and birds may mistake them for food. Microbeads have been banned in the US since 2015, but microplastics remain a significant problem.
Microplastics can sorb and desorb, allowing them to bioaccumulate more toxic pollutants than macroplastics due to their larger surface-to-volume ratio. They have been found in the guts of various marine organisms, from benthic invertebrates to fish and larger mammals. These toxic pollutants include polycyclic aromatic hydrocarbons (PAHs), PCBs, DDT, and toxic metals.
The presence of microplastics in the ocean can have far-reaching consequences. They can alter photosynthesis in phytoplankton and reduce feeding rates in zooplankton, which play a crucial role in storing carbon in the ocean. This disruption to the biological carbon pump can have knock-on effects on ocean acidification, climate change, and nitrogen cycling.
Research into microplastics is ongoing, particularly regarding their potential impact on humans. Some pollutants and additives in microplastics, such as monomers and plasticizers, have been detected in the human body at higher levels than expected through gut exposure, indicating exposure through other routes.
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Agricultural runoff and fertilisers
Agricultural runoff is a significant contributor to ocean pollution. It refers to the water that flows over farms and fields during rainfall or irrigation, picking up pollutants and eventually flowing into nearby water bodies. Farms commonly use various types of fertilisers and pesticides to enhance crop growth and protect against pests. These substances are essential for crop yields but can have detrimental effects on the environment if not properly managed.
Fertilisers, for example, are typically categorised into nitrogen-based, phosphorus-based, and potassium-based types. While nitrogen and phosphorus are essential elements for plant growth, they can become pollutants when they are too abundant in water bodies. This excess of nutrients, primarily nitrogen and phosphorus, leads to a process called eutrophication, promoting the overgrowth of algae and resulting in algal blooms. These blooms can cover large surface areas of water, reducing light penetration and consuming oxygen as they decompose, creating "dead zones" that cannot support marine life.
Pesticides, on the other hand, are designed to be toxic to target organisms, including insects, fungi, and herbs. They include insecticides, herbicides, and fungicides. When washed into water bodies through agricultural runoff, these pesticides can have detrimental effects on aquatic ecosystems and biodiversity. For example, the Great Barrier Reef has suffered extensively from agricultural runoff, with pesticides and herbicides contributing to coral bleaching and reducing overall biodiversity.
Animal waste from livestock farming is another significant contributor to agricultural runoff. Manure contains high levels of nutrients, pathogens, and organic matter, which can be washed into water bodies during rainfall or irrigation. The decomposition of organic matter in manure contributes to increased biological oxygen demand (BOD) in the water, degrading water quality. Large-scale concentrated animal feeding operations (CAFOs) often produce waste that exceeds the land's absorption capacity, leading to spills and leaks that contaminate surface and groundwater with nutrients, bacteria, and other pollutants.
To mitigate the impact of agricultural runoff on ocean pollution, farmers can adopt practices such as reducing tilling intensity, implementing conservation tillage, and improving soil health. By minimising erosion, runoff, and soil compaction, farmers can reduce the chances of nutrients and pollutants reaching waterways. Additionally, managing livestock access to streams and engaging in watershed efforts can help reduce nutrient pollution in water bodies.
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Pesticides and pharmaceuticals
Pesticides are a large and diverse group of manufactured chemicals designed to be toxic to target organisms ("pests"). They include insecticides, fungicides, and herbicides. Insecticides such as organochlorines (e.g. DDT), organophosphates, carbamates, and pyrethroids are toxic to insects, while herbicides like glyphosate and phenoxyacetic acids are used to kill unwanted plants.
Pesticides enter the ocean primarily from land-based sources, with agriculture being a major contributor. They can contaminate water bodies through chemical runoff resulting from improper storage, poor loading and disposal, accidental spills, and inappropriate application. Nonpoint source pollution occurs when pesticides gradually leach into groundwater and surface waters due to runoff and erosion in agricultural fields. Once in the ocean, pesticides can sorb onto suspended particles and settle into the sediment, acting as a secondary source of pollution. Changes in environmental conditions, such as salinity and pH, can release these pesticides back into the water, impacting marine life and human health.
Pharmaceuticals, on the other hand, are chemical compounds designed for therapeutic purposes. They enter the ocean through various pathways, including wastewater discharge, aquaculture, and pharmaceutical manufacturing industries. In Europe, the Water Framework Directive covers both freshwater and transitional waters, and hormones like 17α-ethinyloestradiol and diclofenac have been identified as emerging pollutants. However, there is a lack of data regarding pharmaceutical pollution in many regions, including Africa, South America, and small island nations in Oceania.
The presence of pharmaceuticals in the ocean can have ecological and human health implications. Pharmaceuticals can accumulate in marine sediments at high concentrations, and changes in environmental conditions can release them back into the water. This can expose marine life to these chemicals, potentially impacting their behaviour, growth, and health. Additionally, the consumption of contaminated marine organisms by humans can have unknown consequences.
Addressing pesticide and pharmaceutical pollution requires a range of strategies. Effective pest management practices, such as integrated pest management, can help reduce pesticide use and minimise their impact on the environment. For pharmaceuticals, developing monitoring programmes and implementing proper waste treatment processes can help reduce their entry into marine ecosystems.
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Frequently asked questions
Ocean pollution comes from a variety of sources, with around 80% of ocean pollution originating from land-based sources. These sources include littering, poor waste management, storm water discharge, natural events like tsunamis and hurricanes, runoff from farms, and industrial waste.
Toxic materials in ocean pollution can be broadly categorized into chemicals and trash. Chemical pollutants include nitrogen-phosphorus compounds, pesticides, pharmaceuticals, heavy metals, and petroleum products. Trash includes plastic waste, ranging from microplastics to larger items like detergent bottles and fishing gear.
Toxic materials can enter the ocean through various pathways. Industrial waste and agricultural runoff are directly released into rivers and streams, which eventually flow into the sea. Land-based littering and poor waste management also contribute to the accumulation of toxic materials in the ocean.
Toxic materials have detrimental effects on marine life and ecosystems. They can lead to the destruction of coral reefs, impair the development of shellfish, and accumulate in the tissues of marine organisms, including those consumed by humans. Marine debris, such as abandoned fishing gear, can entangle and harm marine animals, damage habitats, and interfere with navigation safety.
Addressing the issue of toxic materials in ocean pollution requires a combination of preventive measures, regulatory actions, and cleanup efforts. Preventive measures include improving waste management practices, reducing the use of single-use plastics, and promoting the use of biodegradable products. Regulatory actions, such as enacting restrictions on disposable plastic items, have been implemented by several countries. Cleanup efforts may involve removing marine debris and addressing specific pollution hotspots, although it is important to recognize that cleanup may be impossible for some types of pollution.
