3.3 3.a, 3.b, 3.c - Ocean pollution, oil spills and plastic gyres

Sources of ocean pollution

A pollutant is a substance or form of contamination that causes harmful change when introduced in a particular amount and setting. Oceans can dilute and redistribute material, but dilution does not necessarily destroy it. Evaluating pollution requires its source, chemical or physical form, persistence, transport and effects, rather than simply whether the water looks dirty.

Combustion of coal, oil and gas releases carbon dioxide to the atmosphere. Some dissolves in ocean water, altering carbonate chemistry and contributing to acidification. Carbon dioxide can therefore change the ocean system without being dumped directly from a vessel. Warming driven by greenhouse-gas accumulation adds a related pressure, although heat transfer and chemical acidification are distinct mechanisms. NOAA's acidification overview explains the chemical pathway developed further in the next lesson.

Domestic and industrial waste reaches the sea through rivers, drains, poorly managed disposal, atmospheric deposition and direct releases. Plastics can come from packaging, synthetic fibres, industrial pellets and lost fishing equipment. Large items may fragment into microplastics without being completely mineralised into harmless end products. Nutrient-rich sewage and runoff can also stimulate excessive algal growth; decomposition then consumes oxygen, potentially stressing other organisms.

Heavy metals, including mercury and lead, can enter from mining, industry and contaminated runoff. Some chemical forms accumulate in organisms and can transfer through food webs; the behaviour of one metal must not be assumed for every contaminant. The IAEA's September 2013 marine-pollution account distinguishes pollutant sources and biological effects. Persistent contamination of sediment can create a continuing source after an initial release ends.

Nuclear waste and accidental releases can introduce artificial radionuclides. Their distribution depends on currents, chemical form, particles and radioactive decay; a detected radionuclide does not by itself establish the level of biological harm. Historical dumping, nuclear tests and installation-related releases are distinct sources described in the IAEA's marine radioactivity assessment. Monitoring seawater, sediments and organisms is therefore more informative than treating every radioactive material as identical.

Deepwater Horizon impacts

Deepwater Horizon was a drilling platform operating at the Macondo well in the Gulf of Mexico, off Louisiana in the southern United States. An explosion on 20 April 2010 killed 11 workers and led to a major oil release. The well discharged for 87 days before being capped. NOAA's 2020 account gives the release as approximately 3.19 million barrels, or 134 million US gallons. These refer to the same release estimate in different units, not two quantities to add.

Oil affected surface water, the water column, shorelines and deep habitats. Floating oil could coat birds and turtles, while exposure to toxic components affected marine organisms through different pathways. Oil reaching marsh vegetation could damage plants and weaken the roots that help stabilise sediment, increasing vulnerability to erosion. Submerged material also reached deeper habitats; a disappearing surface slick therefore did not establish that all oil or effects had vanished.

The 2016 damage assessment overview describes injury across an interconnected ecosystem. NOAA's 2017 synthesis on marine mammals and sea turtles draws on research beyond the initial spill period. Exposure and recovery varied by species, life stage and location. Mortality is only one measure: impaired reproduction, growth or survival can affect populations after visible contamination declines.

Human activities were disrupted through both ecological damage and protective restrictions. Fisheries closures prevented harvesting in affected waters and interrupted fishing, processing and related businesses. Beaches, boating, recreational fishing and wildlife viewing were also affected, harming tourism and local earnings. NOAA's account of human impacts explains how losses extended beyond the first weeks. Perceptions of contamination could also discourage visitors, while households dependent on one seasonal livelihood had fewer alternatives.

Immediate effects included worker deaths, oil exposure, emergency closures and lost trade. Longer-term concerns included habitat recovery, population-level effects, compensation disputes and the resilience of coastal economies. Not every Gulf location or business suffered equally, and later changes also reflect storms, development and other pressures. A geographical assessment should identify the pathway and timescale rather than attribute every subsequent problem to the spill alone.

Managing the oil spill and recovery

Spill management had several goals: stop the source, reduce exposure, remove or treat oil, protect people and restore damaged resources. These goals required different actions and timescales. Capping stopped the continuing release; permanent well-sealing work followed, while shoreline and ecological recovery continued much longer. NOAA's incident timeline distinguishes these stages.

Booms attempted to contain floating oil or protect sensitive shorelines. Skimmers physically collected surface oil, but waves, dispersed droplets and the enormous area limited what could be recovered. Controlled burning removed some surface oil but required suitable conditions and created air emissions. Chemical dispersants broke oil into smaller droplets, changing its distribution and potentially facilitating degradation. They did not make the oil cease to exist; reduced surface exposure could be accompanied by exposure within the water column. NOAA's containment guidance explains why no method works under all conditions.

Decisions therefore involved trade-offs among habitats and organisms. A method protecting birds or shorelines could have different consequences for organisms below the surface. Clean-up on fragile shores could itself disturb sediment and vegetation, so “more intensive” was not automatically “better”. Monitoring, forecasts and knowledge of sensitive habitats helped responders choose where intervention was most useful.

Economic compensation and ecological restoration addressed different losses. Compensation processes sought to address financial harm to people and businesses, while natural-resource damages supported restoration on behalf of the public. NOAA records court approval in April 2016 of an approximately US$8.8 billion settlement for natural-resource injuries. This was a component of wider legal arrangements, not a payment received by each fishing household or proof that nature had already recovered.