Human activity has led to the spread of toxic pollutants across the world’s oceans as well as the absorbance of a third of carbon dioxide emissions resulting in decreased pH. Despite rising awareness, the impacts of changing ocean chemistry on ecosystems and the species they encompass are yet to be fully understood.
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The unprecedented levels of pollution in the world’s oceans and its effects on humans
Human activities have impacted natural systems by consuming natural resources to fuel the global consumption of food and energy and altering landscapes to make space for infrastructure.
This has led to unprecedented levels of pollution, particularly over the last 100 years, as the consumption of fossil fuels has deregulated atmospheric concentrations of greenhouse gases. For the world’s oceans, this has led to the rise of water temperature as well as the absorption of carbon dioxide, which has led resulted in gradual changes in water chemistry in recent decades.
Pollution can be described as unwanted waste released to air, water, and land by human activity. Today, pollution of the oceans is widespread, with the occurrence of toxic metals, plastics, manufactured chemicals, petroleum, urban and industrial wastes, pesticides, fertilizers, pharmaceutical chemicals, agricultural runoff, and sewage, documented across all oceans.
An estimated 80% of the pollution in the ocean originates from land-based sources, like agricultural fields or industrial runoffs that reach oceans through rivers, atmospheric deposition, and direct discharges. To date, pollutants are ubiquitous and are known to contaminate seas and marine organisms from the high Arctic to the abyssal depths. However, pollution is most highly concentrated along coastlines, which is particularly severe in low- and middle-income countries.
Despite greater awareness of ocean pollution, the nature and magnitude of potential impacts are only beginning to be understood. In a 2020 review by Landrigan, researchers describe the causes and effects of ocean pollution on human health.
From existing literature, authors found plastic is a rapidly increasing component of ocean pollution, with an estimated 10 million metric tons of plastic waste enter the seas each year. Additional emerging issues also included mercury, which is the metal pollutant of greatest concern in the oceans, and the use of chemical fertilizers which has led to more harmful algal blooms.
For humans, methylmercury and industrial polychlorinated biphenyls are pollutants with the worst consequences. In children, they are known to damage developing brains, reduce IQ and increase children’s risks for autism, ADHD and learning disorders, whereas for adults, exposure increases risks for cardiovascular disease and dementia.
Other manufactured chemicals also increase the risk of cancer, cause severe neurological impairment and some have high chances to cause mortality. The researchers also find that the health impacts of ocean pollution fall disproportionately on vulnerable populations in the Global South. However, despite such drastic impacts, pollutants such as metals and toxins are often acute events associated with runoffs and oil spills, but on a global scale, pollution is chronically altering the chemistry of the oceans.
How We Can Keep Plastics Out of Our Ocean | National Geographic
The acidification of the oceans caused by greenhouse gas emissions and effects on organisms
The emission of greenhouse gases has led to the oceans absorbing 30 to 40% of atmospheric carbon dioxide. In turn, this has resulted in the acidification of the oceans, with oceanic pH decreasing gradually.
By the year 2100, if CO2 is emitted at the same rate as today, ocean acidity will increase by about 15%, which has not occurred in the last 400,000 years and would cause an ecological catastrophe on a global scale.
For organisms that rely on water chemistry to develop structures, such as calcifying organisms, ocean acidification would result in widespread erosion, limited development, and high mortality. That is because the structures that many organisms such as mollusks, crustaceans, and corals form are made of calcium carbonate or other forms of calcium, which would dissolve faster under acidified conditions.
Such impacts would cause widespread deterioration of calcifying organisms, which are crucial for ecosystem maintenance as well as to provide aquacultural services for human populations.
In a 2017 study by Laura Falkenberg and Tubb, authors discuss the economic losses associated with ocean acidification. The researchers consider the factors that could affect how much money would be lost if ecosystem services would cease to be provided by calcifying organisms.
The authors discussed how economic effects will vary depending on species and region considered as well as abiotic factors such as spatiotemporal scales of acidification. Despite varying results depending on various factors, all scenarios resulted in negative impacts and economic losses.
Further research is required to improve our understanding of the repercussions of ocean acidification across ecosystems. Despite calcifying organisms being of primary concern, non-calcifying organisms are also impacted, with research indicating GABA receptors may be inhibited in fishes and other species. Studies have shown inhibition of GABA activity affected the cognitive abilities of organisms such as the ability of reef fishes to find reef habitats or the predator response of prey species.
Future considerations – interactions with other stressors, and long-term solutions
Understanding the changes in ocean chemistry is confounded by interactions with other stressors on varying spatiotemporal scales. In oceanic systems, stressors do not occur in isolation, and therefore, the changes in pH are occurring in synergy with pollutants such as microplastics, which are able to carry toxic compounds through the water column.
Changes in ocean chemistry should also consider varying spatial and temporal scales. Incidents such as oil spills are key to consider, as crude oil is long-lived and persistent, and spills are able to alter the chemical properties of water on smaller spatiotemporal scales. On broader scales, long-term decrease in oceanic pH is the primary issue when considering acidification effects.
The health of the oceans is closely associated with human health as the ecosystem services provided by coastal and oceanic systems are key to sustaining human populations into the future. However, the disruption of ocean chemistry, as well as the spread of toxic pollutants, has unpredictable and unprecedented consequences that are yet to be fully understood.
- Falkenberg, L. J., & Tubb, A. (2017). Economic effects of ocean acidification: Publication patterns and directions for future research. Ambio, 46(5), 543–553. https://doi.org/10.1007/s13280-017-0895-9
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- Landrigan, P. J., Stegeman, J. J., Fleming, L. E., Allemand, D., et al. (2020). Human Health and Ocean Pollution. Annals of Global Health, 86(1), 151. https://doi.org/10.5334/aogh.2831
- Lelieveld, J., Bourtsoukidis, E., Brühl, C., et al. (2018). The South Asian monsoon—pollution pump and purifier. Science, 361(6399), 270–273. https://doi.org/10.1126/science.aar2501
- Zhang, B., Matchinski, E. J., Chen, B., Ye, X., Jing, L., & Lee, K. (2019). Marine Oil Spills—Oil Pollution, Sources and Effects. World Seas: An Environmental Evaluation, 391–406. https://doi.org/10.1016/b978-0-12-805052-1.00024-3