Marine Pollution – Some Chemical Sources & Impacts

Oceans cover over 70% of the surface of our planet and the oceanwater comprises over 95% of Earth’s water. This makes oceans the biggest natural resource on Earth. They are vast and deep, hence until recently, dumping and leakage of debris into marine water was never a public health concern. It was generally assumed that the large amount of water of oceans dilutes the trash, chemicals, and other foreign materials that enter the marine environment and therefore no harm is caused due to them.

Marine pollution in general occurs when chemicals, trash, or other human-created substances enter our planet’s oceans causing disturbance to marine life and habitats and thus harmfully effecting the marine ecosystems. There are many types of marine pollution such as chemical, physical (trash), light, and noise pollution.

Chemical pollution refers to harmful chemicals entering the marine waters resulting from human activities such as use of plastics, fertilizers, insecticides, herbicides, oils, and detergents. Chemicals released from vehicles, industries, and sewage also end up causing chemical pollution to the marine environments.  

Mercury is a chemical contaminant that is released from waste incinerators and coal-fired utilities, converts into methylmercury upon entering the marine ecosystem, and accumulates in sea animals that are ultimately consumed by humans. Hundreds and thousands of babies born each year are having dangerously high levels of methylmercury in their blood causing suppression of immune system, delays in brain development in children, and cardiovascular diseases in adults.

Plastic is another source of chemical pollution. It encompasses about 80% of the debris present in the oceans. It is made from petroleum products i.e. crude oil and natural gas in their refined forms, so they can be referred to as refined hydrocarbons after they had undergone many chemical processes in oil refineries. Since plastic does not biodegrade, they usually do not decompose in nature. Some types of plastic do biodegrade, but over a very long period - sometimes 500 years! Plastic usually photodegrades into micro plastic fragments upon oxidation. Since most of the waste that is generated ends up at landfills or oceans, much of the plastic thrown away reaches the ocean through streams, rivers, and blowing of the winds. Some examples of macroscopic plastic debris that reaches the oceans include plastic bags, bottles, food wrappers, cups, spoons, ropes, net, and fishing gear whereas micro plastic pieces that result from the breakdown of large plastic pieces are known as “nano plastics” and are considered to be a great threat as they easily accumulates into the bodies of marine organisms (Depledge, 2013).

Thousands of marine animals are getting killed each year due to ingestion of plastic or by getting entangled by plastic materials. Some marine animals consume floating plastic bags mistaking them for jellyfish and some seabirds consume plastic bottle caps mistaking them for food. The consumption of plastic reduces stomach capacity and appetite, blocks gastric enzyme secretion, hinders and delays growth, ovulation and reproduction, blocks intestines and causes internal injuries in the marine organisms. Many plastic fragments have been discovered in the guts, respiratory tracts, and tissues of many marine birds, turtles, mammals, vertebrates, and invertebrates (Derraik 2002; Sigler, 2014). 

Plasticizers that are added during the production of plastic to promote flexibility and resilience are chemicals that are generally toxic for living organisms in nature such as bisphenol A (BPA) and phthalates. They are hormone-disrupting chemicals since BPA can mimic estrogen and phthalates interferes with testosterone. When male fish are exposed to these hormone-disrupting chemicals, they can develop ovaries (Brander, 2011).

Carbon emissions that result from our burning of fossil fuels are absorbed by the oceans and change the pH of surface waters resulting into ocean acidification. The high acidity decreases the carbonate levels threatening the lives of reefs and shellfish. Mussels, oysters, clams, and other shellfish do not get adequate amount of calcium carbonate in order to build their shells and skeletons. Acidification of ocean waters also causes bleaching of coral reefs exposing fish to its predators (NRDC, 2018).

Pesticides are chemicals used by humans to kill or control pests in agricultural fields. Pesticides are of different types such as herbicides, insecticides, fungicides, rodenticides, etc. A research project carried out in American Samoa studied the land-based sources of marine pollution and has found organophosphate pesticides including Parathion present in coastal streams there although its use is restricted due to its highly toxic nature. The chemicals in it interferes with cholinesterase, an enzyme that aids in the proper working of the nervous systems (Polidoro, Beth A et al, 2017). Another research project carried out in Argentina has discovered the existence of organochlorine pesticides in creek sediments there despite them being banned due to increasing the risk of hormone-related mutations and auto-immune diseases (Miglioranza, Karina S. B, Julia E Aizpún de Moreno, and Victor J Moreno, 2004).

The negative impact of marine pollution is not just limited to the lives of marine organisms, but also impacts human health through seafood consumption and damages caused that alters the ecosystems.

References:

Depledge, M.H et al. “Plastic Litter in the Sea.” Marine Environmental Research 92 (2013): 279–281.

Sigler, Michelle. “The Effects of Plastic Pollution on Aquatic Wildlife: Current Situations and Future Solutions.” Water, Air, & Soil Pollution 225.11 (2014): 1–9.

Derraik, José G.B. “The Pollution of the Marine Environment by Plastic Debris: a Review.” Marine Pollution Bulletin 2002: 842–852. 

Susanne M. Brander et al. “The Ecotoxicology of Plastic Marine Debris.” The American Biology Teacher 73.8 (2011): 474–478.

NRDC (2018). Ocean Pollution: The Dirty Facts. Retrieved on June 27, 2020 from https://www.nrdc.org/stories/ocean-pollution-dirty-facts

Polidoro, Beth A et al. Land-Based Sources of Marine Pollution: Pesticides, PAHs and Phthalates in Coastal Stream Water, and Heavy Metals in Coastal Stream Sediments in American Samoa. Marine Pollution Bulletin 116.1-2 (2017): 501–507.

Miglioranza, Karina S. B, Julia E Aizpún de Moreno, and Victor J Moreno. Land-Based Sources of Marine Pollution: Organochlorine Pesticides in Stream Systems. Environmental Science and Pollution Research 11.4 (2004): 227–232.