Coastal-marine contamination: what it is, how it is produced and how it is combated

Marine contamination, unlike water contamination in general, focuses on human-made products entering the ocean. Although ocean water covers more than 70% of the Earth's surface, we have only begun understanding how human activity affects this aquatic habitat in the last few decades.

Studies carried out in recent years show that degradation, especially in coastal areas, has accelerated markedly over the last three centuries, as industrial discharges and run-off from farms and coastal cities have increased.

A wide range of pollutants (microplastics, harmful substances, light contamination, etc.) affect marine ecosystems. For example, plastics account for 95% of the waste in the Mediterranean Sea, whose contamination accounts for the highest density of floating microplastics in its waters.

Because of the vastness and depth of the oceans, it was believed that they could be used to dump rubbish and chemicals in unlimited quantities without major consequences, and even the advocates of continued dumping had a slogan: ‘The solution to contamination is dilution’. Today, one need only look at the dead zone the size of the state of New Jersey (or the Valencian Community in Spain, some 22,000 square kilometers) that forms each summer in the Mississippi River delta or the 1,600-kilometre expanse of decaying plastics in the North Pacific to realize that this policy of ‘dilution’ has contributed to bringing what was once a thriving ocean ecosystem to the brink of collapse.

The 1972 London Convention, ratified in 1975 by Spain, was the first international agreement put in place to improve the protection of the marine environment and prompted regulatory programmes, prohibiting the dumping of hazardous materials at sea. However, in 2006, an updated agreement, the London Protocol, came into force, which more specifically bans all wastes and materials, except for a short list of items such as dredged spoil.

Many of these pollutants accumulate in the deep ocean, where they are ingested by small marine organisms and enter the global food chain. Large ocean dwellers also suffer the consequences. Scientists have even discovered that medicines ingested by humans that are not fully processed by the body end up in the fish, salt, or seafood consumed.

Different forms of contamination

Marine contamination encompasses many types of contamination that alter the marine ecosystem, including chemical, light, noise and plastic contamination.

Ocean acidification

Marine organisms such as corals and molluscs are under threat from ocean acidification. The sea is becoming more acidic as it absorbs 30% of the carbon dioxide produced by humans. This limits the availability and quality of food from the sea.

As the level of acidity increases and the concentration of carbonates decreases, environmental conditions become corrosive to organisms that use calcium carbonate to produce their shells and skeletons, and the energy expended to overcome the increasingly acidic conditions can reduce the energy for other physiological processes such as reproduction or growth.

Nuclear and isotopic techniques are effective tools for investigating the acidification of the seas, studying and forecasting its effects and supporting policies to combat this problem that contributes to climate change.

Chemical contamination

The introduction of harmful pollutants into the ocean, usually from human activities, including pesticides, herbicides, fertilisers, detergents, oil, industrial chemicals and sewage.

In many cases, ocean pollutants originate from inland water sources far from the coast, such as rivers, groundwater, etc.

For example, nutrient-laden fertilisers applied to farmland often end up in local streams until they are deposited in estuaries and bays. This excess of nutrients triggers massive algal blooms that rob the water of oxygen, leaving dead zones where marine organisms can barely live.

The scientific community is beginning to better understand how certain pollutants that leach into the ocean from other materials affect marine wildlife. PFASs, a chemical found in many household products, accumulate in human and mammalian blood. Even pharmaceuticals ingested by humans, but not fully processed by our bodies, end up in aquatic food webs.

Light contamination

Since the invention of the light bulb, light has spread across the planet, reaching almost all ecosystems. Although often considered a terrestrial problem, scientists are beginning to understand how artificial light at night affects many marine organisms.

Light contamination penetrates underwater, creating a very different world for fish living in shallow reefs near urban environments. Artificial light disrupts the normal signals associated with circadian rhythms, which species have evolved to time their migration, reproduction and feeding, and can make it easier for predators to seek out smaller prey.

Noise contamination

Contamination is not always visible. In large bodies of water, sound waves can propagate and diminish over kilometres. The increasing presence of loud and persistent sounds from ships, sonar devices and oil rigs disturbs the natural noises of the marine environment.

For many marine mammals, such as whales and dolphins, poor visibility and long distances make non-visual underwater communication essential. Toothed whales use echolocation (emitting sounds that reflect off surfaces) to help them ‘see’ in the ocean. Unnatural noises disrupt communication, disrupting the migration, communication, hunting and breeding patterns of many marine animals.

Plastic contamination

It leaches into the ocean through runoff and even intentional dumping. Some plastics accumulate because their degradation rate is slow.

According to some estimates, there are as many as 5.25 trillion plastic particles, with a total weight of 250,000 tonnes floating in the world's oceans. As an example, the amount of plastic in the Atlantic Ocean has tripled since the 1960s and the rubbish patch floating in the Pacific Ocean of almost 1.6 million square kilometres (three times the size of Spain) is a powerful image of our plastic problem.

One of the main culprits is single-use plastics that are dumped directly or indirectly into the ocean.

Another big problem is that among the thousands of tonnes floating around are plastic micro-particles (particles smaller than 5 mm). These particles come from the wear and tear and disintegration of larger plastic debris, granules used in the manufacture of plastics, additives in cleaning and personal care products and synthetic clothing.

These plastics and microplastics are accidentally consumed by many marine mammals because plastic bags, for example, resemble jellyfish, a common food of sea turtles, while some seabirds eat plastic because it releases a chemical that makes it smell like their natural food. Discarded fishing nets also drift for years, trapping fish and mammals.

Pieces of plastic swirl in the water column and reach the depths of the ocean. Scientists have found plastic fibres in corals in the Atlantic Ocean and, more worryingly, they have discovered that corals prefer plastic to food. Moreover, dying marine mammals washing ashore also contain plastics in their stomachs.

Thanks to radiolabelled tracers, it is possible to find out how organic pollutants reach plastic microparticles and how these pollutants are passed on to marine organisms.

In addition, the study of natural archives such as sediment cores, corals and shells provides insight into past contamination of marine ecosystems as carried out by the International Atomic Energy Agency (IAEA) Radiometry laboratory, which uses, for example, lead-210 and caesium-137 geochronology to reconstruct the history of recorded environmental changes. This method helps to assess the rate of accumulation of contamination in marine and coastal ecosystems.

How to fight back?

Many national laws and international agreements have established an explicit ban on the dumping of harmful materials into the ocean, although ensuring compliance remains a challenge and isolated efforts to restore estuaries and bays have had some success, but the contamination is trapped in marine sediments and makes a complete clean-up almost impossible. However, many pollutants persist in the environment and are difficult to remove completely. They often cannot be broken down for long periods or increase in concentration as they move up the food web. As plastic is believed to take hundreds of years to decompose, its presence poses a threat to the marine environment for centuries.

The solution to contamination problems begins with an environmental diagnosis, using nuclear and conventional techniques, and the assessment of mitigation and/or remediation measures to protect ecosystems, which involves constant monitoring of the state of the environment. For this, there are nuclear and isotopic techniques such as the use of isotopes (calcium-45, carbon-14, boron-11 or uranium and thorium), the use of X-rays, X-ray fluorescence spectrometry, mass spectrometry, etc., which are key tools in the fight against marine and coastal contamination.

There are also options to combat contamination such as encouraging recycling and reuse which can minimise plastic contamination, dimming unnecessary lights at night which can limit light contamination or encouraging the responsible use of chemicals through policy and consumer actions that can protect the environment in the future.

It is important to bear in mind that we will not succeed in further degrading the oceans alone, nor in combating marine and coastal contamination, but we can work together with initiatives such as those carried out by the International Atomic Energy Agency (IAEA) or cooperation networks in science and communication such as the Marine-Coastal Stressor Research Network in Latin America and the Caribbean (REMARCO), which employs nuclear and isotopic techniques for peaceful use, the approach to environmental problems of the marine-coastal ecosystems of Latin America and the Caribbean in which they deal with issues such as ocean acidity.