50 for the Future – Reduce marine pollution

Our recent publication, 50 for the Future, lists 50 things that we believe should happen in Scotland over the next 50 years to benefit both people and wildlife. In this week's 50 for the Future article, co-authors Dr Sam Collin and  Pete Haskell from the Scottish Wildlife Trust describe the reality of marine pollution and the importance of reducing the amount of pollutants entering our seas.


Number 32: Substantially reduce the volume of chemical contaminants, artificial nutrients and litter entering the ocean.


Scotland is a maritime nation. With almost 19,000 km of coastline and 470,000 km2 of sea, Scotland is home to spectacular wildlife, successful marine industries, and a standard of well-being that depend on clean, healthy and productive seas. Despite the central role of Scotland's marine environment the current health of marine life, from seagrass beds to whales, and the quality of the waters that surround them, is in decline.

The marine environment faces many pressures, none more so than pollution from human activity. It is estimated that 80% of all marine pollution comes from human activity on land and enters the sea through rivers and streams. It is easy to forget this connection, especially when stood in the middle of a town with no hint of marine life in sight, but the seas have become a sink for all sorts of man-made pollution. 

This pollution can take many forms, some obvious, such as plastic bags and fishing nets, and some less so, such as nutrient run-off from agriculture. But whether visible or not, marine pollution is altering the physical and functional structure of our marine environment in ways we are only just beginning to understand.

To begin to grasp the scale of marine pollution and the impact it has on the marine environment, we first need to identify the three principle (but not exclusive) categories that it falls into: chemical contaminants, artificial nutrients and marine litter. 

Historically, industrial waste water was a primary source of chemical contaminants.

Chemical contamination

Chemical contaminants are substances that have either been purified or manufactured by man. In many cases, these substances occur naturally in the marine environment, in quantities small enough to be relatively benign. However, human activities have increased their production, which, through atmospheric transportation (e.g. acid rain), surface run-off, and direct disposal, has also increased their concentration in the marine environment. 

Chemical contaminants generally fall into three main categories: oil, toxic metals, and persistent organic pollutants. 

  • Oil – when we think of oil pollution we immediately think of oil spills from tankers and oil platforms. Although these events can have catastrophic impacts on the surrounding marine life, their contribution to the total amount of oil released into the world's oceans is relatively small, less than 10%. The majority of oil entering the marine environment actually comes from boats and run-off from the land (from cars and factories for example).
  • Toxic Metals – these include substances such as mercury, cadmium and copper which, when combined with organic compounds, can increase in potency (such as mercury and carbon, which can form the neurotoxin methylmercury). Toxic metals most commonly enter the marine environment through surface run-off, especially in close proximity to industrial, mining, or metal processing sites, but some enter through atmospheric process – for example, the majority of mercury in the oceans was deposited through rain. 
  • Persistent Organic Pollutants (POPs) – these include a variety of substances from a range of different sources – herbicides from the farming industry, and PCBs (coolants and adhesives) and BPAs (e.g. plastic bottles) from the manufacturing industry. As the name suggests, POPs can remain in the marine environment for a long time and tend to accumulate in marine organisms, with apex predators such as  marine mammals containing the highest concentrations. 

Artificial Nutrients

The use of artificial nutrients in the agricultural industry has become an essential requirement for maintaining a reliable crop and meeting public food demands, but the impact these nutrients have on the marine environment is not always obvious and often goes overlooked. Excessive use of fertiliser and water run-off from fields can result in high concentrations of artificial nutrients in rivers, which ultimately leads to nutrient rich estuaries and coastal waters. 

Eutrophication has been considered one of the biggest threats to the marine ecosystem for decades. Increased nutrients can cause algal blooms that quickly deplete the water of oxygen, increase the amount of sediment suspended in the water column and reduce light levels underwater. This can have devastating effects on the ecosystem – fish and other marine organisms can suffocate, benthic species living on the seabed can become smothered and marine plants can die due to a lack of sunlight. The result of all of this is a shift towards a far less productive sea.

An average of 3,000 pieces of litter was recorded on Scotland's beaches in 2015
© Pete Haskell

Marine Litter 

Our coasts are where most people bear witness to the issue of marine litter. Few, if any, Scottish beaches are free from human-related debris. During last year's Great British Beach Clean, organised by the Marine Conservation Society, volunteers recorded on average 3,000 pieces of litter per kilometre of beach in Scotland. And this is only the litter that washes ashore!

Plastic is by far the most ubiquitous material found along the coast and in our seas. Drinks bottles, cotton bud sticks, and carrier bags are some of the most common and conspicuous items. Unfortunately, irresponsible behaviours, such as littering, fly tipping and flushing items down the toilet that our sewage systems can't deal with, are the main cause. Once at sea, these items can entangle marine life and be mistaken for food. 

Not all plastics are big though. Unfortunately, plastic doesn't disappear but instead breaks down into infinitely smaller pieces. Look closer when you're next at the beach and you might find some unrecognizable pieces of plastic that are small fragments of larger items. These small floating plastics find their way into the food chain, often ending up in the stomachs of unsuspecting fish and seabirds.

Look closer still and you discover the world of microplastics – particles less than 5 mm in size. Many of these microplastics are not fragments of larger objects, but were intentionally made this size. They range from larger nurdles – plastic lentil-sized pellets that are shipped across the world in their billions ready to be melted down and moulded into everyday objects – down to 'microbeads' that can be found in certain personal care products, such as face scrubs and toothpastes. When washed down the sink, microbeads pass through our sewage filters, straight into the sea. Astonishingly an estimated 4,360 tonnes of microbeads were used in Europe in 2012. 

Microplastics pose problems to filter feeding animals such as mussels, barnacles and zooplankton, as well as the animals that eat them. Whilst the ingested plastic itself may not always cause direct harm, the chemicals that they attract and absorb can become toxic and poisonous. These toxins are quickly passed up the food chain where they accumulate in top predators, which in many cases can be humans. 

Getting involved with beach cleans is something that everyone can do to help reduce marine litter.

Looking ahead

It is clear that our treatment of the marine environment needs improving. As a nation that depends on the seas for work, recreation and food, we must make concerted steps to make sure it remains healthy. The role of rivers in connecting inland areas with the sea means that, no matter how distant and unconnected to the sea you may feel, your behavior and daily choices can make a difference.  

So what needs to change? Firstly we must review and reassess our reliance on chemicals, fertilisers and plastics in industry, farming and manufacturing. Reducing the use of these pollutants is key to long-term and large-scale change. Investing in research that identifies alternative materials and methods for reducing waste and recycling un-used by-products is essential. The move towards a more circular economy will take time but it must be made a priority.

This large-scale change must be driven by industry, but as consumers we can also assess our own daily habits and identify areas we can improve. Organic fruit and veg, reusable shopping bags, microplastic-free facewash, sustainably-farmed fish, electric cars, the list of low-impact alternatives is continuously growing and becoming more accessible. Improving public understanding of the environmental impacts that certain products can have and providing suitable alternatives is key to changing public behavior on a large scale. 

By changing the behaviour of industries and the general public, further damage to the health of our seas can be prevented. But if our aim is to improve the health of our seas, we must look for novel solutions to cleaning up the pollutants already in the sea – marine litter being an obvious starting point. 

A plastic-free sea is an unrealistic target due to the omnipresence of microplastics but the removal of large objects through contributing to cleaning campaigns like the Marine Conservation Society's Beach Clean or KIMO's Fishing for Litter, or developing innovative technologies that directly remove plastic from the sea, would be a great improvement.

Let us know your thoughts by emailing thefuture@scottishwildlifetrust.org.uk or Tweet @ScotWildlife using #50fortheFuture.

The Scottish Wildlife Trust is a supporter of The Great Nurdle Hunt and The Cotton Bud Project.

 Dr Sam Collin is the Scottish Wildlife Trust's Marine Planning Officer.



Pete Haskell is the Trust's Marketing and Communications Manager. He graduated in Marine Ecology from the University of Plymouth in 2007.


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In this week's 50 for the Future article, co-authors Dr Sam Collin and Pete Haskell describe the reality of marine pollution and the importance of reducing the amount of pollutants entering our seas.

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