While seafood has long been associated with improving mental health due to its nutrient rich nature and high levels of omega-3 fatty acids, researchers are starting to investigate the potential negative side effects of a seafood-rich diet due to increasing levels of marine pollution. 

Marine pollution is a global issue, and a major health concern, as 92% of fish consumed by humans comes from the ocean, specifically from coastal fisheries. 

There are two main toxins resulting from marine pollution that researchers are concerned will affect our mental health now and into the future: mercury and microplastics. While this is still a new area of research and researchers still need to conclusively demonstrate the link between marine pollutants and human health, the negative health implications of mercury poisoning and the chemicals associated with plastic production and the effects of microplastic consumption are well studied.  


Mercury enters the aquatic environment primarily through coal-combustion, electrical power generation and industrial waste disposal. While industrial waste disposal releases pollutants directly into water sources, coal-fired power plants release mercury into the atmosphere. This mercury then makes its way into the ocean through atmospheric deposition, largely as an inorganic form of mercury. It is then converted into an organic form of mercury, known as methylmercury (MeHg), through a process known as methylation by microorganisms living in the soil or water column. This process increases the toxicity of mercury and makes it easier to absorb and more prone to bioaccumulation. The vast majority of mercury found in fish tissue is in the form of methylmercury.

The presence of high levels of mercury in aquatic systems is concerning, as it is very easily absorbed and tends to bioaccumulate up the food chain. Because mercury, or methylmercury, is easily absorbed, it enters the food chain far more easily than other toxic pollutants which are not so readily absorbed. Bioaccumulation is also problematic, because organisms higher up the food chain can have much higher levels of mercury than the levels found in the environments. This is because small organisms absorb a small amount of mercury, but larger organisms than eat lots of smaller organisms, and therefore have a higher concentration of mercury than the animals they consume, as the body is not able to process and excrete these harmful pollutants at the rate that it processes organic material.

Health Implications

Mercury is extremely toxic and very difficult to remove once it has entered the body. Because of this, it has a cumulative effect after multiple exposures. High levels of mercury in the body leads to mercury poisoning, which can severely affect the nervous system functioning and potentially prove fatal. The main health effects of mercury are:

1.     The deterioration of the nervous system

2.     Impaired vision, hearing speech, and ability to walk

3.     Involuntary muscle spasms

4.     The corrosion of skin and mucous membranes

5.     Difficulty with chewing and swallowing


Although plastic waste has long been identified as a major threat to ocean ecosystems, researchers are becoming increasingly concerned by the prevalence of microplastics. Microplastics are tiny particles of plastic which are often invisible to the naked eye. They enter the environment when larger plastic items, such as plastic shopping bags or food containers, are broken down. Because microplastics are so small, they are often consumed by marine animals, either intentionally or by accident, and bioaccumulate up the food chain. In the last ten years, the proportion of fish found to be contaminated with microplastics has doubled from around 15% to 33%. At this rate, we could expect to see around 70% of fish contaminated with microplastics by 2024.

Health Implications

Plastics have been linked with inflammation and disruption of the gastrointestinal tract, as well as disruptions to the endocrine system. The health of the gut has been strongly linked to neurological health, and ingestion of plastic has therefore been implicated in neuro-degenerative disorders. Microplastics are of special concern because they are so easily ingested and have been shown to bioaccumulate. In addition to the ease at which microplastics enter the food chain, the breakdown of plastic exposes more surface area from which the toxins contained in plastic are able to leach out into the environment. These chemicals are not well studied, but some have been shown to disrupt the endocrine system, specifically the adrenal gland, which functions in the stress response in humans. Imbalances in this gland are linked to anxiety and depression, and increased exposure to endocrine disruptors, such as microplastics, is likely to result in the development of psychological disorders.

Health Benefits of Seafood

Although there is a risk of contaminants entering our bodies from seafood, seafood also has many health benefits, and a balanced diet containing fatty fish, such as salmon, is linked to a decreased risk of psychological disorders, such as anxiety and depression. Specifically, fatty fish that are high in omega-3 fatty acids are known as brain food and have been shown to have many health benefits. Fish are also a good source of protein and vitamin D, which are also important nutrients for maintaining a healthy body and mind.

Is It Safe To Still Eat Seafood?

Lowering your seafood consumption can help reduce your risk of mercury poisoning, and may be especially advisable in pregnant and breastfeeding women and young children. However, seafood is a very good source of nutrients, such as omega-3 fatty acids and vitamin D and if you do wish to eat seafood, some are safer to consume than others. Fish or other sea creatures that are lower on the food chain may be safer to eat, as there is less opportunity for bioaccumulation to occur. 

Fish to avoid include:

·      King mackerel

·      Marlin

·      Orange Roughy

·      Shark

·      Swordfish

·      Tilefish (from the Gulf of Mexico)

·      Tuna (Bigeye, Ahi)

Fish low in mercury include:

·      Anchovies

·      Catfish

·      Clam

·      Crab

·      Crayfish

·      Croaker (Atlantic)

·      Flounder

·      Haddock

·      Hake

·      Herring

·      Mackerel (North Atlantic, Chub)

·      Mullet

·      Oyster

·      Perch

·      Pollock

·      Salmon

·      Sardine

·      Scallop

·      Shrimp

·      Sole

·      Squid

·      Tilapia

·      Trout

·      Whitefish

The area from which the organisms are sourced is also an important consideration when it comes to mercury levels – especially in filter feeding animals, such as oysters and mussels. Try avoiding organisms sourced from highly industrial areas, as these are likely to have higher levels of pollutants.

However, an estimated 3 billion people around the world rely on fish as their primary source of protein. Especially in poor rural communities, fish are a vital source of many important nutrients, and reducing seafood consumption may not be a viable option for people in these areas. It is therefore our responsibility as global citizens to reduce ocean pollutants to protect the ocean for all humans and for future generations. 

What Can You Do?

As in most cases, when it comes to reducing your impact on the environment, the most important thing you can do is be a responsible consumer and be aware of your impact on the environment. An easy way to do this at an individual level is to reduce your use of single-use plastics and to source seafood food from sustainable fishing companies, which are committed to reducing plastic waste from fishing. Getting involved in beach clean-ups and supporting ocean clean-up organizations are also a fun way to help keep the oceans healthy.