Consumption of aquatic animals has been always recommended as healthy but the truth is that it can be very detrimental for human health nowadays because of marine pollution from trash and chemicals.
Among the trash that can be found in the oceans, microplastics and microbeads are the ones most commonly found in aquatic animals who are commonly consumed, along with heavy metals which, as time goes by, are accumulated in their cells and tissues.
“Seafood” was by far the most hazardous food for consumption during the years 2004-2013 (pound for pound) as stated by the center for science in the public interest (CSPI) in their 2015 review over foodborne illness in the U.S during these years1.
Microplastics & manmade chemicals
Microplastics are small plastic pieces less than five millimeters long used as scrubbers in cosmetics, hand cleansers and air-blasting which can be harmful to our ocean and aquatic life. Microbeads (MB’s) are tiny pieces of polyethylene plastic added to health and beauty products, such as some cleansers and toothpastes.
A 2019 research from the university of Newcastle in Australia2 found that, on average, people could be ingesting approximately 5 grams of plastic every week, which is the equivalent weight of a credit card. This was the first study to combine data from over 50 studies on the ingestion of microplastic by people. The single largest source of plastic ingestion is through water, of course, both bottled and tap, in a worldwide level (twice as much plastic found in the US or India than in European or Indonesian water) and of the consumables studied, those with the highest recorded plastic levels include shellfish, beer and salt.
Research has shown that the ingestion of microparticles by humans can cause alteration in chromosomes which lead to infertility, obesity, and cancer3, so considering that the annual dietary exposure for European shellfish consumers can amount to 11,000 microplastics per year4, it’s easy to understand that things are pretty serious.
In addition, microplastics have been shown to sorb chemical pollutants from their surrounding environment: More specifically, MBs from personal care products are capable of transferring sorbed pollutants to fishes that ingest them, thus there is a raising concern as to their role in the movement of these pollutants through the food chain5.
Moreover, researchers from Johns Hopkins looked at the impact of eating sea animals contaminated with microplastics and they found that the accumulated plastic could damage the immune system and upset a gut’s balance6.
Polychlorinated biphenyls (PCBs) are a group of manmade chemicals and they are very stable mixtures that are resistant to extreme temperature and pressure. PCBs were used widely in electrical equipment like capacitors and transformers7. Most people are exposed to PCBs by eating contaminated fish, meat, and dairy products8.
There are even associated health risks with PCB’s in human breast milk: PCB exposure in infants is predominantly via breast milk and research has shown that lactational PCB exposure has major detrimental effects on the overall health and development of infants9,10
Furthermore, Phthalate esters (PEs) are a group of chemical plasticizers that are primarily used to soften and make polyvinyl chloride (PVC) flexible11 which are detected in various water samples and have been isolated even in river water and lakes12,13. PCBs and PEs may be leading to the deterioration of semen quality in infertile men without an obvious etiology14. At a recent (2019) study that was conduced in Korea, 14 phthalates were measured in air, water, sediment, and fishes in Asan lake areas. More specifically, Benthic feeding fish such as crucian carp or skygazer contained high level of DEHP.
Finally, there is also a threat from Mycotoxins: they contaminate dried “seafoods” during processing and storage and they represent one more potential health hazard for consumers15.
Fishes and other aquatic animals are the main source of some very dangerous heavy metals such as methyl mercury (one of the most toxic compounds of mercury) which can cause neurological damage (such as Alzheimer disease, memory loss, autism and depression). It’s the most dangerous form of mercury which concentrates in the muscle tissue of fishes, thus, unlike PCBs, dioxins and other organic contaminants that concentrate in the skin and fat, mercury can’t be filtered or cooked out of consumable fishes16. Mercury concentrations in the ocean have increased considerably since the industrial revolution and will continue to increase in the next 50 years. In a study17 that has just been published, conducted in Bosnia and Herzegovina, it was found that heavy metals (Cadmium, Mercury and Lead) were detected in almost all analyzed fishes and “seafood” samples (mostly frozen and canned imported from different parts of the world), with the highest concentrations recorded for mercury in almost all species. Among the ones tested, fresh bluefin tuna and Atlantic canned mackerel were found to be the most contaminated with heavy metals (hazard index close to 1), especially due to mercury. It is worth to note here that some researchers in Colombia18 have suggested that there may be a relationship between the canning process and the metal concentrations. Additionally, in Poland the high consumption of fishes may lead to exceeding the tolerable weekly intake of methylmercury several times (limit of 1.3 μg.kg-1 launched in 2012)19.
One more example of a heavy metal often found in aquatic animals is Arsenic. Inorganic arsenic is highly toxic and can be found in fishes and shellfishes. For instance, a recent study in Turkey20 found that there was a carcinogenic risk from exposure to inorganic arsenic via the consumption of red mullet. A minimum exposure to it can lead to many serious health problems, such as pigmentation changes, skin lesions and hard patches on the palms and soles of the feet and even to skin cancer as well as to cancers of the bladder and lungs21. Sea animals, including finfishes and shellfishes are the largest contributors to arsenic exposure in many human populations, which in its organic composition has generally been considered to be non-toxic although its high concentrations in “seafood”, as well as its often-complex speciation, can lead to complications in assessing arsenic exposure from diet, thus more research is needed in order to comprehensively assess human exposure to arsenic in food22. A very recent study that took place in China23 (which has been the major fishery producer in the Northwest Pacific Ocean for decades), showed that arsenic was the most abundant in crustaceans with the average of 28.84 ± 4.95 mg/kg in dry weight, comparing to molluscs (18.68 ± 2.51 mg/kg) and fishes (9.31 ± 1.45 mg/kg). Therefore the authors recommended urban citizens to reduce the frequency of consuming crustaceans while the authors of another study in China24, concluded that there were health risks from exposure to cadmium and arsenic in some shellfishes and bivalves. Furthermore, a systematic review and meta-analysis of metal concentrations in canned tuna fish in Iran25 concluded that adults and children who consume canned tuna fish in Iran have a carcinogenic risk due to arsenic.
In general, heavy metal toxicity (a chemically significant condition) from fishes’ consumption can create mental damage or lead to reduced mental and central nervous system function as well as to lower energy levels, and damaged blood composition, lungs, kidneys, bones, liver and other vital organs. Long term exposure can possibly lead to slowly progressing physical, muscular, and Alzheimer’s disease, Parkinson’s disease, muscular dystrophy, and multiple sclerosis. Allergies are not uncommon either and a repeated long-term contact with some metals or their compounds may even cause cancer. If it stays unrecognized or inappropriately treated, it can result in significant illness and reduced quality of life which can even result in death26.
Pregnancy & newborns
Prenatal exposure to methyl mercury can result in neurological problems (such as IQ deficits, abnormal muscle tone, reduced attention, motor function, and visuospatial performance). Childhood and adulthood exposure can damage the nervous system and kidneys27 and possibly cause diabetes28.
The (American) National Research Council, in its 2000 report on the toxicological effects of methyl mercury, stated that the population at highest risk is the offspring of women who consume large amounts of fishes and other sea animals16 while a study published in 2018 found elevated levels of mercury in women of child-bearing age, in 21 small island states across the Pacific, Caribbean and Indian Ocean, where fish consumption is high. Moreover, the report estimated that more than 60,000 children are born each year at risk for adverse neurodevelopmental effects due to in utero exposure to methylmercury29 .Furthermore a 2014 study in Boston30 showed that a maternal–fetal transfer was a major source of early life exposure to Cadmium, Mercury and Lead.
Nevertheless, in 2014 the European Food Safety Authority (EFSA) concluded that “consumption of about 1‐2 servings of seafood per week and up to 3‐4 servings per week during pregnancy has been associated with better functional outcomes of neurodevelopment in children compared to no consumption of seafood. Such amounts have also been associated with a lower risk of coronary heart disease mortality in adults and are compatible with current intakes and recommendations in most of the European countries considered.”31 and overall, the current national and international guidelines (19 national and 3 international in total) to pregnant women, on the consumption of aquatic animals, are only advising to limit or avoid the amount of consumption of some specific species such as tuna and mackerel, recommending by this way that pregnant women should only minimize exposure to Hg32. However, scientific publications such as Kimakova et al.’ s (2018)19 are clearly stating that the consumption of fishes is not recommended (especially meat of shark, swordfish and king mackerel), for selected groups of the population: children, women of childbearing age and pregnant women as well as Domingo (2016)33 has stated in his publication : “While prestigious international associations as the American Heart Association have recommended eating fish at least two times (two servings a week), based on our own experimental results, as well as in results from other laboratories, we cannot be in total agreement with that recommendation.”
Another shocking finding related to mercury which is worth to mention is that mercury content in fishes may help explain links that have been found between fishes’ consumption and mental disorders, depression, and suicide34.
More specifically, a study in Japan found a significantly increased risk of suicide in the highest EPA and DHA (long-chain omega-3 polyunsaturated fatty acids (O-3s) that are abundant in fishes & shellfishes) intake groups in male nondrinkers as well as a study in Spain found that a high baseline consumption together with an increased consumption of fishes were associated with an increased risk of mental disorders and a possible explanation could be the mercury accumulation in fishes because it]may increase the risk of depression. This finding is in accordance with a 22 years study in 205,357 US men & women which found that there is a relation between suicide mortality and dietary intake of n-3 and n-6 polyunsaturated fatty acids and fishes.
Dioxins are also often found in fishes (and other animals) and they are of concern because of their highly toxic potential. Once they enter the body, they last a long time because of their chemical stability and their ability to be absorbed by fat tissue, where they are afterwards stored in the body. Their half-life in the body is estimated to be 7 to 11 years35.Their consumption can lead to: Toxic impact on the skin (chloracne – irregular eruptions on the skin surface with thickenings and lumps), changes in the thyroid hormone levels which result to impairment of psychomotor capability, cancerogenicity (lung cancer, gastrointestinal cancer), cause danger to women in the first trimester of pregnancy (death of the embryo or development of malformations)36.
Dioxins and methyl mercury found in fishes may also raise Diabetes Type 2 risk40
The United States Department of Agriculture37 notes that 100grams(g) of shrimp contain 189 milligrams(mg) of cholesterol. On average, eating 200mg of cholesterol per 2000 calories raises LDL-cholesterol (which is known as the bad cholesterol because it blocks blood vessels and increases risk for heart disease) levels by about 8 to 10 mg/dl above what they would be without eating any cholesterol; eating larger amounts of cholesterol produces a further rise. Having too much of the bad type of cholesterol — LDL — puts people at risk for having a heart attack or stroke38,39.
Six separate meta-analysis have found a relation between the consumption of fishes and type 2 diabetes due to the intake of n-3 fatty acid and the consumption of fishes which increase circulating concentrations of glycose and fasting glycose as well as they may lead to a beta-cell dysfunction40.
It is not healthier to consume farmed fishes
Α 2014 study that was conducted in Spain41, found that in general farmed fish was perceived to be less affected by marine pollution, heavy metals and parasites. Additionally, a 2019 study in Turkey42 found that some consumers believed that the farmed fish may be more nutritionally valuable although others were concerned about contamination from polluted waters or contaminated feed. This study also informs us that the consumers were found to have a tendency to consume farmed fish if its antibiotic-free, so their basic concern is on whether or not there is drug use in aquacultures and not in regards to contamination by pollutants. Nevertheless, some findings are showing that the case is exactly the opposite: Based on a 2017 comparative study43 on the intake of toxic persistent and semi persistent pollutants through the consumption of fishes and other sea animals, from two modes of production, (wild-caught and farmed) it’s not healthier because the measured levels of most organic and many inorganic pollutants were higher in aquaculture products, and consequently intake levels if only such products were consumed would be also significantly higher.
Moreover, microplastics are not missing from fish farms. They actually might be an important reservoir of antibiotic resistance genes in recirculating aquaculture system farms44. Additionally, in a research on fishes from an important fish farm and mariculture area in China (Haizhou Bay)45, all fishes were found to have items that were identified as microplastics while one more study at another important mariculture bay of China (Maowei Sea) showed that microplastics found to be widespread in the aquaculture water and biota of the bay46.
Disclaimer: All aquatic animals are sentient beings and have a central nervous system. Thus, they suffer when caught and murdered. Therefore, we should not eat aquatic animals because they have inherent value, not because it’s unhealhty. However, for some people who don’t acknowledge these animals’ inherent value, maybe this kind of information is the only way to help them through the end of their consumption.