Microplastics and Other Pollutants in Oceans and in Seafoods

 

I wrote an article on Friday, July 5, 2024, entitled:

Food Toxins. How Safe Are Our Foods?

https://scientificlogic.blogspot.com/2024/07/food-toxins-how-safe-is-our-foods.html

Today (Sunday, 14 July 2024) I read in the Sunday Star newspaper in Malaysia a brief article on microplastic pollution and its poisoning

Alarm over Malaysia’s Microplastic Footprints

https://thesun.my/local-news/alarm-over-malaysia-s-microplastic-footprint-HA11883444

After reading this short newspaper article, I thought I should elaborate on this health issues since this is one of my areas as a former research food and medical toxicologist

Let’s deal with microplastic first before going into heavy metals and natural toxins found in seafoods.

Microplastics:

Microplastic poisoning refers to the potential health risks associated with the ingestion of microplastics by humans, often through the consumption of fish and seafood that have accumulated these particles from the environment.

 What is our current understanding of microplastic pollution and its potential health impacts?

Let us start with their sizes. Microplastics are small plastic particles less than 5 millimetres in diameter, with nano plastics being even smaller, typically less than 1 micrometre.

Primary sources of microplastics come from manufactured small plastics, such as microbeads in cosmetics and personal care products, and the secondary microplastics are the result from the breakdown of larger plastic items, such as bottles, bags, and fishing nets, due to environmental degradation processes like UV radiation, wave action, and mechanical abrasion.

What are the pathways microplastics enter into seafood?  Microplastics enter the ocean through various means, including improper waste disposal, runoff from land, and breakdown of larger plastic debris. Marine organisms, including fish and shellfish, ingest these particles either directly from the water or indirectly through the food chain.

These microplastics may or may not have potential health risks. Let’s discuss this.

First, ingestion of microplastics can cause physical irritation and inflammation of the gastrointestinal tract. There may also be a risk of absorption and distribution as some microplastics are small enough to cross cell membranes and enter body tissues. There is evidence that particles smaller than 150 micrometres can cross the gut barrier and potentially enter the bloodstream, lymphatic system, and other organs. But will they?

I was thinking if this is possible, because in my thinking even protein, starch and fat molecules need to be broken down by the various kinds proteolytic, carbohydrate and fat enzymes into amino acids, glucose, fructose and galactose and fatty acids before they can be absorbed because of the very tight windows for absorption of large complex molecules let alone microplastics. Can they really be absorbed? I think the best way to find out is to use fish or any other seas foods, after removing their intestines, grills and ineligible external organs and washing their flesh properly and analyse for the presence of microplastic in their edible flesh to determine if there are microplastic been absorbed by their intestines into their flesh washing. If there is none, I think it shows these microplastics could not be absorbed by their digestive gut and intestine into the flesh. These will answer the problem if there is any danger of microplastic from eating fish or any other seafoods instead of studying them on humans which is long-term and extremely difficult to determine

I believe this question is quite logical by bringing up an important point about the body's mechanisms to break down even food before absorbing their nutrients.

Indeed, proteins, carbohydrates, and fats are typically broken down into their smaller components (amino acids, simple sugars, and fatty acids) before absorption. However, the concern with microplastics involves particles that are small enough to potentially bypass some of these protective barriers and mechanisms. The gastrointestinal tract has various barriers to prevent the absorption of large particles. However, some studies have indicated that very small microplastics (especially those in the nanometre range) can potentially cross the gut barrier.

Cells can sometimes engulf very small particles through a process known as endocytosis, allowing them to enter tissues. I think we need research approaches to answer this question by analysing edible flesh of fish and seafood for microplastics as this is a practical and direct method to assess whether these particles can migrate from the gut into the tissue.

Some studies have already taken a similar approach. For example, a study published in "Environmental Science & Technology" found microplastics in the flesh of fish, suggesting that these particles can translocate from the gut into the edible parts of marine organisms.

Some existing studies and findings have found microplastics in the edible tissues of various marine organisms. These findings indicate that, at least in some cases, microplastics can migrate from the gut into the flesh. A study found microplastics in commercially sourced seafood intended for human consumption, raising concerns about human exposure through diet.

Various laboratory toxicity in vitro and in vivo studies have demonstrated that microplastics can cause cellular and tissue-level effects, including inflammation and oxidative stress. However, translating these findings to real-world human health impacts is still ongoing.

Methodological approaches sample preparation is very important by removing inedible parts and thoroughly washing the samples would be essential to avoid contamination and obtain accurate results. Once done, we need to look at the analytical techniques. We have advanced techniques such as Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. We used these analytical techniques to detect and characterize microplastics in biological tissues.

Having said that, we also think about their chemical effects on the body. Microplastics can contain harmful additives, such as phthalates, bisphenol A (BPA), and flame retardants. They can also absorb environmental contaminants like heavy metals, polychlorinated biphenyls (PCBs), and pesticides from the water. They cause reproductive and developmental toxicity, carcinogenicity, and other adverse health effects, besides biological effects. Microplastics can serve as surfaces for microbial communities, including pathogenic bacteria. Ingestion of contaminated microplastics could potentially lead to infections or transmission of antibiotic-resistant genes.

However, currently there is limited direct evidence linking microplastic ingestion to specific health issues in humans. Most studies are observational or based on animal models. Given the known toxicities of the chemicals associated with microplastics, there is concern about potential long-term health effects, but more research is needed to establish concrete links.

Widespread contamination and environmental studies have found microplastics in various marine organisms, including those commonly consumed by humans, such as fish, shellfish, and crustaceans. Microplastics can have an impact on marine life by causing physical harm by reducing feeding and impair growth and reproduction in marine organisms.

In terms of size and absorption microplastics range from nanometres to 5 millimetres. Particles smaller than 150 micrometres are more likely to cross biological barriers. The gastrointestinal tract can absorb microplastics, especially those on the smaller end of the size spectrum. Once absorbed, they can be distributed throughout the body, potentially reaching organs such as the liver, kidneys, and brain.

Mitigation and recommendation are to reduce plastic use. Minimize the use of single-use plastics and opt for reusable alternatives. Ensure proper disposal and recycling of plastic waste to prevent environmental contamination. We can advocate for and support scientific research to better understand the health impacts of microplastics and develop effective mitigation strategies. Support policies and regulations aimed at reducing plastic pollution, such as bans on microbeads and incentives for plastic waste management.

While the full extent of the health impacts of microplastics is still being researched, the potential risks warrant precautionary measures to reduce exposure and environmental contamination.

The concern about microplastic absorption and potential health effects is supported by some evidence, particularly in very small particles. Analysing the presence of microplastics in the edible flesh of fish and seafood is a feasible and valuable approach to better understand the extent of microplastic contamination and its implications for human health.

Continued research in this area, including both direct analysis of seafood and long-term studies on human health, is crucial to fully understand the risks and develop appropriate safety guidelines. There must be ways to assess the real-world impact of microplastic contamination in the food chain.

However, many countries have implemented regulations and safety to limit BPA exposure, especially in products intended for infants and young children, such as baby bottles and Sippy cups. However, ongoing research continues to assess the safety of alternative bisphenols like BPS and BPF.

Heavy Metal Poisoning

Microplastic pollution is not the only problem we may have to deal with. For years now we also face problems with heavy metals particularly involving lead, mercury, and cadmium which is a significant public health concern due to the bio accumulative nature of these metals in marine organisms. These heavy metals can pose serious health risks to humans who consume contaminated seafood. Let’s have some look at each metal, their sources, health effects, and real-world incidences.

 First, we have lead (Pb) contamination in marine environments. This can arise from industrial discharges, mining, leaded gasoline, and lead-based paints. Once in the water, lead can accumulate in the tissues of marine organisms, especially in bivalves like mussels and oysters, and predatory fish. Lead exposure is particularly harmful to the nervous system, especially in children, and can cause cognitive deficits, developmental delays, and behavioural problems. In adults, it can cause hypertension, renal impairment, and reproductive issues. For instance, a study conducted in 2018 on seafood from the Persian Gulf found elevated levels of lead in fish species consumed locally, raising concerns about chronic exposure and health risks to the population. Then earlier in 2016, high levels of lead were found in fish from the Ala Wai Canal in Honolulu, Hawaii, prompting health advisories against consuming fish from this area.

Second, we also face with mercury (Hg) poisoning. The source primarily comes from industrial processes, coal combustion, and gold mining. In the marine environment, inorganic mercury is converted to methylmercury by microorganisms, which then bioaccumulates in the food chain. Predatory fish such as tuna, swordfish, and shark typically have higher levels of methylmercury.  Methylmercury is highly neurotoxic and can impair neurological development in foetuses and young children. In adults, it can cause cognitive and motor dysfunction, cardiovascular problems, and immune system impairment.

A 2017 study analysed mercury levels in fish from the Mediterranean Sea and found that some species, like swordfish, exceeded safe consumption levels set by the European Food Safety Authority.

Another incidence occurred in the Minamata Bay in Japan during the 1950s. That was one of the most infamous cases of mercury poisoning, where industrial discharge of methylmercury led to severe neurological disease and death in the local population.

Third, there is cadmium (Cd) entering into seafood. This metal can enter the marine environment from industrial discharges, battery waste, and agricultural runoff. Shellfish, such as oysters and mussels, tend to accumulate higher levels of cadmium. Chronic exposure to cadmium can lead to kidney damage, bone demineralization, and is classified as a human carcinogen by the International Agency for Research on Cancer (IARC).

There is a study published in 2019 found high levels of cadmium in shellfish from the Bohai Sea in China, raising concerns about the potential health risks to consumers. In 2009, elevated cadmium levels were detected in shellfish from the Gulf of Naples, Italy, leading to restrictions on shellfish harvesting and consumption.

Heavy metal contamination in seafood remains a significant environmental and public health issue. Ongoing monitoring and regulatory measures are essential to mitigate the risks associated with consuming contaminated seafood. Public awareness and dietary guidance can also help reduce exposure to these harmful contaminants.

But that’s not the end of the story. We are talking about microplastics and heavy metals so far.  

Natural Toxins in Seafoods:

What about natural toxins found in seafood? For example, what about paralytic shellfish poisoning, ciguatera fish poisoning and other natural seafood poisoning?  Seafood poisoning can result from consuming contaminated fish or shellfish. Let us briefly look at some of the major types of natural seafood poisoning.

First, there is what we call.  paralytic shellfish poisoning (PSP). These are toxins produced by certain species of algae, such as Alexandrium.

The symptoms presented are tingling and numbness around the mouth, face, and extremities, headache, dizziness, nausea, and in severe cases, respiratory failure and death.  The sources come from bivalve shellfish like mussels, clams, oysters, and scallops

Second, we also have ciguatera fish poisoning (CFP) caused by ciguatoxins. These natural toxins are produced by dinoflagellates, such as Gambierdiscus toxicus. Patients affected by CFP are presented with gastrointestinal symptoms (nausea, vomiting, diarrhoea), neurological symptoms (numbness, tingling, reversal of hot and cold sensation), and cardiovascular symptoms (low blood pressure, slow heart rate). The sources come from reef fish such as barracuda, grouper, snapper, and mackerel.

Third comes from amnesic shellfish poisoning (ASP). The cause comes from domoic acid produced by diatoms, such as Pseudo-nitzschia. The symptoms presented are gastrointestinal such as nausea, vomiting, diarrhoea, and neurological symptoms (confusion, memory loss, disorientation), and in severe cases, seizures and coma. The sources come from shellfish like mussels, clams, oysters, and scallops.

Fourth, we also encounter neurotoxic shellfish poisoning (NSP) caused by brevetoxins produced by the dinoflagellate Karenia brevis. Patients affected have gastrointestinal symptoms (nausea, vomiting, diarrhoea), neurological symptoms (tingling, numbness, reversal of hot and cold sensation), and respiratory symptoms (coughing, wheezing). The sources come from shellfish like clams, oysters, and mussels.

Fifth, we have diarrhetic shellfish poisoning (DSP) Caused by okadaic acid and related toxins produced by dinoflagellates, such as Dinophysis and Prorocentrum. This causes gastrointestinal symptoms (diarrhoea, nausea, vomiting, abdominal pain), with symptoms usually appearing within 30 minutes to a few hours after consumption. Consumption of shellfish like mussels, scallops, and oysters causes DSP.

Sixth, we have also encountered scombroid fish poisoning or histamine fish poisoning caused by high levels of histamine resulting from bacterial spoilage in fish. The symptoms presented are flushing, rash, headache, dizziness, burning or tingling in the mouth, nausea, vomiting, and diarrhoea. The sources come from fish with high histidine content, such as tuna, mackerel, mahi-mahi, and sardines.

Seventh, we have also encountered tetrodotoxin poisoning from pufferfish (fugu). This is tetrodotoxin produced by bacteria associated with pufferfish. This poisoning causes numbness and tingling around the mouth, dizziness, headache, nausea, vomiting, muscle weakness, paralysis, and in severe cases, respiratory failure and death.

Other seafood toxins are azaspiracid shellfish poisoning (AZP) caused by azaspiracids produced by certain species of algae. The clinical presentations are nausea, vomiting, diarrhoea, abdominal cramps, and in severe cases, neurological symptoms. This seafood poisoning comes from bivalve shellfish like mussels, clams, and oysters.

There are also cyanobacterial toxins produced by cyanobacteria (blue-green algae).

The symptoms vary depending on the toxin but can include gastrointestinal symptoms, liver damage, and neurological symptoms.  The source comes from freshwater and brackish water seafood.

Last, but not least, I can think of is, palytoxin poisoning produced by certain marine organisms like zoanthid corals. Here the patient comes down with severe pain, muscle spasms, difficulty breathing, cardiovascular symptoms, and in severe cases, death. The source of this comes from marine organisms such as corals and crabs.

I think the best way is to avoid consuming seafood from areas known for harmful algal blooms. Proper handling and storing seafood at appropriate temperatures to prevent bacterial spoilage.

Some toxins are heat-stable and cannot be destroyed by cooking, so sourcing from safe areas is crucial.

Understanding these different types of seafood poisoning and their sources can help in making informed choices about seafood consumption.

Ju-boo lim

 

References:

 

Studies on microplastics and natural seafood poisons, focusing on their impacts on human health are sourced below:

Microplastics and Human Health

1. Barboza, L. G. A., Vethaak, A. D., Lavorante, B. R. B. O., Lundebye, A.-K., & Guilhermino, L. (2018). "Marine microplastic debris: An emerging issue for food security, food safety and human health." Marine Pollution Bulletin, 133, 336-348.

This review discusses the presence of microplastics in marine environments and their potential impacts on food security, food safety, and human health.

2. Carbery, M., O'Connor, W., & Palanisami, T. (2018). "Trophic transfer of microplastics and mixed contaminants and their impacts on marine organisms." Marine Pollution Bulletin, 133, 191-199.

This study examines the trophic transfer of microplastics and associated contaminants and their impacts on marine organisms and, by extension, human consumers.

3. Smith, M., Love, D. C., Rochman, C. M., & Neff, R. A. (2018). "Microplastics in seafood and the implications for human health." Current Environmental Health Reports, 5(3), 375-386.

This review explores the presence of microplastics in seafood and their potential health implications for humans.

4. Lusher, A. L., Hollman, P. C. H., & Mendoza-Hill, J. J. (2017). "Microplastics in fisheries and aquaculture: Status of knowledge on their occurrence and implications for aquatic organisms and food safety." FAO Fisheries and Aquaculture Technical Paper No. 615. Rome: FAO.

This FAO report provides a comprehensive overview of the occurrence of microplastics in fisheries and aquaculture and their potential implications for food safety.

Natural Seafood Poisons and Human Health

1. Llewellyn, L. E. (2006). "Saxitoxin, a toxic marine natural product that targets a multitude of receptors." Natural Product Reports, 23(2), 200-222.

This review covers the chemistry, biology, and toxicology of saxitoxin, a key toxin responsible for paralytic shellfish poisoning.

2. Fleming, L. E., Kirkpatrick, B., Backer, L. C., Walsh, C. J., Nierenberg, K., Clark, J., ... & Kirkpatrick, G. (2011). "Review of Florida red tide and human health effects." Harmful Algae, 10(2), 224-233.

This paper reviews the health effects associated with red tide events in Florida, which produce brevetoxins responsible for neurotoxic shellfish poisoning.

3. Fleming, L. E., Kirkpatrick, B., & Backer, L. C. (2006). "Ciguatera: Outbreaks, neurotoxicity, and health effects." Current Treatment Options in Neurology, 8(1), 48-58.

This review discusses the clinical manifestations, diagnosis, and treatment of ciguatera fish poisoning.

4. Van Dolah, F. M. (2000). "Marine algal toxins: Origins, health effects, and their increased occurrence." Environmental Health Perspectives, 108 (Supple 1), 133-141.

This article reviews the sources, mechanisms of action, and health effects of various marine algal toxins, including those causing amnesic, diarrhetic, and paralytic shellfish poisoning.

5. Heavy Metal Contamination in Seafood and Human Health: Perspectives from the Persian Gulf - Environmental Research, 2018.
6. Assessment of Lead Contamination in Fish from the Ala Wai Canal - Environmental Monitoring and Assessment, 2016.
7. Mercury Levels in Mediterranean Fish Species - Marine Pollution Bulletin, 2017.
8. Minamata Disease: Methylmercury Poisoning in Japan - Science of the Total Environment, 2001.
9. Cadmium in Shellfish from the Bohai Sea: Risk Assessment for Human Health - Ecotoxicology and Environmental Safety, 2019.
10. Cadmium Contamination in Shellfish from the Gulf of Naples - Food and Chemical Toxicology, 2009.

General Reviews and Reports

1. World Health Organization (2019). "Microplastics in drinking-water." Geneva: WHO.

This comprehensive report by the WHO assesses the occurrence of microplastics in drinking water and the potential risks to human health.

2. European Food Safety Authority (EFSA) (2016). "Presence of microplastics and nano plastics in food, with particular focus on seafood." EFSA Journal, 14(6), e04501.

This EFSA report evaluates the presence of microplastics and nano plastics in food, particularly seafood, and assesses potential human health risks.

These references should provide a solid foundation for understanding the current research on microplastics and natural seafood poisons and their impacts on human health.