Seafood Sickness: Pollution's Impact On Human Health

Seafood is a primary source of protein for billions of people worldwide, but pollution is making it increasingly toxic. Fish absorb toxic chemicals that have been dumped into waterways, and they can also ingest them from eating plastic. Mercury, for instance, often enters the water and soil from household and industrial waste, and it can take 6-12 months for a person to significantly reduce their mercury levels. Other contaminants include PCBs, PBDEs, dioxins, and chlorinated pesticides, which can lead to health problems such as cardiovascular issues and problems with the central nervous system. Harmful algal blooms (HABs) are another source of seafood toxicity, causing illnesses such as ciguatera fish poisoning, scombroid poisoning, and shellfish poisoning.

Mercury poisoning from industrial and household waste

Mercury poisoning is a serious health issue that can result from exposure to mercury, a toxic elemental metal found in the Earth's crust. While mercury occurs naturally, human activities such as industrial processes and household waste incineration significantly contribute to its release into the environment. Improper disposal of products containing mercury, such as batteries, switches, light bulbs, and cosmetics, leads to contamination of landfills, incinerators, and sewage treatment facilities. Mercury then leaches into the ground and water, where it is converted into methylmercury by bacteria. This organic compound accumulates in fish and shellfish, posing a health risk to humans who consume them.

Methylmercury is particularly harmful to the developing fetus and young children, causing developmental issues and cognitive impairments. In adults, mercury poisoning can lead to problems with the central nervous system and adverse effects on the cardiovascular system. The symptoms of mercury poisoning vary depending on the type, dose, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble speaking, and vision or hearing difficulties.

To prevent mercury poisoning, it is crucial to reduce exposure to mercury and its compounds. This includes limiting the consumption of seafood known to contain high levels of mercury, such as swordfish, shark, king mackerel, and tilefish. Pregnant women, nursing mothers, and young children are especially vulnerable and should follow specific guidelines for seafood consumption. Additionally, proper disposal of mercury-containing products and waste is essential, as well as avoiding exposure to industrial and household waste incineration.

In cases of acute mercury poisoning, chelation therapy with dimercaptosuccinic acid (DMSA) or dimercaptopropane sulfonate (DMPS) can improve outcomes if administered promptly. However, the benefits of chelation therapy for long-term exposure are unclear. Overall, the best approach is to minimize mercury exposure and to seek medical attention if exposed or experiencing any symptoms of mercury poisoning.

How plastic waste in oceans contaminates seafood

Plastic waste in the ocean is a pressing issue that has detrimental effects on marine life and ecosystems. It is one of the main causes of marine species extinction, health problems for humans and animals, and the destruction of ecosystems. Plastic waste accounts for 80% of all marine pollution, with an estimated 8 to 10 million metric tons of plastic entering the ocean each year.

Plastic is ingested by marine animals, including fish, seabirds, sea turtles, and marine mammals, causing internal injuries and death. It also gets absorbed into the tissue of fish, transferring up the food chain to bigger fish, marine mammals, and eventually, humans who consume seafood. This transfer of chemicals up the food chain is well-known to scientists. The biggest, fattiest fish, such as tuna and swordfish, tend to have the highest levels of toxic chemicals, such as mercury, polychlorinated biphenyls (PCBs), and other dioxins.

A study published in Nature, Scientific Reports, revealed that fish get these chemicals from ingesting plastic debris. The plastic acts like a sponge, soaking up the chemicals in the water. When ingested by fish, the chemicals are released into their bloodstream and tissue. This was evident in a study where fish that consumed plastic from the San Diego Bay had higher levels of persistent organic pollutants than those that did not.

The presence of plastic in the ocean is a result of littering, improper manufacturing processes, and industrial fishing. It is crucial to address this issue through improved waste management, recycling, and reduced usage of disposable packaging and single-use plastics.

How to reduce exposure to contaminants in fish

Fish are exposed to toxic chemicals in the rivers, bays, and oceans they inhabit. One of the most well-known contaminants in fish is mercury, which enters the water and soil through household and industrial waste incineration, as well as the burning of coal and other fossil fuels. Mercury is converted to methylymercury by bacteria, which is then consumed by plankton and small fish, making its way up the food chain. Other contaminants include PCBs, PBDEs, dioxins, and chlorinated pesticides, which enter the water through industrial and municipal discharges, agricultural practices, and stormwater runoff. These contaminants can have harmful effects on human health, especially for women who are pregnant or breastfeeding, as well as young children.

To reduce exposure to contaminants in fish, here are some recommended guidelines:

• Eat a variety of fish that are low in contaminants: Refer to reliable guides that provide information on the contaminant levels in different types of fish. Choose fish that are known to have lower levels of mercury and other contaminants, such as most species of salmon.
• Follow mercury advisories: Adhere to statewide or local advisories on mercury levels in fish. This is especially important for women who are pregnant, breastfeeding, or planning to become pregnant, as well as for young children.
• Choose smaller, younger fish: Larger, older fish tend to accumulate more contaminants than their smaller, younger counterparts.
• Avoid eating fish skin and fat: Contaminants like PCBs and DDT concentrate in the fatty parts of the fish. By removing and discarding the skin and visible fat before cooking, you can reduce your exposure to these contaminants.
• Properly prepare and cook fish: Grill, broil, or bake the fish on a rack to allow the fat to drip off during cooking. Do not use the drippings for gravy or sauces. This method can reduce your exposure to PCBs and other contaminants by up to 50%. However, it is important to note that this preparation method does not reduce mercury levels, so it is crucial to avoid fish that are high in mercury.
• Choose "light tuna" over "white tuna": Mercury levels in canned light tuna are significantly lower than in canned white (albacore) tuna.
• Check local fish consumption advisories: Before fishing in local waters or consuming locally caught fish, check for any consumption advisories specific to that waterbody.

Ciguatera fish poisoning from contaminated reef fish

Ciguatera fish poisoning (CFP) is a foodborne illness caused by eating reef fish contaminated with ciguatoxins. These toxins are produced by a small marine organism, Gambierdiscus toxicus, which grows on and around coral reefs in tropical and subtropical waters. Ciguatoxin cannot be destroyed by conventional cooking methods, and there is currently no specific treatment or antidote for CFP.

The onset of symptoms depends on the amount of toxin consumed. Symptoms may include gastrointestinal problems such as nausea, vomiting, and diarrhea; neurological issues like headaches, muscle aches, numbness, and dizziness; and cardiovascular problems such as slow heart rate and low blood pressure. These symptoms can last from weeks to years, and in rare cases, even result in death.

To prevent ciguatera fish poisoning, it is recommended to avoid consuming reef fish, particularly high-risk species such as barracuda, grouper, moray eel, amberjack, sea bass, and sturgeon. It is also advised to refrain from eating fish liver, roe, or fish heads, as these parts may contain higher concentrations of toxins.

The risk of ciguatera fish poisoning appears to be increasing due to coral reef deterioration and the growing trade in seafood. It is most commonly found in the Pacific Ocean, Indian Ocean, and the Caribbean Sea.

In addition to ciguatera fish poisoning, consuming seafood can expose individuals to other pollutants, such as mercury, polychlorinated biphenyls (PCBs), and other synthetic and organic pollutants that accumulate in the ocean and are absorbed by fish.

Shellfish poisoning from harmful algal blooms

Neurotoxic shellfish poisoning (NSP) is one of the illnesses commonly associated with HABs. It is characterised by numbness and tingling in the face, hands, and feet, as well as nausea, vomiting, and diarrhea. The symptoms typically resolve within 3 days without treatment. NSP is most prevalent in the Gulf of Mexico and the Southeastern and Mid-Atlantic coasts of the United States. However, it is rare in the US due to the close monitoring of shellfish beds.

Another illness resulting from HABs is ciguatera fish poisoning. Ciguatera occurs when people consume fish that have been exposed to toxins produced by a different type of algae, usually found near Caribbean and Pacific Islands. The ciguatera toxin moves up the food chain, with higher concentrations in larger fish that have fed on smaller fish contaminated with the toxin. Therefore, people are more likely to be poisoned by consuming larger fish like barracuda, king mackerel, and hogfish. Ciguatera symptoms include nausea, vomiting, diarrhoea, and a unique feature called sensory reversal, where cold things feel hot and vice versa. Most people recover from ciguatera without treatment, but symptoms can persist for weeks.

In addition to the risks associated with consuming contaminated seafood, HABs can also cause health issues when people come into direct contact with affected water. Swimming in water with HABs can lead to skin irritation, rashes, itching, and irritation of the nose, eyes, and throat. Inhaling airborne droplets can exacerbate asthma symptoms. Swallowing the water can result in nausea, vomiting, diarrhoea, and abdominal pain.

To prevent poisoning from HABs, it is crucial to avoid contact with discoloured water or water with scum or film on its surface. Recreational activities, such as swimming or boating, should be avoided in such conditions. It is also important to not consume fish from lakes or seas with discoloured water or algal scum.

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