Interactive Science Series

Q: Dr. Krishna, I am from Hyderabad. The local media is reporting about fish dying in the water bodies here because of pollution. If they don't die,  can we eat fish from polluted water?

Krishna: The answer is an emphatic "NO"! Let me provide scientific evidence for my answer now.

We all read/heard that eating fish is good for health.

Omega-3 fatty acids are found in fish—especially oily fish such as salmon, sardines, and herring. These omega-3 fatty acids can help lower your blood pressure, lower your heart rate, and improve other cardiovascular risk factors. Eating fish reduces the risk of death from heart disease, the leading cause of death in both men and women. Fish intake has also been linked to a lower risk of stroke, depression, and mental decline with age. For pregnant women, mothers who are breastfeeding, and women of childbearing age, fish intake is important because it supplies DHA, a specific omega-3 fatty acid that is beneficial for the brain development of infants.

All the above benefits are obtained from eating fish from clean and pure water. But if you eat fish from polluted water, you can expect these detrimental effects ...

A study (1) published in the journal Science Advances reveals a dangerous pollutant lurking in the muscle tissue of certain fish may be a threat to humans. A team of researchers from The Scripps Institution of Oceanography at UC San Diego is among the first to find that ingesting these pollutants can interfere with the human body’s ability to get rid of harmful toxins.

"When we eat contaminated fish, we could be reducing the effectiveness of this critical defense system in our bodies," said the study’s lead author Amro Hamdoun, an associate professor in the marine biology research division at Scripps, in a statement(2). "It’s very important to make sure that those fish don’t end up in our food supply."

Humans have a critical protein called P-glycoprotein, or “P-gp," in their body that fights off harmful toxins. Like a bouncer at the door, P-gp works by expelling foreign chemicals from the body, and can resistant multiple toxic chemicals at once. But without it, toxins have free range to enter into cells with no restraint.

For years, experts suspected a class of pollutants known as the persistent organic pollutants (POPs) were unsafe and had the ability slip past the P-gp bouncer and inflict damage — they just didn’t know exactly how. So Hamdoun and his team set out to determine the cause by analyzing 10 different POPs that obstructed P-gp’s ability to function properly. They found that instead of slipping past P-gp, the pollutants attach themselves to the protein, ultimately stopping it from protecting the body against a variety toxins.

“These environmental chemicals form intimate interactions,” Hamdoun said. “But instead of being expelled, these proteins interfere with the ability of p-glycoprotein from doing its job.”

Researchers label this act of “poisoning the bouncer” a danger for unsuspecting fish eaters.

Heavy metals like mercury and several other poisonous chemicals accumulated in the fish can cause severe harm to human body. Mercury may have toxic effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes (3). Fish that are higher on their respective food chains tend to contain higher levels of total mercury (4). 

 About 80 to 90 percent of organic mercury in a human body comes from eating fish and shellfish, and 75 to 90 percent of organic mercury existing in fish and shellfish is methylmercury, according to a paper published (5).

Once in the water as a pollutant, mercury makes its way into the food chain. Inorganic mercury and methylmercury are first consumed by phytoplankton, single-celled algae at the base of most aquatic food chains. Next, the phytoplankton are consumed by small animals such as zooplankton. The methylmercury is assimilated and retained by the animals, while the inorganic mercury is shed from the animals as waste products. Small fish that eat the zooplankton are exposed to food-borne mercury that is predominantly in the methylated form. These fish are consumed by larger fish, and so on until it gets to humans. 

Because the methylmercury is highly assimilated and lost extremely slowly from fish, there is a steady build-up of this form of mercury in aquatic food chains, such that long-lived fish at the top of the food chain are highly enriched in methylmercury. Methylmercury therefore displays clear evidence of biomagnification, where its concentrations are higher in predator tissue than in prey tissue.

Exposure to organic mercury can cause uncontrollable shaking or tremor, numbness or pain in certain parts of the skin, blindness and double vision, inability to walk well, memory problems, seizures and death with large exposures. Most notable are the effects of mercury on the brain. Mercury poisoning can result in hearing and vision changes, personality changes, memory problems, seizures or paralysis. When children are exposed to mercury, they may have developmental or muscle coordination problems. Mercury interferes with the calcium channels that cells, especially nerve and muscle cells, use to carry out their functions.

The toxicity of methylmercury may also have reproductive consequences. Pregnant woman who eat fish and seafood contaminated with methylmercury may have the increased risk of having a miscarriage, or having a baby with deformities or severe nervous system diseases. These birth defects can happen even if the mother doesn't seem to be poisoned. A study (6) found that eating food contaminated with methylmercury can even alter the chromosomes in humans. 

Chemicals called dioxins and polychlorinated biphenyls (PCBs) can accumulate in foods, including fish. The levels of these chemicals in fish, including farmed fish, are very low and similar to levels in meats and dairy products. Compared with the health benefits of fish intake, the health risks of these chemical levels are very low and should not influence individual decisions about fish intake. Compared with store-bought fish, locally caught freshwater fish may have higher chemical levels, so local advisories should be consulted and when the water is polluted like we have in our city, the PCB contamination can also be suspected.

In animal studies, commercial PCBs elicit a broad range of toxic responses including acute lethality, body weight loss, carcinogenesis, dermal toxicity, fatty liver, genotoxicity, hepatomegaly, immunosuppressive effects, neurotoxicity, porphyria, reproductive and developmental toxicity, thymic atrophy, and thyroid hormone-level alterations (7).

So Scientific evidence clearly states that you only spoil your health by eating fish from polluted water. So now you can take an informed decision about eating fish from your city.

Art work on the same theme by Dr. Krishna Kumari Challa

From http://www.kkartfromscience.com/fromscience.html

CITATIONS

1. http://advances.sciencemag.org/content/2/4/e1600001.full

2. http://ucsdnews.ucsd.edu/pressrelease/pollutants_in_fish_inhibit_hu...

3. http://www.who.int/mediacentre/factsheets/fs361/en/

4. https://www.canada.ca/en/health-canada/services/food-nutrition/repo...

5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3514465/

6. https://www.ncbi.nlm.nih.gov/pubmed/3678208

7. https://www.atsdr.cdc.gov/csem/csem.asp?csem=30&po=10

Updates:

Eating one wild fish same as month of drinking tainted water: study

Eating one freshwater fish caught in a river or lake in the United States is the equivalent of drinking a month's worth of water contaminated with toxic "forever chemicals", new research said recently.

The invisible chemicals called PFAS were first developed in the 1940s to resist water and heat, and are now used in items such as non-stick pans, textiles, fire suppression foams and food packaging.

But the indestructibility of PFAS, per- and polyfluoroalkyl substances, means the pollutants have built up over time in the air, soil, lakes, rivers, food, drinking water and even our bodies.

There have been growing calls for stricter regulation for PFAS, which have been linked to a range of serious health issues including liver damage, high cholesterol, reduced immune responses and several kinds of cancer.

To find out PFAS contamination in locally caught fish, a team of researchers analyzed more than 500 samples from rivers and lakes across the United States between 2013 and 2015.

The median level of PFAS in the fish was 9,500 nanogrammes per kilogram, according to a new study published in the journal Environmental Research.

Eating just one freshwater fish equalled drinking water with PFOS at 48 parts per trillion for a month, the researchers calculated.

Nadia Barbo et al, Locally caught freshwater fish across the United States are likely a significant source of exposure to PFOS and other perfluorinated compounds, Environmental Research (2022). DOI: 10.1016/j.envres.2022.115165

                                                                                         ----

( This below one is from the northern regions of our planet)

Fish consumption still safe despite initial fears over mercury levels

The benefits of consuming traditional foods tend to outweigh the risks of possible mercury contamination, according to a recent study. The research, which was part of a larger biomonitoring project to address community concerns about environmental contaminants in traditional foods, such as fish, also found that mercury exposure in people may be low even when it is sometimes present in elevated levels. Additionally, the researchers discovered that mercury levels in people in northern regions vary by season and region.

Previously, elevated levels of mercury were found in some fish species in some lakes and therefore, communities wanted to know if these sometimes-elevated levels in fish also meant they were elevated in people. The good news is that generally, the exposure in communities we studied was low. It means the benefits of consuming these foods tend to outweigh the risks, which is important for these communities since fish consumption has nutritional, cultural and economic benefits.

In conducting the study, the researchers obtained 443 blood samples and 276 hair samples to determine mercury levels present in the body. Generally, the measured human mercury exposures were relatively low. They also used a Food Frequency Questionnaire to assess fish intake, with 170 people participating. The responses showed that total fish intake peaked in late summer, decreased during the winter and increased again in the spring. Hair mercury levels seemed to follow the same seasonal pattern as fish intake but peaked in the fall.

The advantage of blood monitoring is that it provides an accurate snapshot of recent mercury levels. However, blood samples are more invasive, require specialized personnel to draw them, as well as consistent refrigeration. The researchers wanted to see if hair samples, which are easier to collect and show mercury levels over a larger span of time, could be used at the individual level. They found that the ratios between blood and hair mercury levels were inconsistent, meaning blood levels cannot be accurately estimated for an individual based on a hair sample.

Elevated levels of mercury can have negative effects on human development and health, including increased risk of cardiovascular disease and neurodevelopmental impairment. The Canadian Health Measures Survey measured mercury in human biological samples but did not include participants from the Canadian territories or Indigenous peoples living on reserves.

Mercury can pose serious risks to people's health, but these communities now have a baseline to see what changes occur in the future, especially taking into account those that may be caused by climate change.

 Sara Packull-McCormick et al, Hair to blood mercury concentration ratios and a retrospective hair segmental mercury analysis in the Northwest Territories, Canada, Environmental Research (2021). DOI: 10.1016/j.envres.2021.111800

https://phys.org/news/2021-10-fish-consumption-safe-mercury.html?ut...