Why Do Fish Contain Mercury? A Comprehensive Guide

1. Understanding Mercury Contamination in Fish

Why Do Fish Contain Mercury? This is a crucial question, especially considering the increasing awareness of environmental toxins and their impact on our health. At WHY.EDU.VN, we aim to provide clear and reliable answers to complex questions like this, offering solutions and insights into understanding the complexities of environmental science. Mercury, a naturally occurring element, finds its way into aquatic ecosystems primarily through industrial processes and atmospheric deposition. This results in mercury accumulation in fish, posing potential health risks to humans who consume them. Understanding this process is the first step toward making informed dietary choices and supporting efforts to reduce mercury pollution. This article will explore the sources of mercury, how it accumulates in fish, the risks associated with consuming contaminated fish, and what you can do to protect yourself and your family.

2. Sources of Mercury in the Environment

Where does the mercury that contaminates fish originate? The answer lies in both natural processes and human activities. Understanding these sources is crucial for comprehending the scope of the problem and identifying effective solutions.

2.1. Natural Sources of Mercury

Mercury exists naturally in the Earth’s crust and is released into the environment through several natural processes:

Volcanic Eruptions: Volcanoes release mercury into the atmosphere, where it can travel long distances and eventually deposit into water bodies.
Weathering of Rocks: The erosion of rocks containing mercury can release the element into soil and water.
Geothermal Activity: Geothermal vents and hot springs can also contribute to mercury levels in aquatic environments.

2.2. Human Activities Contributing to Mercury Pollution

While natural sources contribute to mercury levels, human activities are the primary drivers of increased mercury pollution in recent history:

Coal-Fired Power Plants: Burning coal releases mercury into the atmosphere, making coal-fired power plants one of the largest anthropogenic sources of mercury emissions.
Mining Activities: Gold mining, in particular, often uses mercury to extract gold from ore, leading to significant mercury pollution.
Industrial Processes: Various industrial processes, such as the production of chlorine and caustic soda, can release mercury into the environment.
Waste Incineration: Burning waste, especially medical and municipal waste, can release mercury into the atmosphere if not properly managed.
Artisanal and Small-Scale Gold Mining (ASGM): In many developing countries, ASGM practices involve the use of mercury to extract gold, often without proper safety measures, resulting in severe environmental contamination.

Source	Description	Impact on Fish
Coal-Fired Power Plants	Release mercury into the atmosphere when burning coal for electricity generation.	Atmospheric deposition contaminates water bodies, leading to mercury accumulation in fish.
Mining Activities	Use mercury in the extraction process, particularly in gold mining.	Mercury runoff contaminates rivers and lakes, affecting aquatic life and leading to bioaccumulation in fish.
Industrial Processes	Certain industries release mercury as a byproduct.	Industrial discharge contaminates water bodies, resulting in mercury uptake by fish.
Waste Incineration	Burning waste releases mercury into the atmosphere.	Atmospheric deposition contaminates water bodies, leading to mercury accumulation in fish.
Artisanal Gold Mining (ASGM)	Employs mercury to extract gold, especially in developing countries.	Direct contamination of water bodies, leading to high levels of mercury in fish populations.
Volcanic Eruptions	Natural source releasing mercury into the atmosphere.	Atmospheric deposition can increase mercury levels in water bodies, affecting fish.
Weathering of Rocks	Natural erosion of rocks containing mercury.	Releases mercury into soil and water, which can be absorbed by aquatic organisms.
Geothermal Activity	Geothermal vents and hot springs release mercury.	Localized contamination of water bodies, affecting fish in those areas.
Improper Disposal of Items	Discarding items like thermometers, batteries, and fluorescent bulbs containing mercury into the environment.	Mercury can leach into water bodies, contaminating aquatic ecosystems and leading to mercury accumulation in fish.
Agricultural Practices	Some pesticides and fungicides used in agriculture contain mercury compounds.	Runoff from agricultural fields can contaminate water bodies, leading to mercury accumulation in fish.
Dental Amalgams	Dental fillings containing mercury can release small amounts of mercury over time.	Wastewater from dental clinics can contribute to mercury levels in sewage systems and, potentially, water bodies.
Manufacturing of Products	Manufacturing of certain products, such as batteries, lamps, and electronic devices, involves the use of mercury.	Industrial discharge and waste from manufacturing plants can contaminate water bodies, leading to mercury accumulation in fish.
Natural Gas Processing	Natural gas can contain mercury, which is released during processing.	Wastewater from natural gas processing plants can contaminate water bodies, leading to mercury accumulation in fish.
Cement Production	Cement production can release mercury present in the raw materials used.	Atmospheric emissions from cement plants can contribute to mercury deposition in nearby water bodies, affecting fish.
Oil Refining	Crude oil can contain mercury, which is released during the refining process.	Wastewater from oil refineries can contaminate water bodies, leading to mercury accumulation in fish.
Historical Uses	Past industrial activities, such as hat manufacturing (using mercury to process felt), have left behind legacy contamination.	Mercury can persist in soil and sediment, gradually leaching into water bodies and affecting fish over long periods.
Cremation	Burning human remains can release mercury from dental fillings.	Atmospheric emissions from crematories can contribute to mercury deposition in nearby water bodies, affecting fish.
Textile Industry	Some textile dyeing and finishing processes use mercury compounds.	Wastewater from textile mills can contaminate water bodies, leading to mercury accumulation in fish.

3. How Mercury Accumulates in Fish: Bioaccumulation and Biomagnification

Once mercury enters aquatic ecosystems, it undergoes a transformation into methylmercury, a highly toxic organic form. This transformation is primarily carried out by bacteria in water and sediment. Methylmercury is easily absorbed by aquatic organisms and accumulates as it moves up the food chain through two key processes: bioaccumulation and biomagnification.

3.1. Bioaccumulation

Bioaccumulation is the process by which an organism absorbs a substance faster than it loses it. In the case of mercury, small aquatic organisms, such as plankton and algae, absorb methylmercury from the water and sediment. These organisms retain the mercury in their tissues, leading to higher concentrations compared to the surrounding environment.

3.2. Biomagnification

Biomagnification is the increase in the concentration of a substance as it moves up the food chain. When small organisms containing methylmercury are consumed by larger organisms, the mercury is not eliminated but instead accumulates in the tissues of the predator. This process continues up the food chain, resulting in the highest concentrations of mercury in top predators, such as large fish like swordfish, shark, and tuna.

Process	Description	Impact on Mercury Levels in Fish
Bioaccumulation	Organisms absorb methylmercury faster than they eliminate it, leading to higher concentrations in their tissues compared to the surrounding environment.	Small aquatic organisms accumulate methylmercury from water and sediment, setting the stage for further concentration up the food chain.
Biomagnification	The concentration of methylmercury increases as it moves up the food chain because predators consume prey containing methylmercury, which accumulates in their tissues.	Top predator fish accumulate the highest levels of methylmercury due to the consumption of smaller, contaminated fish.

4. Health Risks Associated with Mercury Consumption from Fish

Consuming fish contaminated with mercury can pose significant health risks, especially for certain populations. Understanding these risks is crucial for making informed dietary choices.

4.1. Neurological Effects

Mercury, particularly methylmercury, is a potent neurotoxin. It can damage the brain and nervous system, leading to a range of neurological problems:

Developmental Issues: Exposure to mercury during pregnancy can harm the developing fetus, leading to cognitive deficits, motor skill impairments, and behavioral problems in children.
Cognitive Impairment: In adults, chronic exposure to mercury can lead to memory loss, tremors, and difficulty concentrating.
Nervous System Damage: High levels of mercury can cause nerve damage, resulting in numbness, tingling, and muscle weakness.

4.2. Cardiovascular Effects

Studies have suggested a link between mercury exposure and cardiovascular problems:

Increased Risk of Heart Disease: Mercury can contribute to the development of heart disease by increasing blood pressure and damaging blood vessels.
Arrhythmias: High levels of mercury can disrupt the heart’s electrical activity, leading to irregular heartbeats.

4.3. Kidney Damage

The kidneys are responsible for filtering toxins from the blood, and exposure to mercury can impair their function:

Reduced Kidney Function: Mercury can damage the kidney’s filtering units, leading to reduced kidney function and potentially kidney disease.
Proteinuria: Mercury exposure can cause protein to leak into the urine, an early sign of kidney damage.

4.4. Immune System Effects

Mercury can also affect the immune system, making individuals more susceptible to infections and autoimmune diseases:

Suppressed Immune Function: Mercury can suppress the activity of immune cells, reducing the body’s ability to fight off infections.
Autoimmune Reactions: In some individuals, mercury exposure can trigger autoimmune reactions, where the immune system attacks the body’s own tissues.

4.5. Vulnerable Populations

Certain populations are more vulnerable to the health effects of mercury exposure:

Pregnant Women: Mercury can cross the placenta and harm the developing fetus, leading to developmental problems.
Nursing Mothers: Mercury can be passed to infants through breast milk.
Young Children: Children’s developing brains and nervous systems are more susceptible to the toxic effects of mercury.
People with High Fish Consumption: Individuals who consume large amounts of fish, especially those high in mercury, are at greater risk of exposure.

Health Risk	Description	Vulnerable Populations
Neurological Effects	Mercury is a neurotoxin that can cause developmental issues, cognitive impairment, and nervous system damage.	Pregnant women, nursing mothers, young children, and individuals with high fish consumption.
Cardiovascular Effects	Mercury can increase the risk of heart disease and arrhythmias.	Adults with pre-existing cardiovascular conditions and individuals with high fish consumption.
Kidney Damage	Mercury can reduce kidney function and cause proteinuria.	Individuals with pre-existing kidney conditions and those with high levels of mercury exposure.
Immune System Effects	Mercury can suppress immune function and trigger autoimmune reactions.	Individuals with compromised immune systems and those genetically predisposed to autoimmune diseases.
Other Effects	Mercury exposure has been linked to various other health issues, including reproductive problems, thyroid dysfunction, and gastrointestinal issues.	General population, with potential variations based on individual susceptibility and level of exposure.

5. Fish Species with High and Low Mercury Levels

Not all fish contain the same levels of mercury. Understanding which fish species tend to have higher or lower mercury concentrations can help you make safer dietary choices.

5.1. Fish Species with High Mercury Levels

Generally, large, long-lived predatory fish tend to have the highest mercury levels due to biomagnification:

Swordfish: As a top predator, swordfish accumulates high concentrations of mercury.
Shark: Sharks are also top predators and can contain significant amounts of mercury.
King Mackerel: This large mackerel species is known to have high mercury levels.
Tilefish: Tilefish, particularly those from the Gulf of Mexico, often have high mercury concentrations.
Bigeye Tuna: Larger tuna species like bigeye tend to have more mercury than smaller tuna.
Orange Roughy: This deep-sea fish is known for its high mercury content due to its long lifespan and diet.
Marlin: Similar to swordfish and shark, marlin are top predators and can accumulate high levels of mercury in their tissues.
Spanish Mackerel: A larger type of mackerel that can contain high levels of mercury compared to smaller mackerel species.

5.2. Fish Species with Low Mercury Levels

Smaller, shorter-lived fish that are lower on the food chain generally have lower mercury levels:

Salmon: Wild-caught salmon, especially sockeye and pink salmon, tend to have lower mercury levels. Farmed salmon can also be a good choice.
Sardines: These small, oily fish are low in mercury and high in omega-3 fatty acids.
Herring: Another small, oily fish with low mercury levels.
Anchovies: These tiny fish are a good source of omega-3s and are low in mercury.
Tilapia: This farmed fish is generally low in mercury and is a sustainable seafood choice.
Catfish: Farmed catfish is typically low in mercury.
Cod: This white fish is a good source of protein and is generally low in mercury.
Haddock: Similar to cod, haddock is a lean, white fish that is low in mercury.
Flounder: A flatfish that is generally low in mercury and is a good source of protein.
Pollock: A member of the cod family, pollock is a versatile and affordable fish that is low in mercury.
Canned Light Tuna: While tuna can vary in mercury levels, canned light tuna generally has lower levels than albacore or bigeye tuna.
Shrimp: This popular shellfish is generally low in mercury and is a good source of protein.
Oysters: Farmed oysters are considered low in mercury and are also environmentally sustainable.
Scallops: These mollusks are generally low in mercury and offer a good source of protein and minerals.
Crab: Most types of crab, including blue crab and snow crab, are relatively low in mercury.
Sablefish (Black Cod): Despite being a larger fish, sablefish tends to have lower mercury levels compared to other large predators.

Fish Species	Mercury Level	Notes
Swordfish	High	Avoid or limit consumption, especially for pregnant women and young children.
Shark	High	Limit consumption due to high mercury levels.
King Mackerel	High	Avoid or limit consumption, especially for pregnant women and young children.
Salmon	Low	A good choice, especially wild-caught sockeye and pink salmon.
Sardines	Low	An excellent choice, low in mercury and high in omega-3 fatty acids.
Tilapia	Low	A sustainable and low-mercury seafood option.
Canned Light Tuna	Low	Generally lower in mercury than albacore or bigeye tuna.
Shrimp	Low	A popular and low-mercury shellfish.

6. Recommendations for Safe Fish Consumption

To minimize your exposure to mercury while still enjoying the health benefits of fish, follow these recommendations:

6.1. Guidelines for Different Populations

Pregnant Women and Nursing Mothers:
- Avoid high-mercury fish such as swordfish, shark, king mackerel, and tilefish.
- Limit consumption of albacore tuna to 6 ounces per week.
- Choose low-mercury fish such as salmon, sardines, and tilapia.
Young Children:
- Follow the same guidelines as pregnant women and nursing mothers.
- Adjust portion sizes based on the child’s age and weight.
General Population:
- Vary your fish consumption to include a variety of species.
- Limit consumption of high-mercury fish.
- Choose low-mercury fish more often.

6.2. Portion Sizes and Frequency

The FDA and EPA recommend the following guidelines for fish consumption:

Adults: At least 8 ounces of seafood per week from a variety of fish species.
Children: 1-2 servings of fish per week, with portion sizes adjusted based on age and weight.

6.3. Checking Local Advisories

Mercury levels in fish can vary depending on the location and water body. Check local advisories issued by your state or local health department for specific recommendations on fish caught in your area.

6.4. Tips for Reducing Mercury Exposure

Peel and Trim Fish: Mercury tends to concentrate in the skin and fatty tissues of fish. Peeling the skin and trimming away fatty areas can help reduce mercury exposure.
Cook Fish Properly: Cooking fish does not reduce mercury levels, but it does kill bacteria and parasites that may be present.
Choose Wild-Caught over Farmed: While farmed fish is generally low in mercury, wild-caught fish often has a higher nutritional value.
Consider the Source: Buy fish from reputable sources that follow sustainable fishing practices and monitor mercury levels.

Population Group	Recommendations
Pregnant Women	Avoid high-mercury fish (swordfish, shark, king mackerel, tilefish). Limit albacore tuna to 6 ounces per week. Choose low-mercury fish (salmon, sardines, tilapia).
Nursing Mothers	Follow the same guidelines as pregnant women.
Young Children	Follow the same guidelines as pregnant women, adjusting portion sizes based on age and weight.
General Population	Vary fish consumption to include a variety of species. Limit high-mercury fish. Choose low-mercury fish more often.
Adults	At least 8 ounces of seafood per week from a variety of fish species.
Children	1-2 servings of fish per week, with portion sizes adjusted based on age and weight.
Local Fish Consumers	Check local advisories issued by state or local health departments for specific recommendations on fish caught in your area.
Individuals Concerned About Mercury Exposure	Peel and trim fish, cook fish properly, choose wild-caught over farmed when possible, and buy fish from reputable sources.

7. Environmental and Regulatory Efforts to Reduce Mercury Pollution

Reducing mercury pollution requires a multi-faceted approach involving environmental regulations, technological advancements, and international cooperation.

7.1. Environmental Regulations

Several environmental regulations aim to reduce mercury emissions from various sources:

Clean Air Act (USA): The Clean Air Act regulates mercury emissions from coal-fired power plants and other industrial sources.
Minamata Convention on Mercury: This international treaty aims to protect human health and the environment from the adverse effects of mercury. It covers the entire lifecycle of mercury, from mining to disposal, and promotes the use of mercury-free technologies.
EU Mercury Regulation: The European Union has implemented regulations to reduce mercury emissions and phase out the use of mercury in various products and processes.
National Emission Standards for Hazardous Air Pollutants (NESHAP): Regulations set by the U.S. Environmental Protection Agency (EPA) to control emissions of hazardous air pollutants, including mercury, from specific industrial source categories.

7.2. Technological Advancements

Technological advancements play a crucial role in reducing mercury emissions and cleaning up contaminated sites:

Mercury Control Technologies: These technologies are used in coal-fired power plants to remove mercury from flue gas before it is released into the atmosphere.
Mercury-Free Mining Techniques: Alternative gold mining techniques that do not involve the use of mercury are being developed and promoted.
Remediation Technologies: Technologies such as activated carbon adsorption and chemical stabilization are used to clean up mercury-contaminated soil and water.

7.3. International Cooperation

Mercury pollution is a global problem that requires international cooperation:

Information Sharing: Sharing information and best practices among countries can help improve mercury management and reduce pollution.
Capacity Building: Providing technical and financial assistance to developing countries can help them implement mercury reduction strategies.
Joint Research: Collaborative research efforts can help improve our understanding of mercury cycling and develop more effective remediation technologies.
Global Monitoring Programs: Establishing global monitoring programs to track mercury levels in the environment can help assess the effectiveness of reduction efforts and identify emerging problems.
Promoting Alternatives: Encouraging the adoption of mercury-free technologies and products worldwide through incentives and awareness campaigns.
Enforcement of Regulations: Strengthening enforcement of existing regulations and treaties related to mercury emissions and trade.
Public Awareness Campaigns: Conducting public awareness campaigns to educate individuals about the risks of mercury exposure and how to reduce their footprint.
Supporting Sustainable Practices: Promoting sustainable fishing and agricultural practices that minimize mercury pollution and protect aquatic ecosystems.

Effort	Description	Impact on Mercury Pollution
Environmental Regulations	Regulations like the Clean Air Act and the Minamata Convention aim to reduce mercury emissions from various sources.	Reduces mercury emissions from power plants, industrial processes, and mining activities.
Technological Advancements	Technologies such as mercury control technologies and mercury-free mining techniques help reduce mercury emissions and clean up contaminated sites.	Provides tools for capturing and removing mercury from emissions, as well as alternative methods for mining that don’t rely on mercury.
International Cooperation	Global efforts to share information, build capacity, and conduct joint research can help improve mercury management and reduce pollution.	Enhances global efforts to address mercury pollution through coordinated actions and knowledge sharing.

8. Alternative Ways to Obtain Omega-3 Fatty Acids

While fish is a good source of omega-3 fatty acids, there are alternative ways to obtain these essential nutrients without the risk of mercury exposure.

8.1. Plant-Based Sources of Omega-3s

Flaxseeds: Flaxseeds are a rich source of alpha-linolenic acid (ALA), a type of omega-3 fatty acid.
Chia Seeds: Chia seeds are another good source of ALA and can be easily added to smoothies, yogurt, and baked goods.
Walnuts: Walnuts are a good source of ALA and also contain other beneficial nutrients.
Hemp Seeds: Hemp seeds are a complete protein source and contain ALA omega-3 fatty acids.
Brussels Sprouts: These vegetables contain ALA omega-3 fatty acids.
Edamame: Edamame is another vegetable source with ALA omega-3 fatty acids.

8.2. Omega-3 Supplements

Fish Oil Supplements: Fish oil supplements are a popular way to obtain omega-3 fatty acids, but it’s important to choose high-quality supplements that have been tested for mercury and other contaminants.
Algal Oil Supplements: Algal oil supplements are a vegetarian and vegan-friendly alternative to fish oil. They are derived from algae, which are the primary source of omega-3s in fish.
Krill Oil Supplements: Krill oil supplements are another source of omega-3s, but they may be more expensive than fish oil or algal oil supplements.

8.3. Fortified Foods

Fortified Foods: Some foods, such as milk, yogurt, and eggs, are fortified with omega-3 fatty acids. Check the label to see if a food has been fortified with omega-3s.

Source	Description	Benefits
Flaxseeds	Rich source of alpha-linolenic acid (ALA), a type of omega-3 fatty acid.	Supports heart health, reduces inflammation, and improves brain function.
Chia Seeds	Another good source of ALA, easily added to smoothies, yogurt, and baked goods.	Provides fiber, antioxidants, and minerals, in addition to omega-3s.
Walnuts	Good source of ALA and also contain other beneficial nutrients.	Supports brain health, reduces the risk of heart disease, and provides antioxidants.
Hemp Seeds	Complete protein source and contain ALA omega-3 fatty acids.	Supports muscle growth and repair, provides essential amino acids, and supports heart health.
Brussels Sprouts	Contain ALA omega-3 fatty acids.	Provides vitamins, minerals, and fiber, supporting overall health.
Edamame	Vegetable source with ALA omega-3 fatty acids.	Offers plant-based protein, fiber, and vitamins, supporting a healthy diet.
Fish Oil Supplements	Popular way to obtain omega-3 fatty acids, but choose high-quality supplements tested for contaminants.	Concentrated source of EPA and DHA, supporting heart health, brain function, and reducing inflammation.
Algal Oil Supplements	Vegetarian and vegan-friendly alternative to fish oil, derived from algae.	Provides EPA and DHA without the need for fish, making it a sustainable and ethical choice.
Krill Oil Supplements	Another source of omega-3s, but may be more expensive.	Contains antioxidants and may be more easily absorbed than fish oil.
Fortified Foods	Foods such as milk, yogurt, and eggs, are fortified with omega-3 fatty acids.	Provides omega-3s in commonly consumed foods, making it easier to increase intake.

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11. Frequently Asked Questions (FAQs) About Mercury in Fish

11.1. Is it safe to eat fish during pregnancy?

Yes, it is safe to eat certain types of fish during pregnancy. The FDA and EPA recommend that pregnant women eat 8-12 ounces of low-mercury fish per week, such as salmon, sardines, and tilapia. Avoid high-mercury fish like swordfish, shark, king mackerel, and tilefish.

11.2. How does mercury get into fish?

Mercury enters aquatic ecosystems through natural processes (volcanic eruptions, weathering of rocks) and human activities (coal-fired power plants, mining, industrial processes). Bacteria in water and sediment convert mercury into methylmercury, which is absorbed by aquatic organisms.

11.3. Can you remove mercury from fish by cooking it?

No, cooking fish does not reduce mercury levels. Mercury is bound to the proteins in the fish tissue and is not affected by heat.

11.4. What are the symptoms of mercury poisoning from fish?

Symptoms of mercury poisoning can include neurological problems (memory loss, tremors, difficulty concentrating), cardiovascular effects (increased risk of heart disease), kidney damage, and immune system effects.

11.5. How can I reduce my exposure to mercury from fish?

Choose low-mercury fish species, limit consumption of high-mercury fish, check local advisories, and peel and trim fish to reduce mercury exposure.

11.6. Are farmed fish safer to eat than wild-caught fish in terms of mercury content?

Generally, farmed fish tend to have lower mercury levels compared to wild-caught fish because their diets are controlled and they are often raised in cleaner environments. However, the mercury content can still vary depending on the specific species and farming practices.

11.7. What is the Minamata Convention on Mercury, and how does it help reduce mercury contamination?

The Minamata Convention on Mercury is an international treaty designed to protect human health and the environment from the adverse effects of mercury. It addresses the entire lifecycle of mercury, including mining, trade, use in products and processes, and disposal. By promoting mercury-free technologies and regulating mercury emissions, the convention helps reduce mercury contamination in the environment, including in aquatic ecosystems.

11.8. Can mercury contamination in fish affect pets?

Yes, mercury contamination in fish can affect pets, especially if they are fed fish-based diets regularly. Pets, like humans, can experience neurological, kidney, and immune system effects from mercury exposure. It’s important to choose pet foods that use sustainably sourced fish and monitor the mercury content.

11.9. How do local advisories help in making safe fish consumption choices?

Local advisories provide specific recommendations on fish caught in local water bodies, based on monitoring data of mercury and other contaminants. These advisories help consumers make informed decisions about which fish are safe to eat, how often to eat them, and what preparation methods can reduce exposure to contaminants.

11.10. What are the long-term consequences of mercury exposure from fish consumption?

Long-term consequences of mercury exposure from fish consumption can include chronic neurological problems, increased risk of cardiovascular disease, kidney damage, and immune system dysfunction. Pregnant women and young children are particularly vulnerable to the developmental effects of mercury exposure, which can lead to cognitive and motor skill impairments.

Question	Answer
Is it safe to eat fish during pregnancy?	Yes, certain types of fish are safe. Follow FDA and EPA guidelines for low-mercury fish.
How does mercury get into fish?	Through natural processes and human activities, converted to methylmercury by bacteria.
Can you remove mercury from fish by cooking it?	No, cooking does not reduce mercury levels.
What are the symptoms of mercury poisoning from fish?	Neurological problems, cardiovascular effects, kidney damage, and immune system effects.