Skip to main content

In the pursuit of optimal health, the incorporation of omega-3 fatty acids through fish oil supplements has become increasingly commonplace. While these supplements are renowned for their potential cardiovascular and cognitive benefits, a prudent consideration must be given to the potential risks associated with heavy metal contamination.

Table of contents:

What are the most commonly found toxic metals in omega 3 supplements?

A lot of people have now become aware, that there are three most commonly found toxic metals in omega 3 supplements – mercury, cadmium, and lead. But how do they appear in most of the fish oil supplements around the world, you might ask?

Well, the problems lies in the fact that certain fish, particularly those higher in the food chain, have an inherent tendency to accumulate heavy metals from their aquatic environments. Consequently, fish oil derived from these sources may inadvertently introduce these contaminants into one’s daily supplement regimen. Mercury, a neurotoxin, cadmium and lead, with their cumulative health implications, all pose serious concerns.

View table: Mercury Levels in Commercial Fish and Shellfish (PDF)

Why are they found in most omega 3/fish oil supplements?

Fish, especially large predatory species, can accumulate heavy metals from their environment, primarily through the food chain. Heavy metals can be present in some fish oil supplements due to contamination of the fish used to extract the oil, or other factors such as:


Fish at the top of the food chain, such as tuna, shark, and swordfish, are more likely to accumulate heavy metals. This is because they consume smaller fish, which, in turn, may have ingested metals from their prey. The process of heavy metals accumulating in organisms higher up the food chain is known as bioaccumulation.

Polluted Waters

Fish that live in waters, which are contaminated with industrial pollutants, agricultural runoff, or other sources of heavy metals are more likely to contain elevated levels of these substances. Pollution in oceans and seas can lead to contamination of fish and, subsequently, fish oil.

Quality of Fish Sourcing

The quality of the fish used to produce fish oil supplements can vary. If the fish are sourced from regions with higher levels of pollution or if the sourcing practices are not stringent, there is an increased risk of heavy metal contamination in the final product.

Processing Methods

The methods used to extract and process fish oil can impact its purity. Some manufacturing processes may not adequately remove contaminants like heavy metals. High-quality supplements often undergo processes such as molecular distillation to reduce the levels of contaminants.

Lack of Regulation

While there are regulatory standards for contaminants in fish oil supplements, the enforcement may vary. In some cases, supplements from less regulated markets may have a higher risk of contamination.


The upper tolerable limit (UTL) for mercury, cadmium, and lead exposure in humans is established by health authorities to help prevent adverse health effects associated with mercury toxicity. The tolerable limit can vary based on factors such as age, weight, and health status.

UTL for Mercury

Here are the general guidelines provided by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO):

  • Methyl mercury (from Fish Consumption): Methyl mercury is a form of organic mercury that is primarily found in certain fish and seafood. The U.S. Environmental Protection Agency (EPA) recommends that women of childbearing age, pregnant women, nursing mothers, and young children limit their consumption of fish, high in mercury to avoid adverse developmental effects. The Food and Drug Administration (FDA) advises that these groups should consume no more than 2–3 servings of low-mercury fish per week and avoid certain high-mercury fish.
  • Total Mercury (General Exposure): For total mercury exposure (including exposure from sources other than fish), the U.S. Agency for Toxic Substances and Disease Registry (ATSDR) has set a Minimal Risk Level (MRL) for chronic exposure to mercury vapor. The MRL is 0.3 micrograms of mercury per cubic meter of air (µg/m³).

It’s important to note that these recommendations are general guidelines, and individuals with specific health concerns or conditions may need personalized advice. Additionally, regulations and guidelines may vary by country, so it’s advisable to refer to local health authorities for the most current information. If you have specific concerns about mercury exposure, consulting with a healthcare professional is recommended.

UTL for Cadmium

  • Dietary Intake: The Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA) has set a Provisional Tolerable Monthly Intake (PTMI) for cadmium in food. The PTMI is 25 micrograms per kilogram of body weight. This value is based on the assumption that exposure occurs regularly, and it represents the amount of cadmium that can be ingested each month without appreciable risk.
  • Occupational Exposure: For occupational exposure to airborne cadmium, occupational health and safety agencies, such as the Occupational Safety and Health Administration (OSHA) in the United States, set permissible exposure limits to protect workers. The OSHA Permissible Exposure Limit (PEL) for cadmium in the workplace is 0.005 milligrams per cubic meter of air (mg/m³) over an 8-hour workday.

It’s important to note that chronic exposure to cadmium, even at levels below the established limits, can have cumulative health effects over time. Sources of cadmium exposure include certain foods (especially shellfish, liver, and kidney), tobacco smoke, and occupational settings such as metal smelting and battery manufacturing.

UTL for Lead

Lead is another toxic heavy metal, and exposure to lead can have severe health implications. Similar to mercury and cadmium, there are established guidelines for lead exposure to prevent adverse health effects. Here are some general guidelines:

  • Blood Lead Levels: The Centers for Disease Control and Prevention (CDC) in the United States has established reference levels for blood lead. The reference level for children is 5 micrograms per deciliter (µg/dL). Blood lead levels below this reference level are considered normal. However, there is no known safe level of lead exposure, and adverse effects can occur at lower levels, especially in children.
  • Occupational Exposure: Occupational exposure to lead is regulated by occupational health and safety agencies. For example, the Occupational Safety and Health Administration (OSHA) in the United States sets permissible exposure limits (PELs) for lead in the workplace. The OSHA PEL for lead is 50 micrograms per cubic meter of air (µg/m³) over an 8-hour workday.
  • Environmental Exposure: The Environmental Protection Agency (EPA) has established action levels for lead in various environmental media. For example, the action level for lead in drinking water is 15 parts per billion (ppb).

It’s important to note that lead exposure can occur from various sources, including lead-based paint, contaminated water, and certain occupational settings. Children, pregnant women, and developing fetuses are particularly vulnerable to the harmful effects of lead.

Why is Cadmium bad for your health?

Cadmium is considered harmful to human health due to its toxic properties and the fact that it can accumulate in the body over time. Here are some reasons why cadmium is considered detrimental to health:

1. Toxicity

Cadmium is a heavy metal that can be toxic to various organs and systems in the body, including the kidneys, lungs, and bones. It is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC), meaning there is sufficient evidence to support its carcinogenicity to humans.

2. Accumulation

Cadmium has a tendency to accumulate in the body, especially in the kidneys. Prolonged exposure to even low levels of cadmium can result in the gradual build-up of the metal in tissues, leading to chronic health issues.

3. Kidney Damage

One of the primary concerns with cadmium exposure is its potential to cause kidney damage. Long-term exposure can contribute to the development of renal dysfunction and may increase the risk of chronic kidney disease.

4. Bone Effects

Cadmium can interfere with calcium metabolism and accumulate in bones. Prolonged exposure may lead to a decrease in bone density, potentially contributing to skeletal issues.

5. Respiratory Issues

Inhalation of cadmium dust or fumes can cause respiratory irritation and may lead to lung damage over time. Occupational exposure, such as in certain industrial settings, poses a particular risk.

6. Cardiovascular Effects

Some studies suggest a possible association between cadmium exposure and cardiovascular diseases. Cadmium may contribute to the development of hypertension and increase the risk of cardiovascular events.

7. Reproductive and Developmental Concerns

Cadmium exposure has been linked to adverse effects on reproductive health and development. It may impact fertility and has been associated with developmental issues in infants exposed in utero.

Given these health concerns, it is important to minimize exposure to cadmium.

Why is Lead bad for your health?

Lead is harmful to human health due to its toxic properties. Exposure to lead can have a range of adverse effects, such as:

1.Neurological Effects

One of the most significant concerns with lead exposure is its impact on the central nervous system. Even low levels of lead exposure, especially in children, can result in cognitive and behavioral issues. Lead interferes with the normal development and functioning of the brain, leading to learning disabilities, decreased IQ, and behavioral problems.

2.Developmental Delays

Children, particularly those exposed to lead during critical stages of development, may experience developmental delays and long-term cognitive impairments. Prenatal exposure to lead can affect the developing fetus, leading to issues such as low birth weight and developmental deficits.

3.Behavioral and Emotional Effects

Lead exposure has been linked to changes in behavior and mood, including increased aggression, impulsivity, and irritability. These effects may persist into adulthood, impacting mental health and overall well-being.

4.Gastrointestinal Issues

Lead can affect the gastrointestinal system, leading to symptoms such as abdominal pain, constipation, and nausea.

5.Hematological Effects

Lead interferes with the synthesis of hemoglobin, the oxygen-carrying component of red blood cells. This can result in anemia, particularly in cases of chronic lead exposure.

6.Cardiovascular Effects

Elevated lead levels in the blood have been associated with an increased risk of hypertension (high blood pressure) and cardiovascular diseases. Lead exposure can contribute to damage to blood vessels and the heart.

7. Kidney Damage

Lead is known to accumulate in the kidneys, where it can cause nephrotoxicity (kidney damage). Prolonged exposure to lead may impair kidney function and contribute to chronic kidney disease.

8. Reproductive Issues

Lead exposure can affect reproductive health in both men and women. In women, it may lead to miscarriages, premature births, and developmental issues in newborns. In men, lead exposure has been associated with decreased fertility and abnormalities in sperm.

Why is Mercury bad for your health?

Mercury is considered harmful to human health due to its toxic properties. Exposure to mercury can lead to a range of adverse health effects, and the severity of these effects depends on factors such as the form of mercury, the level of exposure, and the duration of exposure. Here are some reasons why mercury is considered detrimental to health:


Mercury has a pronounced affinity for the nervous system and is known to be neurotoxic. It can cross the blood-brain barrier and interfere with the normal functioning of nerve cells. Prenatal exposure, especially during the early stages of fetal development, can result in developmental delays and neurological issues in children.

2.Kidney Damage

Mercury can accumulate in the kidneys, leading to nephrotoxicity. Chronic exposure to mercury can contribute to kidney damage and impair the organ’s ability to filter and excrete waste products.

3.Cardiovascular Effects

Some studies suggest that exposure to mercury may be associated with cardiovascular issues, including an increased risk of heart attacks and hypertension. However, the evidence in this area is still being studied, and the relationship between mercury exposure and cardiovascular health is complex.

4.Respiratory and Immune System Effects

Inhalation of mercury vapors, typically released from certain industrial processes, can cause respiratory irritation. Mercury exposure may also affect the immune system, potentially leading to immune dysfunction.

5.Developmental and Reproductive Effects

Pregnant women are particularly vulnerable to the harmful effects of mercury. It can cross the placenta and impact the developing fetus, leading to cognitive and developmental issues. In adults, mercury exposure can impact reproductive health and may contribute to fertility problems.

6.Methyl mercury Poisoning

Methyl mercury, a form of organic mercury, is of particular concern. It accumulates in certain fish and seafood, posing a risk to individuals who consume contaminated fish regularly. Long-term exposure to high levels of methyl mercury can lead to mercury poisoning, with symptoms including neurological disturbances, muscle weakness, and sensory impairments.

Heavy metals in seafood

In order to ascertain the quality of various canned and packaged seafood products available in the U.S., Consumer Lab (a leading provider of consumer information and independent evaluations of products that impact health and nutrition) conducted a comprehensive evaluation(1).

The focus of the assessment included popular tuna, salmon, and sardines. Each product underwent testing for the presence of omega-3 fatty acids such as DHA, EPA, and DPA, along with omega-7 fatty acids. Additionally, rigorous scrutiny was applied to identify potential contamination with mercury, arsenic, lead, and cadmium. Consumer Lab’s evaluation also extended to the assessment of the oil in these products, aiming to discern its freshness or potential rancidity.

The comprehensive testing results revealed substantial variations in the omega-3 fatty acid content among different seafood products when consumed at recommended serving sizes. Notably, sardines and salmon emerged as particularly rich sources, providing significantly higher amounts of DHA and EPA compared to tuna. A standard 85-gram serving of sardines delivered an impressive 1,600 mg to 1,800 mg of DHA and EPA, while a 56-gram serving of salmon offered 400 mg to 700 mg. In contrast, canned and packaged tuna exhibited lower levels, ranging from 45 mg to about 440 mg of DHA and EPA per serving.

An exception was noted with one albacore tuna product, boasting 1,294 mg of DHA and EPA per serving. Furthermore, it was observed that some products contained substantially lower amounts of DHA and EPA than indicated on their labels.

In order to steer clear from contaminating your body with these heavy metals, you shouldn’t consume fish high in mercury more than once or twice per week. Furthermore, fish or seafood, high only in arsenic, should not be eaten more than once daily.

According to the study, done by Consumer Lab,” canned and packaged tunas, particularly albacore tunas, were generally the most contaminated with mercury. A tuna product that contained one of the lowest amounts of omega-3s also contained the highest concentration of mercury 0.41 ppm (parts per million), which is just below the EPA’s and FDA’s recommended limit for avoiding fish (0.46 ppm). The same product had the second-highest concentration of arsenic (2.27 ppm).”

However, in the analysis it was found that among the canned seafood options, salmon exhibited the lowest levels of mercury and arsenic. On the other hand, while canned sardines were found to be low in mercury, they displayed elevated levels of arsenic, ranging from 2.13 to 2.17 ppm.

How to avoid these metals and choose the right omega 3/fish oil supplement?

To mitigate these risks, a discerning approach is essential. Begin by selecting supplements from reputable brands committed to stringent quality control measures. Certification from third-party testing organizations such as the International Fish Oil Standards (IFOS) can provide assurance regarding the purity of the product.

Molecular distillation emerges as a noteworthy process in this context. This method, akin to a purification protocol, effectively removes heavy metals from fish oil, enhancing its safety profile. Supplements that have undergone molecular distillation are preferable for those seeking to minimize their exposure to contaminants.

Diversification of omega-3 sources is a strategic consideration as well. Algae-based supplements and plant-derived alternatives, such as flaxseed oil, offer viable options with potentially lower levels of heavy metal content.


In conclusion, an informed and discerning approach to selecting fish oil supplements is paramount. By prioritizing quality, adhering to third-party certifications, and exploring purification processes, you can confidently navigate the nuanced landscape of omega-3 supplementation, ensuring both the benefits and safety of these dietary additions.

Disclaimer: As a service to our readers, MVS Pharma GmbH publishing provides access to our library of archived content – in our blog. Please note the date of last review or update on all articles. No content on this site, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.


Dr. Disha Trivedi

Dr. Disha Trivedi is PhD in Molecular Genetics and Biotechnology. She is working as a medical writer and researcher at MVS Pharma GmbH.