What are the contaminants in herring?

January 13, 2026 •

4 min read

Environmental pollution, including industrial discharges and atmospheric deposition, introduces various contaminants into the marine ecosystem that can accumulate in fish like herring. As a small, oily fish, herring is susceptible to absorbing pollutants from its environment, including chemicals, heavy metals, and microplastics.

Quick Summary

Herring can contain environmental pollutants such as PCBs, dioxins, heavy metals like mercury and cadmium, and microplastics from polluted waters. Contaminant levels vary based on geography, but processing methods can sometimes reduce certain pollutants.

Key Points

Heavy Metals: Herring can contain heavy metals like mercury, cadmium, and lead, though levels are generally lower than in larger predatory fish.
Persistent Organic Pollutants (POPs): Fat-soluble contaminants such as PCBs and dioxins accumulate in herring, particularly those from highly industrialized regions like the Baltic Sea.
Microplastics: Microplastic fibers and fragments have been found in the gastrointestinal tracts of herring, though their link to tissue contaminant levels is debated.
Geographic Variation: Contaminant levels in herring differ significantly based on their habitat, with higher concentrations in more polluted, urbanized waters.
Consumption Guidelines: To minimize risk, consumers can choose herring from less contaminated areas, trim fat and skin, and moderate consumption as part of a varied diet.
Preparation Techniques: Certain preparation methods, like trimming fatty tissue, can reduce exposure to fat-soluble pollutants, while methods do not affect mercury levels.
Environmental Sources: Pollution originates from industrial discharges, wastewater, agricultural practices, and atmospheric deposition, affecting all parts of the marine food web.

Common Contaminants in Herring

Herring, as a forage fish, plays a crucial role in marine food webs, but this position also makes it vulnerable to a range of contaminants from environmental pollution. These substances enter the water from industrial and domestic waste, agricultural runoff, and the burning of fossil fuels.

Heavy Metals

Heavy metals such as mercury, cadmium, lead, and arsenic are common in marine environments and can accumulate in fish tissues. Herring generally has low mercury levels compared to larger predatory fish, but some studies have detected its presence. Cadmium and lead can also be present, with detected levels sometimes exceeding maximum limits, especially in certain geographic regions. Arsenic levels can also fluctuate, potentially linked to seasonal feeding patterns. While salting does not remove heavy metals, some studies suggest that smoking and high heat can reduce mercury levels.

Persistent Organic Pollutants (POPs)

Polychlorinated biphenyls (PCBs) and dioxins are highly persistent, toxic, and fat-soluble organic chemicals.

PCBs: PCBs are industrial compounds formerly used in electrical equipment and other products. Though banned decades ago in many places, their persistence means they remain a significant pollutant. PCBs are found in herring, particularly in urbanized and industrialized areas like Puget Sound and the Baltic Sea, where levels have been shown to exceed fish health thresholds. They accumulate in fatty tissues, posing a risk to marine predators and humans.
Dioxins: These toxic compounds are byproducts of industrial processes and combustion. Like PCBs, they are fat-soluble and accumulate in oily fish. High levels of dioxins and dioxin-like PCBs have been consistently found in fatty fish species like herring from highly polluted regions, such as the Baltic Sea.

Microplastics

Microplastics (MPs) are tiny plastic particles, often fibers or fragments, that are ubiquitous in marine ecosystems and ingested by many fish species, including herring. Studies on Baltic herring have shown that microplastics are present in the gastrointestinal tracts of many fish. While there was previously concern about microplastics acting as a vector for other contaminants, more recent research suggests this link may not be as strong as once thought, with other environmental factors playing a more significant role in overall contaminant load.

Comparison of Contaminants in Herring


Contaminant Type	Source(s)	Health Risk	Persistence in Fish	Accumulation Location
Heavy Metals (e.g., Mercury)	Industrial emissions, coal burning, natural occurrences	Potential harm to nervous system and overall health	Moderate to High (bioaccumulates)	Primarily muscle tissue
Persistent Organic Pollutants (POPs) (e.g., PCBs, Dioxins)	Industrial processes, combustion byproducts	Various adverse health effects, including potential carcinogenicity	Very High (resistant to degradation)	Primarily fatty tissues
Microplastics	Breakdown of larger plastic debris, industrial waste, textiles	Potential link to health issues, can carry other toxins	High	Primarily gastrointestinal tract, can be translocated to other tissues
Bacteria (e.g., Listeria, Vibrio)	Environmental pollution, improper food handling	Foodborne illness	Low (dependent on handling/processing)	Flesh, especially with poor handling

Mitigating Contamination and Ensuring Safe Consumption

To manage the risks associated with contaminants, consumers can take several steps, and regulatory bodies continuously monitor contaminant levels. Research has explored methods to reduce contaminant levels in herring post-harvest, including processing techniques like the pH-shift method, which effectively removes lipids and associated fat-soluble contaminants.

For consumers:

Choose Wisely: Opt for herring from less polluted waters. For example, North Sea herring is generally less contaminated with dioxins than Baltic Sea herring.
Vary Your Diet: Incorporating a variety of seafood with different contaminant profiles is a sound strategy for reducing exposure.
Preparation Matters: For fat-soluble contaminants like PCBs and dioxins, trimming fat and skin before cooking can help, as these compounds accumulate in fatty tissue. Grilling or baking on a rack allows fat to drip away. However, this method will not reduce mercury levels, which are in the muscle.

For the environment:

Reduce Pollution: Addressing industrial discharges and managing waste to reduce the release of pollutants like mercury, PCBs, and plastics into marine ecosystems is the most effective long-term solution.
Monitoring: Regular monitoring of fish stocks and issuing consumption advisories for specific waterbodies helps inform the public of potential risks.

Conclusion

In conclusion, while herring is a nutritious fish rich in omega-3 fatty acids, it is not immune to environmental contaminants. Key contaminants include heavy metals like mercury and cadmium, persistent organic pollutants such as PCBs and dioxins, and microplastics. The level of contamination can vary significantly based on the herring's habitat, with fish from more urbanized and industrialized regions generally showing higher levels of certain pollutants. Consumers can make informed choices by selecting fish from cleaner areas and practicing preparation methods that can mitigate some risks. However, the ultimate solution lies in controlling the sources of environmental pollution to protect marine ecosystems for the long term. For up-to-date guidance, consulting resources like the EPA is recommended.

Frequently Asked Questions

Yes, like nearly all fish, herring contains traces of mercury. However, as a small, forage fish, its mercury levels are generally considered low compared to larger predatory fish higher up the food chain.

Yes, PCBs and dioxins are a concern, particularly in herring from highly polluted areas like the Baltic Sea. These fat-soluble pollutants accumulate in the fish's fatty tissue.

Some cooking methods can reduce certain contaminants. Trimming fat and skin before cooking and then broiling, grilling, or baking on a rack can reduce fat-soluble pollutants like PCBs and dioxins. However, this does not affect mercury, which is in the muscle tissue.

Microplastics (MPs) have been found in herring, but recent studies suggest that ingested MPs may not be a major vector for hydrophobic contaminants compared to environmental sources. However, further research into their full effects is ongoing.

Yes, the fishing location significantly affects contaminant levels. Herring from more industrialized and urbanized water bodies, such as certain parts of the Baltic Sea or Puget Sound, tend to have higher levels of pollutants than those from cleaner waters.

Yes, herring is considered a good choice for pregnant women due to its low mercury content and high omega-3 fatty acids, but it is important to be mindful of its origin. The EPA advises varying fish consumption and consulting local advisories.

Herring is highly nutritious and rich in essential omega-3 fatty acids, vitamin D, vitamin B12, and protein. These nutrients are linked to benefits for heart health, brain function, and overall well-being.

Herring is not typically farmed, and most is wild-caught. However, in aquaculture, contaminants in fish feed or from the surrounding environment can be a factor, with mercury sometimes accumulating from feed or sediments.