Which Seafood Has High Levels of Arsenic and Why?

November 26, 2025 •

5 min read

According to the World Health Organization, inorganic arsenic is a known human carcinogen, but the arsenic found in most seafood is a less harmful organic form. Consumers often wonder what seafood has high levels of arsenic and whether they should be concerned about it. This article delves into the specifics of arsenic accumulation in seafood, examining the differences in arsenic types and identifying which species are known to contain higher concentrations.

Quick Summary

This article explores the types of seafood that contain elevated levels of arsenic, differentiating between the harmless organic forms and the toxic inorganic varieties. It details which marine species and products, such as certain algae, crustaceans, and bottom-feeding fish, tend to accumulate higher concentrations. The article also provides a comparative analysis and addresses potential health risks.

Key Points

Arsenic Exists in Two Forms: Seafood contains primarily non-toxic organic arsenic (arsenobetaine), but a smaller, more toxic inorganic form is also found.
High Total Arsenic in Benthic Species: Bottom-dwelling organisms like shellfish (clams, oysters) and crustaceans (crabs, lobsters) tend to accumulate higher total arsenic levels from sediment.
Hijiki Seaweed is High in Toxic Arsenic: Brown algae such as hijiki seaweed are a notable exception, containing significant levels of the more harmful inorganic arsenic.
Health Risk is Generally Low: For most seafood consumers, the health risk from arsenic is minimal, as the harmless organic form predominates and is quickly excreted by the body.
Risk Depends on Speciation and Source: The true risk depends on the specific type of arsenic (speciation) and the source location, with inorganic arsenic from drinking water generally posing a greater threat than seafood.

Understanding Arsenic in Marine Environments

Arsenic is a naturally occurring element present in seawater, rocks, and soil. Marine organisms can absorb arsenic from their environment, primarily converting it into a less toxic organic form called arsenobetaine. However, certain species and environmental factors can lead to higher total arsenic concentrations, sometimes including the more harmful inorganic arsenic (iAs). Understanding the different forms and their sources is crucial for making informed dietary choices. While total arsenic levels can be high, the health risk depends significantly on the proportion that is inorganic.

The Difference Between Inorganic and Organic Arsenic

There are two main types of arsenic, each with a different level of health concern:

Organic Arsenic: This is the most common form found in seafood, particularly as arsenobetaine. It is considered harmless to humans and is quickly excreted from the body. It is not associated with cancer and is not considered a health risk in the context of typical seafood consumption.
Inorganic Arsenic: The more toxic form, inorganic arsenic is often linked to drinking water contamination but can also appear in certain marine products. Chronic exposure to high levels of inorganic arsenic can lead to various health problems, including cancer.

Factors Influencing Arsenic Levels in Seafood

Several factors can influence the amount and type of arsenic a marine organism accumulates:

Habitat: Organisms that live on or near the seabed, known as benthic species, tend to accumulate more arsenic because sediments typically have higher arsenic concentrations than surface water. This is particularly true for bottom-feeding creatures like crabs, some fish, and bivalves.
Diet: The position of an organism in the food chain affects its arsenic load. Species that consume algae or smaller organisms with high arsenic levels can accumulate more themselves, a process known as biomagnification.
Species: Different species metabolize and store arsenic differently. Some species have a greater capacity to convert inorganic arsenic into the benign organic form.
Location and Water Conditions: The geographical location, water temperature, and salinity can all affect arsenic levels. Pollution from human activities like industrial processes and mining can also increase arsenic concentrations in certain aquatic areas.

Seafood Species with Higher Total Arsenic

While the bulk of total arsenic in these foods is organic and non-toxic, studies consistently show certain categories and species contain higher concentrations. It is important to emphasize that this refers to total arsenic, and the toxic inorganic fraction is typically very low.

Algae and Seaweed

Some types of brown algae are a notable exception, as they can contain significant levels of inorganic arsenic. Hijiki seaweed, in particular, is known for its high inorganic arsenic content and is often recommended to be consumed rarely or avoided. Other brown algae species have also been found to contain elevated levels of inorganic arsenic.

Shellfish and Mollusks

Shellfish and mollusks, including mussels, oysters, and clams, can have higher total arsenic levels due to their feeding habits and proximity to sediment. Crustaceans like crabs and lobsters also tend to contain elevated levels of total arsenic. While the inorganic fraction is often low in these species, it can vary depending on location and local contamination.

Bottom-Feeding Finfish

Some fish that inhabit and feed near the seabed, such as demersal fish like anglerfish and megrim, may accumulate more total arsenic than fish living in open water. Certain types of grouper and king mackerel have also shown higher total arsenic levels in some studies.

Arsenic Levels in Common Seafood: A Comparison


Seafood Category	Total Arsenic Level	Primary Arsenic Form	Primary Health Concern
Finfish	Generally low to moderate.	Mostly arsenobetaine (organic).	Very low, as organic arsenic is harmless.
Shellfish (Crustaceans)	Moderate to high.	Mostly organic, with variable but typically low inorganic fractions.	Low risk in most cases, but depends on local contamination.
Shellfish (Mollusks)	Can be high; levels are highly variable.	Mix of arsenobetaine and arsenosugars.	Generally low, but specific bivalves can have higher inorganic levels.
Brown Seaweed (e.g., Hijiki)	Extremely high total arsenic.	High proportion of inorganic arsenic.	Potentially significant risk due to inorganic content; often advised against consumption.

Conclusion: The Bigger Picture of Seafood Safety

While some seafood, notably brown seaweeds like hijiki and certain shellfish, can have high levels of arsenic, it is crucial to remember the distinction between the organic and inorganic forms. The vast majority of arsenic in commonly consumed fish and shellfish is the harmless organic arsenobetaine, which is rapidly eliminated from the body. Concerns over toxic inorganic arsenic should focus on sources of contamination and species known to accumulate it, especially brown seaweed. For most consumers, the health benefits of eating a varied diet of seafood far outweigh the risks associated with arsenic. Local fish advisories are an excellent resource for specific, location-based information on seafood safety. A balanced diet, rather than the complete elimination of seafood, is the recommended strategy for minimizing overall exposure to potential contaminants. For more detailed risk assessment information, consult the European Food Safety Authority (EFSA) and other reputable health organizations.

Best Practices for Reducing Arsenic Intake

Diversify your seafood consumption: Eat a variety of different seafood species, rather than relying heavily on one type, to minimize exposure to any single contaminant source.
Consult local advisories: Check for specific fish or shellfish advisories in your area, particularly for bottom-dwellers, as contamination can be localized.
Be cautious with hijiki: Limit or avoid consumption of hijiki seaweed due to its high inorganic arsenic content.
Consider preparation methods: Arsenic can be released during cooking, and while this affects the total amount, the form of arsenic is the more critical factor.
Prioritize a balanced diet: Focus on overall dietary health, as the risk from arsenic in most seafood is low and should be considered in the context of total exposure from all sources, including drinking water.

The Role of Arsenic Speciation

Determining the total arsenic content of seafood is insufficient for a health risk assessment. The process of arsenic speciation, which identifies the specific chemical forms, is essential for a more accurate evaluation. Regulatory bodies are increasingly focusing on inorganic arsenic levels for risk assessments.

Sources of Inorganic Arsenic Outside Seafood

While seafood is often mentioned in the context of arsenic, the biggest public health threat from inorganic arsenic comes from other sources. Drinking water in certain areas can contain high levels of inorganic arsenic. Rice and rice products can also absorb inorganic arsenic from soil and water more readily than many other crops.

Monitoring and Regulation

Regulatory efforts are evolving to better address arsenic in food. The European Union, for instance, has adopted maximum levels for inorganic arsenic in specific seafood products. Continuous monitoring is necessary, especially for high-risk products like hijiki seaweed.

Frequently Asked Questions

For most people, the arsenic in seafood is not dangerous. The majority is a harmless organic form called arsenobetaine, which passes through the body without causing harm. The risk comes from specific types of seafood or contaminated locations with high inorganic arsenic.

You should be most cautious with hijiki seaweed, which contains high levels of the toxic inorganic form of arsenic. Certain shellfish from contaminated areas might also have higher inorganic levels, so it's wise to check local advisories.

Shellfish and seaweed accumulate arsenic from their environment more effectively. Shellfish are often bottom-dwellers, and seaweed absorbs the element directly from seawater, storing it in various forms, including toxic inorganic arsenic in some brown algae.

Cooking methods can slightly affect arsenic content, but they do not typically change the chemical form of the arsenic. The primary concern is the ratio of inorganic to organic arsenic in the raw seafood, not how it's prepared.

Inorganic arsenic is highly toxic and linked to health problems like cancer. Organic arsenic, which includes arsenobetaine, is far less toxic and generally not a health risk. Seafood predominantly contains organic arsenic.

Yes, it is generally safe to eat fish regularly. The health benefits of regular fish consumption, particularly omega-3 fatty acids, are well-documented. A varied diet of seafood is recommended to balance nutritional intake and minimize exposure to any single contaminant.

Yes, some regulatory bodies, like the European Union, have adopted maximum levels for inorganic arsenic in certain seafood products. Agencies also monitor and regulate imported products, such as hijiki seaweed, for high arsenic levels.