Most discussions about seafood safety focus on mercury, but arsenic is another heavy metal that can be a concern for some consumers. However, it is a nuance that is rarely discussed: not all arsenic is equally toxic. The arsenic found in seafood is predominantly in a non-toxic, organic form that is harmless to humans. The real risk lies in the inorganic form, which is found in very low amounts in most finfish but can be present in higher, more concerning levels in certain shellfish and seaweed.
Understanding Arsenic in Seafood: Not All Arsenic is Toxic
It is essential to differentiate between the two main types of arsenic found in the environment and in food: organic and inorganic. Ocean-dwelling plants and animals absorb arsenic from seawater and process it into a compound called arsenobetaine, which is a non-toxic, organic form. This is the most common form of arsenic found in fish and is quickly eliminated from the human body without being metabolized. In contrast, inorganic arsenic is the more toxic form, and while it is present in seafood, it is typically in negligible amounts in most fish. The risk of high inorganic arsenic exposure from seafood is primarily limited to certain shellfish from specific regions and particular types of seaweed, such as hijiki.
The Safest Choices: Fish with Minimal Inorganic Arsenic
When seeking fish with the lowest arsenic content, several types stand out based on testing and general environmental factors. Freshwater fish, such as trout, catfish, and tilapia, generally have significantly lower total arsenic concentrations than their marine counterparts. This is because arsenic concentrations are naturally higher in the marine environment than in most freshwater systems. Additionally, certain types of canned salmon, specifically pink and sockeye, have shown no measurable mercury or arsenic in independent lab testing. Smaller, lower-trophic-level fish like Atlantic mackerel, anchovies, and sardines also tend to be low in contaminants.
Comparison of Arsenic Levels in Common Seafood
| Seafood Type | Typical Arsenic Form | Arsenic Contamination Level | Additional Context |
|---|---|---|---|
| Sockeye/Pink Salmon (Canned) | Organic (Arsenobetaine) | Very Low (Inorganic undetectable in some tests) | Excellent source of Omega-3s and Calcium. |
| Freshwater Fish (Trout, Catfish) | Organic/Trace Inorganic | Very Low | Levels are consistently much lower than marine fish. |
| Light Tuna (Canned) | Mostly Organic | Low to Moderate | A 'Best Choice' for low mercury. |
| Sardines | Mostly Organic (higher total) | Low (Inorganic), but can have higher total | Bones are edible and a good source of calcium. |
| Albacore Tuna | Organic/Some Inorganic | Higher than light tuna | A 'Good Choice,' but limit consumption. |
| Some Shellfish | Organic/Inorganic | Variable (can be higher inorganic depending on location) | Generally low in mercury, but vary sourcing. |
Freshwater vs. Marine Fish: A Clear Distinction
Scientific studies have confirmed a stark difference in arsenic levels between freshwater and marine aquatic life. One study found that saltwater fish contained total arsenic levels 6 to 311 times higher than freshwater fish collected in the same area. This is not a cause for alarm, but rather an affirmation that marine life naturally bioaccumulates more arsenic, predominantly the non-toxic organic kind. Therefore, if minimizing all forms of arsenic is a priority, freshwater fish are often the best route. For those who prefer saltwater options, focusing on smaller, lower-trophic-level species remains the best practice for a wider range of contaminants.
Bioaccumulation and Other Influencing Factors
The concentration of contaminants, including arsenic, in fish is influenced by a range of factors. These include the species' position in the food chain (biomagnification), their diet, and the water quality of their habitat. Bottom-dwelling species, or those that eat a diet of crustaceans and mollusks, may have higher uptake. While arsenic is part of the natural marine ecosystem, human industrial activity can also contribute, affecting local water quality. This reinforces the importance of choosing responsibly sourced seafood and varying consumption to minimize any potential exposure. Checking local advisories for fish caught in regional waters is also a recommended step.
How to Choose and Consume Fish Safely
Eating a variety of seafood, including low-mercury and low-arsenic options, is key to reaping the benefits of omega-3s and other nutrients while minimizing risk. The FDA and EPA provide comprehensive advice on which fish are considered 'Best Choices' for low contaminant levels. For those with higher sensitivity or specific health concerns, opting for freshwater fish and specific canned salmon varieties offers the greatest peace of mind. While cooking fish in excess water and discarding the broth can reduce some contaminants, this is not a practical solution for most fish preparation and has a minimal impact on the non-toxic arsenobetaine. Focus instead on responsible sourcing and varied intake.
Conclusion: Prioritize Speciation, Not Just Quantity
To determine which fish has the lowest arsenic content, it is crucial to look past the total arsenic number and understand that the organic form is harmless. Fish like sockeye and pink salmon, as well as freshwater options such as trout and tilapia, offer very low levels of total arsenic, and critically, very little of the toxic inorganic form. By prioritizing smaller fish lower on the food chain and diversifying your seafood consumption, you can enjoy the many nutritional benefits of fish while effectively managing potential exposure to heavy metals. Always rely on authoritative sources like the FDA for guidance and consider the source of your fish when making a choice.
For more information on fish consumption, refer to the FDA's advice about eating fish.
