The Source of Mercury in Fish
Mercury is a naturally occurring element, but human activities, primarily the burning of fossil fuels and certain industrial processes, release it into the atmosphere. It settles into oceans, rivers, and lakes, where bacteria convert it into methylmercury, the organic and most toxic form.
Fish absorb methylmercury from the water they live in and the organisms they eat. The concentration of mercury in a fish's tissue increases as it moves up the food chain, a process known as biomagnification. This means larger, longer-lived predatory fish tend to have the highest mercury levels, while smaller fish and shellfish have the lowest.
Can Cooking Remove Mercury from Fish Soup?
Unfortunately, no. The methylmercury in fish is tightly bound to the muscle tissue (the meat). Cooking methods such as boiling, frying, or baking do not significantly reduce the mercury content. Some studies have shown a decrease in mercury bioaccessibility (how much the body absorbs) after cooking, but the total amount of mercury in the fish remains largely the same. Therefore, selecting the right fish from the start is the most critical step for ensuring a low-mercury soup.
High vs. Low Mercury Fish for Your Soup
Choosing the right species is the most effective way to control the mercury content of your fish soup. The U.S. Environmental Protection Agency (EPA) and Food and Drug Administration (FDA) provide comprehensive guidelines for making smart seafood choices.
Low-Mercury Fish
For soup, prioritize these fish to minimize mercury exposure while gaining nutritional benefits:
- Salmon (canned or fresh/frozen)
- Sardines
- Shrimp
- Catfish
- Cod
- Tilapia
- Haddock
- Pollock
High-Mercury Fish
It is best to avoid using these species in soup, especially for vulnerable groups like pregnant women and young children.
- King Mackerel
- Shark
- Swordfish
- Bigeye Tuna
- Orange Roughy
- Tilefish (especially from the Gulf of Mexico)
Comparison of Mercury Levels in Common Fish
Here is a comparison of average mercury levels in parts per million (ppm) to help guide your choices:
| Fish Species | Average Mercury (ppm) | Recommended Use in Soup |
|---|---|---|
| Swordfish | 0.995 | Avoid |
| Shark | 0.979 | Avoid |
| Bigeye Tuna | 0.689 | Avoid |
| Canned Albacore Tuna | 0.350 | Limit to once a week |
| Cod | 0.111 | Recommended |
| Canned Light Tuna | 0.126 | Recommended (limit total intake) |
| Salmon (Fresh/Frozen) | 0.022 | Recommended |
| Shrimp | 0.009 | Recommended |
| Scallops | 0.003 | Recommended |
Important Considerations for Vulnerable Groups
Pregnant women, breastfeeding mothers, and young children are most susceptible to the neurotoxic effects of mercury. For these groups, it is especially important to follow low-mercury guidelines. For example, the FDA recommends that pregnant or breastfeeding women eat 8-12 ounces per week of a variety of low-mercury seafood. The good news is that for most people, the nutritional benefits of moderate fish consumption, including essential omega-3 fatty acids, outweigh the risk from mercury when low-mercury options are selected. Studies have even shown benefits from consuming certain types of fish soup for prenatal development, reinforcing the need for species awareness.
Sourcing Your Fish Safely
For store-bought fish, choosing species known to have low mercury levels is straightforward. For sport-caught fish, however, it is essential to check local advisories. Mercury levels can vary significantly depending on the body of water the fish is caught in. Local health departments or environmental agencies often publish specific guidance for recreationally caught fish in your area. If no advisory is available, limit consumption from local waters to a single meal per week.
Conclusion
Yes, fish soup can contain mercury, but the amount depends entirely on the type of fish used. Cooking the fish does not reduce the mercury content, as it is bound to the muscle tissue. The key to enjoying nutritious and safe fish soup is to be a mindful consumer, choosing low-mercury species like salmon, cod, and shrimp while avoiding high-mercury predatory fish. By adhering to official guidelines, such as those from the FDA and EPA, and checking local advisories for sport-caught fish, you can confidently include fish soup in a healthy, balanced diet. The rich omega-3 fatty acids and other nutrients provided by fish offer significant health benefits, especially when the risks of mercury exposure are managed with smart choices. For further guidance on mercury in food, the U.S. Food and Drug Administration provides helpful resources on their website: Mercury in Food.
