Has all fish got mercury in them?

Nearly all fish and shellfish contain trace amounts of methylmercury, a naturally occurring compound. The question, "Has all fish got mercury in them?", often leads to consumer confusion, but levels vary dramatically across species, depending on diet and lifespan.

Quick Summary

This article explores how mercury enters the aquatic food chain, the process of bioaccumulation, and the different mercury levels found across various fish types. It provides guidance on safe consumption.

Key Points

• Bioaccumulation: Mercury concentrations increase as it moves up the food chain, meaning larger predators like shark and swordfish have the highest levels.

• Not All Fish are Equal: While traces exist in nearly all fish, mercury levels differ significantly by species, age, and diet.

• Vulnerable Groups: Pregnant women, breastfeeding mothers, and young children are most at risk from mercury exposure and should strictly follow consumption guidelines.

• Safe Consumption: Focusing on low-mercury fish like salmon, sardines, and canned light tuna allows for regular, safe enjoyment of seafood.

• Cooking is Ineffective: Common cooking methods like frying or grilling do not reduce or remove mercury content from fish tissue.

• Informed Choices: Making deliberate seafood choices based on mercury levels is key to balancing the nutritional benefits of fish with potential health risks.

How Mercury Enters the Aquatic Environment

Mercury is a naturally occurring element, but human activities significantly increase its presence in the atmosphere. It settles into water, where microorganisms convert it into toxic methylmercury. Fish and shellfish absorb this methylmercury.

The Process of Bioaccumulation and Biomagnification

Methylmercury binds to fish muscle and isn't easily removed. Bioaccumulation increases up the food chain; large predators like sharks accumulate high levels from eating smaller fish.

High vs. Low Mercury Fish

Mercury levels vary greatly among fish species. The FDA and EPA provide guidance on safer seafood choices.

Comparison of Mercury Levels in Common Seafood (Based on FDA data)

Seafood Type	Average Mercury Concentration (ppm)	Mercury Level	Example Species
Shrimp	0.009	Very Low	All types of shrimp
Salmon (Canned)	0.014	Very Low	Pink, Sockeye
Catfish	0.024	Very Low	Farm-raised
Canned Light Tuna	0.126	Moderate	Skipjack
Canned Albacore Tuna	0.350	High	"White" Tuna
Swordfish	0.995	Very High	-
Shark	0.979	Very High	-
King Mackerel	0.730	Very High	-

List of Seafood by Mercury Content

Very Low Mercury (Eat More Often)

• Shrimp
• Scallops
• Canned Light Tuna (Skipjack)
• Salmon (Canned and Fresh/Frozen)
• Anchovies
• Sardines
• Catfish
• Tilapia

Moderate Mercury (Eat Less Often)

• Canned Albacore Tuna
• Halibut
• Mahi Mahi
• Tuna Steaks (Fresh/Frozen)

High Mercury (Avoid or Limit Significantly)

• Shark
• Swordfish
• King Mackerel
• Marlin
• Bigeye Tuna
• Tilefish (from the Gulf of Mexico)

Making Safe Seafood Choices

The health benefits of fish generally outweigh the risks of mercury for the general population if guidelines are followed. However, pregnant/breastfeeding women and young children are more sensitive to mercury.

Guidelines for Safe Consumption

The FDA and EPA offer specific advice:

• Vulnerable groups should eat 2-3 weekly servings of low-mercury fish and limit albacore tuna.
• The general population should also aim for 2-3 weekly servings of low-mercury options, limiting high-mercury species.
• Eating a variety of fish minimizes exposure from one source.
• Check local advisories for recreationally caught fish.
• Cooking does not reduce mercury in fish.

Consult the FDA's Advice about Eating Fish for detailed information.

Conclusion

While most fish contain trace mercury, levels vary significantly. By choosing lower-mercury species and following health guidelines, consumers can enjoy the nutritional benefits of seafood safely. Prioritizing smaller, non-predatory fish is a key strategy.

Frequently Asked Questions

Is it safe to eat fish that contains mercury?

Yes, it is safe to eat fish that contains mercury, as long as you make informed choices. The key is to consume a variety of fish, focusing on low-mercury species, and to follow recommended portion guidelines, especially if you are pregnant, nursing, or feeding young children.

Which fish have the lowest mercury levels?

Fish with the lowest mercury levels are typically smaller, shorter-lived species that are lower on the food chain. Good examples include salmon, shrimp, sardines, anchovies, pollock, and tilapia.

Does cooking or preparing fish in a specific way reduce its mercury content?

No, cooking does not reduce the mercury content in fish. The methylmercury is tightly bound to the protein in the fish's muscle tissue and cannot be removed by methods like frying, grilling, or boiling.

How do canned light tuna and albacore tuna differ in mercury levels?

Canned light tuna, which is usually made from smaller skipjack tuna, has significantly lower mercury levels than canned albacore (white) tuna. For this reason, consumption of albacore tuna is more restricted, especially for vulnerable populations.

Why do some fish have more mercury than others?

Mercury levels vary based on the fish's diet, lifespan, and position in the food chain. Larger, older, and predatory fish tend to accumulate higher concentrations of mercury through a process called biomagnification.

Are fish oil supplements a source of mercury?

Fish oil supplements are generally not a significant source of dietary mercury. Reputable manufacturers purify the oil to remove contaminants. Authorities like the NSW Food Authority do not advise restricting them for mercury concerns.

What are the health effects of too much mercury from fish?

High levels of mercury exposure are most concerning for developing fetuses and young children, potentially harming their nervous systems. In adults, high exposure can lead to neurological issues like memory problems, tremors, and numbness, though average consumption rarely poses a risk to most adults.