Monitoring and Understanding Mercury Levels in Seafood

Seafood is an important part of a healthy diet, providing beneficial nutrients like protein, omega-3 fatty acids, vitamin B12, and more. However, seafood can also contain low levels of mercury, a heavy metal which can impact nervous system health when consumed in high amounts. To help consumers make informed choices, public health organizations monitor and report on mercury levels in different types of seafood.

How Mercury Gets into Fish and Shellfish

Mercury occurs naturally and enters water bodies through various pathways:

• Natural soil erosion and volcanic activity
• Burning of fossil fuels like coal
• Industrial processes and waste incineration
• Atmospheric deposition from mining operations

Once in water, mercury accumulates in sediment and gets converted by bacteria into methylmercury, its more toxic form. Methylmercury bioaccumulates and biomagnifies up the food chain, reaching highest levels in large, predatory fish and marine mammals. Shellfish can also accumulate mercury by filter-feeding from contaminated waters.

Seafoods with Highest Mercury Levels

Larger longer-living fish tend to contain more mercury since it accumulates over time. Seafoods with highest mercury concentrations include

• Shark
• Swordfish
• King mackerel
• Tilefish
• Bigeye and Ahi tuna

The FDA and EPA recommend women who are pregnant, may become pregnant, or nursing avoid these high-mercury fish. Children under 12 should also limit intake due to developing brains.

Seafoods with Lowest Mercury Levels

Seafoods lower on the food chain with shorter lifespans tend to be lower in mercury. The EPA lists these as best choices:

• Salmon
• Pollock
• Catfish
• Cod
• Shrimp
• Tilapia
• Clams
• Scallops
• Canned light tuna

A healthy diet can include 12 ounces per week of low-mercury seafood, especially fish high in omega-3s like salmon, anchovies, and sardines.

Monitoring Mercury in Seafood

Organizations like the FDA, EPA, and NOAA monitor mercury in commercial seafood through regular testing programs.

The FDA samples and analyzes mercury levels in popular seafood through their Total Diet Study.

NOAA conducts testing and research on mercury in seafood as part of their National Seafood Inspection Laboratory to protect health,

EPA assists in a range of mercury fish tissue monitoring programs to assess water quality and issue consumption advisories.

US Federal Guidance on Mercury in Seafood

Based on monitoring results, federal agencies provide guidance to balance the health benefits and potential risks of seafood.

FDA/EPA Advice

The FDA and EPA recommend:

• Eating 8 to 12 ounces of low-mercury fish per week
• Avoiding high-mercury fish during pregnancy/nursing
• Limiting albacore tuna to 6 ounces weekly when pregnant/nursing

FDA Monitoring Results

FDA mercury results from 1990-2012 show:

• Average mercury in commercial seafood is low overall
• Levels in canned tuna are declining
• Only a few samples exceeded the FDA mercury action level of 1 ppm

EPA Reference Doses

The EPA provides mercury reference doses:

• 0.1 μg/kg body weight per day for pregnant/nursing women
• 0.3 μg/kg body weight per day for children
• 0.7 μg/kg body weight per day for adults

These reflect maximum recommended exposures from all sources including seafood.

International Guidance and Results

Many countries monitor and regulate mercury in commercial seafood. Some findings:

• Canada tests mercury through the Canadian Food Inspection Agency. Average concentrations are below 0.5 ppm.

• In Europe, EFSA set a 1 ppm limit for most fish which 95% of samples met in recent testing.

• Australia/New Zealand limit mercury to 1 ppm and report low observed levels in seafood monitoring.

• Japan has a 0.4 ppm regulation and results show 98% of seafood tested below this level.

Acquired Research Data on Seafood Mercury Levels

To supplement federal monitoring programs, consumer and public health groups conduct their own product testing:

Consumer Reports Study

Consumer Reports analyzed mercury content in tuna samples from retailers in 2012. Findings included:

• 5 of 184 samples exceeded 1 ppm limit
• Albacore tuna averaged 0.45 ppm
• Light canned tuna averaged 0.128 ppm

Oceana Study

Oceana tested mercury in seafood from Atlantic coastal states in 2012 and found:

• Tilefish, swordfish, and king mackerel exceeded 1 ppm
• Bluefish averaged 0.41 ppm
• Halibut averaged 0.21 ppm
• Tuna averaged 0.19 ppm

IPCS Compiled Data

The WHO’s International Programme on Chemical Safety compiled data on mercury in fish showing wide ranges:

• Shark: 0.98-4.54 ppm
• Tuna: 0.17-3.73 ppm
• Cod: 0.005-0.073 ppm
• Salmon: 0.014-0.128 ppm

Level ranges demonstrate how mercury content can vary substantially by location and individual fish sizes.

Best Practices for Consumers

While mercury in seafood is generally low, consumers can take steps to minimize exposure:

• Choose low-mercury fish and limit albacore tuna to 6 ounces weekly when pregnant/nursing
• Check local advisories about contaminated fisheries
• Keep young children’s total mercury below EPA reference dose
• Request small fish like anchovies over king mackerel at restaurants
• Seek a variety of seafood rather than relying on one high-mercury type

Following federal and state guidelines helps ensure that the substantial nutritional benefits of eating seafood outweigh the potential mercury risks.

Responsible agencies continually monitor the marine food web for mercury content and provide consumption recommendations. While top predatory fish tend to accumulate higher mercury levels, federal data show concentrations in most commercial seafood remain low and within acceptable limits. Consumers can easily choose fish and shellfish options with more omega-3s and less mercury as part of a healthy diet.