Mercury Contamination of Commercial Fish

Abstract: Mercury in its methylated form is teratogenic and neurotoxic and is of particular concern to pregnant women, women of child-bearing age, and young children due to the damage a developing child could suffer. The primary source of methylmercury for humans is fish consumption. Although many people consume fish for its health benefits, there is limited information on mercury levels in local commercial fish. I collected 3-5 samples of 34 different types of fish, shellfish, and shrimp from a local Fort Worth market spanning a period of two months. I examined the total mercury in each fish using a DMA mercury analyzer. Swordfish had the highest mercury content (1827.9 mean ppb) and catfish had the lowest mercury content (8.1 mean ppb). In many of the species, there was either an absence of data or deviations from published FDA information on mercury contamination, confirming the need for local monitoring of commercial fish to provide more accurate information to the public concerning mercury contamination in fish.

Micaela Mercer and Dr. Ray Drenner, Biology Department, Texas Christian University,

Ft. Worth, TX 76129

Introduction:

Fish is an excellent source of low fat protein and omega 3-fatty acids in the diet, but many fish also contain high and unhealthy levels of methylmercury.

Mercury contamination primarily affects the central nervous system but is also capable of affecting the kidneys and the gastrointestinal tract as well as causing muscle weakness, skin rashes, and hair loss1.

The developing fetus is especially susceptible to mercury, which can damage the central nervous system, lower IQ, delay the onset of fine motor skills, and lead to poor verbal memory2.

Many states have consumption advisories available for self-caught fish, but few state agencies have examined the concentration of mercury in commercial fish3.

Methods:

Over a period of two months, 34 different species of fresh fish, shellfish, and shrimp were purchased from a local market. Three to five samples of each species were collected.

Each specimen was placed in a freezer bag, labeled, and frozen immediately. A 0.1-0.4g (wet weight) sample was taken from the muscle of each frozen specimen (Fig. 1).

Total mercury was measured in parts per billion by the DMA mercury analyzer (Fig.2). Following EPA protocol, I used Mess-2 and PACS as references, multiple blanks, and two duplicates.

Fig. 1

Fig. 2

Results: The mean concentrations of total mercury in each species tested are shown in Fig. 3. Swordfish had the highest mean concentration of mercury, and catfish had the lowest mean concentration. The maximum concentration for swordfish was above the U.S. FDA action level (1000 ppb w/w). The maximum concentrations of orange roughy and mahi mahi were above the Texas

Department of State Health Services’ action level (700 ppb w/w). The maximum concentrations of yellowfin tuna, chilean sea bass, sable, grouper, and albacore tuna were above the U.S. Environmental Protection Agency’s action level (300 ppb w/w).

Acknowledgements: Special thanks to Jaron Hill of TCU and SRS, specifically SRS Chair Art Busbey.

References: 1 Lipske, M. Which fish are safest to eat? National Wildlife. 2006: 14-5.

2 Schweiger, L. Keeping tabs on mercury. The Scientist. 2005: 9-10.

3 Burger, J, Gochfeld M. 2006. Mercury in fish available in supermarkets in Illinois: Are there regional differences. Science of the Total Environment 367: 1010-1016.

4 Food and Drug Administration (U.S. FDA). 2006. Mercury levels in commercial fish and shellfish. Available: http://www.cfsan.fda.gov/~frf/sea-mehg.html (accessed 5 April 2006).

Fig. 3

Table 1

Discussion: The range of mercury concentrations (ppb) detected between different species of fish is likely due to differences in trophic level, age, and size of fish. Predatory fish at the top of the food chain, as well as older and larger fish, bioaccumulate a greater amount of mercury. I compared values from fish collected in Ft. Worth with values reported by the U.S. FDA (Table 1). Many discrepancies were found between the two data sets, with several species having higher mercury content than the reported FDA values. In twenty of the species analyzed, there was no FDA data available. The lack of reported data for certain species coupled with variations between the two data sets confirms the need to monitor fish from local markets3 as well as the need to make the information available to the public.

Ft. Worth, TX

FDA Data

Mean (ppb) Mean (ppb)

Swordfish 1828 976

Catfish 8 49

Haddock 118 31

Oyster 11 13

Striped bass 49 219

Chilean sea bass

508 386

Bluefish (mahi mahi)

726 337

Monkfish 119 180

Orange roughy

875 554

Sablefish 471 220

Albacore tuna

313 357

Yellowfin tuna

653 325

Scallop 12 50

Halibut 179 252