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The catch is, should you eat it?
Robert H. Boyle
July 12, 1971
A scientist checks mercury levels at a tournament and ends up giving anglers some food for thought
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July 12, 1971

The Catch Is, Should You Eat It?

A scientist checks mercury levels at a tournament and ends up giving anglers some food for thought

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Maximum Suggested Amount of Fish Per Day or Week for a 150-pound Man*

PPM of mercury
in fish

Per
Day

Per
Week

0.05

21 oz.

9 lbs.

0.10

10� oz.

4� lbs.

0.20

5� oz.

2� lbs.

0.30

3� oz.

1� lbs.

0.40

2� oz.

1 1/6 lbs.

0.50 ( FDA limit)

2 oz.

15 oz.

0.75

1? oz.

10 oz.

1.00

1 oz.

7� oz.

1.25

0.85 oz.

6 oz.

1.50

0.7 oz.

5 oz.

*Figures compiled by Dr. Bruce McDuffie, based on the findings of the Swedish Commission for Evaluating the Toxicity of Mercury in Fish.

A man who knows all about mercury inspected fish at first hand on Long Island last month, and what he found was scarcely reassuring to saltwater anglers—at least to those who eat their catch. Dr. Bruce McDuffie, professor of chemistry at the State University of New York at Binghamton and the scientist who originally discovered more than permissible amounts of mercury in swordfish steaks and canned tuna, was on hand for the Shinnecock Swordfish Tournament at Hampton Bays. Unlike the 100 contestants who went out to sea, Dr. McDuffie and three assistants stayed at dockside at Nick's Marina with an array of equipment including a Coleman Mercury Analyzer System. The testing revealed the total amount of mercury in each sample and, based on Government findings for tuna and swordfish, McDuffie felt one might assume that the mercury was methyl mercury, the kind that can be toxic to humans.

McDuffie was there at the express invitation of Walter Margulies, an industrial designer, owner of the marina and a well-known swordfisherman. "We want to find out about the mercury contents in our game fish," Margulies said. "At first I couldn't believe the news about mercury in swordfish. Now I would be very cautious." Actually, Margulies is "not at all displeased from a selfish point of view to see swordfish off the market." Commercial long-lining, which threatened the existence of the species, has stopped, and Margulies hopes that swordfish will come back in sufficient numbers to support a sport fishery.

A number of swords were sighted during the three-day tournament; six fish were hooked (including a 500-pounder) but only one was landed. This fish, a small one caught the first day by Mike Berman aboard the Prowler, weighed 150 pounds, and, inasmuch as it is a general rule that the bigger the fish the more the mercury, McDuffie's analysis of this relative midget was unsettling to anyone thinking of devouring a thick swordfish steak. The fish contained 0.89 parts per million of mercury, almost twice the Food and Drug Administration limit of 0.50 ppm. If a person were really starving for swordfish, he could eat some of this fish, but one bite would be about enough.

According to McDuffie, Swedish scientists have concluded that a 150-pound man could consume 30 micrograms per day of mercury without endangering himself. Similarly, a 100-pound man could ingest 20 micrograms per day and a 200-pound man 40 micrograms. (Some health authorities have warned pregnant women to abstain from fish.) Using the Swedish standard this meant, McDuffie said, that a 150-pound man could eat about an ounce per day of Herman's swordfish without harm (an average serving of fish is seven ounces). "This is assuming, of course, that you are not getting methyl mercury from another source," said McDuffie, "which is not quite the case." For the benefit of fish eaters who wish to restrict their mercury intake to no more than the Swedish standard of 30 micrograms per day, McDuffie produced the consumption chart shown at right.

McDuffie was at Nick's Marina to analyze not only swordfish but any kind of fish or shellfish, and one angler took advantage of the occasion to bring some freshwater species for testing. Two largemouth bass, weighing a pound-and-a-half and a pound, respectively, had come from a five-acre pond in a wildlife sanctuary in Westchester County, N.Y. Surrounded by dense woods, the pond receives no human or agricultural drainage, and thus any mercury in the fish presumably would come from natural erosion of rocks within the sanctuary and/or from atmospheric fallout. (An estimated 1,800 tons of mercury are released in the atmosphere by the burning of coal in the U.S. each year.) The larger bass had 0.30 ppm of mercury, the smaller 0.21 ppm, both near the figure of 0.20 ppm, which some scientists now believe is the natural background level in freshwater fish. McDuffie said that in recent months he has been testing fish in central New York, and he had found high mercury residues in a number of bass, pike and yellow perch.

Three six-inch white perch taken from the Croton Reservoir, part of the New York City water supply system, averaged 0.43 ppm of mercury. This is getting close to the FDA limit, and McDuffie did not think it wise to eat more than a pound of these perch a week, and that to the exclusion of all other fish.

There was some good news for clam eaters. A cherrystone tested less than 0.01 ppm, a soft-shell clam 0.02 ppm. A squid was 0.04 ppm. The tail meat of a 1�-pound lobster was 0.17 ppm, and the meat from the claw of a 10-pound lobster was only 0.07, something of a surprise since it was thought that a big lobster probably would contain more mercury than a small one. "Maybe there's a difference between the claw and tail meats," McDuffie said. With that he analyzed a 7-pound lobster. The claw meat was a safe 0.11 ppm, but the tail meat well exceeded the FDA limit with 0.95 ppm. Just for the sake of science, McDuffie analyzed a small starfish. It had 0.09 ppm of mercury, so it is safe to eat even if uneatable.

The mercury content of two flounders and a fluke was low. Flounders are fairly low in the food chain, at least for a fish, since they feed mainly on clams and other invertebrates. One flounder, caught right at Nick's Marina by McDuffie, an ardent angler himself, had only 0.04 ppm of mercury, while another flounder had 0.09. A fluke weighing 1� pounds had 0.12 ppm. A pesky bait-stealing fish known as a bergall had 0.28 ppm, but a second bergall was 0.53. Small and bony, bergalls are rarely used as food. A 1�-pound black sea bass was 0.26, and a 2�-pound porgy was 0.28.

With game fish, many of them esteemed for the table, the mercury levels began to rise. A small yellowfin tuna weighing only six pounds had 0.29 ppm, well within the FDA limit but, as McDuffie said questioningly, "If a six-pound tuna is 0.29, and the FDA says the average canned tuna tested was little more than 0.30, well...." He then tested a 15-pound yellowfin tuna. It was 0.57 ppm, and a 60-pounder was 0.65 ppm.

A three-pound striped bass was 0.42 ppm, a high level for such a small fish. A 12�-pound striper surpassed the FDA limit with 0.63 ppm of mercury, and a 32-pound striper had about 1.2 ppm, the highest mercury level McDuffie found in any of the fish.

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