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Mercury in Fish Passage
Mercury is an unusual element; it is a metal butis liquid at room temperature. It is also a neurotoxinand a teratogen, as it causes nerve damage and birthdefects. Mercury can be found just about every-05where; it is in soil, in air, in household items, andeven in our food. Everyday objects, such as thermometers,light switches, and fluorescent lightbulbs,contain mercury in its elemental form. Batteriescan also contain mercury, but they contain it in the10form of the inorganic compound mercury chloride.Mercury can also exist as an organic compound,the most common of which is methylmercury.While we can take steps to avoid both elementaland inorganic mercury, it is much harder to avoid15methylmercury.Most of the mercury in the environmentcomes from the emissions of coal-burning powerplants; coal contains small amounts of mercury,which are released into the air when coal burns.20The concentration of mercury in the air frompower plants is very low, so it is not immediatelydangerous. However, the mercury is then washedout of the air by rainstorms and eventually ends upin lakes and oceans.25The mercury deposited in the water does notinstantaneously get absorbed by fish, as elementalmercury does not easily diffuse through cellmembranes. However, methylmercury diffusesinto cells easily, and certain anaerobic bacteria30in the water convert the elemental mercury tomethylmercury as a by-product of their metabolicprocesses. Methylmercury released into the waterby the bacteria diffuses into small single-celledorganisms called plankton. Small shrimp and other35small animals eat the plankton and absorb themethylmercury in the plankton during digestion.Small fish eat the shrimp and then larger fish eat thesmaller fish; each time an animal preys on anotheranimal, the predator absorbs the methylmercury.40Because each animal excretes the methylmercurymuch more slowly than it absorbs it, methylmercurybuilds up in the animal over time and is passed onto whatever animal eats it, resulting in a processcalled bioaccumulation.45As people became aware of the bioaccumulationof mercury in fish, many reacted by eliminatingseafood from their diet. However, seafood containscertain omega-3 fatty acids that are importantfor good health. People who do not eat enough50of these fatty acids, especially eicosapentaenoicacid (EPA) and docosahexaenoic acid (DHA), aremore likely to have heart attacks than people whohave enough EPA and DHA in their diet. Becausefish and shellfish, along with some algae, are the55only sources of these fatty acids, eliminating themfrom our diet might have worse health effects thanconsuming small amounts of mercury.Scientists have studied the effects of mercury byconducting tests on animals and by studying various60human populations and recording the amount ofmercury in their blood. By determining the levels ofmercury consumption that cause any of the knownsymptoms of mercury poisoning, they were ableto identify a safe level of mercury consumption.65The current recommendation is for humans totake in less than 0.1 microgram of mercury forevery kilogram of weight per day. This means thata 70-kilogram person (about 155 pounds) couldsafely consume 7 micrograms of mercury per day.70Since haddock averages about 0.055 microgramsof mercury per gram, that person could safely eat127 grams (about 4.5 ounces) of haddock per day.On the other hand, swordfish averages about 0.995micrograms of mercury per gram of fish, so the7570-kilogram person could safely eat only about 7grams (about one-quarter of an ounce) of swordfishper day.Nutritionists recommend that, rather than elimi-nate fish from our diet, we try to eat more of the80low-mercury fish and less of the high-mercury fish.Low-mercury species tend to be smaller omnivo-rous fish while high-mercury species tend to be thelargest carnivorous fish. Awareness of the par-ticulars of this problem, accompanied by mindful85eating habits, will keep us on the best course forhealthy eating.
1. The author of the passage would most likely agree with which of the following statements?
2. Which choice provides the best evidence for the answer to the previous question?
3. In addition to the levels of mercury in a specific species of fish, people should also consider which of the following when determining a safe level of consumption?
4. As used in line 20, "concentration" most nearly means
5. The passage most strongly suggests which of the following statements is accurate?
6. Which choice provides the best evidence for the answer to the previous question?
7. The main purpose of paragraph 3 is to explain
8. Which of the following pieces of evidence would most strengthen the author's line of reasoning?
9. As used in lines 83-84, "particulars" most nearly means
10. Based on the information in the passage and the graphic, which of the following statements is true?
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