Introduction:
Mercury is a heavy metal that is toxic to humans at low concentrations. Although very small amounts are naturally present in the environment, human activities such as coal combustion and industrial processes have increased its concentration dramatically. Once in an ecosystem, mercury bioaccumulates in organisms such as fish, and its concentration can be biomagnified up the food chain. It is a neurotoxin with a host of negative effects on the brain and nervous system in humans. Therefore, consumption of fish high in mercury is discouraged. In this exercise, we will examine data on mercury content from a variety of common fish and seafood species.
DATA SETS:
Data for Mercury_Fish: FDA 1990-2010, available at http://www.fda.gov/food/foodborneillnesscontaminants/metals/ucm115644.htm
Data for California_Lakes: Davis, J.A., A.R. Melwani, S.N. Bezalel, J.A. Hunt, G. Ichikawa, A. Bonnema, W.A. Heim, D. Crane, S. Swenson, C. Lamerdin, and M. Stephenson. 2010. Contaminants in Fish from California Lakes and Reservoirs, 2007-2008: Summary Report on a Two-Year Screening Survey. A Report of the Surface Water Ambient Monitoring Program (SWAMP). California State Water Resources Control Board, Sacramento, CA. Available at http://www.waterboards.ca.gov/water_issues/programs/swamp/docs/lakes_study/lake_survey_yr2_full_rpt.pdf
We will begin by looking at the average mercury content in a variety of fish species. These data are based on measurements taken during the period from 1990 to 2010. To display the data on the graph select “Mercury Content in Fish” from the drop-down menu. The values displayed on the graph are in ppm, or parts per million. If these values seem small or negligible, recall that mercury is toxic even at very low concentrations.
1. Which species on the graph has the highest average mercury content?
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2. In which species was the highest maximum value recorded over the study period?
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3. All of the species displayed on the y-axis have detectible mercury concentrations. Even though some are so low that they do not register on the graph, they are presented in order of increasing average mercury concentration. Which of the following species had the lowest average value?
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4. The Environmental Protection Agency (EPA) has set a threshold of 0.3 ppm of mercury beyond which fish should not be consumed. On average, does albacore tuna (often sold as canned tuna) surpass this threshold?
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5. In addition to the EPA, other agencies make recommendations regarding mercury intake. For example, the California Office of Environmental Health Hazard Assessment (OEHHA) uses 0.07 ppm as its guideline for the threshold beyond which fish should be consumed less than three times per week. How many species from this list surpass this value (based on average concentration)?
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6. The OEHHA has a less stringent guideline for the threshold beyond which fish should not be consumed than the EPA does. This value is .44 ppm. Which of the following fish should not be consumed based on this recommendation? (Use the average value for comparison.)
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7. Now we will look at freshwater fish sampled from lakes across the State of California. To do so, select “Mercury Content in Lakes.” The data in this graph are based on the average concentration of mercury in fish sampled from individual lakes. Using the same EPA threshold of 0.3 ppm as the threshold for safe consumption, what percent of CA lakes surpass this amount and thus contain fish that would be inadvisable to consume?
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8. There is a recommendation that consumption of fish with a concentration of over 0.07 be limited to no more than three servings per week. What percent of California lakes contain fish that have an average mercury concentration less than this?
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9. Mercury bioaccumulates in fish, meaning that concentration is gradually built up over time with exposure. Additionally, mercury concentrations biomagnify or increase in concentration as you move up the food chain. Which of the following descriptions of hypothetical fish would you expect to have the greatest concentration of mercury?
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10. As a consumer, if you wanted to limit your exposure to mercury, which of the following strategies would be more effective?
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