Question 5.33

3. Eating fish contaminated with mercury can cause serious health problems. Mercury contamination from historic gold mining operations is fairly common in sediments of rivers, lakes, and reservoirs today. A study was conducted on Lake Natoma in California to determine whether the mercury concentration in fish in the lake exceeded guidelines for safe human consumption. A sample of 83 largemouth bass was collected, and the concentration of mercury from sample tissue was measured. Mercury concentration is measured in micrograms of mercury per gram or . Figure 5.28 presents a histogram of the results of the study.

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Figure 5.30: Figure 5.28 Mercury concentration in fish tissue.
  1. Which class interval contains the highest number of data values? Approximately what percentage of the fish in the sample had mercury concentrations that fell within this class interval?
  2. The primary objective of the study was to determine whether mercury concentrations in fish tissue exceeded safety guidelines for human consumption. The U.S. Environmental Protection Agency (USEPA) human-health criterion for methylmercury in fish is . Approximately how many of the fish in the sample had mercury concentrations below the level set by the USEPA (and hence were considered safe for human consumption)?
  3. Approximately what percentage of the sample had mercury concentrations higher than the level set by the USEPA? Show how you arrived at your answer.

3.

(a) The interval between and ; around 28 data values fell within this interval, which means that or approximately 33.7% of the fish had mercury concentrations that fell in this class interval.

(b) Approximatly 56 of the fish had mercury levels below .

(c) Approximately 27 of the fish from the sample had mercury levels at or above . Hence, around 32.5% of the fish in the sample had levels of mercury concentration above the USEPA guidelines.