The vulnerability of inshore environments to contamination due to urban and industrial expansion in Mombasa is discussed in the paper “Metals, Petroleum Hydrocarbons and Organo-chlorines in Inshore Sediments and Waters on Mombasa, Kenya” [Marine Pollution Bulletin (1997) 34: 570– 577]. A geochemical and oceanographic survey of the inshore waters of Mombasa, Kenya, was undertaken during the period from September 1995 to January 1996. In the survey, suspended particulate matter and sediment were collected from 48 stations within Mombasa’s ­estuarine creeks. The concentrations of major oxides and 13 trace elements were determined for a varying number of cores at each of the stations. In particular, the lead concentrations in suspended particulate matter (mg kg-1 dry weight) were determined at 37 stations. The researchers were ­interested in determining whether the average lead concentration was greater than 30 mg kg-1 dry weight. The data are given in the following table along with summary statistics and a normal probability plot.
Lead concentrations (mg kg-1 dry weight) from 37 stations in Kenya
a. Is there sufficient evidence (a = .05) in the data that the mean lead concentration exceeds 30 mg kg-1 dry weight?
b. What is the probability of a Type II error if the actual mean concentration is 50?
c. Do the data appear to have a normal distribution?
d. Based on your answer in (c), is the sample size large enough for the test procedures to be valid? Explain.

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