In Denver, Colorado, environmentalists have discovered a link between high arsenic levels in soil and a crabgrass killer used in the 1950s and 1960s (Environmental Science & Technology, Sept. 1, 2000). The discovery was based, in part, on the accompanying scatterplots. The graphs plot the level of the metals cadmium and arsenic, respectively, against the distance from a former smelter plant for samples of soil taken from Denver residential properties.
a. Normally, the metal level in soil decreases as distance from the source (e.g., a smelter plant) increases. Propose a straight-line model relating metal level y to distance x from the plant. On the basis of the theory, would you expect the slope of the line to be positive or negative?
b. Examine the scatterplot for cadmium. Does the plot support the theory you set forth in part a?
c. Examine the scatterplot for arsenic. Does the plot support the theory of part a? (Note: This finding led investigators to discover the link between high arsenic levels and the use of the crabgrass killer.)

Transcribed Image Text:

140 Cadmium 120 100 80 60 20 200 400 G00 800 1000 1200 1400 Loadenel o (8ylu) uoIRIouoa unjup) Distance south of Globe Plant (m) 250 Arsenic 200 150 100 50 200 400 G00 800 1000 1200 1400 Distance south of Globe Plant (m) (8ylu) uounuouoa ajuasy