Both Hayes (Hayes, 2003) and a Syngenta supported group (Hecker, 2003) conducted laboratory studies to determine whether the testosterone level in the blood of male frogs was altered by the presence of atrazine in the water in which they grew. In these studies, larvae were grown until they reached sexual maturity in water containing an atrazine concentration of 25 g/L. For control purposes, both of these studies grew larvae in water containing a nominal (supposed) atrazine concentration of zero ppb. The graph shown below. indicates the results obtained in the two studies. In its evaluation of the data reported in the MSU (Hecker) study, the EPA noted that the controls used in this study were not free of atrazine but were in fact found to contain "atrazine at levels comparable to those in the 0.1 ppb treatment level" (Steeger, 2003). No atrazine was found in the controls used in the Hayes study (Hayes, 2004). rams/ml) testosterone concentration (nanogra: Blood plasma 10 4 N W - o 00 Hayes Data Hecker Data Control Males Atrazine (25ppb) Control Females Control Males Atrazine (25ppb) Questions 6. What do the Hayes results indicate about the effect of atrazine on the testosterone concentration in the blood of exposed male frogs? 7. What do the MSU (Hecker) results indicate about the effect of atrazine on the testosterone concentration in the blood of exposed male frogs? 8. Consider the EPA's observation about the presence of atrazine in the controls used in the MSU study. Could this observation explain how Hayes and Hecker could both have accurately reported their experimental observations?