Passage V
In wetlands, the herbicides atrazine and alachlor are removed from the water by plant uptake or by adsorption onto soil particles and subsequent bacterial decomposition. Atrazine can also spontaneously break down to form deethylatrazine (DEA).
Three pairs of herbicide-free wetlands were established for a study: open water (O1, O2), submergent (S1, S2), and emergent (E1, E2), as described in Table 1. On 1 day, atrazine was added to O1, S1, and E1 and alachlor was added to O2, S2, and E2 to produce an initial herbicide concentration of 25 g/L in the water in each wetland. Atrazine, alachlor, and DEA concentrations in the water were measured at intervals over the next 120 days (see Figures 1-3).
24. Assume that the volume of water in each wetland remained constant over the 120 days of the study. According to Figure 2, 120 days after alachlor was added, what percent of the original alachlor concentration remained in the water in E2 ?
Your Answer is
Correct Answer is F
Explanation
Look at figure 2, when the abscissa is 120 days, the ordinate alachlor concentration is about 2. The initial alachlor concentration is 25, so 2/25=8%, less than 20% meet