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).

28. As shown in Figure 2, every time the alachlor concentrations in the water in O2, S2, and E2 were measured during the study, the concentrations in S2 and E2 were found to be very similar to the concentration in O2. The most likely explanation for this result is that in S2 and E2:

Answer and Explanation

Your Answer is

Correct Answer is G

Explanation

If the alachlor concentration of the two wetlands S2 and E2 is always close to that of O2, it means that the growth of plants in the three wetlands cannot explain the gradual decrease of alachlor, and other reasons should play a leading role