Question

water - scarce regions increasingly turn to treated wastewater for irrigation, but concerns about heavy metal buildup complicate its use. in a four - year pot experiment in eastern türkiye, researchers irrigated soils with five ratios of treated wastewater to clean water and tracked metal levels using indices such as the contamination factor and pollution load index. soils receiving only wastewater showed the largest increases, with some metals nearing moderate contamination, whereas soils under 25 - 50% wastewater remained classed as unpolluted or low risk and stayed below regulatory thresholds. even in the mixed treatments, however, certain metals continued to accumulate, and the pot design did not capture field processes that could alter metal mobility and plant uptake. the authors therefore suggest that, rather than treating moderate wastewater blending as a permanent guarantee of safety, planners should view it as a provisional strategy that ______.
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which choice most logically completes the text?
(answer : b)
a merits continued evaluation through field studies, since the pot experiment demonstrated that even low wastewater concentrations exceeded contamination thresholds
b offers a practical near - term solution to water scarcity but requires ongoing monitoring and field - scale validation to ensure metal levels remain safe over time
c can reliably address water scarcity without continued surveillance, since controlled experiments have already confirmed that blended treatments keep metal accumulation within safe limits
d demands regular soil testing and adaptive management, given that metals accumulated consistently across all wastewater ratios tested in the study

Explanation:

To solve this, we analyze the context: The experiment shows treated wastewater for irrigation has metal accumulation risks, even in mixed treatments, and pot design doesn't capture field processes. We need a logical continuation for the provisional strategy.

• Option A: Talks about "merits continued evaluation" but the text's focus is on the strategy for planners, not just evaluation. Also, the pot experiment's low concentrations exceeding thresholds is not the main takeaway for the strategy's continuation. Eliminate A.
• Option B: The text says wastewater irrigation (even mixed) has metal accumulation over time and pot design lacks field processes. So a provisional strategy would need monitoring (to check metal levels) and field - scale validation (to account for field processes) to be safe. This fits.
• Option C: The text shows metal accumulation even in mixed treatments and pot design issues, so "without continued surveillance" is wrong. Eliminate C.
• Option D: The text says soils with 25 - 50% wastewater were unpolluted/low risk, so "consistently across all ratios" is false. Eliminate D.

Answer:

B. offers a practical near - term solution to water scarcity but requires ongoing monitoring and field - scale validation to ensure metal levels remain safe over time