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In many dry areas, farmers must rely on treated wastewater to water their crops because fresh water supplies are limited. While this is a smart way to save water, scientists are concerned about what else might be in that water. Small amounts of medicines — such as those used to treat mental health conditions — often remain in treated wastewater.

A new study from Johns Hopkins University brings good news for people who enjoy eating tomatoes and carrots. The research indicates that these plants store most of these chemicals in their leaves, rather than in the parts we usually eat.

The scientists grew tomatoes, carrots, and lettuce in a lab. They added four common medicines — used to treat conditions like depression — to the water. After 45 days, they examined different parts of the plants to determine where the chemicals accumulated.

The findings were consistent: the leaves contained much higher levels of the medicines than the fruits or roots. To illustrate, tomato leaves had more than 200 times the amount of drugs found in the red tomato fruit. In carrots, the leaves held about seven times as much as the orange root we eat.

Why do plants store drugs in leaves? The answer lies in the movement of water through a plant. Plants draw water up from the roots to the leaves. When water reaches the leaves, it evaporates(蒸发) into the air through tiny holes. Nevertheless, the chemicals from the medicine do not escape; they are trapped and remain in the leaf tissue.

Carsten Prasse, one of the researchers, explained that plants struggle to remove these waste products. “They can’t just get rid of them the way humans do,” he said. Consequently, the chemicals build up over time.

The researchers emphasize that this study is not intended to cause alarm. The amounts found in the edible parts of tomatoes and carrots are extremely low. Nevertheless, understanding where these chemicals go helps authorities establish better guidelines for safely using recycled water in farming.

1.1. Why do farmers in dry areas use treated wastewater?

A To lower farming costs.

B To clean the medicine.

C To grow special plants.

D To handle water shortage.

解析：选D。D细节理解题。根据文章第一段第一句：“because fresh water supplies are limited.”可知，农民使用处理过的废水是因为淡水供应有限。故选D。

2.2. What does the phrase “these chemicals” in Paragraph 2 refer to?

A Plant foods.

B Waste things.

C Mental drugs.

D Clean water.

解析：选C。C词意指代题。代词指代通常遵循“就近原则”和“逻辑原则”。第一段末尾提到：“Small amounts of medicines... often remain in treated wastewater.”紧接着第二段开头提到“these chemicals”，逻辑上即指代上文提到的药物成分。选项C中的“Mental drugs”与原文“those used to treat mental health conditions”吻合。故选C。

3.3. Why do leaves contain more drugs than fruits or roots?

A Fruits can push drugs out.

B Leaves get more sunshine.

C Water dries up in leaves.

D Roots stop taking in drugs.

解析：选C。C推理判断题。根据第五段对植物水分运动的解释：“When water reaches the leaves, it evaporates into the air... the chemicals... are trapped.”意思是水在叶子处蒸发，而化学物质被留在了叶片组织中。选项C“Water dries up in leaves”揭示了药物残留的物理原因。故选C。

4.4. What is the probable next step based on the researchers’ findings?

A Grow cleaner carrots.

B Set safety guidelines.

C Build water treatment sites.

D Find more new medicines.

解析：选B。B推理判断题。文章最后一句明确指出：“...understanding where these chemicals go helps... establish better guidelines for safely using recycled water in farming.”科学研究的目的是为了指导实践。研究人员下一步的工作重点是根据残留位置的研究结果，制定更科学的安全使用标准。故选B。