单选题 Rain is not what it used to be. A new study reveals that much of the precipitation in Europe contains such high levels of dissolved pesticides that it could be illegal to supply it as drinking water. Studies in Switzerland have found that rain is laced with toxic levels of atrazine, alachlor and other commonly used crop sprays. "Drinking water standards are regularly exceeded in rain," says Stephan Muller, a chemist at the Swiss Federal Institute for Environmental Science and Technology in Dubendorf. The chemicals appear to have evaporated from fields and become part of the clouds. Both the European Union and Switzerland have set a limit of 100 nanograms for any particular pesticide in a liter of drinking water. But, especially in the first minutes of a heavy storm, rain can contain much more than that. In a study to be published by Muller and his colleague Thomas Bucheli in Analytical Chemistry this summer, one sample of rainwater contained almost 4000 nanograms per liter of 2, 4-dinitrophenol, a widely used pesticide. Previously, the authors had shown that in rain samples taken from 41 storms, nine contained more than 100 nanograms of atrazine per liter, one of them around 900 nanograms. In the latest study, the highest concentrations of pesticides turned up in the first rain after a long dry spell, particularly when local fields had recently been sprayed. Until now, scientists had assumed that the pesticides only infiltrated groundwater directly from fields. Muller warns that the growing practice of using rainwater that falls onto roofs to recharge under — ground water may be adding to the danger. This water often contains dissolved herbicides that had been added to roofing materials, such as bitumen sheets, to prevent vegetation growing. He suggests that the first flush of rain should be diverted into sewers to minimize the pollution of drinking water, which is not usually treated to remove these herbicides and pesticides.

单选题 According to the Swedish scientists, the pesticides in rain______.

单选题 Muller and Bucheli found that 2, 4-dinitrophenol______.

单选题 Scientists used to hypothesize that______.

单选题 Muller warns us not ____ .

单选题 Which of the following can be the best title for the passage?