Cheng Z, van Geen A, Seddique A A, Ahmed K M
Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA.
Environ Sci Technol. 2005 Jul 1;39(13):4759-66. doi: 10.1021/es048065f.
Millions of people in Bangladesh have probably switched their water consumption to wells that meet the local standard for As in drinking water of 50 microg/L as a result of blanket field testing throughout the country. It is therefore important to know if As concentrations in those wells could change over time. To address this issue, we report here precise groundwater As analyses for time-series samples collected from a suite of 20 tube wells containing < or =50 microg/L As and ranging from 8 to 142 m in depth. For 17 out of 20 wells, the standard deviation of groundwater As concentrations was <10 microg/L over the 3-year monitoring period (n = 24-44 per well). Six of the 17 wells are community wells, each of which serves the needs of several hundred people in particularly affected villages. Of the three wells showing larger fluctuations in chemical composition including As, two are very shallow (8 and 10 m). Variations in As concentrations for one of these wells (50 +/- 32 microg/L, n = 36), as well as another shallow well showing smaller variations (48 +/- 5 microg/L, n = 36), appear to be coupled to seasonal precipitation and recharge linked to the monsoon. The other shallow well showing larger variations in composition indicates a worrisome and steady increase in As concentrations from 50 to 70 microg/L (n = 36) over 3 years. The time series of As (30 +/- 11 microg/L, n = 24) and other constituents in one deep community well (59 m) show large fluctuations that suggest entrainment of shallow groundwater through a broken PVC pipe. Even though the majority of wells that were initially safe remained so for 3 years, our results indicate that tube wells should be tested periodically.
由于在孟加拉国全国范围内进行了全面的实地测试，数百万孟加拉国人可能已将他们的用水来源切换至符合当地饮用水中砷含量标准（50微克/升）的水井。因此，了解这些水井中的砷含量是否会随时间变化非常重要。为解决这一问题，我们在此报告了对从一组20口水井采集的时间序列样本进行的精确地下水砷分析，这些水井的砷含量小于或等于50微克/升，深度在8至142米之间。在20口水井中的17口，在3年的监测期内（每口井n = 24 - 44），地下水砷含量的标准偏差小于10微克/升。17口井中有6口是社区水井，每口井为受影响特别严重的村庄中的数百人提供用水。在显示化学成分（包括砷）波动较大的三口井中，有两口非常浅（8米和10米）。其中一口井（50 ± 32微克/升，n = 36）以及另一口显示较小变化的浅井（48 ± 5微克/升，n = 36）的砷含量变化似乎与季节性降水以及与季风相关的补给有关。另一口显示成分变化较大的浅井表明，在3年时间里，砷含量从50微克/升稳步增加到70微克/升（n = 36），令人担忧。一口深社区井（59米）中砷（30 ± 11微克/升，n = 24）和其他成分的时间序列显示出较大波动，这表明通过破裂的PVC管混入了浅层地下水。尽管大多数最初安全的水井在3年内仍保持安全，但我们的结果表明，管井应定期进行检测。
