US Geological Survey, New Jersey Water Science Center, 810 Bear Tavern Road, West Trenton, NJ 08628, USA.
Water Res. 2010 Nov;44(19):5532-44. doi: 10.1016/j.watres.2010.05.047. Epub 2010 Jun 8.
The Cretaceous and Tertiary sediments that underlie the Inner Coastal Plain of New Jersey contain the arsenic-rich mineral glauconite. Streambed sediments in two Inner Coastal Plain streams (Crosswicks and Raccoon Creeks) that traverse these glauconitic deposits are enriched in arsenic (15-25mg/kg), and groundwater discharging to the streams contains elevated levels of arsenic (>80μg/L at a site on Crosswicks Creek) with arsenite generally the dominant species. Low dissolved oxygen, low or undetectable levels of nitrate and sulfate, detectable sulfide concentrations, and high concentrations of iron and dissolved organic carbon (DOC) in the groundwater indicate that reducing environments are present beneath the streambeds and that microbial activity, fueled by the DOC, is involved in releasing arsenic and iron from the geologic materials. In groundwater with the highest arsenic concentrations at Crosswicks Creek, arsenic respiratory reductase gene (arrA) indicated the presence of arsenic-reducing microbes. From extracted DNA, 16s rRNA gene sequences indicate the microbial community may include arsenic-reducing bacteria that have not yet been described. Once in the stream, iron is oxidized and precipitates as hydroxide coatings on the sediments. Arsenite also is oxidized and co-precipitates with or is sorbed to the iron hydroxides. Consequently, dissolved arsenic concentrations are lower in streamwater than in the groundwater, but the arsenic contributed by groundwater becomes part of the arsenic load in the stream when sediments are suspended during high flow. A strong positive relation between concentrations of arsenic and DOC in the groundwater samples indicates that any process-natural or anthropogenic-that increases the organic carbon concentration in the groundwater could stimulate microbial activity and thus increase the amount of arsenic that is released from the geologic materials.
新泽西州内陆沿海平原下的白垩纪和第三纪沉积物中含有富含砷的矿物海绿石。流经这些海绿石矿床的两条内陆沿海平原溪流（Crosswicks 和 Raccoon Creeks）的河床沉积物富含砷（15-25mg/kg），排入溪流的地下水含有高浓度的砷（Crosswicks Creek 一处的砷含量超过 80μg/L），亚砷酸盐通常是主要物种。地下水的溶解氧低、硝酸盐和硫酸盐含量低或无法检测到、可检测到的硫化物浓度以及铁和溶解有机碳（DOC）浓度高，表明在河床下方存在还原环境，并且微生物活动（由 DOC 提供燃料）参与了从地质材料中释放砷和铁。在 Crosswicks Creek 地下水砷浓度最高的情况下，砷呼吸还原酶基因（arrA）表明存在砷还原微生物。从提取的 DNA 中，16s rRNA 基因序列表明微生物群落可能包括尚未描述的砷还原细菌。一旦进入溪流，铁就会被氧化并以沉积物上的氢氧化物涂层的形式沉淀。亚砷酸盐也被氧化并与铁氢氧化物共沉淀或被其吸附。因此，与地下水相比，溪流水中的溶解砷浓度较低，但当沉积物在高流量期间悬浮时，地下水贡献的砷成为溪流中砷负荷的一部分。地下水样本中砷和 DOC 浓度之间存在很强的正相关关系，表明任何增加地下水有机碳浓度的过程——自然的或人为的——都可能刺激微生物活动，从而增加从地质材料中释放的砷量。
