Distribution Of Arsenic In Sediments Research Articles

Species distribution of arsenic in sediments after an unexpected emergent discharge of high-arsenic wastewater into a river

The unexpected emergent discharge of high-arsenic wastewater into water environments results in significantly increased levels of arsenic in water; however, the species distribution of arsenic in sediments has never been reported before for such cases. This study focuses on an As pollution accident in the Dasha River, and uses sequential extraction procedures with deionized water, 1 mol·L−1 MgCl2 at pH = 8, 1 mol·L−1 NaH2PO4 at pH = 5, and 1 mol·L−1 HCl to investigate four binding phases of arsenic (i.e., water soluble, ion-exchangeable, stronglybound, and precipitates) in sediments at different layers in different cross-sections along the river. The average ratio of arsenite (As(III)) to arsenate (As(V)) was found to decrease from 0.74:1 in river water to 0.48:1 in sediment, owing to its higher affinity toward As(V) than As(III). The content of arsenic in the sediments was relatively low and the maximum content was observed to be 36.3 mg·kg−1 for As(III) and 97.5 mg·kg−1 for As(V). As(III) and As(V) showed different binding phases in sediments, and the average fractions of these four species were determined to be 0.09, 0.11, 0.17, and 0.63 for As(III) and 0.03, 0.14, 0.63, and 0.20 for As(V), respectively. For all the sediment samples, the content of arsenic showed no relationship with the characteristics of the sediments such as the particle diameter, the content of organic carbon, Fe, and Mn, although a negative correlation with particle diameter was observed for the sediments in the uppermost 2-cm layer. The unexpected emergent As incident results in the high content of total arsenic in the surface sediment, which may be potential secondary source to the elevated As levels in surface water.

Geographical distribution of arsenic in sediments within the Rio Conchos Basin, Mexico

Arsenic (As) content of sediments from the Rio Conchos and Rio San Pedro in northern Mexico were measured to determine if this toxic metalloid had accumulated to unsafe levels to humans and aquatic life. The spatial distribution of As in each of the six clusters of river and arroyo sediments was analyzed to determine variations with respect to background levels and to infer about potential As sources and sinks. In the northern part of the study area, background concentrations varied little throughout the area and concentrations in river sediments were close to background levels. In the southern part, however, the content of As in arroyo sediment contained a wider range of values and anomalous concentrations. The latter could be traced in part to the presence of mine tailings. As concentrations were below the limit in all studied river stretches and thus do not pose an immediate threat to the river environment, but As content in reservoir sediments exceeded the guideline values. Reservoirs seem to act as a sink for As, warranting closer observation and monitoring.