Presence and mobility of arsenic in estuarine wetland soils of the Scheldt estuary (Belgium)

Abstract

We aimed to assess the presence and availability of arsenic (As) in intertidal marshes of the Scheldt estuary. Arsenic content was determined in soils sampled at 4 sampling depths in 11 marshes, together with other physicochemical characteristics. Subsequently, a greenhouse experiment was set up in which pore water arsenic (As) concentrations were measured 4 times in a 298-day period in 4 marsh soils at different sampling depths (10, 30, 60 and 90 cm) upon adjusting the water table level to 0, 40 and 80 cm below the surface of these soils. The As content in the soil varied significantly with sampling depth and location. Clay and organic matter seem to promote As accumulation in the upper soil layer (0-20 cm below the surface), whereas sulfide precipitation plays a significant role at higher sampling depths (20-100 cm below the surface). The As concentrations in the pore water of the greenhouse experiment often significantly exceeded the Flemish soil sanitation thresholds for groundwater. There were indications that As release is not only affected by the reductive dissolution of Fe/Mn oxides, but also by e.g. a direct reduction of As(V) to As(III). Below the water table, sulfide precipitation seems to lower As mobility when reducing conditions have been sufficiently established. Above the water table, sulfates and bicarbonates induce As release from the solid soil phase to the pore water.

Assessment of Deep Groundwater Quality in Kathmandu Valley Using Multivariate Statistical Techniques

“…The presence of high levels of Fe is possibly a result from the reductive dissolution of Fe oxides under the lower redox levels of groundwater. On the contrary, a negative correlation exhibited by As and ORP indicate the occurrence of high levels of As under reducing groundwater environment; and it is further supported by the existence of positive correlation of As and NH 4 + -N and negative correlation between As and NO 3 --N. The higher concentration of As under reduced groundwater environment is likely due to reductive dissolution of Fe/Mn oxides and direct reduction of As(V) into As(III) (see Du Laing et al 2009). The natural origin and reductive process of As released in groundwater of study area is discussed by Chapagain et al (2009).…”

Dissolved Inorganic Contaminants in a Floodplain Soil: Comparison of In Situ Soil Solutions and Laboratory Methods

“…Here and in the following, all regression analyses were calculated at a confidence level α < 0.1. Although the concentrations of Fe and Mn were rather low (Table 2), the correlation between the concentrations of Fe and As (r=0.45) indicates that dissolved As species originate from reductive dissolution of (hydrous) Fe oxides that have been identified as an important process generally controlling the mobility of As in redoximorphic soils (Davranche and Bollinger 2000;Du Laing et al 2009c). This was particularly confirmed by Rinklebe et al (2005) for a floodplain soil of the Elbe River.…”

“…Arsenic was mostly detected as bound to less crystalline Fe oxides and to smaller parts to organic matter, crystalline Fe oxides, and as silicate residuum. The speciation indicates rather strong bonding and highlights once again the importance of Fe oxides as a major adsorbent of As species in soil (Cancès et al 2005;Du Laing et al 2009c). Zinc was almost equally distributed among all fractions, whereas Cu and Pb were mostly bound to organic matter, indicating the varying affinities of the metals for inorganic or organic surfaces in soil.…”

Assessment of Arsenic Contamination in Deep Groundwater Resources of the Kathmandu Valley, Nepal

“…The higher concentration of arsenic under reduced groundwater environment may be due to Fe/Mn oxides and direct reduction of As(V) into As(III). After an initial increase, arsenic concentration often decreases again as a function of time below water table due to sulfide precipitation, whereas it increases with increasing sulfate concentrations above water table [58]. Under moderately reduced environment (0 to 100 mV), arsenic solubility seemed to be controlled by the dissolution of Fe oxyhydroxides.…”