Impact of systematic change of redox potential on the leaching of Ba, Cr, Sr, and V from a riverine soil into water

Abstract

Floodplain soils are often contaminated with toxic elements such as Ba, Cr, Sr, and V. For an adequate risk assessment of such contaminated sites, the assessment of factors affecting the leaching of those elements from riverine soils into water is fundamental. Since the redox potential (E-H) can be important within this context, we aimed to assess the impact of pre-set redox conditions on the dynamics of Ba, Cr, Sr, and V in a floodplain soil. To achieve this aim, we used an automatic biogeochemical microcosm system allowing computer-controlled regulation of E-H by adapting the supply of N-2 or O-2 to the soil suspension. With this system, the effect of E-H on the dynamics of Ba, Cr, Sr, and V was studied mechanistically. Chromium and V were negatively correlated with E-H possibly due to co-precipitation of these metals with Fe (hydr)oxides at high E-H. Vanadium might additionally be oxidized from more soluble V(IV) to less soluble V(V) with rising E-H. Barium and Sr were positively correlated with E-H, which might be attributed to their association with dissolved organic carbon (DOC). The influence of pH on the dynamics of the studied elements seemed to be of minor importance in our study. A significant negative correlation was observed between the specific UV absorbance at 254 nm (SUVA (254)) and E-H indicating that oxidizing conditions favored the removal of aromatic DOC molecules from solution via binding to Fe (hydr)oxides. Redox potential is important for metal fate in the current study. Results imply an absorption of Cr and V to Fe (hydr)oxides and an interaction with DOC while particularly Ba and Sr dynamics may be influenced by DOC. In the future, different V species in wetland soils under pre-definite redox conditions should be determined and further studies should elucidate the specific role of DOC and sulfur (S) chemistry on the dynamics of the studied metals

Exploiting biogeochemical and spectroscopic techniques to assess the geochemical distribution and release dynamics of chromium and lead in a contaminated floodplain soil

“…These high metal contents in floodplain soils around the Wupper River in Germany have been documented previously (e.g., Frohne et al, 2011Frohne et al, , 2014Frohne et al, , 2015Shaheen and Rinklebe, 2015a,b;, and they are mainly due to the discharge of waste originating from textile and metal industries as well as mining activities during the last centuries. As a consequence, considerable amounts of potentially toxic trace elements can still be found in floodplain soils of the River Wupper (Frohne et al, 2014).…”

“…Thus, this system allows for mechanistic experiments aiming at exploring underlying geochemical processes under fully controlled conditions. This system was successfully employed in previous studies (Anti c-Mladenovi c et al, 2011;Frohne et al, 2011Frohne et al, , 2014Frohne et al, , 2015Rupp et al, 2010;Rinklebe et al, 2016a,b;Shaheen et al, 2014c;Shaheen et al, 2016). Technical details are provided by Yu and Rinklebe (2011) and experimental specifics in Supplemental 2.…”

“…Elevated levels of PTMs, including chromium (Cr) and lead (Pb) in acidic soils may increase the solubility, phytoavailability, and leaching of these metals resulting in an adverse impact on the agricultural environment (Du Laing et al, 2009;Frohne et al, 2015;Ok et al, 2011;Overesch et al, 2007;Rinklebe et al, 2016a;Shaheen and Rinklebe, 2015a,b). Pollution by Cr and Pb is a global environmental concern and a significant issue for environmental protection because Cr and Pb are toxic and potentially mobile Shaheen and Rinklebe, 2014).…”

Amendment of biochar reduces the release of toxic elements under dynamic redox conditions in a contaminated floodplain soil

“…Therefore, the relations between Fe and Mn on the one hand and soil E H on the other hand were positive, while relations between both elements with soil pH were negative in CS and CS + BC (Supplemental 2). An increase of soluble Fe and Mn concentrations due to reductive dissolution under low E H is commonly observed in soils (e.g., Antić -Mladenović et al, 2011;Frohne et al, 2015;Shaheen et al, 2014a,b,c). However, in our experiment, the concentrations of soluble Fe and Mn increased under high E H very likely due to the associated decrease of pH (Fig.…”

“…This system was successfully employed in previous studies (Antić -Mladenović et al, 2011;Rupp et al, 2010;Frohne et al, 2011Frohne et al, , 2014Frohne et al, , 2015Shaheen et al, 2014a). Technical details are provided in Yu and Rinklebe (2011) and experimental specifics in Supplemental 1.…”