Abstract
PurposeSoils that develop on the dumps in historical arsenic mining sites contain high concentrations of As thus constituting a serious environmental risk. This study was aimed to examine the changes in arsenic solubility in mine soils as induced by organic matter introduced with forest litter.Materials and methodsFour large samples of initially developed soils were collected from the dumps remaining in former mining sites and were incubated for 90 days at various moistures: 80% of maximum water holding capacity and 100% (flooded conditions), with and without addition of beech forest litter (BL), 50 g/kg. Soils contained up to 5.0% As. Soil pore water was collected periodically with MacroRhizon suction samplers and examined on As, Mn, and Fe concentrations, pH, Eh, and dissolved organic carbon (DOC). The properties of dissolved organic matter were characterized by UV-VIS spectroscopic parameters A4/A6 and SUVA254.Results and discussionApplication of BL resulted in an intensive release of As from soils, particularly at 100% moisture. As concentrations in soil pore water increased strongly during the first 2 or 4 weeks of incubation and then started to decrease in all cases, except for one flooded soil. As was released particularly intensively from carbonate-containing soils. The mechanisms of As mobilization, including reductive dissolution of Mn and Fe oxides and the competition with DOC for sorption sites on the oxides, were discussed as related to soil properties. Pore water concentrations of DOC were increasing at the beginning of incubation and started to decrease after two or four weeks. Spectroscopic parameters of dissolved organic matter in ZS soils indicated increasing aromaticity and progress of humification.ConclusionsForest litter introduced to mine dump soils causes a mobilization of As into soil pore water. This effect, particularly strong in carbonate-rich soils, is apparently related to high concentrations of DOC and usually declines with time, which may be explained by the progress in humification. The relationships between DOC properties and As speciation in soil pore water should be dissected for better interpretation of experimental results.
Highlights
Arsenic is a toxic element; its mobility in the environment and lability in soil are a matter of concern (Wenzel 2013)
Arsenic concentrations in Polish soils are basically very low, but there are sites associated with historical ore mining, where arsenic occurs in very high concentrations (Karczewska et al 2007, 2013b; Krysiak and Karczewska 2007)
Such an effect may be caused by the presence of anions, such as phosphates, that compete with arsenates for oxide sorption sites and by the changes in soil pH or redox potential (Bolan et al 2013; Lewińska and Karczewska 2013; Wenzel 2013; Arco-Lázaro et al 2016)
Summary
Arsenic is a toxic element; its mobility in the environment and lability in soil are a matter of concern (Wenzel 2013). Arsenic distribution in soil can be modified causing the release of its considerable amounts from soil solid phase into soil solution. Such an effect may be caused by the presence of anions, such as phosphates, that compete with arsenates for oxide sorption sites and by the changes in soil pH or redox potential (Bolan et al 2013; Lewińska and Karczewska 2013; Wenzel 2013; Arco-Lázaro et al 2016). Kim et al (2000) and Han et al (2007) proved that the presence of carbonates in soil may cause enhanced release of arsenic (As III) under anoxic conditions due to formation of stable arseno-carbonate complexes, believed to be As(CO3)2−, As(CO3)(OH)2−, and AsCO3+
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