Antioxidant plant metabolites affect leaching of mineral elements from Callovo‐Oxfordian clays

Abstract

Summary Minerals excavated during industrial activities are stored on the soil surface, exposed to weathering, which leads to the initial development of soil. Plants contribute to soil mineral weathering, mainly by producing acidic or complexing root exudates. In addition, many plants produce antioxidant compounds and phenolic substances that could also contribute to mineral transformation processes, but have rarely been considered in relation to mineral weathering. An incubation experiment was carried out for 2 months under controlled conditions to assess the effects of antioxidant plant metabolites on the weathering processes of a clay mineral. A freshly excavated, sulphur‐rich Callovo‐Oxfordian argillite (COx) sample was artificially leached with three concentrations of three antioxidant compounds (linalool, thymol and carvacrol) or water as a control. The weathering of COx was followed by the analysis of amounts of anions and cations in the leachates. Chlorine, sulphate, nitrate, phosphate, calcium, magnesium and potassium were found in the leachates, whereas iron and aluminium were close to the detection limits. Sulphate leaching reflected oxidation of the pyritic matter contained in COx (mainly fine pyrite particles) by air. Water alone was enough to cause notable leaching of elements such as S and P, but the percentage of leached sulphate increased in the presence of two antioxidant compounds, carvacrol and thymol, and increased to 38% with thymol at 2 mg l−1 compared with the antioxidant‐free control. Thus, antioxidant compounds could contribute to the leaching of elements from COx, depending on their nature and concentration. Highlights We assessed the effects of leaching with antioxidant plant metabolites on COx clay weathering Sulphate leaching reflected the oxidation of pyritic matter (mainly fine pyrite particles) by air Percentage of sulphate leaching increased to 38% with thymol at 2 mg l−1 Antioxidant compounds contribute to the leaching of elements from COx