Abstract

I. INTRODUCTION Chile is the first copper producer in the world, generating a significant residue volume called mining tailings, which are deposited throughout the country. Those residues significantly affecting the environment and besides, generating potential risks such as soil and water pollution, since they are a source of metals, metalloids, and sulfate. In Chile, mining tailings deposits are around 740 of which 469 are inactive and 170 abandoned (SERNAGEOMIN, 2018). To handle these wastes, the phytostabilization strategy implies the establishment of a vegetation cover that accumulates the elements preferably at the root and favors their growth with the application of organic amendments, to recover the landscape. Plants suitable for phytostabilization must be resistant to salinity, water scarcity, generate biomass in a short time and tolerant to metals and sulfates. Carpobrotus chilensis (doca) is a native plant from Chile distributed between La Serena and Valdivia (Riedemann and Aldunate 2000). This plant is generally present on coastal edges, used in urban gardening as ground cover and to contain slopes on roads. The characteristics of this plant are interesting for the phytostabilization of mining tailings. Current studies on mining tailings focus on the metal elements that plants can uptake (Acosta et al., 2018), and research on sulfur absorption in native and ornamental plants are scarce. The main objective was to evaluate the generation of biomass and sulfur absorption of Carpobrotus chilensis cultivated in mining tailings with the addition of organic amendments. II. METHODOLOGY The research was carried out in greenhouse conditions at the Faculty of Agricultural Sciences at the University of Chile between March and August 2018. The mining tailings were obtained from the Ovejería Tailing Dam of CODELCO DAND. The Carpobrotus chilensis (doca) plants were established in mining tailings, with compost addition at a dose of 5.0% (w/ w) and with commercial humic substances addition at a dose of 0.04% (w / w). The compost was obtained from vegetable residues of street markets at La Pintana commune. The commercial humic substance was PowHumus (Humintech GmbH, Germany). The assay had a duration of 180 days. Previously in the mining tailings and organic amendments the main chemical characteristics were determined: pH in aqueous extract (1: 2.5 w/ v), electrical conductivity (EC), organic matter (OM) by calcination at 360 ° C, sulfur (S) available by extraction with calcium dihydrogen phosphate and Cation Exchange Capacity (CEC) with ammonium acetate at pH 7.0. Humic substances were evaluated according to Stevenson's methodology (1994). The evaluation of the total leachate sulfates from the pots was made by summing the loads in mg kg-1. In plants, dry matter and S concentration were determined in aerial and root parts (Sadzawka et al., 2007). For the statistical analysis, an analysis of variance was performed, and the significant differences were evaluated with Tuckey test with p≤0.05. III. RESULTS AND DISCUSSION In relation to chemical properties, the commercial humic substance have a higher CEC, total humic – C and fulvic and humic acids - C than the compost used (Table 1), which indicates a greater chemical reactivity. In relation to the S, the amendments made a significant contribution of this element in comparison to the tailings; however, in the treatments with doca and mining tailings, sulfate leaching decreased with the addition of commercial humic substances (tailings with humic substances: 148.6; tailings with compost: 321.6 and tailings: 265.6 in mg kg-1). These results indicated that the formation of complexes between the S and humic substances decreased sulfate leaching. The doca plant grew in mining tailings without application of amendments, indicated tolerance to the lack of nutrients. However, the application of compost significantly favored the generation of aerial parts and roots biomass in doca (Table 2), an effect that is favorable for phytostabilization. In a similar study, the humic substance addition have not favored the growth of this species (Tapia et al., 2017). In relation to the absorption of S in doca, the application of both amendments increased the S concentration in aerial parts, reaching levels of 0.5%; those levels are considered normal in plants (Havlin et al., 2014). As a result, the compost addition decreased the concentration of S. In general, the concentration of S in doca cultivated in mining tailings was higher in root than in aerial parts, which is one of the objectives of phytostabilization. IV. CONCLUSIONS Carpobrotus chilensis (doca) plants could grow in mining tailings and the application of compost significantly favored their growth. Commercial humic substances decreased the leaching of sulfates which is attributable to their greater composition of humic acids with respect to compost. The cultivation of doca in mining tailings with the application of compost is recommended for the incorporation of vegetation cover and landscape recovery. V. REFERENCES Acosta et al. 2018. Phytoremediation of mine tailings with Atriplex halimus and organic/inorganic amendments. A five-year field case study. Chemosphere 204: 71-78. Havlin, J., Tisdale, S., Nelson, W., Beaton, J. 2014. Soil Fertility and Fertilizers: An Introduction to nutrient management, 8th edition. Pearson, USA. Riedemann, P., Aldunate, G. 2004. Flora nativa de valor ornamental. In: Identificación y propagación. Segunda Edición. Riedemann y Aldunate, Chile (ISSN 956-299-433-3 Inscripción: N° 11689). Sadzawka, A., Grez, R., Moran, M., Saavedra, N., Carrasco, M., Flores, H., Rojas, C. 2007. Métodos de análisis de tejidos vegetales. Instituto de Investigaciones Agropecuarias (INIA), Serie Actas Nº 40. Santiago de Chile. SERNAGEOMIN. 2018. https://www.sernageomin.cl/datos-publicos-deposito-de-relaves/ Stevenson, F.J. 1994. Humus Chemistry. John Wiley and Sons Inc., N.Y., USA. Tapia, Y., Bustos, P., Salazar. O., Casanova, M., Castillo, B., Acuña, E., Masaguer, A. 2017. Phytostabilization of Cu in mine tailings using native plant Carpobrotus aequilaterus and the addition of potassium humates. J Geochem Exploration. 183:102-113.