Uso de la fitoestabilización asistida para facilitar la producción de aromáticas en residuos mineros como estrategia de rehabilitación ambiental y socioeconómica

Laburpena

The intense mining activity carried out in the Cartagena-La Unión Mining District generated large quantities of waste, generating mining ponds or deposits. These mining ponds are characterized by adverse chemical and physical conditions, including high concentrations of metal/oids and salts, low organic matter content and nutrient scarcity, which prevent the growth and development of vegetation. In addition, these wastes present environmental and public health risks due to the dispersion of toxic metal/oids through water and wind erosion processes. To reduce these risks, the formation of quality soils is an essential requirement, as it will favor the colonization, growth, and development of vegetation. In this way, erosion rates will be reduced and thus the transfer of toxic metal/oids to the environment, where the soil created becomes a carbon sink, helping to mitigate the effects of climate change. Moreover, offering an alternative with economic benefits to the owners of mining areas, since aromatic species can be used in the rehabilitation and marketable essential oils can be extracted, achieving an environmental and socioeconomic rehabilitation of the tailing ponds. The general objective of this study was to evaluate the efficiency of aided phytostabilization in the Cabezo Rajao tailing pond, using Piptatherum miliaceum and Coronilla juncea, combined with the addition of organic amendments, such as biochar and compost, and inorganic amendments such as, limestone and zeolite, which improve the physical, chemical and biological conditions of the soil, as well as reducing the availability of metal/oids, which will allow the development of aromatic species (Salvia rosmarinus and Thymus zygis), of economic interest. The experimental design carried out in this study consisted of the application of 7 different treatments in 21 plots located in the Cabezo Rajao mining deposit: (T1)- limestone+biochar, (T2) - limestone+compost, (T3) - limestone+biochar+compost, (T4) - limestone+biochar+zeolite, (T5) - limestone+compost+zeolite, (T6) - limestone+compost+zeolite+biochar and 1 treatment without amendments, (control treatment, only with the original mining residue). Each of these treatments was applied in triplicate. Six samplings were carried out during the study (M0-M5): (M0 - 01/2019; M1 - 03/2019; M2 - 06/2019; M3 - 11/2019; M4 - 05/2020; M5 - 05/2021), which will allow know the evolution of the parameters analyzed over time. Soil samples were taken to study the properties/characteristics, metal/oid concentration, effect on microbial communities and ecotoxicity on Folsomia candida and Enchytraeus crypticus in the different treatments applied in the plots. Similarly, plant samples (stem+root) of P. miliaceum, S. rosmarinus and T. zygis were collected to determine the metal/oid content, and samples of plant material from the two aromatic species for the extraction of essential oils. Once a month, greenhouse gas measurements were taken, and the development of vegetation cover was evaluated in each of the plots. After the application of the amendments (M1), soil properties and nutrients improved, as well as soil structure and the diversity of the microbial community, contributing to improve soil quality and favoring the development of plant cover (P. miliaceum, C. juncea, T. zygis and S. rosmarinus). In relation to the metal/oid contents, the most mobile fractions decreased, turning to the more stable fractions. Cd and Zn concentrations significantly decreased in exchangeable fraction and increased in carbonates fractions and Fe/Mn oxides fraction. Cd concentrations Pb decreased at Fe and Mn oxides fraction and increased at residual fraction and bounded to carbonates. Ecotoxicity bioassays with the different treatments also showed the affinity of the organisms for the amended soils in our study. Regarding bioaccumulation and translocation of metal/oids in plant species, P. milliaceum showed no evidence of bioaccumulation or translocation of metals at the end of the study. T. zygis and S. rosmarinus were not bioaccumulating species, but T. zygis showed As and Cd translocation and S. Rosmarinus Zn and Cd translocation. In general, the metal content in the aerial part did not exceed the máximum phytotoxic values. In addition, these two aromatic species were found to be suitable for the production of essential oils. Out of all the treatments applied, the T5 treatment contributed the most to soil quality. In conclusion, the application of aided phytostabilization based on the amendments applied with the treatment (T5) could prove to be a promising alternative to be applied on a larger scale in future mine site rehabilitation projects.