Contaminación natural y antrópica de arsénico en suelos derivados del plutón de Chiquimula al sureste de la República de Guatemala

Abstract

This study determined concentrations of arsenic in rocks, sediments, soils, waters, plants and common or most used agrochemical to know truthfully natural or anthropogenic sources of arsenic element in an area of 304 km2 located northwest of Chiquimula town, Guatemala. Congruently key objectives were addressed to the determination of arsenic in all possible environments where humans interact and, at the same time, to know and define the origin and the subsequent mobilization of arsenic in every natural environment. To get these objectives we made severals field works that allow the soils characterizations. At the same time we realice the sampling recollections and after their preparation, samples were send to certificated laboratories where they were analized using inducted coupled plasma ICP-MS -ES/ICP-MS. The rocks of the study area have a very high arsenic content, especially highlighting the granodiorite, quartzdiorite and schist, and are controlled by geological processes that have enriched them and the composition of the magma from which they solidified. With physical-chemistry process (weathering) and once they become fragments and sediment, it can be observed that the highest concentration of arsenic is housed in the fragments of quartz and fine sediments. However, when transformed into soil arsenic concentration depends on the amount of this element that exists in the rock on which they are formed. Meanwhile, in the uptaking of arsenic in plants, it is remarkable the role of roots in the concentration of arsenic in surface horizons. Soils, with coarse textures show traslocation to subsurface horizons. From this account, the chemical results of corn plants found that the highest concentration of arsenic is fixed in the roots and leaves, and the lowest concentration occurs in the fruit. Accordingly, the arsenic concentration at the root of plants sampled is closely related to the concentration of bioavailable arsenic in soils where the crop is planted. Furthermore, the contributions of arsenicals sources are also available through herbicides and fertilizers applied. The contributions of arsenic, both natural and anthropogenic, match the increased load of arsenic transported by the water supply during the winter. They are associated with the runoff caused by rainfall, which in turn pulls the arsenic content in soil and particles of weathered rock into rivers and streams. This mobilization evidence conveyors and countless places of concentration or deposition of arsenic in the lower parts of watersheds analyzed in the study area. Note that the concentration of arsenate analyzed in all environments is higher than arsenite, maintaining a ratio 1:16. Finally, this study determines the mainly natural character of arsenic contamination, coming from natural sources or ore of thermal origin that have concentrated heavy metals harmful to humans, but also show contributions from anthropogenic character through agrochemicals used in agriculture.