Chemistry of barite-polluted wetland soils: effects of organic matter, microbial community, and manganese oxides on barium dynamics

Author(s)

Douglas Gomes Viana

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-05-29

Examining board members

Jussara Borges Regitano; Fernando Barboza Egreja Filho; Letícia de Pierri

• Advisor: Jussara Borges Regitano

Abstract

Barite (BaSO4) has high density and low solubility. Therefore, it generally does not pose environmental risks. However, in wetland soils under anoxic conditions (i.e., redox potential less than -100 mV), sulfate can be used as a final electron acceptor during the oxidation of organic matter, being reduced to the sulfide. In this condition, Ba can become bioavailable and become a risk to the environment and living beings. The general objective was to investigate the dynamics of BaSO4 in flooded soils, relationships between carbon sources and rates, and the addition of oxidizing agents (manganese oxide). The thesis begins in chapter two with a study that evaluated the effect of different carbon sources (sewage sludge, rice straw, and rice straw biochar) on the reduction of barite and its effect on the attenuation of the microbial community exposed to the Ba. The relative abundance of Proteobacteria and Pseudomonadaceae decreased in soils contaminated with Ba. Organic additives differed in their potential for the recovery of soil microbial communities. The relative abundance of Pseudomonadaceae in soils contaminated with Ba was recovered by adding biochar, while sewage sludge and rice straw recovered the relative abundance of Firmicutes. Chapter three assessed whether different carbon rates from wastes with different C/N ratios (peat, sewage sludge, and rice straw) affect the geochemical environment. The organic additives differed in their potential to act as an electron source for barite dissolution. The rate, but mainly the source of organic additive, affects the reductive dissolution of barite and, subsequently, the mobility of Ba in barite-contaminated flooded environments. Applying sewage sludge in soils contaminated with barite resulted in higher pH and the lowest redox potential, favoring the highest Ba precipitated as sulfide and the lowest Ba dissolved in the soil solution. The opposite behavior was observed for the soil with rice straw. Applying 1% of C as rice straw combined with the cultivation of plant species capable of phytoextracting Ba could increase the removal of Ba from soils. In comparison, applying 5% of C as sewage sludge can immobilize Ba as sulfide minerals, decreasing their mobility in contaminated soils. Chapter four evaluated the effect of pyrolysis temperature (350°C, 550°C, and 750°C) of sugarcane straw biochar on the bioavailability of Ba. The application of rice straw biochar submitted to a high temperature of pyrolysis (750°C) resulted in an increase in soil pH and a more oxic environment, which did not favor the reduction of sulfate and, subsequently, the dissolution of Ba and its maintenance in bioavailable fractions (i.e., Ba-EX). In contrast, biochar pyrolyzed at a low temperature (350°C) resulted in lower redox potentials, thus increasing the availability of Ba in the soil due to the reductive dissolution of barite. Chapter five sought to evaluate the effect of manganese oxides with different reactivity and their application rates in the geochemical environment, thus affecting the reduction of sulfate and, consequently, the availability of Ba. The application of manganese oxyhydroxides also affected the reductive dissolution of barite and possibly the oxidation of sulfides. Differences in the oxidation states of Mn oxyhydroxides led to different reactivity and oxidation potentials of sulfides. Mn oxyhydroxide application also affected soil fatty acid biomarkers related to the sulfur cycle, which may impact both barite reduction and sulfide oxidation. (AU)

• FAPESP's process: 19/02796-3 - Effects of organic matter and microbial community structure on the availability and phytoremediation of BA (barite) in flooded soils
• Grantee: Douglas Gomes Viana
• Support Opportunities: Scholarships in Brazil - Doctorate