Sorption-desorption and biodegradation of sulfometuron-methyl and its effects on the bacterial communities in Amazonian soils amended with aged biochar.

Sulfometuron-methyl is a broad-spectrum herbicide, used throughout Brazil; however, its environmental impacts in biochar (BC) amended soils is not fully understood. Biochar is known to enhance soil quality but can also have undesired effects such as altering the bioavailability and behavior of herbicides. Microbial communities can degrade herbicides such as sulfometuron-methyl in soils; however, they are known to be affected by BC. Therefore, it is important to understand the tripartite interaction between these factors. This research aimed to evaluate the sorption-desorption and biodegradation of sulfometuron-methyl in Amazonian soils amended with BC, and to assess the effects of the interactions between BC and sulfometuron-methyl on soil bacterial communities. Soil samples were collected from field plots amended with BC at three doses (0, 40 and 80 t ha-1) applied ten years ago. The herbicide sorption and desorption were evaluated using a batch equilibrium method. Mineralization and biodegradation studies were conducted in microcosms incubated with 14C-sulfometuron-methyl for 80 days. Systematic soil sampling, followed by DNA extraction, quantification (qPCR) and 16S rRNA amplicon sequencing were performed. The presence of BC increased the sorption of the herbicide to the soil by 11% (BC40) and 16% (BC80) compared to unamended soil. The presence of BC also affected the degradation of 14C-sulfometuron-methyl, reducing the mineralization rate and increasing the degradation half-life times (DT50) from 36.67 days in unamended soil to 52.11 and 55.45 days in BC40 and BC80 soils, respectively. The herbicide application altered the bacterial communities, affecting abundance and richness, and changing the taxonomic diversity (i.e., some taxa were promoted and other inhibited). A tripartite interaction was found between BC, the herbicide and soil bacterial communities, suggesting that it is important to consider the environmental impact of soil applied herbicides in biochar amended soils.

Organic residues and biochar to immobilize potentially toxic elements in soil from a gold mine in the Amazon.

Waste from gold mining (Au) is a threat to the ecosystem and human health because it contains high levels of potentially toxic elements (PTEs). Organic waste and biochar can be used to recover contaminated soils from mining areas because they have the potential to immobilize PTEs and improve soil fertility, enabling revegetation. The objective of this study was to investigate the efficiency with which organic residues and biochar immobilize PTEs in a multicontaminated soil of a small-scale Au mine in the state of Pará. The soil from a gold mining area was mixed with different proportions (v/v) of coffee ground residues (Bcoffee), Brazil nut tegument residues (BN), açai palm stone residues (A), and Brazil nuts biochar residues to determine which treatment is best for immobilizing PTEs. The treatments with the addition of BN and A resulted in low pH and high contents of organic matter (OM) and phosphor (P) The BN increased the available levels of Ba and reduced the available levels of Ni. The addition of coffee ground residues and biochar increased the uptake of Ba, Pb, and Ni in lettuce plants compared to treatments with BN and A. Plants grown with A showed higher dry matter yield and lower absorption and translocation of PTEs. Thus, the addition of BN and A residues in PTE phytostabilization programs in PTE-multicontaminated soils is a potential possibility.