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Sorption of Monothioarsenate to the Natural Sediments and Its Competition with Arsenite and Arsenate.

ABSTRACT: Monothioarsenate (MTAs^V) is one of the major arsenic species in sulfur- or iron-rich groundwater, and the sediment adsorption of MTAs^V plays an important role in arsenic cycling in the subsurface environment. In this study, batch experiments and characterization are conducted to investigate the sorption characteristic and mechanism of MTAs^V on natural sediments and the influences of arsenite and arsenate. Results show that MTAs^V adsorption on natural sediments is similar to arsenate and arsenite, manifested by a rapid early increasing stage, a slowly increasing stage at an intermediate time until 8 h, before finally approaching an asymptote. The sediment sorption for MTAs^V mainly occurs on localized sites with high contents of Fe and Al, where MTAs^V forms a monolayer on the surface of natural sediments via a chemisorption mechanism and meanwhile the adsorbed MTAs^V mainly transforms into other As species, such as AlAs, Al-As-O, and Fe-As-O compounds. At low concentration, MTAs^V sorption isotherm by natural sediments becomes the Freundlich isotherm model, while at high concentration of MTAs^V, its sorption isotherm becomes the Langmuir isotherm model. The best-fitted maximum adsorption capacity for MTAs^V adsorption is about 362.22 μg/g. Furthermore, there is a competitive effect between MTAs^V and arsenate adsorption, and MTAs^V and arsenite adsorption on natural sediments. More specifically, the presence of arsenite greatly decreases MTAs^V sorption, while the presence of MTAs^V causes a certain degree of reduction of arsenite adsorption on the sediments before 4 h, and this effect becomes weaker when approaching the equilibrium state. The presence of arsenate greatly decreases MTAs^V sorption and the presence of MTAs^V also greatly decreases arsenate sorption. These competitive effects may greatly affect MTAs^V transport in groundwater systems and need more attention in the future.

SUBMITTER: Shan H

PROVIDER: S-EPMC8657673 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundVeterinary pharmaceuticals can enter the environment when excreted after application and burden terrestrial and aquatic ecosystems. However, knowledge about the basic process of sorption in soils and sediments is limited, complicating regulatory decisions. Therefore, batch equilibrium studies were conducted for the widely used antiparasitics abamectin, doramectin, ivermectin, and moxidectin to add to the assessment of their environmental fate.ResultsWe examined 20 soil samples and six sediments from Germany and Morocco. Analysis was based on HPLC-fluorescence detection after derivatization. For soils, this resulted in distribution coefficients K D of 38-642 mL/g for abamectin, doramectin, and ivermectin. Moxidectin displayed K D between 166 and 3123 mL/g. Normalized to soil organic carbon, log K OC coefficients were 3.63, 3.93, 4.12, and 4.74 mL/g, respectively, revealing high affinity to organic matter of soils and sediments. Within sediments, distribution resulted in higher log K OC of 4.03, 4.13, 4.61, and 4.97 mL/g for the four substances. This emphasizes the diverse nature of organic matter in both environmental media. The results also confirm a newly reported log KOW for ivermectin which is higher than longstanding assumptions. Linear sorption models facilitate comparison with other studies and help establish universal distribution coefficients for the environmental risk assessment of veterinary antiparasitics.ConclusionsSince environmental exposure affects soils and sediments, future sorption studies should aim to include both matrices to review these essential pharmaceuticals and mitigate environmental risks from their use. The addition of soils and sediments from the African continent (Morocco) touches upon possible broader applications of ivermectin for human use. Especially for ivermectin and moxidectin, strong sorption further indicates high hydrophobicity and provides initial concern for potential aquatic or terrestrial ecotoxicological effects such as bioaccumulation. Our derived K OW estimates also urge to re-assess this important regulatory parameter with contemporary techniques for all four substances.Graphic abstractSupplementary informationThe online version contains supplementary material available at 10.1186/s12302-021-00513-y.

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Sorption of Monothioarsenate to the Natural Sediments and Its Competition with Arsenite and Arsenate.

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