环境科学与技术最新文献

New sources of rare earth elements (REEs) are needed to support a green energy transition. REEs adsorbed to aluminum-rich clays in weathering deposits represent important resources, but the mechanisms responsible for their retention and ease of extraction are unresolved. Disordered coordination and co-occurrence of multiple species pose challenges to investigating REE adsorption processes via established spectroscopic methods. In this study, we applied element-specific surface crystallography methods to obtain a new perspective on the complexity of REE adsorption mechanisms and affinities. Alumina (001) and (012) crystal surfaces were utilized to evaluate surface-specific controls on Nd(III) and Yb(III) adsorption behavior. The REEs displayed similar total adsorption to alumina (001) as a mixture of inner- and outer-sphere complexes, but Nd displayed a greater proportion of inner-sphere binding. Adsorption of ordered inner- and outer-sphere REE species was substantially lower on alumina (012). These distinct behaviors reflect differences in the surface functional group charging and topography of the two surfaces. However, alumina (012) also hosted a substantial population of disordered adsorbed species, especially for Nd, potentially associated with Al vacancy surface defects. The accumulation of light versus heavy REEs via adsorption in weathering deposits likely results from multiple, competing reactions affected by clay particle morphology. Leaching procedures for resource recovery should account for differential rates of desorption by coexisting inner- and outer-sphere REE surface complexes.

Estuarine transition zones (ETZs) are biogeochemically complex, nutrient-rich environments supporting diverse and productive food webs. They may also be sites of microbial production of methylmercury (MeHg) and bioaccumulation of this neurotoxicant at the base of the food web. However, the environmental drivers controlling these mechanisms are unclear. We studied the pattern of MeHg bioaccumulation in zooplankton along the 200 km ETZ of a large North American estuary, the St. Lawrence Estuary (Québec, Canada). Our approach integrated the dynamic variation in ETZ geochemistry, focusing on MeHg speciation change, alongside ecological factors, including community composition and stable isotopic tracers of diet and habitat. MeHg bioaccumulation decreased with distance downstream along the ETZ, driven by the salinity gradient and traced by the isotopic signature of sulfur in zooplankton. MeHg speciation modeling suggested that complexation to dissolved organic matter may be used as a proxy of the trophic transfer of MeHg to zooplankton. Further, the binding of MeHg to organic matter was reduced by the presence of chloride, thus reducing the trophic transfer of MeHg. We propose a conceptual model for MeHg cycling in ETZ of large estuaries that hypothesizes that higher-level consumers in turbid upstream regions may face heightened risks of MeHg toxicity but that Hg levels diminish drastically as salinity increases.

Wildfires remarkably alter the quantity and quality of dissolved organic matter (DOM) that regulates postfire biogeochemical processes and environmental quality. However, it remains unclear how the heating-induced percent changes (%HIC) in DOM quantity and quality differ among soil types on a wide geographic scale. Here, we used dissolved organic carbon (DOC) quantification, absorption, and fluorescence spectroscopies, and Fourier transform ion cyclotron resonance mass spectrometry to investigate the variations in %HIC in DOM quantity and quality of Chinese soil reference materials after heating at 250 and 400 °C. Our results reveal that as soil pH increased, %HIC in DOC content increased, while %HIC in aromaticity-related indices of DOM decreased for both heating temperatures. Moreover, the %HIC in DOM biolability and contents of aliphatics increased with soil pH for 250 °C heating but remained relatively stable for 400 °C heating. Results suggest that compared to those in acidic soil-dominated forests, wildfires in alkaline soil-dominated forests may cause greater DOM content and biolability in soils, which may facilitate postfire microbial recovery. These findings deepen our understanding of the site-specific impacts of wildfires on DOM and the subsequent implications for biogeochemical cycling and environmental quality across different geographic regions.