Inland surface water plays an important role in global carbon cycling, which responds to transformation between dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). Studies have shown that algae in karst lakes and reservoirs can convert DIC to organic matter (OM) and form stable carbon sinks via photosynthesis. However, the pathways of conversion of inorganic carbon to organic carbon during algal growth remain unclear and need further investigation. In this study, spectroscopic techniques were applied to investigate the variations in algal organic matter (AOM) composition in the growth metabolism of Chlorella vulgaris and Scenedesmus obliquus under simulated karst water condition. The results showed that algal extracellular organic matter (EOM) contained high DIC concentration during the adaptation phase, which formed the carbon source for algal photosynthesis. In addition, DOC in algae increased after entering the stationary phase, while more OM was released into water. As algal growth proceeded, the amino groups in EOM were consumed to produce more aromatic protein-like material, while more lipid material was produced in intracellular organic matter (IOM). The spectral characterization results could intuitively determine AOM dynamics in different growth stages of algae, which can be used for establishing effective approaches for detecting organic carbon variations and responding to regional carbon cycling in karst water.

The health risk of potentially toxic elements (PTEs) via contamination of the food chain has attracted widespread concern. The aim of this study is to evaluate the effects of PTEs in environment and human body (fingernail, hair, and blood) of people living in agricultural soil near arsenic coal mining areas in Xingren County (Guizhou, southwest China). 89 crop samples which included vegetables, rice, maize, and coix seed and their corresponding soils and 17 local surface water and biological tissue samples (41 × 3) in near arsenic coal mining areas were collected, and the concentrations of potentially toxic elements (As, Cd, Cu, Cr, and Pb) in all the samples were determined. The health risk assessment methods developed by the United States Environmental Protection Agency were employed to explore the potential health hazards of PTEs in soils growing crops. Results showed that 4 toxic elements, Cd, Cu, As, and Cr, were found to have different degrees of contamination in soils in the studied area. The total concentration of toxic elements (As, Cr, Cu, and Pb) in fingernail, hair, and blood samples were 90.50, 69.31, and 6.90 mg·kg⁻¹, respectively. Fingernail samples from females were more likely to show exposure to trace metals compared to males. As the age of the subject increased, the concentration of As also increased in all three biological samples. The risk assessment for the mean hazard index value from the consumption of local food crops was 14.81, indicating that consumers may experience adverse, noncarcinogenic health effects. The estimated mean total cancer risk value of was 5.3 × 10⁻³, which was approximately 10 to 1000 times higher than the acceptable range of 10⁻⁶–10⁻⁴, indicating serious carcinogenic risks for local people consuming crops from the area. This study provides evidence that local residents in this study area may be at a high risk of disease caused from toxic element exposure.

Sandy soils in tropical areas are more vulnerable to potential toxic elements as a result of their low nutrition. The composite addition of biochar and phosphate material is considered a promising method of immobilizing toxic metals in sandy soils, but the synergistic effects of this process still need to be further explored, especially in typical tropical vegetables. In this study, a pot experiment was conducted to evaluate the agronomic and toxic metal-immobilization effects of single amendments (phosphate rock, activated phosphate rock, and biochar) and combined amendments, including biochar mixed with phosphate rock (BCPR) and biochar mixed with activated phosphate rock (BCAPR), on vegetables grown in tropical sandy soil. Among these amendments, the composite amendment BCAPR was the most effective for increasing Ca, Mg, and P uptake based on water spinach (Ipomoea aquatica L.) and pepper (Capsicum annuum L.), showing increased ratios of 22.5%, 146.0%, and 136.0%, respectively. The SEM-EDS and FTIR analysis verified that the activation process induced by humic acid resulted in the complexation and chelation of the elements P, Ca, and Mg into bioavailable forms. Furthermore, the retention of available nutrition elements was enhanced due to the strong adsorption capacity of the biochar. In terms of cadmium (Cd) and lead (Pb) passivation, the formation of insoluble mineral precipitates reduced the mobility of these metals within the BCAPR treatments, with the maximum level of extractable Cd (86.6%) and Pb (39.2%) reduction being observed in the tropical sandy soil. These results explore the use of sustainable novel cost-effective and highly efficient bi-functional mineral-based soil amendments for metal passivation and plant protection.