Boron toxicity coefficient calculation and application for ecological risk assessment in reservoir sediments

Abstract B is a potentially toxic element, and its potential ecological influences in aquatic environments have gained increasing attention in recent years, especially in reservoir ecosystems. As the largest freshwater reservoir in China, the estimation of B's ecological risks in the Three Gorges Reservoir (TGR) is critical for national drinking water safety. However, the lack of a toxicity coefficient (Tc) for B limits its ecological risk assessment (Er) in aquatic environments, especially for sediments. In this study, the Tc of B was carefully calculated, considering toxicological, sedimentological, and ecological ranking factors. The Er for B was then assessed for surface sediments collected from the TGR. Enrichment factors (EFs) were also used to identify the influence of human activities on B. The results show that the average concentrations of B in mainstream and tributary sediments were 53.98 mg/kg and 90.88 mg/kg, respectively, slightly higher than sediment background B values in China (48 mg/kg). Additionally, EFs showed that the tributary sediments were moderately enriched in B. The EF-1.5 value was higher than zero, indicating that the stronger anthropogenic influence in tributary sediments than in mainstream sediments. Moreover, chemical speciation of B in TGR sediments was mainly attributed to the residual fraction, indicating weak migration of B in sediments. Furthermore, after calculating Tc according to the principles of Er, it was found that it is more scientific to assign the Tc of B in sediments a value of 2. Based on this Tc value, the Er in the TGR was assessed and it revealed that B in TGR sediments had low ecological risk. The scientific calculation of the Tc provides an important parameter for B ecological risk assessments in aquatic environments in the future.