Ecologically Relevant and pH-dependent Freshwater Quality Criteria for Vanadium in China

Vanadium is an emerging pollutant of concern due to its increasing industrial use and the associated ecological risks in freshwater environments. This study developed a speciation-informed empirical framework for pH-dependent vanadium toxicity in freshwater using experimental and literature data. Linear mixed-effects modeling of published toxicity data showed that vanadium toxicity increased with pH. Acute toxicity tests across pH 6.0-9.0 showed generally consistent pH-dependent responses across the tested taxa. A V species-based log-ratio model associated the observed toxicity pattern with pH-driven changes in the relative abundances of dominant aqueous V(V) species. Using the pH-normalized toxicity dataset, species sensitivity distributions were constructed to derive hazardous concentration thresholds protecting 95% of species. Accordingly, pH-dependent acute criterion and a provisional pH-adjusted chronic criterion were derived. The resulting pH-dependent criteria followed exponential relationships, yielding criterion maximum concentration (acute) and provisional criterion continuous concentration (chronic) values of 4022e^-0.332pH μg/L and 788e^-0.373pH μg/L, respectively, and were used to quantify non-zero ecological risks and associated uncertainties using compiled surface water records. The ACR approach produced lower chronic HC₅ and was retained as a conservative sensitivity scenario. Overall, vanadium toxicity in freshwater appears to be linked to shifts in aqueous speciation, providing a speciation-informed empirical basis for pH-dependent water quality criteria.