Integrating effective concentration modeling with single cell-ICPMS to address the influence of exposure conditions when evaluating mercury-selenium interaction in human neuroblastoma cell line

In this study, the potential protective role of Se(IV) against inorganic Hg-induced cytotoxicity was evaluated in the human neuroblastoma SH-SY5Y cell line using inductively coupled plasma mass spectrometry, both in conventional (ICP-MS) and single-cell (scICP-MS) modes. To this end, Se (25, 50, and 70 μmol Se L -1 ) was tested against equivalent concentrations of inorganic Hg (25, 50, and 70 μmol Hg L -1 ) under both co-exposure and pre-treatment conditions. Cell viability assessed using the MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), showed that Se (IV) at 25 and 50 μmol Se L -1 significantly attenuated Hg(II)-induced cytotoxicity, with pre-treatment demonstrating greater efficacy than co-exposure. Additionally, a chemical speciation model was applied to estimate the effective concentrations of Hg and Se available to cells relative to the nominal doses. scICP-MS measurements revealed heterogeneous Hg uptake among individual cells. Notably, co-exposure with 25 μmol Se L -1 reduced cellular Hg accumulation from 73 fg Hg cell -1 to 61 fg Hg cell -1 , while pre-treatment further decreased it to 42 fg Hg cell -1 . Overall, these findings suggest that selenium mitigates Hg-induced cytotoxicity primarily by reducing intracellular Hg accumulation, highlighting its modulatory role at the single-cell level. By integrating effective concentration modeling with single-cell metal quantification, this work highlights the importance of considering the bioavailable fraction of trace elements in toxicity assessments. • Pre-treatment and co-exposure scenarios reveal distinct Se-Hg cellular interactions. • Se pre-treatment mitigates Hg-induced cytotoxicity more effectively than co-exposure. • Effective concentration modelling improves interpretation of single-cell metal toxicity. • SEC-ICP-MS shows Hg biomolecules-bound, while Se remains mainly free in culture media. • Se pre-treatment reduces both the proportion of cells with high Hg and intracellular Hg levels.