Exploring phosphate impact on arsenate uptake and distribution in freshwater phytoplankton: Insights from single-cell...

In this study, we investigated the interaction between arsenate (As^V) and phosphate (PO₄^3-) in freshwater phytoplankton using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS). This study aimed to elucidate the influence of varying PO₄^3- concentrations on arsenic (As) uptake and distribution at the single-cell level, providing insights into intraspecies diversity. Two species of freshwater phytoplanktons, Scenedesmus acutus and Pediastrum duplex, were cultured under different concentrations of PO₄^3- and As^V in a controlled laboratory environment. Scenedesmus acutus, a species with strong salt tolerance, and Pediastrum duplex, known for its weak salt tolerance, were selected based on their contrasting behaviors in previous studies. SC-ICP-MS revealed non-uniform uptake of As by individual phytoplankton cells, with distinct variations in response to PO₄^3- availability. Arsenic uptake by both species declined with a high PO₄^3- level after 7 days of exposure. However, after 14 days, As uptake increased in S. acutus with higher PO₄^3- concentrations, but decreased in P. duplex. Moreover, our findings revealed differences in cell morphology and membrane integrity between the two species in response to As^V and various PO₄^3- concentrations. S. acutus maintained cell integrity under all experimental culture conditions, whereas P. duplex experienced cell lysis at elevated As^V and PO₄^3- concentrations. This study highlights the varying responses of freshwater phytoplankton to changes in As^V and PO₄^3- levels and underscores the advantages of SC-ICP-MS over conventional ICP-MS in providing detailed, cellular level insights. These findings are crucial for understanding and managing As pollution in aquatic ecosystems.