RESUMEN
In this study, we investigated the interaction between arsenate (AsV) and phosphate (PO43-) in freshwater phytoplankton using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS). This study aimed to elucidate the influence of varying PO43- 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 PO43- and AsV 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 PO43- availability. Arsenic uptake by both species declined with a high PO43- level after 7 days of exposure. However, after 14 days, As uptake increased in S. acutus with higher PO43- concentrations, but decreased in P. duplex. Moreover, our findings revealed differences in cell morphology and membrane integrity between the two species in response to AsV and various PO43- concentrations. S. acutus maintained cell integrity under all experimental culture conditions, whereas P. duplex experienced cell lysis at elevated AsV and PO43- concentrations. This study highlights the varying responses of freshwater phytoplankton to changes in AsV and PO43- 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.
RESUMEN
Salinity stress affects aquatic microalgal growth and their physiological responses have been studied extensively. However, arsenic (As) accumulation and biotransformation by freshwater phytoplankton under a salinity gradient have never been addressed. This study reports a distinctive pattern of As uptake, accumulation, and biotransformation by four axenic freshwater phytoplankton species, i.e., Scenedesmus acutus, Closterium aciculare, Staurastrum paradoxum, and Pediastrum duplex. Phytoplankton cells were incubated in sterilised C medium modified with varying salinity levels (0-5) in association with arsenate and phosphate concentrations. The biotransformation of arsenate (i.e., As(V)) to arsenite (As(III)) and to further methylated species decreased with increasing salinity in the culture medium whereas As accumulation increased. Among the four strains, only S. acutus and S. paradoxum converted As(V) to As(III), with no detected methylated species. In contrast, C. aciculare and P. duplex biotransformed As(V) to As(III) and further to methyl arsenic species, such as DMAA. S. acutus and S. paradoxum exhibited higher accumulation tendency than the other two species. S. paradoxum showed the lowest As reduction rate (i.e., As(V) to As(III)) compared to other species, although, without significant variations. The morphological changes were observed in phytoplankton cells in response to increased salinity stress. Moreover, As(V) concentrations in the culture medium significantly decreased by day 7-14. Thus, this study presents a conceptual model of the As biotransformation pattern by axenic freshwater phytoplankton.