The combined effect of phosphorus forms and zinc on arsenic toxicity and bioaccumulation in Phaeodactylum tricornutum

Microalgae employ transporter proteins that are shared arsenate (As(V)) to efficiently uptake phosphate (dissolved inorganic phosphorus, DIP). Additionally, zinc-activated enzymes, alkaline phosphatase (AP), drive the dissolved organic phosphorus (DOP) assimilation, thereby intricately linking the dynamics of zinc (Zn), phosphorus (P), and As(V). This study investigated the effects of two distinct P forms (DOP and DIP) and Zn levels on the toxicity and bioaccumulation of As(V) in Phaeodactylum tricornutum. The results showed that P. tricornutum showed a marked decrease in chlorophyll a (Chl a), maximal photochemical efficiency of Photosystem II (Fv/fm) parameter for plant stress detection, and cell density in DOP cultures compared with DIP cultures. However, the supplementation of Zn alleviated the development of P. tricornutum in DOP conditions. Furthermore, the results also indicated that the 96-h EC₅₀ values of As(V) toxicity in P. tricornutum was enhanced by DOP, but the addition of Zn alleviates this effect. Moreover, the intracellular As of P. tricornutum was reduced by 35.79 %, and 36.80 % in DOP+Zn culture compared to DOP culture at 0.05, and 0.1 μmol·L⁻¹ As(V) exposures, respectively. However, there were no significant differences between Zn additions to the growth and intracellular As of P. tricornutum in DIP conditions. These results suggest that DOP enhances As toxicity in microalgae, but Zn can significantly attenuate the toxicity and bioaccumulation of As in microalgae under DOP, thereby impacting the cycling of As in marine ecosystems.