Deciphering the Impact of ZnO Nanoparticles and a Sunscreen Product Containing ZnO on Phosphorus Dynamics and Release in Chlorella pyrenoidosa in Aquatic Systems

Abstract

Zinc oxide nanoparticles (ZnO NPs) expedite the conversion of organic phosphorus (OP) into PO 4 −P (Pi), facilitating phosphorus (P) absorption by algae. Our study explored the mechanisms of converting OP (2-aminoethylphosphonic acid (AEP) and β-glycerol phosphate (β-GP)) into Pi in Chlorella pyrenoidosa under P deficiency with sunscreen and ZnO NPs. Cell density followed the order of K 2 HPO 4 > β-GP+ZnO > β-GP > AEP+ZnO > AEP > P-free. ZnO NPs promoted the conversion of β-GP, containing C−O−P bonds (0.028−0.041 mg/ L), into Pi more efficiently than AEP, which possesses C−P bonds (0.022−0.037 mg/L). Transcriptomics revealed Pi transport/ metabolism (phoB (3.99−12.01 fold), phoR (2.20−5.50 fold), ppa (4.49−10.40 fold), and ppk (2.50−5.40 fold)) and phospholipid metabolism (SQD1 (1.85−2.79 fold), SQD2 (2.60−6.53 fold), MGD (2.13−3.21 fold), and DGD (4.08−7.56 fold)) were up-regulated compared to K 2 HPO 4 . 31 P nuclear magnetic resonance spectroscopy identified intracellular P as polyphosphate, orthophosphate, and pyrophosphate. Synchrotron radiation-based X-ray near-edge structure spectroscopy indicated that K 2 HPO 4 and Zn 3 (PO 4 ) 2 in β-GP+ZnO were increased by 8.09% and 7.28% compared to AEP+ZnO, suggesting superior P storage in β-GP+ZnO. Overall, ZnO NPs improved photoinduced electron−hole pair separation and charge separation efficiency and amplified the •OH and •O 2 − levels, promoting OP photoconversion into Pi and algae growth.