Nanoparticle-mediated modulation of microalgae to heavy metal co-exposure stress: A meta-analysis

Nanoparticles (NPs) and heavy metals co-exist as pervasive contaminants in aquatic environments, inevitably interacting with microalgae. Current understanding of the combined stress of NPs and heavy metals on microalgae, despite some revealing studies, is hindered by a narrow investigation scope across NP types, heavy metals, and microalgae. Utilizing a meta-analytic approach with standardized mean difference (SMD) and random-effects models, this study synthesizes 392 observations from 16 global publications to systematically assess NPs' regulatory roles in microalgal responses to heavy metal stress. The results demonstrate that the effects of combined NPs and heavy metals stress on algae is related to algae species, NPs and heavy metals types. In terms of algae species, a stress gain effect is observed in specific green algae such as Chlamydomonas reinhardtii and Scenedesmus obliquus, leading to enhanced cell proliferation rates. In contrast, diatoms exhibit a certain degree of growth inhibition. Regarding NP types, photoactive materials such as quantum dots (QDs) and silver nanoparticles (Ag NPs) amplify toxicity, whereas inert materials like polystyrene nanoparticles (PS NPs) mitigate cellular damage. In terms of heavy metal properties, cadmium (Cd) and lead (Pb) exert distinct stress effects, thereby differentially influencing the physiological status of microalgae. These findings provide mechanistic insights into NPs' pivotal role in modulating microalgal-heavy metal interactions, advancing risk assessment frameworks for aquatic ecosystems impacted by multi-pollutant stress.