Influence of PbS nanoparticle polymer coating on their aggregation behavior and toxicity to the green algae Dunaliella salina

• Lead sulfide nanoparticles (PbS NPs) are toxic to D. salina.
• Gum-Arabic coating alters the toxicity of PbS NPs.
• Cell-NPs agglomerates and lipid peroxidation could explain the toxicity of PbS NPs.
• Shading effect and dissolution do not seem to contribute to the toxicity of PbS NPs.
• Particle–particle interaction was reduced by coating; therefore, PbS NPs were stabilized in the culture media.

The potential hazards of nanoparticles (NPs) to the environment and to living organisms need to be considered for a safe development of nanotechnology. In the present study, the potential toxic effects of uncoated and gum Arabic-coated lead sulfide nanoparticles (GA-coated PbS NPs) on the growth, lipid peroxidation, reducing capacity and total carotenoid content of the hypersaline unicellular green algae Dunaliella salina were investigated. Coatings of PbS NPs with GA, as confirmed by Fourier transform infrared spectroscopy, reduced the toxicity of PbS NPs. Uncoated PbS NP toxicity to D. salina was attributed to higher algal cell-NP agglomerate formation, higher lipid peroxidation, lower content of total reducing substances and lower total carotenoid content. Low levels of Pb2+ in the growth culture media indicate that PbS NP dissolution does not occur in the culture. Also, the addition of 100 μM Pb2+ to the culture media had no significant (P > 0.05) effect on algal growth. The shading of light (shading effect) by PbS NPs, when simulated using activated charcoal, did not contribute to the overall toxic effect of PbS NPs which was evident by insignificant (P > 0.05) reduction in the growth and antioxidant capacity of the algae. When PbS NP aggregation in culture media (without algal cells) was followed for 60 min, uncoated form aggregated rapidly reaching aggregate sizes with hydrodynamic diameter of over 2500 nm within 60 min. Effective particle–particle interaction was reduced in the GA-coated NPs. Aggregates of about 440 nm hydrodynamic diameter were formed within 35 min. Afterwards the aggregate size remained constant. It is concluded that PbS NPs have a negative effect on aquatic algae and their transformation by GA capping affects NPs aggregation properties and toxicity.