A comparison of fate and toxicity of selenite, biogenically, and chemically synthesized selenium nanoparticles to zebrafish (Danio rerio) embryogenesis

Abstract

Microbial reduction of selenium (Se) oxyanions to elemental Se is a promising technology for bioremediation and treatment of Se wastewaters. But a fraction of biogenic nano-Selenium (nano-Se^b) formed in bioreactors remains suspended in the treated waters, thus entering the aquatic environment. The present study investigated the toxicity of nano-Se^b formed by anaerobic granular sludge biofilms on zebrafish embryos in comparison with selenite and chemogenic nano-Se (nano-Se^c). The nano-Se^b formed by granular sludge biofilms showed a LC₅₀ value of 1.77 mg/L, which was 3.2-fold less toxic to zebrafish embryos than selenite (LC₅₀=0.55 mg/L) and 10-fold less toxic than bovine serum albumin stabilized nano-Se^c (LC₅₀=0.16 mg/L). Smaller (nano-Se^cs; particle diameter range: 25–80 nm) and larger (nano-Se^cl; particle diameter range: 50–250 nm) sized chemically synthesized nano-Se^c particles showed comparable toxicity on zebrafish embryos. The lower toxicity of nano-Se^b in comparison with nano-Se^c was analyzed in terms of the stabilizing organic layer. The results confirmed that the organic layer extracted from the nano-Se^b consisted of components of the extracellular polymeric substances (EPS) matrix, which govern the physiochemical stability and surface properties like ζ-potential of nano-Se^b. Based on the data, it is contented that the presence of humic acid like substances of EPS on the surface of nano-Se^b plays a major role in lowering the bioavailability (uptake) and toxicity of nano-Se^b by decreasing the interactions between nanoparticles and embryos.

Keywords:

• Biogenic nanomaterials
• selenium bioremediation
• zebrafish
• EPS
• nanotoxicology

Acknowledgements

The authors would like to thank Gerda Lamers (Leiden University) for the technical help of transmission electron microscopy.

Disclosure statement

The authors declare that there are no conflicts of interest.

Additional information

Funding

This research was supported through the Erasmus Mundus Joint Doctorate Environmental Technologies for Contaminated Solids, Soils, and Sediments (ETeCoS³, FPA no. 2010-0009) and the Marie Curie International Incoming Fellowship Role of biofilm-matrix components in the extracellular reduction and recovery of chalcogens (BioMatch, project No. 103922).