A comparison of fate and toxicity of selenite, biogenically, and chemically synthesized selenium nanoparticles to zebrafish (<i>Danio rerio</i>) 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.