Ecotoxicological assessment of MWCNT-reinforced MOC composites: impacts on model bacteria and eukaryotes with environmental relevance†

Abstract

Composite materials based on magnesium oxychloride cement (MOC), reinforced with multi-walled carbon nanotubes (MWCNT) and their oxidized form (MWCNT-ox), are promising eco-friendly building materials. However, little is known about their ecotoxicological impact. This study pioneers the evaluation of MWCNT-reinforced MOC effect on selected prokaryotic (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa) and eukaryotic (Artemia salina, Sinapis alba, Desmodesmus subspicatus) organisms. Initially, the effects of MWCNT and MWCNT-ox at concentrations of 1 g L⁻¹, 0.1 g L⁻¹, and 0.01 g L⁻¹ on the growth and proliferation of organisms were assessed. While MWCNT samples did not affect bacterial growth or eukaryotic viability, they significantly inhibited bacterial biofilm formation. The antibiofilm effect varied among the tested bacteria, with S. aureus and E. coli being significantly more inhibited than P. aeruginosa. No differences were observed between the effects of MWCNT and MWCNT-ox on bacteria, while MWCNT-ox exhibited higher toxicity toward the tested eukaryotic organisms. Subsequently, MOC reference (MOC-REF) and MWCNT-reinforced MOC samples (MOC-MWCNT, MOC-MWCNT-ox) were prepared and characterized using XRD and SEM-EDS. Ecotoxicological assays confirmed that the composites inhibited both bacterial growth and biofilm formation, a highly desirable outcome, as microbial degradation compromises the longevity of building materials. The incorporation of MWCNT enhanced the antibacterial effect of MOC. Further, the addition of MWCNT and MWCNT-ox to MOC did not affect A. salina mortality, S. alba seed germination, or D. subspitatus growth. However, inhibition of S. alba root growth was observed at the highest tested concentration (1 g L⁻¹) for all MOC samples, regardless of MWCNT presence. Overall, the results indicate a low environmental impact of the prepared MOC-MWCNT and MOC-MWCNT-ox composites.