Environmental safety of energy storing devices using carbon nanotubes: possible impacts of waste in aquatic and terrestrial environments

Abstract

Electric double layer capacitors (EDLC) are energy storage devices based on the charging and discharging electrode-electrolyte interfaces of high surface area materials such as multi-walled carbon nanotubes (MWCNT) and activated carbon (AC). Despite the broad applicability, the final destination of these components is the environment, mainly water and soil, where they can represent impacts on organisms along different trophic levels. Bioassays with Raphidoceles subcapitata, are widely used to evaluate aquatic totoxicity  and oligochaetes are good terrestrial bioindicators. The study aimed to evaluate aquatic and terrestrial toxicity of MWCNT from EDLC-type capacitors using bioindicators, R. subcapitata and Eisenia andrei. The MWCNT material was synthesized by the floating catalyst-based chemical vapor deposition method (FC-CVD) on stainless steel (AISI 304L). The MWCNT concentrations for the assays were 0.1 1.0, 10 and 100 mg.L^–1 for the bioindicator R. subcapitata and the concentrations of 1, 10 and 100 mg.Kg^–1 for bioindicator E. andrei. MWCNT inhibited the algal biomass in a concentration dependent manner at concentrations higher than 10 mg.L^–1. In the soil the presence of MWCNT, at the concentrations tested did not cause mortality in the earthworm, but resulted in a significant mass reduction in the exposed organisms after 14 days. In the cytology analysis, it was not observed the production of micronuclei, but cytoplasmic vacuolization and nuclear atypia in coelomocytes were frequent. In the comet assay, there was a predominance of nucleoids in the stage 1 classification. Thus, no genotoxic effect was demonstrated in these organisms. The concentrations that showed toxic effects are within the range of environmentally expected concentrations. MWCNT are released from EDLC and may pose an occupational and environmental risk.