Carbon nanomaterials differentially impact bioaccumulation and oxidative response of phenanthrene and methyl derivatives in geophagous earthworms (Metaphire guillelmi): A multi-contaminant exposure study

Abstract

Carbon nanomaterials (CNMs) are increasingly released to the terrestrial system, but information on their environmental fate and risk is rather limited. Fullerenes (C60) and two multi-walled carbon nanotubes (outer diameter <8 nm: MW8; >50 nm: MW50) were added to soil to evaluate their impact on bioaccumulation and oxidative response of phenanthrene, 3-methylphenanthrene and 3,6-dimethylphenanthrene by the geophagous earthworm Metaphire guillelmi under single- (F1), bi- (F2) and tri- contaminant (F3) systems. High-sorption CNMs exhibited little or suppression effect on phenanthrene and 3-methylphenanthrene bioaccumulation, whereas these treatments stimulated 3,6-dimethylphenanthrene bioaccumulation (6.1–25.9%), indicating a dissimilar role of CNMs on contaminant uptake as a function of analyte type. Compared to the single-contaminant system, the alleviated suppression effect of certain CNM treatments on bioaccumulation of both compounds in F2 system, as well as the sorption- and dose-dependent bioavailability of two methylphenanthrenes in F3 system revealed significant and dissimilar molecular interactions in multi-contaminant systems. CNMs mitigated the synergetic bioaccumulation of three compounds except for 3,6-dimethylphenanthrene under MW8 co-exposure. Oxidative stress did occur in all three systems but only high-level CNMs in F3 system triggered significant damage with considerable MDA (malondialdehyde) generated in earthworms. This study provides insight into CNM-contaminant exposure and risk under environmentally relevant scenarios and highlights the importance of considering these complexities when assessing overall risk.