Synergistic Mitochondrial Genotoxicity of Carbon Dots and Arsenate in Earthworms Eisenia fetida across Generations: The Critical Role of Binding

The
escalating utilization of carbon dots (CDs) in agriculture
raises ecological concerns. However, their combined toxicity with
arsenic remains poorly understood. Herein, we investigated the combined
mitochondrial genotoxicity of CDs and arsenate at environmentally
relevant concentrations across successive earthworm generations. Iron-doped
CDs (CDs–Fe) strongly bound to arsenate and arsenite,
while nitrogen-doped CDs (CDs–N) exhibited weaker
binding. Both CDs enhanced arsenate bioaccumulation without affecting
its biotransformation, with most arsenate being reduced to arsenite.
CDs–Fe generated significantly more reactive oxygen
species than did CDs–N, causing stronger mitochondrial
DNA (mtDNA) damage. Arsenate further exacerbated the oxidative mtDNA
damage induced by CDs–N, as evidenced by increased
reactive oxygen species, elevated 8-oxo-7,8-dihydro-2′-deoxyguanosine
(8-OHdG) levels, and a higher correlation between 8-OHdG and mtDNA
damage. This was due to arsenic inhibiting the antioxidant enzyme
catalase. This exacerbation was negligible with CDs–Fe because their strong binding with arsenic prevented catalase inhibition.
Maternal mitochondrial DNA damage was inherited by filial earthworms,
which experienced significant weight loss in coexposure groups coupled
with mtDNA toxicity. This study reveals the synergistic genotoxicity
of CDs and arsenate, suggesting that CDs could disrupt the arsenic
biogeochemical cycle, increase arsenate risk to terrestrial animals,
and influence ecosystem stability and health through multigenerational
impacts.