Genetic, epigenetic, and developmental toxicity of Chironomus riparius raised in metal-contaminated field sediments: A multi-generational study with arsenic as a second challenge

Ecotoxicity tests conducted under well-controlled lab conditions often do not reflect the real environmental conditions. To this end, we designed an ecotoxicity test using an aquatic midge, Chironomus riparius, raised in metal-contaminated field sediments (MCFS), which reflect the real environmental conditions, for five consecutive generations (F0–F4) followed by a toxic response to arsenic exposure (as a second challenge). The toxic responses (i.e. DNA damage, DNA methylation, stress response gene expression, and mortality) were compared to those organisms reared in lab sediments (LS). Under the MCFS condition, increased adult emergence was observed for the second and third generations (F1 and F2), while a decreased tendency was evident thereafter (F3 and F4) compared to that of F0. When comparing C. riparius raised in MCFS or LS exposed to arsenic, increased sensitivity (declined survival) was observed in the larvae from F2. However, that tendency was not present in F4 of the MCFS midges, indicating a possible physiological adaptation. Increased DNA damage was observed in the MCFS-exposed organisms (F0, F2, and F4) compared to the those exposed to LS, particularly at F0. Arsenic exposure induced hypermethylation at F0 and, in contrast, hypomethylation at the later generations (F2, F4) in the MCFS-exposed organisms. Global DNA methylation results were supported by the expression of genes involved in enzymatic methylation. Moreover, alterations in oxidative stress related to gene expression showed that significant oxidative stress and perturbation of glutathione reserves occurred under the MCFS and the subsequent arsenic exposure conditions. Overall, our results suggest that multigenerational rearing under MCFS conditions resulted in physiological adaptation of C. riparius to metal exposure, specifically at later generations, which in turn modulated its response to arsenic stress through possible genetic and epigenetic mechanisms.