Cadmium induces toxicological responses in two bioindicator species of distinct trophic levels during early developmental stages? Assays on environmental concentrations and considerations on potential future increases in the environment

The increasing contamination of aquatic environments with cadmium (Cd) poses a serious threat to biodiversity due to its high toxicity. This study aimed to evaluate whether environmentally relevant and elevated concentrations of cadmium (Cd) enhance toxicological responses in two bioindicator species at early developmental stages, representing different trophic levels: Allium cepa (a vascular plant) and Rhamdia quelen (a fish). Three exposure groups were established (5, 50, and 500 µg L-1 of Cd), in addition to a negative control group and a positive control (applied only to the A. cepa assay). Cytogenotoxic, phytotoxic, and bioaccumulative parameters were analyzed in seedlings, while morphological, teratological, and survival endpoints were assessed in fish larvae. A significant reduction in germination rate and root growth of A. cepa was observed across all Cd-treated groups. An increase in the chromosomal aberration index was also observed, primarily due to the occurrence of C-metaphases, chromosomal adhesions, and breaks in the treated groups. Clastogenic effects were more pronounced at the lowest Cd concentration. R. quelen larvae exhibited more severe and concentration-dependent effects, with high mortality rates and numerous body deformities at 50 and 500 µg L-1 of Cd after 48 hr post-fertilization (hpf). The responses were also time-dependent, as increased mortality and teratogenesis were recorded at 5 µg L-1 of Cd after 96 hpf. Even at permissive and environmentally realistic concentrations, Cd proved toxic to both species, with worsened outcomes under scenarios of future increases. The novelty of this article lies in comparing two distinct organisms under the same experimental conditions, examining different markers for ecological risk assessment and guidance, thereby making a relevant contribution to environmental monitoring.