Assessing the disparity: comparative toxicity of Copper in zebrafish larvae exposes alarming consequences of permissible concentrations in Brazil.

Copper (Cu) is a naturally occurring metal with essential micronutrient properties. However, this metal might also pose increased adverse environmental and health risks due to industrial and agricultural activities. In Brazil, the maximum allowable concentration of Cu in drinking water is 2 mg/L. Despite this standard, the impact of such concentrations on aquatic organisms remains unexplored. This study aimed to evaluate the toxicity of CuSO 4 using larval zebrafish at environmentally relevant concentrations. Zebrafish ( Danio rerio ) larvae at 72 hr post-fertilization (hpf) were exposed to nominal CuSO 4 concentrations ranging from 0.16 to 48 mg/L to determine the median lethal concentration (LC 50 ), established at 8.4 mg/L. Subsequently, non-lethal concentrations of 0.16, 0.32, or 1.6 mg/L were selected for assessing CuSO 4 -induced toxicity. Morphological parameters, including body length, yolk sac area, and swim bladder area, were adversely affected by CuSO 4 exposure, particularly at 1.6 mg/L (3.31 mm ±0.1, 0.192 mm 2 ±0.01, and 0.01 mm 2 ±0.05, respectively). In contrast, the control group exhibited values of 3.62 mm ±0.09, 0.136 mm 2 ±0.013, and 0.3 mm 2 ±0.06, respectively. Behavioral assays demonstrated impairments in escape response and swimming capacity, accompanied by increased levels of reactive oxygen species (ROS) and lipid peroxidation. In addition, decreased levels of non-protein thiols and reduced cellular viability were noted. Data demonstrated that exposure to CuSO 4 at similar concentrations as those permitted in Brazil for Cu adversely altered morphological, biochemical, and behavioral endpoints in zebrafish larvae. This study suggests that the permissible Cu concentrations in Brazil need to be reevaluated, given the potential enhanced adverse health risks of exposure to environmental metal contamination.