Toxicidade do cobre em larvas de Danio rerio: implicações alarmantes de concentrações permitidas no Brasil

Abstract

Copper, a naturally occurring metal, plays a crucial role in organism metabolism. However, anthropogenic activities contribute to an increase in its concentration in the environment, heightening the potential for contamination. In Brazil, the maximum allowed limit for copper concentration in drinking water is 2 mg/L; nevertheless, safety for aquatic organisms still presents noteworthy limitations. This study investigated the toxicity of copper in Danio rerio larvae at environmentally relevant concentrations. D. rerio larvae at 72 hours post-fertilization were exposed to nominal copper concentrations (0.16 to 48 mg/L) for 24 hours. Copper toxicity was assessed using sublethal concentrations (0.16, 0.32, and 1.6 mg/L) with D. rerio larvae at 96 hours post-fertilization. As a result, the LC50 was established at 8.4 mg/L. Notably, the highest copper concentration (1.6 mg/L) resulted in a reduction in body length (3.31 mm ± 0.10) and an increase in yolk sac area (0.192 mm² ± 0.01), which, when compared to the control group (3.62 mm ± 0.09, 0.136 mm² ± 0.13), suggests a possible association with interference in the nutrition of these organisms, resulting in developmental impairments. Additionally, the decrease in the swim bladder area (0.01 mm² ± 0.05) compared to the control group (0.30 mm² ± 0.06) raises crucial implications for the buoyancy of these organisms, also affecting the development of active swimming. Copper exposure reduced the escape response and swimming capacity of the larvae, and in a natural environment, these changes may result in increased susceptibility to predation, especially during the early developmental stages. Changes in oxidative parameters were observed, evidenced by an increase in reactive oxygen species and lipid peroxidation, indicating potential cellular damage. Concurrently, the reduction in non-protein thiol levels and cellular viability suggests impacts, partly on antioxidant capacity and mainly on cellular integrity, disrupting homeostasis and compromising larval development. The results highlight that copper exposure, even at concentrations close to or below those allowed in drinking water legislation, induces adverse effects on morphological, behavioral, and biochemical parameters. These findings underscore the urgent need for a reassessment of these concentrations, which, despite not being considered toxic to humans, may compromise aquatic biota.