Metabolic Costs of Emerging Contaminants: Cellular Energy Allocation in Zebrafish Embryos

The use of cellular energy allocation (CEA) as a physiological energetic biomarker is useful for detecting the sublethal effects of environmental contaminants. The CEA assesses the health and energy status of organisms, serving as a reliable indicator for monitoring the health of aquatic ecosystems. This study aimed to evaluate the impact of emerging contaminants already listed as a priority for monitoring in freshwater ecosystems, namely sulfamethoxazole (0.156-2.50 mg/L), trimethoprim (25.0-400 mg/L), 4-chloroaniline (5.21-20.0 mg/L), and 3,4-dichloroaniline (0.38-4.00 mg/L), on the CEA of <i>D. rerio</i> embryos. A standard fish embryo toxicity test was conducted, and an adaptation of the allometric scaling approach was developed through the relationship between the size and the fresh weight of the embryos. All the compounds affected the fractions of the energy reserves (total carbohydrate, lipid, and protein contents) differently, with carbohydrates being the predominant energy fraction and the most responsive indicator. Although the energy consumed showed no significant changes, the CEA was notably altered after exposure to all the contaminants, indicating a direct connection to shifts in the available energy. The CEA alterations may indicate a reallocation of energy toward detoxification, combating the stress of contaminant exposure. Energy allocation biomarkers provide a comprehensive assessment of an organism's physiological state, which is essential for evaluating emerging contaminants' impacts, safeguarding aquatic ecosystems, and shaping effective environmental policies.