Elucidating the Differences in Metal Toxicity by Quantitative Adverse Outcome Pathways.

Area of Science:

• Environmental Toxicology
• Aquatic Toxicology
• Ecotoxicology

Background:

• Metal toxicity differences in aquatic organisms are well-documented but mechanistic understanding remains limited.
• Quantitative understanding of adverse outcome pathways (AOPs) is crucial for assessing metal risks.

Purpose of the Study:

• To investigate the differential toxicity mechanisms of cadmium (Cd) and copper (Cu) in zebrafish larvae.
• To develop a quantitative adverse outcome pathway (qAOP) for metal risk assessment in aquatic environments.

Main Methods:

• Examined bioaccumulation, gene expression (RNA sequencing), physiological responses, and apical effects of Cd and Cu exposure in zebrafish.
• Proposed a novel parameter, internal threshold concentration/bioaccumulation factor (C_IT/BCF), to integrate toxicokinetic and toxicodynamic data.

Main Results:

• Copper exhibited higher toxicity than cadmium in zebrafish larvae due to faster attainment of internal effect thresholds.
• RNA sequencing provided mechanistic insights into the distinct responses to Cd and Cu exposure.
• The C_IT/BCF parameter effectively explained the observed toxicity disparities between the metals.

Conclusions:

• The quantitative adverse outcome pathway (qAOP) framework provides a mechanistic explanation for differential metal toxicity.
• Toxicokinetics and toxicodynamics are critical determinants of metal toxicity at various biological levels.
• The proposed qAOP and C_IT/BCF parameter offer valuable tools for aquatic metal risk assessment.