First report on Technology-Critical Elements in seahorses from Rio de Janeiro, Southeastern Brazil

Electronic waste poses a growing environmental threat due to the presence of metals essential for electronic devices. Improper disposal can lead to severe ecological consequences. This study assessed Technology-Critical Elements (TCE) in Longsnout seahorses (Hippocampus reidi) along the Rio de Janeiro coast. Dorsal fin samples from 50 individuals across five locations (Guanabara Bay, Armação dos Búzios, Ilha Grande Bay, Araruama Lagoon, and Arraial do Cabo) were analyzed by the ICP-MS technique. Various metals were detected, with titanium present at the highest concentrations (19.8 ± 28.5 mg kg^-1 in females and 11.9 ± 16.9 mg kg^-1 in males). Significant differences in TCE levels were found across sites, where Guanabara Bay samples contained higher neodymium and erbium, while Armação dos Búzios exhibited the lowest thulium, lutetium, and rubidium concentrations. Arraial do Cabo presented notably lower lutetium levels than Guanabara Bay. Negative correlations were observed between seahorse height and praseodymium, lanthanum, europium, rubidium, and titanium, suggesting potential growth impacts. No significant sex-based differences were detected. These findings highlight the importance of monitoring TCE accumulation in marine species, particularly in vulnerable ecosystems. This study provides baseline data on E-waste contamination impacts on marine biodiversity, emphasizing the need to mitigate anthropogenic pollution to protect aquatic life and maintain ecological balance.