The impact of salinity on copper-induced toxicity in Palaemon spp.: effects on survival, morphological deformities, and toxicity indicators

Heavy metal contamination, resulting from pollution, presents serious threats to aquatic species and has far-reaching consequences for ecosystem health. This study investigates the acute toxicity of copper (Cu) on grass shrimp (Palaemon spp.), a key species in North American estuaries. We exposed shrimp to a range of copper concentrations (0, 0.25, 0.50, 1.0, and 2.0 ppm) and salinities (1, 5, 10, and 20 ppt) over periods of 3, 6, 9, 12, 24, 48, 72, and 96 h. We hypothesized that exposure to 1.0 ppm Cu and 10 ppt salinity would reduce copper toxicity; but contrary to our expectations, optimal shrimp survival occurred at 20 ppt salinity and 0.25 ppm Cu. Copper solutions were prepared using CuSO₄·5H₂O, and toxicity was monitored using indicators such as mortality, abdominal curvature, discoloration, and mobility. Water quality remained stable throughout the study, with dissolved oxygen consistently at 8.675 ± 0.187 ppm, pH at 6.88 ± 0.088, and temperature at 28.75 ± 0.244 ℃. Copper toxicity increased at lower salinities, with the highest mortality and quickest onset observed at 1 ppt. Mortality was lowest at 0.25 ppm Cu, while 2.0 ppm Cu induced the highest mortality across all salinities, supporting a dose–response relationship. LC50 values increased with salinity, with the highest survival rates occurring at 20 ppt. These findings highlight the protective role of higher salinity in mitigating copper toxicity, emphasizing the need for further research on the long-term ecological consequences of copper contamination in estuarine ecosystems.