O 2 , hypersalinity, and Cu 2+ potentiate the toxicity of H 2 S in erythrocytes of a marine invertebrate

Environmental stressors frequently occur in combination and may produce additive or antagonistic effects. In sulfidic environments, H 2 S exposure may be accompanied by hypoxia, a range of salinities and heavy metals. However, whether these stressors interact is unknown. We tested this using erythrocytes from the H 2 S‐tolerant marine polychaete Glycera dibranchiata . Erythrocytes were exposed for 24 h at 15 ?C to abiotic stressors simultaneously: H 2 S (0.03‐0.3%), anoxia, salinity (13‐51 ppt), and Cu 2+ (33‐133 µM). Cell viability was measured using propidium iodide and calcein green AM labeling. Compared to control conditions (normoxia, 32 ppt salinity, and no H 2 S or Cu 2+ ), 0.03% H 2 S did not change cell viability, but 0.3% H 2 S decreased cell viability by 71%. Anoxia alone and salinity alone did not decrease viability, whereas during H 2 S exposure cell viability was increased by anoxia and decreased by hypersalinity. Cu 2+ at 33 µM decreased cell viability by 6%, but when combined with 0.03% H 2 S cell viability was reduced by 76%. Although the combination of anoxia, hypersalinity, and Cu 2+ , did not affect viability, all other combinations of three stressors showed a significant effect. These results suggest that the toxicity of H 2 S is increased by normoxia, hypersalinity, and Cu 2+ , indicating that realistic, complex environmental conditions must be considered when investigating H 2 S toxicity.