Separate and combined effects of cadmium (Cd) and nonylphenol (NP) on growth and antioxidative enzymes in Hydrocharis dubia (Bl.) Backer

Cadmium (Cd) is considered a priority pollutant, and nonylphenol (NP) is a common organic pollutant in water environments. However, the ecological risks of combined Cd and NP pollution have not been fully elucidated. In this study, the effects of Cd, NP, and Cd-NP on the growth and physiology of Hydrocharis dubia (Bl.) Backer were studied. The results indicated that Cd-NP joint toxicity is concentration-dependent. The joint toxicity of Cd and NP on H. dubia was antagonistic when the concentrations of Cd + NP were 0.01 + 0.1/1 mg/L. At 0.5 + 0.1/1 mg/L, Cd and NP had a strong synergistic effect on H. dubia. In addition, plant growth was significantly inhibited, and the chlorophyll contents were significantly reduced under Cd, NP, or Cd-NP exposure. The plant's antioxidant enzyme system was destroyed. The activities of superoxide dismutase (SOD) and catalase (CAT) were significantly decreased under NP-only exposure. The activity of SOD was significantly decreased under Cd-only and under joint exposure. Compound pollution exceeded the oxidative defense capacity of the plants, so the H2O2 content increased significantly. Our results indicated that the ecotoxicity of NP combined with Cd may be exacerbated in aquatic environments and cause obvious damage to H. dubia.