Toxicity of chlortetracycline and oxytetracycline on Vallisneria natans (Lour.) Hare

Abstract

Tetracyclines are frequently detected in water bodies due to their widespread use in aquaculture and animal husbandry. A hydroponic experiment was conducted to explore the phytotoxic effects of Vallisneria natans (Lour.) Hare exposed to various concentrations of chlortetracycline (CTC) and oxytetracycline (OTC) (0, 0.1, 1, 10, 30, 50 and 100 mg/L) for 7 days (7 D) and 14 days (14 D), respectively. The results showed that similar to OTC treatment for 7 D, the relative growth rates (RGR) and catalase (CAT) activity of V. natans , after 7 D of CTC exposure, decreased significantly at 10 mg/L and 30 mg/L, respectively. The content of soluble protein notably decreased when CTC ≥ 10mg/L and OTC ≥ 30mg/L. The hydrogen peroxide (H 2 O 2 ) content was significantly stimulated when OTC ≥ 10mg/L, while it hardly changed when exposed to CTC. After 14 D, the malondialdehyde (MDA) and H 2 O 2 contents of V. natans were significantly higher than those of the control group under high concentration of OTC (≥ 30mg/L), but they didn’t change significantly under high concentration of CTC. The activity of polyphenol oxidase (PPO), under CTC treatment after 14 D, showed first a significant increase then decrease, the maximum value (125% of the control) was notice at 10 mg/L CTC, while it remained unchanged when exposed to OTC. The soluble protein content significantly decreased at 10 mg/L CTC and 0.1 mg/L OTC, respectively. The RGR, CAT and peroxidase (POD) activities, similar to OTC treatment after 14 D, decreased evidently when CTC was 10 mg/L, 30 mg/L and 0.1 mg/L, respectively. CTC and OTC harm the chlorophyll content of V. natans after 14 D, and the reduction of chlorophyll a and carotenoid were more pronounced than chlorophyll b. The results suggest that CTC and OTC both have negative effect on the growth of V. natans , and OTC can cause oxidative damage in V. natans but CTC harm the metabolism process without inducing oxidative damage. Overall, the toxicity of OTC to V. natans is stronger than that of CTC.