Single And Combined Toxicological Effects Of Tetracycline And Zinc On Aquatic Plants

With the rapid development of intensive farming and aquaculture activities,tetracycline and zinc are widely used as feed additives in livestock and aquaculture because of their functions of disease prevention and growth promotion.Due to the widespread usage,incomplete metabolism of organisms and inefficient removal,tetracycline is frequently detected in water and has become an emerging pollutant.The coexist of tetracycline and Zn(II)in natural water bodies is common and may affect aquatic organisms.At present,there are few studies on the effects of tetracycline and the combined effect of tetracycline and Zn(II)on aquatic plants.We conducted an experiment to explore the ecological sensitivities of Hydrocharis dubia(Bl.)Backer,Trapa natans and Vallisneria natans(Lour.)Hara to tetracycline.The growth and physiological responses of these three plants under different tetracycline concentrations(0,0.1,1,10,30,50 mg/L)after 1 day(D)and 14 days(D)were measured.We also studied the growth and physiological responses of V.natans to different tetracycline concentrations(1,10,50 mg/L)combined with different levels of Zn(II)(0.1,1,10mg/L)after treatment of 14 D.These studies will provide a theoretical basis for the ecological study of aquatic plants and the joint ecotoxicological risks of tetracycline and Zn(II).The results showed that:(1)after 1D treatment of tetracycline,some significant changes occurred in antioxidant enzyme activities of T.natans and V.natans under tetracycline stress.Indicators of H.dubia showed no significant changes except for proline.After 14 D,high concentrations of tetracycline(? 1 mg/L)significantly inhibited the relative growth rate(RGR)and soluble protein content of T.natans,but did not affect the growth and protein of V.natans and H.dubia.In terms of oxidative damage,the malondialdehyde(MDA)contents of T.natans and V.natans did not increase significantly under tetracycline stress.The MDA content of H.dubia was significantly increased at 50 mg/L.To cope with oxidative stress,H.dubia,T.natans and V.natans can activate antioxidant defense systems,including the superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),and polyphenol oxidase(PPO).These antioxidant enzymes behaved differently in different plants.Chlorophyll a,b and total chlorophyll of H.dubia were significantly reduced at ? 10 mg/L tetracycline;chlorophyll a of T.natans were significantly decreased at ? 30 mg/L tetracycline;V.natans showed no significant changes.(2)Under the single and combined existence of tetracycline and Zn(II),tetracycline mainly inhibited the root and stolon growth of V.natans,and Zn(II)mainly harmed the biomass accumulation,soluble protein and photosynthetic pigments.The coexistence of low concentrations of tetracycline and Zn(II)can alleviate the toxic effects on V.natans of each other,but the combination of high concentrations of tetracycline and Zn(II)increased the damage to carotenoid and oxidative balance of V.natans.The Abbott modelling was used to evaluate the type of interaction of tetracycline and Zn(II)on V.natans.The relative ratio of yellow leaves,RGR,total chlorophyll content and MDA content were selected as indexes in Abbott.Tetracycline combined with low concentration of Zn(II)has an antagonistic effect on plant growth inhibition,but an additive effect on the inhibition of chlorophyll content;when combined with high concentration of Zn(II)(10 mg/L),the additive effect occurred in plant growth Inhibition and antagonistic effect in the destruction of chlorophyll.However,almost all the interactions of tetracycline and Zn(II)on the content of MDA in V.natans showed an additive or synergistic effect.In summary,the growth and physiological responses of H.dubia,T.natans and V.natans to tetracycline are different.The antioxidant systems of T.natans and V.natans were more sensitive and effective in combating the oxidative damage caused by tetracycline than H.dubia,which can protect T.natans and V.natans from membrane lipid peroxidation.The photosynthetic pigments and oxidation balance of H.dubia were more susceptible to tetracycline.However,the growth of T.natans was more vulnerable to tetracycline.Taken together,V.natans had the strongest resistance to tetracycline stress.The joint of tetracycline and Zn(II)could change the phytotoxicity of both sides.The type of interaction on V.natans was related to the concentration ratio and the location of their coexistence.As the concentration of Zn(II)increases,the toxicity of combined stress to growth increases,and the toxicity to chlorophyll decreases.More attention should be paid to the toxicity of tetracycline and Zn(II)when they coexist.The coexistence of tetracycline and Zn(II)could increase the oxidative stress even when they coexist in low concentrations.