| Sodium dehydroacetate(Na-DHA)is a kind of feed additive widely used in livestock and poultry culture,which has high antiseptic effect.About 50%of Na-DHA is excreted in feces and urine in prototype after use,and enters the environment with organic manure or through livestock farm sewage system,which may cause ecological toxicity to microorganisms,animals and plants in the environment.There are few reports on the environmental behavior and ecotoxicology of Na-DHA in soil.This paper intends to study the degradation characteristics of Na-DHA in soil and its effects on soil microorganisms,pakchoi,and earthworms,evaluate the ecotoxicity of Na-DHA in soil environment,and deepen the understanding of the environmental behavior and toxicity of NA-DHA.An HPLC method was developed to determination of Na-DHA in soil.The soil samples were extracted by ultrapure water,magnesium sulfate and sodium hydroxide were added to remove impurities in the samples and improve the recovery rate,and then analyzed by HPLC.Agilent C18 column,methanol-0.02 mol/L ammonium acetate(60:40,v/v)as the mobile phase,the flow rate was 1.0 mL/min,the detection wavelength was 293 nm,and the temperature was 35℃.The results showed that the Na-DHA sample peak retention time was around 4.5 min with good peak shape,and the linear relationship was good in the range of 0.1～50.0 mg/L with r2=0.9998.In the concentration range of 1.0 mg/kg,5.0 mg/kg and 10.0 mg/kg,the average recovery rate of the samples was 85.09%～101.58%,the intra-day coefficient of variation was 1.10%～2.00%,and the inter-day coefficient of variation was 1.18%～2.53%.The detection limit and quantitative limit of Na-DHA were 0.3 mg/kg and 0.5 mg/kg.Which could meet the detection requirements of Na-DHA content in soil.Use this method to detect the degradation changes of Na-DHA in soils with different water content,organic matter content,and microbial activity.The degradation half-life was calculated by fitting the degradation curve with a one-stage kinetic model.The results showed that in the concentration range of 1～20 mg/kg,Na-DHA degraded rapidly in soil,with a half-life of 16.6～17.9 h based on the first-order kinetic model.There is no significant difference in the degradation rate of Na-DHA due to soil moisture content.After removal of organic matter and sterilization,the degradation half-life of Na-DHA in soil was significantly prolonged compared with that before treatment(P<0.01).Na-DHA was added to the soil at 5,10,and 20 mg/kg,and the effects of different times on soil respiration,ammonification and nitrification were analyzed.The results showed that the impact on soil respiration mainly showed a trend of "promotion-inhibition-recovery".The impact on the intensity of soil ammonification is manifested as inhibitory effect(P<0.01);The effect on the intensity of soil nitrification is mainly manifested as "low promotion and high suppression".The filter paper germination experiment of pakchoi seeds was conducted at four exposure levels of 0,25,50,and 75 mg/L;A pot experiment was conducted on pakchoi,with 7 exposure levels of 0,10,25,50,100,250,and 500 mg/L groups.Two experiments were conducted to determine the effects of different exposure levels on the germination,growth indicators,plant pigments,and antioxidant enzymes of pakchoi seeds.The results showed as the exposure concentration was higher than 100 mg/L,the germination potential and germination index of pakchoi seeds were inhibited(P<0.05).10～75 mg/L Na-DHA promoted plant weight and length of pakchoi(P<0.05),and inhibited plant weight and length of pakchoi at 100～500 mg/L(P<0.05),and the inhibitory effect increased with the increase of concentration.It had significant inhibitory effect on the root length of pakchoi(P<0.05).The effect on plant pigment showed a trend of "promotion-inhibition" under 10～50 mg/L exposure concentration stress,and inhibition effect under 100～500 mg/L exposure concentration stress(P<0.01).The activity of antioxidant enzyme increased at the early exposure concentration of 10～50 mg/L,and decreased significantly with the extension of exposure time(P<0.01).At 100～500 mg/L exposure,the activity of antioxidant enzymes was significantly decreased during the whole experiment period(P<0.01).An HPLC method was developed to determine Na-DHA in earthworm tissue samples.The samples were extracted with acetonitrile-water,added with magnesium sulfate and glacial acetic acid,and detected by HPLC,Agilent C18 column,methanol-0.02 mol/L ammonium acetate(55:45,v/v)as the mobile phase,the flow rate was 1.0 mL/min,the detection wavelength was 293 nm,and the temperature was 35℃.The retention time of Na-DHA peak was about 6.1 min,and the peak shape was good.When the concentration of 1.0 mg/kg、5.0 mg/kg and 10.0 mg/kg were added,the average recovery of samples was 91.57%～109.59%.Using this detection method,the enrichment behavior of Na-DHA in earthworms was studied by storage experiments.The results showed that earthworms enriched Na-DHA rapidly,and the highest concentration of Na-DHA was found 3～6 hours after a single exposure.In multiple exposure experiments,Na-DHA had an obvious enrichment effect in earthworms,which was affected by both exposure concentration and exposure time.Na-DHA was rapidly degraded in earthworms,and the degradation half-life was prolonged with the increase of exposure concentration.In summary,this study found that Na-DHA degrades rapidly in soil and is affected by the physicochemical properties of the soil.Na-DHA increased microbial respiration intensity at low exposure concentrations in soil and significantly inhibited nitrification and ammonification in soil.Na-DHA had no significant effect on seed germination.Na-DHA had no significant effect on seed germination.In the pot experiment,continuous irrigation with different concentrations of Na-DHA had significant effects on the growth,plant pigments and antioxidant enzyme activities of pakchoi.The accumulation behavior of Na-DHA in earthworms was investigated,and it was proved that Na-DHA exposed in soil could accumulate in earthworms.These results suggest that Na-DHA residues in soil may be ecologically toxic,which should be paid more attention and be further studied. |
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