Environmental Behavior Research And Risk Assessment Of Gibberellic Acid In The Agricultural Soils

As the most widely used plant growth regulator in the world,gibberellic acid is used in huge amounts for years,but its environmental behaviors have been lacking attention.For a long time,GA₃ has been neglected because it is considered to be a low-toxic or even non-toxic pesticide.Therefore,there has been few relevant research on the detection of GA₃ and its degradation products in the environment,especially in the soil.In this paper,through indoor batch experiment,indoor column experiment,Hydrus-1D model and risk assessment model,the adsorption,migration,natural attenuation,and microbial degradation of GA₃ in the soil were comprehensively explored,and the simulation and evaluation of its potential pollution in the environment was made.The main conclusions drawn in this article are as follows:（1）Three agricultural soils（Jixian soil,Yunnan soil and Inner Mongolia soil）have no adsorption effect on GA₃ for the adsorption rate of GA₃ in the three agricultural soils are less than 5%within 48 h.The migration of GA₃ in the three agricultural soils is basically the same as that of Br^-,and the blocking effect of the soil on GA₃ is quite small.Without considering the existence of natural degradation,GA₃ has a great risk of entering the groundwater;（2）Regarding the natural attenuation of GA₃ in the three saturated agricultural soils,GA₃ attenuated completely in both sterilized and unsterilized Inner Mongolia soil within 17 days in the Inner Mongolia soil;within 21 days,GA₃ degraded 94%in the sterilized group and 93%in the non-sterilized group in the Jixian soil;besides,GA₃degraded 96%in the non-sterilized group within 25 days in Yunnan soil,and 89%in the sterilized group within 45 days.The adding domesticated GA₃ degrading flora can significantly accelerate the degradation rate of GA₃ in the soil.In the non-sterilized group,GA₃ was degraded by 73%in 9 days;and in the sterilized group,GA₃ was degraded by 82%in 9 days.Compared with the two sets of blank samples,the degradation efficiency is increased twice.The degradation products of GA₃ in the soil are mainly isomerized gibberellic acid（Iso-GA₃）and gibberellenic acid（GEA）.In special,the existence and toxicity of Iso-GA₃ in the environment should be paid further attention;（3）The simulation results of the Hydrus-1D model based on the calculated soil parameters of GA₃ in the three agricultural soils are fitting the experimental results,with the R²all greater than 0.9;with the soil model length of 2 m and under the simulated conditions of the 240-hour time-length and total GA₃-input amounts of 100 mg,8.41mg,4.13 mg and 45 mg of GA₃ entered groundwater in Jixian soil,Yunnan soil and Inner Mongolia soil in the Hydrus-1D model,respectively,which indicate that there is great migration risk of GA₃ in Inner Mongolia soil.It is evaluated that the RF level of GA₃ in the three agricultural soils isⅣ,which indicate that GA₃ is a kind of mobile pesticide;the AF value is mostly below 0.0001 with the levelⅠ,which indicate that GA₃is unlikely to pollute the groundwater,except for the condition of sterilized Yunnan soil in the paddy field（3q）withthe level ofⅡ,which indicate that in the soil with a slower degradation rate,the migration risk of GA₃ still needs attention.The comprehensive cytotoxicity index of GA₃ based on LC₅₀（96 hr）is 2.6 mg/L,and the comprehensive cytotoxicity index based on LD₅₀ is 869.73 mg/kg.According to the WHO acute toxicity classification standard for foreign compounds,the toxicity of GA₃ in nature will increase after hydrolysis,so that the comprehensive toxicity of GA₃ and its derivatives needs further study.