Environmental Behavior Of Oxaziclomefone And Its Toxicity Response

Oxaziclomefone is an organic heterocyclic herbicide developed by Bayer Crop Science and Mitsubishi Petrochemical Corporation.It has high effectiveness against weeds,wide applicability,and long duration of action,and can be used to control weeds in both paddy fields and dry land.Although many studies have been conducted on its preparations and applications,there have been few reports on residual determination,environmental behavior,and biological toxicity.To provide a reference for the scientific use and safety assessment of oxaziclomefone in paddy fields,an optimization of the analysis method for oxaziclomefone was performed,followed by indoor simulations and field experiments to examine its environmental behavior and biological toxicity.(1)This paper presents a Qu ECh ERS sample pretreatment method using multi-walled carbon nanotubes as the purification agent and combines it with high-performance liquid tandem mass spectrometry(HPLC-MS)to detect Oxaziclomefone residues in rice field water,soil,plants,rice husk,and brown rice.This method has a detection limit of 0.002-0.003 mg/kg,a quantification limit of 0.006-0.012 mg/kg,an average recovery rate of 92.71-109.66%,and a relative standard deviation of 0.84-5.42%.According to the EU SANTE Method Validation Guide and existing pesticide Maximum Residue Limit(MRL)in China,this method can meet the residue detection requirements for oxaziclomefone in the rice field environment.(2)To gain a better understanding of the residual behavior of oxaziclomefone in paddy fields,tests were conducted on its degradation pattern at different application doses.The results revealed that the amount of remaining oxaziclomefone in rice plants was 2.08-4.46 mg/kg,much higher than the 0.63-1.18 mg/kg detected in the soil.The half-lives of oxaziclomefone in soil and plants were determined to be 3.2-3.5 days and 37.9-41.0days,respectively.Forty-five days after application,traces of oxaziclomefone residue could still be detected in plants and soil.At the time of rice harvest,the residuals of oxaziclomefone in paddy water,plants,husks and brown rice all fell below the detection limit of the method,while the residuals in the soil fell below the quantification limit of the method.Nonetheless,since it is employed during the early stages of crop growth,it is unlikely to pose any risk to the environment or food consumers.(3)To evaluate the stability of oxaziclomefone in water,crops,and soil surfaces,tests were carried out on its hydrolysis behavior under different p H,initial concentration,and temperature conditions,as well as its photolysis characteristics under high-pressure mercury lamp and xenon lamp The results of the digestion test showed that the degradation rate of oxaziclomefone was significantly higher in a neutral environment than when exposed to acidic or alkaline environments,with the order being neutral >alkaline > acid.With increasing temperature,the rate of hydrolysis of oxaziclomefone is significantly accelerated,suggesting that temperature promotes its hydrolysis.As the initial concentration of oxaziclomefone increases,the hydrolysis rate decreases slightly.The results of photolysis tests revealed that the half-lives of oxaziclomefone under mercury and xenon lamps were 10.6-13.5 minutes and 124.4-158.6 minutes,respectively,suggesting that the photolysis rate of oxaziclomefone is much faster than that of xenon lamp irradiation.The main degradation products of oxazolomide under xenon lamp irradiation are 6-methyl-5-phenyl-1,3-oxazole-4-ketone,1,3-dichloro-5-isopropylbenzene,and phenylacetone.(4)To gain further insight into the stability of oxaziclomefone in soil,tests were conducted on its degradation pattern in four different types of soil inside a room,and the effects of soil biology,temperature,organic matter content,and water content on the degradation of Oxaziclomefone in soil were investigated.The results show that the degradation of oxaziclomefone in various soils follows a first-order kinetic equation,with the fastest rate of degradation recorded in black soil with a half-life of 81.3 days and the slowest in red loam with a half-life of 115.7 days.The degradation of oxaziclomefone in soil was positively correlated with mucus content,p H,cation exchange,organic matter,and organic carbon content.The half-life of oxaziclomefone degradation was significantly longer in the four sterilized soils than in the non-sterilized soils,suggesting that soil organisms play a critical role in Oxaziclomefone degradation.At different temperatures,organic matter,and water content,the half-life of oxaziclomefone degradation in soil decreases with increasing temperature,organic matter,and water content,suggesting that higher temperatures,organic matter,and water content all contribute to the degradation of oxaziclomefone in soil.(5)To assess the safety of oxaziclomefone in the environment,tests were conducted on its adsorption/desorption and migration in four different types of soil inside a room.The results showed that the four soils had a strong adsorption capacity for oxaziclomefone,while its motility in the soil was weak;The adsorption kinetics of oxaziclomefone in the soil is best described by the Elovich model,which indicates that the adsorption kinetics of oxaziclomefone is a heterogeneous diffusion process with a significant change in activation energy throughout the process.The Freundlich model was found to accurately describe the isothermal adsorption-desorption behavior of oxaziclomefone in soil,suggesting that the adsorption sites of oxaziclomefone in soil are not homogeneous.Results from thin-film tomography on four soils showed low mobility of oxaziclomefone,most of which was found in the 0-10 cm portion of the upper soil column.This suggests that oxaziclomefone does not readily enter groundwater and thus poses a low risk to the environment.(6)To determine the weeding effect and biological safety of oxaziclomefone,the control effect of oxaziclomefone on weeds in paddy fields and the safety of Oxaziclomefone on rice growth was tested in the field,and the toxicity of Oxaziclomefone on zebrafish,Selenastrum capricornutum,and Eisenia foetidawase tested in the laboratory.Results from field trials showed that oxaziclomefone had a good control effect on seed from barnyard grasses and millet grass infields,but a relatively poor control effect on broad-leaved sedge and host-diffuse grasses.The control effect of10% oxaziclomefone SC 30 to 60 g.a.i./ hm2 on barnyard grasses and millet reached89.7 to 96.4% 30 days after treatment,and 55.1 to 76.7% on heterophyte sedge and hedyotis,which is safe for rice growth.As a result,oxaziclomefone is suitable for weed control in rice fields.The results of the indoor bioassay showed that oxaziclomefone had96 h-LC50>1000 mg/L for zebrafish,72 h-EC50>800 mg/L for Selenastrum capricornutum,and 48 h-LC50>1000 for Eisenia fetida vermis μ G/cm2,artificial soil method 14 d-LC50 ≥ 1000 mg/kg.As a result,oxaziclomefone is lowly toxic to zebrafish,Selenastrum capricornutum,and Eisenia foetida,and is ecologically safe when used in the field.