Studies On The Photochemical Degradation Of Isoproturon On The Soil Surface

In this thesis,the effects of adding dose of isoproturon,soil moisture,pH value,nitrate and nitrite,chemical fertilizers(urea and KH₂PO₄),heavy metal ions and light sources on photodegradation of isoproturon on the soil surfaces have been studied.The main results were summarized as follows:1.Under HPHL,the half life of photolysis was shortest at 40μg·g^-1level.The photolytic rate at 20μg·g^-1and 80μg·g^-1levels were slower than at 40μg·g^-1 level.During the photodegradation of isoproturon on the soil surface,the photolytic rate in the prophase was obviously faster than in the anaphase.The reason was possibly related to the molecule density on the soil surface.2.The photodegradation of isoproturon on the soil surface under HPHL was accelerated with the increasing of soil moisture.At 40μg·g^-1level,the half-life period fell from 1.66 h at 40%of soil moisture to 1.04 h at 80%.That was mainly because the water in soil strengthens the mobility of pesticide molecule in soil.3.Under HPHL,the photolytic rates of isoproturon on the soil surface ranged as pH7＞pH9＞pH4.It meant that isoproturon was steady to acid and alkali,which was also a chemical property of isoproturon.4.NO₃^- and NO₂^- showed remarkable photo-quenching effects on the photodegradation of isoproturon on the soil surface.After 5h of illumination,the photo-quenching rates of NO₃^- were 8.30～24.20%,and NO₂^- were 14.69～30.62%.As the adding dose of NO₃^- increased,the photo-quenching effects of NO₃^- weakened insteadly,and the half-life periods were extended to 2.09,1.96,1.28 times.5.Under UV light,urea showed the photo-sensitive effect on the photodegradation of isoproturon on the soil surface.With the adding dose of urea increasing,the photo-sensitive effect of urea got greater.At 1:1 of the adding dosage rate of urea and isoproturon,the photo-sensitive rate of urea was 8.68%.During the three adding dosage rates,KH₂PO₄ had effect only at 5:1 level.6.Under UV light,the effects of Pb²⁺,Cu²⁺,Cr⁶⁺and Cd²⁺on the photodegradation of isoproturon on the soil surface increased in turn.They made the half-life period of photodegradation prolonged 0.01,0.15,0.31,0.47 times,and the photo-quenching rates were 31.77%,19.35%,21.28%and 28.64%respectively.When there was Cr⁶⁺in soil sample,the photolytic rates of isoproturon on the soil surface ranged as 5:1＜1 :1＜1:5.7.Under HPHL,UV light and sunlight,the photodegradations of isoproturon on the soil surface all followed the first-order kinetics.The photolytic rates ranged as HPHL＞UV light＞sunlight,and their photolysis half-life periods were 1.50 h,6.67 h and 8.31 d respectively.8.Photoproducts of isoproturon on the soil surface include aniline,4-isopropylaniline, and maybe N-(4-(2-hydroxy-1-methylethyl)phenyl)-N',N'-dimethylurea or N-(4-(1-hydroxy-1-methylethyl)phenyl)-N',N'-dimethylurea,which resulted from N-demethylation,phenyl-deisopropylation and hydroxylation.