Soil Pollution In Edible Bamboo Shoot Plantations In Zhejiang And Degradation Of Chlorpyrifos

Edible bamboo shoot is one of the most popular Chinese traditional foods.The annual output value of edible bamboo shoot is increasing all the time in the past several decades and it has become the first choice for farmers to get rich in rural areas.However,with the increasing intensity of management in bamboo plantations,especially the wide application of mulching with organic materials in winter time,insect pests and diseases become more and more serious.Consequently,more and more chemical pesticides were used for disease and insect pest control,leading to high pollution of pesticide residues in soil and the food-safety problem of edible bamboo shoot.In the present study,several hundreds of soil samples from Phyllostachys praecox plantations were collected in 6 major areas of Zhejiang province,the pesticide residues from these samples were tested,and the polluting status and dynamic characteristics of soil pollution were analyzed by comparing the different types of plantations and also with the historic data,which were collected 10 years ago.In addition,the major pesticide,chlorpyrifos,was selected according to it residues and occurrence rate and used as the target for soil pollution control.The results are as follows:(1)Thirteen organic chemicals were detected from the edible bamboo shoot plantations in 6areas(Deqing,Linan,Fuyang,Longyou,Jinyun and Qingyuan)through Zhejiang province,including?-HCH,?-HCH,?-HCH,?-HCH,p,p'-DDT,p,p'-DDE,quintozene,chlorothalonil,dicofol,chlorpyrifos,dimethoate,cypermethrin and fenvalerate.Among all the detected pesticides,chlorpyrifos had the highest detection rate of nearly 50%,the maximum residue of 200.00 ng/g.Compared to the historic data,which were collected during 2003-2004,the number of detected pesticides were 9 less,both concentration and occurrence rate of all these detected residues were obviously lower than those in 10 years ago.(2)Management measures have a significant impact on soil pesticide residues,such as:mulching with organic material,land background,lime application and mulching with new mountainside soil.They are the main factors influencing the level of soil pollution from pesticide residues.(3)Results of lab test showed that the degradation rate of chlorpyrifos by Acinetobacter sp.,Bacillus cereus and Pseudomonas aeruginosa were 89.46 ± 4.72%,83.07 ± 5.83% and 75.59 ±1.14% respectively after 20 days.Significant differences were observed(F = 26.323,df = 3;P =0.0002),comparing to the control(59.33 ± 4.39%).Lime was proved to be able to promote the degradation of chlorpyrifos effectively.Significant degrading effect was observed when the lime dosage was 0.006 g/L after 20 days of application(F = 38.873,df = 1;P = 0.0034).(4)Results of field-site experiments showed that both lime and lime nitrogen could promote the degradation of chlorpyrifos effectively.The half-life of chlorpyrifos were 12.38 d,8.25 d,6.73 d and10.35 d respectivelywhen lime was applied with dosage of 85,135,185 and 235 g/m2.While the half-life of control was 19.80 d.Similarly,the average half-life of chlorpyrifos were 16.12 d,11.75 d and 11.00 d respectivelywhen lime nitrogen was applied with dosage of 60,90 and 120 g/m2,and were shortened obviously compared with the control.(5)Results of field-site experiments showed that the degradation rates of chlorpyrifos respectively were 93.38 ± 0.55% and 94.69 ± 0.92% after being treated with the bacterial solution of Bacillus cereus and Acinetobacter sp.for 63 days,and the control was 90.45 ± 1.54%.No obvious difference was observed(F = 4.959,df = 2;P = 0.054),indicating the different degrading effect of bacteria in different environments.(6)Considering the status of soil acidification of bamboo plantations in Zhejiang,and also the results of our experiments,we recommend to use alkaline fertilizer(dosage of lime: 185 g/m2;lime nitrogen: 90 g/m2)to control the soil pollution of chlorpyrifos.