Residual Dynamics Of Two Organophosphorous Pesticides On Greengrocery And Their Removal Using Various Methods

It was researched that the residue trends of chlorpyrifos and profenofos on greengrocery in different seasons in greenhouse and open field, and the efficiencies of various methods in the removal of these two organophosp- horous pesticides on greengrocery were evaluated. The results were as follows:1. The extraction and analytical methods of chlorpyrifos and profenofos on greengrocery were set up. Chlorpyrifos and profenofos residue were extracted with ethyl acetate from vegetables samples and then analyzed with GC-14B gas chromatography equipped with flame photometric detector(FPD) and a packed column named 3%OV-225(1m×3mm i.d.). The operating conditions were described below: pressure of carrier gas (99.99%nitrogen), hydrogen, and air were 50 kPa, 100 kPa and 80 kPa, respectively. Temperature of injector and detector was 250℃and 260℃, respectively, and basic single-step heating pattern of the column oven was showed as follows: initial temperature, 200℃, initial time,4min; program rate, 30℃/min; final temperature, 250℃, final time,2min.Under these conditions, the retention time for chlorpyrifos and profenofos was 5.3min and 7.1min,respectively, and limit of detection was 0.1ng and 0.3ng, respectively.The recovery rates from greengrocery with concentrations of 0.5mg/kg, 1mg/kg, 5mg/kg were 95.3-101.1% for chlorpyrifos and 96.3-99.0% for profenofos. The results showed that this method could meet the requirement for analysis of chlorpyrifos and profenofos residues.2. The residual trends of chlorpyrifos on greengrocery were studied by potted plant experiment in greenhouse and open field. The results indicated that the degradation speed of chlorpyrifos on greengrocery was different when pesticide was applied in different season, and the degradation rate was faster in spring than that in winter. In spring, the degradation rate of chlorpyrifos in open field was slightly faster than that in greenhouse, but there was no significant difference. 3. The residual trends of profenofos on greengrocery was studied by potted plant experiment in greenhouse and open field. The results indicated that the degradation speed of profenofos on greengrocery in spring was slightly faster than that in winter, however, there was no significant difference between them. The degradation rate of profenofos on greengrocery in open field was slightly faster than that in greenhouse, but there was also no significant difference.4. Five methods (tap water, sodium hydrogen carbonate, sodium carbonate, acetic acid and sodium chloride) of pesticide residue reduction were evaluated from greengrocery which was applied with two pesticides including chlorpyrifos and profenofos. The results indicated that all methods played roles in the reduction of pesticide residue. The efficiencies of washing with aqueous solutions of 4% sodium hydrogen carbonate, 0.3% sodium carbonate, 2% sodium chloride and 2% acetic acid on chlorpyrifos reduction was 34.4%, 29.8%, 38.1% and 21.8%, respectively, being more effective than tap water washing. However, they had no significant difference on profenofos reduction compared to tap water washing.5.Washing with aqueous solutions of detergent, boiling water, sodium carbonate, sodium hydrogen carbonate and sodium chloride was evaluated for chlorpyrifos residue reduction on greengrocery and compared with simple tap water washing, and the efficiencies of storage in the elimination of chlorpyrifos residue was also evaluated. The results indicated that various methods played different roles in the reduction of pesticide residue. The degradation rate increased with the increase of temperature, the reduction of pesticide residue was 26.0% at 18.5℃storage after seven days. The remains of pesticide residue became lower with the higher water temperature, the removal rate was 10.7% at normal temperature, 19.8% at 45℃, 35.0% at 100℃at the same time. The residue removal accelerated under washing with detergent, and removal rate of washing with 0.5% detergent was 23.2%. Alkaline solutions were very effective in the reduction of pesticide residue, washing with 0.3% sodium carbonate solution led to a loss of 29.8%, 4% sodium hydrogen carbonate, 34.4%. Washing of sodium chloride solution were also very effective in the reduction of pesticide residue.6. The efficiencies of sodium hypochlorite in degrading chlorpyrifos in water and in the elimination of chlorpyrifos residue on greengrocery was evaluated. The results indicated that degradation rate of chlorpyrifos increased at lower pH or higher concentration in water,for example, the percentage of degradation being 97.4% and 100% by 20mg/L and 500mg/L sodium hypochlorite in 5 min at pH5.0, respectively. Washing with sodium hypochlorite solutions was also effective in the removal of chlorpyrifos residue on greengrocery, the removal rate being 34.4-70.6%.7. The impact on effect of tap water washing time in the removal of chlorpyrifos and profenofos residue on greengrocery was researched. The results indicated removal rate of two organophosphorous pesticides increased with more tap-washing time in some degree, but beyond specific time, the removal rate did not increase further.8. The efficiencies of tap water washing for 15min in the elimination of two pesticides from greengrocery applied chlorpyrifos and profenofos for different days. The removal rate was 19.8%, 12.7% and 7.5% on chlorpyrifos reduction, 54.6%, 31.4% and 26.6% on profenofos reduction in 2d, 4d and 7d. The results showed the removal rate descended with longer sampling time.