Study On Migration And Transformation Patterns Of Pb In Reclaimed Water-Soil-Vegetable System

Alternative tap water irrigation with reclaimed water becomes an important initiative to solve the shortage of water resources in Xinjiang area. Total quantity and forms of Pb in urban sewage change after the sewage treatment, Pb enters into soil, vegetables and even fruits with irrigation. Long-term reclaimed water irrigation will exert an effect on the quality of soil, vegetables and fruits in irrigated area, so stepping up the monitoring need be done during the agricultural irrigation to prevents the accumulative pollution of Pb. In-depth study about migration and accumulation patterns of Pb in reclaimed water-soil-vegetable system, which is quantitative and qualitative positioning research of Pb in system, it can make accurate assessment of Pb pollution level in soil, vegetables and fruits and offer theoretical basis for vegetable security production and scientific use of reclaimed water.This research explores the migration and accumulation patterns of Pb in reclaimed water-soil-vegetable system through the water centrifugal experiment, Pb morphological experiment, thin planting with special anion exchange membrane experiment and in vitro experiment.1. Centrifuging five water samples under different rotating speed: tap water, reclaimed water, tap water+SS+Pb, distilled water+SS+Pb, reclaimed water+SS+Pb(Pb2+=0.2 mg/L, SS=0.6 mg/L). Pb content in liquid supernatant and sediment were measured, it turned out that Pb content in liquid supernatant reducing while Pb content in sediment increasing with velocity improved. Under 500 r/min rotate speed, Pb is the highest in supernatant and lowest in sediment. Under 8000 r/min rotate speed, the difference value of Pb in supernatant and sediment is: distilled water+SS+Pb>tap water+SS+Pb>reclaimed water+SS+Pb≈ reclaimed water.2. In 2014, pot experiments were carried out on pakchoi, radish and chili with four irrigation treatment: tap water, tap water+Pb, reclaimed water, reclaimed water+Pb(Pb2+=0.2 mg/L), and the chemical speciation of Pb in soil, vegetable and soil leachates were detected by using modified BCR method. The result shows: Pb in tap water and reclaimed water mainly exists in water-soluble state B0, Pb in water samples does not exceed the National Farmland Irrigation Standard(GB5084-2005). Pb in soil and soil leachate mainly exists in residue form B4. Pb in soil does not exceed the secondary standard in Soil Environment Quality Standard(15618GB-1995). Pb in vegetables mainly exists in water-soluble state B0 and oxidizable state B3, Pb content in edible parts of three vegetables is: pakchoi>radish>chili, all exceed the National Food Safety Standard(GB2762-2012). In conclusion, strict control on the quantity of Pb and its effective species in agricultural irrigation water should be put into action for agricultural food safety.3. Thin planting with special anion exchange membrane experiments were carried out on pakchoi, radish and chili with four irrigation treatment ice: tap water, tap water+Pb, reclaimed water, reclaimed water+Pb(Pb2+=0.2 mg/L). Pb percent contents of different dot on the membrane were measured with LEO 1430 vp SEM and OXFORD EDS after harvest, then the data were ploted isogram with Surfer 8.0 to realize the Pb positioning analysis in the soil. The results showed that: without plant roots, Pb distributes unevenly in soil. With roots, Pb accumulates at the bottom, its migration rate ranked as: tap water, tap water+Pb>reclaimed water, reclaimed water+Pb.4. Putting the homogenate of vegetable edible parts into ZRS-8GD dissolution tester in order to imitating the gastrointestinal digestion, measuring Pb concentration of simulated gastric phase and simulated intestinal phase and vegetables, doing the safety evaluation for eating. The experimental results indicate that content of Pb is: simulated gastric phase>simulated intestinal phase, both are less than total content of Pb in vegetables. Bioaccessibility of Pb is: simulated gastric phase>simulated intestinal phase. PTWI of Tap Water radish is exceeding the standard for children, the rest are no threat so far.