Accumulation Of Heavy Metals In Taro(Colocasia Esculenta (L.)Schoot) And Water Bamboo(Zizania Latifolia (Griseb.) Stapf)&the Risk Assessment Of Their Residues In The Main Production Areas

A pot culture experiment was carried out to investigate the accumulation of lead and cadmium in taro and their effects on taro’s growth. Besides, the contents of lead, cadmium and arsenic in soil and plant samples were measured for five and four production areas of taro and water bamboo, respectively. The ecological risk of heavy metals in soils was evaluated by using the NCPI, PERI and GAI indexes. The health risks of heavy metals accumulated in edible organs were assessed by using EDI and THQ(建议用全称)indexes. The main results are as follows:1. The accumulation of Pb and Cd in soil was detected to be dose-dependent. Significant higher level of Pb was deteted in all organs tested for taro when soil was supplemented with250mg/kg or more of Pb, as compared to the control. For the treatment of500mg/kg of Pb in soil, the highest level of Pb was detected in leaf, followed by edible bulb and leaf stalk. While no obvious difference in Pb accumulation was detected between the low concentration of Cd treatment (0.5mg/kg) and the control. When Cd was increased to1.5mg/kg soil, enrichment of Cd was evident in taro plant, the order of Cd in different orgrans was leaf stalk> edible bulb> leaf.2. The number of functional leaf and tiller of son taro showed not obvious change while height, length and width of leaf varied along with the concentration of Pb or Cd supplemented to soil, that is a inhibiting effect under Pb stress but a adverse effect under Cd stress.3. Some physiological and biochemical parameters were measured for taro plants under Pb or Cd stress. At seedling stage, the chlorophyll and soluble sugar content increased under low concentration of Pb, but decreased at higher level of Pb. The MDA and soluble protein content increased along with the amount of Pb supplemented to soil. Under Cd stress, all the parameters above increased in a dose-dependent way. The activity of SOD declined, while the activity of POD and CAT increased under either Pb or Cd stress. At corm swollen stage, there was no obvious change of chlorophyll content, but a significant rise of MDA was observed. The soluble sugar and soluble protein increased at low concentration of Pb, but declined at higher level of Pb stress. The chlorophyll content decreased, while MDA and soluble protein increased, and the soluble sugar declined at low level of Cd stress, but increased under higher level of Cd stress.4. Pb and Cd had a obvious negative effect on the yield of taro. The yield under different level of Pb stress was34.2%,46.6%,45.1%,52.2%and53.5%of that under non-stress condition. The corresponding numbers were56.5%,38.3%,21.9%,38.9%and31.8%for taro yield under Cd stress, as compared to non-stressed control.5. The content of heavy metals in soil (Pb, Cd or As) meet the Environmental Quality Standards in Soil (GB15618-1995) in the production areas of taro and water bamboo except that the Cd accumulation in GX-LJV, ZJ-WJW and ZJ-HZ exceeded the standard by50%,20.8%and15.0%, respectively. Cd was observed to generate higher risk compared with Pb or As in the production areas of taro and water bamboo. In GX-LP and ZJ-YH, maximal accumulation of Cd caused a considerable potential ecological risk, and a moderate potential ecological risk was caused by average accumulation of Cd, with the highest SPI or Igeo value. A moderate potential ecological risk for the maximal or average accumulation of Cd in HB-HC, JX-YS, ZJ-JH and ZJ-TX was observed. The high Igeo value of Pb (>0) indicated that there was a possible risks of Pb in GX-LP, FJ-FD, JX-YS and ZJ-YH.6. In the production areas of taro, an order of enrichment factor of Cd>As>Pb indicated Cd had a bigger ability of moving from soils to plant than Pb, which is consistent with fact that Pb is prone to accumulate in underground bulb and Cd is in easily accumulated in stalk in pot experiment. However, in the production areas of water bamboo, the transferring capacity was in order of As>Cd>Pb with higher accumulation of Pb or Cd in leaf than in cane shoot, which is opposite for As.7. There was a heavier pollution of Cd in the production areas of taro than Pb. Cd pollution was found in soil as well as plants in GX-LJV, and in soil from JX-YS. In addtion, plant samples are not uniformly contaminated in the same production area. Plant samples of AH-YBV2, AH-DXV, AH-SJV were contaminated with Cd in AH-YX, but other samples could not be polluted, indicating sources of heavy metals during agricultural production was complicated and the artificial factors may be an important sources for heavy metals pollution. 8. There was high accumulation of Pb but low accumulation of Cd in the edible organs. Compared to maximal allowable limit, the maximal accumulation of Pb in mother taro and son taro was53.2and21.7folds, respectively. However, only2.48folds and1.85folds of Cd concentration compared to maximal allowable limit was found in mother taro and son taro respectively. Although few edible organs samples were polluted by Cd or Pb, Cd in taro organs heavily exceeded the maxim allowable limit in JX-YS. The Taget Harzard Quetien (THQ) of Cd in JX-YS is more than1.0for children and close to1.0for adult, indicating health risks from Cd. Although As residues was far below the national standard in various production areas, the THQ for As and TTHQ was more than1.0in the majority of taro regions and all the water bamboo regions, which suggested a potential health risks from As in the production areas of taro and water bamboo.