Effects of Soil Passivating Agents on Lead/Cadmium/ Chromium Contents in Vegetables

  Objective   Commercial soil passivating agents were compared for their effects on the heavy metal uptakes by leafy vegetables in the field of acidic soil in Fujian.

  Method  A farm in Pingnan county contaminated with Pb, Cd, and Cr was selected to conduct the tests for determining the effects of 8 passivating agents on yield and heavy metal content of Pakchoi (Brassica rapa subsp. chinensis) in the 1^st season and Chinese cabbage (B. rapa subsp. pekinensis) in the 2^nd season grown on the lot. pH and DTPA-extractable in the soil were measured to correlate them with the migration of the heavy metals to the vegetables.

  Result   (1) Application of either the heavy metal passivator, OSA, or Tebbe Calcium Conditioner significantly increased the yield of Pakchoi by up to 84.2% and Chinese cabbage by up to 65.4% over control. (2) Yonker Soil Conditioner or OSA produced the most significant rises on the soil pH to 5.25 on the lot during the 1^st season when Pakchoi were planted and 4.76 in the subsequent season for growing Chinese cabbages. (3) Sea Crown Soil Conditioner significantly reduced DTPA-extracted Cd in the soil of the Pakchoi lot by 31.0% and of the Chinese cabbage lot by 25.4% over control. Among the treatments, Yonker and Sea Crown rendered the highest reductions on the DTPA-extracted Pb, while OSA and Kangyuan Soil Conditioner on DTPA-extracted Cr in both vegetable lots. (4) Of all the agents applied, the best results by comparing to control were found with OSA, which significantly decreased Pb in Pakchoi by 41.5% and in Chinese cabbages by 46.0%, with OSA or Yonker, which significantly decreased Cd in Pakchoi by 46.0% and in Chinese cabbages by 34.6%, and with Ten-thousand-mu Organic Fertilizer or Yonker, which significantly reduced Cr in Pakchoi by 73.2% and in Chinese cabbages by 60.6%. In the soil, OSA, Tebbe, or Yonker also effectively reduced the Cd at the Pakchoi lot to be within the national safety standard limit. (5) Positive correlations between the Pb, Cd, and Cr contents in vegetables and the DTPA-extractable in soil (P＜0.01), as well as a negative correction between the heavy metals in vegetables and soil pH (P＜0.01). It suggested that the passivating agents raised the pH of the acidic soil and effectively lowered and mitigated the heavy metals migration from the soil resulting in significant reduction on Pb/Cd/Cr in Pakchoi and Chinese cabbages grown on the land.

  Conclusion  It appeared that the tested passivator OSA and conditioner Yonker were effective in remediating Pb/Cd/Cr-polluted acidic soils for vegetable farming.