Transfer of heavy metals from sludge amended soil to vegetables and leachates

ชื่อเรื่อง Transfer of heavy metals from sludge amended soil to vegetables and leachates ผู้ดำเนินการ (1) Land Development Department, Phaholyothin, Chatujak, Bangkok, 10900 Thailand (2) Department of Soil science, Kasetsart University, Phaholyothin, Chatujak, Bangkok, 10900 Thailand (3) Chemistry Department, The Royal Veterinary & Agricultural University, Thorvaldsensensvej 40, DK-1871Frederiksberg C., Copenhagen, Denmark บทคัดย่อ         Application of sludge to tropical agricultural soils is under evaluation. The advantage of sludge is to provide plant nutrients but the problem of pollution with heavy metals remains to be clarified. To obtain information on heavy metal release from soil and their accumulation in vegetables and soils, lysimeter experiments were carried out. Two rotations of Chinese kale (Brassica oleracea L.) was grown in sludge amended soil (Typic Kandiustults) in the lysimeters which were placed under open air in Bangkok and run for a period of 2x40 days. Mean temperature and precipitation during growth of the first and second kale was 26 oC; 80.4 mm and 29 oC; 118.1 mm, respectively. Two sludge types, municipal and industrial sludges, were applied separately to the lysimeters at rates of 125, 250 and 375 kg N ha–1. Chemical fertilizer (N-P2O5-K2O : 20-10-10) at a rate of 125 kg N ha–1 was used as a control. The seven treatments, each with three replicates, were arranged in a completely random design. Two weeks after planting of the kale, weekly analysis of Cd, Cu and Pb in leachates from the lysimeters were carried out. The kale was harvested when 40 days old and analyzed for the content of Cd, Cu and Pb. The results from the lysimeter experiments showed that heavy metal concentrations in the edible part of Chinese kales did not exceed the threshold values for food contamination. Trace amounts of heavy metals were detected in leachates but most of the added heavy metals (Cd: > 83 %, Cu: > 98 %. Pb: > 86 %) remained in the soil during the period of 135 days. To further characterize the bonding and release rates of Cd, Cu and Pb in the sludge amended and non-amended soils from the lysimeter studies, release experiments were carried out using stirred flow-through reactors. Release experiments were run for 7 days at a steady state pH in the range 2.9 to 7.1. The release experiments showed that the release rates were strongly dependent on pH, with much higher rates at lower than higher pH, and with higher release and weaker bonding of Cu in the sludge-amended soil compared with the non-amended soil. The release of Cd showed an anomaly with exceptional low release rates at low pH reflecting a strong bonding of Cd in the studied soil.

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