Cadmium and lead redistribution in different fractions of humus in an oxisol treated with compost

• Main Authors: Fang-Ying Su, 蘇芳瑩
• Other Authors: Zeng-Yei Hseu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/04569256013434697747

碩士 === 國立屏東科技大學 === 環境工程與科學系 === 94 === Understanding the relationship between heavy metals in the soil and various humic substances in the compost facilitates the risk evaluation on site hazard with composts as a modifier for soil polluted by heavy metals. Therefore, after adding bark compost (30 Mg/ha) into a kind of oxisol selected in southern Taiwan, the research further added different amount of cadmium chloride and lead chloride solutions for the empirical experiment. Cadmium and lead contents in the soil were 20, 40, 60, 80 mg/kg and 200, 400, 600, 800 mg/kg. After incubation period, soil humic substances discrimination was conducted at various points of time, as well as DTPA performed to extract effective cadmium and lead from the soil. The purpose was to investigate the redistribution of heavy metals, i.e., cadmium and lead, in the strong red acid clay soil after the application of compost. It was revealed from the results that, with different concentrations of cadmium chloride and lead chloride added into the soil mixed with bark compost, the positive correlation in quadratic curve between DTPA extract and the concentration of cadmium and lead reached r2>0.9908 and r2>0.9653, respectively. In other words, the application of bark compost reduced amounts of cadmium and lead that can be extracted by DTPA. This is particularly significant in the cases of higher concentration. As for the variation in concentrations of soluble cadmium and lead, cadmium release had a negative correlation in the quadratic curve with the amount of compost added (r2>0.715), while lead release had a positive correlation with the amount added (r2>0.6862). This was particularly obvious with higher concentrations. As for the variation in concentration of cadmium in humic acid fractions, the results showed irregular alternation at different test days (r2>0.858); but in the 120th day, cadmium concentration in the humic acid fraction increased. The variation in concentration of lead in humic acid fraction showed that it was higher with application of compost at every test day, and a negative correlation in the quadratic curve was found between the amount added and lead concentration (r2>0.9881). Moreover, the variation of cadmium concentration in fulvic acid fraction was irregular during incubation, while before the 90th day, the concentration of effective cadmium decreased (r2>0.8357). However, it increased after the 120th day (r2=0.9772). The variation of lead concentration in fulvic acid fraction revealed that the application of compost increased lead content in the fulvic acid fraction, and a positive correlation in quadratic curve was found between lead concentration and the amount added (r2>0.9394). Further, the variation of cadmium concentration in residual fraction was irregular with compost added in different days (r2>0.8086) till the 120th day when the amount of residual cadmium decreased since it was partially dissolved into the humic substances. As for the variation of lead concentration in residual fraction, samples added with compost showed lower readings than those not added at every different test day(r2>0.9783). This indicated that the chelation effect caused absorption of lead into humic substances, reducing the amount of lead in residual fraction.