| 英文摘要 |
This is the term report on the investigation of heavy metal contamination in the agricultural lands at Tali Area, Taichung City, executed in the period from August 18, 2011 to August 17, 2012.
Total 888 farmland soil samples were collected and examined for heavy metal content. The results of 193 farmland blocks exceeded the control standards of heavy metal content in farmland soil. Accordingly, the area of agricultural lands polluted by heavy metals, including chromium, copper, nickel and zinc, was estimated to be 25.4 hectares. Geographical statistics was applied to determine the areas of farmlands polluted by heavy metals, and locate the sources and proliferation pathways of pollution. The method of “paired differences t statistical tests” was used to compare the current results with the data gathered by TARI. It was found that the average yearly increases of the chromium, nickel and zinc contents in the topsoil samples, determined using aqua regia extraction, were 0.094, 0.062 and 0.076 kg per hectare, respectively. The heavy metals in the sediments of irrigation canals were mainly chromium, copper, nickel, and zinc. The occurrences of chromium, copper, nickel and zinc were also detected in water samples and the total amount of chromium in some of the water samples exceeded the irrigation water quality standards. For the farmland soils with the contents of heavy metals exceeding the control standards, the correlations of the heavy metal contents in the topsoil with those in the corresponding mud sediment and water were determined to be 86% and 57.1%; the correlation between the heavy metal contents in mud sediment and water was 30%. As the irrigation canals in the same irrigation system show similar pollution characteristics, it can be inferred that the factories in the nearby areas has significant contribution to the occurrence of heavy metal pollution. The industrial waste water released into the irrigation canals was used by the farmers to irrigate their farmland, which consequently results in the accumulation of heavy metals in the farmlands.
Based on the method of location correlation, this project has provided a list of suspected sources of pollution for the local environmental agency to strengthen inspection and to facilitate claims for environmental damage compensation. As revealed in this research, heavy metals are detected in the wastewater of four factories which has failed to meet the water examination standard; as the historical inspection record showed, a total of fourteen factories have released waste water which does not meet the wastewater release standard into nearby irrigation canals. This study suggests that the owners of the above-mentioned factories are required to pay for the damages they have incurred, and the early-warning system has to be established in order to protect farmlands from heavy metal pollution.
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