dc.description.abstract | Although in Taiwan the government has set up industrial zones to control the treatment and discharge of industrial wastewater separately, there are still factories located in the suburbs and discharging untreated effluents directly into irrigation channels. Such situations have led to contamination of farmland with heavy metals. Of the metals appearing in the agricultural soil, copper is the most frequently detected one, followed by zinc and nickel. It is noted that current control standards for farmland soil in Taiwan only regulate the total metal concentration. While the impact of heavy metals on the environmental matrix is indeed related to the total concentrations, it is the bioavailability of the metals under particular environmental conditions that plays the key role in determining the potential risk exerted on the ecosystem health. In view of this, this study selected the agricultural lands in the Puxinxi River Basin that had been polluted by heavy metals as the test sites, and used the method of sequence selective extraction (but in the final step hydrofluoric acid was replaced by hydrochloric acid) to investigate the phase distribution of heavy metals in the soil, with a hope to assess the potential risks. Results showed that digestion of the residual phase with hydrochloric acid gave results comparable to hydrofluoric acid, as evidenced by the relative extraction percentage (RPD) that was < 20%. In addition, Tessier sequence extraction results showed that: (1) chromium was predominantly associated with the residual phase; (2) the distribution of lead, zinc, and nickel was mainly in the manganese or iron-oxide phases and residual phase; (3) copper mostly stayed in the manganese/iron oxides, organic and residual phases; (4) the majority of cadmium resided in the exchangeable and residual phases. Lastly, the Spearman correlation analysis showed that the total concentrations of heavy metals were significantly correlated with the concentrations of the metal in the manganese/iron oxide phase and the organic phase, respectively, suggesting that these two phases may be the key determinants of risks pertaining to heavy metal contamination. | en_US |