铅锌矿废水污染水稻土Cd的化学形态与生物有效性研究

Chemical Speciation and Bioavailability of Cadmium in Paddy Soils Contaminated by Mining Wastewater from a Lead-Zinc Mine,China

土壤中金属的各种化学形态监测对评价它的移动性和生物有效性非常重要。对利用铅锌矿废水>50a而受到重金属污染的水稻土及水稻植株进行了采样、分析。用微波消解法消解土壤中总量Cd和植物中Cd含量,分别用DTPA溶液和模拟胃肠液(氨基乙酸经HCl酸化至pH1.5于37℃模拟的胃肠液环境)浸提土壤Cd的植物有效态和动物/人“吞食后生物有效态”(简称SBET态),用Tessier连续浸提法(略有修改)进行土壤Cd的形态分析。所有溶液中的Cd均用原子分光光度计进行检测。结果表明,总体上,土壤Cd以残渣态存在,其占到总量的60%以上;土壤中Cd的植物有效性(DTPA提取量)明显比其动物有效性(SBET提取量)低,其仅相当于后者的13.8%,表明该地区土壤由于受到来自铅锌矿废水的Cd污染而对当地动物/人的潜在生态危害远远大于当地种植的水稻等农作物;Fe-Mn氧化物结合态Cd与土壤Cd的植物有效性(DTPA态)及动物/人“吞食后生物有效性”(即SBET态)相关性最好,有机结合态Cd次之。本研究可以为建立土壤Cd数据库提供基础信息,也可用于说明Cd的形态(分析)对矿区土壤Cd的生物有效性的重要性。

Determination of various chemical forms of a metal in soils is important to evaluate its mobility and bioavailability. Both soils and rice plant were sampled from a paddy field in Lechang lead/zinc mine area in north Guangdong province. The study soils and rice plants are still irrigated with local lead-zinc mining wastewater after irrigation with wastewater for 50 years. Microwave digestion method was used to extract total Cd in soils and rice plants, DTPA solution and a synthetic gastroenterological fluid prepared by dissolving 60.06 g glycine in 2L deionized water and adjusted to pH 1.5 with HC1 （12.1 M） were utilized for the extraction ofthe plant-available Cd and the animal/human- extractable Cd （named SBET-Cd in this paper） of soils, respectively. Exchangeable, carbonate, Fe-Mn oxides, organic and residual form of Cd in soils was determined by a modified sequential extraction procedure based on Tessier et al. （1979）. Cadmium in all extracts was analyzed using atomic absorption spectrophotometer （AAS）. The result showed that, generally, the average amount of each particulate-bound Cd in the surface soils followed the order, residual （accounting for 62.7% of the total） 〉 carbonate-bound （16.9 %） 〉 exchangeable （11.3%） 〉 Fe-Mn oxide-bound （4.9%） 〉 organic-bound （4.2%）. The respective DTPA- and SBET-extractable Cd averaged 0.48 mg·kg^-1 and 3.47mg·kg^-1, indicating that the plant-availability of Cd in soils was significantly lower than its animal/human-availability in the human/animal gastrointestinal tract and, thus, implying that the potential ecological risk for local animal and/or human was heavily severer than for rice plant by Cd from the wastewater from local lead-zinc mine. Among the five chemical fractions according to the modified Tessier method, the Fe-Mn oxide-bound Cd was correlated most significantly with the bioavailability. Moreover, the organic-bound Cd was only next to the Fe-Mn oxide-bound Cd in correlation with the Cd availability of the soils. These could provide basic data in establishing a soil Cd database and also address the importance of Cd speciation in assessment of Cd bioavailability in mine soils.