模拟酸雨对羟基磷灰石稳定化土壤镉的分布、可浸出性及生物可给性的影响

通过室内土柱淋溶实验,以0.5%的质量比向镉污染土壤中添加羟基磷灰石(HAP),以不施HAP土壤为对照,考察p H 3.5、4.5和5.6的模拟酸雨对土壤镉的分布、可浸出性、生物可给性及其健康风险的影响。结果表明:酸雨淋溶显著降低了对照处理表层土壤p H,添加HAP增加了土壤对酸雨淋洗的缓冲能力,土壤p H较对照高约1个单位。对照处理酸雨p H的降低加剧了Cd在土柱内的下移,但HAP处理各土层全Cd分别较对照0~5 cm和5~10 cm土壤高出8.54~10.0、3.13~3.29 mg·kg-1。对照处理土壤在酸雨作用下可浸出性Cd含量从0~5 cm的0.17~0.23 mg·L-1增加到10~20 cm的0.61~0.68 mg·L-1,但HAP处理各土层可浸出性Cd维持在0.45~0.50 mg·L-1。总体上,对照和HAP处理土壤胃液和肠液阶段溶解态Cd含量及胃液阶段Cd的生物可给性均随酸雨p H的降低而降低。与对照相比,HAP处理土壤增加了胃液和肠液阶段溶解态Cd含量及胃液阶段Cd的生物可给性,但显著降低了肠液阶段Cd的生物可给性。对照和HAP处理土壤胃液和肠液阶段无意摄入土壤中Cd对儿童的每月允许摄入量PTMI(Provisional tolerable monthly intake)贡献率均随酸雨p H的降低而降低,且HAP处理显著高于对照。以上结果表明高强度酸雨淋溶下,HAP能够有效提高土壤对酸雨的缓冲能力,降低土壤Cd的淋失,但增加了表层土壤Cd的生物可给性及人体健康风险,需要引起特别关注。

Effects of simulated acid rain on distribution, leachability and bioaccessibility of cadmium in a contaminated soil immobilized by hydroxyapatite

A leaching experiment was conducted to study the distribution, leachability and bioaccessibility of cadmium (Cd) in soil with and without 0.5% (W/W) hydroxyapatite (HAP) amendment, under simulated acid rain (SAR) with pH at 3.5, 4.5 and 5.6. Results showed that soil pH in the control soil was decreased with leaching of SAR, but pH in HAP treated soil increased by about 1 unit compared with the con trol soil. Decreases in SAR pH increased the migration of Cd to the deeper soil column in the control soil, whereas Cd was strongly fixed in HAP treated soil and the Cd concentrations in 0~5 and 5~10 cm soil were 8.54~10.0 and 3.13~3.29 mg·kg^-1 higher than those of the control soil, respectively. In the control soil, leaching of SAR increased TCLP-extractable Cd from 0.17~0.23 mg·L^-1 at a depth of 0~5 cm to 0.61~0.68 mg·L^-1 at a depth of 10~20 cm, whereas it ranged from 0.45 to 0.50 mg·L^-1 at a depth of 0~20 cm in the HAP treated soil. Generally, bioaccessible concentrations and bioaccessibility of Cd in gastric and small intestinal phases decreased with decreasing SAR pH in all soil samples. However, the bioaccessible concentration and bioaccessibility of Cd in gastric and small intestinal phases were higher in the HAP treated soil than in the control soil, but bioaccessibility of Cd in small intestinal phase was lower. In gastric and small intestinal phases, the rates of oral ingestion soil Cd to the provisional tolerable monthly intake (PTMI) recommended by WHO in all soils decreased with de creasing of SAR pH, but were higher in the HAP treated soil than in the control soil. These findings indicate that HAP treated soil can effectively increase acid buffer capacity and decrease the leaching loss of Cd. However, the bioaccessibility and health risk from the oral ingestion of soil Cd in HAP treated soil are higher than in the control soil. Thus more attentions should be paid when HAP is used to immobilize Cd in acidic soils.