摘要
为探究肥料生产场地的NH_3-N(氨氮)分布特征及环境风险,以我国某肥料生产场地为研究对象,在场地调查基础上,对场地土壤和地下水NH_3-N的空间分布进行分析,并以人体健康和场地地下水为保护对象分别讨论了土壤NH_3-N风险控制目标值的计算方法.结果表明:①目标场地土壤中w(NH_3-N)为0. 03~15 000 mg/kg,水平方向上高值区集中分布于核心生产区及原辅料堆场,垂向上总体表现为由上至下随深度增加呈先逐步升高后降低的趋势,并且富集于人工填土与原状粉质黏土交界处,粉质黏土阻碍NH_3-N向下迁移,并随地层结构变化其迁移深度不同.②场地上层滞水和潜水中ρ(NH_3-N)分别为19. 10~3 320和0. 03~219 mg/L,超标率分别为100%和57. 89%,并且地下水与土壤的NH_3-N在水平空间分布上具有重叠特征.③因NH_3-N主要通过呼吸吸入挥发性气体产生暴露,并且仅有经呼吸暴露的毒性参数,故采用《污染场地风险评估技术导则》中经呼吸暴露途径的非致癌效应风险控制值计算模型来计算土壤NH_3-N的控制目标,通过代入场地实测土壤Kd(土-水分配系数),得到居住用地下的土壤NH_3-N控制目标值为9 195 mg/kg;若考虑保护地下水水质安全,据三相或两相平衡模型耦合NH_3-N在包气带衰减和地下水稀释作用,当目标场地地表无积水的入渗条件下得到的控制目标值为6 203 mg/kg;当地层从上至下呈饱和含水条件时,土壤NH_3-N控制目标为811 mg/kg.计算值可用作不同场地进行土壤NH_3-N风险管控的参考目标,实际应用中可结合不同地块环境条件、不同受体和保护目标,选择相应的风险控制值对场地进行风险管控.此外,土壤和地下水的NH_3-N污染控制均可考虑采用工程措施和制度控制来进行.
To explore the pollution characteristics and environmental risks of ammonia-nitrogen at fertilizer production sites, the concentrations of ammonia-nitrogen in the soil and groundwater of an abandoned fertilizer factory were analyzed. The control target values for soil ammonia-nitrogen were calculated by considering the protection of human health and groundwater,respectively. The results showed that the concentrations of the soil ammonia-nitrogen at the site were between 0. 03 and 15,000 mg/kg. The abnormally high pollution areas were in the central production areas and material storage areas. The vertical distribution of ammonia-nitrogen in the soil showed a trend of gradually increasing and then decreasing with the increase of depth in the profile. At different migration depths,the peak concentration of ammonia-nitrogen always appeared at the interface between the upper artificial fill and the undisturbed silty clay. The fine silty clay prevented the ammonia-nitrogen from migrating downward,and the ammonia-nitrogen had different migration depths as a result of the change of stratigraphic texture. Moreover,the site was subjected to heavy groundwater pollution of ammonia-nitrogen. The concentrations of ammonia-nitrogen in perched water and phreatic water were 19. 10-3,320 and 0. 03-219 mg/L,respectively,which was 100% and57. 89% above the contamination limits,respectively. According to the layout of the original factory,the ammonia-nitrogen pollution of groundwater and soil had similar spatial distribution patterns. Because currently only toxicity parameters of inhalation exposure route were available for ammonia-nitrogen,the control target of soil ammonia-nitrogen was calculated by using the calculation model of the non-cancer effect risk control value by considering only the inhalation exposure route in the Technical Guidelines for Risk Assessment of Contaminated Sites. Using site-specific measured the soil-water distribution coefficient( Kd),the control target value of ammonia-nitrogen in the soil was determined to be 9195 mg/kg based on an assumption of residential land use scenario. With regard to the protection of groundwater quality,the soil control target values were calculated using the three-or two-phase equilibrium coupled groundwater dilution model and the decay process within unsaturated zone. Depending on the scenario assumptions that there was a surface ponding or not,the control target values were 6203 and 818 mg/kg,respectively. Different control target values should be selected according to the different environmental conditions,and both soil and groundwater should be controlled by means of engineering measures and institutional control.
引文
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