氮肥企业退役地块氨氮污染及其风险研究

基于氮肥企业退役地块土壤、地下水、土壤气和室内空气中氨氮的实测数据,分析了氨氮在各地块中的污染水平和分布特征,评估了氨氮污染的人体健康风险,分析了氨挥发造成的刺激性异味风险和对室内空气质量的影响,及氨氮迁移转化对附近地表水和下游地下水水质的污染风险.分析发现,4个地块中土壤和地下水氨氮含量均表现较强的变异性,土壤中氨氮最高浓度分别高达12700.00,2420.00,2920.00,2370.00mg/kg,地下水中氨氮最高值分别高达7550.00,5100.00,847.00,3760.00mg/L.在平面分布上,4个地块中土壤和地下水较高浓度氨氮均主要分布在生产区和污水处理区,在垂向分布上4个地块间存在差异,氮肥厂I的土壤以黏土为主,多数点位氨氮含量随深度增加而递减,氮肥厂II、III和IV的土壤以粉土/粉砂或粉土夹粉黏为主,氨氮含量总体呈现随深度增加而增加的趋势.4个地块中,仅氮肥厂I在最保守条件下土壤中氨氮的最高危害熵(1.54)略超可接受风险水平(1.0).氮肥厂II和IV的土壤气和室内空气中检出氨浓度范围分别为≤ 9.88mg/m³和≤ 0.18mg/m³,对室内空气质量未产生不利影响.氮肥厂I和II紧邻河流监测井中的氨氮浓度超《地表水环境质量标准》中IV类(1.5mg/L)标准1.05~409.33倍,氮肥厂III和IV污染区地下水中氨氮浓度在至少4次监测结果中有轻微降低,且在下游监测井中发现硝态氮的积累.分析结果表明,4个地块在现状条件下土壤和地下水氨氮污染的人体健康风险较低,对室内空气质量影响较小.但地块地下水中氨氮是附近地表水和下游地下水环境的长期污染源,氨氮转化的硝态氮更易向下游迁移.建议今后处理氮肥企业退役地块氨氮污染时将其对地表水和下游地下水环境的污染风险纳入考虑.

Pollution characteristics and environmental risks of ammonia nitrogen in retired nitrogen fertilizer plant sites

Based on the concentrations of NH₄⁺-N in soil, groundwater, soil gas, and indoor air from abandoned nitrogen fertilizer plants sites, the polluted level and distribution characteristics of NH₄⁺-N in these sites were analyzed, the human health risks for exposure to the NH₄⁺-Nin soil and groundwater were evaluated, and the effects of ammonia volatilization on the risk of irritating odors and indoor air quality, as well as the impact on nearby surface water and downstream groundwater with NH₄⁺-N migration and transformation was also evaluated. The results showed that the concentrations of NH₄⁺-N in the soil and groundwater significantly varied in all four sites. The highest concentrations of NH₄⁺-N in the soil of the four sites were as high as 12700.00, 2420.00, 2920.00, and 2370.00mg/kg, respectively, and the highest concentrations in the groundwater were up to 7550.00, 5100.00, 847.00, and 3760.00mg/L, respectively. The high concentration of NH₄⁺-N was mainly distributed around production and the sewage treatment areas. The vertical distribution of NH₄⁺-N in soil was different in four sites, in which the NH₄⁺-N concentration mainly decreases with the increase of depth in site I, in which the soil is mainly clay, while the NH₄⁺-N concentration generally showed an increasing trend with increasing depth in site II, III and IV that the soil is mainly silt sand or silty clay. The hazard quotient of NH₄⁺-N was calculated in site I with a value of 1.54, which slightly exceeded the acceptable risk level (1.0). The concentrations of NH₃ (g) detected in soil gas and indoor air were ≤9.88mg/m₃ and ≤0.18mg/m₃, respectively, which had no adverse effects on indoor air quality. The concentration of groundwater NH₄⁺-N in site I and II nearby the surface water exceeded 1.05to 409.33times the Category IV (1.5mg/L) standard in the Environmental Quality Standards for Surface Water. The concentrations of groundwater NH₄⁺-N in site III and IV were slightly decreased during four times monitoring and the accumulation of nitrate nitrogen was found in the downstream monitoring wells. The results suggested that the human health risk of NH₄⁺-N in the four sites were low, and the impact on indoor air quality was weak. However, the groundwater NH₄⁺-N in the site was a pollution source for nearby surface water and downstream groundwater environment in the long term, and the nitrate nitrogen transformed by NH₄⁺-N was more likely to migrate downstream.This study provides a scientific basis and practical experience for considering the environmental pollution risks of surface water and groundwater when dealing with NH₄⁺-N in a site of nitrogen fertilizer plants in the future.