地球化学元素高背景农作区土壤剖面重金属来源解析及污染评价

Source identification and pollution assessment of heavy metals in soil profile of agricultural area with high background of geochemical elements

为探明典型地球化学元素高背景农作区土壤剖面重金属的含量及污染风险,以四川省富顺县典型农作区田和旱地为研究对象,明晰其土壤中重金属元素(Cd、Cr、Cu、Ni、Pb、Zn)的垂直分布特征,并利用正定矩阵因子分析法(PMF)探究其重金属污染来源,基于PMF得到的源成分谱,利用地累积指数法和内梅罗综合风险指数法分析区域内每种源对重金属累积及污染风险的贡献.结果表明,Cd、Cr、Cu、Ni、Pb和Zn在水田土壤剖面中的含量分别为0.19—0.62、47.94—51.15、19.90—21.02、25.61—29.67、18.75—22.15、59.24—71.13 mg·kg^(−1),旱地土壤剖面中的含量分别为0.15—0.62、47.53—58.39、18.91—22.04、25.26—32.13、17.45—21.75、59.78—77.58 mg·kg^(−1).6种重金属中仅Cd元素含量的平均值高于四川省背景值.水田和旱地土壤的Cd和Pb具有明显的表聚性,而Cr、Cu、Ni、Zn则随土层加深整体呈先降低后增加的趋势.PMF模型结果表明农业源的贡献率随土层加深而降低,在表土层中的贡献尤为突出(水田,50.6%;旱地,55.1%),混合源的贡献率随土层加深而升高,在底土层中的贡献尤为突出(水田55.5%;旱地58.7%),自然源的贡献率受土层影响不大、较为均匀,为21.3—33.3%.基于源成分谱的污染累积与生态风险评价表明,研究区土壤Cd元素存在较强的污染累积和生态风险,且以农业源的风险最大,混合源风险最小;其余5种重金属元素无污染累积风险,但存在轻微生态风险.3种源中以农业源对生态风险的贡献最大,平均达65.3%,其次为混合源(29.1%),自然源贡献率平均仅为5.6%.研究结果表明,应重点关注该区域土壤重金属Cd污染问题,且需加强对农业源的防治.

In order to investigate the content and pollution risk of heavy metals(HMs)in the soil profile of typical agricultural areas with high background of geochemical elements,the vertical distribution characteristics of HMs(Cd,Cr,Cu,Ni,Pb,Zn)in soils of paddy field and dryland that collected from a typical agricultural area in Fushun County,Sichuan Province were studied;the sources of HM pollution were explored by using positive matrix factorization(PMF);and the contribution of each source to the pollution assessment in the region was analyzed by using Geoaccumulation Index()and Nemerow Integrated Risk Index(NIRI).The results showed that the contents of Cd,Cr,Cu,Ni,Pb and Zn in the soil profile of paddy field were 0.19—0.62,47.94—51.15,19.90—21.02,25.61—29.67,18.75—22.15,and 59.24—71.13 mg·kg^(−1),respectively.The contents of the above six HMs in dryland soil profile were 0.15—0.62,47.53—58.39,18.91—22.04,25.26—32.13,17.45—21.75,and 59.78—77.58 mg·kg^(−1),respectively.Among the six HMs,only the average content of Cd was higher than the background value in Sichuan Province.Meanwhile,Cd and Pb had obvious surface aggregation in paddy field and dryland soil,whereas Cr,Cu,Ni and Zn decreased first and then increased with the deepening of soil layer.The results of PMF model showed that the contribution rate of agricultural source was the highest in the topsoil layer(paddy field,50.6%;dryland,55.1%),and decreased with the deepening of soil layer.The contribution rate of mix source also increased with the deepening of soil layer,but the largest contribution was in subsoil(paddy field,55.5%;dryland,58.7%).In addition,the contribution rate of lithogenic source was not changed with soil layer,the values were ranging from 21.3%to 33.3%.The pollution accumulation and ecological risk assessment based on source component spectrum showed that there were moderately polluted accumulation and considerable ecological risk of Cd in the study area.Furthermore,the risk of the agricultural source was the highest,and the risk of mixed source was the least.The other five heavy metals have no cumulative pollution risk,but have slight ecological risk.Among the three sources,agricultural source contributed the most to the ecological risk,with an average contributed rate was 65.3%,followed by mixed source(29.1%),and natural sources contributed only 5.6%.In conclusion,it needs to pay more attention to the problem of soil Cd pollution in this region,and the prevention and control of agricultural sources should be strengthened.