广西典型岩溶地区重金属在土壤⁃农作物系统中累积特征及其影响因素

Distribution and accumulation of heavy metals in soil⁃crop systems from a typical carbonate rocks area in Guangxi

为了揭示碳酸盐岩区土重金属高背景值区土壤⁃农作物系统中重金属的迁移和累积特征,选择广西典型碳酸盐岩高背景值区,系统采集了大宗农作物及其配套耕层土145组,分析了耕层土壤和农作物中As、Cd、Cr、Pb、Hg、Cu、Ni、Zn的含量,并通过统计分析、计算生物富集因子及相关分析等方法,开展重金属元素在典型岩溶区土壤⁃农作物中累积特征及其影响因素研究.结果表明,研究区耕层土壤重金属含量显著高于广西和全国表层土壤平均值,其中,Cd、Zn含量是广西表层土壤平均值的1.3倍和4.9倍,是全国表层土壤平均值的1.5倍和7.3倍.依据GB 15618—2018和GB 2762-2017,耕层土壤中As、Cd、Cr、Cu、Hg、Ni、Pb、Zn的点位超标率分别为43.45%、88.97%、14.48%、8.28%、4.14%、9.66%、6.90%、33.79%,水稻中仅有Cd和Hg超标,超标率分别为6%和2%,分析显示耕层土壤中重金属含量与农作物籽实中重金属含量无对应关系.不同土壤⁃农作物系统中,Zn元素迁移能力最强,Cr元素迁移能力最弱;晚稻对Cd、Hg、As、Cr,玉米对Zn的吸收富集能力强;重金属元素在水稻和玉米中的生物富集因子普遍较低,明显低于非碳酸盐岩区农田土壤.相关分析显示,土壤pH、有机质、Fe_(2)O_(3)和Al_(2)O_(3)与重金属元素生物富集因子呈显著负相关,土壤中Se元素能够有效抑制农作物对重金属元素的吸收;随着土壤中碳酸盐含量增加,重金属从土壤向水稻的迁移受到抑制,但对玉米对重金属的吸收无显著影响.

Heavy metal pollution in agricultural soil has harmful effect on plant growth,inducing enormous economic loss.In order to investigate the effects of heavy metal in soil⁃crop systems of a typical carbonate rocks area in Guangxi,China,145 sets of crops and their rhizosphere soil were collected from Daxin,Guangxi.Accumulation characteristics of heave metals(As,Cd,Cr,Pb,Hg,Cu,Ni,and Zn)in soil and crops were analyzed and determined in this study by statistical analysis.Analysis of heavy metals concentration(As,Cd,Cr,Pb,Hg,Cu,Ni,and Zn)showed that heavy metals Cd and Zn were 1.3 times and 4.9 times than that of the top soil in Guangxi,and 1.5 times and 7.3 times than that of the top soil in the country.In soil plough layer,heavy metals As,Cd,Cr,Cu,Hg,Ni,Pb,and Zn sites are exceeded the standard(GB 15618-2018),with 43.45%,88.97%,14.48%,8.28%,4.14%,9.66%,6.90% and 33.79%standard-exceeding rate,respectively.Concentrations of Cd and Hg in rice,however,were above only the 6%(Cd)and 2%(Hg)of the standard(GB 2762-2017).Thus,there is no relationship between heavy metals uptake of crops and heavy metals in soil.In different soil⁃crop systems,migration capacity of Zn is the strongest while Cr is the weakest.Compared to rice grains and corn from non⁃carbonate rocks area,rice grains and corn from carbonate rocks area contain fewer heavy metals.The late rice shows strong ability to absorb and accumulate Cd,Hg,As,and Cr.Corn has a strong ability to absorb and accumulate Zn.Correlation analysis showed that soil pH,organic matter,Fe_(2)O_(3),and Al_(2)O_(3) were significantly negatively correlated with heavy metal bioconcentration factors.In addition,selenium in the soil could effectively inhibit the absorption of heavy metals by crops.Migration of heavy metals from soil to rice is inhibited by an increase in the carbonate content.But the carbonate content has no significant effect on the absorption of heavy metals by corn and fruit crops.