典型菜地土壤汞在小白菜和胡萝卜可食部位的富集规律

对广东省蔬菜种植面积较大的10个城市典型菜地土壤和蔬菜（小白菜和胡萝卜）对应采样，分析217个蔬菜可食部位中重金属汞（Hg）质量分数及对应土壤中Hg全量和有效态质量分数，研究大田条件下小白菜和胡萝卜可食部位富集Hg的规律。结果表明，广东省菜地土壤存在一定的Hg污染，约20％的土壤超过国家土壤环境质量标准（GBl5618－1995）中二级标准值，但小白菜和胡萝卜中Hg质量分数较低，均值分别为0．0012和0．0013mg·kg-1，仅2个小白菜样品Hg质量分数超过国家食品卫生标准《食品中污染物限量》（GB2762-2005）中的限值0．01mg·kg-1。TGA提取的土壤有效态Hg质量分数与土壤Hg全量显著正相关，TGA提取Hg量仅占土壤总Hg质量分数的3％-4％。小白菜和胡萝卜对Hg的富集系数分别为0．90％和0．94％，表明土壤中绝大部分的Hg不易转化迁移、为蔬菜吸收。小白菜和胡萝卜可食部位Hg质量分数与土壤中Hg全量和有效态质量分数均存在显著的线性关系，其中蔬菜与土壤Hg有效态质量分数的关系优于其与土壤Hg全量的关系。依据国家食品卫生标准，通过拟合回归方程计算出的保障小白菜和胡萝b质量安全的菜地土壤Hg有效态质量分数临界值分别为O．038和0．063mg·kg-1。计算出的土壤Hg全量临界值远大于我国现行土壤环境质量标准的二级标准值，表明该标准值对于保障广东省小白菜和胡萝b质量安全来说可能过于严格。

Accumulation of mercury in edible parts of pakchoi and carrot at typical vegetable plots

Two vegetable species, pakchoi （Brassica chinensi L.） and carrot （Daucus carota L.var. sativa DC.）, and their rooting soils were sampled in vegetable plots in 10 cities of large vegetable producing area in Guangdong. The mercury （Hg） contents in vegetables and total and available Hg contents in soils were determined to study Hg accumulation in edible parts of vegetables under field conditions. The results showed that about 20% of the sampled soils had higher Hg contents than the class II threshold of Environmental quality standard for soils （GB 15618-1995）, indicating soil Hg contamination. The pakchoi and carrot showed low Hg contents of 0.001 2 and 0.001 3 mg＇kgl respectively, with only 2 pakchoi samples exceeding the maximum level of Hg in vegetables （0.01 mg·kg-1） set by national food hygiene standard （GB 2761-2005）. Available Hg content extracted with TGA-Na2HPO4 in soil, positively correlated with total Hg, was about 3%-4% of total Hg content. The accumulation coefficients for Hg of pakchoi and carrot were 0.90% and 0.94% respectively, suggesting their low accumulating ability for Hg. Mercury contents accumulated in edible parts of pakchoi and carrot presented linear correlations with both total and TGA-extractable Hg contents in soil, with better fit when using TGA-extractable Hg than total Hg in soil. Based on the regression equations and the statutory limit＇of Hg in vegetables, the soil thresholds of TGA-extractable Hg were calculated to be 0.038 and 0.063 mg·kg-1 for pakchoi and carrot, respectively. Calculated soil thresholds of total Hg were much higher than the class II limits of Environmental quality standard for soils, suggesting current soil quality standard might overestimate the risk of pakchoi and carrot being contaminated by Hg in Guangdong.