Effects of soil properties on heavy metal accumulation in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) in Pearl River Delta, China

This study was conducted to investigate the effects of soil properties on the heavy metal accumulation in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) at the field scale. The concentrations of cadmium (Cd), mercury (Hg), and chromium (Cr) in topsoil and vegetable samples from Nanhai district of Foshan city in the Pearl River Delta (PRD) were analyzed. The results showed that 56.5% of the soil samples exceeded the grade II of the Chinese Soil Environmental Quality Standard (GB 15618-1995) for Hg concentrations, while 8.70% and 17.4% of the vegetable samples exceeded the criteria of the Chinese Safety Qualification of Agricultural Products (GB 18406.1-2001) for Cd and Hg concentrations, respectively. The calculated bio-concentration factor (BCF; i.e., the ratio of the metal concentration in the edible parts of flowering Chinese cabbage to that in soil) values were ranked as: Cd (0.1415) > Cr (0.0061) > Hg (0.0012) (p < 0.01), which demonstrated that Cd was easier to be accumulated in the edible parts of flowering Chinese cabbage than Hg and Cr. Furthermore, the following relationships between (bio-concentration factor) BCF values (BCFs) and soil physicochemical properties were concluded from our results: i) the mean BCFs of coarse-textured soils were higher than those of fine-textured soils; ii) the BCFs decreased with increasing soil pH; iii) the soils with high organic matter(OM) and Cation exchange capacity (CEC) have low BCFs, resulting from their high sorption capacities for Cd, Hg, and Cr. The stepwise linear multiple regression analyses showed that total metal concentrations and available calcium in soils were two main factors controlling the accumulation of Cd, Hg, and Cr in the flowering Chinese cabbage.