Geochemical cadmium anomaly and bioaccumulation of cadmium and lead by rapeseed (Brassica napus L.) from noncalcareous soils in the Guizhou Plateau

Highlights: • B. napus may uptake excessive Cd and Pb from naturally Cd-enriched noncalcareous soil. • Soil type dependent regional Cd anomaly (mean 0.43 mg kg⁻¹) was characterized. • (Bio)availability of Cd, but not Pb is high in noncalcareous soil. • Reliable Cd soil-rapeseed relationships were derived using soil variables. • Field data suggest that surface contamination may overestimate Pb uptake in B. napus. The cruciferous crop, oil rapeseed (Brassica napus L.), may bioaccumulate excessive cadmium (Cd) and lead (Pb) as well, from Cd-enriched noncalcareous soils in Guizhou province of southwestern China. Field paired soil-rapeseed sampling and greenhouse experiment were performed to characterize the Cd anomaly in rapeseed-planting soils and to predict the bioaccumulation of Cd and Pb in raw seeds using soil variables. The results indicated that total soil-Cd concentrations averaged 0.43 mg kg⁻¹ (range 0.11–1.41 mg kg⁻¹) from field investigation; and a soil type dependent Cd anomaly was observed. Besides, cumulative frequency of total soil-Cd was plotted to be helpful in delimitation of regional Cd anomalies. Rapeseeds readily bioaccumulated Cd from soils as validated by greenhouse experiment and field data. Contrary results were observed in relation to rapeseed Pb levels measured from greenhouse experiment (very low) and field (very high) which was likely due to soil particle contamination as indicated by the considerably higher ratio of Pb to Cd level in seeds harvested from fields. Based on multiple stepwise regression analysis, reliable Cd soil−rapeseed relationships, but less reliable for Pb, were derived using either total or (bio)available metal concentrations and were further inversely used to derive local soil Cd criteria (e.g., total soil-Cd based, 2.5 mg kg⁻¹) based on Hygienic Standard for Feeds (GB13082-2001). Although seed Cd levels (<feed standard) observed in field data indicated a least human dietary risk, however, high (bio)availability of Cd, but not Pb, in Cd-enriched acid soil still poses high environmental risks and may threaten food safety of other crops.