Transfer of a cyanobacterial neurotoxin, β-methylamino-l-alanine from soil to crop and its bioaccumulation in Chinese cabbage.

Most cyanobacteria can synthesize the notorious neurotoxin β-methylamino--alanine (BMAA) that is transferred and bioaccumulated through natural food webs of aquatic ecosystems and ultimately arises the potential human health risks by the consumption of BMAA-contaminated aquatic products. Fertilization of cyanobacterial composts in farmlands may also lead to BMAA contamination in soil and its possible transfer and bioaccumulation within major crops, thereby threatening human health. In this study, we first detected a high level of BMAA (1.8-16.3 μg g) in cyanobacterial composts. In order to assess the health risks from cyanobacterial composts, we planted Chinese cabbage, a favourite vegetable in China, in BMAA-contaminated soil (4.0 μg BMAA/g soil) and detected the levels of free and protein-associated BMAA in soil and crop organs during the whole growth cycle by HPLC-MS/MS, respectively. Our results demonstrated that BMAA indeed transferred from soil to root, stem and leaf of Chinese cabbage during the growth cycle. The BMAA level finally accumulated in the edible portions was much higher than the initial level in soil, including 13.82 μg g in leaf and 4.71 μg g in stem. The discovery of the neurotoxin BMAA in this vegetable, an ending in human consumption, not only provides a BMAA transfer pathway in farmland ecosystems, but also is alarming and requires attention due to the potential risk of cyanobacterial composts to human health.