Phytotoxicity of arsenic compounds on crop plant seedlings.

The effects of inorganic and organic arsenic on the germination and seedling growth of 10 crop plants were investigated to elucidate the relationship between toxicity and the arsenic chemical states. Two types of soils, soil A and B, were also tested to determine how physicochemical properties of soils were related to toxicity of arsenic and the sensitivity of the plants. All tested plant species, except mung bean and cucumber, showed inhibition of germination by two types of inorganic arsenic, arsenite, and arsenate, while the organic arsenic compound, dimethylarsinic acid (DMA), had no inhibitory effects on plants in soil A. In contrast, the growth of seedlings of all 10 plant species was sensitive to the presence of arsenic. The sensitivity of the plants toward inorganic arsenic compounds showed similar trends but differed for DMA. Overall, seedling growth was a more sensitive endpoint to arsenic toxicity than germination, and the relative toxicity of arsenic compounds on plants was arsenite > DMA > arsenate. Interestingly, the sensitivity of wheat varied significantly when the soil was changed, and the DMA was most toxic rather than arsenite in soil B. Thus, the systematic study employed here provides insights into the mechanisms of arsenic toxicity in different plant species and the role of physicochemical properties of soils.