Size-dependent uptake of chromium colloids in rice (Oryza sativa L.)

Chromium (Cr) contamination in agricultural soils poses a significant threat to food safety. In paddy soil, Cr tends to exist as colloidal Cr, instead of soluble Cr. However, little is known regarding the absorption capability of colloidal Cr in rice. Therefore, this study explores the differential absorption of soluble and colloidal Cr in rice through hydroponic experiments, further investigating size-dependent uptake of Cr colloids, focusing on the role of endocytosis and the effects of adding endocytosis inhibitors. The results demonstrate the accumulation of Cr in rice roots for treatments with 100 μM soluble Cr (Cr-EDTA), 28 nm Cr colloid, and 62 nm Cr colloid were 40.0, 797, and 2033 mg/kg, respectively. The reason for this phenomenon is that colloidal Cr is more likely to be adsorbed onto the cell wall, which increases the potential for rice to absorb colloidal Cr, particularly the larger Cr colloids. When endocytosis in rice was inhibited by wortmannin, the absorption of Cr colloid with small size was reduced by 7.30%-26.6%, thereby highlighting the important role of endocytosis in the uptake of 28 nm particles in rice. In contrast, the uptake of soluble Cr and larger colloids were less affected by endocytosis inhibition. This study underscores the importance of considering colloidal Cr and its particle size when assessing the risks associated with heavy metal pollution in agriculture. The findings have significant implications for managing soil contamination and ensuring food safety.