Foliar uptake, translocation and accumulation of heavy metals from atmospheric deposition in crops

The problem of excessive heavy metals in agricultural products has aroused widespread public concern in recent years. Most previous studies have shown the absorption mechanism of heavy metals by roots, and have clarified that crops absorb and transfer heavy metals to the aboveground plant parts through a series of transport cells. Effective prevention or control of heavy metal pollution in agricultural products could be achieved by proper identification of sources of the heavy metals. However, the contribution of atmospheric deposition to the accumulation of heavy metals in agricultural crops as well as the absorption, transport and accumulation mechanisms of heavy metals in leaves are still unclear. We summarized and compared the absorption, transport, partition, accumulation mechanisms and main influencing factors of heavy metals in leaves and roots from two ways of heavy metal absorption and accumulation. The transport coefficient and contribution rate of heavy metals to the edible parts of crops under the two absorption pathways were compared. For the literatures without direct transport and transport coefficients, the heavy metal content data in atmosphere, soil and crops were extracted and further processed and calculated. The results showed that heavy metals could be absorbed by roots and leaves simultaneously, but the mechanisms of absorption, transport, partition and detoxification were quite different. In many cases, the heavy metals absorbed by roots are not the only source or even the main source of heavy metals accumulation in edible parts of crops. Atmospheric deposition of heavy metals contribute significantly to their accumulation in agricultural products. This study aids our understanding of the sources, absorption and transport mechanisms of heavy metals in edible parts of crops. It also provides theoretical guidance for taking effective heavy metal prevention and control measures which could promote safe production of agricultural products.