Cadmium and zinc transport and accumulation in two plant species and the associated risk of dietary exposure to animals.

摘要

Cadmium is a nonessential, toxic, heavy metal which enters the environment due to anthropogenic activities. Cadmium is toxic to both plants and animals. Cadmium accumulates in edible portions of crop plants and also exceeds the permissible limits. Since Cd accumulates in edible portions, the main source of Cd for animals and humans is through plant foods. Food chain transfer of Cd also poses a potential risk to animals and humans. Zinc, on the other hand is an essential element to both plants and animals. However, elevated concentrations of Zn can also be phytotoxic to plants. Cadmium and Zn are presumed to be transported and remobilized in the plants via similar pathways.; The objectives of both the studies were to examine the transport and accumulation of Cd by two different plant species and how this accumulation can impact the consumers of this plant tissue.; The field study was conducted at a Cd contaminated site at Crab Orchard National Wildlife Refuge. The main goal of this study was to assess the impact of Cd accumulation on the growth of the dominant grass species on this site, D. clandestinum and the impact on its consumer (deer). The results showed that D. clandestinum accumulated an elevated concentration of Cd in the vegetative tissues. However, evidence from this study does not indicate any immediate risk to the deer.; The second study used Brassica juncea to study how timing of Cd exposure and interactions with Zn influenced the transport and accumulation in different tissues, especially seeds. From this study it is apparent that seed set stage is the critical in the plant's life cycle in determining Cd accumulation in seeds. Cd uptake was affected by Zn only in roots. Zinc and Cd did not have any protective effect in the translocation and accumulation of Cd to the seeds. Although Cd and Zn reached phytotoxic concentrations in the tissues, it does not pose any risk to humans. In fact, concentrations of Zn in the seeds are higher than the concentrations usually found in cereals which might be beneficial due to increase in micronutrient density in seeds.