Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/1995
Publication Date: N/A
Interpretive Summary: Cadmium levels in soils have increased because of cadmium emission from metallurgical industries, mining and smelting operations, and incineration of plastic containers and batteries. Addition of sewage sludge and phosphate fertilizers to soil has also contributed to the increased levels of cadmium. Cadmium has no essential biological function, and it is highly toxic to plants, animals, and humans. Plant species and cultivars differ widely in their ability to absorb, accumulate, and tolerate cadmium. Research was undertaken to examine the level of cadmium tolerance in four economically important plant species. Influx of cadmium into roots and subsequent transport to shoots appears to be a major mechanism by which plant species regulate cadmium accumulation and tolerance to cadmium toxicity. Therefore such parameters could be useful in selecting plants that exclude cadmium from their root and shoot or economical harvestable parts, thereby one could reduce levels of cadmium from the food chain.
Technical Abstract: Cadmium (Cd) has no known essential biological function, but it is toxic to plants, animals, and humans. A promising approach to prevent Cd from entering the food chain would be to select and/or create Cd-accumulating plants to remediate contaminated soils or develop Cd-excluding plants to reduce Cd flow from soil into foods. The present study was undertaken to examine the differences in Cd influx, transport, and accumulation among five plant species in relation to plant tolerance to Cd toxicity. Ryegrass (Lolium perenne L.) had the least reduction in dry matter which may be due to its lowest Cd transport rate (TR) to shoots at all Cd levels among the plant species tested. White clover (Trifolium repens L.) was the most sensitive species to Cd toxicity likely because of its highest Cd influx rate (IR) and high TR when plants were grown at low Cd2+ activity (less than or equal to 8 uM). The high tolerance of cabbage (Brassica oleracea var. capitata L.) to moderate Cd toxicity (less than or equal to 14 uM) appeared to be mainly due to the detoxification of Cd inside plant tissue since it recorded the highest TR and relatively high IR for Cd among the test species. At Cd2+ activities up to 28 uM, the Cd uptake ratios of shoot/root for ryegrass were, on average, about 50-fold and 27-fold lower than that for cabbage and maize (Zea mays L.), respectively. These results showed that Cd could be easily transported into shoots of cabbage and maize, but was mainly confined to roots of ryegrass. We suggest that influx and transport rates, especially transport rate, could be used as plant physiological parameters for screening Cd-excluding genotypes among monocotyledonous plants.