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United States Department of Agriculture

Agricultural Research Service

Research Project: PLANT VARIATION IN CD, PB, ZN AND AS ACCUMULATION AND BIOAVAILABILITY AND METHODS TO LIMIT RISK
2009 Annual Report


1a.Objectives (from AD-416)
Characterize the influence of zinc and iron concentrations in edible crop tissues on bioavailability of crop cadmium to animals; characterize potential transfer of soil lead, arsenic, and copper by vegetable crps grown on long-term orchard soils and other contaminated agricultural soils and methods to prevent this transfer; characterize genetic resources and inheritance of grain Cd to reduce cadmium in durum wheat, flax, and nonoilseed sunflower and release improved lower Cd germplasm; develop methods to identify levels of heavy metals, such as lead, arsenic and cadmium that might be food safety/security risks to give us the tools to prevent contamination of food of both plant and animal origin.


1b.Approach (from AD-416)
1) conduct animal feeding studies on the effect of dietary iron, zinc and calcium supply, and crop Zn level, on absorption of Cd in lettuce, polished rice and other crops for which Cd is important in understanding of human Cd risks from foods (durum wheat; bread wheat; etc.).
2)Grow commercial and garden carrot varieties with a wide range of properties on contaminated orchard soils rich in Pb and As; include tests of soil amendments expected to reduce uptake of Pb or As. Measure in vitro bioaccessibility and if needed bioavailability of crop Pb or As to animals. Examine metal residues in peel layer vs. internal storage root tissue..
3)Complete testing of inheritance of grain Cd concentration in sunflower hybrids, flax genotypes shown to differ in grain Cd accumulation, and durum wheat breeding lines; assist plant breeders develop germplasm releases with lower Cd than present commercial types. Examine physiology of genetic differences in Cd accumulation in relation to soil properties where crops are grown..
4)Test methods for rapid direct analysis, or preparation or extraction of Cd, As, and/or Pb in foods of plant or animal origin for spectrometric analysis at lower cost than present usual methods of analysis and verify the application of the methods developed for commercial food samples.


3.Progress Report
Plant uptake of trace metals can pose a health concern if the metal concentrations are too high. The effect of several soil factors in limiting uptake of cadmium in lettuce was assessed; soil zinc and organic matter concentrations were found reduced cadmium uptake. Biosolids applications enhanced this effect. Feeding trials have been delayed and a new collaborator is being sought.

The mechanism of how carrots accumulated lead much more than potatoes grown in lead-arsenate contaminated soils was discovered and involved the movement of lead through the xylem elements which are in the center of the carrot root. Additional experiments were conducted to assess the effects of iron, phosphorus, and organic carbon in reducing lead and arsenic uptake by carrots. Phosphorus application decreased leachable lead but increased leachable arsenic. Byproducts high in calcium and iron concentrations were the most effective in reducing the leachability of arsenic, while compost and high carbon coal ash were the least effective in reducing the leachability of arsenic. These findings will provide action agencies and producers with strategies to reduce the risks of using such lead arsenate contaminated orchard soils for crop production.

In cooperation with durum wheat breeders in Montana, germplasm samples from genetic trials were analyzed to select cultivars which were poor cadmium accumulators. This will aid in the development of alternative new crops for dryland soils in western U.S.


4.Accomplishments
1. Use of zinc fertilizer and limestone can reduce cadmium uptake by leafy vegetables. Lettuce, spinach, and other leafy vegetables cannot be grown in certain soils high in cadmium concentrations because cadmium is readily taken up by these plants resulting in plants that exceed international standards. A series of experiments were conducted to determine the effects of zinc fertilizers and the use of lime on the cadmium uptake. Results indicated that increasing the soil pH to neutral or alkaline conditions with limestone and adding zinc fertilizer substantially reduced cadmium uptake to concentrations that were well below the international standard. This approach will allow farmers to utilize soils that previously could not be used for producing leafy vegetables.

2. Mechanism discovered for lead accumulation in carrots grown in lead-arsenic contaminated soils. Some orchard lands which have high lead and arsenic levels are being converted to vegetable production. Experiments using three cultivars of carrots and three cultivars of potato were conducted to determine the lead and arsenic uptake by these vegetable and the potential health risk from these soils. Results showed that lead concentrations were much higher in the peeled carrots and tops compared to the carrot peel, and in some cases lead levels were higher than levels considered safe for human consumption. Arsenic levels were much higher in carrot peel and tops than the peeled carrots. Lead and arsenic concentrations in the potatoes grown on the lead-arsenate contaminated orchard soils were lower in both peeled potatoes and peel compared to the carrots. The higher accumulation of lead in peeled carrot roots is attributed to the movement of lead through the xylem elements which are in the center of the carrot root. Thus, although potatoes can be safely grown in old orchard soils, producers should not grow carrots in these soils.

3. Strategies developed to control lead and arsenic availability in old orchard soils. The effectiveness of calcium, iron, phosphorus, and carbon materials on the solubility of lead and arsenic in old orchard soils was examined. Studies showed that phosphorus application decreased leachable lead but increased leachable arsenic. Byproducts high in calcium and iron concentrations were the most effective in reducing the leachability of arsenic, while compost and high carbon coal ash were the least effective in reducing the leachability of arsenic. These findings will provide action agencies and producers with strategies to reduce the risks of using such lead arsenate contaminated orchard soils for crop production.


Review Publications
Chen, W., Li, L., Chang, A.C., Wu, L., Khosrivafard, M., Chaney, R.L. 2008. Characterizing the Solid-Solution Coefficient and Plant Uptake Factor of As, Cd and Pb in California Croplands. Agriculture, Ecosystems and Environment. 129:212-220.

Codling, E.E., Faucette, L.B., Cardoso-Gendreau, F.A., Sadeghi, A.M., Pachepsky, Y.A., Shelton, D.R. 2009. Storm Water Pollution Removal Performance of Compost Filter Socks. Journal of Soil and Water Conservation. 38:1233-1239.

Last Modified: 4/18/2014
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