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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
2007 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
There is a detailed plan for a feeding experiment developed to test the effect of intrinsic Zn in lettuce on bioavailability of intrinsic Cd. The plan follows the approach developed in feeding sunflower kernels and rice grain. Rats are fed diets with 20% ground lettuce which are fully adequate in Fe-Zn-Ca, or marginal in Fe-Zn-Ca for 35 days to condition the rats to the bioavailability of Fe and Zn in the diets, then feeding the test diets with 109-Cd label added for 24 hours followed by feeding the unlabeled diets for 14 additional days to deplete a Cd turnover pool formed in the small intestine. Then intestine, liver and kidney will be collected for analysis of Cd, Fe and Zn. It is expected that the substantial supply of Fe and Zn in lettuce leaves will inhibit Cd absorption by the animals.

Using chelator-buffered nutrient solutions which allow us to grow lettuce with highly controlled Cd and Zn levels, and normal levels of other nutrients, we grew several kg of lettuce with desired composition for test were grown and prepared for feeding. The lettuce with low Zn contains about 4 mg Cd/kg and 20 mg Zn/kg dry weight, while the high Zn lettuce contains about 4 mg Cd/kg and 480 mg Zn/kg dry weight. One more crop must be grown to have all needed lettuce ready for the feeding experiment.

Three cultivars of carrot, one cultivar of lettuce and four cultivars of Irish potatoes were grown on five orchard soils with a history of lead arsenate application. Root crops were peeled and both peel and peeled crop submitted for analysis. Harvested plants samples were freeze-dried and analyzed for arsenic and lead using microwave digestion using methods which avoided dust contamination of the tissue samples. As and Pb determined using ICP-OES and ICP-MS. Important findings were obtained in that the peeled carrot but not the peeled potato contained significantly increased Pb when grown on the high Pb orchard soils. It is now evident that Pb can be trapped within the xylem of carrots during growth; potato has only phloem connections and avoids significant internal Pb even on Pb contaminated soils. Peel of potato is contaminated when grown on such soils.

Tests were conducted to assess the effect of amendment of orchard soils with iron oxides and phosphate to immobilize soil Pb and As. The short and long term effects of iron and phosphate on the bioaccessiblity of As and Pb from orchard soils were determined. Addition of phosphate without Fe increased the mobility of soil As, but reduced bioaccessibility of soil Pb. Addition of both chemicals reduced mobility of both Pb and As. Two manuscripts were prepared.

Cooperated with durum wheat breeders in ND, MT, and AZ in analyzing genetic lines from replicated field plots to aid in selection of genetic materials for field testing in 2007. Data provided to cooperators in time to prepare seed for planting.

Began new cooperation in testing other crops grown on dryland as new crops, e.g., camelina; new crop grown in association with durum wheat to allow characterization of relative Cd accumulation compared to known crops.


4.Accomplishments
The concentrations of As and Pb in the carrot root reflect the soil As and Pb concentrations. The carrots that were grown on the soils with the largest As and Pb concentrations have the highest tissue As and Pb. Pb was within the peeled carrot mass, indicating that Pb which was being translocated up the carrot xylem got trapped with in storage root xylem. This pattern of Pb movement into edible crop tissues was not apparent in potato which is phloem fed without an internal xylem which could retain Pb. The applications of phosphate increased water extractable As and Pb solubility in two orchard soils. Glycine extractable (bioaccessible) Pb concentration reduced significantly with the application of iron plus phosphorus. Manuscripts on the effects of lime, ion and phosphate were accepted for publication in peer reviewed journals.

In cooperation with breeders in MT, noted that irrigation with melt water substantially lowered durum grain Cd levels compared to standard dryland production methods. These results indicate that background levels of chloride in dryland is strongly increasing durum grain Cd to levels which exceed Codex wheat limits compared to levels below Codex limit when melt water irrigation occurred. Irrigation of durum wheat is not commonly conducted on northern great plains.

The role of crop nutritional properties, and of co-current crop Zn, in the bioavailability of crop Cd to humans is increasingly recognized as having been technically demonstrated. Acceptance of bioavailability variation in international Cd risk debate remains challenging.

Findings explain how carrot but not other root vegetables and most other crops attain Pb contamination when grown on historic orchard soils rich in Pb and As. These findings provide valuable information to vegetable crop growers, the Food and Drug Administration (FDA), and land developers on the use of these old orchards.


5.Significant Activities that Support Special Target Populations
None


6.Technology Transfer

Number of non-peer reviewed presentations and proceedings3

Review Publications
Codling, E.E., Dao, T.H. 2007. Effect of lime, phosphorus and iron on lead and arsenic solubility in lead-arsenate contaminated orchard soils. Communications in Soil Science and Plant Analysis. 38:903-919.

Khoshgoftarmanesh, A.H., Chaney, R.L. 2007. Preceding affects cadmium and zinc of wheat grown in saline soils of central Iran. Journal of Environmental Quality. 36:1132-1136.

Lucena, J.J., Chaney, R.L. 2006. Response of cucumber plants to low doses of different synthetic iron chelates in hydroponics. Journal of Plant Nutrition. 30:795-809.

Last Modified: 8/27/2014
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