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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
2010 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
Detailed a plan for feeding experiments to test the effect of intrinsic Zn in lettuce on bioavailability of intrinsic Cd. The complete amount of lettuce needed for the feeding experiment to test whether Zn in lettuce affected bioavailability of Cd in lettuce was grown and prepared for feeding trial. ARS researchers at Beltsville Human Nutrition Research Center were contacted and a cooperator to conduct the feeding test was identified. This feeding study with rats, using the methods of two ARS researchers but without radioactive Cd addition to the test, diets will be conducted during FY-2011.

Data from the experiment on uptake of lead and arsenic from lead-arsenate contaminated soils by carrots was analyzed and manuscript is will be submitted during FY 2010. The second experiment (effect of iron, phosphorus and organic carbon in reducing lead and arsenic uptake by carrots) is being conducted. The availability of the ICP-MS to provide precise Pb analysis for low concentrations in plant tissues allowed progress in this research.

Cooperated with durum wheat breeders in MT by analyzing genetic lines from replicated field plots to aid in selection of genetic materials for field testing in 2009. Data provided to cooperators in time to prepare seed for planting.

The next step in demonstrating the utility of the combination of Zn fertilizer plus limestone to reduce Cd uptake by Romaine lettuce and spinach is a field test in Salinas Valley, we sought cooperators to conduct the field work. Because California Agricultural Experimental Station scientists suffer from budget problems in CA, and lettuce growers are focused on pathogen contamination issues more than Cd issues, the previous cooperators were unable to cooperate in a field test. Thus a new cooperator was sought at the USDA-ARS location in Salinas, CA. An ARS lettuce breeder will cooperate in testing this method to reduce Cd accumulation by lettuce and other crops from the CA mineralized soils, and in examining genetic variation in lettuce Cd accumulation on Salinas Valley soils. Soil and lettuce genotype samples have been analyzed to select cultivars for the field test, and a soil location for the field test.

The demonstration that Zn fertilizer can markedly reduce Cd concentration in lettuce and spinach grown on Cd-mineralized Lockwood and related soils of Salinas Valley, CA, will offer growers a method to return to using these soils for vegetable crop production. Knowledge of cultivar variation in Cd accumulation can support improvement in the crop (lower Cd accumulation selection during breeding), or offer knowledge about availability of lower Cd cultivars for commercial growers.


4.Accomplishments
1. LOCALIZATION OF PB IN CARROT XYLEM. In previous work, we showed that Pb was accumulated in peeled carrots when they were grown on Pb-arsenate contaminated orchard soils, while very little Pb was accumulated in potatoes. These findings suggested that the Pb was accumulated within the xylem which grows thru carrot storage roots, but not thru potato. Experiments were conducted to test localization of Pb in carrots grown on both orchard and urban garden soils. Carrots were grown on the soil and then X-ray Absorption Spectroscopy (XAS) was conducted to evaluate the localization of Pb in carrot root cross sections. µ-X-Ray Fluorescence showed that the Pb was indeed localized nearly totally within the xylem portion of the root. The chemical form of Pb in the xylem is also being examined using XAS. Other common garden root crops (radish, redbeet and turnip) were also found to accumulate Pb in their xylem and XAS examination is being planned. Trapping of Pb in the xylem of carrot root explains the unusual accumulation of Pb in carrots grown on old orchard soils, answering the questions raised by the U.S. FDA which initiated this part of the project. Finding indicates the need to test the bioavailability of Pb caught in the xylem; it could be chloropyromorphite with very low bioavailability.

2. NEW TEST METHOD SHOWS THAT PB IN URBAN GARDEN SOILS HAS LOWER BIOACCESSIBILITY THAN ASSUMED BY EPA. The most important risk from Pb contaminated soils is the potential for absorption of Pb by children which inadvertently ingest soil and soil-contaminated housedust. Present EPA guidance on soil Pb is based on analysis of total Pb. Research has shown that soils differ in the bioavailability of Pb, and that phosphate and compost amendment can substantially reduce the soil Pb bioavailability. In addition, chemical extraction methods to measure the “bioaccessibility” of soil Pb have been developed which correlate well with the bioavailability of soil Pb to animal test models including humans, pigs and rats. Present bioaccessibility test methods are quite expensive. A much simpler method was developed and evaluated soils from the Joplin soil remediation test which have been fed to test animals to validate the extraction method. The new bioaccessibility extraction method results matched the results of feeding the Joplin control and remediated soil to humans and rats. Urban garden soils from Baltimore commonly contained 2-15% bioaccessible Pb of total Pb, in strong contrast with the EPA assumption that soil Pb is 60% bioaccessible. Improved understanding that Pb in urban garden soils actually has much lower bioavailability than assumed by EPA means that a much higher fraction of urban gardeners could safely garden their existing soils without risking their children thru foods grown on the soil or inadvertent soil ingestion by children.

3. DURUM WHEAT GERMPLASM WITH LOWER CD GENERATED BY BREEDING PROGRAMS. In cooperation with breeders in MT, AZ and CA, analyzed germplasm samples from genetic trials in these states to support durum wheat breeders information needs to select lower Cd cultivars. By analysis of grain of durum wheat, the breeders and growers have been provided information needed to breed improved lower Cd cultivars or choose alternative crops with lower Cd accumulation.


Review Publications
Codling, E.E. 2009. Effect of flooding lead-arsenate contaminated orchard soil on growth, arsenic and lead accumulation in rice. Communications in Soil Science and Plant Analysis. 40:2800-2815.

Chaney, R.L., Green, C.E., Ajwa, H., Smith, R.F. 2009. Zinc Fertilization Plus Liming to Reduce Cadmium Uptake by Romaine Lettuce on Cd-Mineralized Lockwood Soil. Proceedings of the International Plant Nutrition Colloquium 16, Paper 1252, 7 pp. On line.

Scheckel, K.G., Chaney, R.L., Basta, N.T., Ryan, J.A. 2010. Advances in Assessing Bioavailability of Metal(loid)s in Contaminated Soils. Advances in Agronomy. 17:409-439.

Khoshgoftarmanesh, A.H., Schulin, R., Chaney, R.L., Daneshbakhsh, B., Afyuni, M. 2010. Micronutrient-Efficient Genotypes for Crop Yield and Nutritional Quality in Sustainable Agriculture: A Review. Agronomy for Sustainable Development. 30:83-107.

Whitall, D., Hively, W.D., Leight, A.K., Hapeman, C.J., Mcconnell, L.L., Fisher, T., Codling, E.E., Rice, C., Mccarty, G.W., Sadeghi, A.M. 2010. Pollutant fate and spatio-temporal variability in the choptank river estuary: factors influencing water quality. Science of the Total Environment. 408:2096-2108.

Last Modified: 9/23/2014
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