Location: Adaptive Cropping Systems Laboratory
Project Number: 8042-42430-001-00-D
Project Type: In-House Appropriated
Start Date: Feb 23, 2016
End Date: Feb 22, 2021
Objective 1: Characterize effects of flood and soil management on As (inorganic and total) and Cd accumulation in rice grain. 1A: Does alternate wetting and drying (AWD) irrigation management reliably lower inorganic As (iAs) in rice grain without causing excessive grain Cd in rice genotypes? 1B: Develop extraction and analysis methods to rapidly measure the inorganic As (iAs) in rice grain samples. Objective 2: Characterize competition of other cations with Cd accumulation by rice and vegetables. 2A: Clarify whether increased Zn2+ activity reduces Cd2+ accumulation by spinach, lettuce and rice and whether plant Zn deficiency causes up-regulation of Zn transporters which increases uptake of Zn and Cd compared to Zn-sufficient crops. 2B: Clarify whether increased manganese (Mn2+) is more important than Zn2+ in inhibiting uptake of Cd2+ by rice and vegetables from nutrient solutions with environmentally relevant activity of Cd2+. Objective 3: Characterize effects of soil amendments on Pb, Cd and As accumulation by garden crops to improve advice to urban gardeners regarding risk reduction for contaminated urban soils. 3A: Characterize the effects of soil amendments and mulch on Pb and Cd accumulation by garden crops from contaminated urban garden soils. 3B: Characterize the effects of soil amendments on Pb and Cd accumulation by crops grown in contaminated urban gardens. Objective 4: Continue evaluation of the effects of crop species and crop Zn on bioavailability of crop Cd to animals. Test whether crop Zn concentration and crop species affect the bioavailability of crop Cd to monogastric animals in order to clarify if crop species and crop Zn should be included in technically valid limits for Cd in crops.
Because rice accumulates higher levels of inorganic As (iAs) than other crops, regulations are being imposed on iAs in rice grain which are lower than achieved by some growers. More aerobic soil management both lowers grain iAs and increases grain Cd. In order to identify methods to produce rice with lower levels of iAs, samples of rice grain from cooperators’ field tests of the effect of irrigation management, genetic variation, and soil amendment application will be analyzed for iAs and Cd (which may be increased by aerobic soil management to lower grain iAs). Previous methods for analysis of iAs in rice were so expensive that few samples could be evaluated to identify the needed genetic variation and irrigation management variation needed to lower grain iAs. An improved method for simple analysis of iAs using hydride generation from only iAs in samples was developed and will be validated by an international inter-laboratory project. Simpler and faster methods to extract iAs and Cd from rice flour will be evaluated so that market demanded analyses might be made available to the industry. Chelator-buffered nutrient solution methods will be developed to test the competition among elements for absorption of Cd by rice and spinach using levels of Cd, Mn and Zn chemical activity in the solution similar to soil solution. Recent studies indicated that Cd is absorbed on a Mn transporter in rice, but a Zn transporter in other species. Flooded soil production increases dissolved Mn but reduces dissolved Zn in rice soils until fields are drained; after drainage, much higher Cd absorption can occur. Cooperators field tests of irrigation management which limits both As and Cd in grain will be investigated. In other soils, crop Cd accumulation may exceed allowable limits in spinach and lettuce. High natural soil Cd and low Zn in spinach production fields in California allows excessive Cd accumulation in spinach and lettuce. Characterizing the direct competition among these trace elements in representative crop species will clarify needed management changes to limit Cd accumulation by both crop groups. Besides testing direct inhibition of Cd uptake by Zn and Mn in both species, the effect of Mn and Zn deficiency on up-regulation of the uptake rate of Cd will be evaluated. The potential utility of soil amendments on uptake of Pb, Cd and As by garden crops, and bioaccessibility of soil Pb to mammals will be evaluated both in the greenhouse, and when improved methods have been identified, will be tested in cooperating urban gardens with high soil Pb, Cd or As. Because food Cd limits presently do not consider variation in Cd bioavailability among crops, or the effect of crop Zn on Cd bioavailability, the effect of usual co-contaminating Zn on accumulation of diet Cd by weanling pigs will be tested with diets containing 20% Romaine lettuce or spinach. Bioavailability will be evaluated by analyzing duodenum, liver and kidney from test animals. These studies should provide evidence that the effect of Zn on Cd absorption, and effect of spinach oxalate on Cd absorption should be included in international regulation of Cd in crops.