Arsenic uptake and toxicity threshold for lettuce plants (Lactuca sativa L.) grown in poultry litter amended soils

Poultry litter (PL) is used as a soil amendment agriculture, and can contain toxic As, which can accumulate in soils and absorb by plants. A greenhouse study was conducted to evaluate the uptake of As in Kirkham and Sunset soils which received PL for over 20 years. The soils received 0, 5, 10, 15, 20, and 25 mg kg-1 arsenic and black seeded ‘Simpson’ lettuce grown. At maturity, plants were divided into roots and shoots, and analyzed for total As. Shoot dry weight declined regardless of soil series or whether poultry litter was applied. Harvest index decreased linearly with increasing As concentrations and was lowest at the 25 mg kg-1 level. As in shoots and roots was greater on Sunset compared to Kirkham soil and greater in PL than in non-PL soils. Root and shoot As was greater in Kirkham NPL than PL soils, 5 times greater in roots than shoots of plants in Kirkham soils, and 11 times higher in roots than shoots of plants in PL-amended Kirkham soils. There were 109 µg/plant As in Sunset soils and 78.7 µg/plant in the Kirkham soil. Toxicity threshold in Kirkham and Sunset soils was 20 and 10 mg kg-1 decreasing leaf area, plant height and yield 46 and 83% in Kirkham and Sunset soils, respectively. As in the edible parts was low and acute exposure was not problematic. Transfer factor in PL amended soils was higher in roots than shoots in Kirkham than Sunset soil, and decreased with increasing soil As.