Abstract
Among the toxic elements, Cd has received considerable attention in view of its association with a number of human health problems. The objectives of this study were to evaluate the Cd availability and accumulation in soil, transfer rate and toxicity in lettuce and rice plants grown in a Cd-contaminated Typic Hapludox. Two simultaneous greenhouse experiments with lettuce and rice test plants were conducted in a randomized complete block design with four replications. The treatments consisted of four Cd rates (CdCl2), 0.0; 1.3; 3.0 and 6.0 mg kg-1, based on the guidelines recommended by the Environmental Agency of the State of São Paulo, Brazil (Cetesb). Higher Cd rates increased extractable Cd (using Mehlich-3, Mehlich-1 and DTPA chemical extractants) and decreased lettuce and rice dry matter yields. However, no visual toxicity symptoms were observed in plants. Mehlich-1, Mehlich-3 and DTPA extractants were effective in predicting soil Cd availability as well as the Cd concentration and accumulation in plant parts. Cadmium concentration in rice remained below the threshold for human consumption established by Brazilian legislation. On the other hand, lettuce Cd concentration in edible parts exceeded the acceptable limit.
Highlights
In the last decades, Cd concentration in the environment have increased more than other heavy metals (Alloway, 1995)
For rice plants, Li et al (2009) found no decrease in shoot and root dry matter and grain yields of rice plants grown in soil treated with soluble Cd, where the highest Cd rate did not exceed 1.0 mg kg-1
In the State of São Paulo, the use of DTPA solution is recommended as official extractant of metal micronutrients (Fe, Mn, Cu and Zn) from soils, due to the positive and high correlations between soil and plant metal concentrations in several field studies (Abreu et al, 2007)
Summary
Cd concentration in the environment have increased more than other heavy metals (Alloway, 1995). Cadmium bioavailability depends on the concentration in the soil solution, which in turn depends on Cd release from soil colloids. Cadmium release from or adsorption to soil colloids is mainly affected by (in decreasing order of importance): (a) soil solution pH; (b) soil cation exchange capacity (CEC); (c) organic matter (OM) content; (d) clay content; (e) redox potential; and (f) presence of other elements in the soil system (Alleoni et al, 2005; Kabata-Pendias & Mukherjee, 2007; Sposito, 2008). The major part of soil Cd (55–90 %) occurs freely in solution as cationic species (Cd2+) (Kabata-Pendias & Mukherjee, 2007). Irrespectively of soil type or contamination source, the major part of soil Cd is found in a highly available form (Sterckeman et al, 2009)
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