Effects of Cadmium, Copper, Lead, and Zinc Contamination on Metal Accumulation by Safflower and Wheat

Abstract

Accumulation of heavy metals (HMs) in cultivated soils is a continuing environmental problem in many parts of the world. An increase in HM concentration can enhance uptake of toxic metals by crops and enter the human food chain. In this study, the uptake behavior of wheat and safflower was evaluated in a calcareous soil by using 12 undisturbed columns in which half were artificially contaminated. Heavy metals in the form of CdCl₂ (15 mg Cd kg^{− 1}), CuSO₄ (585 mg Cu kg^{− 1}), Pb(NO₃)₂ (117 mg Pb kg^{− 1}), and ZnCl₂ (1094 mg Zn kg^{− 1}) were sprayed on the soil surface and completely mixed in the top 10 cm. The background total concentrations of Cd, Cu, Pb and Zn were 1.6, 29.5, 17.5 and 61.2 mg kg^{− 1}, respectively. After metal application, half of the columns (3 contaminated and 3 uncontaminated) were sown with wheat (Triticum aestivum) and the other half with safflower (Carthamus tinctorious) and grown for 74 days until maturity. After harvesting, soil columns were cut into 10-cm sections and analyzed for HNO₃- and DTPA-extractable metal concentrations. Metal concentrations were also measured in different plant tissues. The results showed that artificial contamination of topsoil decreased the transpiration rate of wheat by 12% and that of safflower by 6%. In contaminated columns, Cd, Cu, Pb, and Zn accumulation in wheat shoot was greater by 8.0-, 1.9-, 3.0-, and 2.1-fold than the control, respectively. Accordingly, these numbers were 46.0-, 1.3-, 1.7-, and 1.6-fold in safflower shoot. Soil contamination with HMs resulted in a 55% decrease in shoot dry matter yield of wheat while it had no significant effect on shoot dry matter of safflower. The normalized water consumption for safflower was therefore not affected by metal contamination (≈ 13 mm H₂O g^{− 1} of dry weight for all safflower and uncontaminated wheat treatments), while contaminated wheat was much less water efficient at about 27 mm H₂O g^{− 1} dry weight. It was concluded that although artificial contamination had a negative effect on wheat growth, it did not affect safflower's normal growth and water efficiency.

Keywords:

• Metal accumulation
• evapotranspiration
• heavy metals
• calcareous soil

Notes

* Average of three replications ± standard deviation

* Total applied irrigation = 588.5 mm

^† ET stands for actual evapotranspiration

^‡ W: uncontaminated wheat, W+M: contaminated wheat, S: uncontaminated safflower, S+M: contaminated safflower

§In each column, means with similar letters (a, b, c) are not significantly different at 0.05 level according LSD test

* Average of three replications ± standard deviation

^†W: uncontaminated wheat, W+M: contaminated wheat, S: uncontaminated safflower, S+M: contaminated safflower

^‡In each column means with similar letters (a, b, c, d) are not significantly different at 0.05 level according LSD test

* Average of three replications ± standard deviation

^†W: uncontaminated wheat, W+M: contaminated wheat, S: uncontaminated safflower, S+M: contaminated safflower

^‡In each column means with similar letters (a, b, c, d) are not significantly different at 0.05 level according LSD test. For each plant tissue in each column, means with similar letters in parentheses ((a), (b), (c), (d)) are not significantly different at 0.05 level according LSD test

* Average of three replications ± standard deviation

^†For ratios calculation, total heavy metal mass in shoots was divided to the total heavy metal mass of the roots

^‡W: uncontaminated wheat, W+M: contaminated wheat, S: uncontaminated safflower, S+M: contaminated safflower

§In each column means with similar letters (a, b, c, d) are not significantly different at 0.05 level according LSD test

* Average of three replications ± standard deviation

^† W: uncontaminated wheat, W+M: contaminated wheat, S: uncontaminated safflower, S+M: contaminated safflower

^‡For each metal in a column, means with similar letters (a, b, c, d) are not significantly different at 0.05 level according LSD test