Availability of heavy metals to cabbage grown in sewage sludge amended calcareous soils under greenhouse conditions

Abstract

Compared to noncalcareous soils, data on the soil-to-plant transfer of heavy metals and their response to sewage sludge (SS) in calcareous soils with diverse properties are limited. Cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) transfer from soil to cabbage (Brassica oleracea L. var. capitata) under greenhouse conditions in 30 diverse soils amended with two types of sewage sludge (non-spiked and spiked with heavy metals) were investigated. Three transfer factors were calculated for heavy metals in three treated soils including control soils (CS), soils treated with non-spiked SS (NSS), and soils treated with spiked SS (PSS). The bio-concentration factor of heavy metals from soil to root (BCFRoots) in cabbage in three treatments was as follows: CS: Pb > Cu > Co > Zn > Ni; NSS: Pb > Co > Cu ≥ Zn > Ni; and PSS: Pb > Cd > Zn > Co > Cu > Ni. The same order was found for the bio-concentration factor of heavy metals from soil to shoots (BCFShoots) in PSS, and in CS and NSS treatments except that the position of Co, Cu, and Zn was changed. Based on the heavy metals translocation from plant roots to shoots, Cd, Cu, and Zn were the heavy metals that posed the highest risk due to the higher shoot content in all treatments, whereas Ni and Pb posed relatively lesser risk. Generally, the percentage of sand and silt in BCFRoots and BCFShoots was quite effective for Co, Ni, and Zn and it seems that soil texture is an important variable in heavy metals bioavailability. In conclusion, our findings highlight the significance of using SS to increase cabbage growth in soils contaminated with heavy metals. Furthermore, cabbage may be a good choice for phytoremediation of heavy metal-contaminated calcareous soils in terms of soil remediation. Novelty statement In recent years, sewage sludge production has increased as well as related waste disposal strategies because of the increasing population and growing demand for agricultural products. Sewage sludge utilization as a low-cost fertilizer has spread in some parts of Iran and the world. On the other hand, unnecessary and unproductive use of sewage sludge results in the accumulation of heavy metals in soils, adding them to food and the potential risk to human health. Currently, work on the transfer of heavy metals from soil to plant after soil treated with sewage sludge has focused on the bioavailability of heavy metals using specific extractants. The assessment of the transfer of heavy metals from soil to different parts of plants using sewage sludge has been less studied. In this study, the transfer of heavy metals (Cd, Co, Cu, Ni, Pb, and Zn) from several soils (30 soils samples) having diverse physical and chemical properties to the tissues of the cabbage plant in control soils, and two types of sewage sludge (nonspiked and spiked with heavy metals) were investigated. The novelty of this study is that the measured bio-concentration factor of heavy metals from soil to root and from soil to shoot and translocation of heavy metals from plant roots to shoots and correlations between these parameters and soil properties are reported for the first time in diverse calcareous soils.