Salinity modifies heavy metals and arsenic absorption by the halophyte plant species Kosteletzkya pentacarpos and pollutant leaching from a polycontaminated substrate.

Abstract

Phytomanagement of polycontaminated soils is challenging, especially in areas simultaneously affected by salinity. The wetland halophyte plant species Kosteletzkya pentacarpos was cultivated in a column device allowing leachate harvest, on a polycontaminated spiked soil containing Cd (6.5 mg kg−1 DW), As (75 mg kg−1 DW), Zn (200 mg kg−1 DW) and Pb (300 mg kg−1 DW) and irrigated with salt water (final soil electrical conductivity 5.0 ms cm−1). Salinity increased Cd bioavailability in the soil and Cd accumulation in the shoots while it had an opposite effect on As. Salinity did not modify Pb and Zn bioavailability and accumulation. Cultivating plants on the polluted soil drastically reduced the volume of leachate. In all cases, salinity reduced the total amounts of heavy metals removed by the leachate and significantly increased the proportion of Cd and Zn removed by the plants. Heavy metal contamination induced a decrease in shoot dry weight and an increase in malondialdehyde (an indicator of oxidative stress); both symptoms were alleviated by the additional presence of NaCl but this positive impact was not related to increase in protecting phytochelatins synthesis. It is concluded i) that bioavailability estimated by the 0.01M CaCl2 extraction procedure is not fully relevant from the heavy metal mobility, ii) that salinity decreased heavy metal percolation, especially in soils cultivated with K. pentacarpos and iii) that salinity improves plant tolerance to heavy metals in K. pentacarpos and that this species is a promising plant material for phytoremediation of polycontaminated soils.