Mutual effect of Phragmites australis, Arundo donax and immobilization agents on arsenic and trace metals phytostabilization in polluted soils

This study assessed the suitability of Phragmites australis and Arundo donax for the aided phytostabilization of metal(loid)s in polluted soils treated with an iron-rich water treatment residue (Fe-WTR), a municipal solid waste compost (MSW-C) and their combination (Fe-WTR + MSW-C). The three soils under study (S1, S2, S3) showed very high total concentrations of As (from 371 to 22,661 mg·kg− 1 d.w.) and variable amounts of co-occurring trace metals (TMs) (i.e. Pb, 74–2162; Zn, 57-1535 and Cu, 19–412 mg·kg− 1 d.w.). Results showed that P. australis and A. donax biomass was significantly increased in all the amended soils and followed the order: MSW-C > Fe-WTR + MSW-C > Fe-WTR > Control. For both plant species grown in the amended soils, metal(loid)s concentration in below ground organs were higher than those in above ground tissues. In S1 soil (the most polluted and acidic; pH 3.77), the highest As bioaccumulation factors (BAFs) were recorded for plants grown on untreated soil (approx. 45% higher with respect to those recorded for plants in treated soils), where the concentration of labile As was significantly higher with respect to amended soils. By contrast, in S2 and S3 soils, the most effective As bioaccumulator plants were grown on soils treated with compost, even if the addition of this amendment induced a decrease of the soil As extractability. Similar results were detected for TMs in S1 soil, where P. australis and A. donax grown on soil amended with compost showed the highest Pb, Zn and Cu BAFs, while variable results were detected in S2 soil. The lowest As translocation factors (TFs ≪ 1.0) were detected for plants grown on compost-amended soils (25 and 51, 34 and 50, 64 and 55% lower with respect to P. australis and A. donax control plants in S1, S2 and S3 soils respectively), while TMs translocation from roots to shoots was more variable and depending on soil, TMs, amendment and plant species. Overall, our results indicate the suitability of P. australis and A. donax, and of Fe-WTR and MSW-C, for the aided phytostabilization of soils contaminated with arsenic and trace metals.