Soil contamination with organic and inorganic compounds constitutes an important environmental and human health problem worldwide. Soil contamination with trace elements gives great cause for concern due to their toxicity, non-biodegradable nature and potential for bioaccumulation and biomagnification. Similarly, soil contamination with organic compounds, especially persistent organic pollutants (POPs), constitutes an important hazard due to their toxicity, persistence/recalcitrance and high fat solubility.
Several strategies can be used to reduce the toxic effects of soil contaminants on humans and ecosystems. Among these strategies, phytostabilization is a phytoremediation option focused on the reduction of trace element bioavailability, while promoting the microbial degradation (bioremediation) of organic contaminants in the rhizosphere. Organic amendments are often included in phytostabilization and bioremediation initiatives to stimulate plant growth and microbial degradation. Likewise, the application of nanoscale Zero-Valent Iron particles (nZVI) is also an interesting option for the treatment of contaminated soil, especially when targeting chlorinated organic contaminants.
The aim of this study was to evaluate the effectiveness of organic amendments (composted horse manure, sewage sludge) for the nZVI-assisted phytostabilization of soil simultaneously contaminated with lindane (100 mg kg-1 DW soil) and Zn (2500 mg kg-1 DW soil) using Brassica napus plants. A factorial design was used to assess the expected beneficial effects of the organic amendments, the application of nZVI and the growth of B. napus on (i) reduction of Zn bioavailability, (ii) degradation of lindane and (iii) recovery of soil health.
Among others, the following parameters were measured to quantify the effect of treatments on soil health recovery: bioavailable Zn, total lindane, microbial biomass C, total bacteria and fungi by qPCR, bacterial and fungal structural diversity by amplicon sequencing (16S, 18S), potentially mineralizable N, enzyme activities (dehydrogenase, β-glucosidase, β-glucosaminidase, arylsulphatase, xylosidase, phosphatase, Leu-aminopeptidase), respiration, and water soluble organic carbon.
The addition of nZVI reduced the concentration of bioavailable Zn and lindane. Microbial biomass and activity were highly stimulated in treated soils, especially in the presence of amendments. We concluded that the combination of B. napus growth, addition of organic amendments and application of nZVI is highly promising for the remediation of soils simultaneously contaminated with trace elements and organic compounds.
This work was funded by the NANORRIZORREM-2 project (AGL2016-76592-R).</i>