NanoFASE Case Study: Rhizosphere Influence on Bioavailability of Ag-NP to Wheat In Soil Exposures

Silver nanoparticles can enter the soil through the application of sewage sludge to agricultural land. The silver in the sewage sludge will most likely be in the transformed, sulphidised form. Plants growing on this agricultural land will therefore be exposed to silver which may accumulate in their tissues. The rhizosphere can modify the soil environment surrounding the roots. NanoFASE investigated whether different soil fractions (bulk soil, loosely attached soil or rhizosphere soil including its microbial community) had differential influence on the availability of Ag to the plants.

Study aim

This study investigates the effect of the soil microbial community and the rhizosphere on the bioavailability of three silver forms (Ag0 Engineered Nanomaterials, Ag2S ENM and AgNO3) to wheat, Triticum aestivum.

 

 

Experimental approach

Overview
 
  1. Three different Ag forms were spiked in Lufa 2.2 soil.
  2. Seeds were planted in the different treatment soils after 7 days.
  3. Plant roots and soils were sampled at 7 and 14 days post-emergence.
  4. Three soil fractions at increased distances from the wheat roots were collected. The three soil fractions were:  bulk soil (no plant root influence), loosely attached soil and rhizosphere soil.
  5. Total Ag concentration was measured in plant roots and soil fractions.
  6. Soil fraction pH and dissolved organic carbon (DOC) was also measured.
  7. Bacterial and microeukaryote community structures in the different soil fractions were analysed using   16S and 18S rDNA sequencing.

Compartment involved:  

Rhizosphere soil
Loosely-attached soil
Bulk soil

NP type/size:

20 nm Ag NP PVP coated (AppNano)
Ag2S NP 27 nm (AppNano)

Species:
Wheat (Triticum aestivum)
 
Bioassay:

Bioaccumulation assay
Extractable Ag assay

Results
  • After 14 days there was increased extractable Ag in the rhizosphere soils compared to the bulk soil.
  • There was a positive relationship between accumulation and extractable Ag in the rhizosphere soil compared to the bulk soil for the Ag NP forms
  • 20 nm pristine lowered bacterial and fungal diversity compared to other treatments but did not vary over 14 days.
  • Rhizosphere soil had lower variation in diversity compared to bulk soil.
 

Parameters

 
  • Bioaccumulation factor - \(BAF\)
  • CaCl2 and DTPA extractable Ag in soil fractions
  • Dissolved organic carbon (DOC) and pH in soil fractions
  • Growth rate \(k_g\)
  • Bacterial and fungal community richness and diversity

Read more

Read also
 

Visit the NanoFASE Library to read summaries of these reports:

NanoFASE Report D9.4 Validated parameter  set on uptake and toxicokinetics of aged NMs in aquatic and terrestrial organisms and for biomagnification potential (summary of internal report)

 

Gao X, Avellan A, Laughton S, Vaidya R, Rodrigues SM, Casman EA, Lowry GV. (2018) CuO Nanoparticle Dissolution and Toxicity to Wheat (Triticum aestivum) in Rhizosphere Soil. Environ Sci Technol. 2018 Mar 6; 52 (5): 888-897.

Stegemeier, J. P., et al. (2015). "Speciation Matters: Bioavailability of Silver and Silver Sulfide Nanoparticles to Alfalfa (Medicago sativa)." Environ Sci Technol. 49(14): 8451-8460.

Contact

 

Amaia Green Etxabe

Centre for Ecology and Hydrology (CEH)
Wallingford, UK

 

 

Elma Lahive

Centre for Ecology and Hydrology (CEH),
Wallingford, UK