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The goals of this project are to quantify and understand the retention of nanomaterials (NMs) by biochar (BC) macroparticles, to evaluate the reversibility of binding, and to determine the effects of BC addition to soil on the bioavailability of NMs to plants and earthworms. We chose four NMs that have relevance to agroecosystems: n-Ag0, n-CeO2, n-C60 fullerene and MWCNTs. <P>The specific objectives of the proposal are: Objective 1- To quantify and characterize the binding and binding reversibility of NMs to macroscopic BC particles in aqueous suspensions as a function of solution composition and BC surface and pore characteristics (including the effects of weathering) with the goal of establishing a mechanistic model for these interactions. This objective will include a determination of the effect of BC addition on the retention of NMs in soil columns. Objective 2- To determine the impact of BC nanostructure and weathering on the biological effects of engineered nanomaterials in plant and earthworm bioassays with and without soil. The effect of biochar on plant/worm biomass, transpiration, photosynthetic potential, reactive oxygen species production, and particle accumulation will be determined. An essential goal of this objective is to determine the correlation between bioavailability and physical availability as assessed in Objective 1.
Non-Technical Summary:<br/>
Nanomaterials are used in electronics, chemicals, transportation, health-care, cosmetics, pharmaceuticals, food processing, and agriculture. They can enter agricultural soils directly as additives in pesticide and fertilizer formulations, or indirectly as contaminants in recycled water and municipal solid wastes applied to crop lands. Due to their small size and characteristic properties, a number of nanomaterials are toxic to soil organisms and may be taken up by certain crop plants. The potential risks posed to consumers , farmers, food crops, and the environment require a deep understanding of their chemical, physical, and biological fate in soil. The mobility and biological accessibility of nanoparticles in soil depends critically on how, and how strongly, they bind to each other and to soil particles; yet, almost nothing is known about such behaviors. "Black carbon" is an important component of soil as a result of the input of charcoal from natural and deliberate fires and from the growing practice of adding charred biomass waste (biochar) to improve soil fertility. The goals of this project are to obtain a comprehensive understanding of how and to what degree nanoparticles bind to black carbon, and to determine the effects of black carbon addition on the bioavailability of nanomaterials by representative crop plants (corn, soybean, lettuce, tomato) and animals (earthworms). We chose four nanomaterials relevant to agro-ecosystems: nanosilver, nanoceria, fullerenes and carbon nanotubes. These nanomaterials are now used, or proposed for use in agrichemicals and many consumer products.
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Approach:<br/>
We will quantify and characterize microscopically the heteroaggregation of NMs with a range of prepared biochars in aqueous suspension as a function of solution composition (pH, ionic strength, divalent metal cation concentration, dissolved organic matter concentration), BC surface and pore characteristics, and the effects of environmental weathering of BC. A special focus will be on binding reversibility. Further, for each of the NMs we will determine the impact of BC nanostructure and weathering on biological uptake and toxicity with respect to crop plants (corn, soybean, lettuce, tomato) and earthworm (two species), with and without soil, and evaluate correlations between bioavailability and physical availability.
<P>The study is designed to shed light on a number of critical questions about the physical behavior and biological availability of selected NMs in the presence of BC:
<br/>1)The retention of NMs by BC and the influence on retention of solution composition such as ionic strength, pH, divalent metal ion (Ca, Mg) concentrations, and DOM colloids.
<br/>2)The influence of BC chemical properties on NM retention. Chemical properties are functions of the formation conditions and weathering effects.
<br/>3)The role played by pore size distribution, addressing the question of NM entrance into pore networks. Pore properties also depend on formation conditions and weathering effects.
<br/>4)The reversibility of NM retention.
<br/>5)The effects of weathering processes of BC particles on retention of NMs, including oxidation and deposition of organic matter and soil colloids.
<br/>6)The influence of BC on transport of NMs through soil.
<br/>7)The impact of BC chemical properties and weathering on NM accumulation and toxicity to plant and worm species.