Abstract

The nanoparticles of TiO2 (TiO2 NP) have been used as a plant-growth stimulant or catalyst in pesticide formulas. However, due to high resistance of TiO2 NP to abiotic weathering, dissolved Ti is unlikely to act as an active compound in these preparations. Even if soil is acidic, TiO2 NP do not dissolve easily and preferably remain as undissolved particles. The low dissolution rates of inorganic nanoparticles in the soil environment make Ti in TiO2 NP largely unavailable for plants and soil microorganisms. To characterize the behavior of TiO2 NP in soil under different pH conditions, we analyzed TiO2 NP-size distribution in two soil materials, an alkaline and acidic one. We also cultivated Aspergillus niger, a fungus ubiquitously found in soils, in the growth medium spiked with TiO2 NP to assess accumulation of the nanoparticles in fungus. In soil suspensions, the dissolved Ti was present in low concentrations (up to 0.010 mg L−1). Most of the TiO2 NP remained in particulate form or appeared as aggregates sized 100–450 nm. In experiment on Ti accumulation by A. niger, TiO2 NP either settled down to the bottom of the flask with growth medium or were actually accumulated by the fungus; about 7.5% of TiO2 NP were accumulated in fungal mycelia. Most of the TiO2 NP remain in particulate form in soil solutions, regardless of soil pH. Filamentous fungus A. niger has the ability to accumulate bioavailable TiO2 NP, which hints at the possibility that some soil fungi can affect spatial distribution of this type of nanoparticles in soils.

Highlights

  • Titanium (Ti) is one of the most abundant elements in soil, sediments and weathered rocks.In natural waters, the levels of soluble Ti range from 4 pM at the surface of ocean waters [1]to 100 μM in hot spring waters [2]

  • Batch sorption experiments were conducted to explore the distribution of TiO2 NP in liquidand solid-phase and to determine the amount of dissolved Ti in soil solutions

  • Our results suggest that the properties of alkaline agricultural soil and properties of an acidic forest soil affect the distribution of TiO2 NP in soil suspension in a similar way (Figure 1f)

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Summary

Introduction

To 100 μM in hot spring waters [2]. This is due to a very low dissolution rate and high resistance of Ti minerals to chemical weathering [3]. The TiO2 NP are used as additives in pesticides and other complex formulations as either an active ingredient or a carrier. They increase adhesion or accelerate the degradation of the organic pesticides [13,14,15,16,17]. They can negatively affect roots and Agronomy 2020, 10, 1833; doi:10.3390/agronomy10111833 www.mdpi.com/journal/agronomy

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