Transport and Retention Behavior of ZnO Nanoparticles in Two Natural Soils: Effect of Surface Coating and Soil Composition

Abstract

The widespread use of nanoparticles (NPs) in consumer goods could put these materials in the waste stream, potentially to soil and sediments. However, little is known about their transport in water and soils. In this study, transport behavior and attachment of ZnO NPs in soil components were studied through column experiments and sequential extraction, respectively. Bare and sodium citrate coated ZnO NP suspended in CaCl2 solutions at different ionic strengths, were passed through glass columns packed with sandy soils (SS) and sandy loam soils (SLS) and the effluents were analyzed by ICP-OES. The distribution of Zn in soil particles was studied by electron microprobe (EMP). Results showed that 99% of Zn/ZnO NPs was retained in SLS and 68% ~ 99% was retained in SS, for ionic strengths varying from 0 to 1 mM. Travel distances (cm) for bare ZnO NPs in SS and SLS were 19.2 and 5.3, respectively, while for coated NPs the distances were 21.4 and 6.9 cm, respectively. The surface coating reduced deposition rates from 0.73 to 0.65 and from 2.28 to 1.74 for SS and SLS, respectively. In both soils the amounts of uncoated NPs in the exchangeable fraction were less than 1%; however, 30% of coated NPs remained in the exchangeable fraction. EMP mapping showed that Zn/ZnO NPs associated with silica and aluminum, which are indicators of soil clay minerals. Long term observations are still needed to evaluate the bioavailability to plants of Zn released from coated and uncoated ZnO NPs.

Toxicity of ZnO Nanoparticles, ZnO Bulk, and ZnCl2 on Earthworms in a Spiked Natural Soil and Toxicological Effects of Leachates on Aquatic Organisms

“…This is consistent with the highest toxicity shown by the salt, but it contrasts with the Zn body concentrations as listed in Table 3. ZnO-NPs were the Zn species with the highest content in the nonreactive pool indicating that they were associated with less accessible forms according with Zhao et al (2012). However, these data were obtained during a short time period (35 days), and the accessible Zn fraction might increase over time due to Zn release from ZnO-NPs (Coutris et al 2012).…”

“…Sequential extraction has been used extensively to assess the partitioning of trace elements in environmental samples. However, literature involving the application of this technique to NPs is scarce (Coutris et al 2012;Zhao et al 2012). In this work, only fractions involved in displacement processes were obtained because they are related to the labile Zn portion and more easily accessible to soil-inhabiting organisms (earthworms in this work).…”

“…Despite this, most studies have been performed in artificial media. Therefore, experiments performed with natural soils are important for the study of NPs toxicity because these more realistically resemble environmental conditions (Zhao et al 2012). Regarding organisms, more information is available about freshwater receptors compared with organisms that live in the soil (Kahru and Dubourguier 2010).…”

Integrating ecotoxicity and chemical approaches to compare the effects of ZnO nanoparticles, ZnO bulk, and ZnCl2 on plants and microorganisms in a natural soil

“…Although it is unlikely that chemical extraction techniques can mimic the process of metal absorption or uptake in organisms, such techniques provide good estimates of the bioaccessibility of metals in the environment. Based on the experience and knowledge gained from studies of the bioavailability of trace metals in soils, the application of similar techniques to estimate bioavailability of metal oxide NPs holds promise (Coutris et al 2012;Zhao et al 2012b).…”

Alginate modifies the physiological impact of CeO2 nanoparticles in corn seedlings cultivated in soil

“…The CeO 2 NPs had primary particle size of (8 ± 1) nm, hydrodynamic size of (1373 ± 32) nm, and zeta potential of -0.62 (±2.9) mV (25 mg/L in distilled water; Zetasizer Nano-ZS 90, Malvern, Germany).The soil was collected from Texas Agri-Life Research Center at El Paso (Texas A&M University System, USA). The properties of the soil were introduced in previous paper (Zhao et al, 2012b). The soil was air-dried and sieved through a 1 mm mesh prior to experimental use.…”