Impact of ZnO and ZnS nanoparticles in sewage sludge-amended soil on bacteria, plant and invertebrates

Terrestrial bioassays for assessing the biochemical and toxicological impact of biosolids application derived from wastewater treatment plants

Wastewater treatment plants (WWTP) are facilities where municipal wastewater undergoes treatment so that its organic load and its pathogenic potential are minimized. Sewage sludge is a by-product of this process and when properly treated is preferentially called "biosolids". These treatments may include some or most of the following: thickening, dewatering, drying, digestion, composting, liming. Nowadays it is almost impossible to landfill biosolids, which however can well be used as crop fertilizers. Continuous or superfluous biosolids fertilization may negatively affect non-target organisms such as soil macro-organisms or even plants. These effects can be depicted through bioassays on terrestrial animals and plants. It has been shown that earthworms have been affected to various degrees on the following endpoints: pollutants' bioaccumulation, viability, reproduction, avoidance behavior, burrowing behavior. Collembola have been affected on viability, reproduction, avoidance behavior. Other terrestrial organisms such as nematodes and diplopods have also shown adverse health effects. Phytotoxicity have been caused by some biosolids regimes as measured through the following endpoints: seed germination, root length, shoot length, shoot biomass, root biomass, chlorophyll content, antioxidant enzyme activity. Very limited statistical correlations between pollutant concentrations and toxicity endpoints have been established such as between juvenile mortality (earthworms) and As or Ba concentration in the biosolids, between juvenile mortality (collembola) and Cd or S concentration in the biosolids, or between phytotoxicity and some extractable metals in leachates or aquatic extracts from the biosolids; more correlations between physicochemical characteristics and toxicity endpoints have been found such as between phytotoxicity and ammonium N in biosolids or their liquid extracts, or between phytotoxicity and salinity. An inverse correlation between earthworm/collembola mortality and stable organic matter has also been found. Basing the appropriateness of biosolids only on chemical analyses for pollutants is not cost-effective. To enable risk characterization and subsequent risk mitigation it is important to apply a battery of bioassays on soil macro-organisms and on plants, utilizing a combination of endpoints and established protocols. Through combined analytical quantification and toxicity testing, safe use of biosolids in agriculture can be achieved.

Ecotoxicological characterization of engineered biochars produced from different feedstock and temperatures

Biochar (BC) engineering, which has recently gained a lot of interest, allows designing the functional materials. BC modification improves the properties of pristine biochar, especially in terms of adsorption parameters. An interesting type of modification is the introduction of metals into the BC's structure. There is a knowledge gap regarding the effects of modified BC (e.g., BC-Mg, BC-Zn) on organisms. The aim of this study was the ecotoxicological evaluation of BC-Mg and BC-Zn composites, received under diverse conditions from willow or sewage sludge at 500 or 700 °C. The ecotoxicological tests with bacteria Vibrio fischeri (V. fischeri) and invertebrates Folsomia candida (F. candida) were applied to determine the toxicity of BC. The content of toxic substances (e.g., polycyclic aromatic hydrocarbons (PAHs), heavy metals (HMs), environmentally persistent free radicals (EPFRs)) in BC were also determined and compared with ecotoxicological parameters. The ecotoxicity of studied BCs depends on many variables: feedstock type, pyrolysis temperature and the modification type. The Zn and Mg modification reduced (from 28 to 63 %) the total Ʃ16 PAHs content in willow-derived BCs while in SL-derived BCs the total Ʃ16 PAHs content was even 1.5-3 times higher compared to pristine BCs. The Zn modified willow-derived BCs affected positively on F. candida reproduction but showed inhibition of luminescence V. fischeri. BC-Mg exhibited harmful effect to F. candida. The ecotoxicological assessment carried out sheds light on the potential toxicity of BC-Zn and BC-Mg composites, which are widely used in the removal of heavy metals, pharmaceuticals, dyes from waters and soils.

Sustainable agricultural use of sewage sludge: impacts of high Zn concentration on on Folsomia candida, Enchytraeus crypticus, Lactuca sativa, and Phaseolus vulgaris

Zinc (Zn) is an essential micronutrient for plants and an important component for maintaining soil quality. Commonly found in the soil due to anthropogenic activities, such as industrialization and application of organic waste as fertilizers, in high concentrations, Zn may induce soil toxicity, affecting important communities, such as edaphic fauna. Despite its high concentrations found in the environment, Zn bioavailability can be affected by the type of soil, organic matter content and pH. In this work, Zn had its toxicity evaluated in a natural tropical soil, sampled in São Paulo-Brazil, for two soil invertebrates (Folsomia candida, Enchytraeus crypticus) and two seeds (Lactuca sativa and Phaseolus vulgaris), through ecotoxicological tests. The invertebrate E. crypticus was exposed to Zn concentrations of 10.0 (T1); 100.0 (T2); 150.0 (T3); 200.0 (T4); 400.0 (T5) mg Zn kg-1 of dry soil, while F. candida, L. sativa and P. vulgaris were exposed to Zn concentrations of 100.0; 200.0; 400.0; 800.0 (t6); 1600.0 (t7); and 2000.0 (t8) mg Zn kg-1 of dry soil. The outcome evaluated were seed germination, for L. sativa and P. vulgaris, and reproduction, for F. candida and E. crypticus. The EC50 obtained for E. crypticus, F. candida, L. sativa, and P. vulgaris were 261.5, 1089.7, 898.5, and 954.5 mg Zn kg-1 of dry soil, respectively, being E. crypticus the most sensitive organism, and only at the highest Zn's concentrations the organisms' reproduction and seeds' germination showed a statistically significant inhibitory effect (p < 0.05). Therefore, this work's results showed that Zn does not present significant toxicity for the tested soil organisms and seeds and that at 100 mg Zn kg-1 of dry soil it can be beneficial to F. candida and E. crypticus' reproduction and L. sativa's germination. These results imply that the presence of Zn in low concentrations, both in soil and biofertilizers, such as sewage sludge, not only is not a concern, but it can even benefit certain crops and functions of edaphic organisms, which may contribute to the engagement of sustainable agricultural practices and the quest for food security.

Assessing the potential chronic, sublethal and lethal ecotoxicity of land-applying biosolids on Folsomia candida and Lumbricus terrestris

The ecotoxicity of biosolids has been studied extensively using single-compound toxicity testing and 'spiking' studies; however, little knowledge exists on the ecotoxicity of biosolids as they are land-applied in the Canadian context. The purpose of this study is to elucidate the chronic, sub-lethal (i.e., behavioural), and lethal impacts of land- applying biosolids on the environmentally relevant Folsomia candida (springtails) and Lumbricus terrestris (earthworms) and concomitantly ascertain whether the use of biosolids for nutrient amendment is a sustainable practice. This study is part of a larger multi-compartment programme which includes terrestrial plants and aquatic arthropods. After a review of existing government protocols and research, the current study suggests new environmentally relevant bioassays as to elucidate the true nature of the potential ecotoxicity of land-applying biosolids, within a laboratory context. Specifically, protocols were developed (e.g., shoebox bioassays for L. terrestris sub-lethal testing) or modified (e.g., using Evans' boxes (Evans 1947) for chronic and sub-lethal testing on L. terrestris). Subsequently, two biosolids were tested on springtails and earthworms using avoidance and reproductive bioassay endpoints, at application rates that represent standard (8 tonnes ha^-1) and worst-case scenarios (22 tonnes ha^-1). Results indicated no effect of biosolids at the environmentally relevant concentration; the worst-case scenario exhibited a positive significantly significant relationship (indicating preference for treatment conditions). We suggest that further assessment of the potential ecotoxicological impact of biosolids employ (i) environmentally relevant organisms, (ii) appropriate bioassays including the use of whole-organism endpoints, and (iii) multi-kingdom testing (e.g., Kingdom Plantae, Animalia) to comprehensively elucidate answers. Lastly, in situ (field assays) are strongly encouraged for future studies.

Zinc Oxide Particles Can Cause Ovarian Toxicity by Oxidative Stress in Female Mice Model

Introduction

Zinc oxide nanoparticles (ZnO NPs) participate in all aspects of our lives, but with their wide application, more and more disadvantages are exposed. The goal of this study was to investigate the toxicity of ZnO NPs in female mice ovaries and explore its potential mechanism.

Methods

In this study, adult female mice were orally exposed to 0, 100, 200, and 400 mg/kg ZnO NPs for 7 days. We explored the underlying mechanisms via the intraperitoneal injection of N-acetyl-cysteine (NAC), an inhibitor of oxidative stress, and salubrinal (Sal), an inhibitor of endoplasmic reticulum (ER) stress.

Results

The results indicated that serum estradiol and progesterone levels declined greatly with increasing ZnO NPs dosage. Hematoxylin and eosin (HE) staining revealed increased atretic follicles and exfoliated follicular granulosa cells. Moreover, at the transcriptional level, antioxidant-related genes such as Keap1 and Nrf2, and ER stress-related genes PERK, eIF2α, and ATF4 were markedly upregulated. In addition, the expression of Caspase12, Caspase9, and Caspase3, which are genes related to apoptosis, was also upregulated in all ZnO NPs treatment groups. Serum malondialdehyde (MDA) content was remarkably up-regulated, whereas superoxide dismutase (SOD) activity was down-regulated. The 400 mg/kg ZnO NPs treatment group suffered the most substantial harm. However, ovarian damage was repaired when NAC and Sal were added to this group.

Conclusion

ZnO NPs had toxic effects on the ovary of female mice, which were due to oxidative stress, ER stress, and the eventual activation of apoptosis.

Effects of zinc oxide nanoparticles transformation in sulfur-containing water on its toxicity to microalgae: Physicochemical analysis, photosynthetic efficiency and potential mechanisms

The environmental transformation of nanomaterials will have a significant impact on their ecotoxicity. Sulfidation process is one of the most important transformation processes in the aquatic environment. Although the sulfidation of ZnO nanoparticles (ZnO NPs) has been previously reported, the transformation characteristics and the relationship between the transformation process and toxicity mechanism to aquatic organisms, especially microalgae, require further study. Therefore, we systematically investigated the transformation properties of ZnO NPs in sulfur-containing water and its impact on the toxicity to microalgae. The results showed that the transformation products of ZnO NPs mainly contained ZnS nanoparticles, and their contents increased with the increase of sulfur-zinc molar ratio in the aqueous solution. After the first week of treatment, the sulfidized ZnO NPs showed less toxicity to microalgae than the pristine ZnO NPs, and interestingly, they exhibited higher toxicity over time. The zinc ions and transformation products played a major role in different treatment periods, resulting in different toxicity. The results of photosynthetic pigments, photosynthetic efficiency, and the relative electron transport rates indicated that the sulfidation process of ZnO NPs had a remarkable influence on algal photosynthesis. These newly acquired results will help us explore the transformation characteristics of ZnO NPs and reasonably assess their potential risks in the aquatic environment.

Pristine and sulfidized ZnO nanoparticles alter microbial community structure and nitrogen cycling in freshwater lakes

Zinc oxide nanoparticles (ZnO NPs) and its sulfidized form (ZnS NPs) are increasingly entering into freshwater systems through multiple pathways. However, their impacts on the composition and function of sedimentary microbial communities are still largely unknown. Here, two kinds of lake-derived microcosms were constructed and incubated with ZnO NPs, or ZnS NPs to investigate the short-term (7 days) and long-term (50 days) impacts on sedimentary microbial communities and nitrogen cycling. After 7 days, both ZnO NPs and ZnS NPs dosed microbial communities experienced distinct alterations as compared to the undosed controls. By day 50, the structural shifts of microbial communities caused by ZnO NPs were significantly enlarged, while the microbial shifts induced by ZnS NPs were largely resolved. Additionally, ZnO NPs and ZnS NPs could significantly alter nitrogen species and nitrogen cycling genes in sediments, revealing their non-negligible impacts on nitrogen cycling processes. Furthermore, our data clearly indicated that the impacts of ZnO NPs and ZnS NPs on nitrogen cycling differed distinctly in different lake-derived microcosms, and the impacts were significantly correlated with microbial community structure. Overall, this research suggests that the entrance of pristine or sulfidized ZnO NPs into freshwater systems may significantly impact the sedimentary microbial community structure and nitrogen cycling.

Contrasted fate of zinc sulfide nanoparticles in soil revealed by a combination of X-ray absorption spectroscopy, diffusive gradient in thin films and isotope tracing

Incidental zinc sulfide nanoparticles (nano-ZnS) are spread on soils through organic waste (OW) recycling. Here we performed soil incubations with synthetic nano-ZnS (3 nm crystallite size), representative of the form found in OW. We used an original set of techniques to reveal the fate of nano-ZnS in two soils with different properties. ⁶⁸Zn tracing and nano-DGT were combined during soil incubation to discriminate the available natural Zn from the soil, and the available Zn from the dissolved nano-⁶⁸ZnS. This combination was crucial to highlight the dissolution of nano-⁶⁸ZnS as of the third day of incubation. Based on the extended X-ray absorption fine structure, we revealed faster dissolution of nano-ZnS in clayey soil (82% within 1 month) than in sandy soil (2% within 1 month). However, the nano-DGT results showed limited availability of Zn released by nano-ZnS dissolution after 1 month in the clayey soil compared with the sandy soil. These results highlighted: (i) the key role of soil properties for nano-ZnS fate, and (ii) fast dissolution of nano-ZnS in clayey soil. Finally, the higher availability of Zn in the sandy soil despite the lower nano-ZnS dissolution rate is counterintuitive. This study demonstrated that, in addition to nanoparticle dissolution, it is also essential to take the availability of released ions into account when studying the fate of nanoparticles in soil.

The co-occurrence of Zn-and Cu-based engineered nanoparticles in soils: The metal extractability vs. toxicity to Folsomia candida

The presence of engineered nanoparticles (ENPs) in soil gradually increases, among others due to the nano-agrochemicals application. So far, the co-existence of different ENPs in soil is poorly examined. Here, the metal extractability and toxicity of soils spiked (300 mg kg^-1) singly and jointly with Zn- and Cu-based ENPs or metal salts were tested. The samples were aged for 1 and 90 days. The predicting available metal component of ENPs concentrations were determined by different methods including soil pore water collection and batch extractions with H₂O, CaCl₂ or DTPA. Survival and reproduction of Folsomia candida were also evaluated. The combined effect of ENPs on the extractability of metals was mainly found with DTPA characterized by the highest leaching capacity among the used extractants. In fresh soil, the mixtures of ENPs differentiated only DTPA-extractable Cu level, while aging resulted in changes in both Zn and Cu concentrations leached by CaCl₂ or DTPA. However, the character of the combined effect was an ENPs- and soil type-dependent, whereas the mixtures of metal salts mostly provided higher Zn and Cu recovery than the individual compounds. The pattern of co-toxicity of metal-oxide ENPs was also time-dependent: the antagonistic and synergistic effect was observed in the samples after 1 and 90 days, respectively. However, the toxicity was weakly related with extractable concentrations in both single and joint treatment of metal compounds. The distinct joint effect patterns of ENPs imply the need for more in-depth investigation of mechanisms of activity of ENPs mixtures in soil.

Effects of TiO2 and ZnO nanoparticles on vermicomposting of dewatered sludge: studies based on the humification and microbial profiles of vermicompost

Nanoparticles (NPs) are prevalent in dewatered sludge, and their presence increases the environmental risks associated with the subsequent sludge treatment process. However, until now, their potential effects on sludge vermicomposting have not been clarified. This study investigated the effects of NPs on sludge humification and microbial profiles during vermicomposting by comparing fresh dewatered sludge substrates with substrates mixed with 0 mg/kg NPs (control), 100 mg/kg TiO₂, 500 mg/kg TiO₂, 100 mg/kg ZnO, and 500 mg/kg ZnO. The results showed that addition of TiO₂ and ZnO NPs to sludge did not significantly affect the growth rate of earthworms and the superoxide dismutase activity in their guts during vermicomposting. Moreover, higher concentrations of the selected NPs promoted the humification index of sludge by 20.7-49.6%, through the formation of polysaccharides, aromatic substances, and organic acids in final vermicomposts. Compared with the control without NP addition, bacterial community diversity was enhanced in treatments with TiO₂ and ZnO NPs, and dominant genera differed according to the type and concentration of NPs. This study suggests that the presence of TiO₂ and ZnO NP residuals modify the microbial community of sludge, thus promoting sludge humification during vermicomposting.

Chemical transformations of nanoscale zinc oxide in simulated sweat and its impact on the antibacterial efficacy

Nanoscale zinc oxide (n-ZnO) is widely used in personal care products and textiles, thus, it would likely be released into human sweat. To better evaluate the potential human health risks of n-ZnO, it is essential to understand its chemical transformations in physiological solutions, such as human sweat, and the resulting changes in the n-ZnO bioavailability. Here, two types of n-ZnO, ZnO nanoparticles (ZnO-NPs) and nanorod-based ZnO nanospheres (ZnO-NSs) were synthesized and incubated in 3 types of simulated sweat with different pH values and phosphate concentrations. The content of Zn₃(PO₄)₂ in the transformed n-ZnO was quantified by selective dissolution of Zn₃(PO₄)₂ in 0.35 M ammonia solution where 100% and 5.5% of Zn₃(PO₄)₂ and ZnO were dissolved, respectively. The kinetics analysis indicated that by 24-48 h the content of Zn₃(PO₄)₂ reached the maximum, being 15-21% at pH 8.0 and 45-70% at pH 5.5 or 4.3. Interestingly, no correlation was observed between the rate constants of Zn₃(PO₄)₂ formation and the specific surface areas of n-ZnO, implying that chemical transformations from n-ZnO to Zn₃(PO₄)₂ in the simulated sweat might not be simply attributed to dissolution and precipitation. Using a variety of characterization techniques, we demonstrated the formation of a ZnO‒Zn₃(PO₄)₂ core-shell structure with the shell consisting of amorphous Zn₃(PO₄)₂ at pH 8.0 and additionally of crystalline Zn₃(PO₄)₂ and Zn₃(PO₄)₂•4H₂O at pH 5.5 or 4.3. The phosphate-induced transformation of n-ZnO in the simulated sweat at pH 5.5 and 4.3 greatly reduced the antibacterial efficacy of n-ZnO through moderating the nanoparticle dissolution, indicating limited bioavailability of the NPs upon transformation. The results improve the understanding of the fate and hazards of n-ZnO.

Positive effects of metallic nanoparticles on plants: Overview of involved mechanisms

Engineered nanoparticles (NPs) are considered as potential agents for agriculture as fertilizers, growth enhancers and pesticides. Therefore, understanding the mechanisms that are responsible for their effects is important. Various studies demonstrated that the application of nontoxic concentrations can promote seed germination, enhance plant growth and increase the yield. Moreover, NPs can be used to protect plants from environmental impacts such as salt or drought stress and diminish accumulation and toxicity of heavy metals. NPs can serve as a source of micronutrients (e.g. ZnO, iron- and manganese-based NPs), thus increasing fitness and helps plants to cope with stress conditions. TiO₂ and iron-based NPs are able to delay senescence and speed-up cell division via changes in phytohormonal levels. The application of some NPs can promote the activity of enzymes such as amylase, nitrate reductase, phosphatase, phytase and carbonic anhydrases, which are involved in metabolism and nutrient acquisition. E.g. ZnO and TiO₂ NPs can stimulate chlorophyll biosynthesis and photosynthetic activity. Iron-based and CeO₂ NPs enhance stomata opening resulting in better gas exchange and CO₂ assimilation rate. NPs can also modulate oxidative stress by the stimulation of the antioxidant enzymes such peroxidases and superoxide dismutase. However, the knowledge about the fate, transformation, and accumulation of NPs in the environment and organisms is needed prior to their use in agriculture to avoid negative environmental impacts. Higher or lower toxicity of various NPs was established for microorganisms, plants or animals. In this overview, we focused on the possible mechanisms of Ag, ZnO, TiO₂, Fe-based, CeO₂, Al₂O₃, and manganese-based NPs responsible for their positive effects on plants.

Responses of soil bacteria and fungal communities to pristine and sulfidized zinc oxide nanoparticles relative to Zn ions

Zinc oxide nanoparticles (ZnO NPs) are attracting much interest due to their potential toxicity and ubiquity in consumer products. However, understanding of pristine and transformed ZnO NPs impact on soil microbial communities is still limited. Here, we explored changes in the microbial communities of soils treated with pristine and sulfidized ZnO NPs (s-ZnO NPs), and their corresponding Zn ions (ZnSO₄) for 30 and 90 days exposures at 100 and 500 mg Zn kg^-1. The similarity in bacterial community responses was observed between ZnO NPs and s-ZnO NPs, and these Zn treatments significantly affected the bacterial communities at 90 days, which exhibited distinct patterns compared to ZnSO₄. The single-time tested DTPA and H₂O extractable Zn ions could not fully explain the observed ZnO NPs and s-ZnO NPs impact on bacterial communities. The two most dominant phylum Nitrospirae and Actinobacteria, associated with the reduction of NH₄⁺-N and dissolved organic carbon, demonstrated significant changes in soils exposed to ZnO NPs and s-ZnO NPs. This suggests the potential long-term impact of transformed ZnO NPs on soil carbon and nitrogen cycling. For fungal communities, we did not find the distinct response patterns of fungal communities between nanoparticulate and ionic Zn exposures.

The chronic effects of CuO and ZnO nanoparticles on Eisenia fetida in relation to the bioavailability in aged soils

The bioavailability and bioaccumulation of metal-based engineered nanoparticles (ENPs) in soils need to be evaluated in environmentally relevant scenarios. The aim of this study was an analysis of potentially available metal-component ENPs (nano-ZnO and nano-CuO) in soils. Earthworms (Eisenia fetida) were used to examine the bioaccumulation potential of ENPs. Micro-particles (micro-ZnO and micro-CuO) and metal salts (ZnCl₂ and CuCl₂) were used to evaluate the nano-effect and the activity of dissolved ions, respectively. Zn- and Cu-compounds were added to sandy loam and silt loam at a concentration of 10 mg kg^-1. The bioavailable fractions of metals were extracted from soil using H₂O, MgCl₂ with CH₃COONa or EDTA. EDTA was the most effective extractant of Zn and Cu (10.06-11.65 mg Zn kg^-1 and 2.69-3.52 mg Cu kg^-1), whereas the H₂O-extractable metal concentration was at the lowest level (1.98-2.12 mg Zn kg^-1 and 0.54-0.82 Cu mg kg^-1). The bioavailable metal concentrations were significantly higher in silt loam than sandy loam soil, which was related to the higher pH value of silt. There were no significant differences between the Zn content in the earthworms incubated in the two soils, which may confirm the auto-regulation of the Zn content by earthworms. However, the bioaccumulation of Cu was strongly correlated with the extractable Cu concentrations. The juvenile earthworms accumulated Cu and Zn more than adults. Based on our results, aging neutralized the differences between the ionic and particulate effects of metal-compounds.

Too small to matter? Physicochemical transformation and toxicity of engineered nTiO2, nSiO2, nZnO, carbon nanotubes, and nAg

Engineered nanomaterials (ENMs) refer to a relatively novel class of materials that are increasingly prevalent in various consumer products and industrial applications - most notably for their superlative physicochemical properties when compared with conventional materials. However, consumer products inevitably degrade over the course of their lifetime, releasing ENMs into the environment. These ENMs undergo physicochemical transformations and subsequently accumulate in the environment, possibly leading to various toxic effects. As a result, a significant number of studies have focused on identifying the possible transformations and environmental risks of ENMs, with the objective of ensuring a safe and responsible application of ENMs in consumer products. This review aims to consolidate the results from previous studies related to each stage of the pathway of ENMs from being embodied in a product to disintegration/transformation in the environment. The scope of this work was defined to include the five most prevalent ENMs based on recent projected production market data, namely: nTiO₂, nSiO₂, nZnO, carbon nanotubes, and nAg. The review focuses on: (i) models developed to estimate environmental concentrations of ENMs; (ii) the possible physicochemical transformations; (iii) cytotoxicity and genotoxicity effects specific to each ENM selected; and (iv) a discussion to identify potential gaps in the studies conducted and recommend areas where further investigation is warranted.

Residuals, sludge, and biosolids: Advancements in the field

Advancements in the field of residuals, sludge, and biosolids have been made in 2019. This review outlines the major contributions of researchers that have been published in peer-reviewed journals and conference proceedings throughout 2019 and includes brief summaries from over 125 articles. The review is organized in sections including life cycle and risk assessments; characteristics, quality, and measurement including micropollutants, nanoparticles, pathogens, and metals; sludge treatment technologies including dewatering, digestion, composting, and wetlands; disposal and reuse including adsorbents, land application and agricultural uses, nutrient recovery, and innovative uses; odor and air emissions; and energy issues.

Nanomaterial Transformations in the Environment: Effects of Changing Exposure Forms on Bioaccumulation and Toxicity

In the environment, nanomaterials (NMs) are subject to chemical transformations, such as redox reactions, dissolution, coating degradation, and organic matter, protein, and macromolecule binding, and physical transformations including homo or heteroagglomeration. The combination of these reactions can result in NMs with differing characteristics progressing through a functional fate pathway that leads to the formation of transformed NM functional fate groups with shared properties. To establish the nature of such effects of transformation on NMs, four main types of studies are conducted: 1) chemical aging for transformation of pristine NMs; 2) manipulation of test media to change NM surface properties; 3) aging of pristine NMs water, sediment, or soil; 4) NM aging in waste streams and natural environments. From these studies a paradigm of aging effects on NM uptake and toxicity can be developed. Transformation, especially speciation changes, largely results in reduced potency. Further reactions at the surface resulting in processes, such as ecocorona formation and heteroagglomeration may additionally reduce NM potency. When NMs of differing potency transform and enter environments, common transformation reaction occurring in receiving system may act to reduce the variation in hazard between different initial NMs leading to similar actual hazard under realistic exposure conditions.

Opposite effects of the earthworm Eisenia fetida on the bioavailability of Zn in soils amended with ZnO and ZnS nanoparticles

The increasing release of metallic nanoparticles (NPs) or their sulfidized forms into soils have raised concerns about their potential risks to soil ecosystems. Hence, there is a need for novel strategies to remediate metallic NPs pollution in soils. In this study, to explore the feasibility of using earthworm Eisenia fetida to manage soils contaminated with metallic NPs, we simultaneously investigated the chronic soil toxicities of ZnO NPs and ZnS NPs to E. fetida, and the effects of E. fetida on Zn extractability in soils amended with ZnO NPs and ZnS NPs. After a 28 d exposure, survival rate and weight loss of earthworms were not impacted by either ZnO NPs or ZnS NPs at a concentration of 400 mg Zn per kg soil. Further, while ZnO NPs activated earthworm antioxidative system, ZnS NPs resulted in significant alleviation of oxidative damage in earthworm. The presence of earthworms significantly decreased the bioavailability of Zn in ZnO NPs contaminated soil, whereas significantly increased the bioavailability of Zn in ZnS NPs contaminated soil. These findings implied that the earthworm E. fetida could play an important role in altering the mobilization of metals originating from metallic NPs in soils, which may further aid in the development of a method for the treatment of metallic NPs pollution in soils.