The effect of pH and ageing on the fate of CuO and ZnO nanoparticles in soils

Predicting environmental concentrations of nanomaterials for exposure assessment - a review

There have been major advances in the science to predict the likely environmental concentrations of nanomaterials, which is a key component of exposure and subsequent risk assessment. Considerable progress has been since the first Material Flow Analyses (MFAs) in 2008, which were based on very limited information, to more refined current tools that take into account engineered nanoparticle (ENP) size distribution, form, dynamic release, and better-informed release factors. These MFAs provide input for all environmental fate models (EFMs), that generate estimates of particle flows and concentrations in various environmental compartments. While MFA models provide valuable information on the magnitude of ENP release, they do not account for fate processes, such as homo- and heteroaggregation, transformations, dissolution, or corona formation. EFMs account for these processes in differing degrees. EFMs can be divided into multimedia compartment models (e.g., atmosphere, waterbodies and their sediments, soils in various landuses), of which there are currently a handful with varying degrees of complexity and process representation, and spatially-resolved watershed models which focus on the water and sediment compartments. Multimedia models have particular applications for considering predicted environmental concentrations (PECs) in particular regions, or for developing generic "fate factors" (i.e., overall persistence in a given compartment) for life-cycle assessment. Watershed models can track transport and eventual fate of emissions into a flowing river, from multiple sources along the waterway course, providing spatially and temporally resolved PECs. Both types of EFMs can be run with either continuous sources of emissions and environmental conditions, or with dynamic emissions (e.g., temporally varying for example as a new nanomaterial is introduced to the market, or with seasonal applications), to better understand the situations that may lead to peak PECs that are more likely to result in exceedance of a toxicological threshold. In addition, bioaccumulation models have been developed to predict the internal concentrations that may accumulate in exposed organisms, based on the PECs from EFMs. The main challenge for MFA and EFMs is a full validation against observed data. To date there have been no field studies that can provide the kind of dataset(s) needed for a true validation of the PECs. While EFMs have been evaluated against a few observations in a small number of locations, with results that indicate they are in the right order of magnitude, there is a great need for field data. Another major challenge is the input data for the MFAs, which depend on market data to estimate the production of ENPs. The current information has major gaps and large uncertainties. There is also a lack of robust analytical techniques for quantifying ENP properties in complex matrices; machine learning may be able to fill this gap. Nevertheless, there has been major progress in the tools for generating PECs. With the emergence of nano- and microplastics as a leading environmental concern, some EFMs have been adapted to these materials. However, caution is needed, since most nano- and microplastics are not engineered, therefore their characteristics are difficult to generalize, and there are new fate and transport processes to consider.

Biochar and metal-tolerant bacteria in alleviating ZnO nanoparticles toxicity in barley

The constant use of zinc oxide nanoparticles (ZnO NPs) in agriculture could increase their concentration in soil, and cause a threat to sustainable crop production. The present study was designed to determine the role of spore-forming and metal-tolerant bacteria, and biochar in alleviating the toxic effects of a high dose of ZnO NPs (2000 mg kg^-1) spiked to the soil (Haplic Chernozem) on barley (Hordeum sativum L). The mobile compounds of Zn in soil and their accumulation in H. sativum tissues were increased significantly. The addition of biochar (2.5% of total soil) and bacteria (10¹⁰ CFU kg^-1) separately and in combination showed a favorable impact on H. sativum growth in ZnO NPs polluted soil. The application of bacteria (separately) to the contaminated soil reduced the mobility of Zn compounds by 7%, due to loosely bound Zn compounds, whereas only biochar inputs lowered Zn mobile compounds mobility by 33%, even the combined application of biochar and bacteria also suppressed the soil Zn mobile compounds. Individual application of biochar and bacteria reduced the Zn plant uptake, i.e., underground parts (roots) by 44% and 20%, and in the above-ground parts of H. sativum plants by 39% and 13%, respectively, compared to ZnO NPs polluted soil treatments. Biochar, both separately and in combination with bacteria improved the root length by 48 and 85%, and plant height by 53 and 40%, respectively, compared to the polluted control. The root length and plant height decreased by 52 and 40% in ZnO NPs spiked soil compared clean soil treatments. Anatomical results showed an improvement in the structural organization of cellular-sub-cellular tissues of root and leaf. The changes in ultrastructural organization of assimilation tissue cells were noted all treatments due to the toxic effects of ZnO NPs compared with control treatment. The results indicate that metal-tolerant bacteria and biochar could be effective as a soil amendment to reduce metal toxicity, enhance crop growth, and improve soil health.

Dissolution kinetics and solubility of copper oxide nanoparticles as affected by soil properties and aging time

Nano copper oxide (CuO NP) was added to eight soils to study the effect of aging time of copper on the concentration of diethylenetriaminepentaacetic acid (DTPA)-extracted copper (DTPA-Cu), with bulk copper oxide (CuO BP) and copper nitrate [Cu(NO₃)₂] used for comparison. Moreover, the effect of soil properties on the dissolution of CuO NP was studied. A dissolution model was used to quantitatively describe the dissolution kinetics of CuO NPs in different soils. The results showed that the concentration of DTPA-Cu decreased with increasing aging time in soils spiked with Cu(NO₃)₂, while the concentration increased to varying degrees in soils spiked with CuO NPs or CuO BPs. In acidic soils, the equilibrium concentrations of DTPA-Cu were 93.3-98.7 mg·kg^-1 for CuO NP treatments, 65.5-94.3 mg·kg^-1 for CuO BP treatments, and 81.4-90.0 mg·kg^-1 for Cu(NO₃)₂ treatments, which were greater than those in alkaline soils (43.4-56.9 mg·kg^-1, 6.26-8.61 mg·kg^-1, and 73.9-80.0 mg·kg^-1, respectively). In acidic soils, DTPA-Cu equilibrium concentration ranked the different forms of copper treatments as CuO NPs > Cu(NO₃)₂ > CuO BPs, while in alkaline soils, the order was Cu(NO₃)₂ > CuO NPs > CuO BPs. The dissolution rate constants and solubility of CuO NPs were 0.33-6.42 and 37.1-100.1 mg·kg^-1, respectively. Pearson correlation analysis indicated that the dissolution parameters of CuO NPs were negatively correlated with soil pH and positively correlated with the contents of organic matter, clay, iron oxides, and aluminum oxides. Further, the dissolution rate constant and solubility of CuO NPs could be well predicted by soil pH and the content of free or amorphous aluminum. Our study identified the main factors controlling the dissolution of CuO NPs in farmland soils and highlighted the higher availability of CuO NPs in acidic soils.

Distinct response patterns of bacterial communities in Ag- and ZnO-rGO nanocomposite-amended silt loam soils

The widespread application of metal-based nanoparticle (MNPs)/reduced graphene oxide (rGO) composites inevitably leads to their release into soils. However, we lack a detailed understanding of the bacterial community response to MNPs-rGO exposure in farmland soils. Here, we conducted a soil microcosm experiment to analyze the potential impact of MNPs-rGO on bacterial communities in two field soils via high-throughput sequencing. The change in alpha diversity of bacterial communities was more susceptible to Ag-rGO and ZnO-rGO treatments than CuO-rGO. In both soils, MNPs-rGO significantly changed the bacterial community structure even at a low dose (1 mg kg^-1). The bacterial community structure was most strongly affected by Ag-rGO at 30 days, but the greatest changes occurred in ZnO-rGO at 60 days. The differences in soil properties could shape bacterial communities to MNPs-rGO exposure. Distance-based redundancy analysis and functional annotation of prokaryotic taxa showed that some bacterial species associated with nitrogen cycling were greatly influenced by Ag-rGO and ZnO-rGO exposure. In sum, Ag-rGO and ZnO-rGO may potentially affect bacterial communities and nitrogen turnover under long-term realistic field exposure. These findings present a perspective on the response of bacterial communities to MNPs-rGO and provide a fundamental basis for estimating the ecological behavior of MNPs-rGO.

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.

Effect of soil leaching on the toxicity thresholds (ECx) of Zn in soils with different properties

Currently, the scientific basis for establishing soil environmental criteria is lacking. In order to establish reasonable soil environmental criteria values suitable for soils with different properties, this study selected soils from 16 different sites to determine the toxicity threshold of Zn based on toxicity tests of barley root elongation. In addition, leaching treatments were set up in seven soils with different properties to eliminate the influence of the accompanying anions (Cl-) on the determination of the Zn toxicity threshold. The results indicated that the toxicity thresholds of different soils vary greatly. The EC10 and EC50 ranges of barley root elongation in 16 kinds of non-leached soils were 18.5 mgkg-1 to 1618.7 mgkg-1 and 277.9 mgkg-1 to 3179.8 mgkg-1, respectively. The hormesis effect appeared in the dose response of Zn, and relative barley root elongation reached more than 150%. Leaching significantly reduced the Zn toxicity in acidic soils. The variation ranges of the leaching factor (LF) in the seven soils were LF10 = 1.1-9.3, LF50 = 1.0-3.2. The LF prediction model indicated that pH explained 81.4% of the LF variation (p < 0.01). The soil pH, cation exchange capacity (CEC), and conductivity (EC) explained 97.8% of the EC50 variation in the leached soil (p < 0.01). The results provide reference values for Zn environmental criteria.

Measuring ZnO nanoparticles available concentrations in contaminated soils using the diffusive gradient in thin-films (DGT) technique

A major gap in understanding nanomaterials behaviour in the environment is a lack of reliable tools to measure their available concentrations. In this research we use diffusive gradients in thin films (DGT) for measuring concentrations of zinc oxide nanoparticles (ZNO NPs) in soils. Available nanoparticle concentrations were assessed by difference, using paired DGT devices with and without 1000 MWCO dialysis membranes to exclude NPs. We used ZnO because its toxic effects are accelerated through dissolution to Zn²⁺. Our test soils had different pH and organic matter (OM) contents, which both affect the dissolution rate of ZnO NPs. Woburn (pH ≈ 6.9, OM ≈ 1.8%) and Lufa (pH ≈ 5.9, OM ≈ 4.2%) soils were spiked to a single concentration of 500 mg of ZnO NPs per 1 kg of soil and the available concentrations of ZnO NPs and dissolved zinc were evaluated in 3, 7, 14, 21, 28, 60, 90, 120, 150 and 180 day intervals using DGT. The results showed that the dissolution of ZnO NPs, as well as the available concentrations of both dissolved and nanoparticulate Zn, was much higher in Lufa soil than in Woburn. This work demonstrates that DGT can be used as a simple yet reliable technique for determining concentrations of ZnO NPs in soils and probing its dissolution kinetics.

Smart nanomaterial and nanocomposite with advanced agrochemical activities

Conventional agriculture solely depends upon highly chemical compounds that have negatively ill-affected the health of every living being and the entire ecosystem. Thus, the smart delivery of desired components in a sustainable manner to crop plants is the primary need to maintain soil health in the upcoming years. The premature loss of growth-promoting ingredients and their extended degradation in the soil increases the demand for reliable novel techniques. In this regard, nanotechnology has offered to revolutionize the agrotechnological area that has the imminent potential over conventional agriculture and helps to reform resilient cropping systems withholding prominent food security for the ever-growing world population. Further, in-depth investigation on plant-nanoparticles interactions creates new avenues toward crop improvement via enhanced crop yield, disease resistance, and efficient nutrient utilization. The incorporation of nanomaterial with smart agrochemical activities and establishing a new framework relevant to enhance efficacy ultimately help to address the social acceptance, potential hazards, and management issues in the future. Here, we highlight the role of nanomaterial or nanocomposite as a sustainable as well stable alternative in crop protection and production. Additionally, the information on the controlled released system, role in interaction with soil and microbiome, the promising role of nanocomposite as nanopesticide, nanoherbicide, nanofertilizer, and their limitations in agrochemical activities are discussed in the present review.

Influences and mechanisms of nanoparticles on pentachloronitrobenzene accumulation by earthworms

Pesticides and nanoparticles may coexist in soil; however, influences of nanoparticles on accumulation of pesticides in terrestrial organisms are still unclear. This study aims to investigate the influences and mechanisms of metal oxide nanoparticles (nano ZnO and nano CuO) on accumulation of pentachloronitrobenzene (PCNB) in earthworms and their combined toxicity. The earthworms were cultivated in the soil spiked with nanoparticles (10, 50, 250 mg/kg) and PCNB (100 μg/kg) for 21 days. The concentrations of PCNB in earthworms in binary exposure treatments (PCNB + ZnO and PCNB + CuO) reached 2.47 and 3.13 times of that in individual PCNB exposure treatment, indicating that nanoparticles facilitated the accumulation of PCNB in earthworms. The contents of reactive oxygen species (ROS) in earthworms in treatments PCNB + ZnO 250 and PCNB + CuO 250 reached 379 and 316 fluorescence intensity/mg Protein, respectively, which were significantly higher than that in control group (183 fluorescence intensity/mg protein), indicating that nanoparticles would cause oxidative stress to earthworms. Earthworm coelomocytes were extracted from healthy earthworms and cultivated in culture media in cytotoxicity tests. Changes of intracellular ROS contents and cell viability suggested that PCNB and nanoparticles caused serious oxidative damage to earthworm coelomocytes, thus leading to the damage of cell membrane and cell death. In in vivo tests, changes of biomarkers (ROS and malondialdehyde) demonstrated that these pollutants injured the earthworms. Increased accumulation of PCNB in binary exposure treatments was due to the damage of body cavity caused by nanoparticles. This study provides a novel hypothesis for nanoparticles facilitating organic pollutants entering terrestrial organisms and determines whether nanoparticles would bring about greater environmental risks of other pollutants.

Combined effect of nano-CuO and nano-ZnO in plant-related system: From bioavailability in soil to transcriptional regulation of metal homeostasis in barley

The co-existence of engineered nanoparticles (ENPs) in the environment is an emerging issue remaining poorly investigated. The present study aimed at analyzing the fate of binary mixtures of CuO and ZnO ENPs in a soil-plant system. The ENPs were singly or jointly dosed into soil at 300 mg kg^-1 and aged for 7 and 30 days. To evaluate nano-specific effects, individual and combined treatments of metal salts were also applied. Interactions between ENPs and soil-grown barley Hordeum vulgare were determined in terms of biomass, plant mineral composition as well as expression of genes regulating metal homeostasis (ZIP1,3,6,8,10,14, RAN1, PAA1,2, MTP1, COPT5) and detoxification (MT1-3). The bioavailability of Zn and Cu in bulk soil and in the rooting zone was determined using the 0.01 mol L^-1 CaCl₂ extraction. After combined treatment of ENPs, the extractable concentrations of Cu and Zn were lower than upon individual exposure in bulk soil. The opposite tendency was noted for metal salts. Genes related to metal uptake (ZIP) and cellular compartment (PAA2, RAN1) were mostly up-regulated by single rather than combined application of ENPs. The single and joint exposure to metals salts induced the down-regulation of these genes.

Long-term dissolution and transformation of ZnO in soils: The roles of soil pH and ZnO particle size

The ongoing use of ZnO nanoparticles (NPs)-associated commercial products results in large release of ZnO NPs into soils and has prompted systematic investigation regarding their fractionation and fate in soils. To date, little information is available about the long-term dissolution and transformation of ZnO NPs in different soils. The distribution and speciation of Zn in two different soils (i.e., Red soil (RS) and Wushantu soil (WS)) treated with either ZnO NPs or bulk ZnO were elucidated by combining soil incubation study with synchrotron-based techniques. Results revealed that ZnO NPs and bulk ZnO were almost dissolved after 1 day, indicating their rapid dissolution upon entering RS (pH-acidic). Rapid dissolution of ZnO NPs was also observed even in WS (pH- circumneutral). The solubilized Zn²⁺ released from ZnO particles was completely transformed into stable forms (e.g., Zn-Al LDH, Zn-OM, and Zn(OH)₂) and Zn-Al LDH was the dominant species in WS after incubation for 360 days. A majority of solubilized Zn²⁺ released from ZnO particles was also transformed into Zn-Al LDH precipitate in RS. The findings of this study facilitate a better understanding of the fate of ZnO in soils, which could be leveraged for remediation of ZnO-polluted soils.

Zinc oxide nanoparticles: potential effects on soil properties, crop production, food processing, and food quality

The use of zinc oxide nanoparticles (ZnO NPs) is expected to increase soil fertility, crop productivity, and food quality. However, the potential effects of ZnO NP utilization should be deeply understood. This review highlights the behavior of ZnO NPs in soil and their interactions with the soil components. The review discusses the potential effects of ZnO NPs on plants and their mechanisms of action on plants and how these mechanisms are related to their physicochemical properties. The impact of current applications of ZnO NPs in the food industry is also discussed. Based on the literature reviewed, soil properties play a vital role in dispersing, aggregation, stability, bioavailability, and transport of ZnO NPs and their release into the soil. The transfer of ZnO NPs into the soil can affect the soil components, and subsequently, the structure of plants. The toxic effects of ZnO NPs on plants and microbes are caused by various mechanisms, mainly through the generation of reactive oxygen species, lysosomal destabilization, DNA damage, and the reduction of oxidative stress through direct penetration/liberation of Zn2+ ions in plant/microbe cells. The integration of ZnO NPs in food processing improves the properties of the relative ZnO NP-based nano-sensing, active packing, and food/feed bioactive ingredients delivery systems, leading to better food quality and safety. The unregulated/unsafe discharge concentrations of ZnO NPs into the soil, edible plant tissues, and processed foods raise environmental/safety concerns and adverse effects. Therefore, the safety issues related to ZnO NP applications in the soil, plants, and food are also discussed.

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.

Soil properties can evoke toxicity of copper oxide nanoparticles towards springtails at low concentrations

Copper oxide nanoparticles (CuO-NP) are used as an efficient alternative to conventional Cu in agriculture and might end up in soils. They show a high toxicity towards cells and microorganisms, but only low toxicity towards soil invertebrates. However, most existing soil ecotoxicological studies were conducted in a sandy reference soil and at test concentrations ≥100 mg Cu/kg soil. Therefore, there is a knowledge gap concerning the effect of soil texture on the toxicity of CuO-NP at lower, more realistic test concentrations. In our study, a sandy reference soil and three loamy soils were spiked with CuO-NP at up to four concentrations, ranging from 5 to 158 mg Cu/kg. We investigated 28-day reproduction as well as weight and Cu content after 14-day bioaccumulation and subsequent 14-day elimination for the springtail Folsomia candida. For the first time we analysed the size distribution of CuO-NP in aqueous test soil extracts by single particle-ICP-MS which revealed that the diameter of CuO-NP significantly increased with increasing concentration, but did not vary between test soils. Negative effects on reproduction were only observed in loamy soils, most pronounced in a loamy-acidic soil (-61%), and they were always strongest at the lowest test concentration. The observed effects were much stronger than reported by other studies performed with sandy soils and higher CuO-NP concentrations. In the same soil and concentration, a moderate impact on growth (-28%) was observed, while Cu elimination from springtails was inhibited. Rather than Cu body concentration, the diameter of the CuO-NP taken up, as well as NP-clay interactions might play a crucial role regarding their toxicity. Our study reports for the first time toxic effects of CuO-NP towards a soil invertebrate at a low, realistic concentration range. The results strongly suggest including lower test concentrations and a range of soil types in nanotoxicity testing.

Nano-Fertilization as an Emerging Fertilization Technique: Why Can Modern Agriculture Benefit from Its Use?

There is a need for a more innovative fertilizer approach that can increase the productivity of agricultural systems and be more environmentally friendly than synthetic fertilizers. In this article, we reviewed the recent development and potential benefits derived from the use of nanofertilizers (NFs) in modern agriculture. NFs have the potential to promote sustainable agriculture and increase overall crop productivity, mainly by increasing the nutrient use efficiency (NUE) of field and greenhouse crops. NFs can release their nutrients at a slow and steady pace, either when applied alone or in combination with synthetic or organic fertilizers. They can release their nutrients in 40–50 days, while synthetic fertilizers do the same in 4–10 days. Moreover, NFs can increase the tolerance of plants against biotic and abiotic stresses. Here, the advantages of NFs over synthetic fertilizers, as well as the different types of macro and micro NFs, are discussed in detail. Furthermore, the application of NFs in smart sustainable agriculture and the role of NFs in the mitigation of biotic and abiotic stress on plants is presented. Though NF applications may have many benefits for sustainable agriculture, there are some concerns related to the release of nanoparticles (NPs) from NFs into the environment, with the subsequent detrimental effects that this could have on both human and animal health. Future research should explore green synthesized and biosynthesized NFs, their safe use, bioavailability, and toxicity concerns.