**1. Introduction**

Nanoparticles (NPs) are assemblies of atoms in the size range less than 100 nanometers (i.e., one nm = billionth of a meter, which is roughly ten times the size of an individual atom). Apart from size, NPs may also be classified by of their physical parameters, such as electrical charge, chemical characteristics, shapes, and origin (natural vs. artificial). Regardless of how NPs are classified and defined, at these length scales, the properties of particles may deviate significantly from those of the equivalent bulk material indicating that changes in physical and chemical properties of materials depend on the dimensions of the particle. For example, at the surface of nanoparticles, significantly greater fractions of atoms are expected to be exposed and disordered rather than confined in the bulk crystalline structure for nanoparticles. This structural modification causes the nanoparticles to be more reactive and prone to greater dissolution than the bulk materials. In addition, thermodynamic analyses illustrate that adsorption on smaller particles decrease the free energy and the activation energy barrier of the system to a greater degree than adsorption on larger particles; thus, the driving force for adsorption onto smaller particles is larger and more favored. As a result, NPs possess higher surface reactivities than larger particles of the same phase, subsequently affecting the metal and organic ion availability and sequestration much more significantly than the larger particles of the same phase. However, more work still is needed to fully understand the chemical reactivity dependence on the particle size and the impact of the nanosized particles in the environment.

The presence of mineral nanoparticles has been reported in a range of natural environments. Such nanoparticles can arise from a variety of mechanisms, including chemical weathering processes, precipitation from relatively saturated solutions in hydothermal and acid mine drainage environments, evaporation of aqueous solutions in soils, and biological formation by a variety of different microorganisms [1–9]. When compared with larger particles of the same material, mineral nanoparticles possess a number of unique and potentially important physical, chemical, and magnetic properties. Interestingly, while a number of these unique features of mineral nanoparticles have been extensively studied with respect to their applications in the medicine, pharmacotherapies, semiconductor, microelectronics, and catalysis industries, comparatively little is known about the properties of nanoparticles with respect to their potential importance in natural environments (e.g., enhanced adsorption coefficients and chemical reactivities). Recent studies have reported a ubiquitous presence of different types of nanoparticles in virtually all water domains, including the oceans, surface waters, groundwater, atmospheric water, and even treated drinking water [10–16]. Wigginton et al. [17] reported these naturally occurring environmental nanoparticles can play a critical role in determining an important chemical characteristics and the overall quality of natural and engineered waters. Moreover, aquatic nanoparticles have the ability to influence environmental and engineered water chemistry and processes in a much different way than similar materials of larger sizes. Zhu et al. [18] reported toxic effects of a range of metal oxide nanoparticles on zebra fish while Li et al. [19] investigated ecotoxicological impacts of metal oxide nanoparticles released to aquatic environments on *Ceriodaphnia dubia*, a species of water flea. They reported chronic exposure of nanoparticles induced a significant increase of severe stress response. Pakrashi et al. [20] also reported that the aluminum oxide nanoparticles play a significant role in the cytotoxicity towards freshwater algae. They identified that the surface charge driven interaction between the aluminum oxide nanoparticles and the cell surface functional groups are the dominating reaction mechanism resulting in the cell membrane damage and increased oxidative stress. Their study also elucidated the dissolution of the nanoparticles and release of Al+3 ions into the solution caused enhanced cytotoxicity. The particle aggregation of NPs and ion release from the nanoparticles will significantly alter the solution phase dynamics and the subsequent change will cause challenging ecological problems in understanding the impact of NPs in an environmental matrices.

At a broader Earth ecosystem scale, naturally occurring iron nanoparticles have been found to significantly impact global biogeochemical of various metals and metalloid ions [21]. Iron nanoparticles are of particular interest since iron oxide nanoparticle surface chemistry and the subsequent reactions within the interface between the water and iron nanoparticles determine the long-term fate and transport behavior for nutrients and pollutants in natural systems [22–24]. Iron oxide nanoparticles have been shown to be an effective agent for hazardous waste site remediation [25]. Tagliabue et al. [26] have shown that iron nanoparticles can drive primary productivity of the ocean where its biogeochemical systems rely primarily on iron and suggested that iron nanoparticles can play an integral role

**333**

*Novel Applications of Nanoparticles in Nature and Building Materials*

in global ocean biogeochemistry. Nowack and Bucheli [27] also provided evidence of ubiquitous presence of nanoparticles including those engineered ones in the aquatic environments and presented comprehensive results from ecotoxicological studies to show that only certain nanoparticles have effects on organisms under environmental conditions, though mostly at elevated concentrations. They argued that the assessment of the risks posed by nanoparticles in the environment should be re-considered and re-evaluated especially when the current available technology and analytical tools lack to measure materials in the nanometer scale. Recent article by Hyden et al. [21] reviewed the current analytical approaches that can be used to characterize natural Fe nanoparticles using a synchrotron-based X-ray spectro-microscopic techniques (more details in section. They measured suspended Fe nanoparticles collected from fluvial, marine, and lacustrine surface waters. They successfully identified different oxidative state Fe into ferrous, ferric and magnetite classes of Fe nanoparticles (10–100 nm). The heterogeneity of iron oxidation state within the collected samples was attributed to the possible presence of nanoparticle aggregates, and to the low degrees of crystallinity and ubiquitous presence of impurities in natural samples. Their results provided an important baseline for natural nanoparticle speciation in pristine aquatic systems and elucidated the importance of inter-particle variability, which should be considered as an important variable for making accurate biogeochemical models. Furthermore, their study suggests that the fate of released engineered or natural Fe nanoparticles must be considered as a time

dependent kinetic reactions as they evolve and transform in natural systems.

interact with biota in a more complex environment will be discussed.

From an environmental perspective, one of the most important features of mineral nanoparticles is their high characteristic surface area, which potentially allows them to act as powerful sink of contaminant ions through sorption processes. Higher mobility of nanomaterials in the environment is expected due to its colloidal properties and it implies a greater potential of exposure and persistence for nanomaterials in the environment. Classsical thermodynamic forces such as attractive London-van der Waals and attractive or repulsive electrical double-layer forces (e.g., the classic Derjaguin, Landau, Verwey and Overbeek or DLVO forces) that are known to influence particle attachment deviate significantly when particle size gets small in the nanometer range as shown in **Figure 1**. The stability of colloidal nanoparticles is greatly influenced by the presence of adsorbed natural organic matter. Without any functionalized surface modification in water, colloidal nanoparticles will tend to grow to become larger particles through aggregation and flocculation in order to stabilize the disordered structure of surfaces and to reduce the excess surface energy. Hence, understanding the surface reactions on nanoparticles are of particularly important and deserve more investigations as current models and predictions do not apply and cannot accurately predict the fate and transport of

This review attempts to investigate the environmental impacts of naturally occurring nanoparticles by studying their unique properties and sorption reactions

**2. Naturally occurring nanoparticles**

the nanoparticles in the environment.

This review covers recent advances made in identifying nanoparticles in aqueous phase from a variety of sources, and advances in understanding their very interesting properties and reactivity that affect the chemical characteristics and behavior of natural water and soil. More specifically, an overview of recent scientific advances enhancing the understanding of the (i) sources and (ii) fate of nanoparticles, (iii) the effects of nanoparticles in simplified studies, and (iv) how nanoparticles

*DOI: http://dx.doi.org/10.5772/intechopen.97668*

#### *Novel Applications of Nanoparticles in Nature and Building Materials DOI: http://dx.doi.org/10.5772/intechopen.97668*

*Novel Nanomaterials*

sized particles in the environment.

impact of NPs in an environmental matrices.

At a broader Earth ecosystem scale, naturally occurring iron nanoparticles have been found to significantly impact global biogeochemical of various metals and metalloid ions [21]. Iron nanoparticles are of particular interest since iron oxide nanoparticle surface chemistry and the subsequent reactions within the interface between the water and iron nanoparticles determine the long-term fate and transport behavior for nutrients and pollutants in natural systems [22–24]. Iron oxide nanoparticles have been shown to be an effective agent for hazardous waste site remediation [25]. Tagliabue et al. [26] have shown that iron nanoparticles can drive primary productivity of the ocean where its biogeochemical systems rely primarily on iron and suggested that iron nanoparticles can play an integral role

free energy and the activation energy barrier of the system to a greater degree than adsorption on larger particles; thus, the driving force for adsorption onto smaller particles is larger and more favored. As a result, NPs possess higher surface reactivities than larger particles of the same phase, subsequently affecting the metal and organic ion availability and sequestration much more significantly than the larger particles of the same phase. However, more work still is needed to fully understand the chemical reactivity dependence on the particle size and the impact of the nano-

The presence of mineral nanoparticles has been reported in a range of natural environments. Such nanoparticles can arise from a variety of mechanisms, including chemical weathering processes, precipitation from relatively saturated solutions in hydothermal and acid mine drainage environments, evaporation of aqueous solutions in soils, and biological formation by a variety of different microorganisms [1–9]. When compared with larger particles of the same material, mineral nanoparticles possess a number of unique and potentially important physical, chemical, and magnetic properties. Interestingly, while a number of these unique features of mineral nanoparticles have been extensively studied with respect to their applications in the medicine, pharmacotherapies, semiconductor, microelectronics, and catalysis industries, comparatively little is known about the properties of nanoparticles with respect to their potential importance in natural environments (e.g., enhanced adsorption coefficients and chemical reactivities). Recent studies have reported a ubiquitous presence of different types of nanoparticles in virtually all water domains, including the oceans, surface waters, groundwater, atmospheric water, and even treated drinking water [10–16]. Wigginton et al. [17] reported these naturally occurring environmental nanoparticles can play a critical role in determining an important chemical characteristics and the overall quality of natural and engineered waters. Moreover, aquatic nanoparticles have the ability to influence environmental and engineered water chemistry and processes in a much different way than similar materials of larger sizes. Zhu et al. [18] reported toxic effects of a range of metal oxide nanoparticles on zebra fish while Li et al. [19] investigated ecotoxicological impacts of metal oxide nanoparticles released to aquatic environments on *Ceriodaphnia dubia*, a species of water flea. They reported chronic exposure of nanoparticles induced a significant increase of severe stress response. Pakrashi et al. [20] also reported that the aluminum oxide nanoparticles play a significant role in the cytotoxicity towards freshwater algae. They identified that the surface charge driven interaction between the aluminum oxide nanoparticles and the cell surface functional groups are the dominating reaction mechanism resulting in the cell membrane damage and increased oxidative stress. Their study also elucidated the dissolution of the nanoparticles and release of Al+3 ions into the solution caused enhanced cytotoxicity. The particle aggregation of NPs and ion release from the nanoparticles will significantly alter the solution phase dynamics and the subsequent change will cause challenging ecological problems in understanding the

**332**

in global ocean biogeochemistry. Nowack and Bucheli [27] also provided evidence of ubiquitous presence of nanoparticles including those engineered ones in the aquatic environments and presented comprehensive results from ecotoxicological studies to show that only certain nanoparticles have effects on organisms under environmental conditions, though mostly at elevated concentrations. They argued that the assessment of the risks posed by nanoparticles in the environment should be re-considered and re-evaluated especially when the current available technology and analytical tools lack to measure materials in the nanometer scale. Recent article by Hyden et al. [21] reviewed the current analytical approaches that can be used to characterize natural Fe nanoparticles using a synchrotron-based X-ray spectro-microscopic techniques (more details in section. They measured suspended Fe nanoparticles collected from fluvial, marine, and lacustrine surface waters. They successfully identified different oxidative state Fe into ferrous, ferric and magnetite classes of Fe nanoparticles (10–100 nm). The heterogeneity of iron oxidation state within the collected samples was attributed to the possible presence of nanoparticle aggregates, and to the low degrees of crystallinity and ubiquitous presence of impurities in natural samples. Their results provided an important baseline for natural nanoparticle speciation in pristine aquatic systems and elucidated the importance of inter-particle variability, which should be considered as an important variable for making accurate biogeochemical models. Furthermore, their study suggests that the fate of released engineered or natural Fe nanoparticles must be considered as a time dependent kinetic reactions as they evolve and transform in natural systems.

This review covers recent advances made in identifying nanoparticles in aqueous phase from a variety of sources, and advances in understanding their very interesting properties and reactivity that affect the chemical characteristics and behavior of natural water and soil. More specifically, an overview of recent scientific advances enhancing the understanding of the (i) sources and (ii) fate of nanoparticles, (iii) the effects of nanoparticles in simplified studies, and (iv) how nanoparticles interact with biota in a more complex environment will be discussed.

### **2. Naturally occurring nanoparticles**

From an environmental perspective, one of the most important features of mineral nanoparticles is their high characteristic surface area, which potentially allows them to act as powerful sink of contaminant ions through sorption processes. Higher mobility of nanomaterials in the environment is expected due to its colloidal properties and it implies a greater potential of exposure and persistence for nanomaterials in the environment. Classsical thermodynamic forces such as attractive London-van der Waals and attractive or repulsive electrical double-layer forces (e.g., the classic Derjaguin, Landau, Verwey and Overbeek or DLVO forces) that are known to influence particle attachment deviate significantly when particle size gets small in the nanometer range as shown in **Figure 1**. The stability of colloidal nanoparticles is greatly influenced by the presence of adsorbed natural organic matter. Without any functionalized surface modification in water, colloidal nanoparticles will tend to grow to become larger particles through aggregation and flocculation in order to stabilize the disordered structure of surfaces and to reduce the excess surface energy. Hence, understanding the surface reactions on nanoparticles are of particularly important and deserve more investigations as current models and predictions do not apply and cannot accurately predict the fate and transport of the nanoparticles in the environment.

This review attempts to investigate the environmental impacts of naturally occurring nanoparticles by studying their unique properties and sorption reactions

#### **Figure 1.**

*A nanoparticle of 5 nm core diameter with different organic molecules drawn to scale.*

with various environmental constituents and by comparing those results of the nanoparticles to that of microparticles to elucidate the role of nanoparticles in the environment. A wide range of nanoparticle phases has been reported in various environmental conditions as shown in **Table 1**. Of particular, the dependence of aquatic chemical reactivity of iron oxides on particle size is important because iron oxide plays a key role in the geocycling of elements, rock weathering and soil formation, as well as in the transport of aqueous metal species and contaminants. Iron oxide clusters are also found in living organisms (e.g., plants, bacteria, molluscs, fish, birds, and humans). They are also applied to (nano)technologies, including alternative energy, catalysis, electronics, optoelectronics, memory devices, corrosion protection, cleaning of waters and control of acid mine drainage, radioactive waste storage and disposal, flotation, pigments, magnetocaloric refrigeration, colour imaging, biochemical engineering, sensors, and other surface-based


**335**

**Figure 2.**

*Novel Applications of Nanoparticles in Nature and Building Materials*

applications. Such wide diversity in occurrence and application of iron oxides stems from the richness of their physical, chemical, and structural properties with continuous or sudden change between them, which in turn originates from the transition character of iron and the complex crystal and electronic structures of its

Hematite (α-Fe2O3) is one of the most naturally abundant iron oxide mineral phases [12, 22–24, 28]. It is also a commonly present in a nanoparticle form, occurring in soils, acid mine drainage effluent, and on bacterial surfaces as well as in atmospheric dusts (**Figure 2**). Iron is one of the essential element in governing the biogeochemical cycling of nutrients in marines and sedimentary environments. During the iron cycling process in those environment, various nanostructures of iron oxides and oxyhydroxides form and persist under certain conditions, especially at redox and pH interfaces [29]. Recent surveys on the global budget of naturally occurring iron oxide nanostructures suggest 105 Tg (teragram) of iron oxide including hematite phase is introduced annually in soil by mass [30]. The ubiquitous existence of hematite nanoparticles has a significant implication on fate on toxic heavy metal contaminants. For example, heavy metals such as Cr and U that are introduced to environments by anthropogenic activities such as mining and spills can be effectively sequestered by iron oxide nanostructures through sorption and precipitation reactions due to the thermodynamically active nanomorphologies and crystallinity of the nanparticulate phase. It has been shown that the adsorption capacities of Cr and U by ferrihydrite decrease remarkably with either increasing

*(A) Powder X-ray diffraction pattern of hematite microparticles (HM) compared with the reference XRD pattern of hematite46 and the TEM image of HM; (B) Powder X-ray diffraction pattern of hematite* 

*nanoparticles (HN) compared with the reference XRD pattern of hematite.*

*DOI: http://dx.doi.org/10.5772/intechopen.97668*

compounds.

**2.1 Iron oxide nanoparticles**

#### **Table 1.**

*Examples of naturally occurring nanoparticles in various environments.*

#### *Novel Applications of Nanoparticles in Nature and Building Materials DOI: http://dx.doi.org/10.5772/intechopen.97668*

applications. Such wide diversity in occurrence and application of iron oxides stems from the richness of their physical, chemical, and structural properties with continuous or sudden change between them, which in turn originates from the transition character of iron and the complex crystal and electronic structures of its compounds.
