Some of The Main Types of Nanoengineered Nanoparticles Reported as Nanotoxic

Some of the main types of nanoengineered nanoparticles reported as toxic are (among others) fullerenes, carbon nanotubes (CNTs), inorganic nanoparticles, organic nanoparticles and quantum dots (QDs).

Introduction

Following up the approach initiated in my article "The Roots of Nano-Fear Decoded", and continuing with the approach taken in my previous article - "Indicators of Nanotoxicity" - I will now address another nanotoxicity topic: some of the main types of nanoengineered nanoparticles reported as nanotoxic. Later on, I will attempt to point out ways and propose solutions in order fight and prevent nanotoxicity.

Some of the main types of nanoengineered nanoparticles reported as toxic are (among others):

• Fullerenes; 
• Carbon nanotubes (CNTs);
• Inorganic nanoparticles;
• Organic nanoparticles;
• Quantum dots (QDs).

Fullerenes

Fullerenes are nanoparticles in the form of spherical cages containing 28 to 100+ carbon atoms.

The most studied fullerene contains 60 carbon atoms. This particular type of fullerene is a hollow sphere and its atomic arrangement consists of pentagons and hexagons of carbon interconnected.

The fullerenes show the capability of being subjected to extreme pressures and regain its original shape when pressure is no longer applied - something equal or identical to resilience, I would say.

When the fullerenes are not modified, these molecules do not react with each other.

However, when fullerenes are engineered, some specific carbon atoms may be replaced by other atoms. Consequently, the nanoengineered fullerenes show the capacity of establishing bonds with other molecule. The physical result obtained is a material hard and elastic at the same time.



Carbon nanotubes

Carbon nanotubes (CTNs) are hollow cylinders consisting of a crystalline form of carbon molecules arranged into a hexagonal network of carbon atoms. CNTs can have diameters around 0.7 nm.

Regarding the CNTs length, this can vary between a few nanometres to several millimetres. Each end of a CTN can be opened or closed by a fullerene half-molecule. 

Regarding the complexity of the CNTs wall, there are two main groups of CTNs. These CNTs can have:

• A wall consisting of a single layer: Single-Walled Carbon NanoTubes (SWCNTs);
• A wall consisting of several layers: Multi-Walled Carbon NanoTubes (MWCNTs). MWCNTs can also be perceived as a coaxial arrangement of carbon cylinders of increasing diameters having a common axis.

The diameter of MWCNTs can reach values such as 20 nm. MWCNTs are chemically and thermally very stable. The nanofabrication of MWCNTs normally requires the presence of metals. The presence of these metals (e.g. Co, Fe, Ni, and Mo) can play a significant role on the toxicity of these MWCNTs.

It is considered that a CNT having the dimensions 20 nm width x 2.000 nm length may have 100 x more surface area than a spherical nanoparticle with a diameter of 20 nm. Under specific conditions, this can interpreted as an indicator of high toxicity of the CNTs.

On the other hand, CNTs show a great tendency to agglomerate. This fact may be a cause for a significant reduction of the total area of CNTs capable of interacting with Human cells or their components.


Inorganic Nanoparticles

Inorganic nanoparticles are frequently insoluble or show a poor solubility. Inorganic nanoparticles can be composed of pure metals or various inorganic alloys.

Among the inorganic nanoparticles, nano-titanium dioxide (nano-TiO2) is one of the most studied due to their nanotoxic effects.


Organic Nanoparticles

Organic nanoparticles are also frequently insoluble or show a poor solubility. Organic nanoparticles can be composed of various organic substances. These various organic substances are commonly insoluble polymers. Different organic radicals can be grafted to these insoluble polymers.However, organic nanoparticles can also be materials involving entrapment, encapsulation or surface adsorption of a bioactive substance.


Quantum Dots

Quantum dots (QDs) are nanoengineered nanoparticles.

The main properties of QDs are:

• High photostability;
• Strong light absorbance;
• Excitation by single-wavelength;
• Size-tunable emission.

Due to their physical properties, QDs are considered semiconductor nanocrystals.

QDs are usually composed of a core of a semiconductor material enclosed in a shell of another semiconductor material with a larger spectral band-gap. 

A typical QD has a diameter ranging from 2 to 8 nm.

QDs are extremely diversified. Therefore, the toxicity of QDs requires to be carefully characterized individually for each type of QD.

Indicators of Nanotoxicity

Despite being presented here some of the indicators of nanotoxicity of nanoparticles, there is still a wide gap of knowledge in regard to this specific topic and nanotoxicology as a whole. However, in spite of the wide gap of knowledge, many worthy efforts and a whole series of hard work in this field are underway already. Nevertheless, many challenges are still waiting to be overcome.

Preface

In the alignment of my article "The Roots of Nano-Fear Decoded", and preceding the approach taken in my previous article - "Nanotoxicity in Humans" - I will now address a nanotoxicity overview, dedicated to indicators of nanotoxicity. Later on, I will attempt to point out ways and propose solutions in order fight and prevent nanotoxicity.


Introduction

Traditionally, in toxicological studies carried out at macroscale or bulkscale, the toxic effects are normally correlated to the quantity of toxic product to which individuals are exposed.

This rule of the thumb means that "the greater the mass of toxic substance absorbed, the greater the toxic effect on individuals exposed".


Specific Surface

However, in the case of nanotoxic nanoengineered nanoparticles, once again the macroscale rules don’t apply. It has been demonstrated that the measured nanotoxic effects are not linked to the mass of the nanotoxic nanoengineered nanoparticles.

Several studies find a reasonable correlation between the specific surface of a nanotoxic nanoengineered nanoparticle and its nanotoxic effects.


Several Additional Parameters

On the other hand, several parameters can additionally contribute to the nanotoxicity of nanotoxic nanoengineered nanoparticles. Furthermore, with the currently limited existing scientific knowledge regarding nanotoxicity and nanotoxicology, it is extremely complex to weight the relative impact of each of these factors in order to predict accurately the toxicity of a new nanotoxic nanoengineered nanoparticle under study.

The published scientific literature links the observed nanotoxic effects of nanotoxic nanoengineered nanoparticles to a wide range of different chemical and physical parameters, such as, for example:

• Number of nanotoxic nanoengineered nanoparticles;
• Size of nanotoxic nanoengineered nanoparticles;
• Shape of nanotoxic nanoengineered nanoparticles;
• Surface charge of nanotoxic nanoengineered nanoparticles;
• Crystalline structure of nanotoxic nanoengineered nanoparticles;
• Concentration of nanotoxic nanoengineered nanoparticles;
• Porosity of nanotoxic nanoengineered nanoparticles;
• Electrostatic attraction potential of nanotoxic nanoengineered nanoparticles;
• Degree of agglomeration of the nanotoxic nanoengineered nanoparticles;
• Hydrophilic/hydrophobic behaviour of nanotoxic nanoengineered nanoparticles;
• Synthesis method employed on the nanotoxic nanoengineered nanoparticles;
• Post-synthesis modifications of nanotoxic nanoengineered nanoparticles.

Final Comments

Despite being presented here some of the indicators of nanotoxicity of nanoparticles, there is still a wide gap of knowledge in regard to this specific topic and nanotoxicology as a whole.

However, in spite of the wide gap of knowledge, many worthy efforts and a whole series of hard work in this field are underway already. 

Nevertheless, many challenges are still waiting to be overcome.

Nanotoxicity in Humans

Routes for entry of nanotoxic nanoengineered nanoparticles into the Human body. Destinations of nanotoxic nanoengineered nanoparticles, after entering the Human body.

Preface

Following my article "The Roots of Nano-Fear Decoded", I start here an attempt to approach nanotoxicology and nanotoxicity. Later on, I will attempt to point out ways and propose solutions in order fight and prevent nanotoxicity.



Introduction

As I wrote in "Nanopollution Revised", addressing nanopollution without addressing nanotoxicology is (theoretically and practically) an artificial effort, I would say. Nanopollution is present in the environment, which in turn affects the biosphere (including Humans). The biosphere is exposed to the nanotoxicity and thereby contaminates the environment. There is therefore a circle inseparable. However, due to space limitations, this article will try to address the nanotoxicology and nanotoxicity.

Of course, what I write is in line with the way I understand this issue in the present.

Not all nanoparticles are nanotoxic. In my personal opinion, naturally occurring nanoparticles are not toxic. I can possibly consider some exceptions - if supported by scientific evidence (e.g. nanotoxic natural occurring nanoparticles released in forest fires). However, unfortunately not all forest fires are of natural origin. Nature has already demonstrated many times that knows how to ensure balance and harmony rather than the Mankind knows how. The Mankind must increasingly learn the lessons that nature has to teach us all.

Furthermore, even though some exceptions as valid, it does not seem to me that the nanotoxicity of naturally occurring nanoparticles has meaning when compared with the nanotoxicity (under study) on some nanoengineered nanoparticles.

Moreover, I believe that not all nanoengineered nanoparticles are toxic. In other words, I believe that:

• Only a part of them are nanotoxic;
• Some are harmless to the health;
• And others are beneficial to the health.

Of course that my personal opinion has to be demonstrated scientifically, based on evidences.

Nanotoxicity obviously affects all living beings (including of course Humans). I will focus this article on some aspects of nanotoxicity in Humans, caused by the nanoengineered nanoparticles which are nanotoxic.


Routes For Entry of Nanotoxic Nanoengineered Nanoparticles Into The Human Body

Generally, nanotoxic nanoengineered nanoparticles can enter into the Human body through incidental and/or involuntary episodes. These incidental and/or involuntary episodes may be associated with a lack of knowledge by Humans. Therefore, through episodes of incidental and involuntary nature, the nanoparticles can enter the human body via (not necessarily in that order):

• Inhalation;
• Cutaneous;
• Ingestion;
• Other.

As an example, Humans can:

• Inhale incidentally and/or involuntarily air contaminated with nanotoxic nanoengineered nanoparticles;
• Incorporate into their bodies incidentally and/or involuntarily, through their skin (via cutaneous respiration) air contaminated with nanotoxic nanoengineered nanoparticles;
• Eat incidentally and/or involuntarily food contaminated with nanotoxic nanoengineered nanoparticles; 
• Drink incidentally and/or involuntarily water and consumer drinks contaminated with nanotoxic nanoengineered nanoparticles.

Destinations of Nanotoxic Nanoengineered Nanoparticles, After Entering The Human Body

After entering the Human body, nanotoxic nanoengineered nanoparticles can undergo different fates:

1. Can be totally or partially excreted;
2. Can be totally or partially metabolized;
3. Can be totally or partially cumulated into cells, tissues and organs.

Nanotoxic nanoengineered nanoparticles can be excreted, for example:

• Through the kidneys, during the blood filtration in which the nanotoxic nanoengineered nanoparticles are to be a product of excretion (a constituent of the urine);
• Through the intestines, during the formation of faeces and excreted through the anus;
• Through the sweat glands in order to be excreted in sweat during perspiration;
• Through the lungs (after venous blood having executed gas exchanges with the lung alveoli) being released into the environment during the exhalation.

Nanotoxic nanoengineered nanoparticles can be metabolized: 

• In the liver; 
• In the spleen.

Nanotoxic nanoengineered nanoparticles can circulate in the blood stream and lymphatic vessels. Through this path, they can travel around the entire Human body and eventually accumulate into diverse organs (e.g. brain cells).

Insoluble or low solubility nanotoxic nanoengineered nanoparticles in biological fluids are a great cause for concern.

Some insoluble or low solubility nanotoxic nanoengineered nanoparticles can pass through the several defence mechanisms of the Human body. Thus, these insoluble or low solubility nanotoxic nanoengineered nanoparticles can then be transported through the body in insoluble form. Therefore, some insoluble or low solubility nanotoxic nanoengineered nanoparticles can pass to the bloodstream (blood vessels and/or lymphatic vessels) after passing through the respiratory membranes (pulmonary alveoli, through gas exchanges) and/or gastrointestinal membranes. These insoluble or low solubility nanotoxic nanoengineered nanoparticles are then distributed to various organs and eventually can accumulate at specific locations. 

Other insoluble or low solubility nanotoxic nanoengineered nanoparticles find a direct shortcut to the brain: after inhalation, travel along the olfactory nerves and penetrate directly into the brain neurons.


Final Comment

Given my personal belief that nanotoxicity of nanoparticles is practically caused only by nanotoxic nanoengineered nanoparticles, nanotoxicology and nanotoxicity are relatively new subjects that emerged after the appearance of nanofabrication.