In the last few decades, nanomaterials have been applied in various fields, including pharmaceutical, medical, agriculture, food, cosmetics, and many others. As nanomaterials are extremely small, inhalable, poorly soluble, and can penetrate and interact with tissues, they are required to be stored, handled, and disposed of safely.
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Nanomaterials and their Risk to Humans and the Environment
Nanomaterials are materials whose size ranges from 1nm to 100 nm at a nanometre scale and come with varying morphologies, such as rod, spherical, dots, tubes, and sheets.
Nanomaterials exhibit a large surface-to-volume ratio with many unique properties (e.g., thermal, electrical, optical, chemical, and biological). Some of the properties that have increased its range of applications are antimicrobial, thermal insulation, UV blocking, enhancement of mechanical strength, water repellent, self-cleaning, and more.
Some nanomaterials naturally occur in nature (e.g., sand and pollen), while most are manufactured artificially. As they are extremely small, they behave differently from the bulk materials. Scientists have reported that exposure to natural nanoparticles heavily outweighs that of engineered or artificially synthesized nanoparticles.
There are different ways in which humans are exposed to nanomaterials. For instance, nanomaterials can be inhaled, accidentally injected or ingested, and through dermal contact. Humans are also exposed to engineered nanomaterials as they are used in paints, cosmetics, electronics, textiles, and food packaging, but it must be mentioned that all nanoparticles are not harmful.
Very few studies are available related to the risk assessment of nanomaterials to human health and the environment. According to some of the studies, inhaled nanomaterials are deposited in the respiratory tract, leading to inflammation and potentially damaging lung cells and tissues.
Several nanomaterials can easily enter cellular membranes and damage intercellular organelles, which may disrupt cellular functions. Additionally, researchers have reported that some nanomaterials are pyrophoric or readily combustible. These nanomaterials pose a threat of unwanted explosion or fire.
Risk Assessment of Nanomaterials
Due to the non-existence of many studies related to the long-term effects of nanoparticle exposures on users, it is important to devise strict precautionary measures. It is imperative to assess the full range of risks associated with every nanomaterial and develop effective preventive/control measures to reduce harmful effects after exposure.
In industries, the European Union and National Legislation regulate the production and use of nanomaterials. One of the difficulties in assessing risks associated with nanomaterials is their varied properties related to their different structural characteristics (e.g., size, shape, molecular state).
Some metal nanomaterials commonly used in many industries are zinc oxide and titanium dioxide, which are non-toxic to humans but exhibit antimicrobial properties that can affect microbial ecology. Thereby, a thorough risk assessment of nanomaterial exposure to all living organisms is extremely important.
Scientists have recommended the classification of nanomaterials based on their physical structure and each group is further subjected to risk assessments, i.e., analyzing nanomaterials for carcinogenic, mutagenic, or toxic manifestations. Some key factors in which nanomaterials are classified are solubility, surface area, and size.
Safe Handling of Nanomaterials
At present, guidelines for nanoparticle safety are not clear and differ between institutes or industries. However, some organizations, such as the Swiss Federal Office of Public Health (FOPH) and the US Occupational Safety and Health Administration (OSHA) provided guidelines or recommendations to individual facilities to promote the safe handling of nanoparticles.
One of the suggestions in safety guidelines for nanoparticle handling includes using laminar airflow, with airflow directed towards the user, during the synthesis of nanomaterials. Additionally, the use of ventilated enclosure or local exhaust ventilation with negative pressure and equipped with HEPA filters is recommended.
All laboratories must store nanomaterials in abled containers indicating the chemical content and form (e.g., nano zinc oxide). Persons directly dealing with nanomaterials must wear long-sleeved clothes, shoes made of low-permeable materials, chemical-resistant gloves, safety glasses to protect eyes from chemical splash, and a laboratory coat. Studies have shown that non-woven fabrics (e.g., high-density polyethylene textiles) can block nanomaterial exposure more effectively compared to cotton-based products.
Although several studies have shown that nanomaterials suspended in solution pose lesser hazards, spraying, sonication, pouring, or shaking of the nano-based solution increases the risk of inhalation exposure. Scientists stated that nanomaterials fixed in a matrix pose the least hazards as long as it is not subjected to mechanical disruption (e.g., burning, cutting, and grinding).
According to a report, the majority of people working with nanoparticles are not fully aware of the hazards associated with nanoparticle exposure. Thereby, scientists believe that creating safety posters for nanoparticle laboratories and nano-based industrial workplaces would help substantially minimize a lack of awareness.
Proper Disposal of Nanomaterials
Although the existing guidelines for the disposal of nanoparticles are not clear, it has been highly recommended not to dispose of unused nanomaterials in regular trash or a drain. Typically, individual laboratories determine if they require a specific method for disposal, except when they use chemicals that fall under the domain of regulations for macro-sized chemicals.
For instance, several institutes, including Virginia Tech, Massachusetts Institute of Technology, and the University of California at Berkeley, classify nanowaste (e.g., hazardous and non-hazardous) before disposal.
Ultimately, all nanoparticles end up at a wastewater treatment facility, a recycling facility, a landfill, or an incineration plant. Studies have shown that carbon-based nanoparticles can be eliminated via incineration at a high temperature. For instance, carbon nanotubes can be destroyed only at incineration above 850 ºC. The European Union stated that all incineration plants must have a flue gas treatment system to scrub away contaminants.
References and Further Reading
Nanomaterials Safety Guidelines. (2022) Stoney Brook University. [Online] Available at: https://ehs.stonybrook.edu/programs/laboratory-safety/general-laboratory-safety/nanomaterials-safety-guidelines.php
Understanding the hazards of nanomaterials. (2022) [Online] Available at: https://www.hse.gov.uk/index.htm
Managing nanomaterials in the workplace. (2022) [Online] Available at: https://osha.europa.eu/en/emerging-risks/nanomaterials.
Lewis, L. A., et al. (2016) Innovating Nanoparticle Safety: Storage, Handling, and Disposal Processes. [Online] Available at: https://digitalcommons.wpi.edu/iqp-all/3204
Groso, A., et al. (2010) Management of nanomaterials safety in research environment. Particle and Fibre Toxicology, 7(40). https://doi.org/10.1186/1743-8977-7-40