Risk Management of Nanoparticles in the Workplace

Introduction

Engineered nanomaterials (NMs) are the building blocks of nanotechnologies which involve the design, synthesis, characterization, production and integration of structures, devices and systems by controlling the shape and size at the nanoscale for instance, in the size range of 1 to 100 nanometers. The term NMs refers to materials with external dimensions, or internal structures that exhibit different chemical, physical or biological characteristics, and thus behave differently, with respect to larger particles with the same chemical composition. Despite some properties can be extrapolated from the macroscale, others change drastically below a certain size. This could involve mechanical, optical, electrical, magnetic and biological properties of NMs. NMs have a much larger number of particles, and specific surface area per unit of mass than coarser particles. 

An increasing variety of NMs are synthesized and characterized in research laboratories, and new applications are continuously developed and transferred to industrial production. Types of NMs include, but are not limited to, carbon nanotubes, fullerenes, quantum dots, metals, and metal oxides. There are already more than 1 300 commercially available products, including a wide range of consumer products [1]. Over time, applications will be found in all spheres of human activities: agriculture, medical, biomedical, cosmetics, defense, energy, automotive, aeronautics, construction, electronics, energy, etc. As new applications are developed and are implemented into large scale production, there is a clear shift in the manpower potentially exposed to NMs from the research laboratories to the industrial plant level. This means that the volume handled, and the number of workers potentially exposed increase rapidly as well as the potential level of exposure. At term, millions of workers will handle NMs and NMs containing products. It is then essential to develop and promote the implementation of safe risk management strategies to avoid accidents or the development of occupational diseases.

Risk assessment of occupational exposure to NMs

It is well known that the greatest absorption of dusts in the work environment normally occurs through the pulmonary route. A major reason for concern related to exposure to NMs is that there is an increasing weigh of evidence that many particles in the nano-scale are more toxic than their coarser counterparts for the same mass. This is based on differences with regard to lung deposition, alveolar clearance, inflammatory response, granuloma formation, etc. The toxicity seems closely related to the number of particles, size, shape, surface area, surface activity and solubility of the NMs. In addition, there is growing evidence that NMs whose shape is fiber-like show length dependent pathogenic behavior which could be asbestos-like if inhaled in sufficient quantity. Although major trends are emerging that warn of various toxic effects, it seems that each NM could have its own toxicity [2].

There is little documentation on NMs-specific explosion risks. Nonetheless, it is possible to anticipate their behaviour by extrapolation based on knowledge related to fine and ultrafine powders. However, this approach cannot be practiced with certainty, given the chemical and physical properties that are often unique to nanometric dimensions. In general, the violence and severity of an explosion and the ease of ignition tend to increase as particle size decreases: the finer the dust, the greater the pressure and the lower the ignition energy. Thus, the NMs should tend to be more reactive, even explosive, than larger-scaled particles of the same chemical composition [3].

Risk assessment is a major step in risk management because the level of preventive measures to implement should be directly related to the level of risk, the risk being a function of the hazard and the level of contamination/exposure. Risk assessment is therefore a way of determining whether the conditions prevailing in the work environment can allow the emission of toxic NMs into the ambient air at concentrations high enough to impair workers’ health or can allow the accumulation of solid aerosols of flammable or explosive NMs at concentrations, and under conditions that favor the occurrence of an accident. A variety of instruments exist which can measure the different parameters related to the toxicity of NMs. Strategies have already been proposed for the evaluation of the contamination level [3, 4] and new instruments are under development with the objective of specific evaluation of the workers’ exposure to NMs in the breathing zone.

In most situations, quantitative risk assessment is currently impossible to establish and a level of uncertainties remain. When the available information required for a quantitative risk assessment is insufficient, it is recommended that the approach of the “Control Banding” model be used. Control Banding will determine safe but realistic means of controls to be implemented [3, 5].

Risk management of NMs in the workplace

In a context of different levels of knowledge regarding hazards and the occupational exposure level, a preventive approach based on good industrial hygiene practices should be used when the level of uncertainty is low but a precautionary approach should be used when the level of uncertainty is high [6, 7]. This means that, when faced with a high degree of scientific uncertainty, the possible negative impacts should be reduced by minimizing occupational exposure, among other factors. Special attention must be paid to the NMs that involve major or little-known health risks, and that have low solubility in biological fluids. To ensure that the right decisions are made to manage the risks, a prevention program specific to the facility should be developed, implemented, reassessed regularly and improved as needed [7, 8]. The means of control used should allow circumscribing as much as possible NMs dispersion in the air and on equipments to avoid any workers’ exposure. The means of controlling exposure must consider all the work-related aspects: installations, processes, equipment, activities, tasks, workstations, and workers’ movements. These means are based on the design of the premises, engineering techniques, administrative procedure and the use of personal protective equipment [4, 7-9]. During the presentation, these aspects will be illustrated by a real case in an industrial plant [9]. The great importance and possible approaches to the dissemination of knowledge and the support to the implementation of risk management into research laboratories and industrial plants will also be discussed as they are critical aspects to put research into practice.  

Conclusion

The toxicity or explosivity of the NMs as well as the worker’s exposure level is seldom well established. Despite this situation, the use of existing data, and strategies combined to the expertise developed in risk management make it possible to efficiently manage the potential risks posed by NMs in the workplace through an integrated prevention program. Quebec researchers clearly put research into practice by playing a major role in the translation/adaptation of scientific knowledge to the different stakeholders’ culture, and invest efforts to transfer research results to the workplaces.