Particulate hazardous substances are substances, mixtures, or articles that occur in the form of small particles. Once they have been stirred up, such small particles can stay suspended for a long time in the air as dust and may be inhaled in certain situations. Inhaled particulate hazardous substances can therefore pose a danger to human health. Inhalable dust can contain particles so tiny that they are able to penetrate into the highly sensitive tiny air sacs (alveoli) in the lungs. The proportion of alveolar (respirable) dust contained in many kinds of dust therefore has to be identified in addition to the proportion that is inhalable.

Sources of particulate dusts

There may be a range of reasons for the release of particulate dusts, which can be composed of various substances and have various morphological ("morphological”: relating to the shape of a particle) characteristics. For example, Mineral, sooty, or metallic dusts or wood dust may be released in workplaces. Depending on the work process and the protective measures that are in place, employees can experience widely differing levels of exposure. Large releases of dust may occur, for example, in industrial sectors such as mining, construction, metalworking (e.g. during welding), chemicals, and wood processing. But people can also be exposed to dust containing particulate hazardous substances outside the workplace, for example through high concentrations of fine particles from road traffic, combustion processes (heating, fireworks, forest fires), or when renovating their homes.

Health consequences of dust exposure

The body responds to the inhalation of dust with the defensive and cleaning mechanisms of its mucous membranes and alveolar cells. Many of the particles that enter the upper respiratory tract can simply be coughed out with lung mucous and removed from the body. By contrast, particles that penetrate deep into the lung must be proactively ingested and removed by phagocytes. Irrespective of the chemical composition of the inhaled particles,  excessive exposure to dust can therefore overwhelm the lungs’ self-cleaning systems, particularly in the case of prolonged exposure. This can lead to respiratory problems and allergic reactions. Some kinds of particle remain in the lung tissues for a very long time because of either their composition (e.g. silica dust) or their morphology (e.g. fibrous asbestos). These "inert dusts” ("inert”: chemically inactive) cannot be degradedby the human body. As a result, chronic diseases such as silicosis or asbestosis may develop, sometimes leading to very serious diseases such as asbestos-related lung cancer.

Fibre pathogenicity paradigm

In addition to the general hazard of dusts, the chemical composition of soluble dusts and, particularly in the case of inert dusts, the morphology of the particles influence how dangerous they are. For instance, there are aerodynamic reasons why fibrous dust particles are able to penetrate far deeper into the lung than comparably heavy granular ("granular”: granule-shaped particles, with spherical rather than elongated shapes) particles. The pulmonary phagocytes are therefore confronted with unfavorably bulky shaped particles. Because fibrous dusts are insoluble and remain in lung tissue for a long time (i.e. are biopersistent), they can have effects that are many times more harmful than those of granular dusts. Asbestos is the best-known example of a material with toxic effects due to the shape of its fibres. The hazard of fibrous dusts is explained by the "fibre pathogenicity paradigm”, according to which the elongated shape of respirable and biopersistent particles is the cause of their carcinogenicity.

Nanomaterials

The differentiated assessment of possible risks connected with individual particle sizes and/or shapes has been extended into the nanometre ("nanometre”: one thousand-millionth of a metre) range at BAuA. The nanoparticles and nanofibres that have been developed over the last two decades as the nanotechnology revolution has progressed are some of the smallest objects produced by industrial processes. When they are released as dust made up of either individual fibres or as small, low-density, agglomerated clumps, there is a high probability that they will penetrate into the sensitive alveoli when inhaled. This is why it is important to isolate such materials’ possible toxic effects at an early stage and reliably determine the types and volumes of particles and fibres released in the workplace, in spite of their small size. BAuA is playing an active, committed role in the development of suitable measurement methodologies and assessment criteria.

Innovative materials

On account of their multiplicity, the advanced materials that are being developed are referred to generically as "innovative materials”. There is a need to investigate what hitherto unsuspected health implications they could have. It is, for example, to be clarified whether composites that contain nanofibres and anisotropic ("anisotropic”: having physical and/or chemical properties that differ when measured in different directions) materials might release respirable, biopersistent, fibrous fragments when they are processed and recycled or suffer mechanical failure, as has been observed during the processing of carbon fibre-reinforced materials and other products.

All these "innovative materials” pose specific health risks, which can be inferred from the toxicological profiles of the substances in which they are present and employees’ levels of exposure to those substances.

Statutory protection against particulate hazardous substances

Several acts, ordinances, and bodies of rules/regulations have been adopted with the aim of protecting human health against excessive exposure to particulate hazardous substances. The handling of hazardous substances in the workplace is governed by a number of pieces of legislation (e.g. the Hazardous Substances Ordinance (Gefahrstoffverordnung)), and sub-legislative rules and regulations (e.g. technical rules). Limit values for permissible exposures in the workplace have consequently been set for a range of substances. The order in which protective measures are to be implemented has been stipulated for work areas that exceed these limit values with the STOP principle. This requires the Substitution (replacement) of hazardous substances first, then Technical and Organisational protective measures, and lastly the provision of Personal protective equipment.

BAuA is tasked with conducting research that prepares the way for the adoption of scientifically based rules and regulations on protection against particulate hazardous substances in the workplace. This is done by developing detection methods and measurement procedures with which particulate materials can be quantified and characterised. The standardisation of new methods and the amendment of rules and regulations are supported by BAuA’s contributions to the deliberations of diverse expert bodies. All these activities are helping to further reduce the risks faced when particulate hazardous substances are handled.