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Nail dust and the use of personal protective equipment--face masks, a review.

The use of high speed nail drills in podiatric practice for the reduction of thickened toenails (onychogryphosis, onychauxis and onychomycosis) is generally accepted. Studies have shown that during the reduction process large quantities of nail dust are created which contain particulates of varying sizes (Abramson and Wilton 1992) and comprise a wide variety of contaminants (Burrows and McLarnon 2006), all of which become airborne. This article explores the anatomical structure of the nail plate and its potential relationship with the shapes and sizes of the airborne particles, the contaminants contained within and the risk posed by these airborne particles to the clinician's respiratory health and therefore the level of respiratory personal protective equipment necessary to reduce this risk.

Following the use of a high speed abrasive nail drill, the reason for the fine particulate dust can, in part, be attributed to the anatomical structure of the nail plate. The human toenail is approximately 1.3mm thick and is a composite of 3 layers. The hard uppermost, dorsal layer comprises dense keratinised cells, which resemble the shape of a disc with irregular edges, arranged in an overlapping, 'roof-tile' manner to form a waterproof and smooth (Farren et al. 2004), tough, convex surface that is visible (Technical Brief 2009)--see Figure 1.

The thicker, yet flexible intermediate layer rests inferior to the dorsal layer and supports it (Forslind 1975). This layer consists of keratin molecules arranged as microfibrils, held firmly together by inter-molecular covalent, disulphide bonds, which lie at right angles to the direction of nail plate growth, unlike hair (Forslind 1975). The ventral layer, which lies closest to the nail bed and thus anchors the whole nail plate to the nail bed, is the thinnest layer and develops, in part, from the epidermal cells of the nail bed, unlike the dorsal and intermediate layers which originate from the nail matrix cells situated at the proximal portion of the nail plate (de Berker and Angus 1996). A greater contribution to the formation of the ventral layer is sometimes made by the nail bed and has been found in hyperkeratotic nail dystrophies which shows that nail bed behaviour can change in disease (de Berker and Angus 1996). The human toenail is therefore able to be a tough but flexible structure providing protection to the sensitive toe apex. The dorsal and ventral layers are thought to offer resistance to longitudinal bending (Farren et al. 2004).

The dorsal layer then (and potentially the intermediate and ventral layers), with its overlapping keratinocytes, when exposed to high speed abrasion probably fractures and yields particles of varying sizes and shapes into the air, see Figure 2.

Abramson and Wilton (1985) report that the nail dust particles range in size from 0.8 micrometres ([micro]m) to 1.6 pm but Donaldson et al. (2003) found from their measurement of nail drill dust bag contents that the sizes can range from 0.1 pm up to 71 pm. Although the larger particles fall to the ground (Davies and Savage 1980), the smaller particles can remain airborne for up to 30 minutes (Larato et al. 1996). In fact Purkiss (1997), measured nail dust particulates in the air for up to 10 hours following a clinical session. More recently Tinley et al. 2014 identified the mould Aspergillus residing in the nasal cavities of 44% of the podiatry sample group and reported that Aspergillus is able to stay airborne for in a room for up to 16 hours. This has the implication that those particles that are not extracted via the nail drill dust extraction system are available for inhalation by the podiatrist. From electron microscopy, Donaldson et al. (2003) identify that the dust particles are also plate-like' in appearance and so oscillate whilst falling to the ground like 'a piece of paper', explaining why these particles stay airborne for longer. Donaldson et al. (2003) also report that the majority of particulates within nail dust are of the sizes 2.6-5 [micro]m which would mean that the dust is respirable, it can enter the nose and mouth and be deposited throughout the respiratory system and in particular the lungs. In an earlier study, Abramson and Wilton (1992) reported that due to the size of the nail dust particles, 1-2 [micro]m from their measurements, 86% of the airborne nail dust is capable of reaching the bronchioles and alveoli and, importantly, 31% of the inhaled dust would remain in the alveoli. Larger particles, i.e. those above 20 [micro]m, deposit in the mouth, larynx and pharynx.

Particulate deposition in lungs poses a health risk in general (Cook 2016) but where there are organisms living in the nail dust particulates then airborne contamination is increased. Following exposure to this contaminated environment, Abramson and Wilton (1992) found that podiatrists have a greater prevalence of precipitating the immunoglobulin E antibody for the common dermatophyte Trichophyton rubrum (T. rubrum) compared to the general public. This finding builds on an earlier study, Davies et al. 1983, where the researchers estimated that 14% of the then State Registered Chiropodist profession had antibodies to T. rubrum. Also Davies et al. (1983) reported that chiropodists demonstrated a greater commonality for restricted lung disease than other sedentary workers. The health implications of breathing in nail dust were, however, challenged in a study by Gatley (1991) from which he concluded that among those chiropodists within the study who had a high prevalence of respiratory symptoms, most of these symptoms were both minor and sited in the upper (not lower) respiratory tract and that there was no clear relationship between these symptoms and work when compared to a matched control group. More recent studies however identify numerous dermatophytic (including Trichophyton species and Epidermophyton species), nondermatophytic (moulds, Gram positive and negative bacteria) organisms and endotoxins from bacterial membranes present in nail dust and report that exposure to these organisms mayincrease the riskof respiratoryinfections/ diseases e.g. asthma, sinusitis, chronic cough and bronchitis and also allergic reactions to the Trichophyton species, (Donaldson et al. 2003, Alonso et al. 2003, Burrows and McLarnon 2006, Hainsworth et al. 2015 and Nowicka et al. 2016). Indeed infection with and sensitization to Trichophyton has been identified as an aetiological factor in the development of asthma (Woodfolk 2005).

The risk of inhaling contaminated airborne particulates which pose a real and substantial negative consequence for respiratory health is increased if the clinician does not wear or wears inadequate personal protective clothing. Purkiss (1997) reports that if the nail dust particles are smaller than 3 pm then simple, disposable, paper based face masks will not offer adequate respiratory protection. Tinley et al. (2014) report from their study that of the 47 podiatrists that responded to a question about the wearing of face masks whilst operating a nail drill, only 3 wore a specialised mask, the remaining clinicians wore either basic surgical 2 ply paper based or simple, disposable, paper based face masks or nothing at all. Indeed the risk of inadequate respiratory protection further increases when the simple paper based mask becomes 'wet' through normal respiration (Tinley et al. 2014).

Guidelines on the use of podiatric nail drills (Society of Chiropodists and Podiatrists 2000) identify that under The Health and Safety at Work Act 1974 and subsequent legal regulations, e.g. Personal Protective Equipment at Work Regulations 1992 (revised in 2002), the wearing of face masks (also called respirators) is required both during the operation of the nail drill and for a period of time afterwards whilst the particles remain in the clinical environment.

The face mask worn, to be effective, must conform to the European Standard EN149:2001+A1:2009 and the European Filtering Face Piece (FFP) Standards of FFP1NR, FFP2NR and FFP3NR (NR--Non Reusable) depending on the level of Occupational Exposure Limit (OEL) and, more recently, Workplace Exposure Limit (WEL) of nontoxic dust and fumes. FFP1NR masks offer protection to the wearer where the level of contaminants is 4 times the OEL/WEL, FFP2NR masks up to 10 times the OEL/ WEL and FFP3NR up to 20 times OEL/WEL. Generally FFP1NR and FFP2NR masks are recommended for podiatric use when using a nail drill (Society of Chiropodists and Podiatrists 2000). In order to deliver this level of respiratory protection the face mask to be used should have: a) electrostatic filtration, i.e. the negatively charged portion of the nail dust will be attracted to the positively charged part of the face masks material and vice versa--in other words the dust will stick' to the mask and not the clinicians lungs and; b) mechanical filtration with a high dust holding capacity for later disposal, e.g. Protex S2 and S2V respirators (Cuxson Gerrard & Co. Ltd.). Because these masks are disposable and maintenance free there are no Control of Substances Hazardous to Health (COSHH) reporting requirements. These masks should fit the face snuggly and be comfortable, be used for up to 8 hours and stored between usage by folding, ensuring the inner surfaces are folded together and are thus free from contamination. The masks should also carry the European Conformity (CE) mark indicating that the performance, materials and packaging are to an approved standard. The use of nail drills is a vital part of the foot health professionals treatment offer. Using drills, however, poses a potential health risk to the clinician through the production of airborne nail dust which may also be contaminated with pathogens. The use of appropriate PPE, which importantly includes the face mask, is critical to preventing respiratory contamination. Face masks must conform to European and UK Standards to offer an effective barrier and so protection against airborne nail dust contaminants and associated health related risks.

References

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Nowicka D., Nawrot U., Wlodarczyk K., Pajaczkowska M., Patrzalek A., Pecak A., Mozdyniewicz P., Fleischer M. (2016) Detection of dermatophytes in human nail and skin dust produced during podiatric treatments in people without typical clinical signs of mycoses. Mycoses. Vol.59 (6), pp.379-382

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MICHAEL RATCLIFFE, BSc, MSc, Cert.Ed, PGCert, DPodM
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Date:Jan 1, 2017
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