The risks of inhaling potentially dangerous crystalline silica dust from sand arenas are highlighted in a study carried out in Ireland.
The likes of sand, animal feed and bedding materials can create dusty work environments for equestrian staff, increasing their risk for a range of respiratory problems, particularly if their employment is indoors.
Potential airborne exposure risks include inhalable and respirable organic dusts, microorganisms, endotoxins and β-Glucans, all of which have been evaluated among equestrian workers.
However, less is known about exposure to inorganic dusts, such as respirable crystalline silica. It is a natural component of sand and has been associated with a range of respiratory diseases, in particular silicosis and lung cancer.
Sand is regularly used in the equestrian sector as a surface or footing material in indoor and outdoor arenas, on training tracks for racehorses, on lungeing arenas and on horse walkers.
Kathleen Bulfin and her colleagues from the University of Ireland Galway and the Institute of Occupational Medicine in Edinburgh, Scotland, set out to evaluate a single equestrian worker’s personal exposure to respirable crystalline silica and respirable dust.
The study centred on one small to medium-sized Irish equestrian centre managed and operated by a self-employed worker.
The centre stabled, on average, 30 horses for training and a further 15 horses for riding lessons. It had one indoor arena of about 6000 square metres and two outdoor arenas.
All were surfaced using silica sand and shredded carpet mix.
The indoor arena was under the same roof as the tacking and grooming area. There was no mechanical ventilation. To reduce dust levels in the indoor arena, the surface was occasionally dampened using a water hose mounted on a ladder, moved around the arena for a maximum of one hour.
However, this water suppression regime was rarely performed and only if there were no competing work tasks to be carried out.
Typical duties included cleaning horse stables, lungeing horses, free-jumping two to four young horses a day, delivering lessons both indoors and outdoors, grooming, tacking and untacking horses, which was always performed in the indoor arena, and grading or raking the surface of all arenas.
The worker’s dust exposure was assessed over 16 full shifts from June to August 2018. The sampling occurred for the full work shift, including short breaks which were always taken in the arena canteen.
Sampling times ranged from 480 to 540 minutes, with the worker spending 75% to 85% of their work time in the indoor arena or nearby.
It was found the worker was exposed, on average, to respirable dust concentrations of 0.12 mg per cubic metre and respirable crystalline silica concentrations of 0.02 mg per cubic metre.
Respirable crystalline silica exposures of between 0.01 to 0.09 mg per cubic metre were measured on days when the indoor arena surface was not watered, compared to lower exposures (below 0.03 mg per cubic metre) on days when the indoor arena was watered.
“However, manual watering is time-intensive and less likely to be implemented in practice,” the study team reported in the International Journal of Environmental Research and Public Health.
Exposure concentrations of respirable crystalline silica in the study were less than the Irish occupational exposure limit of 0.1mg per cubic metre and also below the level set under the European Union Carcinogens and Mutagens directive.
However, they were higher than the United States National Institute for Occupational Safety and Health recommended exposure limit of 0.05mg per cubic metre, given that the worker’s exposure concentrations ranged from 0.01 to 0.09mg per cubic metre.
The authors noted that previous research among US industrial sand workers suggest that exposures as low as 0.05 mg per cubic metre can present an increased lung cancer risk, which is further increased among smokers.
The relative risk for lung cancer mortality associated with 40 years of exposure (with a 15-year lag period) at the concentrations measured in the study is estimated to represent an increase of between 0.4% and 3.8%.
“Given that occupational cancer is the leading cause of work-related deaths in the EU, further research is required to characterise respirable crystalline silica exposures and other potential airborne hazards created as a result of the use of different footing materials and additives including, for example, recycled textiles and synthetic carpets in equestrian arenas.”
The small-scale study had provided new data on dust exposure among equestrian workers, the researchers said.
“Respirable crystalline silica exposures are within the range considered to be associated with increased risk for lung cancer.
“The use of dust control solutions such as water suppression should be promoted for equestrian work in horse riding arenas.
“Equestrian workers need to receive occupational health training on the health risks associated with respirable crystalline silica exposure.”
The study team said that the study, although limited by sample numbers, provided a significant way forward in characterising equestrian workers’ exposure to respirable dust and respirable crystalline silica.
Measured silica concentrations approached the recommended Irish limit of 0.1 mg per cubic metre, which could suggest an increased lung cancer risk for this occupational group.
“But since the study represents just one worker from this industry, further exposure studies are required.”
The researchers said automated watering systems would be recommended, as competing work tasks limit the time that the equestrian worker can spend on manual watering.
“Further studies are required to promote awareness within the sector of the exposure risks associated with footing materials used on indoor equestrian arenas and the impact of increased knowledge and understanding of the risks involved.”
The full study team comprised Bulfin, Hilary Cowie, Karen Galea, Alison Connolly and Marie Ann Coggins.
Occupational Exposures in an Equestrian Centre to Respirable Dust and Respirable Crystalline Silica
Kathleen Bulfin, Hilary Cowie, Karen S. Galea, Alison Connolly and Marie Ann Coggins.
Int. J. Environ. Res. Public Health 2019, 16(17), 3226; https://doi.org/10.3390/ijerph16173226