Particulate Matter Characterization in Equestrian Riding Arenas

Particulate matter (PM) from hay and bedding contributes to common respiratory disease in horses, but horses and handlers are also exposed to irritating levels of dust arising from the footing material used as the arena riding surface. Airborne total and respirable PM in two indoor equine riding arenas was quantitatively studied using gravimetric methods during 5 to 10 h when the arenas were occupied by horse activity and over three sessions each to coincide with footing dust suppression management. Samplers were positioned approximately 0.5 m above the arena surface, which consisted of inorganic, low-moisture, sand-soil footing in one arena and organic stall waste material footing in the second arena. Footing materials were characterized in terms of moisture content, elemental analysis, and particle size distribution. Qualitative evaluations of captured dust particle size and shape were performed using scanning electron microscopy, which determined that spherical fine particles dominated. Both total dust (0.600 mg m(-3) with organic footing; 0.706 mg m(-3) with inorganic footing) and respirable dust (0.327 mg m(-3) with organic footing; 0.429 mg m(-3) with inorganic footing) levels were lower than expected compared to data from stable dust studies. Dust detection did not vary systematically with dust suppression but rather was associated with the overall quality of the footing present in the arena. Dust detection in the arenas was best calculated according to the level of horse activity during sampling. Total dust levels were 0.778 mg m(-3) and 3.395 mg m(-3) (organic and inorganic footing, respectively) when calculated based on time the arena was occupied by horses. Total dust levels were 2.5 to 3 times higher during times of horse activity faster than a walk than during more sedentary activity. Respirable particles were about half of the total dust during riding activity. When observing horses moving in an arena, it is readily apparent that dust is suspended in the air behind the tread of the horse's hooves, and its suspension is transient in nature. Horses in this study were apparently not exposed to a quantity of respirable dust particles in the riding arena comparable to that found in their stall environment.