Runners battered from the harsh pounding inflicted by asphalt may find solace in mulch running tracks, which use ground wood chips or rubber particles to provide improved cushioning for weary ankles and knees. However, mulch tracks do pose their own unique set of problems, and the added comfort may not be worth the potential health risks.
Many mulch running tracks feature tiny rubber particles derived from recycled tyres. While soft and cushioning, these particles contain hidden dangers like lead and other harmful toxins. When soil microbes begin breaking down the mulch, the decomposing rubber particles release these toxins into the environment.
The Connecticut Agricultural Experiment Station conducted a laboratory study on rubber mulch particles and discovered as many as two dozen chemicals were released during decomposition, including such harmful compounds as benzothiazole, a skin and eye irritant; butylated hydroxyanisole, a recognized carcinogen; n-hexadecane, a severe irritant; and 4-(t-octyl) phenolthe, a corrosive substance that’s destructive to mucous membranes. Repeated and prolonged exposure to these chemicals could pose a wide variety of health risks, from allergic responses and neurological development issues to cancer.
Running on mulch tracks poses an increased risk of respiratory irritation. The simple act of running kicks up the rubber particles and tyre dust, while the intense physical exertion creates a need for sometimes deep, laboured breathing. The combination leads to a greater risk of inhaling the dangerous particles, not only hindering performance but also presenting serious health concerns. In extremely hot weather, rubber mulch may even produce a foul odor that can further complicate breathing.
Although running on hot asphalt can be draining, rubber mulch tracks provide little in the way of relief. Dr. Curtis E. Swift of Colorado State University conducted a study that found rubber mulch can produce temperatures as high as 78 degrees C. Runners must remember to stay hydrated on mulch tracks to prevent heatstroke. The high surface temperatures may also prove taxing on shoes and feet.
Weather and other environmental conditions can limit the effectiveness of rubber mulch tracks as well. Heavy rains and winds can disperse the rubber particles. In comparison, organic materials like wood chips tend to clump together when wet or in the midst of decomposition, helping them stay in place. Since they lack these same cohesive properties, rubber mulch particles can get kicked from the track and spread out over time, reducing their shock absorption qualities and requiring more maintenance.
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