https://s3.wp.wsu.edu/uploads/sites/403/2015/03/rubber-mulch.pdf
"It is abundantly clear from the scientific literature that rubber should not be used as a landscape
amendment or mulch. There is no question that toxic substances leach from rubber as it degrades,
contaminating the soil, landscape plants, and associated aquatic systems. While recycling waste tires is
an important issue to address, it is not a solution to simply move the problem to our landscapes and
surface waters.
The Bottom Line
• Rubber mulch is not as effective as other organic mulch choices in controlling weeds
• Rubber mulch is highly flammable and difficult to extinguish once it is burning
• Rubber mulch is not permanent; like other organic substances, it decomposes
• Rubber mulch is not non-toxic; it contains a number of metal and organic contaminants with
known environmental and/or human health effects"