Gardeners often take the decision between adding wood mulch or rubber mulch into their garden very seriously and rightly so. Both types of mulches do different things for your garden, whether is beneficial or harmful. Here is some information on both rubber mulch and wood mulch, broken down by topic.
Both types of mulches contain toxins that can leak into your soil, so there really is not a clear answer when it comes to this.
Wood mulches usually contain wood that has been dyed, used pallets, and others that were once used for industrial purposes. This means that the mulch can have arsenic, creosote, and other things. Because the wood used in most wood mulch is used, they only way to be positive that the wood mulch you have is safe is to use mulch made only from tree bark and has not been treated or primped for any purpose.
Rubber mulch also has a used quality because it is made from old tires. Zinc can be leaked into your soil by just the rubber itself but think about the amount of unknown chemicals it has just due to what the mulch is made of. Any chemicals the tires came across at one point could be in that mulch, and then in your garden.