I have a raised cedar garden bed, roughly 10 inches high. In the surrounding area is black dyed mulch. If I fill the beds with good topsoil should I worry about the dyed mulch leaking into the soil? Could I even put the garden bed on top of the dyed mulch? I only plan to plant tomatoes, peppers, etc., no root type vegetables.
Dyes mulch is not made from trees.
Dyed mulches (black, red, green and other colors) are usually (with few exceptions) made up of recycled wood waste. This trash wood can come from old hardwood pallets, old decking, demolished buildings or worse yet pressure treated CCA lumber. CCA stands for Chromium, Copper and Arsenic; chemicals used to preserve wood. This ground up trash wood is then sprayed with a tint to cover up inconsistencies in the wood and give it a uniform color.
This dyed wood mulch does not break down to enrich the soil as good mulch should. Instead it leaches the dye along with the possible contaminants (chromium, copper, arsenic and others) into the soil harming or even killing beneficial soil bacteria, insects, earthworms and sometimes the plants themselves. These wood mulches actually rob the soil of nitrogen by out-competing the plants for the nitrogen they need for their own growth. Dr. Harry Hoitink, Professor Emeritus at Ohio State University, warns that dyed mulches are especially deadly when used around young plants and in newer landscapes.
Do not allow children or pets in areas in which dyes mulch has been or is being used.
Can't tell you how safe it is for a variety of reasons. Definitely don't put the raised bed on top of the mulch. That's pointless.
The dye may contain toxins but I did contact one dye manufacturer and was assured that they're black dye was safe to use around edible plants but not sure that applies to all black mulch dies. One common ingredient is carbon black which is made using petroleum products and may possibly be carcinogenic.
Even play wood mulch can be toxic at least to plants. The wood itself can contain harmful substances. Cheaper wood mulches can contain scraps from all sorts of sourced including pressure treated wood. If it's not a wood mulch, rubber mulch has it's own issues. Sometimes if the mulch isn't handled/stored correctly toxic gases can form in it so if it smells bad don't use it.
If you want to be on the safe side I'd avoid dyed mulch near vegetables. I personally like to use natural cedar mulch.