Health and Environmental Effects of heavy metals on lawns and gardens

Metals in Ash is bad but EPA claims metals in sludge biosolids is good.

Ash
Backyard burning also produces ash residue, which can contain toxic metals such as mercury, lead, chromium, and
arsenic. These metals can be toxic when ingested. When a person ingests hazardous amounts of lead, for example,
he or she may experience high blood pressure, cardiovascular problems, kidney damage, and brain damage.
Unaware of the potential danger, some people scatter the ash in their gardens or bury it on their property. Garden
vegetables can absorb and accumulate these metals, which can make them dangerous to eat. Children playing in the
yard or garden can incidentally ingest soil containing these metals. Also, rain can wash the ash into groundwater and
surface water, contaminating drinking water and food.