Which industrial facility is most likely to produce sludge and heavy-metal wastes?
a. aleather tannery
b. amedical center
c. a nuclear power plant
d. a steel-smelting facility

The answer is A. A leather tannery. A tannery produces a sludge as a byproduct that is high in various toxic elements including chromium, a heavy metal that is highly toxic. Other pollutants produced include sodium, calcium, sulfur, magnesium, phosphate, copper, tin, lead, arsenic cadmium and zinc. Tannery effluent is an extremely toxic pollutant that could cause great harm if released into the environment, and for that reason, the tannery industry needs to be highly regulated and managed. 

Mg is used to measure mass