Toxicological Impact of Heavy Metals During Sustainable Brick Production from Bagasse and Fly Ash: A Review

The utilization of waste materials in the construction technology is today considered an important key to meet sustainability level goals and reduce carbon dioxide emissions through a minimum use of virgin production chains. Coal fly ash (CFA) and sugarcane bagasse ash (SBA) are the two types of waste byproducts for which there has been promising reuse in a sustainable brick. Both ashes are characterized by their high contents of silica and alumina that makes them of potential interest as partial substitutes for clay in fired bricks or as precursors in geopolymerization. But the trace amount of heavy metals such as arsenic, cadmium, chromium, lead, mercury, nickel and zinc in the materials may cause some toxicological threat to human health and ecosystem if it is not well immobilized during its fabrication as well as usage. This review summarises information on the chemical composition of CFA-, and SBA-brick constituents, i.e. raw materials used in bricks including those substituting conventional brick materials, methods by which heavy metals are sequestered in bricks, toxicological pathways following exposure to leachates from such bricks and leaching regulations and risk assessment specifications globally. It also presents the mitigation approaches to minimize metal toxicity, discusses analytical difficulties and finally outlines future research perspective necessary to elevate safe and sustainable ash masonry use.