Bioavailability of Heavy Metals in Coal Ash: A Systematic Review

Background: Coal ash is the second largest industrial waste stream in the U.S., after mining wastes. In the United States, coal power plants produce 140 million tons of coal ash each year (Sierra Club 2017). Coal ash, the waste by product of burning coal, contains several toxic chemicals including arsenic, chromium, mercury, lead, selenium and other heavy metals. These toxic chemicals can cause several types of health impacts, including cardiovascular diseases, respiratory diseases, cancer, and neurodevelopmental disorders. For years’ coal burning power plants have been disposing the coal ash into coal ash sites; impoundments; nearby water sources; or landfills, increasing exposure to heavy metals and health risk to those communities living nearby. Objectives: Given the limited health studies on coal ash exposure, our objective was to apply the Navigation Guide systematic review methodology to answer the question: What is the heavy metals bioavailability of coal ash in water? Bioavailability is the proportion of total metals that are available for incorporation into biota (bioaccumulation), or the ability to be absorbed by an organism. This systematic literature review focuses on the pathway of heavy metals from coal ash particles by studying the bioavailability and leaching of heavy metals in water to address the potential human health impacts through ingestion. Methods: The literature review was conducted using the Navigation Guide, in which we specified the study question, select the evidence, evaluated the risk of bias of individual studies, and evaluated the overall quality and strength of the evidence. Results: Our search retrieved a total of 36 unique records, of which 7 included the inclusion criteria. We concluded that the risk of bias was high across studies, and assigned a “low” quality 2 rating to the overall body of evidence. We identified recruitment strategy, confounding, and other bias as the most common risk of bias. Comparing the evidence and results of the studies was challenging, but in several of them, studies found a significant concentration of heavy metals after sequential extraction tests. Discussion: Results from the studies demonstrate evaluating the bioavailability and leaching factors of heavy metals in coal ash is complex and depends on several factors, including chemical speciation, pH, absorption, particulate size, temperature, and the surrounding environment. Conclusion: We concluded that there was “limited evidence of toxicity” to determine the bioavailability of heavy metals from coal ash in surface water