Utilization of mussel shell to remediate soils polluted with heavy metals

Soil pollution by “heavy metals” and metalloids can be due to various sources, such as mining and industrial activities, application of fertilizers, pesticides, livestock residues, and other wastes with high metal content. Therefore, soil pollution by heavy metals can represent risks for humans and ecosystems, mainly due to direct ingestion or contact with contaminated soils, or by introduction into the food chain, or by decreasing the quality of food (safety and marketability) through phytotoxicity. Moreover, high concentrations of heavy metals can be even more hazardous than those associated with organic pollutants. In general, metals do not undergo microbial or chemical degradation in the soil, and, therefore, this kind of pollution persists for a long time. Recently, the remediation of environmental pollution, particularly soil pollution, has been considered a key aspect of great concern, both at social and public administration levels and for researchers, and primarily when focusing on efficient, low-cost technologies to reach it. Along these lines, one of the alternatives is using mussel shells to retain pollutants, as it is a very abundant and low-cost by-product. Galicia (NW Spain) is one of the leading producers of mussel (Mytilus galloprovincialis) together with China, various Mediterranean countries, the Russian Federation, Ukraine, and South Africa, among others. In Galicia, it is estimated that approximately 120,000 tons of mussels are processed each year in the canning industry, while the rest of the production is dedicated to the sale of fresh products. During the processing of the raw material in the canning industry, shells are removed, which accounts for around 32% of the total weight of the mussel. Consequently, the industry dedicated to processing mussels generates between 65,000 and 93,000 tons of waste each year just in this Autonomous Community in Spain. Given this high quantity, it has been necessary to propose treatment and/or recycling alternatives. In Galicia, this material was traditionally used as a soil amendment to raise pH in acid soils since calcium carbonate is its main component, but other uses are being considered in recent years. Among them, its potential to immobilize heavy metals in soils is noteworthy due to its high pH in conjunction with other physicochemical characteristics that make it suitable as a sorbent. Therefore, this chapter reviews the feasibility of using mussel shells as an efficient material to remediate soils polluted with heavy metals and the mechanisms involved in such processes.