A Comprehensive Review on Heavy Metal Toxicity in Coastal Sediments

Heavy metal toxicity is becoming a growing environmental concern worldwide. The estuary's surface waters and sediments are finally being transported to the coastal areas. During this transportation, the water and sediments carry numerous elements. The essential elements like nutrition are nitrates, phosphates, silicates, and sulphates, which are required for aquatic life, and non-essential elements contribute to pollution. The input of these essential and non-essential elements is being contributed by nature and anthropogenic activities. Due to the increase in urbanization and anthropogenic activities like agricultural, industrial, thermal power plants, dye factories, inland fisheries, small and significant scale industries, as well as recreational activities, are the sources of heavy metal toxicity. The toxic heavy metals, including mercury, cadmium, chromium, and lead, are leading to biological toxicity. Environmental standards are being modified due to increasing concerns. However, naturally occurring heavy metals and metalloids are drawn from parent rocks and absorbed by aquatic organisms, such as benthic organisms, which fix some heavy metal ions. Flora and fauna also absorb these ions, reducing their concentration. However, due to climatic factors like temperature and pH, these metal ions get adsorbed on the surface of the sediments. During hydrodynamic forces, they get released back into the water and vary seasonally.