**2.1 Heavy metal contamination in the marine ecosystem**

Metal concentrations in the marine environment are estimated to be in the nanogram to microgram per liter (liquid phase) or per gram range as they are found naturally components of the earth's crust (solid phase). Concentrations of important heavy metals (Zn, Pb, Cd, Cu, Sn, and Hg) in the marine environment have increased by five to ten times in the past few decades compared to values recorded fifty to one hundred years ago [15]. The global increase in metal contamination in marine ecosystems has been mainly driven by economic development and accelerated industrialization in recent decades. Metals enter aquatic systems and accumulate in various ways, as shown in **Figure 1**. Changes in physicochemical parameters such as salinity, redox potential, temperature, pH, and organic ligand concentrations could cause metals

#### **Figure 1.**

*Major routes for metals contamination and bioaccumulation in the aquatic environment.*

### *Heavy Metal Contamination in the Coastal Environment and Trace Level Identification DOI: http://dx.doi.org/10.5772/intechopen.106653*

to disintegrate from a solid phase once adsorbed into marine sediments. As a consequence, the toxicity, mobility, and bioavailability of metals are largely determined by the environment [15, 16]. Important terrestrial and aquatic ecosystems, including mangrove forests, intermittently and permanently flooded wetlands, and tidal flats, are found in the coastal environment, which is highly dynamic and ecologically complex. These enriched ecosystems are at risk due to environmental consequences and human encroachment. The wastes from scrapped ships, including oils and persistent organic pollutants (POPs), enter the coastal bay, which is home to a variety of marine life, including many endangered and vulnerable species; pollution has been identified as one of three major transboundary issues affecting the marine ecosystem. Heavy metals can accumulate in aquatic habitats to toxic levels because they are not biodegradable, although some metals are essential to the ecosystem's function. Metals are eventually integrated into the sediment at the bottom, where organisms (benthic organisms) can gather them. Heavy metals affect aquatic life at greater levels. Cadmium and copper concentrations in the water surrounding shipbreaking zones were high enough to affect fish spawning and death. In coastal areas, a higher concentration of mercury and tin has delayed the development of mollusks, and lead has reduced the nesting capacity of marine birds [17].

Low levels of dissolved metals in seawater may or may not present a hazard to marine biota but some species have shown a tendency to accumulate the metals from the water. Li et al. [18] studied the effects of chelating agents on the uptake and accumulation of cadmium by *Mytilus edulis*. Complexation of cadmium with either EDTA, humic and alginic acids, or pectin doubles both rate of accumulation and the final tissue concentration. Yap et al. [19] determined trace metal (Hg, Cd, Cu, Ag, Zn, and Pb) concentrations in mussels from the estuaries were compared with those of coastal and offshore regions in the southeastern North Sea. Bandara et al. [20] reported that tributyltin contamination in marine gastropod; *Thais clavigera* and mussels, *Perana perana*, *Perna viridis*, *Crassostrea madrasensis,* and *Crassostrea cuculata*. Levels of selected heavy metals in sediments collected from subtidal areas off the Iranian coastline of the Arabian Gulf were measured by Pourang et al. [21]. This study concluded that the concentrations of Cd, Pb, and Ni in the sediments (2.9, 90.5, and 64.9 μg/ g dry weight, respectively) were notably higher than global baseline values. Assessment of contaminants in Dubai coastal region, United Arab Emirates, was conducted by Al-Darwish et al. [22]. This study found that the highest concentrations of the selected metals were found in chronically polluted areas and reported elevated levels of Cu, Ni, and Zn in comparison with background levels of unpolluted sediments in the Arabian Gulf, which is heavily occupied by a variety of industries.
