**3. Assessment of metal pollution level**

The absolute concentration of metals in marine sediments never indicates the degree of contamination coming from either natural or anthropogenic sources because of its grain-size distribution and mineralogy characteristic [43, 44]. Normalization of metal concentrations to grain sizes, specific surface area, and reactive surface phases such as Li and Al is a common technique to remove artifacts in the data due to differences in depositional environments [45–47]. This method allows researchers to compare the contamination level directly even if the samples were collected at different locations. The most common normalization technique used is enrichment factor (EF) where this technique uses common elements such as Al, Li, and Fe as normalizer and index of geoaccumulation (Igeo) or compares the normalized concentration to average crustal abundance data [47, 48].

In order to examine to sediment status, the determined element concentrations normally were compared to the published background concentrations. Literature data on average world shale or sediment cores or sediments from pristine such as undisturbed wetlands and non-industrialized regions were analyzed to establish the background values. However, to reduce the metal variability caused by the grain sizes and mineralogy of the sediments and to identify anomalous metal contribution, geochemical normalization has been used with various degrees of success by employing conservative elements [49, 50]. Researchers have proposed various elements as normalizer, and these elements have the potential for the environmental studies. Some of them are lithium, Li [51–53]; aluminum, Al [54, 55]; scandium, Sc [56]; cesium, Cs [57, 58]; cobalt, Co [59]; and thorium, Th [60, 61]. Among all proposed normalizers, conservative elements, Li and Al, have been widely applied in marine and coastal study [62–64].

The concentration of metals in marine sediments cannot indicate the degree of contamination coming from either natural or anthropogenic sources because of grain-size distribution and mineralogy [44, 65]. Normalization of metal concentrations to sediment size, specific surface area, and reactive surface phases such as Li and Al is a common technique to remove artifacts in the data due to differences in depositional environments [46, 66]. This allows for a direct comparison to be made between contaminant levels of samples taken from different locations.

Based on the researches by several geochemists [67, 68], if an EF value is between 0 and 1.5, it is suggested that the metals may be entirely from crustal materials or natural weathering processes. If an EF is greater than 1.5, it is suggested that a significant portion of metals has arisen from non-crustal sources or anthropogenic pollution [61, 69].

 Another common approach to evaluate the metal pollution in sediments is the index of geoaccumulation (Igeo) introduced by Müller [70] in order to determine and define metal contamination in sediments by comparing current concentrations with the background levels. Similar to metal enrichment factor, Igeo can be used as a reference to estimate the extent of metal pollution in sediments. The Igeo value is calculated by using the following equation:

$$\mathbf{I}\_{\mathsf{geo}} = \mathsf{log}\_2\left(\mathsf{C}\_n/\mathsf{LSB}\_n\right) \tag{1}$$

where Cn is the measured concentration of the element (n) in the sediment and Bn is the geochemical background concentration of the element (n). Factor 1.5 is the correction of background matrix factor due to the lithogenic effects [70]. The upper continental crust values of the studied metals are the same as those used in the aforementioned enrichment factor calculation [71]. Müller [70] has distinguished seven classes of the Igeo from Class 0 to Class 6. The highest class (Class 6) reflects at least 100-fold environment above the background value.


*Sediment and Organisms as Marker for Metal Pollution DOI: http://dx.doi.org/10.5772/intechopen.85569* 


 Tomlinson et al. [72] elaborated that the application of pollution load index (PLI) provides a simple way in assessing marine and coastal sediment quality by metal pollution. This assessment is a quick tool in order to compare the pollution status of different places [73]. PLI represents the number of times by which the metal concentrations in the sediment exceed the background concentration and gives a summative indication of the overall level of metal toxicity in a particular sample or location [74, 75]. PLI can provide some understanding to the public of the surrounding area about the quality of a component of their environment and indicates the trend spatially and temporarily [76]. In addition, it also provides valuable information to the decision-makers toward a better management on the pollution level in the studied region.

PLI is obtained as contamination factor (CF). This CF is the quotient obtained by dividing the concentration of each metal with the background value of the metal. The PLI can be expressed from the following relation:

$$\mathsf{PLL} = \left(\mathsf{CF}\_1 \times \mathsf{CF}\_2 \times \mathsf{CF}\_3 \times \mathsf{CF}\_4 \times \mathsf{CF}\_n\right)^{1/n} \tag{2}$$

where n is the number of metals studied and the CF is the contamination factor. The CF can be calculated from

= ( / ) (3)

The PLI value more than 1 can be categorized as polluted, whereas less than 1 indicates no pollution at the study area [77, 78].
