**5. Assessment of sediment pollution status**

To evaluate the metals contamination in sediment, determined element concentrations were compared with background concentrations. Literature data on average world shale or sediment cores or sediments from pristine such as undisturbed wetlands, non-industrialized regions were analyzed to establish the background values. However, to reduce the metals variability caused by the grain sizes and mineralogy of the sediments, and to identify anomalous metals contribution, geochemical normalization has been used with various degrees of success by employing conservative elements [12, 13]. Various elements have been proposed in the literatures to be clay mineral indicators and hence to have the potential for the environmental studies. Some of them are lithium, Li [14–16]; aluminum, Al [17, 18]; scandium, Sc [19]; cesium, Cs [20, 21]; cobalt, Co [22]; and thorium, Th [23, 24]. Among above conservative elements, Li and Al have been widely applied in wetlands and mangroves study [25–27]. Li also has been proposed by Loring [14] as an alternative for Al in high latitude areas in Western Europe and North America. Alternatively, Li meets the basic criteria for use as a normalizing element for metals pollution [14] because of several factors, namely, it is a lattice component of fine-grained major trace-metal-bearing minerals such as the phyllosilicates and clay minerals; it reflects the granular variability of its host mineral component, and it is a conservative element.

to estimate the extent of metal pollution in sediments. The Igeo is defined by the following

is the measured concentration of the examined element (n) in the sediment and B<sup>n</sup>

geochemical background concentration of the element (n). Factor 1.5 is the background matrix correction factor due to the lithogenic effects [43]. The upper continental crust values of the metals of interest are the same as those used in the aforementioned enrichment factor calculation [44]. Muller [43] 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 (**Table 1**).

Tomlison et al. [45] elaborated that the application of pollution load index (PLI) provides a simple way in assessing mangrove, estuarine, and coastal sediment quality. This assessment is a quick tool in order to compare the pollution status of different places [46]. PLI represents the number of times by which the metal concentrations in the sediment exceed the background concentration, and give a summative indication of the overall level of metals toxicity in a particular sample or location [47, 48]. The 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 [49]. In addition, it also provides valuable information to the decision makers toward a better management on the pollution level in

PLI is obtained as contamination factors (CFs). This CF is the quotient obtained by dividing the concentration of each metal with the background value of the metal. The PLI can be

PLI = (CF<sup>1</sup> × CF<sup>2</sup> × CF<sup>3</sup> × CF<sup>4</sup> × CFn)

where, n is the number of metals studied and the CF is the contamination factor. The CF can

CF = (Metals concentration in samples/Background metals concentration)

**Class Value Sediment quality**

0 Igeo ≤ 0 Practically uncontaminated 1 0 < Igeo < 1 Slightly contaminated 2 1 < Igeo < 1 Moderately contaminated

4 3 < Igeo < 1 Heavily contaminated

6 5 < Igeo < 1 Extremely contaminated

**Table 1.** Classification of sediment quality based on Igeo value.

3 2 < Igeo < 1 Moderately to heavily contaminated

5 4 < Igeo < 1 Heavily to extremely contaminated

1/n

/1.5Bn)

is the

35

Metals Pollution in Tropical Wetlands http://dx.doi.org/10.5772/intechopen.82153

Igeo = log<sup>2</sup> (C<sup>n</sup>

equation:

where C<sup>n</sup>

the studied region.

be calculated from:

expressed from the following relation:

The absolute concentration of metals in marine sediments never indicates the degree of contamination coming from either natural or anthropogenic sources because of grain-sizes distribution and mineralogy [26, 28, 29]. Normalization of metals 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 [30–34]. This allows for a direct comparison to be made between contaminant levels of samples taken from different locations. One of the most common normalization techniques is converting trace metal concentrations to enrichment factors (EF) by normalizing metals concentrations to a common element (usually Al or Fe) [35–37]. The EF value can be calculated according to the following formula:

 Enrichment Factor (EF) <sup>=</sup> (Metal concentration/Normalizer) sample \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ( Metal concentration/Normalizer) background

Based on the researches by several geochemists [38–41], 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 have arisen from noncrustal sources or anthropogenic pollution [24, 42].

Another commonly used criterion to evaluate the heavy metals pollution in sediments is the index of geoaccumulation (Igeo) originally introduced by Muller [43] in order to determine and define heavy metals 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 is defined by the following equation:

**5. Assessment of sediment pollution status**

34 Wetlands Management - Assessing Risk and Sustainable Solutions

a conservative element.

following formula:

To evaluate the metals contamination in sediment, determined element concentrations were compared with background concentrations. Literature data on average world shale or sediment cores or sediments from pristine such as undisturbed wetlands, non-industrialized regions were analyzed to establish the background values. However, to reduce the metals variability caused by the grain sizes and mineralogy of the sediments, and to identify anomalous metals contribution, geochemical normalization has been used with various degrees of success by employing conservative elements [12, 13]. Various elements have been proposed in the literatures to be clay mineral indicators and hence to have the potential for the environmental studies. Some of them are lithium, Li [14–16]; aluminum, Al [17, 18]; scandium, Sc [19]; cesium, Cs [20, 21]; cobalt, Co [22]; and thorium, Th [23, 24]. Among above conservative elements, Li and Al have been widely applied in wetlands and mangroves study [25–27]. Li also has been proposed by Loring [14] as an alternative for Al in high latitude areas in Western Europe and North America. Alternatively, Li meets the basic criteria for use as a normalizing element for metals pollution [14] because of several factors, namely, it is a lattice component of fine-grained major trace-metal-bearing minerals such as the phyllosilicates and clay minerals; it reflects the granular variability of its host mineral component, and it is

The absolute concentration of metals in marine sediments never indicates the degree of contamination coming from either natural or anthropogenic sources because of grain-sizes distribution and mineralogy [26, 28, 29]. Normalization of metals 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 [30–34]. This allows for a direct comparison to be made between contaminant levels of samples taken from different locations. One of the most common normalization techniques is converting trace metal concentrations to enrichment factors (EF) by normalizing metals concentrations to a common element (usually Al or Fe) [35–37]. The EF value can be calculated according to the

Based on the researches by several geochemists [38–41], 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 have

Another commonly used criterion to evaluate the heavy metals pollution in sediments is the index of geoaccumulation (Igeo) originally introduced by Muller [43] in order to determine and define heavy metals contamination in sediments by comparing current concentrations with the background levels. Similar to metal enrichment factor, Igeo can be used as a reference

sample \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ( Metal concentration/Normalizer)

background

Enrichment Factor (EF) <sup>=</sup> (Metal concentration/Normalizer)

arisen from noncrustal sources or anthropogenic pollution [24, 42].

$$\mathbf{I}\_{\mathrm{geo}} = \log\_2\left(\mathbf{C}\_n/1.5\mathbf{B}\_n\right)$$

where C<sup>n</sup> is the measured concentration of the examined element (n) in the sediment and B<sup>n</sup> is the geochemical background concentration of the element (n). Factor 1.5 is the background matrix correction factor due to the lithogenic effects [43]. The upper continental crust values of the metals of interest are the same as those used in the aforementioned enrichment factor calculation [44]. Muller [43] 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 (**Table 1**).

Tomlison et al. [45] elaborated that the application of pollution load index (PLI) provides a simple way in assessing mangrove, estuarine, and coastal sediment quality. This assessment is a quick tool in order to compare the pollution status of different places [46]. PLI represents the number of times by which the metal concentrations in the sediment exceed the background concentration, and give a summative indication of the overall level of metals toxicity in a particular sample or location [47, 48]. The 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 [49]. 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 factors (CFs). 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:

$$\text{PLI} = \left(\text{CF}\_1 \times \text{CF}\_2 \times \text{CF}\_3 \times \text{CF}\_4 \times \text{CF}\_n\right)^{1/n}$$

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


CF = (Metals concentration in samples/Background metals concentration)

**Table 1.** Classification of sediment quality based on Igeo value.

The PLI value more than 1 can be categorized as polluted whereas less than 1 indicates no pollution at the study area [50, 51].

**7. Tolerable intake**

metals (**Table 2**).

Shellfish

Food category not specific

n.m.: not mentioned.

regions.

Beside fishes, shellfish such as oysters and mussels are an important source of dietary protein in coastal communities. Depending on consumer, those shellfish can be "swallowed" or masticated normally, increasing the surface contact between food and digestive fluids. The consumer will consume whole soft part of the shellfish (**Figure 9**); therefore, in the pollution study which relates to human health, the metals content is examined in toto or shellfish flesh. To safeguard public health, who consumes these organisms, maximum acceptable concentrations of toxic contaminants have been established in various countries. As a result, there is a specific legislation for shellfish, which establishes the maximum allowed concentration for

**Figure 9.** Oyster in toto tissue use for metals study in relation to human health. Photo by Ong Meng Chuan.

European community n.m. n.m. 1 1.5 n.m. 0.5–1.0 [57] Spain 20 n.m. 1 5 n.m. 0.5 [58] Australia 30 150 2 2 1 0.5 [59] China n.m. n.m. 0.1 0.5 1.0 0.3 [60] Hong Kong n.m. n.m. 2 6 1.4 0.5 [61] Singapore n.m. n.m. 1 2 1 0.5 [62]

Malaysia 30 50 1 2 n.m. 0.5 [63] Thailand 20 133 n.m. 1.0 2 0.5 [64] Brazil 30 50 1 2 n.m. 0.5 [65]

**Table 2.** Maximum permissible levels (expressed in mg/kg wet weight) of metals in shellfish from different countries or

**Cu Zn Cd Pb As Hg References**

Metals Pollution in Tropical Wetlands http://dx.doi.org/10.5772/intechopen.82153 37
