**3.2 Pollution indices**

### *3.2.1 Contamination index and mean contamination index*

Contamination indices determined for each of the six TMs in the five sampling stations and the mean contamination index are presented in **Table 6**. Sediments from *Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems… DOI: http://dx.doi.org/10.5772/intechopen.110244*

stations S1 and S4 were respectively contaminated with As and Cd and recorded 5.00 as the contamination index (**Table 6**). The other stations were free in As and Cd.

Regarding Hg, a CI value of 1.67 was observed at stations S1, S3, and S5. For Mn, the lowest CI (0.00) was observed at station S2, while the highest (2.35) occurred at station S4. Pb exhibited CI values of 1.07 and 3.93 for stations S5 and S1, respectively. The mean contamination indices (MCI) varied from 0.01 to 1.93. The highest MCI value was observed in S1 sediments, while le lowest one occurred in S2 ones (**Table 6**).

### *3.2.2 Contamination factor (CF)*

The spatial variation of CF values for the studied TMs is shown in **Figure 1**. The CF values for As ranged from 0.0 to 834.22 with a mean value of 166.84. The highest CF value for As was observed in sediments from station S1 (**Figure 1a**). For cadmium, only S4 presented a CF (73.53) greater than zero (**Figure 1b**). For the whole study area, the average CF value for Cd was 14.71. The CF values for Fe varied from 0.44 to 1033.09, with a mean value of 327.67 (**Figure 1c**).

The highest CF values for Fe were observed at S4 and S5 close to the ADFM and the boats' cemetery respectively (**Figure 1c**). Hg was detected in sediments from S1, S3, and S5 only and exhibited a CF value of 0.89 for the same three sampling points (**Figure 1d**). The lowest CF values calculated for the present study were observed for


**Table 5.**

*Concentrations of trace metals in Abobo-Doume in comparison to other local studies and the world averages.*


### **Table 6.**

*Contamination index and mean contamination index in Abobo-Doume fish market sediments.*

*Heavy Metals – Recent Advances*

### **Figure 1.**

*Contamination factors of trace metals in Abobo-Doume fish market area. (a): arsenic, (b): cadmium, (c): iron, (d): mercury, (e): manganese, and (f): lead.*

Mn with CF values ranging from 0.000 to 0.004, and a mean of 0.002 (**Figure 1e**). The CF values for Pb varied from 0.00 to 14.91. The highest CF for Pb was observed in sediments from S1 and S5 (**Figure 1f**). The average CF value for Pb was 3.80.

### *3.2.3 Pollution load index (PLI)*

The pollution load index (PLI) was calculated for the different stations and the results are presented in **Figure 2**. The PLI values varied from 0.00 (S2) to 0.50 (S1). Regarding the PLI values, the sampling stations were in the following ascending rank in TMs contamination: S2 < S3 < S5 < S4 < S1.

*Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems… DOI: http://dx.doi.org/10.5772/intechopen.110244*

**Figure 2.** *Spatial variation of the pollution load index (PLI) in the sampling stations.*

### *3.2.4 Enrichment factor (EF)*

The spatial variation of enrichment factors for the TMs is presented in **Figure 3**. Arsenic exhibited a high EF value of 1886.182 in station S1. On the opposite, no enrichment effect was observed elsewhere (**Figure 3a**). EF values for Cd were low with values ranging from 0.0 to 0.071 in S4 sediments (**Figure 3b**). No enrichment in Cd was observed for S2, S3, and S5 sediments. For Hg, the calculated EFs ranged from 0.002 to 2.019. The highest EF value for Hg was determined for sediments in S1 (**Figure 3c**). The EF values observed for Mn were low compared to the other TMs ones with values that varied from 0.0 to 0.004 (**Figure 3d**). EFs for Pb ranged from 0.0 to 33.716 (**Figure 3e**). The highest EF value for Pb was observed in S1 sediments, while those in S2, S3, and S4 exhibited no enrichment status (**Figure 3e**).

### *3.2.5 Geoaccumulation index (Igeo)*

Spatial variations of Igeo calculated for each of the TMs are presented in **Figure 4**. For arsenic, the Igeo values were of (�13.87) for stations S2, S3, and S5, and 9.12 for station S1, respectively. The Igeo value was not determined at station S4 due to its concentration that was below the detection limit (**Figure 4a**).

The Igeo values for Cd were all negative (�9.58), except S4 with a value of 5.62 (**Figure 4b**). Regarding Fe, the Igeo values were all positive and varied from 4.11 to 9.43, except S1 with a negative Igeo value of (�1.76) (**Figure 4c**). For Hg, the Igeoobtained values were all negative with a common value of �0.75 (**Figure 4d**). The Igeo values for Mn were all negative and ranged from (�19.59) to (�8.58) (**Figure 4e**). For Pb, the Igeo values were 3.31 and 1.44 in S1 and S5 sediments, respectively, and a common and negative value (�14.64) in S2, S3, and S4 sediments (**Figure 4f**).

### **4. Discussion**

### **4.1 Trace metals distribution in Abobo-Doume sediments**

The arsenic concentration found in S1 sediments (1668.43 mg/kg, was more than 834 times higher than the Upper Continental Crust (UCC) value of 2.0 (**Table 4**). This high As content highlighted the presence of a potential source of arsenic located in the watersheds. For cadmium, only station S4 exhibited a concentration (7.5 mg/kg) higher than the UCC reference value of 0.102 mg/kg, so found

**Figure 3.**

*Spatial variation of the enrichment factor (EF) in sediments. (a): arsenic, (b): cadmium, (c): mercury, (d): manganese, and (e): lead.*

contaminated (**Tables 4** and **5**). Station S4 is located in front of the Abobo-Doume Fish Market. Therefore, socioeconomic activities linked to fisheries and domestic activities seem to be the major sources of cadmium in this area. Concentration ranges of 5.57–372.5 mg/kg [30], and 0.05–8.36 mg/kg [11] were reported in sediments collected in urban bays in the Ebrié Lagoon. These ranges of Cd concentrations were above the ones in ADFM area (**Table 5**). In addition, the average value of 1.5 mg/kg

### *Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems… DOI: http://dx.doi.org/10.5772/intechopen.110244*

observed for the whole study area was fairly above the reported World Average value of 1.4 mg/kg (**Table 5**) [16]. Iron concentrations values observed in the present study were in the range of 0.0–4900 mg/kg [30] and below those (18.1–104.14 mg/kg) reported for sediments collected elsewhere in the Ebrie Lagoon (**Table 5**) [31]. The maximum value of Fe observed in the present study was 12 times lower than the world average value of 57405.9 mg/kg [18]. The highest concentration of Fe observed in S4 sediments is linked to the corrosion of iron materials used by people working at the ADFM, such as fish-smoking materials. Mercury is one of the chemical that can have hazardous effects on marine organisms and finally on humans as these organisms' consumers. The observed Hg concentration was in the range of the Upper Continental Crust value of 0.056 mg/kg [29]. Thus, regarding the obtained results for this study, sediments along ADFMF were free of mercury (**Tables 4** and **5**). Mn is an essential element due to its biological benefits for both human and marine organisms [32]. As for iron and cadmium contents, the highest concentration of Mn in surface sediments was recorded at S4, the closest to the Abobo-Doume Fish Market (**Table 4**). Mn concentrations observed in sediments along the ADFM were below those of the range (18.28 to 281.0 mg/kg) reported by [11] on one hand, and, on the other hand than the world average value of 975.3 mg/kg and the Upper Continental Crust [29] one of 527.0 mg/kg (**Tables 4** and **5**).

Pb concentrations observed in S5 and S1 were found contaminated in Pb with contents four and fourteen times higher than the Upper Continental Crust value [29]. At S2, S3, and S4, Pb concentration was below the UCC value. Pb concentrations observed at S1 and S5 were higher than the concentrations reported by Ref. [31] in sediments collected in urban bays that are considered to be highly polluted with several organic and metallic compounds [31, 32]. The observed Pb contents were below the maximum value reported by Tuo et al. [11], and the average value for the study area (64.57 mg/kg) was lower than the world average concentration of Pb (**Tables 4** and **5**).

### **4.2 Pollution indices**

According to the contamination index (CI) value of 5.0 (**Table 6**), sediments collected in S1 (Restaurant) were contaminated in As, suggesting a source of As in the area. Regarding Cd, only sediments in S4 (Abobo-Doume Fish Market) were found to be contaminated with a CI value of 5.0. For Fe, the stations were in the following ascending rank of contamination: S1 < S2 < S3 < S5 < S4 (**Table 6**). The CI indices values highlighted the contamination in sediments from stations S3, S4, and S5. Sediments from stations S2 and S4 were safe regarding Hg. For Mn contents, sediments in S4 were the most contaminated, followed by those of S5S1 and S3, while S2 was found to be safe (**Table 6**). For Pb, sediments in S1 (Restaurant) were contaminated, followed by those in S5. Sediments from S2, S3, and S4 were safe regarding Pb contamination. In consideration of all of the six studied TMs through the mean contamination index (MCI), sediments in S1 (Restaurant) and S4 (Abobo-Doume Fish Market) were the most affected, followed by S5, S3, and S2 (**Table 6**). According to the MCI values, the Abobo-Doume Fish Market sediments were in the following descending rank of contamination: S1 > S4 > S5 > S3 > S2.

Considering the highest observed contamination factor (CF) value (834.22 > 40), sediments in S1 (Restaurant) were of an extremely high enrichment status (**Table 1** and **Figure 1a**). For S2 to S5, a deficiency to minimal enrichment occurred (**Table 1**

and **Figure 1a**). According to the determined CFs, sediments collected near the ADFM were extremely enriched with Cd, a toxic trace metal even at low concentrations in the environment (**Table 1** and **Figure 1b**), and the other stations were found to be safe for Cd contamination. CF values for Fe revealed an extremely high enrichment in S4, S5 and S3, sediments, a very high enrichment in S2 sediments and a deficiency to minimal enrichment for S1 (**Table 1** and **Figure 1c**). For Hg, all of the determined CF values were below 2.0, which suggests a deficiency to minimal enrichment of sediments for the present study, with a particular concern for stations S1, S3, and S5 (**Table 1** and **Figure 1d**). CF values observed for Mn were very low and close to zero. These CF values highlighted a minimal enrichment of the studied sediments with Mn (**Table 1** and **Figure 1e**). Considering the CFs for Pb, significant and moderate enrichments were respectively observed in sediments from S1 and S5 (**Table 1** and **Figure 1f**). The observed pollution load indices (PLI) observed in sediments for all of the samples were less than one. Therefore, according to the PLI criteria, no deterioration of sediment quality occurred during the present study (**Figure 2**).

The enrichment (EF) observed for As in S1 sediments suggests an extremely high enrichment, so potential source of As in this part of the lagoon banks (**Table 2** and **Figure 3a**). EF values for Cd observed were less than 2.0 and indicate that the sediments were of minimal enrichment status in the study area (**Table 2** and **Figure 3b**). For Hg, the EF values denote a deficiency to minimal enrichment, particularly for sediments in S1 (**Table 2** and **Figure 3c**). EF values for Mn were close to zero, indicating the absence of any excessive enrichment of sediments in Mn (**Table 2** and **Figure 3d**). For Pb, a high EF value was observed in sediments from S1 in relation with an extremely high enrichment (**Table 2** and **Figure 3e**). Due to the fact that Pb is a very toxic TM, there's a need regarding all of the potential sources of sediment contamination in the lagoon's banks around this sampling point (Restaurant).

Sediments in S1 exhibited a high Igeo value for As, which indicates extreme pollution of these sediments (**Table 3** and **Figure 4a**). According to Muller's [16] classification for geoaccumulation index, sediments collected at station S4 were in the extremely contaminated class, while those of S1, S2, S3, and S5 were unpolluted with the Cd (**Table 3** and **Figure 4b**). According to these observed Igeo values, the sediments were unpolluted with Fe at S1, from strongly to extremely polluted quality at S2, and extremely contaminated at S3 to S5 (**Table 3** and **Figure 4c**). For Hg, the exhibited Igeo values in the range of NC to (�0.75 < 0), indicate that the sediments along the ADFM were unpolluted with Hg (**Figure 4d**). The negative Igeo values for Mn indicated that the sediments were in the unpolluted range for all of the studied areas (**Table 3** and **Figure 4e**). The Igeo values of Igeo values observed for Pb indicate that sediments from S2, S3, and S4 were unpolluted regarding Pb (**Figure 4f**). However, sediments from station S1 (Igeo = 3.31) and S5 (Igeo = 1.44) were strongly and moderately polluted, respectively (**Figure 4f**).

Several pollution indices were used to assess the contamination level of surface sediments collected in Ebrié Lagoon along with the Abobo-Doume Fish Market (ADFM) (**Table 6** and **Figures 1**–**4**). The metallic contamination levels in sediments observed at the different sampling stations are summarized in **Table 7**. According to the Contamination Factor (CF) values, very high contamination of sediments was observed at all of the studied stations with arsenic, cadmium, iron, lead, and low contamination for the mercury contents (**Table 7**). All of the observed PLI values were below 1. Therefore, for the present study and considering the PLI observed values, the sediments collected at the five stations were found safe

*Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems… DOI: http://dx.doi.org/10.5772/intechopen.110244*

**Figure 4.**

*Spatial variation of Igeo values in Abobo-Doume fish market sediments. (a): arsenic, (b): cadmium, (c): iron, (d): mercury, (e): manganese, and (f): lead.*

regarding metallic contamination (**Figure 2** and **Table 7**). At station S1, the EF values highlighted extremely high and very high enrichments of sediments in As and Pb, respectively. A moderate enrichment in Hg was observed in sediments from station S1 (**Table 7**). For station S2, the sediments were safe in trace metals regarding the observed EF values. A deficiency to minimal enrichment levels in Hg


### **Table 7.**

*Contamination levels according to the selected contamination indices in sediments from the different sampling stations.*

and Cd were observed at stations S3 and S4, respectively. Sediments from station S5 were of deficiency to minimal enrichment levels in mercury and lead (**Table 7**). According to the Igeo values, sediments from station S1 were of bad quality due to their respective extremely and strongly polluted levels in As and Pb (**Table 7**). Sediments from stations S2 to S5 were of strong to extreme pollution levels regarding the Igeo values for Fe. Otherwise, extreme pollution of sediments from station S4 was observed, while moderate pollution in Pb occurred in sediments collected at station S5. The PLI values do not take into account the real state of sediment contamination with each of the studied trace metals taken individually. This parameter is rather useful when it is used for the classification of several sampling stations. Indeed, by considering this PLI parameter alone, one would be tempted to believe that the sediments studied were safe despite the high contents of As, Pb, and Cd observed at several stations.

With regard to Hg, a very toxic element and without any biological positive effect, its presence in sediments is already alarming. Indeed, the contamination of sediments by mercury as well as arsenic, lead, and cadmium could have serious consequences on the survival of benthic organisms on one hand, and on the quality of the fishery resources of this part of the Ebrie Lagoon, on the other hand, the other pollution indices seem to better reflect the levels of contamination of the chemical elements taken individually. For the present study, the contamination factor (CF) seems to be the one that takes into account the low levels of concentrations for the determination of the sediments quality. Indeed, among the calculated pollution indices, it was the one that took into account the presence of mercury, even at a low concentration.

*Use of Several Pollution Indices for Metal Contamination Assessment in Aquatic Ecosystems… DOI: http://dx.doi.org/10.5772/intechopen.110244*
