**4.3 Organic pollutant pollution**

PAH concentration in the surface sediment from Ramisi, Sabaki, and Tana rivers was in the range of BDL-0.16, 0.06–7.98, and 0.78–13.20 ng/g, respectively. Higher concentration of PAH in Tana river could be as a result of rapid urbanization, industrialization, gasoline or diesel fuel from fishing boats, and high erosion activities in their catchment areas. The concentrations were, however, lower compared to those reported by Chen and coworkers [58] who recorded concentration ranges of 362.00–15, 667.00 ng/g (dw) for Weihe river, a river draining arid and semiarid regions as Tana river.

The surveyed sites in Lamu, namely, Wange Fish Port, proposed Lamu Port, and Mokowe Fish port, had PAH concentration of less than 10.00 ng/g (dw). This is because the port is still under construction and un-operational. The PAH levels were lower than the levels observed in Kilindini port (range: <50.00–37,800.00 ng/g dw) with a mean concentration of 6086.00 ng/g dw. The PAH level in Kilindini was, however, higher than levels reported by Saleem et al. [59, 53] in Karachi harbor (mean: 27.52 ng/g dw) and [54, 60] in Kaohsiung harbor, Taiwan (range: 472.00– 16,201.00 ng/g; mean 5764.00 ng/g). High level of PAH was observed in Kilindini due leakage of combusted and un-combusted fuel from intense shipping activities, oil spills experienced in Makupa creeks, and oil terminal activities in Kilindini


**Table 1.**  *Decadal comparison of trace metals of the Kenyan coastal sediment with the set international standards for sediment quality.* 

#### *Decadal Pollution Assessment and Monitoring along the Kenya Coast DOI: http://dx.doi.org/10.5772/intechopen.82606*

port as well as ferry services. This port serves many shipping vessels involved in cargo importation for Kenya as well as the landlocked countries in East Africa. The total OCPs namely HCN, Heptachlor, Hepoxide, 2,4′ DDE, Cis chlordane, Trans Nonachlor, 4,4'DDE, 2,4' DDD, 4,4' DDD, 2,4′ DDT, 4,4′ DDT, and Mirex in sediments from Ramisi, Sabaki, and Tana estuarine areas ranged between ND-0.13, 0.37–1.81, and 0.03–3.94 ng/g respectively. The concentration of OCP reported by this study (range: 0.03–3.94 ng/g) was lower compared to the levels reported for Tana estuary by Lalah et al. [61, 55] (range: <0.003–108.51 ng/g). This confirms the reduction in utilization of the products containing OCPs in Kenya.

 The DDT and its metabolites 2,4′ DDE, 4,4′ DDE, 2,4' DDD, 4,4' DDD, 2,4′ DDT, and 4,4′ DDT were detected in the surface sediment in both Sabaki and Tana river estuaries. The highest concentrations of ∑6 DDTs were recorded in Tana river (11.57 ng/g dw) compared to Sabaki (2.34 ng/g dw) and Ramisi (0.23 ng/g dw). This suggests that even though DDT was banned in Kenya in 1986, there could still be illegal use of DDT in Kenya [56].

 The DDE-to-DDD ratio for Ramisi, Sabaki, and Tana river estuaries were 0.20, 0.16, and 0.17 respectively, suggesting an aerobic degradation of DDT to DDD in the areas via dehydrochlorination and oxidation processes [18, 62]. The study revealed high ratios (above 0.5) for Ramisi (3.38), Sabaki (2.82), and Tana rivers (2.10), indicating a historical input of DDT into the estuaries. The historical input of DDT into marine environment has similarly been reported by Aly Salem et al. [63] for Egyptian Mediterranean Coast, as well as Lu et al. [28] for Poyang Lake, China. This shows the reduced application of DDT in some part of the world.

 High concentration of PCBs was observed in River Tana estuary (range: 4.94–7.99 ng/g dw) compared to concentration in Ramisi (ND-0.15 ng/g dw) and Sabaki (0.58–2.40 ng/g dw) which could be attributed to leakage or inadvertent disposal of materials used in transformers and capacitors along the Tana river channel since Tana river holds the Seven Folks hydropower dams which generate approximately 49% of Kenyan electricity.

### **4.4 Ecological risk assessment of pollution along the Kenyan Coast**

 According to [64], some of the estuaries and peri-urban stations (Mwena, Ramisi, Sabaki, Umba, Lamu, Kibuyuni, Sii Island, and Makupa) could be classified as eutrophic given that they have phosphates levels >0.021 mg/L whereas Shimoni and Gazi could be classified as oligotrophic. Trace metal concentrations in estuaries (River Sabaki and Tana mouth) except for Pb and Cr (**Table 1**) in the sediments were below the effect range-low (ER-L)/effect range-median (ER-M). This indicates that high concentration may pose adverse effects [65].

Sediment quality criteria and concentration ranges of PAHs, PCBs, and DDT contaminants are summarized in (**Table 2**). The ∑PAHs, ∑PCBs, and ∑DDT concentration in sediment from Ramisi, Sabaki, and Kilindini were below ER-L and ER-M suggesting the low ecological risk of these compounds to sediment-dwelling


**Table 2.** 

*Comparison of PAH, DDT, and PCB (ng/g dw) concentrations in sediments of the study area with the sediment quality guidelines (SQG).* 

 organisms. However, the concentration level of ∑DDT was higher than ER-L in Tana estuary but was significantly lower than the ER-M values suggesting that the accumulated DDT in sediments in Tana estuary could have a potential ecotoxicological impact on the benthic fauna.
