**1. Introduction**

Kenya is experiencing an increase in human population, urbanization, and industrialization which is characterized by massive utilization of natural resources coupled with an increase in waste production [1]. UNEP GEF-funded WIOLaB project identified that over 70% of pollutants entering marine and coastal ecosystems originate from the land [2]. Many pollutants from these land-based sources (such as sewage, oil hydrocarbons, sediments, nutrients, pesticides, litter, and plastics and toxic wastes) enter the sea via rivers and surface runoff [3]. For instance, sewage is still being indiscriminately discharged into peri-urban creeks of Mombasa [4].

Kenya's coastal waters are thus continuously enriched with large amounts of nutrients, particularly nitrogen (N) and phosphorus (P), silica (Si) and sulfur (S) from anthropogenic activities and wastewater from households and industries [4] despite the fact that effluent pollution had been identified as the most serious of all land-based threats to the marine environment and an area which requires more attention [5]. Excessive nutrient enrichment results in nutrient pollution and eutrophication with severe economic, environmental, and ecological implications to the marine environment due to the shift in the Redfield ratio [6]. Some of the impacts of nutrient enrichment include increased abundance and biomass of phytoplankton and macroalgae [7]; reduced light penetration; increased development of hypoxic, anoxic, and dead zones [8, 9]; changes in phytoplankton community structure and alteration of food chains and webs [10]; development of harmful algal blooms that may produce substances toxic to aquatic organisms or humans [11]; dieback of seagrasses, algal beds, and corals [12, 13]; loss of biodiversity; and increased incidences and duration of harmful algal blooms [14].

The other class of contaminants that are discharged through sewage, surface runoff, and industrial discharge includes heavy metals and persistent organic pollutants (POPs). Trace metals such as lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), mercury (Hg), arsenic (As), and zinc (Zn) are not easily degraded in the natural environment and are bioaccumulated along the food chain [15]. They are also known to affect productivity, reproduction, and survival of marine organisms and can be hazardous to human health at elevated concentrations [15].

Persistent contamination of organic pollutants (POPs), such as organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) in the aquatic environment is a worldwide problem [16]. The anthropogenic input of these POPs in the Indian Ocean includes industrial and sewage effluents, storm water drains, shipping activities, spillage, rivers, atmospheric fallout, coastal activities, and natural oil seeps. For instance, these compounds have been used extensively in Kenya for various applications in industries and agriculture [17]. They are characterized by long-term stability (not easily degradable in the environment and can persist in sediments for decades or even centuries), bioaccumulative nature, long-range transport capability, and may have high toxic effects on aquatic living organisms [18, 19]. These chemicals have since been replaced with organophosphate and carbamate, which are less persistent in the environment under the Stockholm Convention on Persistent Organic Pollutants [20, 21]. However, their residues are still present in the marine environment.

Among the natural radionuclides, alpha emitters (e.g. 210Po) have been reported to have significant radiological effects resulting from their accumulation in organisms [22]. 210Po is a naturally occurring radioactive material (NORM) alpha-emitter occurring in very low concentrations in the environment as a part of the uranium decay chain. 210Po has a radioactive half-life of 138.4 days and is produced in the marine environment from the decay of 210Pb (which is a daughter isotope derived from 226Ra dissolved in seawater). 210Pb can also be introduced into marine environment directly from the atmosphere from the decay of 222Rn [22, 23]. It is ubiquitously distributed in rocks, soils, making up earth's crust, in the atmosphere and in natural waters [24]. It can also be derived in insignificant quantities from lead-containing wastes from uranium, vanadium, and radium refining operations [25]. The activity of 210Po in the environment has increased in the past due to human activity such as fossil fuel combustion, use of phosphate fertilizers in agriculture, and discharge of domestic and industrial sewage.

UNEP-GEF WIO-LaB Project identified municipal and industrial effluents, contaminated surface runoff including groundwater and agricultural runoff [2] as the major sources of land-based pollution and microbial contamination, suspended solids, chemical pollution, marine litter (including debris), and eutrophication

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

(harmful/nuisance algal blooms) as priority pollution categories in the WIO region. In Kenya, limited action has been taken to control or manage pollution. For instance, only a couple of studies have been carried out to determine long-term pollution status or their impacts on marine and coastal ecosystems and the potential human health.

During the assessment and monitoring program, water matrix was analyzed for nutrient pollution whereas sediments were analyzed for trace metals, radionuclides, and POP contamination. Sediment was the preferred matrix for persistent pollutants given that it a known sink and an archive of pollutants brought into the aquatic environment from direct discharges, surface runoff, atmospheric fallout, and nonpoint source [19, 26, 27]. The distribution of these contaminants in sediments can serve as a useful index of pollution and potential environmental risks [17, 28].
