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River sediments are known to contain natural radionuclides, the concentrations of which if beyond certain limits can cause adverse health effects. The sediments from Ogun river provide large quantities of sand for construction purposes in Nigeria. Despite this, data are scarce on the natural radionuclides: 40K, 226Ra and 232Th distribution in the river sediments.

The measurement of radioactivity of Ogun river sediment from the source in Oyo state around Ago Fulani through Ogun state, down to the sink in Lagos Lagoon was designed

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to establish the trends of the distribution of radionuclides through the measurement of the concentrations of these natural radionuclides in the river sediments and to establish the current status of the radiological implications of that environment. The assessment involves the measurement of radiation dose equivalents for reasons related to the radioactivity in the sediments of the river since sediments are derived from weathering and erosion of rocks and soil, these sediments contain certain concentrations of naturally occurring radionuclides which will depend on the concentrations of such radionuclides in rocks and soil of their origin. Human and industrial activities around the river may also increase the level of radioactivity in the sediments. The three states through which the river passes, are heavily industrialised cities: Lagos and Sango – Ota (Ogun state) for instance, about six major industries including Vitabiotics, Nestle, Glaxos, Smith kline, Sona Breweries and Nigerian German chemicals discharge their wastes into the river. The aim of this work is to investigate the extent of radioactive pollution in the river, if any, and to assess if sediment materials obtained from this river used for the construction of dwellings are radiologically safe. The aim is achieved through the following objectives:

i. To investigate and interpret the distribution of radionuclides in the sediments along Ogun river course.

ii. To provide a baseline data on the distribution of natural radionuclides in sediments from Ogun river.

iii. To investigate if there are obvious/significant variations in the radionuclides‘

concentrations due to different locations based on economic activities.

iv. To evaluate the environmental gamma dose rates and other radiation hazard indices for determining the health implications through the use of the sediments from the river for construction purposes.

v. To determine the excess lifetime cancer risk associated with the use of the sediments as building material.

vi. To carry out geotechnical study of the sediments.

vii. To determine the distribution of basic mineral composition and heavy minerals (opaque and non- opaque) in the river sediments.

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LITERATURE REVIEW 2.1 Radioactivity in River Sediments

A river is a natural watercourse usually freshwater, flowing toward an ocean, a lake, a sea or another river. In few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be termed by several other names, including stream, creek and brook. In the United States a river is generally classified as a watercourse more than 18 metres wide. The water in a river is usually in a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. Rivers are a part of the hydrological cycle. Water within a river is generally collected from precipitation through surface runoff, groundwater recharge, springs, and the release of water stored in glaciers and snowpacks (Marriam, 2010).

Rivers are of immense importance geologically, biologically, historically and culturally although they contain only about 0.0001% of the total amount of water in the world at any time. They are vital carriers of water and nutrients to areas around the earth (Murugesan, 2004). They are crucial components of the hydrological cycle, acting as drainage channels for surface water. The world‘s rivers drain nearly 75% of the earth‘s land surface (Iwena, 2000). Rivers play vital roles in the provision of habitat, nurishments and means of transport to many organisms, travel routes for exploration, recreation and even commerce, importantly they leave valuable deposits of sediments, such as gravel and sand, even forming floodplains where many cities were built (Murugesan, 2004).

Sediments are particles of organic or inorganic matter that accumulate in a loose, unconsolidated form that settles at the bottom of water bodies as a result of the erosive force of water‘s contact with rock, soil and plant materials (Thompson, 2007). There are two primary sources for particles accumulating as sediments today, the detrital sediments – originated and are transported as solid particles derived from weathering of the land accumulations and the other is known as the chemical sediments originating from the dissolved materials derived from weathering which are precipitated from water streams, lakes, or the ocean accumulations (Murugesan, 2004; Oyebanjo, 2010).

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Radioactivity in river sediments originates from the near surface, from exposed igneous, volcanic and sedimentary rocks. Some of these rocks are easily eroded and others most especially the crystalline and the metamorphic rocks are affected by streams only when altered in the surface layers, (Joshua and Oyebanjo, 2010). Radionuclides have an affinity for silts and clays in the soils. These soils and attached radionuclides are subject to sheet erosion and transport into streams and rivers, the fine sediments are most representative of the sediment transport of radionuclides (Purtymun et al., 1980). In spite of the low concentrations in the aquatic environment, the aquatic behaviour of radionuclides plays an important role in the ecosystem, since water is crucial to life and it is one of the prime agents that help to move and distribute elements on the earth (Khan et al., 2003; Isikaye, 2009).

Distribution of sediments is determined by climate (temperature), environmental factors (nutrients, possible chemical reactions, activity of physical environment) supply, size and rate of accumulation (Thompson, 2007). Resources from sediments are sand and gravel for construction, phosphorite for fertilizers, sulphur for sulphuric acid for industry, coal for energy, oil and gas for energy and transportation. Manganese nodules for Mn, Fe, Co, Cu and Ni, etc (Thompson, 2007).

Sand whether found on beaches or in rivers and streams, is mostly quartz grain (Ramasamy et al., 2010). The weathering of rocks such as granites form the quartz grain, grains of other weather-resistant minerals too are found in quartz sand as well. The use of sand and gravel are of two categories, some are used in construction where it may be mixed with other materials or used as it is. The second use is the industrial use, where the sand and gravel are used in some way in the production of other materials (Murugesan, 2004).

Along with industrial development of the world, water reservoirs, such as soil become, although in considerably smaller degree, the place of accumulation of different kind of contaminants. Introduction of organic, inorganic, and radioactive substances produces dramatic, often irreversible changes of physicochemical and biological properties of these reservoirs. The geochemical composition of sediments, gathering on the bottom of rivers and water reservoirs is a very good indicator of quality of surface waters and the presence of contaminants (Jan et al., 2006).

Although soil has always been important to humans and their health, it is also providing a resource that can be used for shelter and food production. Through ingestion, inhalation and

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dermal absorption, the mineral, chemical and biological components of soil can be directly detrimental to human health. Example of such effect to human is cancers caused by the inhalation of fibrous or radon gas derived from the radioactive decay of uranium in soil minerals (Abdulkareem, 2009). The knowledge of uranium concentration in sediments and soils is important not only to assess the contamination level but also to understand the transference processes which have occurrence at different trophic levels of the feed chain (Ricardo et al., 2009). Dim et al., (2000) determined the uranium – thoriun levels of the Kubanni river sediments in the Northern Nigerian Basement Complex and was observed to be enriched with mean values of 9.06 and 21.44 (ppm) respectively. The high geochemical mobility of radionuclides in the environments allows them to move easily and to contaminate mainly the environment with which human come in contact. Uranium -238, in particular is easily mobilized in ground water and surface water. As a result, uranium and its decay product enter the food chain through irrigation water, and enter the water supply through ground water, well and surface water streams and rivers (Otton, 1994). Igneous rock like granite has high concentration of uranium. Also the solubility of 232Th in natural water such as river is detected in high concentration in sediments and deposits (Arogunjo, 1994).

Moreover, 232Th and 238U are more abundant in sedimentary rocks than in igneous and metamorphosed sediments (Egunyinka et al., 2009). Kullab et al., (2006) determined the concentrations of some naturally occurring radioisotopes in sediments of the Kufranja river basin in Jordan, by means of γ-ray spectrometry and found that the natural radioactivity level of river sediment could be affected by the natural radionuclides concentration in soil and rock, since most of the sediments that settle in river are silts and sands derived from weathering and erosion of rock and soil. Oni et al., (2011), measured the natural radioactivity level in the coastal areas of Nigeria by gamma counting of river sediment samples and results showed that the radioactivity concentrations of 40K, 226Ra and 228Ra in the sediment samples of oil producing areas were 122.39 ± 47.49; 18.93 ± 12.53 and 29.31 ± 18.67 Bq /kg respectively, in the sediment samples from the non oil producing areas, the respective mean values were 88.48 ± 8.22, 14.87 ± 3.51 and 16.37 ± 3.87 Bq /kg respectively. The concentrations of natural radionuclides: ⁴⁰K, 238U and 232Th in the sediment of rivers and streams in the Northern part of Ibadan City, Nigeria was examined by Fasewa (2007) and the mean radioactivity concentrations obtained were (0.0564 ± 0.0056), (0.0128 ± 0.0017) and

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(0.0175 ± 0.0037) kBq/kg respectively. Some other researchers from different countries in the world had also carried out different works on the measurement of activity concentrations of naturally occurring radionuclides in sediments, few of such works are presented in Table 2.1. Human activities such as application of phosphate fertilizer in surrounding farmlands and the discharge of both industrial and domestic waste into rivers and stream may also increase the radioactivity levels in water sediments (Isinkaye, 2009). Considerable amounts of natural radionuclides can be found in river sediments as the end result of fertilizer washing and industrial activities (Krmar et al., 2009; Ramasamy et al., 2009). The environmental uranium and partial thorium concentrations are increased due to the fertilizers. Usually fertilizers are considered to technologically enhance natural radiation (El Gamal et al., 2007).

The presence of radionuclides in phosphatic fertilizers have been reported by several studies (Guimond and Hardin, 1989; Khan et al., 1998; Zielinski, et al., 2000; San Miguel et al., 2003; Becegato et al., 2008).

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Table 2.1: Activity concentrations (Bq/kg) of naturally occurring radionuclides obtained by researchers from different parts the world

S/N Country 40K 226Ra 232Th References

1 India (Kali river) 296.0 - 525.0 (394.7) 34.1 - 49.4 (40.1)** 4.6 - 12.2 (6.9)

Narayana et al., (2007) 2

Bangladeshi (Shango

River) 212- 292 (255) 21.6 - 28.3 (25.4)** 52.4 - 61.7 (57.5)

Chowdhurry et al., (2009)

3 Algeria (Algiers Bay) 56 - 607 (374)

4.45 - 25.04

(15.8)** 6.5 - 31.7 (19.5)

Benemar et al., (1997) 4 China (Wei River)

514.8 - 1175.5

(833.3) 10.4 - 39.9 (21.8) 15.3 - 54.8 (33.1) Xinwei et al., (2008) 5 Egypt (Eastern Desert) 298.6 – 955.8 9.7 – 19.0 10.0 – 17.7 Harb, (2008) 6 Egypt, Wadi Nugrus, 306.7 -626.0

24.7 - 86.45 (43.91)**

20.3 - 48.72

(26.62) Abdel-Razek(2008)

7 Turkey 155.7 -868.7 26.8 - 49.8 ** 17.06 - 35.62

Kam and Bozkurt (2007)

8 Bengal 118 - 608 5.9 - 27.9 10.4 - 64.0 Alam et., (1997)

9 Pakistan (647.4) (32.9) (53.6)

Matiullah et al., (2004)

** = 238U, ( ) = mean concentration

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