Project – Spatial Distribution of Microplastics and Selected Water-Quality Indicators in Urban Surface Waters: A Comparative Assessment of Selected Water Bodies in Ogun State.

CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

The increasing presence of plastic materials in the environment has become a major environmental concern because of their persistence, widespread use and gradual fragmentation into smaller particles. Plastics are used extensively in packaging, household materials, textiles, construction, agriculture and other commercial activities. However, inadequate waste collection, indiscriminate disposal, open dumping and poor drainage management contribute to the movement of plastic waste into rivers, streams, ponds and other surface-water environments. Through exposure to sunlight, physical abrasion, temperature changes and other environmental processes, larger plastic materials gradually break down into smaller particles known as microplastics. Microplastics are commonly defined as plastic particles smaller than five millimetres, although their shapes, polymer composition and physical characteristics vary considerably. Their small size and persistence make them difficult to remove from aquatic environments once released (Andrady, 2011; GESAMP, 2015).

Microplastics have attracted growing scientific attention because they can occur in different aquatic environments and interact with organisms, sediments and other pollutants. They may enter water bodies directly as small particles from industrial and domestic sources or indirectly through the breakdown of larger plastic waste. Common sources include synthetic textile fibres, deteriorating plastic packaging, personal-care products, tyre wear, industrial activities and poorly managed municipal waste. Rainfall runoff, erosion, drainage channels and wastewater discharge can transport these particles from urban settlements into nearby surface waters. Their distribution is influenced by factors such as water movement, rainfall, land use, particle density, shape and the characteristics of the receiving water body. Consequently, microplastic contamination is not necessarily uniform across different locations, even within the same geographical area (Hidalgo-Ruz et al., 2012; Horton et al., 2017).

The occurrence of microplastics in surface water is also important because aquatic environments receive several forms of domestic, commercial, agricultural and industrial waste. Rivers, streams, reservoirs and ponds may function as pathways through which plastic particles move across different parts of a watershed. Some particles remain suspended in the water column, while others settle into bottom sediments or are transported downstream. Their distribution may therefore vary according to the physical characteristics of each water body, including flow rate, depth, sediment composition and surrounding land-use activities. Research has established that microplastics are widely distributed in freshwater systems and that rivers can serve as important pathways through which plastic debris is transported from land-based sources into larger aquatic environments (Eerkes-Medrano, Thompson, & Aldridge, 2015; Wagner et al., 2014).

Beyond their physical presence, microplastics may have implications for aquatic organisms and the ecological condition of surface waters. Small aquatic organisms may mistake microplastic particles for food and ingest them, potentially exposing them to physical stress and associated chemical substances. Microplastics can also interact with other contaminants in the aquatic environment, although the extent and significance of these interactions depend on the polymer type, particle characteristics, surrounding water chemistry and environmental conditions. Their presence may therefore indicate weaknesses in plastic-waste management and provide useful information for assessing the environmental pressures affecting aquatic ecosystems. However, the detection of microplastics alone does not automatically establish that a water body is unsafe for human consumption; such conclusions require appropriate assessment of exposure, contaminant levels and relevant water-quality standards (Wright, Thompson, & Galloway, 2013; Koelmans et al., 2019).

Water quality is an important measure of the physical, chemical and biological condition of water and its suitability for particular uses. In surface-water environments, selected indicators such as pH, temperature, electrical conductivity, turbidity, dissolved oxygen, biochemical oxygen demand and total dissolved solids provide information about environmental conditions and possible pollution pressures. These parameters are important because changes in them may reflect the influence of domestic wastewater, industrial effluents, agricultural runoff, organic matter and other pollutants entering a water body. For instance, high turbidity may indicate the presence of suspended materials, while dissolved oxygen levels provide information about the oxygen available to aquatic organisms. The interpretation of these indicators is strengthened when they are assessed together rather than in isolation, because water quality is influenced by several interacting physical, chemical and biological processes (Chapman, 1996; APHA, AWWA, & WEF, 2017).

The relationship between microplastic distribution and conventional water-quality indicators is an important area of environmental investigation. Although microplastics are physical contaminants and are not themselves conventional water-quality parameters, their occurrence may be associated with environmental conditions that also influence other indicators. For example, urban runoff and wastewater discharge may introduce microplastics alongside suspended solids, organic matter and dissolved substances. The concentration and distribution of particles may also be affected by water movement, turbidity, conductivity and other site-specific conditions. Nevertheless, the relationship between microplastics and individual water-quality parameters should be established through field measurements and laboratory analysis rather than assumed. Comparative studies can therefore help determine whether variations in microplastic abundance and characteristics correspond with differences in selected water-quality indicators across different water bodies (Eerkes-Medrano et al., 2015; Koelmans et al., 2019).

In Nigeria, the management of plastic waste presents an important environmental challenge, particularly in rapidly urbanising areas where population growth, commercial activities and inadequate waste-disposal infrastructure place pressure on drainage systems and surface-water environments. Plastic materials discarded on roadsides, open spaces, markets and drainage channels may be washed into nearby streams and rivers during rainfall. The situation is relevant to Ogun State because the state contains urban and semi-urban settlements, industrial and commercial activities, agricultural areas and different surface-water resources that may experience varying degrees of human influence. Studies of plastic pollution in Nigerian aquatic environments have drawn attention to the need for improved monitoring, waste management and environmental protection. However, understanding the extent of microplastic contamination requires location-specific sampling and laboratory-based investigation rather than relying solely on general observations of plastic waste (Ogunola, Onada, & Falaye, 2018; Auta, Emenike, & Fauziah, 2017).

Ogun State provides a relevant setting for examining the spatial distribution of microplastics and selected water-quality indicators because its water bodies are situated within environments that differ in settlement patterns, land use and human activities. Surface waters located near densely populated communities, markets, roads, industrial facilities or agricultural areas may experience different pollution pressures from those situated in less intensively developed locations. These differences may influence the abundance and characteristics of microplastics as well as the measured physical and chemical properties of the water. A comparative assessment of selected water bodies in Ogun State is therefore necessary to establish the occurrence and spatial variation of microplastics, determine the condition of selected water-quality indicators and examine possible relationships between the two sets of environmental variables. The findings can provide baseline information for environmental monitoring, pollution-control planning and sustainable management of surface-water resources in the state.

1.2 Statement of the Problem

The increasing use and improper disposal of plastic materials have created environmental challenges for aquatic ecosystems, particularly in areas where waste collection and disposal systems are inadequate. Plastic materials discarded on land may be transported by rainfall runoff and drainage channels into rivers, streams and other surface-water bodies. Over time, these materials may fragment into microplastics, which are difficult to detect through ordinary visual inspection and may remain in aquatic environments. Although plastic pollution is widely recognised as an environmental problem, the presence and distribution of microplastics in individual freshwater systems cannot be accurately established without systematic sampling and laboratory analysis (GESAMP, 2015; Li, Liu, & Chen, 2018).

In Ogun State, differences in population density, settlement development, commercial activities, agricultural practices and waste-disposal conditions may expose surface-water bodies to varying levels of pollution. Water bodies located close to urban settlements and drainage channels may receive plastic particles and other contaminants from domestic and commercial activities, while those in less developed environments may experience different pollution pressures. A recent study by Shokunbi, Makanju, Nneoma, and Shokunbi (2025) investigated microplastics in raw water, treated water and tap water in a semi-urban area of Ogun State, demonstrating that microplastic occurrence is a relevant local environmental concern. However, evidence from drinking-water sources and distribution systems does not automatically establish the spatial distribution of microplastics in different natural surface-water bodies across the state.

Another problem concerns the limited understanding of how microplastic occurrence relates to conventional water-quality conditions in the selected water bodies. Surface waters may contain microplastics alongside suspended solids, organic matter and dissolved substances introduced through runoff, wastewater discharge and other human activities. However, the relationship between microplastic abundance and indicators such as pH, temperature, electrical conductivity, turbidity, dissolved oxygen and total dissolved solids may differ from one location to another. Without collecting and analysing microplastic data alongside selected water-quality measurements, it may be difficult to determine whether differences in particle abundance correspond with variations in the physical and chemical characteristics of the water. This limits the availability of integrated environmental information needed for effective water-quality monitoring (Eerkes-Medrano et al., 2015; Li et al., 2018).

Furthermore, the absence of comparative, location-specific information can limit the ability of environmental authorities, researchers and other stakeholders to identify water bodies that may require closer monitoring or improved pollution-control measures. A study that examines only general plastic pollution may not reveal the concentration, shape, size distribution and spatial variation of microplastic particles in individual water bodies. Similarly, measuring conventional water-quality indicators without examining microplastics may overlook an emerging category of aquatic contamination. It is against this background that this study seeks to assess the spatial distribution of microplastics and selected water-quality indicators in selected surface-water bodies in Ogun State. The study will provide comparative evidence on microplastic abundance and characteristics, variations in selected water-quality parameters and the possible relationships between them, thereby contributing to environmental monitoring and the management of surface-water resources in the state.

1.3 Objectives of the Study

The main objective of this study is to assess the spatial distribution of microplastics and selected water-quality indicators in selected surface-water bodies in Ogun State.

The specific objectives are to:

1. Determine the abundance and concentration of microplastics in selected surface-water bodies in Ogun State.

2. Examine the physical characteristics of identified microplastics, including their size, shape and colour.

3. Assess selected water-quality indicators, including pH, temperature, electrical conductivity, turbidity, dissolved oxygen and total dissolved solids, in the selected water bodies.

4. Compare the spatial distribution of microplastics across the selected water bodies and examine their relationship with the selected water-quality indicators.

1.4 Research Questions

The following research questions will guide the study:

1. What is the abundance and concentration of microplastics in the selected surface-water bodies in Ogun State?

2. What are the physical characteristics of identified microplastics in terms of size, shape and colour?

3. What are the levels of selected water-quality indicators in the selected surface-water bodies?

4. How does the spatial distribution of microplastics vary across the selected water bodies, and what relationship exists between microplastic abundance and selected water-quality indicators?

1.5 Research Hypothesis

The following null hypothesis will be tested at a 0.05 level of significance:

H₀: There is no statistically significant relationship between microplastic abundance and selected water-quality indicators in the selected surface-water bodies in Ogun State.

1.6 Significance of the Study

This study will be significant to environmental scientists and researchers because it will provide information on the occurrence, abundance and physical characteristics of microplastics in selected surface-water bodies in Ogun State. The findings will contribute to existing knowledge of freshwater microplastic pollution, particularly in an area where more location-specific research is needed. The study may also provide baseline information for subsequent investigations into the sources, movement and environmental implications of microplastics in freshwater ecosystems.

The study will be useful to environmental management agencies, particularly those responsible for water-resource protection, pollution control and environmental monitoring. Information on the spatial distribution of microplastics and selected water-quality indicators may assist these agencies in identifying locations that require closer environmental observation. The findings may also support the development of appropriate monitoring programmes and strategies for reducing the entry of plastic waste into surface-water environments.

The findings will also benefit government authorities and policymakers in Ogun State by providing scientific information that can support environmental planning and waste-management policies. Evidence of microplastic occurrence in selected water bodies may strengthen the need for improved plastic-waste collection, responsible disposal practices, public environmental awareness and effective management of drainage systems. The study may also contribute to policy discussions on the protection of freshwater resources from emerging contaminants.

Local communities and residents who depend on surface-water resources for domestic, agricultural, recreational and other purposes may benefit from the information generated by the study. Although the detection of microplastics does not independently establish that water is unsafe for consumption, the findings may increase public awareness of emerging aquatic pollutants and the importance of protecting water bodies from indiscriminate waste disposal.

Finally, the study will serve as a reference material for students and future researchers in environmental science, aquatic ecology, environmental management, chemistry and related disciplines. It may provide a foundation for further studies involving seasonal variations, polymer identification, sediment contamination, aquatic organisms and the possible environmental effects of microplastics in Ogun State.

1.7 Scope of the Study

The study will focus on the spatial distribution of microplastics and selected water-quality indicators in selected surface-water bodies in Ogun State, Nigeria. It will involve the collection of water samples from predetermined sampling locations within the selected water bodies. The selection of sampling locations will consider differences in surrounding land use, human activities, accessibility and possible sources of pollution.

The study will examine the abundance and concentration of microplastics in the collected water samples. It will also investigate their physical characteristics, particularly particle size, shape and colour. Where laboratory facilities permit, polymer identification may be carried out using appropriate analytical techniques such as Fourier-transform infrared spectroscopy (FTIR).

The selected water-quality indicators will include pH, temperature, electrical conductivity, turbidity, dissolved oxygen and total dissolved solids. These parameters will be measured using appropriate field and laboratory procedures. The results will be compared across the selected water bodies to determine spatial variations and examine possible relationships between microplastic abundance and the measured water-quality indicators.

The study will be limited to selected surface-water bodies and sampling locations in Ogun State. It will not cover all rivers, streams, reservoirs and other water bodies in the state. It will also not constitute a comprehensive assessment of all possible chemical pollutants or establish the health effects of microplastic exposure on humans.

1.8 Operational Definition of Terms

Microplastics: Small plastic particles measuring less than five millimetres in size that may occur in aquatic environments as a result of direct release or the fragmentation of larger plastic materials.

Spatial Distribution: The pattern of occurrence and variation of microplastic particles across different geographical locations or sampling points within the selected surface-water bodies.

Microplastic Abundance: The number of microplastic particles identified in a given volume of water, commonly expressed as particles per litre (particles/L).

Surface Water: Water occurring naturally on the Earth’s surface, including rivers, streams, lakes, ponds and reservoirs.

Water Quality: The physical, chemical and biological characteristics of water that determine its environmental condition and suitability for different uses.

Water-Quality Indicators: Measurable physical and chemical parameters used to assess the condition of water, including pH, temperature, electrical conductivity, turbidity, dissolved oxygen and total dissolved solids.

pH: A measure of the acidity or alkalinity of water.

Electrical Conductivity: A measure of the ability of water to conduct electrical current, which is influenced by the concentration of dissolved ions.

Turbidity: The degree of cloudiness or reduced transparency of water caused by suspended particles and other materials.

Dissolved Oxygen: The amount of oxygen dissolved in water and available to aquatic organisms.

Total Dissolved Solids (TDS): The total concentration of dissolved substances, including minerals, salts and other inorganic and organic materials, present in water.

Comparative Assessment: The systematic examination of differences and similarities in microplastic abundance, physical characteristics and water-quality indicators among the selected water bodies.

Sampling Location: A predetermined geographical point within a selected water body where water samples are collected for analysis.

Project – Spatial Distribution of Microplastics and Selected Water-Quality Indicators in Urban Surface Waters: A Comparative Assessment of Selected Water Bodies in Ogun State.