Biochemical Assessment of Fish from Polluted Creeks in Rivers State: Heavy Metals, Antioxidant Enzyme Activities, and Human Health Risk

Biochemical Assessment of Fish from Polluted Creeks in Rivers State: Heavy Metals, Antioxidant Enzyme Activities, and Human Health Risk

Abstract

Fish from polluted creeks often accumulate heavy metals that can disrupt biochemical balance and threaten human health. This study assessed the concentration of selected heavy metals and antioxidant enzyme activities in fish species collected from polluted creeks in Rivers State, Nigeria. Samples of Tilapia zilli and Clarias gariepinus were collected from three polluted sites and one control area. Atomic absorption spectrophotometry determined metal levels (lead, cadmium, chromium, and zinc), while standard biochemical assays evaluated superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) activities in fish tissues. Results revealed significantly higher (p < 0.05) metal concentrations in fish from polluted creeks compared to the control. SOD and CAT activities declined, while MDA levels increased, indicating oxidative stress. Estimated daily intake and hazard quotient values suggested potential health risks for humans consuming contaminated fish. The study emphasizes the need for pollution control, continuous biomonitoring, and environmental health education in the Niger Delta region.

CHAPTER ONE

1.0 Introduction

1.1 Background of the Study

The Niger Delta region, especially Rivers State, is known for its rich aquatic ecosystems and significant crude oil exploration. However, decades of oil spills, gas flaring, and industrial discharge have seriously degraded its water bodies. Consequently, fish—one of the major protein sources for local communities—are increasingly exposed to pollutants, including heavy metals.

Heavy metals such as lead, cadmium, and chromium are toxic even at low concentrations. They bioaccumulate in fish tissues and may induce oxidative stress through free radical generation. Antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT) act as the body’s natural defense system, protecting tissues from oxidative damage. When pollutant exposure overwhelms these defenses, lipid peroxidation markers such as malondialdehyde (MDA) rise, signaling potential biochemical injury.

Over time, the consumption of contaminated fish poses health hazards to humans, including liver dysfunction, neurological damage, and kidney impairment. Hence, assessing the biochemical status of fish from polluted creeks helps to identify early warning signs of ecosystem distress and human health threats.

1.2 Statement of the Problem

Industrial and oil-related discharges have continuously contaminated creeks in Rivers State. While environmental monitoring has focused largely on water and sediment quality, limited information exists on biochemical alterations in aquatic organisms, especially fish. Without such data, it becomes difficult to understand pollution’s full impact on the food chain and human health. Therefore, this study investigates heavy metal accumulation and antioxidant enzyme responses in fish from polluted creeks to evaluate associated health risks.

1.3 Aim and Objectives of the Study

The main aim of this study is to assess the biochemical effects of heavy metal pollution in fish from selected creeks in Rivers State and evaluate potential human health risks.

Specific objectives are to:

1. Determine concentrations of selected heavy metals (Pb, Cd, Cr, Zn) in fish tissues.

2. Measure antioxidant enzyme activities (SOD and CAT) and lipid peroxidation (MDA) levels.

3. Compare biochemical alterations between polluted and control sites.

4. Estimate health risk indices for humans consuming contaminated fish.

1.4 Research Questions

1. What are the concentrations of heavy metals in fish from polluted creeks?

2. How do heavy metal levels affect antioxidant enzyme activities and oxidative stress?

3. What level of health risk do consumers face from eating these fish?

1.5 Significance of the Study

This research is crucial because fish form an integral part of the diet in Rivers State. The study provides biochemical evidence of aquatic pollution and its potential transfer to humans through food consumption. Furthermore, it will guide environmental agencies, fisheries departments, and health authorities in designing policies that promote safer water resources and sustainable fish consumption. The findings also serve as a scientific reference for students and researchers in environmental biochemistry and toxicology.

1.6 Scope of the Study

The study focuses on selected creeks in Rivers State known for industrial pollution and oil-related discharges. It covers the analysis of heavy metal concentrations, antioxidant enzyme activities, and risk assessments associated with fish consumption.

1.7 Operational Definitions

• Heavy Metals: Metallic elements like lead, cadmium, and chromium that can be toxic at low concentrations.

• Antioxidant Enzymes: Biological molecules such as SOD and CAT that protect cells from oxidative damage.

• Lipid Peroxidation (MDA): A biochemical process that indicates oxidative stress in tissues.

• Health Risk Assessment: The process of estimating potential health impacts due to exposure to contaminants.

CHAPTER TWO

2.0 Literature Review

2.1 Heavy Metals in Aquatic Ecosystems

Heavy metals enter aquatic environments through industrial waste, oil spills, and agricultural runoff. Unlike organic pollutants, they are non-biodegradable and tend to persist in water and sediments. Over time, they accumulate in aquatic organisms, particularly in fish, through gill absorption and food ingestion. Studies have shown that high levels of lead and cadmium impair fish metabolism, growth, and reproduction.

2.2 Bioaccumulation in Fish

Fish are effective bioindicators of environmental pollution. Their ability to accumulate metals depends on water chemistry, feeding habits, and exposure duration. Metals bind to proteins in gill and liver tissues, interfering with enzyme functions and energy metabolism. Therefore, analyzing fish biochemistry provides a reliable reflection of environmental contamination levels.

2.3 Oxidative Stress and Antioxidant Defense

When heavy metals enter the body, they generate reactive oxygen species (ROS) such as superoxide anions and hydrogen peroxide. These molecules damage lipids, proteins, and DNA. Antioxidant enzymes like SOD and CAT neutralize ROS and maintain cellular balance. However, excessive metal exposure suppresses these enzymes, leading to increased oxidative stress. Elevated MDA levels indicate the extent of lipid peroxidation and oxidative injury.

2.4 Health Risks from Contaminated Fish

Humans who regularly consume contaminated fish face risks of heavy metal toxicity. Lead exposure can damage the nervous system and impair brain function, while cadmium affects kidney filtration and bone metabolism. Chromium, though essential in trace amounts, becomes toxic when present in excess. Assessing human health risk through estimated daily intake (EDI) and hazard quotient (HQ) helps identify safe consumption levels.

2.5 Related Studies in Nigeria

Previous studies in the Niger Delta have reported significant heavy metal contamination in aquatic environments. For instance, Nwaichi et al. (2020) found elevated Pb and Cd levels in fish from polluted sites in Port Harcourt. Similarly, Ijeoma et al. (2021) observed suppressed antioxidant enzyme activities in fish exposed to refinery effluents. Despite these reports, there remains limited data linking biochemical responses in fish to potential health risks in consumers, justifying the present study.

2.6 Theoretical Framework

The Oxidative Stress Theory underlies this study. It proposes that exposure to environmental pollutants like heavy metals disrupts the balance between pro-oxidants and antioxidants, leading to cellular and tissue damage. This framework explains how pollution-induced oxidative stress in fish could have downstream effects on human health.

2.7 Conceptual Framework

Polluted creek water → Heavy metal accumulation in fish → Disruption of antioxidant defense (SOD, CAT) → Increased oxidative stress (MDA) → Biochemical alterations → Human exposure through fish consumption → Health risk (organ toxicity).