Comparative Evaluation Of Biocorrosion Resistance Of Carbon Steel, Copper, Zinc, And Aluminium In Mangrove Swamp, Rainforest Soil, Riverine, And Coastal Marine Environments In Nigeria

Biocorrosion, also known as microbiologically influenced corrosion (MIC), is a naturally occurring degradation process in which microbial activity accelerates the deterioration of metals in aqueous and soil environments. It is a complex electrochemical process influenced by environmental conditions, material properties, and microbial communities that colonize metal surfaces. Globally, MIC is responsible for significant economic losses in marine, oil and gas, and infrastructure sectors due to pipeline failure, equipment degradation, and structural instability (Little & Lee, 2007; Videla & Herrera, 2009; Xu et al., 2023; Ogboeli et al., 2024).

In coastal and tropical regions, corrosion is intensified by high humidity, elevated temperatures, salinity, and abundant microbial activity. These conditions are particularly prevalent in wetland ecosystems such as mangrove swamps, riverine floodplains, rainforest soils, and coastal marine environments. Such environments provide ideal conditions for sulfate-reducing bacteria (SRB), iron-oxidizing bacteria, and other microbial communities that facilitate electrochemical reactions leading to metal deterioration (Enning & Garrelfs, 2014; Lv et al., 2024; Nimame et al., 2026).

The Niger Delta is one of the most environmentally dynamic and industrially significant regions in West Africa due to its extensive oil and gas exploration activities. However, the region is also characterized by severe environmental degradation, including oil spills, gas flaring, and contamination of soil and water bodies. These anthropogenic activities increase the concentration of corrosive agents such as chlorides, sulphates, hydrocarbons, and heavy metals, which enhance both chemical and microbiological corrosion processes (Nduka & Orisakwe, 2011; Akpoveta et al., 2010; Ogboeli et al., 2024).

Studies have shown that coastal marine environments in the Niger Delta exhibit elevated chloride concentrations and salinity levels, which significantly accelerate pitting corrosion in susceptible metals such as carbon steel and zinc. Mangrove swamp environments, on the other hand, are rich in organic matter and anaerobic conditions that promote the growth of sulfate-reducing bacteria, which produce hydrogen sulfide (Hâ‚‚S) that is highly corrosive to metallic structures (Essien, et al., 2012; Melchers et al., 2021; Ogboeli et al., 2024; Nimame et al., 2026). Riverine and rainforest soil environments also contribute to corrosion processes through fluctuating moisture content, acidity variations, and microbial diversity.

Different engineering materials respond differently to these environmental stressors. Carbon steel, although widely used due to its mechanical strength and affordability, is highly susceptible to corrosion in aggressive environments. Zinc and aluminium provide moderate resistance due to their ability to form protective oxide layers; however, these layers can be compromised in chloride-rich or highly acidic conditions. Copper and its alloys are generally considered more corrosion-resistant due to their noble electrochemical properties and antimicrobial activity, which inhibits microbial colonization and biofilm formation (Frankel, 1998; Jia et al., 2019; Revie & Uhlig, 2008).

The protective behavior of metals is strongly linked to passivation mechanisms. Aluminium forms a stable oxide layer (Al₂O₃), which provides initial protection but is vulnerable to localized pitting in chloride-rich environments. Copper, in contrast, forms a stable patina composed of copper oxides and carbonates that offers long-term protection in both atmospheric and aquatic conditions. This makes copper particularly suitable for marine and microbial-rich environments where biofouling and MIC are dominant concerns.

In Nigeria, particularly within the Niger Delta region, infrastructure such as pipelines, offshore platforms, jetties, and storage tanks are constantly exposed to aggressive environmental conditions. The combination of industrial pollution and natural wetland characteristics creates a unique corrosion environment that is both chemically and biologically active. Despite this, limited comparative studies have systematically evaluated the biocorrosion resistance of commonly used engineering materials across multiple environmental zones within the region.

Furthermore, previous studies have largely focused on either chemical corrosion or microbiological corrosion independently, without integrating both environmental physicochemical parameters and microbial dynamics in a single comparative framework. This presents a significant gap in understanding the synergistic effects of environmental variables and microbial activity on metal degradation processes in tropical ecosystems.

Therefore, this study focuses on the comparative evaluation of biocorrosion resistance of carbon steel, copper, zinc, and aluminium across mangrove swamp, rainforest soil, riverine, and coastal marine environments in Nigeria. It integrates physicochemical characterization, microbial analysis, and corrosion rate determination to provide a comprehensive understanding of material performance under natural field conditions. The findings are expected to contribute to material selection strategies, infrastructure durability planning, and corrosion mitigation approaches in environmentally sensitive regions such as the Niger Delta.

2. THEORETICAL FRAMEWORK OF THE STUDY

This study is grounded in two foundational theories: Microbiologically Influenced Corrosion (MIC) Theory and Electrochemical Corrosion Theory (Mixed Potential Theory).

1. Microbiologically Influenced Corrosion (MIC) Theory

The MIC Theory, developed by Von Wolzogen Kühr and Van der Vlugt, explains how microorganisms, particularly sulfate-reducing bacteria (SRB), accelerate metal deterioration through microbial metabolic activities. The theory introduced the concept of cathodic depolarization, whereby microbial activity enhances anodic dissolution and corrosion progression on metallic surfaces.

In the present study, the theory provides the basis for understanding the role of microbial populations in influencing the corrosion behaviour of Carbon Steel, Copper, Zinc, and Aluminium across the Mangrove Swamp, Rainforest Soil, Riverine, and Coastal Marine environments. It also supports the integration of microbiological analysis in evaluating corrosion severity under tropical environmental conditions.

2. Electrochemical Corrosion Theory (Mixed Potential Theory)

The Mixed Potential Theory proposed by Carl Wagner and Walter Traud explains corrosion as the result of simultaneous anodic and cathodic electrochemical reactions occurring on a metal surface. The theory states that corrosion behaviour is controlled by the balance between oxidation and reduction reactions under specific environmental conditions.

In this study, the theory explains the varying corrosion resistance of Carbon Steel, Copper, Zinc, and Aluminium in different tropical environments. It provides a scientific basis for interpreting the observed corrosion rates, particularly the superior resistance of Copper and the high susceptibility of Carbon Steel in saline and microbial-rich environments such as the Coastal Marine and Mangrove Swamp habitats.

3. MATERIALS AND METHODS

Study Area: The study was conducted in four representative tropical environments within the Niger Delta region of Nigeria: mangrove swamp, rainforest soil, riverine (freshwater), and coastal marine habitats. These sites were selected to capture a wide range of physicochemical and microbiological conditions, including variations in salinity, pH, dissolved oxygen, and microbial activity, which are known to influence biocorrosion processes.

Materials Used: Test coupons of four metals commonly used in engineering and oil & gas infrastructure were employed: Carbon Steel, Copper, Zinc, and Aluminium. Each coupon was cut to uniform dimensions of 50 mm × 25 mm × 3 mm. Prior to exposure, all coupons were mechanically polished with progressively finer grades of emery paper (up to 1200 grit), degreased with analytical-grade ethanol, rinsed thoroughly with distilled water, and air-dried. Initial weights were recorded using a digital analytical balance (precision ± 0.0001 g).

Additional materials included nylon strings and non-corrosive holders for sample suspension, sterile sampling containers, and analytical reagents. Portable field instruments used included a pH meter, salinity meter, dissolved oxygen meter, and GPS device.

Experimental Design: A completely randomized design was adopted. In each environment, three replicate coupons of each metal type were exposed for 90 days under natural field conditions. This resulted in a total of 48 coupons (4 metals × 4 environments × 3 replicates).

Exposure Procedure: Soil environments (Mangrove Swamp and Rainforest Soil): Coupons were buried at a depth of 10–15 cm. Aquatic environments (Riverine and Coastal Marine): Coupons were suspended at approximately 1 m below the water surface using non-corrosive nylon strings. Coupons were retrieved at 30-day intervals for visual observation and finally at 90 days for detailed analysis.

Determination of Corrosion Rate: After retrieval, corrosion products were carefully removed using Clarke’s solution (for ferrous metals) and appropriate cleaning solutions for non-ferrous metals, following ASTM G1-03 standard procedures. Coupons were then rinsed, dried, and re-weighed. Weight loss was calculated as:

Weight Loss = W0​−Wt​

Where:

Wâ‚€ = initial weight (mg)

Wₜ = final weight (mg)

Corrosion rate was determined using: Corrosion Rate (mm/year)

Where:

K = constant (87.6),

W = weight loss (mg),

A = exposed surface area (cm²),

T = exposure time (hours),

D = density of metal (g/cm³)

Microbiological Analysis: Biofilm samples were collected from coupon surfaces using sterile swabs. Samples were serially diluted and cultured on Nutrient Agar (for total heterotrophic bacteria), MacConkey Agar (for Gram-negative bacteria), and Potato Dextrose Agar (for fungi). Plates were incubated at 28 ± 2°C for 24–48 hours (bacteria) and 5–7 days (fungi). Microbial counts were expressed as Colony Forming Units (CFU/mL). Predominant isolates were identified using standard morphological, Gram staining, and biochemical tests.

Physicochemical Analysis: Water and soil samples from each site were analyzed for pH, temperature, salinity, dissolved oxygen, chloride, sulphate, and organic matter content using standard methods outlined by the American Public Health Association (APHA, 2017).

Data Analysis: Data were analyzed using SPSS version 26. Descriptive statistics (mean ± standard deviation) were computed. One-way and two-way Analysis of Variance (ANOVA) were used to determine significant differences in corrosion rates across metals and environments. Post-hoc tests (Tukey’s HSD) were performed for multiple comparisons. Pearson correlation analysis was conducted to examine relationships between environmental parameters and corrosion rates. Statistical significance was set at p < 0.05.

4. RESULTS

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