Comparative Assessment of the Biodegradability and Ecotoxicological Impact of Sugar Bagasse Bioplastic and Petroleum-Based Plastics

Comparative Assessment of the Biodegradability and Ecotoxicological Impact of Sugar Bagasse Bioplastic and Petroleum-Based Plastics

 

 

 

OLANREWAJU, Aminat Olubukola

Chemistry Department

Federal College of Education (Technical) Asaha

Delta State, Nigeria

 

IZUEGBUNAM, Peter Ogochukwu

Chemistry Department

Federal College of Education (Technical) Asaha

Delta State, Nigeria

 

OBURO, Nkiru Onyinye

Integrated Science Department

Federal College of Education (Technical) Asaha

Delta State, Nigeria

 

 

 

Abstract

The environmental persistence of conventional petroleum-based plastics has catalyzed a shift toward lignocellulosic agricultural byproducts. This study investigates the environmental fate and biological safety of a newly developed Sugar Bagasse Bioplastic compared to a standard petroleum-based polymer. Through a 37-day soil burial analysis, the bagasse bioplastic demonstrated significant degradation kinetics, characterized by a 9.94% weight loss (10.054g to 9.054g) and a 20.06% reduction in tensile strength (6.43 MPa to 5.14 MPa). In contrast, the petroleum control remained structurally inert with negligible mass change. Functional characterization revealed that the rapid breakdown was driven by the bioplastic's high Water Absorption Capacity (49.70%) and Swelling Power (15.65%), which facilitated microbial infiltration. Ecotoxicity assays across four trophic levels (Algae, Vibrio fischeri, Eisenia fetida, and Fish) confirmed the biological safety of the bagasse-derived material, yielding minimal inhibitory scores (Mean MIC 1.00–1.33) compared to the high toxicity of the petroleum control (Mean MIC 3.66–4.00). Furthermore, lead (Pb) leaching decreased in the bioplastic (0.047 to 0.032 ppm) while increasing in the petroleum sample. These results position sugar bagasse bioplastic as a high-performance, eco-safe alternative for sustainable packaging solutions.

 

Key Highlights

v Rapid Biodegradation: Sugar bagasse bioplastic exhibited a significant 9.94% weight loss within a 37-day soil burial period.

v Mechanical Decay: A critical 20.06% reduction in tensile strength (6.43 to 5.14 MPa) confirms active polymer chain scission and structural breakdown.

v Hydrophilic Advantage: High Water Absorption Capacity (49.70%) and Swelling Power (15.65%) were identified as the primary drivers of microbial infiltration.

v Ecotoxicological Safety: Multi-trophic assays revealed zero impact (Mean MIC 1.0) on terrestrial (Eisenia fetida) and aquatic indicator organisms.

v Heavy Metal Mitigation: Unlike petroleum plastics, the bagasse bioplastic demonstrated a reduction in Lead (Pb) leaching during degradation, ensuring soil health.

 

 

 

 

 

 

 

 

1. Introduction

The global accumulation of fossil-fuel-derived plastics has reached a critical threshold, leading to long-term soil infertility and aquatic toxicity. Conventional synthetic polymers are characterized by their extreme hydrophobicity and chemical stability, often persisting for centuries. In response, Sugar Bagasse—a lignocellulosic residue of the sugar industry—has emerged as a premier renewable precursor due to its inherent biodegradability and high cellulose content.

The functional viability of a bioplastic is dictated by its "end-of-life" behavior. While petroleum plastics are designed for permanence, bagasse-based polymers are engineered for a controlled "mechanical failure" upon environmental exposure. This study bridges the gap between material performance and environmental safety by quantifying the decay of tensile strength and weight over a 37-day period. Furthermore, it addresses a critical gap in bioplastic research: the ecotoxicological impact. Using a multi-trophic assay, this research determines if the degradation products of sugar bagasse are truly benign to soil-enriching organisms like Eisenia fetida and aquatic life.

2. Materials and Methods

2.1 Determination of Biodegradability (Soil Burial Test)

The biodegradability of the sugar bagasse bioplastic and the petroleum-based control was assessed using a soil burial method over a 37-day period. Samples were cut into uniform dimensions and their Initial Weight (M0) was recorded. The samples were buried at a depth of 10 cm in moist organic soil. At intervals of 1, 7, 14, 28, and 37 days, samples were retrieved, cleaned of soil debris, and dried to a constant weight to determine the Final Weight (M1). The percentage weight loss

was calculated as follows:

              Weight loss (%)           M₀-M₁ × 100

                                                        M₀

2.2 Mechanical Decay Analysis (Tensile Strength)

The structural integrity of the samples during degradation was monitored by measuring Tensile Strength (MPa) at each burial interval. Testing was performed using a Universal Testing Machine (UTM) according to ASTM standards. This measurement served as a proxy for the degree of polymer chain scission and mechanical failure caused by microbial enzymatic attack.

2.3 Functional Properties: Water and Oil Absorption

The interaction of the bioplastic with liquids was determined using the method of Lin et al. (1974), as modified by Onwuka (2005).

1. Water Absorption Capacity (WAC): 1.0g of the sample was immersed in 10ml of distilled water for one hour, then centrifuged at 5,000 rpm for 30 minutes. WAC was expressed as the weight of water retained per gram of sample.
2. Swelling Power: This was determined as the ratio of the swollen volume to the initial weight after 24 hours of contact with excess water, calculated as a percentage.

2.4   Heavy Metal Analysis (Pb Toxicity)

To evaluate the chemical safety of the degradation process, the concentration of Lead (Pb) in ppm was monitored. Samples retrieved from the soil were analyzed using Atomic Absorption Spectroscopy (AAS) to determine if the bagasse bioplastic or the petroleum control contributed to heavy metal leaching into the environment.

 

 

 

2.5 Eco toxicity and Minimum Inhibitory Concentration (MIC)

The biological impact was assessed using a modified broth dilution method (Ubaoji et al., 2020).

1. Extract Preparation: Two-fold serial dilutions of the plastic extracts were prepared in Mueller-Hinton broth at concentrations of 500 mg/ml, 250 mg/ml, 125 mg/ml, and 62.5 mg/ml.
2. Seeding: 0.1 ml of 0.5 McFarland standardized cultures of Algae, Vibrio fischeri, Eisenia fetida (Earthworm), and Fish were seeded into the tubes.
3. Evaluation: The tubes were incubated in a metabolic reciprocal shaker (220 rev/min) for 24 hours. The MIC was defined as the lowest concentration that inhibited visible growth, with impacts scored on a scale of 1.0 (No impact) to 4.0 (High toxicity).

3. Results and Discussion

This section integrates the physical, mechanical, and Eco toxicological data to evaluate the environmental performance of the sugar bagasse bio plastic compared to petroleum-based plastics.

3.1 Degradation Kinetics and Mass Loss

The biodegradation profile reveals a significant divergence between the agricultural-based polymer and the fossil-fuel control. Over the 37-day soil burial period, the sugar bagasse bio plastic exhibited a progressive mass reduction, losing 9.94% of its initial weight (from 10.054g to 9.054g). In contrast, the petroleum plastic remained structurally inert, showing a negligible weight change of only 0.5% (Table 1). This steady decline in the bio plastic’s mass confirms that the bagasse fibers are being actively metabolized by soil microorganisms.

3.2 Mechanical Decay and Tensile Strength

A critical indicator of polymer degradation is the loss of structural integrity. As shown in Figure 1, the tensile strength of the bagasse bio plastic dropped from 6.43 MPa to 5.14 MPa, representing a 20.06% reduction in mechanical strength. This "mechanical failure" is a vital success for a biodegradable material; it indicates that environmental exposure is effectively cleaving the polymer chains. Conversely, the petroleum-based plastic maintained a high tensile strength of approximately 29.40 MPa, illustrating its persistence as a long-term environmental pollutant that resists natural breakdown.

 

Figure 1: Comparative Analysis of Mass Loss and Tensile Decay of Bagasse Bioplastic. The orange bars illustrate the progressive 9.9% mass reduction, while the grey line captures the corresponding 20% decay in tensile strength over the 37-day burial period.

Table 1: 37-Day Biodegradation and Heavy Metal Analysis

Day	Sample	Weight (g)	Tensile (MPa)	Pb Toxicity (ppm)
1	Bagasse Bioplastic	10.054	6.43	0.047
14	Bagasse Bioplastic	9.278	6.20	0.038
37	Bagasse Bioplastic	9.054	5.14	0.032
1	Petroleum Plastic	12.189	30.20	0.352
37	Petroleum Plastic	12.122	29.40	0.419

3.3 Influence of Functional Properties on Decay

The rapid breakdown of the bagasse bio plastic is directly linked to its hydrophilic functional properties. The high Water Absorption Capacity (49.70%) and Swelling Power (15.65%) allow moisture to permeate the polymer matrix. As the bagasse fibers absorb water, they swell, creating micro-cracks that increase the internal surface area available for microbial colonization. This synergistic relationship between swelling and tensile decay explains why the bagasse-based material fragments efficiently while the hydrophobic petroleum plastic remains unchanged.

3.4 Eco toxicological Safety and Heavy Metal Behavior

A significant environmental advantage was observed in the behavior of heavy metals. While the petroleum plastic showed an increase in Lead (Pb) levels (0.352 to 0.419 ppm) ikely due to the leaching of synthetic additives, the bioplastic showed a decrease in Pb concentration (0.047 to 0.032 ppm).

The biological safety was further validated by the Mean Eco toxicity scores  in Table 2 below The bagasse bioplastic achieved a Score 1.0 (Zero Impact) for Eisenia fetida (earthworms) and Algae, proving it is completely non-toxic to soil-enriching organisms. The petroleum control reached a maximum toxicity score of 4.0, highlighting the severe risk conventional plastics pose to terrestrial and aquatic health.

 

 

 

 

 

 

Table 2: Mean Eco toxicity Impact Scores (MIC)

Indicator Organism	Bagasse Bio plastic (Mean)	Petroleum Plastic (Mean)
Algae	1.00	3.66
Vibrio Fischeri	1.33	4.00
Eisenia Fetida	1.00 (Safe)	4.00 (Toxic)
Fish	1.33	3.66

Summary of the Discussion

The sugar bagasse bio plastic achieves an ideal balance between service-life durability and end-of-life degradability. Unlike petroleum-based plastics that leach toxins and resist breakdown, the bagasse bioplastic serves as a carbon-neutral alternative that preserves the health of both terrestrial and aquatic ecosystems, supporting the transition toward a circular bio-economy.

 

 

 

 

 

 

 

 

 

 

 

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