Effects of biodegradable P3HB on the specific growth rate, root length and chlorophyll content of duckweed, Lemna minor

Plastics of the Future? An Interdisciplinary Review on Biobased and Biodegradable Polymers: Progress in Chemistry, Societal Views, and Environmental Implications

Global demand to reduce polymer waste and microplastics pollution has increased in recent years, prompting further research, development, and wider use of biodegradable and biobased polymers (BBPs). BBPs have emerged as promising alternatives to conventional plastics, with the potential to mitigate the environmental burdens of persistent plastic waste. We provide an updated perspective on their impact, five years after our last article, featuring several recent advances, particularly in exploring broader variety of feedstock, applying novel chemical modifications, and developing new functionalities. Life-cycle assessments reveal that environmental performance of BBPs depends on several factors including feedstock selection, production efficiency, and end-of-life management. Furthermore, the introduction of BBPs in several everyday life products has also influenced consumer perception, market dynamics, and regulatory frameworks. Although offering environmental advantages in specific applications, BBPs also raise concerns regarding their biodegradability under varying environmental conditions, potential microplastic generation, and soil health impacts. We highlight the need for a circular approach considering the entire polymer life cycle, from feedstock sourcing, modification and use, to end-of-life options. Interdisciplinary research, collaborative initiatives, and informed policymaking are crucial to unlocking the full potential of BBPs and exploiting their contribution to create a circular economy and more sustainable future.

The dual impact of tire wear microplastics on the growth and ecological interactions of duckweed Lemna minor

Tire wear microplastics (TWMs) are continuously generated during driving and are subsequently released into the environment, where they pose potential risks to aquatic organisms. In this study, the effects of untreated, hydrated, and aged (in stream water) TWMs on the growth, root development, photosynthesis, electron transport system (ETS) activity, and energy-rich molecules of duckweed Lemna minor were investigated. The results indicated that untreated and aged TWMs have the most pronounced negative effects on Lemna minor, as evidenced by reduced growth and impaired root development. In contrast, the effects of hydrated TWMs were less pronounced compared to untreated and aged TWMs. The negative effects associated with untreated and hydrated TWMs are primarily attributed to the abrasive nature of these particles, which physically damage the plant tissue. On the other hand, aged TWMs showed a different mode of action as they serve as transport vectors for algae. Once introduced into a new environment via aged TWMs, these algae competed with Lemna minor for available nutrients and space, further impairing the growth, root length, photosynthetic efficiency, and carbohydrate content of Lemna minor. This study revealed the dual threat posed by TWMs: direct physical damage from newly released particles and indirect ecological disruption from aged particles that facilitate the spread of algae.

Ecotoxicity of Biodegradable Microplastics and Bio-based Microplastics: A Review of in vitro and in vivo Studies

As biodegradable and bio-based plastics increasingly replace conventional plastics, the need for a comprehensive understanding of their ecotoxicity becomes more pressing. This review systematically presents the ecotoxicity of the microplastics (MPs) from different biodegradable plastics and bioplastics on various animals and plants. High doses of polylactic acid (PLA) MPs (10%) have been found to reduce plant nitrogen content and biomass, and affect the accumulation of heavy metals in plants. Their phytotoxicity becomes more pronounced when blended with polybutylene adipate terephthalate (PBAT) MPs. Polyhydroxybutyrate (PHB) and polybutylene succinate (PBS) MPs show lower phytotoxicity than PLA MPs. At high doses, PLA and PHB MPs may cause dose-dependent developmental toxicity to aquatic organisms. Nano-PLA could induce oxidative stress and genetic damage in insects, indicating its toxicity could be size-dependent and affected by weathering. PBAT MPs have been observed to affect plant growth at lower concentrations (0.1%) than PLA MPs, while polycaprolactone (PCL) affected seed germination only at high temperatures. PCL MPs and extracts could also cause developmental and reproductive toxicity, alter metabolisms, and induce oxidative stress in aquatic organisms at high concentrations. Polypropylene carbonate (PPC) ( > 40 g/kg) MPs have caused earthworm behavioral changes. Non-biodegradable bioplastics are potentially toxic to embryos, larvae, immune systems, reproductive systems, and endocrine systems of animals. However, it is important to note that toxicity studies are still lacking for biodegradable and bio-based plastics, particularly PHB, PBS, PCL, PPC, starch-based, and non-biodegradable bioplastics. More research into the MPs of these plastics is essential to better understand their ecotoxicity and applicability.

Biodegradation of poly-3-hydroxybutyrate after soil inoculation with microbial consortium: Soil microbiome and plant responses to the changed environment

Biodegradable plastics play a vital role in addressing global plastics disposal challenges. Poly-3-hydroxybutyrate (P3HB) is a biodegradable bacterial intracellular storage polymer with substantial usage potential in agriculture. Poly-3-hydroxybutyrate and its degradation products are non-toxic; however, previous studies suggest that P3HB biodegradation negatively affects plant growth because the microorganisms compete with plants for nutrients. One possible solution to this issue could be inoculating soil with a consortium of plant growth-promoting and N-fixing microorganisms. To test this hypothesis, we conducted a pot experiment using lettuce (Lactuca sativa L. var. capitata L.) grown in soil amended with two doses (1 % and 5 % w/w) of P3HB and microbial inoculant (MI). We tested five experimental variations: P3HB 1 %, P3HB 1 % + MI, P3HB 5 %, P3HB 5 % + MI, and MI, to assess the impact of added microorganisms on plant growth and P3HB biodegradation. The efficient P3HB degradation, which was directly dependent on the amount of bioplastics added, was coupled with the preferential utilization of P3HB as a carbon (C) source. Due to the increased demand for nutrients in P3HB-amended soil by microbial degraders, respiration and enzyme activities were enhanced. This indicated an increased mineralisation of C as well as nitrogen (N), sulphur (S), and phosphorus (P). Microbial inoculation introduced specific bacterial taxa that further improved degradation efficiency and nutrient turnover (N, S, and P) in P3HB-amended soil. Notably, soil acidification related to P3HB was not the primary factor affecting plant growth inhibition. However, despite plant growth-promoting rhizobacteria and N2-fixing microorganisms originating from MI, plant biomass yield remained limited, suggesting that these microorganisms were not entirely successful in mitigating the growth inhibition caused by P3HB.

Effects of poly(3-hydroxybutyrate) [P(3HB)] coating on the bacterial communities of artificial structures

The expanding urbanization of coastal areas has led to increased ocean sprawl, which has had both physical and chemical adverse effects on marine and coastal ecosystems. To maintain the health and functionality of these ecosystems, it is imperative to develop effective solutions. One such solution involves the use of biodegradable polymers as bioactive coatings to enhance the bioreceptivity of marine and coastal infrastructures. Our study aimed to explore two main objectives: (1) investigate PHA-degrading bacteria on polymer-coated surfaces and in surrounding seawater, and (2) comparing biofilm colonization between surfaces with and without the polymer coating. We applied poly(3-hydroxybutyrate) [P(3HB)) coatings on concrete surfaces at concentrations of 1% and 6% w/v, with varying numbers of coating cycles (1, 3, and 6). Our findings revealed that the addition of P(3HB) indeed promoted accelerated biofilm growth on the coated surfaces, resulting in an occupied area approximately 50% to 100% larger than that observed in the negative control. This indicates a remarkable enhancement, with the biofilm expanding at a rate roughly 1.5 to 2 times faster than the untreated surfaces. We observed noteworthy distinctions in biofilm growth patterns based on varying concentration and number of coating cycles. Interestingly, treatments with low concentration and high coating cycles exhibited comparable biofilm enhancements to those with high concentrations and low coating cycles. Further investigation into the bacterial communities responsible for the degradation of P(3HB) coatings identified mostly common and widespread strains but found no relation between the concentration and coating cycles. Nevertheless, this microbial degradation process was found to be highly efficient, manifesting noticeable effects within a single month. While these initial findings are promising, it's essential to conduct tests under natural conditions to validate the applicability of this approach. Nonetheless, our study represents a novel and bio-based ecological engineering strategy for enhancing the bioreceptivity of marine and coastal structures.