Spring 2025

Bioplastics – What They Are and Understanding Their Environmental Fate

By Ifeoluwa Bamgbose, M.S., DABT, and Haley Gadol, Ph.D.

In order to understand the nature of bioplastics, it is necessary to understand how plastics are categorized based on their feedstock and environmental fate.  As discussed in Tymchak’s article in this issue of Trends, plastics are synthetic organic polymers made of smaller repeating carbon-based chemical units called “monomers.”  Plastics can be grouped into two categories based on their monomer source:  conventional or petroleum-based plastics, which are derived from petroleum or natural gas, and bio-based plastics, which are produced from renewable biomass sources like plants or algae.  Structurally, bio-based plastics can be identical to petroleum-based plastics if they are made using the same monomer(s), but the source of the monomer(s) differs.  For example, polyethylene can be produced using different sources of the ethylene monomer.  Ethylene is sourced mainly from a petrochemical process called “steam cracking” (petroleum-based), but bio-polyethylene is produced using ethylene made from ethanol derived from plant materials, such as sugarcane or sugar beets (bio-based).

Furthermore, plastics, regardless of monomer source, may meet the criteria to be considered biodegradable.  In general, materials are considered biodegradable when they can be broken down into small molecules (e.g., water, carbon dioxide, methane) by microorganisms under certain conditions.  In addition, more specific standards of biodegradability can be tested for using standardized experimental conditions.  For example, a substance is considered “readily biodegradable” if it degrades using at least 60 percent of its theoretical oxygen demand within 28 days using the Organisation for Economic Co-operation and Development (OECD) Test Guideline No. 301, or “inherently biodegradable” if it degrades to produce 20 percent of its theoretical maximum inorganic carbon over twelve weeks using OECD Test Guideline No. 302 (US EPA, 2008).

Bioplastics vs. Petroleum-Based Plastics

This brings us to the term “bioplastics,” which refers broadly to plastics made from biologically sourced polymers (bio-based), and plastics that are considered biodegradable (whether bio-based or petroleum-based).  According to European Bioplastics (2022), bioplastics can be classified into three main types (see Figure) based on their monomer source and ability to degrade:  (1) bio-based and not biodegradable (e.g., bio-polyethylene); (2) petroleum-based and biodegradable (e.g., polycaprolactone); and (3) bio-based and biodegradable (e.g., polylactides [PLAs]).  In recent years, bioplastics have been used increasingly in a range of applications in various sectors (see Table), including food packaging, textiles, and agriculture.

Compostable plastics are biodegradable; however, not every biodegradable plastic is compostable.”

Regardless of use and source, biodegradable plastics (bio-based and petroleum-based) can have a large spectrum of different end-of-life options (Gioia et al., 2021), including reuse, recycling (e.g., primary, mechanical, chemical, upcycling); recovery (e.g., incineration/energy recovery, composting); environmental degradation (e.g., biodegradation in soil and water); and disposal (e.g., landfill and incineration/non-energy recovery).  For example, biodegradable plastics used as mulch are intended to degrade in soils, while other biodegradable plastic products, like utensils and packaging materials, are designed generally to be industrially compostable (Yu and Flury, 2024).  “Compostability” is sometimes used interchangeably with “biodegradability” because the composting process is done using biodegradation.  However, compostable materials degrade under controlled conditions, characterized primarily by forced aeration and natural heat production from biological activity to produce organic material that can be used as compost (i.e., fertilizer).  Compostable plastics are biodegradable; however, not every biodegradable plastic is compostable (US EPA, 2024).

Sources, Types, and Uses of Bioplastics

While it may be assumed that bioplastics will degrade faster than conventional plastics, the fate of bioplastics is highly dependent on environmental conditions, including temperature, moisture, pH, and many other abiotic factors (Emadian et al., 2017), as well as plastic properties, such as crystallinity, surface area, and formulation (Payanthoth et al., 2024).  While some bioplastics (e.g., PLAs) are designed to be biodegradable under specific conditions (e.g., industrial composting), achieving complete biodegradation can be challenging and time consuming under natural environmental conditions, and some bioplastics may persist in aquatic environments for years (Krasowska and Heimowska, 2023).  Additionally, various studies indicate that bioplastics can break down into biodegradable microplastics (BMPs) that are similar to conventional petroleum-based microplastics (Fang et al., 2024; Nik Mut et al., 2024; Piyathilake et al., 2024; Qin et al., 2021; Wei et al., 2021; Weinstein et al., 2020; Yu and Flury, 2024), and the long-term fate of BMPs is unknown (Fang et al., 2024).

While some bioplastics are marketed as being more environmentally friendly than conventional petroleum-based plastics, due to their biodegradability and/or renewable sources of monomers, more research is needed to better understand the environmental fate, transport, exposure, and potential risk of bioplastics and BMPs to humans and the environment.