Expanded polystyrene foam, commonly known by the trade name Styrofoam, is widely used for packaging and insulation due to its low weight and excellent thermal properties. The white foam is essentially a plastic that has been expanded with air, making it over 95% air by volume. When this material enters a waterway, it does not dissolve or undergo meaningful decomposition. The definitive answer to whether Styrofoam breaks down in water is no, it does not biodegrade in the natural environment. The material’s persistence creates unique environmental challenges stemming from its stable chemical structure.
The Science of Polystyrene: Why It Resists Decomposition
Styrofoam is chemically composed of polystyrene, a synthetic polymer made from repeated units of the styrene monomer. This polymer is characterized by a long chain of carbon atoms, known as the backbone, with large, ring-shaped phenyl groups attached to every other carbon atom. The resulting structure is highly stable and gives the material its rigidity and durability.
True decomposition, or biodegradation, requires living organisms like bacteria or fungi to use the material as a food source, breaking down the chemical bonds with specific enzymes. Polystyrene’s long, complex molecular chains and its lack of naturally occurring counterparts mean that common microbes in aquatic environments do not possess the necessary enzymatic machinery to cleave the strong carbon-carbon bonds. Furthermore, the material is highly hydrophobic, meaning it repels water, which limits the ability of water-dwelling microorganisms and their enzymes to even access the polymer surface to initiate a reaction.
This chemical inertness is why polystyrene resists breakdown by most dilute acids, bases, and salts found in water. While specialized microbes have been identified in laboratories that can degrade polystyrene, these processes are extremely slow and impractical under natural conditions. The polymer’s high molecular weight also prevents microorganisms from transporting the material into their cells, which is necessary for complete breakdown.
Physical Breakdown: From Foam to Microplastics
Although Styrofoam does not chemically decompose, it fragments into smaller pieces through physical and mechanical processes. This fragmentation is driven by environmental factors, primarily exposure to ultraviolet (UV) radiation from sunlight and physical abrasion from wind and waves. UV light causes photodegradation, weakening the polymer chains near the surface of the material, which makes the structure brittle.
The physical action of waves, currents, and sand causes the weakened material to break apart. A single piece of foam is gradually reduced into mesoplastics, then into microplastics, which are defined as plastic pieces smaller than five millimeters. This process is a change in size, not a change in the fundamental chemical composition of the polymer.
The foamed structure of expanded polystyrene is particularly vulnerable to this fragmentation because it is composed of thin, interconnected polymer walls. This structure makes it easier for the material to crumble into tiny particles compared to solid plastics. These resulting microplastic fragments are persistent pollutants that can remain in the environment for hundreds of years, accumulating in sediments and throughout the water column.
Ecological Impact of Non-Degradable Materials
The fragmentation of Styrofoam into microplastics introduces significant risks, particularly in aquatic ecosystems. Microplastics are easily ingested by a wide range of marine life, from small zooplankton and invertebrates up to fish and birds. Once consumed, these particles can become lodged in the digestive tract, potentially blocking the passage of food or giving the animal a false sense of satiation.
Beyond the physical danger, chemical concerns are associated with these tiny plastic fragments. Polystyrene microplastics can act as carriers for other pollutants, adsorbing persistent organic pollutants (POPs) and heavy metals from the surrounding water onto their surfaces. When an organism ingests the plastic, these concentrated toxins can leach into the animal’s tissues, potentially transferring up the food chain. The plastic itself can also leach small amounts of toxic components, such as the unreacted styrene monomer, into the environment or into the organisms that consume it.
Responsible Disposal and Sustainable Alternatives
Since expanded polystyrene is virtually permanent in the environment, proper disposal is necessary, though recycling the material presents specific challenges. The high-volume, low-density nature of the foam means it is costly to transport and process, and specialized infrastructure is required to melt and re-pelletize the material. Consumers should check with local waste management facilities, as many communities offer drop-off locations or specialized collection events for clean foam packaging.
To reduce the pollution problem at its source, several sustainable alternatives are being developed and implemented. Molded pulp, made from recycled paper and cardboard fibers, can be shaped to offer cushioning for protective packaging. Materials grown from the root structure of fungi, known as mycelium packaging, offer a fully compostable, natural foam replacement. For loose-fill applications, starch-based foams made from renewable sources like corn or potato starch are available, which dissolve safely in water.