Most plastic water bottles end up in one of three places: a landfill, an incinerator, or a recycling facility. In the United States, only about 29% of PET plastic bottles and jars are recycled. The rest sit in landfills for centuries, get burned, or escape into the environment where they slowly fragment into smaller and smaller pieces.
What Happens in a Landfill
The majority of plastic water bottles end up buried in landfills, and once there, they do almost nothing. PET plastic, the type used for water bottles, shows negligible biodegradation under the oxygen-starved conditions inside a landfill. Unlike food scraps or paper, which break down within months or years, a plastic bottle can persist for 200 to 500 years. Even then, it never fully disappears. It just fractures into progressively tinier fragments.
This persistence is partly what makes PET so useful as a container: it resists chemical breakdown, moisture, and microbial attack. But that durability becomes a problem when the bottle is waste. Buried under layers of trash and soil, shielded from sunlight and oxygen, a PET bottle encounters almost none of the forces that could degrade it. Studies simulating landfill conditions found that even PET bottles manufactured with biodegradation-promoting additives showed no measurable breakdown in soil burial tests mimicking landfill oxygen levels.
How Bottles Break Into Microplastics
Bottles that end up in the open environment, along roadsides, in rivers, or floating in the ocean, face a different fate. Sunlight is the primary driver. UV radiation triggers a chain of chemical reactions inside the plastic: molecules break apart, the surface becomes brittle, and tiny cracks form. Over time, those cracks widen and pieces chip off, creating microplastics (fragments smaller than 5 millimeters) and even nanoplastics too small to see.
Heat and physical abrasion accelerate the process. A bottle tumbling in ocean waves while baking in sunlight degrades faster than one sitting still on dry land. The internal structure of the plastic weakens as UV exposure continues, losing the molecular connections that hold it together. This creates stress within the material that eventually causes the surface to erode and shed particles. Those particles enter soil, waterways, and the food chain when marine animals and other organisms ingest them.
What Leaches From the Plastic
Even before a bottle breaks apart physically, it can release chemicals into the water it holds. The most studied concern is antimony, a metal used as a catalyst in manufacturing more than 90% of the world’s PET plastic. At room temperature (around 25°C), antimony leaching is low and stays within safety limits. But when bottles are exposed to heat, the picture changes quickly.
At 50°C (122°F), which is easily reached inside a car on a warm day, antimony concentrations in bottled water climbed to 8.5 parts per billion within 24 hours in one study, exceeding the EPA’s maximum contaminant level of 6 ppb. After seven days at that temperature, levels reached nearly 17 ppb. This means bottles stored in hot warehouses, left in vehicles, or exposed to direct sunlight during shipping can accumulate antimony at levels that regulators consider problematic.
How Recycling Actually Works
The bottles that do make it to a recycling facility go through a multi-stage industrial process to become usable plastic again. It starts with collection and sorting: bottles arrive mixed with other plastics, labels, metal caps, and food residue. Workers and automated systems separate PET from other polymer types, since mixing different plastics together produces weak, low-quality material. Even mixing different colors of PET lowers the quality of the final product.
After sorting, the bottles are shredded into small flakes, typically between 0.4 and 8 millimeters across. These flakes are washed thoroughly to strip away adhesives, dirt, labels, and any remaining food residue. Contamination at this stage matters enormously. If a batch of plastic waste is too contaminated with non-PET materials or food residue, the entire load may be diverted to a landfill or incinerator instead of being recycled.
Clean flakes are dried and then melted down through a process called extrusion, which pushes the molten plastic through machinery that forms it into small pellets known as rPET. These pellets become the raw material for new bottles, polyester clothing, carpet fiber, or food packaging. The whole process essentially melts the old bottle down and reshapes it, but each round of recycling can degrade the plastic’s quality slightly, which is why recycled PET often ends up in lower-grade products rather than new bottles.
What Happens When Bottles Are Burned
About 19% of all plastic waste globally, over 72 million tons per year, is incinerated. Some of this happens in municipal waste-to-energy plants designed to generate electricity from trash. Others are open burns in regions without formal waste infrastructure. The health and environmental consequences vary dramatically depending on the temperature.
At lower, smoldering temperatures around 500°C, burning plastic produces high levels of particulate matter and volatile organic compounds. These tiny particles are a major contributor to premature death worldwide and are linked to respiratory, cardiovascular, and nervous system damage. The smoke also contains persistent organic pollutants like dioxins and polycyclic aromatic hydrocarbons, chemicals associated with increased cancer risk for workers and people living near incineration sites.
Modern municipal incinerators operating at very high temperatures (980 to 1,200°C) achieve near-complete combustion, which significantly reduces these toxic byproducts. But residual pollutants can still remain in the ash, and even well-controlled facilities release carbon dioxide. Burning plastic is, in chemical terms, burning fossil fuel, since PET is derived from petroleum.
Why So Few Bottles Get Recycled
With a recycling rate of only 29% in the U.S., most bottles never reach a recycling facility. Several practical barriers explain the gap. Many communities lack curbside recycling programs, or their programs don’t accept all types of plastic. Bottles tossed into public trash cans bypass recycling entirely. Even bottles placed in recycling bins can be rejected if they’re contaminated with food, still have non-recyclable caps attached, or are mixed with incompatible materials.
The economics also work against recycling. Producing new PET from petroleum is often cheaper than collecting, sorting, cleaning, and reprocessing used bottles. This means recycling facilities depend on favorable market conditions and policy incentives to stay viable. Contamination compounds the cost problem: the more sorting and cleaning a batch requires, the less economically attractive it becomes. When contamination levels are too high, the material is simply landfilled, even after a consumer made the effort to recycle it.