Landfills contaminate groundwater, release potent greenhouse gases, pollute the air with toxic compounds, and create long-term health risks for nearby communities. In 2019, roughly 750 million tonnes of municipal solid waste went into sanitary landfills worldwide, and another 1.1 billion tonnes ended up in uncontrolled dumpsites or burned in the open. That’s a massive amount of material packed into the ground, and the problems it causes don’t stop when a landfill closes. They can persist for decades.
Groundwater Contamination From Leachate
When rain filters through buried waste, it picks up a toxic cocktail called leachate. This liquid contains high concentrations of dissolved organic matter, inorganic ions, and heavy metals including iron, manganese, copper, zinc, arsenic, cadmium, lead, mercury, and hexavalent chromium. Industrial chemicals like di(2-ethylhexyl) phthalate (a common plasticizer), chloroform, and bromochloromethane have also been detected in leachate at measurable levels. If this liquid reaches an aquifer, it can render groundwater unsafe to drink.
Modern landfills use thick plastic liners to contain leachate, and lab testing suggests these liners can last well over a century under ideal conditions. At moderate temperatures with limited chemical stress, nominal failure of a composite liner system is predicted to exceed 260 years. But “ideal conditions” is the key phrase. In practice, liners can be punctured during construction, degraded by chemical exposure, or compromised by shifting soil. No liner lasts forever, and the waste it’s meant to contain will still be there long after the liner begins to fail.
Forever Chemicals in Landfill Waste
One of the most alarming pollutants leaching out of landfills is PFAS, the “forever chemicals” found in nonstick cookware, waterproof clothing, food packaging, and firefighting foam. These compounds don’t break down in the environment. EPA data shows that leachate from municipal solid waste landfills contains an average of 1,400 nanograms per liter of PFOA and 260 nanograms per liter of PFOS. To put that in context, the EPA’s proposed maximum contaminant level for drinking water is just 4 nanograms per liter for each of those chemicals. That means typical landfill leachate contains PFOA at roughly 350 times the proposed drinking water limit.
When leachate is collected and sent to wastewater treatment plants, those facilities generally can’t remove PFAS effectively. The chemicals pass through treatment and enter rivers, lakes, or irrigation systems. Landfills are now recognized as one of the largest concentrated sources of PFAS entering the water cycle.
Greenhouse Gas Emissions
Buried organic waste, everything from food scraps to paper products, breaks down without oxygen. This anaerobic decomposition produces methane, a greenhouse gas roughly 80 times more potent than carbon dioxide over a 20-year period. A landfill typically produces gas at a stable rate for about 20 years after waste is placed, but smaller quantities continue seeping out for 50 years or more.
Gas collection systems can capture some of this methane and convert it to energy, but they’re far from perfect. Collection efficiency varies widely depending on the type of cover material and how much of the landfill the system reaches. Published estimates range from 50% to near 100% at any given moment, but when you account for the full lifespan of a landfill, including the years before a collection system is installed, the weighted efficiency drops to somewhere between 55% and 91%. That means a significant share of methane escapes into the atmosphere no matter what.
Toxic Air Pollution
Methane isn’t the only gas that escapes. Landfills emit a range of volatile and semi-volatile organic compounds that directly affect air quality and human health. Aromatic compounds (like benzene and toluene) and halogenated compounds (chlorinated solvents, for example) are the primary drivers of cancer risk from landfill gas. Even seemingly benign byproducts of organic decomposition, like ethyl acetate and acetone, have been measured at concentrations that exceed acceptable health thresholds.
The lungs are the primary target. People living downwind of active landfills can be exposed to a mix of these compounds through everyday breathing. The health effects range from headaches and allergic reactions to elevated long-term cancer risk.
Health Risks for Nearby Communities
Living within a few kilometers of a landfill is linked to measurable health consequences. A large multisite cohort study found that hydrogen sulfide exposure from landfills, the gas responsible for the characteristic rotten-egg smell, was associated with higher mortality from lung cancer and respiratory diseases. For every incremental increase in hydrogen sulfide concentration, lung cancer mortality risk rose by about 10%.
The effects weren’t limited to adults. Children aged 0 to 14 living near landfills showed a 6% higher rate of hospitalization for acute respiratory infections compared to children living farther away. Researchers also found excess risks for non-Hodgkin lymphoma and cancers of the liver, pancreas, and kidney among male residents near certain sites. Studies near a large landfill outside Rome linked proximity to higher rates of laryngeal and bladder cancer, alongside increased hospitalizations for heart and lung conditions.
It’s worth noting that many landfill-adjacent communities are also near other pollution sources like incinerators or industrial facilities, which complicates the picture. But the respiratory effects, particularly from inhaling microorganisms, endotoxins, and aerosols generated during waste collection and burial, have been documented independently of those other exposures.
Nothing Really Decomposes
One of the most common misunderstandings about landfills is that waste breaks down and disappears over time. It doesn’t, at least not in any meaningful sense. Landfills are designed to be dry and oxygen-free, which slows decomposition to a crawl. Researchers have excavated landfills and found decades-old newspapers still readable and hot dogs still recognizable.
Organic waste does partially decompose under anaerobic conditions, but the process is extremely slow. The bulk of gas production happens within the first 20 years, yet slowly decomposing materials continue emitting gas for 40 years or longer. Plastics, metals, and glass persist essentially unchanged for centuries. A landfill isn’t a composting system. It’s a storage facility, and the waste you put in it today will largely still be there when your grandchildren are old.
The Problem Doesn’t End at Closure
When a landfill reaches capacity, it’s capped with soil and synthetic covers, but it still requires active management. Federal regulations require owners to maintain a detailed cost estimate for post-closure monitoring and maintenance, covering the leachate collection systems, groundwater monitoring wells, gas venting infrastructure, and erosion control for the cap. This post-closure care period typically lasts 30 years at minimum, though many sites need attention far longer than that.
During those decades, someone has to pay for pumping and treating leachate, testing surrounding wells for contamination, maintaining gas collection equipment, and repairing any damage to the cover. If the company that operated the landfill goes bankrupt or walks away, the financial burden shifts to local governments and taxpayers. Closed landfills also can’t easily be redeveloped. The land settles unevenly as waste compresses, methane continues venting, and any construction risks puncturing the cap and restarting contamination.
The core problem with landfills is that they convert a short-term convenience (getting rid of trash cheaply) into a long-term liability that outlasts the people who created it. Every ton of waste buried today commits a community to decades of monitoring, ongoing pollution risk, and permanent loss of usable land.