PCBs, or polychlorinated biphenyls, are a group of synthetic chemicals that were widely used in industrial equipment from the 1920s through 1979, when the United States banned their production. Despite that ban, PCBs persist in water sources decades later because they barely break down in the environment. The EPA sets a legal limit of 0.5 micrograms per liter for PCBs in drinking water, with an ultimate safety goal of zero.
What PCBs Are and Why They Persist
PCBs are a class of 209 related chemical compounds, called congeners, made by attaching chlorine atoms to a two-ringed carbon molecule. The more chlorine atoms attached, the more resistant the compound becomes to breakdown. PCBs resist acids, alkalis, and heat, which is exactly why manufacturers valued them for electrical transformers, capacitors, hydraulic fluids, and lubricants. That same chemical stubbornness is what makes them dangerous: once released into the environment, they stick around for decades.
PCBs dissolve poorly in water but readily in fats and oils. In an aquatic environment, this means they don’t simply float around in the water column. Instead, they bind to sediment on the bottom of rivers, lakes, and harbors, creating long-term contamination reservoirs that continue releasing PCBs slowly over time.
How PCBs Get Into Water
Most PCB contamination traces back to industrial activity near waterways. Factories that manufactured or used PCB-containing equipment discharged waste directly into rivers and bays for decades before the chemicals were banned. Those legacy contamination sites remain the primary source in many water bodies today.
Urban stormwater runoff is another major pathway. Rain washes PCBs from contaminated soils, old building materials, and deteriorating electrical equipment into storm drains that flow into rivers, lakes, and coastal waters. Research on San Francisco Bay identified urban runoff from local watersheds as a particularly significant route for PCB entry. Contaminated sediment sites within the Bay itself also continue feeding PCBs into the food web. Other sources like wastewater treatment plant discharge and atmospheric deposition contribute smaller amounts.
Bioaccumulation: From Trace Amounts to Toxic Levels
Even when PCB concentrations in open water are extremely low, the chemicals concentrate dramatically as they move up the food chain. This process, called biomagnification, starts with tiny organisms like phytoplankton absorbing PCBs from the water. Because PCBs dissolve in fat rather than water, they accumulate in the organisms’ tissues rather than being flushed out.
Small fish and zooplankton eat enormous quantities of phytoplankton, concentrating the PCBs further in their own fatty tissues. Each step up the food chain multiplies the concentration again. By the time you reach top predators like lake trout, large salmon, or fish-eating birds, the PCB levels in their fatty tissues can be millions of times higher than the concentration in the surrounding water. This is why fish consumption advisories are one of the most common public health responses to PCB contamination, and why eating contaminated fish is a more significant exposure route than drinking the water itself for most people.
Health Effects of PCB Exposure
PCBs are classified as probable human carcinogens by both the EPA and the International Agency for Research on Cancer. Studies of workers with occupational exposure found associations with liver and biliary tract cancers. In animal studies, rats fed commercial PCB mixtures throughout their lifetimes developed liver cancer.
Cancer isn’t the only concern. PCB exposure in animal studies causes immune system suppression, thyroid disruption, and impaired reproduction. Human evidence supports some of these findings as well: studies suggest the immune system may be affected in children born to and nursed by mothers who had elevated PCB exposure. Adults and children can come into contact with PCBs by drinking contaminated water, eating contaminated fish, or even accidentally swallowing water while swimming in contaminated lakes or rivers.
Why Children and Pregnant Women Face Greater Risk
Children take in more PCBs relative to their body weight than adults do, and their developing brains, nervous systems, immune systems, and reproductive organs are more vulnerable to disruption. The prenatal period carries particular risk because PCBs cross the placenta freely.
A study of 242 newborns whose mothers ate moderate amounts of contaminated lake fish during pregnancy found measurable consequences at birth. Exposed infants weighed 160 to 190 grams less than unexposed infants, and their head circumference was 0.6 to 0.7 centimeters smaller. The smaller head size was disproportionate even when accounting for birth weight and gestational age, suggesting a specific effect on brain growth. Researchers controlled for 37 potential confounding variables, including socioeconomic status, maternal age, and smoking, and none explained the differences.
Drinking Water Standards and Limits
The EPA regulates PCBs in public drinking water under the Safe Drinking Water Act. The maximum contaminant level (MCL), which is the legally enforceable limit, is 0.5 micrograms per liter (equivalent to 0.5 parts per billion). The maximum contaminant level goal, representing the level at which no health effects are expected, is zero. That gap between the legal limit and the safety goal reflects a practical reality: achieving absolute zero is not feasible with current treatment technology, so the enforceable standard is set as low as treatment systems can reliably achieve.
Public water systems are required to test for PCBs and report results. If your water comes from a municipal supply, your utility publishes an annual Consumer Confidence Report (sometimes called a water quality report) that lists contaminant levels, including PCBs if they’ve been detected. These reports are typically available on your water utility’s website or by request.
How PCBs Are Detected in Water
Testing for PCBs in water requires specialized laboratory analysis. The standard approach involves extracting a roughly one-liter water sample with a chemical solvent that pulls PCBs out of the water. The concentrated extract is then run through a gas chromatograph equipped with a highly sensitive electron capture detector, which can identify and measure individual PCB compounds at very low concentrations.
This type of testing is not something you can do with a home test kit. If you have concerns about PCBs in a private well, particularly if you live near a former industrial site or Superfund location, you would need to send a sample to a certified environmental laboratory. State environmental or health departments can often direct you to accredited labs and may offer guidance on whether testing is warranted based on known contamination in your area.
Reducing Your Exposure
For most people on a public water system, PCBs in tap water are not the primary exposure route. Municipal treatment and monitoring keep levels well below the legal limit in the vast majority of systems. The bigger concern is dietary, particularly through fish caught in contaminated waters. State and local fish consumption advisories exist for thousands of water bodies across the country, and checking these before eating recreationally caught fish is the single most effective step you can take.
If you rely on a private well near an industrial area or known contamination site, laboratory testing is the only way to know your PCB levels. Activated carbon filtration systems, including granular activated carbon filters used in some whole-house or point-of-use setups, are effective at removing PCBs from drinking water. Standard pitcher-style carbon filters may reduce levels but are not specifically rated for PCB removal at the concentrations that matter.