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What does 25 ppm PCBs in water mean?
To answer this question, 25 ppm is a very high PCB concentration in water, and is much more significant than 50 ppm in soil. In the sections below, I will explain first what the "ppm" means, then I will explain why 25 ppm in water is significant.
What is a ppm?
Concentrations of pollutants in the environment are often reported as ppm, ppb, ppt, etc. These are abbreviations for parts per million, parts per billion, parts per trillion, etc. PCB concentrations are never actually measured in these units - it is simply a convenient way to report the PCB concentration. The units "ppm" means one part PCB for one million parts of something else. If the "something else" is water, the real units are mg/l which means one milligram of PCB per litre of water. If the "something else" is soil, the real units are mg/kg which means one milligram of PCB per kilogram of soil. Other equivalent concentrations are listed in the table below. It is very important to understand that although one part in a million, billion or trillion seems like an insignificant quantity, it is not when dealing with toxic chemicals.
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Water sample |
Soil sample |
Parts per million |
mg/l ug/ml ng/ul |
mg/kg ug/g ng/mg |
Parts per billion |
ug/l ng/ml pg/ul |
ug/kg ng/g pg/mg |
Parts per trillion |
ng/l pg/ml fg/ul |
ng/kg pg/g fg/mg |
What does 25 ppm PCBs in water mean?
Water cannot dissolve this much PCBs – the maximum amount of PCBs that can be dissolved in water ranges from 0.00076 ppm to 1.6 ppm, depending on which PCB congeners are present. The commercial PCB mixtures used by Westinghouse have aqueous solubilities in the range of .003 to 0.25 ppm, meaning that this is the maximum amount that can be dissolved in water. (Erickson, 1997). Therefore, in order to find 25 ppm PCBs in water, there must be some contaminated sediment or contaminated oil in the water sample. Both sediment and oil can contain very high concentrations of PCBs.
How does 25 ppm PCBs in water compare to water quality criteria?
The regulatory limits for PCB discharges to surface water are generally set so low that they reflect the limits of detection using laboratory equipment. The Clean Water Act establishes a water quality criterion for chronic exposure through drinking water and fish ingestion as 79 pg/l (0.000000079 ppm). Acute toxicity is estimated to occur above 2 ppb (.002 ppm). The Safe Drinking Water Act proposes a maximum contaminant level of 0.5 ppb PCB (Erickson, 1997). PCB water quality criteria are also established at the State level and on site-specific bases.
What does this mean for Lemon Lane and Illinois Central/Quarry Spring?
Until we have an official report showing the location of the samples, the sample collection method, and the laboratory analytical methods, it is premature to say what high reading means for Illinois Central/Quarry Spring and Lemon Lane. There is enough PCB contaminated oil and sediment at Lemon Lane to contaminate groundwater and surface water forever.
Reference: Erickson, Mitchell D., 1997. The Analytical Chemistry of PCBs. CRC Press/ Lewis Publishers, Boca Raton, Florida.
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Warning! Eat no fish from Clear Creek, Pleasant Run, Salt or Richland Creeks.
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