Total Trihalomethanes in Kentucky’s Streams and Rivers


Trihalomethanes are one of the main byproducts of chemical water disinfection systems and other chemical contaminations. Total Trihalomethanes (TTHMs) are prevalent in chlorinated water supplies, according to the US Environmental Protection Agency (EPA).

TTHM Chemical Formation

TTHMs are formed when chlorine, a common disinfectant, is added to water containing organic materials, which occurs in most water treatment plants. TTHMs are tasteless and odorless, and generally form in greater quantities in warmer climates and particularly in warmer seasons.

Currently, chlorination is the chief method for water disinfection in the United States. TTHM formation is a greater danger in larger water treatment operations because large treatment plants must chlorinate the water for a greater amount of time, and larger water sources tend to have higher concentrations of organic matter. Limiting the amount of organic matter taken into water treatment plants has been identified by the EPA as the most effective way of reducing TTHM and other disinfection byproduct formation.

TTHMs versus Waterborne Disease

Historically, TTHMs have not been heavily regulated because the carcinogenic risk of TTHMs (discussed below) is less significant than the risk of waterborne disease if drinking water was not chlorinated.

The EPA has in no way recommended that disinfection be withheld or reduced in order to reduce TTHM concentration, which is why organic matter limitation is the recommended method of TTHM reduction.

Health Risks of TTHMs

At elevated levels, TTHMs have been associated with increased risk of cancer and detrimental reproductive effects. Specifically, TTHMs have been linked to bladder, rectal, and pancreatic cancers. TTHMs have also been implicated in certain types of spine and neural birth defects, as well as kidney, liver, and central nervous system problems in teens and adults.

However, there are many discrepancies in the research, and there is not currently a scientific consensus on what dangers low-level doses of TTHMs might pose over a long period of time. However, there is a consensus that high doses of TTHMs do pose a clear risk, hence the EPA has issued two different regulations that impose limits on TTHM levels and provide recommendations for ways of reducing TTHM levels, particularly through organic matter limitation with activated carbon.

EPA Regulation of TTHMs: Stage 2 Disinfectants and Disinfection Byproducts Rule

Currently, the EPA limits TTHM Maximum Contamination Levels (MCL) at 0.08 mg/L or 80 ppb, and there are Maximum Contaminant Level Goals (MCLGs) for some of the individual TTHM constituents, including bromodichloromethane (zero), bromoform (zero), dibromochloromethane (0.06 mg/L), and chloroform (0.07 mg/L).

MCLs are legally mandated maximum levels, while MCLGs are not legally required, but are recommended contamination maximums.

Many activists and scientists have argued that the MCL for TTHMs should be lowered, but conclusive scientific evidence for even 0.08 mg/L levels of TTHMs being harmful is nonexistent.

TTHMs in Kentucky and Letcher County

Certain water districts in Kentucky have high levels of TTHMs, which sometimes exceed the MCL. On average, Kentucky has had 152 violations of the EPA MCL for TTHMs since 2004.

Additionally, the Letcher County Water District has the third-highest TTHM level in the state, with a 92.18 ppb TTHM level, which exceeds the 80 ppb MCL. A 98 ppb level is estimated to correlate with a 1 in 100,000 cancer risk.



This article was written by Ian Jaffe, a Duke University Robertson Scholar. Ian has interned with Headwaters this summer, researching local water quality and economic development opportunities. 


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