U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004–3032

February 2007

Studies on Disinfection By-Products and Drinking Water

Printed on recycled paper

Drinking water is disinfected with 

chemicals to remove pathogens, such 

as Giardia and Cryptosproridium, and 

prevent waterborne diseases such as 

cholera and typhoid. During disinfection, 

by-products are formed at trace concentrations. Because some of these byproducts are suspected carcinogens, 

drinking water utilities must maintain the 

effectiveness of the disinfection process 

while minimizing the formation of byproducts. 

During disinfection, the type and 

concentration of the disinfection byproducts formed depends on the type and 

amount of dissolved organic carbon present in the source water and on the chemical disinfectant used. These disinfectants 

include any or a combination of chlorine, 

ozone, chlorine dioxide, or chloramines. 

Chlorine is the most common disinfectant 

in the United States, because it is effective, easy to use, 

and inexpensive. When chlorine is used for disinfection, 

it produces halogenated by-products. Specific compound 

classes, such as trihalomethanes and haloacetic acids, 

make up a majority of these halogenated by-products. 

Trihalomethanes have been shown to cause cancer in 

laboratory animals, and some haloacetic acids produce 

liver tumors in mice. Increased incidence of spontaneous 

abortions or stillbirths, or latent effects such as cancer, 

have been attributed to exposure to low concentrations of 

disinfection by-products. The fate of these disinfection 

by-products in the environment and ways to change the 

potential of source water to produce them is an important 

aspect of drinking-water research. 

The fate of these disinfection by-products in the 

environment has been investigated in several studies by 

scientists of the U.S. Geological Survey (USGS). As 

water moves through wastewater treatment wetlands, most 

disinfection by-products are removed through volatilization, sorption, or degradation (Stricos-Martin, 1998; Keefe 

and others, 2004). At a constructed demonstration wetland 

near Phoenix, Arizona, USGS scientists found that the 

trihalomethanes decreased as much as 97 percent, while 

haloacetic acids decreased as much as 96 percent (Rostad 

and others, 2000a). 

USGS scientists also investigated the fate of disinfection by-products during ground-water recharge. When 

disinfected wastewater recharges an aquifer, the disinfection by-products (volatile and nonvolatile) persist in the 

ground water as the recharged water moves downward and 

away from the source (Barber and others, 1997). 

The major concern of drinking-water utilities is the 

potential of a source water to form disinfection byproducts. Waters from different hydrologic sources and 

conditions have different potentials to form disinfection 

by-products. Utilities have long mixed water from different sources to balance effective disinfection with the 

formation of disinfection by-products and the final 

composition of the treated water. 

Determining the composition of source water and 

understanding the hydrologic conditions and processes 

that cause changes in its potential to form disinfection byproducts may help utilities produce better drinking water. 

USGS studies have shown that as water passes through a 

wetland, the amount of dissolved organic carbon increases 

(Barber and others, 2001), and the increase in dissolved 

organic carbon increases the water’s formation potential 

for disinfection by-products (Rostad and others, 2000a). 

Changes in vegetation in wetlands and around reservoirs 

Sampling for distribution by-products in wetlands near Phoenix, Arizona.
that store drinking water may help minimize inputs of 

organic carbon to these source waters. 

Along the Mississippi River from Minneapolis to New 

Orleans, USGS scientists found that the dissolved organic 

carbon concentration decreased with distance downstream 

(Rathbun, 1995). The formation potentials of the surface 

waters to form disinfection by-products decreased also, 

paralleling the decrease in dissolved organic carbon. The 

highest dissolved organic carbon and formation potentials 

were found in the Upper Mississippi River.

Ground water often is used as a drinking water source. Spreading basins are used 

in California to infiltrate reclaimed surface 

water into an aquifer in order to recharge 

ground-water resources. The quality of the 

reclaimed water is improved as it infiltrates 

downward through the aquifer material 

(Schroeder, 2003). USGS scientists found 

that the formation potential of reclaimed 

water did not appear to be affected much 

by infiltration through an aquifer during ground-water 

recharge (Rostad and Rathbun, 2003). However, a study 

of the dissolved organic carbon showed a more complex 

process. Aquifer recharge removed about 60 percent of 

the dissolved organic carbon from the reclaimed water, but 

the remaining 40 percent that was partially derived from 

organic matter in the aquifer was more reactive in producing disinfection by-products than the 60 percent that was 

removed (Leenheer and others, 2001; Rostad, 2002).

A limestone aquifer in northern Florida was investigated where the surface water connects to ground water 

through a karstic limestone formation. Holes and tunnels 

Sampling for dissolved organic carbon and 

disinfection by-product information potential in 

north central Florida

Sampling for dissolved organic carbon and disinfection by-product formation potentials at spreading basins 

for ground-water recharge, southern California
in the limestone provide direct pathways for the flow of 

surface water into the aquifer below. The surface-water 

sources are called blackwater streams because of high 

concentrations of dissolved organic carbon. The ground 

water had much lower concentrations of dissolved organic 

carbon than the surface water above. 

The tendency to form disinfection by-products from 

the tannin-derived blackwater and the infiltrated ground 

water in the limestone aquifer in northern Florida were 

quite different (Rostad and others, 2000b). The dissolved 

organic carbon was fractionated by USGS scientists in 

order to determine which fractions were the most reactive in producing disinfection by-products. The drastic 

decrease in dissolved organic carbon during infiltration 

produced only minor differences in the distribution of 

the fractions of dissolved organic carbon, except for the 

colloid fraction. In this study, the colloid fraction was 

essentially removed during infiltration through the limestone karst.

USGS scientists found that this colloid fraction, 

which has large particles, was the most reactive in producing disinfection by-products. In surface waters, the colloid 

fraction contributes a significant portion of the dissolved 

organic carbon, and that portion is very reactive. The 

Surface water seeping into ground water through limestone karst in north central Florida

loss of this reactive colloid fraction in the ground water 

had the most significant effect on reducing the formation 

potential. Although the hydrophobic acid fraction was the 

most abundant fraction in the ground water, it had lower 

reactivity in producing disinfection by-products than other 

fractions. The most effective disinfection for a drinking-water utility using this ground water would involve 

removing the most reactive fraction of dissolved organic 

carbon prior to disinfection. 

Studies such as these provide vital information to 

help drinking-water utilities understand the causes for 

the changes they find in the formation potential of their 

source waters. If certain parts of the organic matter in 

source waters produce more disinfection by-products 

than other parts, the drinking-water utilities may be able 

to focus their drinking-water treatment on the fraction most responsible for the formation of disinfection 

by-products. This will assist drinking-water utilities in 

minimizing the formation of disinfection by-products 

while maintaining effective disinfection at a reasonable 

cost. Additional research is needed to better understand 

the reactive fractions of the dissolved organic matter and 

to address removal of the dissolved organic carbon fractions that are not removed by present water-treatment 

processes. 
References Cited

Barber, L.B., Brown, G.K., Leenheer, J.A., Noyes, T.I., Rostad, C.E., and Thorn, K.A., 1997, Organic contaminants 

that persist during aquifer storage and recovery of reclaimed water in Los Angeles County, California: American 

Water Resources Association, Annual Conference and Symposium on Conjunctive Use of Water Resources, 

Aquifer Storage and Recovery, Long Beach, California, October 19–23, 1997, p. 261–272. 

Barber, L.B., Leenheer, J.A., Noyes, T.I., Stiles, E.A., 2001, Nature and transformation of dissolved organic matter in 

treatment wetlands: Environmental Science and Technology, v. 35, p. 4805–4816.

Keefe, S.H., Barber, L.B., Runkel, R.L., Ryan, J.N., 2004, Fate of volatile organic compounds in constructed wastewater treatment wetlands: Environmental Science and Technology, v. 38, p. 2209–2216.

Leenheer, J.A., Rostad, C.E., Barber, L.B., Schroeder, R.A., Anders, R., Davisson, M.L., 2001, Nature and chlorine 

reactivity of organic constituents from reclaimed water in groundwater, Los Angeles County, California: Environmental Science and Technology, v. 35, p. 3869–3876.

Rathbun, R.E., 1995, Potentially Deleterious Effects of Chlorinating Mississippi River Water for Drinking Purposes, 

in Contaminants in the Mississippi River, 1987–92: U.S. Geological Survey Circular 1133, p. 136–140.

Rostad, C.E., 2002, Fate of disinfection by-products in the subsurface in Aiken, G.R. and Kuniansky, E.L. eds., U.S. 

Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: U.S.

Geological Survey Open-File Report 02–89, p. 26–29.

Rostad, C.E., Martin, B.S., Barber, L.B., Leenheer, J.A., and Daniel, S.R., 2000a, Effect of a constructed wetland on 

disinfection by-products, Removal processes and Production of precursors: Environmental Science and Technology, v. 34, p. 2703–2710.

Rostad, C.E., Leenheer, J.A., Katz, B.G., Martin, B.S., Noyes, T.I., 2000b, Characterization and disinfection byproduct formation potential of natural organic matter in surface and ground waters from northern Florida, 11th 

Chapter in the American Chemical Society Symposium Series 761, Natural Organic Matter and Disinfection Byproducts: Characterization and Control in Drinking Water, p. 154–172. 

Rostad, C.E., Rathbun, R.E., 2003, Distributions of halogenated organic compounds, Chapter 11 in Schroeder, R.A., 

ed., Water-quality changes and organic-carbon characterization during recharge with recycled water at a research 

basin in Montebello Forebay, Los Angeles, California: U.S. Geological Survey Water-Resources Investigations 

Report 03–4146, p. 109–115. 

Schroeder, R.A., ed., 2003, Water-quality changes and organic-carbon characterization during recharge with recycled water at a research basin in Montebello Forebay, Los Angeles, California: U.S. Geological Survey WaterResources Investigations Report 03–4146. 

Stricos-Martin, B., 1998, Effects of wetlands on disinfection by-products and their formation potentials: Golden, 

Colorado School of Mines, Master of Science thesis, 109 p.

Colleen E. Rostad (cerostad@usgs.gov)

For more information, contact:

Chief Scientist, Hydrology

Branch of Hydrologic Research

U.S. Geological Survey

409 National Center

12201 Sunrise Valley Drive

Reston, VA 20192