A few months later, Flint told its residents
that their water had high levels of organic
molecules called trihalomethanes. These
molecules are similar to methane molecules
(CH4), but three of the hydrogen atoms are
replaced with halogen (group 17) atoms—
fluorine, chlorine, bromine, or iodine. The
four most common trihalomethanes are
dibromochloromethane (CHClBr2), dichloro-bromomethane (CHCl2Br), trichloromethane
(CHCl3)—better known as chloroform—and
Trihalomethanes are a concern because
they have been linked with numerous health
concerns, including liver, kidney, lung, and
heart conditions. When the chlorine used to
disinfect water reacts with algae, leaves, and
weeds, trihalomethanes are produced.
Toxic levels of lead
Trihalomethanes are just one group of
chemicals associated with water contamination. Lead is another. This metal was a popular
choice for use as water pipes for centuries.
The Romans used the dense metal because
of its durability and malleability. Water pipes
are no longer made from lead, but older cities,
such as Flint, still rely on lead pipes—in addi-
times, they found that the 13,000 ppb reading
It is important to note that no level of lead
in the water supply is considered safe, but the
U.S. Environmental Protection Agency has set
a maximum level of lead contamination in the
tap water in 90% of homes at 15 ppb—also
known as the “action level.” That particular
sample of Flint water had a lead level close to
1,000 times the action level.
Oxidizing agents in water, such as dissolved
oxygen, can react with exposed lead pipes
causing soluble Pb2+ ions to enter the supply. Two chemical reactions are involved: 1)
oxidation, and 2) reduction. Both reactions are
called redox reactions, for short. In the oxidation reaction, lead loses electrons and forms
Pb2+ ions, as follows:
2 Pb (s) ➔ 2 Pb2+(aq) + 4 e–
In the reduction reaction, oxygen gains
electrons, as follows:
4 e– + 2 H2O (l) + O2 (aq) ➔ 4 OH– (aq)
Together, the oxidation and reduction reactions combine to give the full
2 Pb (s) + O2 (g) + 2 H2O (l)
➔ 2 Pb(OH) 2 (s)
January 2015: Flint
announces that the water
contains high levels of trihalomethanes, in violation
of the Safe Drinking Water
Act, but city officials tell
residents that the water is
LeAnne Walters’s son
develops rashes. High
levels of lead are
detected in the water
in her home.
tion to those made from copper and iron—
to transport water to people’s homes. No one
knows exactly how many lead pipes are used
in the United States, but the number is in the
millions. In addition to the pipes themselves,
lead is also found in alloys (mixtures of metals) in other parts of the plumbing system.
For example, the solder used to join pipes
together is an alloy of tin and lead.
In Flint, massive levels of lead entered the
water system. In one sample of water taken
from a Flint home, a lead level of 13,000 parts
per billion (ppb) was found. The chemists who
tested the water were skeptical at first. But
after repeating the experiment a number of
Water tests positive
for E. coli
advisory is issued
in parts of Flint.
www.acs.org/chemmatters 6 ChemMatters | DECEMBER 2016/JANUAR Y 2017
Above left, Otto Schwake, a postdoctoral microbiologist at
Virginia Tech, tested Flint tap water for waterborne pathogens.
Top, water flowing from a faucet in a hospital in Flint, Mich.
Above, pipes from the Flint water distribution system after the
city decided to use water from the local Flint River.
Right, water samples from Flint
collected by Virginia Tech scientists