Threats to Human Health: Use of Chlorine, an Obsolete Treatment Technology - Global Drinking Water Management and Conservation - page 190

Chapter 9
Threats to Human Health: Use
of Chlorine, an Obsolete Treatment
Technology

9.1 Introduction

Although chlorine is not the only disinfecting agent available to the water supply
industry, it is the most widely used disinfectant in North America. It is currently
employed by over 98 percent of all US water utilities that disinfect drinking water
(Calomiris and Christman 1998 ). However, it is ineffective against parasitic proto-
zoans Cryptosporidium parvum and Giardia lamblia. The use of chlorine as a
disinfectant has one major drawback. Disinfection byproducts (DBPs) are formed
through chemical reaction between natural organic matters (NOMs) and the disin-
fectant (i.e. chlorine, chloramine and chlorine dioxide) in the treatment of drinking
water. Chlorinated DBPs have been recognized as a potential public health concern
in drinking water since DBPs were

first reported in the1970s 1 and identi ed as a

carcinogen in 1976 (National Cancer Institute 1976 ). Since then, more than 700
chemical compounds associated with DBPs such as trihalomethanes (THMs) and
haloacetic acids (HAAs) have been identi

ed, which are estimated to account for
approximately 50 percent of the total organic halides (TOX) formed by chlorination
(Villanueva et al. 2014 ). As the main DBPs, THMs make up around 20 30 percent

of TOX, and they are the most commonly regulated (Itoh et al. 2011 ). In particular,
the maximum acceptable concentration of total THMs in the European Union (EU),
Canada, and Ontario is 100

-

μ g/L, but in Ontario a further reduction to 80 μ g/L was

under active consideration (in 2008 2009), to bring it in line with the USEPA, which

also has a maximum Acceptable Concentration (MAC) of 80 μ g/L. However, as of
May 2014, the MAC in Ontario and Canada is still 100

-

g/L.
It is clear that the long-term health risks associated with the use of chlorine are
being recognized. However, the sampling requirement for THMs is somewhat lax:
samples are supposed to be a

μ

“ running annual average ” or a moving average of the

four past quarters; a single result that exceeds the 100 g/L is not interpreted as

μ

1

In 1974, Rook ( 1974 ) first discovered DBPs in the Netherlands.