Diapositiva 1

1
Disinfection By-Products in drinking water a
comparison between chlorine and chlorine dioxide
University of Modena and Reggio Emilia Department
of Public Health Sciences
Aggazzotti G, Fantuzzi G, Righi E, Predieri G,
Giacobazzi P.
University of Modena and Reggio Emilia
Department of Public Health Sciences Via Campi
287, 41100 Modena (Mo) - Italy
Introduction Drinking water disinfection with
chlorine (sodium hypochlorite) and chlorine
dioxide is commonly applied worldwide because of
its low costs and ease of use. However, water
disinfection can form several Disinfection
By-Products (DBPs) potentially dangerous for
human health. Trihalomethanes (THMs), chlorite
and chlorate are the most widespread and may have
harmful effects on human health. Particularly,
THMs exposure has been associated with cancer
risk and adverse pregnancy outcomes some of
THMs, such as the most dominant species,
chloroform and bromodichloromethane, are
considered as animal carcinogenic and classified
as 2B by the International Agency for Research on
Cancer. The aim of this study is to compare the
presence of DBPs in drinking water after either
chlorine or chlorine dioxide treatments.
Material and methods In July 2005 - February
2006, 12 waterworks (9 supplied by ground water
and 3 by mixed spring and surface water 4 using
chlorine and 8 chlorine dioxide for
disinfection), all managed by Agenzia dAmbito
per i Servizi Pubblici di Modena ATO in
Northern Italy, were sampled twice in summer and
in winter. In each sampling session, 4 water
samples were collected (Fig. 1) just before and
immediately after the treatment, at the tap close
to the disinfection plant and far from the plant.
Main DBPs (THMs, chlorite, chlorate, bromate and
haloacetic acids) were investigated by
ECD-headspace gaschromatography and Ionic
Chromatography/Mass Spectrometry IC/MS
techniques.
0
FIG.1 Sampling scheme 0 before disinfection,
1 immediately after the treatment, 2 at the
tap close to the disinfection plant and 3 far
from the plant
FIG.2 Total THMs levels, in summer and winter, at
different distances from the disinfection
plant in waterworks using chlorine and
chlorine dioxide
Results 14 samples of source water, collected
from 7 waterworks, showed the presence of
chlorate (range 1-65 µg/l) and 2 samples, within
the same water plant, showed traces of chloroform
(0.2 µg/l). After disinfection, THMs showed very
low values, on the whole (range lt0.01-26 µg/l).
Levels after chlorine treatment ranged from 0.3
to 26 µg/l (median value at point 3 3.5 µg/l),
while in those chlorine dioxide treated samples
ranged from lt0.01 to 1 µg/l. (median value at
point 3 0 µg/l). Moreover, concentrations
increased according to the distance from the
disinfection plant and were usually higher in
summer than in winter, mainly at point 3.
Chloroform appeared the most represented DBP
brominated THMs were measured at detectable
levels in chlorine treated samples only (range
lt0.01-1). Fig.2 compares the results of total
THMs, in winter and summer, in two water works
adopting chlorine and chlorine dioxide
disinfection treatment respectively.
Chlorite was evidenced in all chlorine dioxide
treated samples (range 21-290 µg/l median value
at point 3 96 µg/l), while no chlorite was
evidenced in chlorine treated samples, as
expected. Concentrations did not show significant
differences according to the distance from the
disinfection plant in 6 out of 8 waterworks, the
values appeared higher in winter compared to
summer levels. Fig. 3 shows the levels of
chlorite in winter and summer in two waterworks
both using chlorine dioxide treatment. Chlorate
was detected both in chlorine dioxide treated
samples (range 1-276 µg/l median value at point
3 44 µg/l), and chlorine treated samples (range
2-188 µg/l median value at point 3 26 µg/l).
Fig. 4 shows chlorate levels in summer and winter
in two waterworks adopting different disinfection
treatments. Bromate and haloacetic acids were
never evidenced in any sample.
FIG.3 Chlorite level, in summer and winter, at
different distances from the disinfection
plant in waterworks using cholorine dioxide
FIG.4 Chlorate level, in summer and winter, at
different distances from the disinfection
plant in waterworks using chlorine and
cholorine dioxide
Conclusions On the whole, the levels of the
investigated DBPs in drinking water samples from
12 waterworks in Northern Italy, did not show
concentrations of public health concern. Neither
chlorine nor chlorine dioxide form THMs at high
levels in our samples this is due to source
water which contains very low amount of organic
substance even in case of surface water. However,
the concentrations increase according to the
distance in time and space, but they never exceed
the THMs Italian limit (30µg/l). Chlorite,
produced by chlorine dioxide treatment only,
deserves attention as little information is
available on its chemical reactions and fate in
drinking water within each water system. More
important to be investigated is the presence of
chlorate, even though at levels lower than
chlorite but unexpectedly present in several
source water samples and in all the treated water
samples, whatever disinfection treatment is used.
While it is difficult to explain the presence of
chlorate in source water, chlorate after
treatment could be related to the solution of
sodium hypochlorite used both as single
disinfectant and to generate chlorine dioxide.

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Correspondence Prof.ssa Gabriella Aggazzotti -
Dipartimento di Scienze di Sanità Pubblica - Via
G. Campi, 287 - 41100 Modena Italy E-mail
g.aggazzotti_at_unimore.it