Talking about online documents, have you checked this one ?
http://www.inchem.org/documents/ehc/ehc/ehc216.htm
Makes me think twice,
"
2. CHEMISTRY OF DISINFECTANTS AND DISINFECTANT BY-PRODUCTS
2.1 Background
The use of chlorine (Cl2) as a water disinfectant has come under
scrutiny because of its potential to react with natural organic matter
(NOM) and form chlorinated disinfectant by-products (DBPs). Within
this context, NOM serves as the organic DBP precursor, whereas bromide
ion (Br-) serves as the inorganic precursor. Treatment strategies
generally available to water systems exceeding drinking-water
standards include removing DBP precursors and using alternative
disinfectants for primary and/or secondary (distribution system)
disinfection. Alternative disinfectant options that show promise are
chloramines (NH2Cl, monochloramine), chlorine dioxide (ClO2) and
ozone (O3). While ozone can serve as a primary disinfectant only and
chloramines as a secondary disinfectant only, both chlorine and
chlorine dioxide can serve as either primary or secondary
disinfectants.
Chloramine presents the significant advantage of virtually
eliminating the formation of chlorination by-products and, unlike
chlorine, does not react with phenols to create taste- and
odour-causing compounds. However, the required contact time for
inactivation of viruses and Giardia cysts is rarely obtainable by
chloramine post-disinfection at existing water treatment facilities
(monochloramine is significantly less biocidal than free chlorine).
More recently, the presence of nitrifying bacteria and nitrite
(NO2-) and nitrate (NO3-) production in chloraminated distribution
systems as well as the formation of organic chloramines have raised
concern.
The use of chlorine dioxide, like chloramine, can reduce the
formation of chlorinated by-products during primary disinfection.
However, production of chlorine dioxide, its decomposition and
reaction with NOM lead to the formation of by-products such as
chlorite (ClO2-), a compound that is of health concern.
If used as a primary disinfectant followed by a chloramine
residual in the distribution system, ozone can eliminate the need for
contact between DBP precursors and chlorine. Ozone is known to react
both with NOM to produce organic DBPs such as aldehydes and increase
levels of assimilable organic carbon and with bromide ion to form
bromate.
A thorough understanding of the mechanisms of DBP formation
allows microbial inactivation goals and DBP control goals to be
successfully balanced. This chapter examines a range of issues
affecting DBP formation and control to provide guidance to utilities
considering the use of various disinfecting chemicals to achieve
microbial inactivation with DBP control.
2.2 Physical and chemical properties of common disinfectants and
inorganic disinfectant by-products
The important physical and chemical properties of commonly used
disinfectants and inorganic DBPs are summarized in Table 1.
2.2.1 Chlorine
Chlorine, a gas under normal pressure and temperature, can be
compressed to a liquid and stored in cylindrical containers. Because
chlorine gas is poisonous, it is dissolved in water under vacuum, and
this concentrated solution is applied to the water being treated. For
small plants, cylinders of about 70 kg are used; for medium to large
plants, tonne containers are common; and for very large plants,
chlorine is delivered by railway tank cars or road (truck) tankers.
Chlorine is also available in granular or powdered form as calcium
hypochlorite (Ca(OCl)2) or in liquid form as sodium hypochlorite
(NaOCl; bleach).
Chlorine is used in the form of gaseous chlorine or hypochlorite
(OCl-). In either form, it acts as a potent oxidizing agent and often
dissipates in side reactions so rapidly that little disinfection is
accomplished until amounts in excess of the chlorine demand have been
added. As an oxidizing agent, chlorine reacts with a wide variety of
compounds, in particular those that are considered reducing agents
(hydrogen sulfide [H2S], manganese(II), iron(II), sulfite [SO32-],
Br-, iodide [I-], nitrite). From the point of view of DBP formation
and disinfection, these reactions may be important because they may be
fast and result in the consumption of chlorine.
Chlorine gas hydrolyses in water almost completely to form
hypochlorous acid (HOCl):
Cl2 + H2O -> HOCl + H+ + Cl-
The hypochlorous acid dissociates into hydrogen ions (H+) and
hypochlorite ions in the reversible reaction:
HOCl <-> H+ + OCl-
Hypochlorous acid is a weak acid with a p Ka of approximately
7.5 at 25?C. Hypochlorous acid, the prime disinfecting agent, is
therefore dominant at a pH below 7.5 and is a more effective
disinfectant than hypochlorite ion, which dominates above pH 7.5.
The rates of the decomposition reactions of chlorine increase as
the solution becomes more alkaline, and these reactions can
theoretically produce chlorite and chlorate (ClO3-); they occur
during the electrolysis of chloride (Cl-) solutions when the anodic
and cathodic compartments are not separated, in which case the
chlorine formed at the anode can react with the alkali formed at the
cathode. On the other hand, hypochlorous acid/hypochlorite (or
hypobromous acid/hypobromite, HOBr/OBr-) can be formed by the action
of chlorine (or bromine) in neutral or alkaline solutions."
What about this ?
"1.5.2.3 Uncertainties of epidemiological data
Even in well designed and well conducted analytical studies,
relatively poor exposure assessments were conducted. In most studies,
duration of exposure to disinfected drinking-water and the water
source were considered. These exposures were estimated from
residential histories and water utility or government records. In only
a few studies was an attempt made to estimate a study participant's
water consumption and exposure to either total THMs or individual
species of THMs. In only one study was an attempt made to estimate
exposures to other DBPs. In evaluating some potential risks, i.e.,
adverse outcomes of pregnancy, that may be associated with relatively
short term exposures to volatile by-products, it may be important to
consider the inhalation as well as the ingestion route of exposure
from drinking-water. In some studies, an effort was made to estimate
both by-product levels in drinking-water for etiologically relevant
time periods and cumulative exposures. Appropriate models and
sensitivity analysis such as Monte Carlo simulation can be used to
help estimate these exposures for relevant periods.
A major uncertainty surrounds the interpretation of the observed
associations, as exposures to a relatively few water contaminants have
been considered. With the current data, it is difficult to evaluate
how unmeasured DBPs or other water contaminants may have affected the
observed relative risk estimates.
More studies have considered bladder cancer than any other
cancer. The authors of the most recently reported results for bladder
cancer risks caution against a simple interpretation of the observed
associations. The epidemiological evidence for an increased relative
risk of bladder cancer is not consistent -- different risks are
reported for smokers and non-smokers, for men and women, and for high
and low water consumption. Risks may differ among various geographic
areas because the DBP mix may be different or because other water
contaminants are also present. More comprehensive water quality data
must be collected or simulated to improve exposure assessments for
epidemiological studies.
Note: After the printing of the document, Dr James Huff kindly
brought to the attention of the Secretariat that a study on the
carcinogenicity of sodium hypochlorite, and another on the
carcinogenicity of bromodichloromethane, chlorodibromomethane, bromoform,
chlorine, and chloramine, were not cited in the document. The authors'
abstracts of these studies are given below.
Soffritti M, Belpoggi F, Lenzi A, Maltoni C (1997) Results of long-term
carcinogenicity studies of chlorine in rats. Ann NY Acad Sci,
837: 189-208.
Four groups, each of 50 male and 50 female Sprague-Dawley rats, of the
colony used in the Cancer Research Center of Bentivoglio of the Ramazzini
Foundation, 12 weeks old at the start of the study, received drinking
water containing sodium hypochlorite, resulting in concentrations of active
chlorine of 750, 500, and 100 mg/l (treated groups), and tap water (active
chlorine < 0.2 mg/l) (control group), respectively, for 104 weeks. Among
the female rats of the treated groups, an increased incidence of lymphomas
and leukemias has been observed, although this is not clearly dose related.
Moreover, sporadic cases of some tumors, the occurrence of which is extremely
unusual among the untreated rats of the colony used (historical controls),
were detected in chlorine-exposed animals. The results of this study confirm
the results of the experiment of the United States National Toxicology
Program (1991), which showed an increase of leukemia among female Fischer
344/N rats following the administration of chlorine (in the form of sodium
hypochlorite and chloramine) in their drinking water. The data here presented
call for further research aimed at quantifying the oncogenic risks related to
the chlorination of drinking water, to be used as a basis for consequent
public health measures.
Dunnick JK, Melnick RL (1993) Assessment of the carcinogenic potential of
chlorinated water: experimental studies of chlorine, chloramine, and
trihalomethanes. J Natl Cancer Inst, 85: 817-822.
BACKGROUND: Water chlorination has been one of the major disease prevention
treatments of this century. While epidemiologic studies suggest an association
between cancer in humans and consumption of chlorination byproducts in
drinking water, these studies have not been adequate to draw definite
conclusions about the carcinogenic potential of the individual byproducts
PURPOSE: The purpose of this study was to investigate the carcinogenic
potential of chlorinated or chloraminated drinking water and of four organic
trihalomethane byproducts of chlorination (chloroform, bromodichloromethane,
chlorodibromomethane, and bromoform) in rats and mice.
METHODS: Bromodichloromethane, chlorodibromomethane, bromoform, chlorine, or
chloramine was administered to both sexes of F344/N rats and (C57BL/6 x C3H)F1
mice (hereafter called B6C3F1 mice). Chloroform was given to both sexes of
Osborne-Mendel rats and B6C3F1 mice. Chlorine or chloramine was administered
daily in the drinking water for 2 years at doses ranging from 0.05 to 0.3
mmol/kg per day. The trihalomethanes were administered by gavage in corn oil
at doses ranging from 0.15 to 4.0 mmol/kg per day for 2 years, with the
exception of chloroform, which was given for 78 weeks.
RESULTS: The trihalomethanes were carcinogenic in the liver, kidney, and/or
intestine of rodents. There was equivocal evidence for carcinogenicity in
female rats that received chlorinated or chloraminated drinking water; this
evidence was based on a marginal increase in the incidence of mononuclear
cell leukemia. Rodents were generally exposed to lower doses of chlorine and
chloramine than to the trihalomethanes, but the doses in these studies were
the maximum that the animals would consume in the drinking water. The highest
doses used in the chlorine and chloramine studies were equivalent to a daily
gavage dose of bromodichloromethane that induced neoplasms of the large
intestine in rats. In contrast to the results with the trihalomethanes,
administration of chlorine or chloramine did not cause a clear carcinogenic
response in rats or mice after long-term exposure.
CONCLUSION: These results suggest that organic byproducts of chlorination are
the chemicals of greatest concern in assessment of the carcinogenic potential
of chlorinated drinking water."
When you're sure about something you have to be sure you read everything you know.
Peace,
MAIA
--------------------
Spiritual being, living a human experience ... The Shroomery Mandala
 
Use, do not abuse; neither abstinence nor excess ever renders man happy.
Voltaire
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, anyway you're right... oh forget it.
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