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.: Chlorine & Iron Related Bacteria
For several reasons, routine chemical
disinfectants that effectively
wipe out other bacteria are only modestly successful against iron bacteria.
Iron bacteria build up in thick layers,
each forming a slime around
bacterial cells that keeps disinfectants from penetrating beyond the surface
cells. In addition, mineral iron dissolved in water can absorb much of the
disinfectants before they reach the bacterial cells.
Chemical reactions occur far slower at the
cool temperatures common in wells, and bacterial cells need a long exposure
to the chemical for treatment to be effective.
Even if chlorine kills all the bacterial cells in the water, those in the
groundwater can be drawn in by pumping or drift back into the well.
Because of these factors, thoroughly treating an iron bacteria infestation
requires more than simply dumping chlorine into the well
Since the
discovery of chlorinating by-products in drinking water in 1974, numerous
toxicological studies (studies on the health effects from exposure to high
dosages contaminants usually involving animals in a lab) have been conducted.
These studies have shown several
disinfection by-products to be carcinogenic in laboratory animals (e.g.,
including
bromate, certain
trihalomethanes and
haloacetic acids). Some disinfection by-products have also been shown to
cause adverse reproductive or developmental effects in laboratory animals (e.g.,
chlorite and certain
trihalomethanes and
haloacetic acids).
Disinfection by-products
are formed
when disinfectants used in water treatment plants react with bromide and/or
natural organic matter (i.e., decaying vegetation) present in the source water.
Different disinfectants produce different types or amounts of disinfection
by-products. Disinfection by-products for which regulations have been
established have been identified in drinking water, including trihalomethanes,
haloacetic acids, bromate, and chlorite.
Trihalomethanes (THM)
are a group of four chemicals that are formed along with other disinfection
by-products when chlorine or other disinfectants used to control microbial
contaminants in drinking water react with naturally occurring organic and
inorganic matter in water. The trihalomethanes are chloroform,
bromodichloromethane, dibromochloromethane, and bromoform.
EPA has
published the
Stage 1 Disinfectants/Disinfection Byproducts Rule to regulate total
trihalomethanes (TTHM) at a maximum allowable annual average level of
80 parts per billion. This standard will replace the current standard of a
maximum allowable annual average level of 100 parts per billion in December 2001
for large surface water
public water systems. The standard will become effective for the first time
in December 2003 for small surface water and all ground water systems.
Haloacetic Acids (HAA5)
are a group of chemicals that are formed along with other disinfection
by-products when chlorine or other disinfectants used to control microbial
contaminants in drinking water react with naturally occurring organic and
inorganic matter in water. The regulated haloacetic acids, known as HAA5, are:
monochloroacetic acid, dichloroacetic acid, trichloroacetic acid,
monobromoacetic acid, and dibromoacetic acid. EPA has published the
Stage 1 Disinfectants/Disinfection By-products Rule to regulate HAA5 at
60 parts per billion annual average. This standard will become effective for
large surface water
public water systems in December 2001 and for small surface water and all
ground water public water systems in December 2003.
------------------------
Bromate
is a chemical that is formed when ozone used to disinfect drinking water reacts
with naturally occurring bromide found in source water. EPA has established the
Stage 1 Disinfectants/Disinfection Byproducts Rule to regulate bromate at
annual average of
10 parts per billion in drinking water. This standard will become effective
for large
public water systems by December 2001 and for small surface water and all
ground public water systems in December 2003.
------------------------
Chlorite
is a byproduct formed when chlorine dioxide is used to disinfect water. EPA has
published the
Stage 1 Disinfectants/Disinfection Byproducts Rule to regulate chlorite at a
monthly average level of 1 part per million in drinking water. This standard
will become effective for large surface water
public water systems in December 2001 and for small surface water and all
ground water public water systems in December 2003.
Sourced from US E.P.A.
publicly available documents
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