This is an HTML version of an attachment to the Official Information request 'Nitrate concentrations in Christchurch drinking water in the past 5 years'.
Inorganic chemicals
Maximum Acceptable Value for Nitrate (Short-term)
Based on health considerations, the concentration of nitrate (as NO3-) in drinking-water should
not exceed 50 mg/L.

Maximum Acceptable Value for Nitrite (Short-term)
Based on health considerations, the short-term concentration of nitrite (as NO2-) in drinking-
water should not exceed 3 mg/L.

Maximum Acceptable Value for Nitrate plus Nitrite (Short-term)
The sum of the ratios of the concentrations of each to its Maximum Acceptable Value (short-
term) should not exceed 1.

DWSNZ (2008): Maximum Acceptable Value for Nitrite (Long-term and Provisional)
Based on health considerations, the long-term concentration of nitrite (as NO2-) in drinking-
water should not exceed 0.2 mg/L.  The WHO guideline value for chronic (long-term) effects of
nitrite is considered provisional owing to uncertainty surrounding the relevance of the observed
adverse health effects for humans and the susceptibility of humans compared with animals.

Note that WHO (2011) no longer includes a long-term (chronic) guideline value for nitrite.
Nitrate and nitrite are included in the plan of work of the rolling revision of the WHO Guidelines for
Drinking-water Quality.
The Prescribed Concentration or Value (PCV) for nitrate in England and Wales is 50 mg/L as
nitrate.  The Prescribed Concentration or Value (PCV) for nitrite in England and Wales is 0.5 mg/L
as nitrite at the consumers’ taps and 0.1 mg/L at the WTP.  See Notes.
The  maximum  contaminant  level  or  MCL  for  nitrate  (USEPA  2009/2011)  is  10  mg/L  as  N,  and  1
mg/L for nitrite as N, or a total of 10 mg/L.  The maximum acceptable concentration in Canada is 10
mg/L for nitrate as N, and 1 mg/L for nitrite as NIn cases where nitrite is measured separately from
nitrate, the concentration of nitrite should not exceed 3.2 mg/L as NO -
2 .
The Australian Drinking Water Guidelines (NHMRC, NRMMC 2011) state that based on health
considerations, the guideline value of 50 mg-NO3/L (as nitrate) has been set to protect bottle-fed
infants  under  3  months  of  age.    Up  to  100  mg-NO3/L can be safely consumed by adults, and by
children over 3 months of age.  Where a water supply has between 50 and 100 mg-NO3/L nitrate,
active measures are required to ensure that those caring for infants are aware of the need to use
alternative water sources in making up bottle feeds for babies under 3 months of age.  Based on
health considerations, the concentration of nitrite in drinking water should not exceed 3 mg-NO2/L
(as nitrite).
Note  that  50  mg/L  nitrate  as  NO -
3   is  equivalent  to  11.3  mg/L  as  N,  3  mg/L  nitrite  as  NO2  is
equivalent to 0.9 mg/L as N, and 0.2 mg/L nitrite as NO -
2  is equivalent to 0.06 mg/L as N.
Sources to Drinking-water
1. To Source Waters
Nitrate and nitrite can enter the aquatic environment from the oxidation of vegetable and animal
debris and animal excrement.
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Inorganic chemicals
Nitrate and nitrite can also enter water from agricultural, domestic and industrial discharges.  Nitrate
is used in chemical fertilisers, oxidising agents in the chemical industry, in the manufacture of glass,
enamels for pottery, matches, pickling meat and in the production of explosives.  A major source of
nitrate is from municipal wastewaters and septic tanks.  Nitrite is also used as a corrosion inhibitor in
industry, and as a food preservative, especially for curing meats.
2. From the Treatment Processes
The chlorination of raw waters containing significant amounts of ammonia or nitrite may lead to
increases in nitrate through their oxidation.  As 70% or more of the chlorine consumed during the
oxidation of ammonia leads to nitrogen (the gas) production, the increase in nitrate concentrations is
likely to be small unless ammonia concentrations are high.
3. From the Distribution System
Nitrite can be formed chemically in distribution pipes by Nitrosomonas bacteria during stagnation of
nitrate-containing and oxygen-poor drinking-water in galvanised steel pipes, or if chloramination is
used to provide a residual disinfectant but its occurrence is almost invariably sporadic.  Nitrification
in distribution systems can increase nitrite levels, usually by 0.2 – 1.5 mg/L.
Forms and Fate in the Environment
Nitrate and nitrite are naturally occurring ions which make up part of the nitrogen cycle.  Nitrate is
the oxidised form of combined nitrogen found in natural waters and in dilute aqueous solutions is
chemically unreactive.  Under anaerobic conditions nitrate may be reduced to nitrite and ammonia.
Nitrite is seldom present in surface waters at significant concentrations but may be present in
groundwaters.  High nitrite concentrations are generally indicative of contamination.  Incomplete
nitrification of ammonia and denitrification of nitrate result in the biochemical production of nitrite
which is generally present only under anaerobic conditions.
Typical Concentrations in Drinking-water
Nitrate was routinely measured in New Zealand drinking-water supplies as part of the Department of
Health three yearly surveillance programme.  Of 1908 samples analysed between 1983 and 1989, 14
samples (0.7%) contained concentrations equal to or exceeding the 1984 MAV of 10 mg/L (N).
The P2 Chemical Determinand Identification Programme, sampled from 673 zones, found nitrate
concentrations to range from “not detectable” (nd) to 30 mg/L as NO3-N, with the median
concentration being 0.2 mg/L (Limit of detection = 0.1 mg NO3-N/L).  The Priority 2 Identification
Programme found 6 distribution zones supplying drinking-water to a total of 1017 people with
nitrate at greater than the MAV (ESR 2001).
In 2012 the Canterbury District Health Board stated that 33 of 289 wells tested in Canterbury
exceeded the MAV for nitrate, the majority being around Ashburton.
26,177 water utilities in the US reported detecting nitrate in tap water since 2004, according to
EWG's analysis of water quality data supplied by state water agencies, with the highest concentration
being 30 mg/L as N.
Nitrite was not measured routinely in New Zealand drinking-water supplies as part of the
Department of Health three yearly surveillance programme.
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Inorganic chemicals
The P2 Chemical Determinand Identification Programme, sampled from 227 zones, found nitrite
concentrations to range from “not detectable” (nd) to 0.088 mg/L, with the median concentration
being “nd” (Limit of detection = 0.005 NO -
2  -N mg/L).  The Priority 2 Identification Programme
found no distribution zones supplying drinking-water with nitrite at greater than the MAV (ESR
2,719 water utilities in the US reported detecting nitrite in tap water since 2004, according to EWG's
analysis of water quality data supplied by state water agencies, with the highest concentration being
2.78 mg/L as N.
Removal Methods
Nitrate is not removed from water by classical methods of treatment.  Ion exchange systems have
been developed for removing nitrate, but dilution with water of lower nitrate concentration from
another source, where one is available, is commonly used.
Treatment of the water with an oxidising agent such as chlorine will convert the nitrite to nitrate.
The nitrate can then be treated as explained for nitrate.  The USEPA Maximum Concentration Level
(MCL) for nitrite indicates that the concentration at which it might be of concern is ten times less
than the MCL for nitrate.  The oxidation of high nitrite levels to nitrate therefore will not create an
unacceptably high nitrate concentration in the water, unless the nitrate level is already high, or the
nitrite level is extremely high.
Analytical Methods
Referee Method
Cadmium Reduction Method (APHA 4500-NO -E).
Some Alternative Methods
Ion Chromatography Method (APHA 4110B; USEPA 300.1).
Nitrate Electrode Method (APHA 4500-NO  D).
Referee Method
Colorimetric Method (APHA 4500-NO  B).
Some Alternative Methods
Ion Chromatography Method (APHA 4110 B; USEPA 300.1).
Health Considerations
For nitrate, the main sources of exposure are vegetables, especially leafy vegetables.  Other food
sources include baked and processed cereal products and cured meat.  For an average adult
consumer who lives in an area with low drinking-water contamination, total exposure to nitrate from
food and water is estimated to be about 60 to 90 mg per person per day, of which at least 90% is
from food.  For high consumers of vegetables, the intake of nitrate may reach 200 mg per person per
day.  Similar intakes could result from high consumption of water contaminated with more than 50
mg/L nitrate (as NO -
3 ).
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Inorganic chemicals
For nitrite, the main source of exogenous human exposure is also food.  Important sources include
cereal products, vegetables and cured meat.  Over the last 30 years, the relative contribution of cured
meat to dietary exposure to nitrite for an average consumer has decreased from about 40% to about
20%.  For high consumers of cured meat, the relative contribution may have reached 90%.  The total
intake of exogenous nitrite is estimated to be about 0.75 to 2.2 mg per day for an adult with an
average food consumption pattern.
Ingested nitrate is absorbed readily and completely from the upper small intestine.  Nitrite may be
absorbed directly from the stomach as well as from the small intestine.  When nitrate levels in
drinking-water exceed 50 mg/L as NO -
3 , drinking-water may become the major source of total
nitrate intake, especially for bottle-fed infants.
The toxicity of nitrate in humans is thought to be due solely to its reduction to nitrite.  Bacteria are
responsible for most of the conversion of nitrate to nitrite in the gastrointestinal system.
Consequently, the risk of methemoglobinemia from ingestion of nitrate depends not only on the dose
of nitrate, but also on the number and type of enteric bacteria.  In healthy adults, available data
suggest about 5% of a dose of nitrate is reduced to nitrite by bacteria in the mouth.  Conversion of
nitrate to nitrite may also occur in the stomach if the pH of the gastric fluid is sufficiently high (above
pH 5) to permit bacterial growth.  This is of concern in adults with diseases such as achlorhydria or
atrophic gastritis.  It is commonly accepted that infants younger than 3 months may be highly
susceptible to gastric bacterial nitrate reduction, as their stomach pH is generally higher than in
In Hungary in 1975 to 1977, 190 cases of methaemoglobinaemia were reported, 94% in infants less
than three months of age.  The nitrate level in drinking water was more than 100 mg/L in 92% of
cases and between 40 and 100 mg/L in the remaining 8%.  In 1982, 96 cases of
methaemoglobinaemia were reported.  All cases were associated with privately dug wells, and 92%
of the patients were three months of age or younger.  Nitrate levels in drinking water were above
100 mg/L in 93% of cases and between 40 and 100 mg/L in the remaining 7%.  WHO (1985).
For over 40 years, there has existed a widespread belief that nitrate in drinking water is a primary
cause of infantile methemoglobinemia.  Hunter Comly originally proposed this theory in 1945 in a
report in the Journal of the American Medical Association after treating several infantile
methemoglobinemia victims.  Comly proposed that because nitrite is known to react directly with
hemoglobin to form methemoglobin, nitrate from drinking water must be converted to nitrite within
the gastrointestinal tract of infants.  Because many infants did not appear susceptible to
methemoglobinemia from nitrate-contaminated water, Comly suggested that the nitrate-to-nitrite
conversion might only occur in the presence of a bacterial infection of the upper gastrointestinal
tract, where such reactions could occur before nitrate is absorbed.  The nitrate-derived nitrite could
then react with haemoglobin to form methemoglobin and, in sufficient quantities, lead to the cyanosis
of methemoglobinemia.  This theory was reinforced by the fact that cyanosis typically subsided once
an infant was switched to an uncontaminated water supply.  Comly's hypothesis became widely
accepted as further research revealed a consistent pattern of elevated well water nitrate levels in
infantile methemoglobinemia cases.  Limiting infant exposure to nitrate was thus decided to be the
most prudent approach to protecting infant health, and a committee from the American Public Health
Association conducted a nationwide survey to determine a safe level of nitrate in water.  A total of
278 cases with 39 deaths were compiled.  The results showed that methemoglobinemia incidence
correlated with increasing nitrate levels.  Because no infantile methemoglobinemia cases were
observed with concentrations <10 ppm nitrate-nitrogen, the United States and the World Health
Organization established a maximum contaminant level (MCL) of 10 ppm nitrate-N for nitrate in
drinking water.  Over the last 20 years, however, a more complex picture of infantile
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Inorganic chemicals
methemoglobinemia causation has emerged which indicates that current limits on drinking water
nitrate may be unnecessarily strict.  It is now well established that diarrhoeal illness and some
gastrointestinal disturbances, typically accompanied by diarrhoea and/or vomiting, can lead to
methemoglobinemia in young infants without exposure to high-nitrate drinking water or exposure to
abnormal levels of nitrate through food.  There are literally dozens of reported infantile
methemoglobinemia cases associated with diarrhoea without exposure to nitrate-contaminated water.
Because diarrhoea was a prominent symptom in the majority of drinking water linked
methemoglobinemia cases, the evidence suggests that diarrhoea and/or gastrointestinal
infection/inflammation, not ingested nitrate, are the principle causative factors in infantile
methemoglobinemia.  A survey in Germany found that 53% of 306 infantile methemoglobinemia
cases reported diarrhoea.  Contrary to some reports, diarrhoea and vomiting are not symptoms that
typically accompany cyanosis, methemoglobinemia due to oxidant drug exposure, or genetic
abnormalities in haemoglobin.  Avery (1999), and discussed in WHO (2011).
Methaemoglobinaemia in infants appears to be associated with simultaneous diarrhoeal disease.
Authorities should therefore be all the more vigilant that water to be used for bottle-fed infants is
microbiologically safe when nitrate is present at concentrations near the guideline value or in the
presence of endemic infantile diarrhoea.  Water should not be used for bottle-fed infants if the
concentration of nitrate is above 100 mg/L as NO3 but can be used if the concentration is between 50
and 100 mg/L if the water is microbiologically safe and there is increased vigilance by medical
authorities (WHO 2011).
The primary health concern regarding nitrate and nitrite is the formation of methaemoglobinaemia,
so-called blue-baby syndrome.  Nitrate is reduced to nitrite in the stomach of infants, and nitrite is
able to oxidise haemoglobin (Hb) to methaemoglobin (metHb), which is then unable to transport
oxygen around the body.  The reduced oxygen transport becomes clinically manifest when metHb
concentrations reach 10% or more of normal Hb concentrations; the condition, called
methaemoglobinaemia, causes cyanosis and, at higher concentrations, asphyxia.  The normal metHb
level in infants under 3 months of age is less than 3%.  Other susceptible groups include pregnant
women and people with a deficiency of glucose-6-phosphate dehydrogenase or methaemoglobin
reductase.  Methaemoglobinaemia in infants also appears to be associated with simultaneous
exposure to microbial contaminants, e.g. Addison and Benjamin (2004).
Walton (1951) described a survey performed by the American Public Health Association to identify
clinical cases of infantile methemoglobinemia that were associated with ingestion of nitrate-
contaminated water.  A total of 278 cases of methemoglobinemia were reported.  Of 214 cases for
which data were available on nitrate levels in water, none occurred in infants consuming water
containing <10 mg nitrate-nitrogen/L (1.6 mg nitrate-nitrogen/kg/day).  There were 5 cases (2%) in
infants exposed to 11 - 20 mg nitrate-nitrogen/L (1.8 - 3.2 mg/kg/day), 36 cases (17%) in infants
exposed to 21 - 50 mg/L (3.4 - 8.0 mg/kg/day), and 173 (81%) in infants exposed to >50 mg/L (>8
mg/kg/day).  Based on these studies of nitrate contamination and occurrence of methemoglobin the
USEPA set the maximum contaminant level or reference dose for oral intake of 10 mg/L nitrate as N
(USEPA 1987, revised 1991).
Nitrate is not mutagenic in bacteria and mammalian cells in vitro.  Chromosomal aberrations were
observed in the bone marrow of rats after oral nitrate uptake, but this could have been due to
exogenous N-nitroso compound formation.  Nitrite is mutagenic, causing morphological
transformations in in vitro systems.
IARC (2005) stated that “Ingested nitrate or nitrite under conditions that result in endogenous
nitrosation is probably carcinogenic to humans (Group 2A).  The underlying mechanism is
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endogenous nitrosation, which in the case of nitrate must be preceded by reduction to nitrite.  Nitrate
and nitrite are interconvertible in vivo.  Nitrosating agents that arise from nitrite under acidic gastric
conditions react readily with nitrosatable compounds, especially secondary amines and alkyl amides,
to generate N-nitroso compounds.  Many N-nitroso compounds are carcinogenic.”  However, the
weight of evidence indicates that there is unlikely to be a causal association between gastric cancer
and nitrate in drinking-water.
The reference dose or RfD (USEPA 1991/2009/2011) for nitrate as N is 1.6 mg/kg/d, and for nitrite
as N it is 0.16 mg/kg/d (USEPA 1997/2009/2011).
As  at  October  2015  ATSDR  ( quotes a minimal
risk level (MRL) for nitrate of:
4 mg/kg/d for acute-duration oral exposure (1 to 14 days)
4 mg/kg/day for intermediate-duration oral exposure (15 – 364 days)
4 mg/kg/day for chronic-duration oral exposure (>364 days).
As  at  October  2015  ATSDR  ( quotes a minimal
risk level (MRL) for nitrite of:
0.14 mg/kg/d for acute-duration oral exposure (1 to 14 days)
0.1 mg/kg/day for intermediate-duration oral exposure (15 – 364 days)
0.1 mg/kg/day for chronic-duration oral exposure (>364 days).
The livestock guideline value for nitrite (as NO -
2 ) is 30 mg/L.  Nitrate (as NO3 ) concentrations less
than 400 mg/L in livestock drinking water should not be harmful to animal health; stock may tolerate
higher nitrate concentrations in drinking water provided nitrate concentrations in feed are not high.
Water containing more than 1500 mg/L nitrate (as NO -
3 ) is likely to be toxic to animals and should
be avoided (ANZECC/ARMCANZ 2000).  These guidelines were to have been updated in 2012.
Derivation of Maximum Acceptable Values
Nitrate (short-term)
The  MAV  of  50  mg/L  (as  NO -
3 ) is to protect against methaemoglobinaemia in bottle-fed infants
(short-term exposure).  In epidemiological studies, methaemoglobinaemia was not reported in infants
in areas where drinking-water consistently contained less than 50 mg of nitrate per litre.
The epidemiological evidence for an association between dietary nitrate and cancer is insufficient,
and the MAV for nitrate in drinking-water is established solely to prevent methaemoglobinaemia,
which depends upon the conversion of nitrate to nitrite.  Although bottle-fed babies are the most
susceptible, occasional cases have been reported in some adult populations.
Nitrite (short-term)
The short-term MAV of 3 mg/L (as NO -
2 ) is to protect against methaemoglobinaemia in bottle-fed
infants.  The WHO (2011) guideline value for nitrite of 3 mg/L as nitrite (or 0.9 mg/L if reported as
nitrite-nitrogen) is based on human data showing that doses of nitrite that cause
methaemoglobinaemia in infants range from 0.4 mg/kg body weight to more than 200 mg/kg body
weight.  By applying the lowest level of the range (0.4 mg/kg body weight), a body weight of 5 kg
for an infant and a drinking-water consumption of 0.75 litre, a guideline value of 3 mg/L (rounded
figure) can be derived.
Earlier, WHO had stated that animal studies were inappropriate to establish a firm No-Observable-
Adverse-Effect Level (NOAEL) for methaemoglobinaemia in rats.  Therefore, a pragmatic approach
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Inorganic chemicals
was followed, accepting a relative potency for nitrite and nitrate with respect to methaemoglobin
formation of 10:1 (on a molar basis), and a provisional MAV of of 3 mg/L had been adopted for
Nitrite (long-term)
The long-term MAV had been based on the next paragraph.  WHO (2011) now states: “However,
owing to the uncertainty surrounding the susceptibility of humans compared with experimental
animals, this value which was considered provisional has now been suspended and is being subjected
to review in light of evidence on the differences in nitrite metabolism between laboratory rodents and
The  0.2  mg/L  (as  NO -
2 )  MAV  in  the  2008  DWSNZ  for  long-term  exposure  for  chronic  effects  of
nitrite was considered provisional owing to uncertainty surrounding the relevance of the observed
adverse health effects for humans and the susceptibility of humans compared with animals.  The
occurrence of nitrite in the distribution system as a consequence of chloramine use will be
intermittent, and average exposures over time should not exceed the provisional MAV.  The nitrite
MAV (long-term exposure) is based on allocation to drinking-water of 10% of JECFA ADI of 0.06
mg/kg of body weight per day, based on nitrite-induced morphological changes in the adrenals, heart
and lungs in laboratory animal studies.
Nitrate:Nitrite ratio
Because of the possibility of simultaneous occurrence of nitrite and nitrate in drinking-water, the sum
of  the  ratio  of  the  concentration  of  each  to  their  short-term  MAVs,  as  shown  in  the  following
formula, should not exceed 1:
£ 1
where C  =  concentration, and MAV  =  Maximum Acceptable Value
Note related to short-term MAVs.
The short-term MAVs for nitrite and nitrate have been established to protect the health of infants,
particularly those that are bottle-fed.  Community water suppliers providing drinking-water that
exceeds the short-term MAVs will need to find a procedure for advising parents of new-born babies.
The WHO (2007) states that in areas where household wells are common, health authorities may
wish to take a number of steps to ensure that nitrate contamination is not or does not become a
problem.  Such steps could include targeting mothers, particularly expectant mothers, with
appropriate information about water safety, assisting with visual inspection of wells to determine
whether a problem may exist, providing testing facilities where a problem is suspected, providing
guidance on disinfecting water or where nitrate levels are particularly high, providing bottled water
from safe sources or providing advice as to where such water can be obtained.
The MAV for nitrate in the 1995 and 2000 DWSNZ was 50 mg/L as NO -
3 , and the MAV for nitrite
was 3 mg/L as NO -
2 .  The 1995 datasheet stated:
The epidemiological evidence for an association between dietary nitrate and cancer is
insufficient, and the MAV for nitrate in drinking-water is established solely to prevent
methaemoglobinaemia, which depends on the conversion of nitrate to nitrite.  Although
bottle-fed babies are the most susceptible, occasional cases have been reported in some adult
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As a result of recent evidence of the presence of nitrite in some water supplies, it was
concluded that a MAV for nitrite should be proposed.  However, the animal studies were
inappropriate to establish a firm NOAEL for methaemoglobinaemia in rats.  Therefore a
pragmatic approach was followed, accepting a relative potency for nitrate and nitrite with
respect to methaemoglobin formation of 10:1 (on a molar basis), and a PMAV for nitrite of 3
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