WHO Aquatic Safety Guidelines 4. Chemicals


Chemical hazards
Chemicals found in pool water can be derived from a number of sources: the source
water, deliberate additions such as disinfectants and the pool users themselves (see
Figure 4.1). This chapter describes the routes of exposure to swimming pool chemicals,
the chemicals typically found in pool water and their possible health effects.
While there is clearly a need to ensure proper consideration of health and safety
issues for operators and pool users in relation to the use and storage of swimming pool
chemicals, this aspect is not covered in this volume.
Figure 4.1. Possible pool water contaminants in swimming pools and similar environments
4.1 Exposure
There are three main routes of exposure to chemicals in swimming pools and similar
• direct ingestion of water;
• inhalation of volatile or aerosolized solutes; and
• dermal contact and absorption through the skin.
Chemicals in pool,
hot tub and spa water
Source water-derived:
disinfection by-products;
pH correction chemicals;
lotions (sunscreen, cosmetics,
soap residues, etc.)
Disinfection by-products:
e.g. trihalomethanes;
haloacetic acids;
nitrogen trichloride
4.1.1 Ingestion
The amount of water ingested by swimmers and pool users will depend upon a range
of factors, including experience, age, skill and type of activity. The duration of exposure
will vary signifi cantly in different circumstances, but for adults, extended exposure
would be expected to be associated with greater skill (e.g. competitive swimmers),
and so there would be a lower rate of ingestion in a comparable time than for
less skilled users. The situation with children is much less clear. There appear to be
no data with which to make a more detailed assessment. A number of estimates have
been made of possible intakes while participating in activities in swimming pools and
similar environments, with the most convincing being a pilot study by Evans et al.
(2001). This used urine sample analysis, with 24-h urine samples taken from swimmers
who had used a pool disinfected with dichloroisocyanurate and analysed for
cyanurate concentrations. All the participants swam, but there is no information on
the participant swimming duration. This study found that the average water intake
by children (37 ml) was higher than the intake by adults (16 ml). In addition, the
intake by adult men (22 ml) was higher than that by women (12 ml); the intake by
boys (45 ml) was higher than the intake by girls (30 ml). The upper 95th percentile
intake was for children and was approximately 90 ml. This was a small study, but
the data are of high quality compared with most other estimates, and the estimates,
are based upon empirical data rather than assumptions. In this volume, a ‘worst case’
intake of 100 ml for a child is assumed in calculating ingestion exposure to chemicals
in pool water.
4.1.2 Inhalation
Swimmers and pool users inhale from the atmosphere just above the water’s
surface, and the volume of air inhaled is a function of the intensity of effort and time.
Individuals using an indoor pool also breathe air in the wider area of the building
housing the pool. However, the concentration of pool-derived chemical in the pool
environment will be considerably diluted in open air pools. Inhalation exposure will
be largely associated with volatile substances that are lost from the water surface, but
will also include some inhalation of aerosols, within a hot tub (for example) or where
there is signifi cant splashing. The normal assumption is that an adult will inhale approximately
10 m3 of air during an 8-h working day (WHO, 1999). However, this
will also depend on the physical effort involved. There will, therefore, be signifi cant
individual variation depending upon the type of activity and level of effort.
4.1.3 Dermal contact
The skin will be extensively exposed to chemicals in pool water. Some may have a
direct impact on the skin, eyes and mucous membranes, but chemicals present in pool
water may also cross the skin of the pool, hot tub or spa user and be absorbed into the
body. Two pathways have been suggested for transport across the stratum corneum
(outermost layer of skin): one for lipophilic chemicals and the other for hydrophilic
chemicals (Raykar et al., 1988). The extent of uptake through the skin will depend
on a range of factors, including the period of contact with the water, the temperature
of the water and the concentration of the chemical.
4.2 Source water-derived chemicals
All source waters contain chemicals, some of which may be important with respect
to pool, hot tub and spa safety. Water from a municipal drinking-water supply may
contain organic materials (such as humic acid, which is a precursor of disinfection
by-products), disinfection by-products (see Section 4.5) from previous treatment/
disinfection processes, lime and alkalis, phosphates and, for chloraminated systems,
monochloramines. Seawater contains high bromide concentrations. In some circumstances,
radon may also be present in water that is derived from groundwater. Under
such circumstances, adequate ventilation in indoor pools and hot tubs will be an
important consideration. WHO is considering radon in relation to drinking-water
quality guidelines and other guidance.
4.3 Bather-derived chemicals
Nitrogen compounds, particularly ammonia, that are excreted by bathers (in a number
of ways) react with free disinfectant to produce several by-products. A number of
nitrogen compounds can be eluted from the skin (Table 4.1). The nitrogen content
in sweat is around 1 g/l, primarily in the form of urea, ammonia, amino acids and
creatinine. Depending on the circumstances, the composition of sweat varies widely.
Signifi cant amounts of nitrogen compounds can also be discharged into pool water
via urine (Table 4.1). The urine release into swimming pools has been variously estimated
to average between 25 and 30 ml per bather (Gunkel & Jessen, 1988) and be
as high as 77.5 ml per bather (Erdinger et al., 1997a), although this area has not been
well researched.
The distribution of total nitrogen in urine among relevant nitrogen compounds
(Table 4.1) has been calculated from statistically determined means of values based on
24-h urine samples. Although more than 80% of the total nitrogen content in urine
is present in the form of urea and the ammonia content (at approximately 5%) is
low, swimming pool water exhibits considerable concentrations of ammonia-derived
compounds in the form of combined chlorine and nitrate. It therefore appears that
there is degradation of urea following chemical reactions with chlorine.
Sweat Urine
Portion of total
nitrogen (%)
Portion of total
nitrogen (%)
Urea 680 68 10 240 84
Ammonia 180 18 560 5
Amino acids 45 5 280 2
Creatinine 7 1 640 5
80 8 500 4
Total nitrogen 992 100 12 220 100
a Adapted from Jandik, 1977
Table 4.1. Nitrogen-containing compounds in sweat and urinea
In a study on the fate of chlorine and organic materials in swimming pools using
analogues of body fl uids and soiling in a model pool, the results showed that organic
carbon, chloramines and trihalomethanes all reached a steady state after 200–500 h
of operation. Only insignifi cant amounts of the volatile by-products were found to
be lost to the atmosphere, and only nitrate was found to accumulate, accounting for
4–28% of the dosed amino nitrogen (Judd & Bullock, 2003). No information is
available on concentrations of chemicals in actual swimming pool water from cosmetics,
suntan oil, soap residues, etc.
4.4 Management-derived chemicals
A number of management-derived chemicals are added to pool water in order to
achieve the required water quality. A proportion of pool water is constantly undergoing
treatment, which generally includes fi ltration (often in conjunction with coagulation),
pH correction and disinfection (see Chapter 5).
4.4.1 Disinfectants
A range of disinfectants are used in swimming pools and similar environments. The
most common are outlined in Table 4.2 (and covered in more detail in Chapter 5).
They are added in order to inactivate pathogens and other nuisance microorganisms.
Chlorine, in one of its various forms, is the most widely used disinfectant.
Some disinfectants, such as ozone and UV, kill or inactivate microorganisms as
the water undergoes treatment, but there is no lasting disinfectant effect or ‘residual’
that reaches the pool and continues to act upon chemicals and microorganisms in the
water. Thus, where these types of disinfection are used, a chlorine- or bromine-type
disinfectant is also employed to provide continued disinfection. The active available
disinfectant in the water is referred to as ‘residual’ or, in the case of chlorine, ‘free’ to
distinguish it from combined chlorine (which is not a disinfectant). In the case of
a Usually used in combination with residual disinfectants (i.e. chlorine- or bromine-based)
Table 4.2. Disinfectants and disinfecting systems used in swimming pools and similar environments
Disinfectants used
most frequently in large,
heavily used pools
Disinfectants used
in smaller pools
and hot tubs
Disinfectants used
for small-scale and
domestic pools
• Gas
• Calcium/sodium
• Electrolytic generation
of sodium hypochlorite
• Chlorinated isocyanurates
(generally outdoor pools)
Chlorine dioxidea
• Liquid bromine
• Sodium bromide +
Lithium hypochlorite
Hydrogen peroxide/
bromine, as the combined form is also a disinfectant, there is no need to distinguish
between the two, so ‘total’ bromine is measured.
The type and form of disinfectant need to be chosen with respect to the specifi c requirements
of the pool. In the case of small and domestic pools, important requirements are
easy handling and ease of use as well as effectiveness. In all cases, the choice of disinfectant
must be made after consideration of the effi cacy of a disinfectant under the circumstances
of use (more details are given in Chapter 5) and the ability to monitor disinfectant levels.
1. Chlorine-based disinfectants
Chlorination is the most widely used pool water disinfection method, usually in the
form of chlorine gas, sodium, calcium or lithium hypochlorite but also with chlorinated
isocyanurates. These are all loosely referred to as ‘chlorine’.
Practice varies widely around the world, as do the levels of free chlorine that are
currently considered to be acceptable in order to achieve adequate disinfection while
minimizing user discomfort. For example, free chlorine levels of less than 1 mg/l are
considered acceptable in some countries, while in other countries allowable levels may
be considerably higher. Due to the nature of hot tubs (warmer water, often accompanied
by aeration and a greater user to water volume ratio), acceptable free chlorine levels
tend to be higher than in swimming pools. It is recommended that acceptable levels
of free chlorine continue to be set at the local level, but in public and semi-public
pools these should not exceed 3 mg/l and in public/semi-public hot tubs these should
not exceed 5 mg/l. Lower free chlorine concentrations may be health protective when
combined with other good management practices (e.g. pre-swim showering, effective
coagulation and fi ltration, etc.) or when ozone or UV is also used.
Using high levels of chlorine (up to 20 mg/l) as a shock dose (see Chapter 5) as a
preventive measure or to correct specifi c problems may be part of a strategy of proper
pool management. While it should not be used to compensate for inadequacies of
other management practices, periodic shock dosing can be an effective tool to maintain
microbial quality of water and to minimize build-up of biofi lms and chloramines
(see Sections 4.5 and 5.3.4).
Chlorine in solution at the concentrations recommended is considered to be
toxicologically acceptable even for drinking-water; the WHO health-based guideline
value for chlorine in drinking-water is 5 mg/l (WHO, 2004). Concentrations signifi –
cantly in excess of this may not be of health signifi cance with regard to ingestion (as
no adverse effect level was identifi ed in the study used), even though there might be
some problems regarding eye and mucous membrane irritation. The primary issues
would then become acceptability to swimmers.
The chlorinated isocyanurates are stabilized chlorine compounds, which are widely
used in the disinfection of outdoor or lightly loaded swimming pools. They dissociate
in water to release free chlorine in equilibrium with cyanuric acid. A residual of cyanuric
acid and a number of chlorine/cyanuric acid products will be present in the water.
The Joint FAO/WHO Expert Committee on Food Additives and Contaminants
(JECFA) has considered the chlorinated isocyanurates with regard to drinking-water
disinfection and proposed a tolerable daily intake (TDI) for anhydrous sodium dichloroisocyanurate
(NaDCC) of 0–2 mg/kg of body weight (JECFA, 2004). This would
translate into an intake of 20 mg of NaDCC per day (or 11.7 mg of cyanuric acid per
day) for a 10-kg child. To avoid consuming the TDI, assuming 100 ml of pool water is
swallowed in a session would mean that the concentration of cyanuric acid/chlorinated
isocyanurates should be kept below 117 mg/l. Levels of cyanuric acid should be kept
between 50 and 100 mg/l in order not to interfere with the release of free chlorine,
and it is recommended that levels should not exceed 100 mg/l. However, although no
comprehensive surveys are available, there are a number of reported measurements of
high levels of cyanuric acid in pools and hot tubs in the USA. Sandel (1990) found
an average concentration of 75.9 mg/l with a median of 57.5 mg/l and a maximum of
406 mg/l. Other studies have reported that 25% of pools (122 of 486) had cyanuric
acid concentrations greater than 100 mg/l (Rakestraw, 1994) and as high as 140 mg/l
(Latta, 1995). Unpublished data from the Olin Corporation suggest that levels up to
500 mg/l may be found. Regular dilution with fresh water (see Chapter 5) is required
in order to keep cyanuric acid at an acceptable concentration.
2. Chlorine dioxide
Chlorine dioxide is not classed as a chlorine-based disinfectant, as it acts in a different
way and does not produce free chlorine. Chlorine dioxide breaks down to chlorite and
chlorate, which will remain in solution; the WHO health-based drinking-water provisional
guideline value for chlorite is 0.7 mg/l (based on a TDI of 0.03 mg/kg of body
weight) (WHO, 2004), and this is also the provisional guideline for chlorate. There is
potential for a build-up of chlorite/chlorate in recirculating pool water with time. In order
to remain within the TDI levels of chlorate and chlorite, they should be maintained
below 3 mg/l (assuming a 10-kg child and an intake of 100 ml).
3. Bromine-based disinfectants
Liquid bromine is not commonly used in pool disinfection. Bromine-based disinfectants
for pools are available in two forms, bromochlorodimethylhydantoin (BCDMH)
and a two-part system that consists of sodium bromide and an oxidizer (usually hypochlorite).
As with chlorine-based disinfectants, local practice varies, and acceptable
total bromine may be as high as 10 mg/l. Although there is limited evidence about
bromine toxicity, it is recommended that total bromine does not exceed 2.0–2.5 mg/l.
The use of bromine-based disinfectants is generally not practical for outdoor pools and
spas because the bromine residual is depleted rapidly in sunlight (MDHSS, undated).
There are reports that a number of swimmers in brominated pools develop eye
and skin irritation (Rycroft & Penny, 1983). However, Kelsall & Sim (2001) in a
study examining three different pool disinfection systems (chlorine, chlorine/ozone
and bromine/ozone) did not fi nd that the bromine disinfection system was associated
with a greater risk of skin rashes, although the number of bathers studied was small.
4. Ozone and ultraviolet
Ozone and UV radiation purify the pool water as it passes through the plant room,
and neither leaves residual disinfectant in the water. They are, therefore, used in conjunction
with conventional chlorine- and bromine-based disinfectants. The primary
health issue in ozone use in swimming pool disinfection is the leakage of ozone into
the atmosphere from ozone generators and contact tanks, which need to be properly
ventilated to the outside atmosphere. It is also appropriate to include a deozonation
step in the treatment process, to prevent carry-over in the treated water. Ozone is a
severe respiratory irritant, and it is, therefore, important that ozone concentrations in
the atmosphere of the pool building are controlled. The air quality guideline value
of 0.12 mg/m3 (WHO, 2000) is an appropriate concentration to protect bathers and
staff working in the pool building.
5. Other disinfectants
Other disinfectant systems may be used, especially in small pools. Hydrogen peroxide
used with silver and copper ions will normally provide low levels of the silver and copper
ions in the water. However, it is most important that proper consideration is given
to replacement of water to prevent excessive build-up of the ions. A similar situation
would apply to biguanide, which is also used as a disinfectant in outdoor pools.
4.4.2 pH correction
The chemical required for pH value adjustment will generally depend on whether
the disinfectant used is itself alkaline or acidic. Alkaline disinfectants (e.g. sodium
hypochlorite) normally require only the addition of an acid for pH correction, usually
a solution of sodium hydrogen sulfate, carbon dioxide or hydrochloric acid. Acidic
disinfectants (e.g. chlorine gas) normally require the addition of an alkali, usually a
solution of sodium carbonate (soda ash). There should be no adverse health effects
associated with the use of these chemicals provided that they are dosed correctly and
the pH range is maintained between 7.2 and 8.0 (see Section 5.10.3).
4.4.3 Coagulants
Coagulants (e.g. polyaluminium chloride) may be used to enhance the removal of
dissolved, colloidal or suspended material. These work by bringing the material out
of solution or suspension as solids and then clumping the solids together to produce
a fl oc. The fl oc is then trapped during fi ltration.
4.5 Disinfection by-products (DBP)
Disinfectants can react with other chemicals in the water to give rise to by-products (Table
4.3). Most information available relates to the reactions of chlorine, as will be seen from
Tables 4.4–4.11. Although there is potentially a large number of chlorine-derived disinfection
by-products, the substances produced in the greatest quantities are the trihalomethanes
(THMs), of which chloroform is generally present in the greatest concentration, and
the haloacetic acids (HAAs), of which di- and trichloroacetic acid are generally present in
the greatest concentrations (WHO, 2000). It is probable that a range of organic chloramines
could be formed, depending on the nature of the precursors and pool conditions.
Data on their occurrence in swimming pool waters are relatively limited, although they
are important in terms of atmospheric contamination in enclosed pools and hot tubs.
When inorganic bromide is present in the water, this can be oxidized to form
bromine, which will also take part in the reaction to produce brominated by-products
such as the brominated THMs. This means that the bromide/hypochlorite system of
disinfection would be expected to give much higher proportions of the brominated
by-products. Seawater pools disinfected with chlorine would also be expected to show
a high proportion of brominated by-products since seawater contains signifi cant levels
of bromide. Seawater pools might also be expected to show a proportion of iodinated
by-products in view of the presence of iodide in the water. In all pools in which free
halogen (i.e. chlorine, bromine or iodine) is the primary disinfectant, no matter what
form the halogen donor takes, there will be a range of by-products, but these will be
found at signifi cantly lower concentrations than the THMs and HAAs. The use of
ozone in the presence of bromide can lead to the formation of bromate, which can
build up over time without adequate dilution with fresh water (see Chapter 5).
While chlorination has been relatively well studied, it must be emphasized that
data on ozonation by-products and other disinfectants are very limited. Although
those by-products found commonly in ozonated drinking-water would be expected,
there appear to be few data on the concentrations found in swimming pools and
similar environments.
Both chlorine and bromine will react, extremely rapidly, with ammonia in the water,
to form chloramines (monochloramine, dichloramine and nitrogen trichloride)
and bromamines (collectively known as haloamines). The mean content of urea and
ammonia in urine is 10 240 mg/l and 560 mg/l, respectively (Table 4.1), but hydrolysis
of urea will give rise to more ammonia in the water (Jandik, 1977). Nitrogencontaining
organic compounds, such as amino acids, may react with hypochlorite to
form organic chloramines (Taras, 1953; Isaak & Morris, 1980).
During storage, chlorate can build up within sodium hypochlorite solution, and this
can contribute to chlorate levels in disinfected water. However, it is unlikely to be of con-
a UV is a physical system and is generally not considered to produce by-products
Table 4.3. Predominant chemical disinfectants used in pool water treatment and their
associated disinfection by-productsa
Disinfectant Disinfection by-products
Chlorine/hypochlorite trihalomethanes
haloacetic acids
chloral hydrate (trichloroacetaldehyde)
chloropicrin (trichloronitromethane)
cyanogen chloride
Ozone bromate
carboxylic acids
brominated acetic acids
Chlorine dioxide chlorite
trihalomethanes, mainly bromoform
bromal hydrate
cern to health unless the concentrations are allowed to reach excessive levels (i.e. >3 mg/l),
in which case the effi cacy of the hypochlorite is likely to be compromised.
Ozone can react with residual bromide to produce bromate, which is quite stable
and can build up over time (Grguric et al., 1994). This is of concern in drinking-water
systems but will be of lower concern in swimming pools. However, if ozone were
used to disinfect seawater pools, the concentration of bromate would be expected to
be potentially much higher. In addition, bromate is a by-product of the electrolytic
generation of hypochlorite if the brine used is high in bromide. Ozone also reacts
with organic matter to produce a range of oxygenated substances, including aldehydes
and carboxylic acids. Where bromide is present, it can also result in the formation of
brominated products similar to liquid bromine.
More data are required on the impact of UV on disinfection by-products when
used in conjunction with residual disinfectants. UV disinfection is not considered to
produce by-products, and it seems to signifi cantly reduce the levels of chloramines.
4.5.1 Exposure to disinfection by-products
While swimming pools have not been studied to the same extent as drinking-water,
there are some data on the occurrence and concentrations of a number of disinfection
by-products in pool water, although the data are limited to a small number of
the major substances. A summary of the concentrations of various prominent organic
by-products of chlorination (THMs, HAAs, haloacetonitriles and others) measured
in different pools is provided in Table 4.4 and Tables 4.9–4.11 below. Many of these
data are relatively old and may refl ect past management practices. Concentrations
will vary as a consequence of the concentration of precursor compounds, disinfectant
dose, residual disinfectant level, temperature and pH. The THM found in the greatest
concentrations in freshwater pools is chloroform, while in seawater pools, it is usually
bromoform (Baudisch et al., 1997; Gundermann et al., 1997).
1. Trihalomethanes
Sandel (1990) examined data from 114 residential pools in the USA and reported average
concentrations of chloroform of 67.1 μg/l with a maximum value of 313 μg/l. In hot
spring pools, the median concentration of chloroform was 3.8 μg/l and the maximum
was 6.4 μg/l (Erdinger et al., 1997b). Fantuzzi et al. (2001) reported total THM concentrations
of 17.8–70.8 μg/l in swimming pools in Italy. In a study of eight swimming
pools in London, Chu & Nieuwenhuijsen (2002) collected and analysed pool water
samples for total organic carbon (TOC) and THMs. They reported a geometric mean1
for all swimming pools of 5.8 mg/l for TOC, 125.2 μg/l for total THMs and 113.3 μg/l
for chloroform; there was a linear correlation between the number of people in the pool
and the concentration of THMs. The pool concentrations of disinfection by-products
will also be infl uenced by the concentration of THMs and the potential precursor compounds
in the source and make-up water.
THMs are volatile in nature and can be lost from the surface of the water, so they
will also be found in the air above indoor pools (Table 4.5). Transport from swimming
pool water to the air will depend on a number of factors, including the concentration
in the pool water, the temperature and the amount of splashing and surface
1 Mean values in Table 4.4 are arithmetic means.
disturbance. The concentrations at different levels in the air above the pool will also
depend on factors such as ventilation, the size of the building and the air circulation.
Fantuzzi et al. (2001) examined THM levels in fi ve indoor pools in Italy and found
mean concentrations of total THMs in poolside air of 58.0 μg/m3 ± 22.1 μg/m3 and
concentrations of 26.1 μg/m3 ± 24.3 μg/m3 in the reception area.
Strähle et al. (2000) studied the THM concentrations in the blood of swimmers
compared with the concentrations of THMs in pool water and ambient air (Table
4.6). They showed that intake via inhalation was probably the major route of uptake
of volatile components, since the concentration of THMs in the outdoor pool water
was higher than the concentration in the indoor pool water, but the concentrations in
air above the pool and in blood were higher in the indoor pool than in the outdoor
pool. This would imply that good ventilation at pool level would be a signifi cant
contributor to minimizing exposure to THMs. Erdinger et al. (2004) found that in
a study in which subjects swam with and without scuba tanks, THMs were mainly
taken up by the respiratory pathway and only about one third of the total burden was
taken up through the skin.
Studies by Aggazzotti et al. (1990, 1993, 1995, 1998) showed that exposure to
chlorinated swimming pool water and the air above swimming pools can lead to an
increase in detectable THMs in both plasma and alveolar air, but the concentration in
alveolar air rapidly falls after exiting the pool area (Tables 4.7 and 4.8).
2. Chloramines, chlorite and chlorate
Exposure to chloramines in the atmosphere of indoor pools was studied in France by
Hery et al. (1995) in response to complaints of eye and respiratory tract irritation by
pool attendants. They found concentrations of up to 0.84 mg/m3 and that levels were
generally higher in pools with recreational activities such as slides and fountains.
Erdinger et al. (1999) examined the concentrations of chlorite and chlorate in
swimming pools and found that while chlorite was not detectable, chlorate concentrations
varied from 1 mg/l to, in one extreme case, 40 mg/l. Strähle et al. (2000)
found chlorate concentrations of up to 142 mg/l. The concentrations of chlorate
in chlorine-disinfected pools were close to the limit of detection of 1 mg/l, but the
mean concentration of chlorate in sodium hypochlorite-disinfected pools was about
17 mg/l. Chlorate concentrations were much lower in pools disinfected with hypochlorite
and ozone, and the chlorate levels were related to the levels in hypochlorite
stock solutions.
3. Other disinfection by-products
A number of other disinfection by-products have been examined in swimming pool
water; these are summarized in Tables 4.9–4.11. Dichloroacetic acid has also been
detected in swimming pool water. In a German study of 15 indoor and 3 outdoor
swimming pools (Clemens & Scholer, 1992), dichloroacetic acid concentrations
averaged 5.6 μg/l and 119.9 μg/l in indoor and outdoor pools, respectively. The mean
concentration of dichloroacetic acid in three indoor pools in the USA was 419 μg/l
(Kim & Weisel, 1998). The difference between the results of these two studies may
be due to differences in the amounts of chlorine used to disinfect swimming pools,
sample collection time relative to chlorination of the water, or addition or exchanges
of water in the pools.
Disinfection by-product concentration (μg/l)
type Reference
Chloroform BDCM DBCM Bromoform
Mean Range Mean Range Mean Range Mean Range
Poland 35.9–99.7 2.3–14.7 0.2–0.8 0.2–203.2 indoor Biziuk et al., 1993
Italy 19–94 indoor Aggazzotti et al., 1993
93.7 9–179 indoor Aggazzotti et al., 1995
33.7 25–43 2.3 1.8–2.8 0.8 0.5–10 0.1 0.1 indoor Aggazzotti et al., 1998
USA 37.9 indoor Copaken, 1990
Armstrong &
Golden, 1986
4–402 1–72 <0.1–8 <0.1–1 outdoor
3–580 1–90 0.3–30 <0.1–60 indoor
<0.1–530 <0.1–105 <0.1–48 <0.1–183 hot tub
Germany 14.6 2.4–29.8 indoor Eichelsdörfer et al., 1981
43 14.6–111 outdoor
Lahl et al., 1981
Ewers et al., 1987
198 43–980 22.6 0.1–150 10.9 0.1–140 1.8 <0.1–88 indoor
0.5–23.6 1.9–16.5 <0.1–3.4 <0.1–3.3 indoor
<0.1–32.9 <0.1–54.5 <0.1–1.0 <0.1–0.5 hydrotherapy
<0.1–0.9 <0.1–1.4 <0.1–16.4 2.4–132 hydrotherapy
3.6–82.1 1.6–17.3 <0.1–15.1 <0.1–4.0 outdoor
94.9 40.6–117.5 4.8 4.2–5.4 1.8 0.78–2.6 indoor Puchert et al., 1989
80.7 8.9 1.5 <0.1 indoor Puchert, 1994
74.9 11.0 3.0 0.23 outdoor
.3–27.8 0.69–5.64 0.03–6.51 0.02–0.83 indoor Cammann & Hübner, 1995
1.8–28 1.3–3.4 <0.1–1 <0.1 indoor Jovanovic et al., 1995
Schössner & Koch, 1995
Stottmeister, 1998, 1999
8–11 indoor
14. 0.51–69 2.5 0.12–15 0.59 0.03–4.9 0.16 <0.03–8.1 indoor
30. 0.69–114 4.5 0.27–25 1.1 0.04–8.8 0.28 <0.03–3.4 outdoor
4.3 0.82–12 1.3 0.19–4.1 0.4 0.03–0.91 0.08 <0.03–0.22 hydrotherapy
3.8 6.4 (max.) spa Erdinger et al., 1997b
7.1–24.8 indoor pool Erdinger et al., 2004
Denmark 145–151 indoor Kaas & Rudiengaard, 1987
Hungary 11.4 .<2–62.3 2.9 <1.0–11.4 indoor Borsányi, 1998
UK 121.1 45–212 8.3 2.5–23 2.7 0.67–7 0.9 0.67–2 indoor pools Chu & Nieuwenhuijsen, 2002
Table 4.4. Concentrations of trihalomethanes measured in swimming pool water
BDCM = bromodichloromethane; DBCM = dibromochloromethane
4.5.2 Risks associated with disinfection by-products
The guideline values in the WHO Guidelines for Drinking-water Quality can be used to
screen for potential risks arising from disinfection by-products from swimming pools
and similar environments, while making appropriate allowance for the much lower
quantities of water ingested, shorter exposure periods and non-ingestion exposure. Although
there are data to indicate that the concentrations of chlorination by-products
in swimming pools and similar environments may exceed the WHO guideline values
for drinking-water (WHO, 2004), available evidence indicates that for reasonably
well managed pools, concentrations less than the drinking-water guideline values can
be consistently achieved. Since the drinking-water guidelines are intended to refl ect
tolerable risks over a lifetime, this provides an additional level of reassurance. Drinking-
water guidelines assume an intake of 2 litres per day, but as considered above,
ingestion of swimming pool water is considerably less than this; recent measured data
(Section 4.1.1) indicate an extreme of about 100 ml (Evans et al., 2001). Uptake via
skin absorption and inhalation (in the case of THMs) is proportionally greater than
from drinking-water and is signifi cant, but the low oral intake allows a margin that
can, to an extent, account for this. Under such circumstances, the risks from exposure
to chlorination by-products in reasonably well managed swimming pools would be
considered to be small and must be set against the benefi ts of aerobic exercise and the
risks of infectious disease in the absence of disinfection.
Levels of chlorate and chlorite in swimming pool water have not been extensively
studied; however, in some cases, high chlorate concentrations have been reported,
which greatly exceeded the WHO provisional drinking-water guideline (0.7 mg/l)
and which would, for a child ingesting 100 ml of water, result in possible toxic effects.
Exposure, therefore, needs to be minimized, with frequent dilution of pool water with
fresh water, and care taken to ensure that chlorate levels do not build up in stored
hypochlorite disinfectants.
The chloramines and bromamines, particularly nitrogen trichloride and nitrogen
tribromide, which are both volatile (Holzwarth et al., 1984), can give rise to signifi
cant eye and respiratory irritation in swimmers and pool attendants (Massin et
al., 1998). In addition, nitrogen trichloride has an intense and unpleasant odour at
concentrations in water as low as 0.02 mg/l (Kirk & Othmer, 1993). Studies of subjects
using swimming pools and non-swimming attendants have shown a number of
changes and symptoms that appear to be associated with exposure to the atmosphere
in swimming pools. Various authors have suggested that these were associated with
nitrogen trichloride exposure in particular (Carbonnelle et al., 2002; Thickett et al.,
2002; Bernard et al., 2003), although the studies were unable to confi rm the specifi c
chemicals that were the cause of the symptoms experienced. Symptoms are likely to be
particularly pronounced in those suffering from asthma. Yoder et al. (2004) reported
two incidents, between 2001 and 2002, where a total of 52 people were adversely affected
by a build-up of chloramines in indoor pool water. One of the incidents related
to a hotel pool, and 32 guests reported coughs, eye and throat irritation and diffi culty
in breathing. Both incidents were attributed to chloramines on the basis of the clinical
syndrome and setting. Hery et al. (1995) found that complaints from non-swimmers
were initiated at a concentration of 0.5 mg/m3 chlorine species (expressed in units
of nitrogen trichloride) in the atmosphere of indoor pools and hot tubs. It is recommended
that 0.5 mg/m3 would be suitable as a provisional value for chlorine species,
Table 4.5. Concentrations of trihalomethanes measured in the air above the pool water surface
Disinfection by-product concentration (μg/m3)
Pool type Reference
Chloroform BDCM DBCM Bromoform
Mean Range Mean Range Mean Range Mean Range
Italy 214 66–650 19.5 5–100 6.6 0.1–14 0.2 indoor1) Aggazzotti et al., 1995
140 049–280 17.4 2–58 13.3 4–30 0.2 indoor1) Aggazzotti et al., 1993
169 35–195 20 16–24 11.4 9–14 0.2 indoor1) Aggazzotti et al., 1998
Canada 597–1630 indoor Lévesque et al., 1994
Germany 65 9.2 3.8 indoor1) Jovanovic et al., 1995
36 5.6 1.2 indoor2)
5.6 0.21 outdoor1)
2.3 outdoor1)
3.3 0.33–9.7 0.4 0.08–2.0 0.1 0.02–0.5 <0.03 outdoor1) Stottmeister, 1998, 1999
1.2 0.36–2.2 0.1 0.03–0.16 0.05 0.03–0.08 <0.03 outdoor2)
39 5.6–206 4.9 0.85–16 0.9 0.05–3.2 0.1 <0.03–3.0 indoor1)
30 1.7–136 4.1 0.23–13 0.8 0.05–2.9 0.08 <0.03–0.7 indoor2)
USA <0.1–1 <0.1 <0.1 <0.1 outdoor3) Armstrong & Golden, 1986
<0.1–260 <0.1–10 <0.1–5 <0.1–14 indoor3)
<0.1–47 <0.1–10 <0.1–5 <0.1–14 hot tub3)
BDCM = bromodichloromethane; DBCM = dibromochloromethane
a Measured 20 cm above the water surface
b Measured 150 cm above the water surface
c Measured 200 cm above the water surface
Table 4.6. Comparison of trihalomethane concentrations in blood of swimmers after a 1-h
swim, in pool water and in ambient air of indoor and outdoor poolsa
THM concentration (mean, range)
Indoor pool Outdoor pool
Blood of swimmers (μg/l) 0.48 (0.23–0.88) 0.11 (<0.06–0.21)
Pool water (μg/l) 19.6 (4.5–45.8) 73.1 (3.2–146)
Air 20 cm above the water surface (μg/m³) 93.6 (23.9–179.9) 8.2 (2.1–13.9)
Air 150 cm above the water surface (μg/m³) 61.6 (13.4–147.1) 2.5 (<0.7–4.7)
a Adapted from Strähle et al., 2000
Table 4.7. Concentrations of trihalomethanes in plasma of 127 swimmersa
THM No. positive/no. samples
Mean THM
Range of THM
Chloroform 127/127 1.06 0.1–3.0
BDCM 25/127 0.14 <0.1–0.3
DBCM 17/127 0.1 <0.1–0.1
a Adapted from Aggazzotti et al., 1990
Table 4.8. Comparison of trihalomethane levels in ambient air and alveolar air in swimmers prior
to arrival at the swimming pool, during swimming and after swimminga
THM levels (μg/m3) at various monitoring timesb
Ambient air 20.7 ± 5.3 91.7 ± 15.4 169.7 ± 26.8 20.0 ± 8.4 19.2 ± 8.8
Alveolar air 9.3 ± 3.1 29.4 ± 13.3 76.5 ± 18.6 26.4 ± 4.9 19.1 ± 2.5
Ambient air n.q. 10.5 ± 3.1 20.0 ± 4.1 n.q. n.q.
Alveolar air n.q. 2.7 ± 1.2 6.5 ± 1.3 2.7 ± 1.1 1.9 ± 1.1
Ambient air n.q. 5.2 ± 1.5 11.4 ± 2.1 n.q. n.q.
Alveolar air n.q. 0.8 ± 0.8 1.4 ± 0.9 0.3 ± 0.2 0.20 ± 0.1
Ambient air n.q. 0.2 0.2 0.2 n.q.
Alveolar air n.q. n.q. n.q. n.q. n.q.
a Adapted from Aggazzotti et al., 1998
b Five competitive swimmers (three males and two females) were monitored A: Prior to arrival at the pool; B: After 1 h resting at poolside
before swimming; C: After a 1-h swim; D: 1 h after swimming had stopped; and E: 1.5 h after swimming had stopped. D and E
occurred after departing the pool area. n.q. = not quantifi ed
Table 4.9. Concentrations of haloacetic acids measured in swimming pool water
MCAA = monochloroacetic acid; MBAA = monobromoacetic acid; DCAA = dichloroacetic acid; DBAA = dibromoacetic acid; TCAA = trichloroacetic acid
Disinfection by-product concentration (μg/l)
type Reference
Mean Range Mean Range Mean Range Mean Range Mean Range
Germany 26 2.6–81 0.32 <0.5–3.3 23 1.5–192 0.57 <0.2–7.7 42 3.5–199 indoor Stottmeister & Naglitsch, 1996
32 2.5–174 0.15 <0.5–1.9 8.8 1.8–27 0.64 <0.2–4.8 15 1.1–45 hydrotherapy
26 2.5–112 0.06 <0.5–1.7 132 6.2–562 0.08 <0.2–1.3 249 8.2–887 outdoor
30 hot tub Lahl et al., 1984
25–136 indoor
2.3–100 indoor Mannschott et al., 1995
Disinfection by-product concentration (μg/l)
type Reference
Mean Range Mean Range Mean Range
Germany 6.7–18.2 indoor Puchert, 1994
Stottmeister, 1998, 1999
<0.5–2.5 outdoor
13 0.13–148 2.3 <0.01–24 1.7 <0.01–11 indoor
9.9 0.22–57 0.62 <0.01–2.8 1.5 <0.01–7.8 hydrotherapy
45 <0.01–0.02 2.5 <0.01–16 1.3 <0.01–10 outdoor
24 indoor Baudisch et al., 1997
49 seawater
Table 4.10. Concentrations of haloacetonitriles measured in swimming pool water
DCAN = dichloroacetonitrile; DBAN = dibromoacetonitrile; TCAN = trichloroacetonitrile
Table 4.11. Concentrations of chloropicrin, chloral hydrate and bromal hydrate measured in swimming pool water
Disinfection by-product concentration (μg/l)
type Reference
Chloropicrin Chloral hydrate Bromal hydrate
Mean Range Mean Range Mean Range
Germany 0.1–2.6 indoor Schöler & Schopp, 1984
0.32–0.8 indoor Puchert, 1994
<0.01–0.75 outdoor Stottmeister, 1998, 1999
0.32 0.03–1.6 indoor
0.20 0.04–0.78 hydrotherapy
1.3 0.01–10 outdoor
265 indoor Baudisch et al., 1997
230 seawater Baudisch et al., 1997
0.5–104 indoor Mannschott et al., 1995
expressed as nitrogen trichloride, in the atmosphere of indoor swimming pools and
similar environments. However, more specifi c data are needed on the potential for
exacerbation of asthma in affected individuals, since this is a signifi cant proportion of
the population in some countries. There is also a potential issue regarding those that
are very frequent pool users and who may be exposed for longer periods per session,
such as competitive swimmers. It is particularly important that the management of
pools used for such purposes is optimized in order to reduce the potential for exposure
(Section 5.9).
4.6 Risks associated with plant and equipment malfunction
Chemical hazards can arise from malfunction of plant and associated equipment. This
hazard can be reduced, if not eliminated, through proper installation and effective
routine maintenance programmes. The use of gas detection systems and automatic
shutdown can also be an effective advance warning of plant malfunction. The use of
remote monitoring is becoming more commonplace in after-hours response to plant
and equipment malfunction or shutdown.
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