THE SWIMMING POOL ENVIRONMENT
Swimming-pool environment is a complex and dynamic ecosystem that can be
affected by the type of swimming-pool (indoor, outdoor,…) and by
other factors, including water temperature, ventilation, climate,
location, purpose of use (competition, relaxation, recreational
activities) and swimming habits, particularly swimmer´s
hygiene4-6. In the case of an indoor swimming-pool,
the environment consists of the water in the pool, the air above the
pool within the natatorium, and the people in the pool
(biota)2.
Both organic and inorganic compounds are continuously entering this
ecosystem via filling waters (tap water, seawater, thermal
water…), disinfectant addition (chlorine, bromine, ozone,
UV…), pharmaceuticals and personal care products (analgesics,
antibiotics, sunscreens, lotions, cosmetics, soaps…) and human
body excretions (urine, sweat, saliva…). Interactions between all
these compounds generates CBPs, some of which are of health
concern7.
The addition of chlorine-based disinfectants (chlorine gas, sodium or
calcium hypochlorite, di- or trichloroisocyanurates) to the
swimming-pools water releases hypochlorous acid (HClO), which is the
active biocide. HClO is a weak acid with a pKa of 7.5 at 25°C that
reversely dissociates into hypochlorite (ClO−) and
hydrogen ion. The sum of HClO and ClO− is referred to
as free chlorine. HClO is a non-specific biocide that inactivates most
waterborne pathogens but also reacts with organic matter to produce a
wide range of CBPs8. Compared to tap water, CBPs
formation in pools is much more important due to the higher input of
organic matter and the constant addition of
disinfectants9. In chlorinated-pools, major groups of
CBPs include chloramines,
trihalomethanes (THMs), haloacetics acids (HAAs), haloacetaldehydes
(HALs) and haloacetonitriles (HANs) (Figure 1 ).
Chloramines are formed as a result of the reaction of HClO with urea and
other nitrogenous compounds brought by swimmers. This group comprises
monochloramine (chloramide, NH2Cl), dichloramine
(chlorimide, NHCl2) and trichloramine (nitrogen
trichloride, NCl3). Monochloramine and dichloramine (the
sum of which is referred to as combined chlorine) are mainly found in
water. Trichloramine, which is 400 times more volatile than its two
congeners, is mainly found in the air at levels that are inversely
proportional to the ventilation rate of indoor
swimming-pools10,11. The odour and taste of water are
mainly affected by the monochloramine/dichloramine ratio and the
trichloramine concentration. This last compound is also responsible for
the distinctive odour of indoor pools, wrongly attributed to
chlorine9.
THMs represent between 5 to 10% of total organohalogens in
swimming-pool water and air, with chloroform (CHCl3)
being the dominant species8. THMs are generated from
the complex reaction between active chlorine and naturally present or
imported carbonaceous organic matter. Parameters influencing the
formation of THMs include: organic matter concentration, chlorine
concentration, contact time, water pH, temperature, and bromine ion
concentrations12. THMs are generally well absorbed by
inhalation, ingestion or skin contact.
Haloacetics acids (HAAs), haloacetaldehydes (HALs) and haloacetonitriles
(HANs) are less frequent CBPs and therefore described in theonline supplementary material .