Formation of Trihalomethanes in Swimming Pool Water ...

Immediately after insertion chloroform concentration starts to rise while concentration of freechlorine declines. Concentration of free chlorine reached 0.13 mg/l after three hours,chloroform concentration was 7.0 µg/l after this time. A couple of additional peaks could beidentified. One of these peaks was trichloroacetonitril rising parallel to chloroform. Data forthis compound are given as peak area.Chlorination of bacteria yields similar results. Figure 6 displays development of free andcombined chlorine, as well as chloroform and trichloracetonitril during chlorination ofwashed cultures of Pseudomonas aeruginosa dissolved in tap water and disinfected withlaboratory grade Na-hypochlorite solution. Kinetics of the reaction is about the same asreaction of human skin with chlorine. Figure 7 depicts results of a similar experiment usingStaphylococcus aureus as test organisms. Staphylococcus aureus is a gram positivemicroorganism and therefore differs in organisation of the cell walls.It is known since long that some organic compounds like citric acid are precursors ofchloroform formation. Kinetics of chloroform formation by citric acid is shown in figure 8.Reaction kinetics is first order in citric acid. Compared to reaction of hypochlorite withmicroorganisms or with the skin, reaction rate is slightly slower.Due to its water solubility and its vapour pressure, chloroform will escape from the pool waterand can be detected in swimming pool air. Kinetics of chloroform formation and outgassingfrom pool water is not known up to now. In order to investigate these basic chemical aspectsof DBP formation chemistry, decline of chloroform and formation of bromoform wasmeasured after addition of KBr to swimming pool water. Hypochlorite is a stronger oxidantthan hypobromite, therefore chloroform formation will stop and bromoform will be formed inthe presence of bromide in the water.6e+53,00,775e+52,50,66Trichloracetonitril (Peak area)4e+53e+52e+5Free Cl [mg/l]2,01,51,00,5Free ClComb ClChloroformTrichloracetonitril0,50,40,30,20,1Comb. Cl [mg/l]5432Chloroform [ug/l]1e+50,00,010-40 -20 0 20 40 60 80 1000Figure 6: Chlorination of Pseudomonas aeruginosa. Formation of combined chlorine,chloroform and trichloracetonitril, decline of free chlorine.We added KBr to swimming pool water thus stopping the formation of chloroform nearlyimmediately. The only THM formed after addition of sufficient amounts of KBr will bebromoform, and chloroform will only escape from the water.4

Two series of analysis have been performed on two subsequent days. During the first day,chloroform concentration was monitored from 9 am to 10 pm. First sample was taken 1 hourbefore opening of the pool, last sample was taken 1 hour after closure. During the first day,chloroform concentration in the water rises from 8 µg/l to 12 µg/l. The next day, thischloroform concentration was still present in the water. However, chloroform concentrationdeclines immediately after KBr is added to the water. Half-life of chlorofom concentration inthe pool water is app. 2 h.1,8e+63,20,310Trichloracetonitril [Peak Area]1,6e+61,4e+61,2e+61,0e+68,0e+56,0e+54,0e+5Free Cl [mg/L]3,02,82,62,42,22,01,81,6Free ClComb ClChloroformTrichloracetonitril0,20,1Comb Cl [mg/L]8642Chloroform [µg/L]2,0e+51,40,00,01,20-60 -30 0 30 60 90 120 150 180 210 240MinutesFigure 7: Chlorination of Staphylococcus aureus. Formation of combined chlorine,chloroform and trichloracetonitril, decline of free chlorine.16141412w/o KBr: CHCl3w KBr: CHCl31210Chloroform [µg/L]10864CHl3 µg/l8642020 1 2 3 4 5 6Minutes008:00:00 12:00:00 16:00:00 20:00:00DaytimeFigure 8: Chlorination of citric acid.Formation of chloroform.Figure 9: Decline of CHCl3 concentration inswimming pool water after addition of KBr.5

DiscussionIt is well known that chlorination of drinking waters produces trihalomethanes (THMs) andother chlorinated byproducts. Drinking water supplies contain sundry organic compounds thatare distinct to the area; originate from natural processes, such as flora and fauna decay; andare collectively called natural organic matter (NOM) (Barret and Krasner 2000; Croué et al1999; Menear and Amy 1996). These naturally occuring organics, such as humic and fulvicmaterials, serve as precursors for Disinfection Byproducts in drinking water (Reckhow et al1990). Cells of the human skin as well as bacterial cells and algae cells and their excretedmetabolic products may contribute to the DBP precursor pool in swimming pools, producingboth THMs and haloacetonitriles upon chlorination. Whilst there are many papers describingdetails of THM production by chlorination of algae (Plummer 2001) and humic (Reckhow1990) and fulvic acids (Miller and Uden 1983; Oliver 1983)), there is only little informationon THM formation by chlorination of human skin or bacteria.The fate of organic nitrogen and carbon introduced into a swimming pool by users has beenstudied using a model pool (Judd and Bullock 2003). The authors used a synthetic „BodyFluid Analogen” (BFA) containing organic amino compounds and citric acid. Ourinvestigations show that chloroform concentrations in swimming pools can be explained byreaction of chlorine with human skin as well as by reaction with microorganisms present inthe water or brought in by bathers and additionally by chemical reactions of compounds likecitric acid.87Skin Chloroform [µg/L]65432100 1 2 3 4 5 6 7Pseudomonas aeruginosa Chloroform [µg/L]Figure 10: Comparison of kinetics of skin chlorination and chlorination of PseudomonasaeruginosaFigure 10 shows the correlation of chloroform kinetics of a suspension of Pseudomonasaeruginosa and chlorination of human skin. Results indicate that similar reactions take placealthough the identity of the precursors is not known. Reaction rate of citric acid is slower.Nevertheless this compound can contribute significantly to THM concentrations in swimmingpools because of its high concentration in urine. Release of organic acids like oxalic acid andcitric acid can be as high as 3 g/day. The formation of THM in by citric acid can be catalysed6

in the presence of copper ions in the water (Blatchley et al 2003). Additionally, citric acid isfrequently used in swimming pools as a component of cleaning agents.Rate of decrease of chloroform in a swimming pool, were chloroform formation was stoppedusing a KBr based reaction, indicates that chloroform formation in swimming pools isbasically a fast process. Half live of chloroform under these conditions was 2 hours whilstwithout addition of KBr chlorform concentration was rising with about 0.5 µg/l*h. However,THM concentrations in the pool where these measurements have been made were lowcompared to other pools because of awater slide and massage jet outlets in the pool.Further investigations will show which of these reactions is the main contributor tochloroform formation in swimming pools.LiteratureBarrett, S. E., Krasner, S., Eds. Natural Organic Matter and Disinfection By-Products:Characterization and Control in Drinking Water; ACS Symposium Series, Vol. 761;American Chemical Society: Washington, DC, 2000.Blatchley ER 3rd, Margetas D, Duggirala R: Copper catalysis in chloroform formation duringwater chlorination. Water Res. 37 (2003) 4385-4394.Croué, J.-P.; Korshin, G. V.; Benjamin, M., Eds. Characterization of Natural Organic Matterin Drinking Water; American Water Works Association: Denver, CO, 1999.Erdinger L, Kühn KP, Kirsch F, Feldhues R, Frobel T, Nohynek B, Gabrio T: Pathways oftrihalomethane uptake in swimming pools. Int J Hyg Environ Health. 207 (2004) 571-575.Judd SJ, Bullock G: The fate of chlorine and organic materials in swimming pools.Chemosphere 51 (2003) 869-879.Minear, R. A., Amy, G. L. Eds. Water Disinfection and Natural Organic Matter:Characterization and Control; ACS Symposium Series, Vol. 649; American ChemicalSociety: Washington, DC, 1996.Oliver BG: Dihaloacetonitriles in drinking water: algae and fulvic acid as precursors. EnvironSci Technol 17 (1983) 80-83.Plummer JD, Edzwald JK: Effect of ozone on algae as precursors for trihalomethane andhaloacetic acid production. Environ Sci Technol 35 (2001) 3661-3668.Reckhow DA, Singer PC, Malcolm RL: Chlorination of humic materials: Byproductformation and chemical interpretations. Environ Sci Technol 24 (1990) 1655-1664.7