Cyanuric Acid Stabilizer What Is All the Fuss About?

Cyanuric Acid Stabilizer What is all the fuss about?

Ellen Meyer, Arch Chemicals February 9, 2017 NPC Conference New Orleans LA

. Chemistry of cyanuric acid (CYA) . Impact on build up of CYA . Impact on water balance . Chlorine stabilization with cyanuric acid . The effect of cyanuric acid on chlorine kill rates . In the lab . In the pool . Recent Crypto data . Implications for pool maintenance . Sanitizer residuals . Remediation procedures . Measurement issues . CYA control

Cyanuric Acid Isocyanuric Acid Enol tautomer Keto tautomer

+ 3 HOCl + H2O

Isocyanuric Hypochlorous Trichloroisocyanuric Acid Acid Acid

Cl3Cy

- HCl2Cy Cl2Cy

- ClCy2- H2ClCy HClCy

- 2- 3- H3Cy H2Cy HCy Cy

100

- -2 Cy-3 H3Cy H2Cy HCy

40 pKa 6.88 pKa 11.40 pKa 13.5 % Species %

0 0 2 4 6 8 10 12 14 pH

100% 90% 80% 70% [H2ClCy]

[HClCy–] 60% [ClCy2–] 50% [HCl2Cy]

%Species 40% [Cl2Cy–] 30% [Cl3Cy] 20% [HOCl] 10% [OCl-] 0% 0 2 4 6 8 10 12 14 pH AvCl = Available Chlorine, TDS = Total Dissolved Solids 7 ©2017 Lonza Cyanuric Acid Equilibria with Cl (O’Brien) 1 ppm AvCl, 20 ppm CYA, pH 7.5, 800 ppm TDS, 85 °F

100% 90% 80% 70% [H2ClCy]

[HClCy–] 60% [ClCy2–] 50% [HCl2Cy]

%Species 40% [Cl2Cy–] 30% [Cl3Cy] 20% [HOCl] 10% [OCl-] 0% 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 pH

• How much does CYA build up over time?

Molecular weight = 232.41

Atom Number of Molecular weight, Weight % atoms g/mole Carbon (C) 3 3 x 12.01 15.5% Nitrogen (N) 3 3 x 14.01 18.1% Oxygen (O) 3 3 x 16.00 20.7% Total 3C+3N+3O = CYA 9 126.06 54.2% Chlorine (Cl) 3 3 x 35.45 45.8%

• Add cyanuric acid independent of sanitizer – 95-100% granular cyanuric acid • Add chlorinated cyanuric acid as sanitizer/shock – Trichloroisocyanuric acid • 54% CYA, so for every 100 lb of trichlor added to a pool, 54 lb of CYA is added – Dichloroisocyanuric acid • Hydrated (49% CYA) • Anhydrous (57% CYA) – Rough rule of thumb • For every pound of trichlor or dichlor added, you are adding ~½ pound of CYA

300

200 CYA (ppm) CYA

100

 Minimum pH 7.2, Maximum pH 7.8  MAHC 5.7.3.4.1, APSP-11 7.1

 pH 7 = neutral [H+] = [OH-]

 pH <7.2  Corrosion of plaster, grout and metal  Eye irritation

 pH >7.8  Scale, mineral precipitation  Eye irritation  Chlorine less effective

To lower pH  Acids contribute H+ to lower pH  Muriatic acid = hydrochloric acid + -  HCl (aq) ↔ H + Cl )  Dry acid = sodium bisulfate + 2-  NaHSO4 ↔ H + Na+ + SO4  Carbon dioxide (CO2) - +  CO2 + H2O ↔ HCO3 + H To raise pH  Bases take away H+ to raise pH

 Soda ash = sodium carbonate (Na2CO3) + + -  Na2CO3 + H ↔ 2Na + HCO3 -  HCO3 = bicarbonate

 Lowering pH by adding CO2 - +  CO2 + H2O => HCO3 + H

 Raising pH by losing CO2 to the air - +  HCO3 + H => CO2 + H2O  pH will drift up when carbonate alkalinity is present  Faster in spas  High temperatures  Aeration of the water

What is Alkalinity ? Measure of pH buffering capacity

 Buffer = something that keeps the pH from going up and down quickly

 Something that absorbs H+ when an acid is added

 Something the contributes H+ when a base is added

 Carbonate

- +  HCO3 + H ↔ H2CO3 - +  When acid is added HCO3 + H → H2CO3 - +  When base is added H2CO3 → HCO3 + H

100

80 Buffers best at pH where two lines cross

60 Carbonic Acid Bicarbonate Carbonate - 2- H2CO3 HCO3 CO3

40 % Species %

 Cyanuric acid (stabilizer) does provide buffer capacity

 Cyanuric acid does not gas off and make pH drift like carbonate buffers

 Cyanuric acid is measured in alkalinity test

 Cyanuric acid does not provide corrosion protection for plaster

 You must have carbonate alkalinity to protect plaster

↔ + + H

100

Cyanuric acid Cyanurate H Cy H Cy-

40 3 2 % Species %

For water balance need carbonate alkalinity Example :

 Total Alkalinity (TA, measured value) = 90

 Stabilizer (measured value) = 120 (high, but common near season’s end) pH Replace 1/3 with  Carbonate Alkalinity 7.9 1/ 2.7 = 90 - 1/3 (120) 7.7 1/ 2.9 7.5 1/ 3.2 = 90 - 40 7.3 1/ 3.6 = 50 (low) 7.1 1/ 4.2

Low Carbonate Alkalinity  pH changes abruptly and frequently with small chemical additions  Water may be corrosive in one area of pool and scaling in another  Overall- water will be more corrosive  pH of water drifts with the pH of the sanitizer

High Carbonate Alkalinity  pH changes slowly - stays around 8.0 to 8.4 and returns even after adjustment with acid  pH of water drifts up  Water will cause scaling and may appear cloudy or dull

Adjusting Alkalinity

 To lower carbonate alkalinity

 Muriatic acid (hydrochloric acid, HCl(aq))

 Dry acid (sodium bisulfate, NaHSO4) - +  HCO3 + H → CO2 + H2O  Other acidic pool chemicals (trichlor, chlorine gas)

 To raise carbonate alkalinity

 Sodium bicarbonate (NaHCO3)

 Soda ash (sodium carbonate, Na2CO3)  Will raise pH too  Other pool chemicals (calcium hypochlorite)

CYA, %Loss ppm 0 35% 10 12% 20 5% 30 3% 40 2%

Stabiliser (Cyanurate) Use in Outdoor Swimming Pools mg/L = ppm http://www.health.nsw.gov.au/environment/factsheets/Pages/stabiliser-cyanurate.aspx

100 pH %HOCl 5.0 99.7% 80 7.0 77.5% 60 7.5 52.2% 8.0 25.7%

40 9.5 1.1% Percent HOCl Percent 20

0 5 6 7 8 9 10 11 pH

Dissociation constant from G. C. White, Handbook of Chlorination, Second Edition, Van Nostrand Reinhold Company, New York, 1986 27 ©2017 Lonza Cyanuric Acid Equilibria with Cl (O’Brien) 1 ppm AvCl, 20 ppm CYA, pH 7.5, 800 ppm TDS, 85 °F

100% 90% 80% 70% [H2ClCy]

[HClCy–] 60% [ClCy2–] 50% [HCl2Cy]

%Species 40% [Cl2Cy–] 30% [Cl3Cy] 20% [HOCl] 10% [OCl-] 0% 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 pH

50% 45% CYA, %HOCl for 40% ppm 1 ppm FC

35% 0 47%

30% 5 13% 1 ppm FC 25% 2 ppm FC 10 7%

%HOCl 3 ppm FC 20% 20 3% 4 ppm FC 15% 50 1% 10 ppm FC 10%

 Concentration x Time = CT . Usually 3 log (99.9%) reduction in ppm∙minutes . Will vary with pathogen strain, temperature, pH, etc. . Assumed to be linear

 If CT = 100 ppm minutes Then  It will take 100 minutes to kill the organism with 1 ppm Or  It will take 1 minute to kill the organism with 100 ppm

 Tests conducted with chlorine demand free water with 1 ppm chlorine at pH 7.5, 77° F, no CYA

Organism Time E. coli O157:H7 Bacterium <1 minute Hepatitis A Virus About 16 minutes Giardia Protozoan About 45 minutes Cryptosporidium Protozoan About 15,300 minutes (10.6 days)

 These values will be higher in the presence of CYA

Robinton 1967 E. coli 5 Robinton 1967 S. faecalis Robinton 1967 Staph. aureus

4 CT, ppm ppm min CT, 3

0 0 50 100 150 200 250 300 350 400 CYA, ppm

Fitzgerald 1967 S. faecalis 40 Golaszewski 1994 P. aeruginosa 35 Robinton 1967 E. coli 30 without without CYA Robinton 1967 S. faecalis 25 Robinton 1967 Staph. aureus

20 CYA CT / CYA 15

Values from EPA LT1ESWTR Disinfection Profiling and Benchmarking, 2003 EPA 816-R-03-004, pH 7-9, 25 °C, 3-log

Pathogen CT CT CT CC Free Chlorine (FC), Chloramine (CC), / CT FC ppm min ppm min

Giardia 45 750 17 Viruses 2 497 249

35 ©2017 Lonza Effect of CYA on Chlorine Kill Rates • Fitzgerald 1967 ──●── No CYA −−○−− With CYA – 0.5 ppm AvCl used – 1:1 molar AvCl:N = 5:1 ppm (by weight) – Cyanuric acid does not appear to hinder the activity of combined chlorine

With 0.1 ppm NH3-N, there is enough nitrogen for all of the chlorine to be present as combined chlorine.

36 ©2017 Lonza Effect of CYA on Chlorine Kill Rates- In Pool Water Study Total Pools Results (stabilized) Yamashita 1988 19(9) Time (minutes) required for inactivation of poliovirus, ~1 ppm AvCl Unstabilized Stabilized Polio 40 sec >3 min Yamashita 1990 6(3) Time (minutes) required for inactivation of poliovirus, 1 ppm AvCl Unstabilized Stabilized Polio <1 min >2-5 min

37 ©2017 Lonza Effect of CYA on Bacterial Counts in Pools Study Total Pools (stabilized) Results- Percent of Pools that Passed the Criteria Kowalski 1966 15 (7) 1960 %Pass Unstabilized Stabilized 138 (7) 1963 ‘60 Total 82 88 ‘63 Total 90 98 ‘60 e coli 96 98 ‘63 e coli 89 96 Rakestraw 1994 (Pinellas 486(396) %Pass Unstabilized Stabilized 1992 study) <500 HPC 86 91 No T Colif 84 92 No F Colif 90 95 No non Colif 41 32 Favero 1964 12 (3) More Pseudomonas in stabilized pools Low bather load 6 (3) %Pass Unstabilized Stabilized e. Coli 83 72 Staph 97 80 Total count 64 47 LeGuyader 1988 3749 (1055) %Pass Unstabilized Stabilized No Staph 50 40 No Pseud 97 86 No Colif 100 99 Black 1970 83(28) %Pass Unstabilized Stabilized No Colif 82 64 Yamashita 1990 6(3) %Pass Unstabilized Stabilized No Adenovirus 100 100 No Colif 100 92 Total plate counts 92 50 38 ©2017 Lonza Implications for Pool Maintenance- Continuous Treatment • Association of Pool and Spa Professionals (APSP) – APSP-11 • CYA <100 ppm • Model Aquatic Health Code (MAHC) – MAHC 5.7.3 Disinfection • FAC – 1.0 ppm no CYA – 2.0 ppm with CYA • CYA – <90 ppm, most venues – 0 ppm for spas and therapy pools

Effect of CYA on Cryptosporidium (pH 7.5, 25°C) (Murphy et al. 2015)

Average FC Average CYA Average Time 3-log10 Average Estimated 3-log10 conc. (mg/L) conc. (mg/L) inactivation (hr) CT value (mg·min/L)

21.6 0 8.2 10,500 21.1 8 14.1 17,800 19.1 16 27.5 31,500

40.6 0 5.1 12,400 40.9 9 6.2 15,300 38.3 15 8.4 19,400

Effect of CYA on Cryptosporidium (pH 7.5, 25°C) (Murphy et al. 2015) Did not get 3-log removal with >16 ppm CYA

Average FC Average CYA Average time 1-log10 Average Estimated 1-log10 conc. (mg/L) conc. (mg/L) inactivation (hr) CT value (mg·min/L)

21.6 0 2.7 3,500 21.2 48 61.9 76,500

40.6 0 3.7 4,100

38.5 46 17.2 40,000

• 100 ppm CYA – 20 ppm AvCl

• 72 hours (3 days) 0.8-log10 • 144 hours (6 days) 1.6-log10

– 40 ppm AvCl

• 24 hours 0.8-log10 • 72 hours 1.4-log10

• MAHC 6.5 – Close pool – Remove fecal material (no vacuum) – pH ≤7.5, temperature ≥77°F – Operating filter while maintaining chlorine – Test for chlorine multiple places – Use only non-stabilized chlorine for remediation

• MAHC 6.5 Remedial treatment – Use the following CT values for treatment

Contaminant Unstabilized Stabilized Formed stool 50 ppm min 100 ppm min (2 ppm 25 min) (4 ppm 25 min) Diarrheal stool 15,300 ppm min Lower CYA to ≤15 ppm, and (20 ppm 12.75 hours) 20 ppm for 28 hours 30 ppm for 18 hours 40 ppm for 8.5 hours Vomit 50 ppm min 100 ppm min Blood 0 0

– Unstabilized • Circulate through secondary disinfection system to achieve 1 oocyst/100 ml – Stabilized • Circulate through secondary disinfection system to achieve 1 oocyst/100 ml, or • Drain

• Test Methods – Melamine precipitation – Test strips – Most test methods have 100 ppm maximum • Need to dilute if reading is near maximum • MAHC set 90 ppm maximum CYA limit due to testing issues >100 ppm • Effect of CYA on ORP

• This test is notoriously inaccurate • Melamine precipitation provides insoluble complex • Turbidity measurements prone to time dependence as well as interference • Test is influenced by lighting conditions • Results can be operator dependent • If result is near top endpoint of method (i.e. >80 ppm), the sample should be diluted and run again

• Interference • Water temperature • Effect • High temperatures, above 90 °F, can result in readings as much as 15 ppm low • Low temperatures, below 60 °F, can result in readings that are 15 ppm high • How you can tell • Measure water temperature • What to do • Warm sample to ideal temperature of 75 °F

48 ©2017 Lonza CYA precipitation? • The previous slide would indicate that cold water reading will be higher than warm water readings • Then why are winter time CYA readings often lower than summer? • Temperature of water in the pool vs. temperature of sample when analyzed – Previous slide has to do with testing interference from temperature of sample when analyzed – Low CYA readings in winter may not be test interference, they may indicate CYA precipitation at low temperatures in the pool (anecdotal evidence)

• Interference • pH • Effect • Inaccurate results • How you can tell • Measure pH • What to do • Adjust pH to the ideal range of 7.4 to 7.6

• Nernst equation can be used to look at theoretical potential vs. CYA concentration • These values should not be taken as absolute • Many factors will affect an ORP reading and the slope of this line • Nernst equation: E = Eo - (RT/nF) x ln ([Cl-]/[HOCl][H+])

1.19 Constants used: 1.18

Eo = 1.49 V 1.17 R = gas constant 1.16 T = 85 °F 1.15 n = 2 electrons

• Interference • Probe fouling from CYA • Effect • Reading may be low or sluggish to respond • How you can tell • Clean probe and see if the reading changes • What to do • Clean probes according to manufacturer’s directions • To prevent contamination, store probes according to manufacturer’s directions

Two effects from CYA 1. Lowering of ORP due to lowering of HOCl 2. Probe fouling with CYA

52 ©2017 Lonza CYA Control- Removal • Drain the pool – Water restrictions – Cost (water, treating fill water) • Activated carbon – Efficiency is low – Cost – Possible disposal issues • Melamine precipitation – Operational issues (staining, solids don’t settle, etc.) • Unproven technologies

 Assume  100 ppm CYA in pool  1 lb Trichlor/10,000 gal/day used  Cleveland TN utility rates ($2.21/ft3, ~0.3¢/gal)

Daily water Trichlor CYA residual removal to Yearly cost in used AvCl used CYA added added maintain 100 ppm replacement Pool size (lbs/day) (lbs/day) (lbs/day) (ppm/day) (gal) water ($) 10,000 1.0 0.90 0.56 6.7 665 717 25,000 2.5 2.25 1.39 6.7 1663 1794 50,000 5.0 4.50 2.78 6.7 3326 3587 75,000 7.5 6.75 4.16 6.7 4990 5381 100,000 10.0 9.00 5.55 6.7 6653 7175 1,000,000 100.0 90.00 55.52 6.7 66529 71745

• Control additions of CYA – Prudent use of CYA – Prudent use of stabilized sanitizers

56 ©2017 Lonza References • Amburgey, J.E., and J.B. Anderson. (2011). Disposable Swim Diaper Retention of Cryptosporidium-sized Particles on Human Subjects in a Recreational Water Setting. Journal of Water and Health. 9(4): 653-658. • Amburgey, J.E., Walsh, K.J., Fielding, R.R., and M.J. Arrowood. (2012). Removal of Cryptosporidium and Polystyrene Microspheres from Swimming Pool Water with Sand, Cartridge, and Precoat Filters. Journal of Water and Health. 10(1): 31-42. • Amburgey, James. E., Jonathan M. Goodman, Olufemi Aborisade, Ping Lu, Caleb L. Peeler, Will H. Shull, Roy R. Fielding, Michael J. Arrowood, Jennifer L. Murphy, and Vincent R. Hill, Are Swimming Pool Filters Really Removing Cryptosporidium?, available from pwtag.org. • Anderson JR. A study of the influence of cyanuric acid on the bactericidal effectiveness of chlorine. Am J Public Health Nations Health. 1965 Oct;55(10):1629-37. • Belosevic, FEMS Microbiol Lett. 2001, 204(1) 197-203. • Black AP, Keirn MA, Smith JJ Jr, Dykes GM Jr, Harlan WE. The disinfection of swimming pool water. II. A field study of the disinfection of public swimming pools, Am J Public Health Nations Health. 1970 Apr; 60(4):740-50. • Campbell, A.T. et al. 1995. Inactivation of oocysts of Cryptosporidium parvum by Ultraviolet radiation, Water Research, 29(11), 2583. • Chappell CL, Okhuysen PC, Sterling CR, DuPont HL. Cryptosporidium parvum: intensity of infection and oocyst excretion patterns in healthy volunteers. J Infect Dis 1996;173:232--6. • Clancy, J.L., Hargy, T. M., Marshall, M. M., Dyksen, J. E. 1997, Inactivation of Cryptosporidium parvum oocysts in water using ultraviolet light, Conference proceedings, AWWA International Symposium on Cryptosporidium and Cryptosporidiosis, Newport Beach, CA. • Craik, Water Res. 2001, 35(6) 1387-98. • DuPont HL, Chappell CL, Sterling CR, Okhuysen PC, Rose JB, Jakubowski W. The infectivity of Cryptosporidium parvum in healthy volunteers. N Engl J Med 1995;332:855--9. • Favero, M. S., C. H. Drake, and G. B. Randall. 1964, Use of staphylococci as indicators of swimming pool pollution. U. S. Public Health Reports, 79:61-70. • Fitzgerald GP, DerVartanian ME. Factors influencing the effectiveness of swimming pool bactericides. Appl Microbiol. 1967 May;15(3):504-9.

57 ©2017 Lonza References • Fitzgerald GP et al. Pseudomonas aeruginosa for the evaluation of swimming pool chlorination and algicides. Appl Microbiol. 1969 Mar;17(3):415-21. • Gerba, C.P. Assessment of enteric pathogen shedding by bathers during recreational activity and its impact on water quality, Quantitative Microbiology, 2000, 2, 55-68. • Golaszewski G et al. The kinetics of the action of chloroisocyanurates on three bacteria: Pseudomonas aeruginosa, Streptococcus faecalis, and Staphylococcus aureus. Water Research 1994;28(1): 207-217. • Goodgame RW et al. Intensity of infection in AIDS-associated cryptosporidiosis. J Infect Dis. 1993 Mar;167(3):704-9. • Hijnen, Water Res. 2006, 40(1) 3-22. • Hlavsa MC et al., 2014, MMWR 63(1), 6-10. • Jokipii L, Jokipii AMM. Timing of symptoms and oocyst excretion in human cryptosporidiosis. N Engl J Med 1986;315:1643--7. • Keuten, M.G.A., Schets, F.M., Schijven, J.F., Verberk, J.Q.J.C., Van Dijk, J.C., Definition and quantification of initial anthropogenic pollutant release in swimming pools, Water Research, 2012, 46, 3682-3692. • Korich DG et al. Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability. Appl Environ Microbiol. 1990 May;56(5):1423-8. • Kowalski, X., Hilton, T. B., Comparison of chlorinated cyanurates with other chlorine disinfectants, Public Health Reports, 1966, 81(3), 282-288. • LeGuyader, M., Grateloup, I., Relative importance of different bacteriological parameters in swimming pool water treated by hypochlorite or chloroisocyanurates, Journal Francais d’Hydrologie, 1988, 19, Fasc 2, 241-250. • Linden, Water Sci. Tech. 2001, 43(12) 171-4. • Lu, Ping. (2012). Enhanced removal of cryptosporidium parvum oocysts and cryptosporidium-sized microspheres from recreational water through filtration, Doctoral Dissertation. University of North Carolina at Charlotte. • Murphy, J. L., Arrowood, M.J., Lu, X., Hlavsa, M.C., Beach, M.J., Hill, V.R., Effect of Cyanuric Acid on the Inactivation of Cryptosporidium parvum under Hyperchlorination Conditions, Environmental Science and Technology, 2015, 49(12), 7348-7355

58 ©2017 Lonza References • O’Brien, J. E., Hydrolytic and ionization equilibria of chlorinated isocyanurate in water, Ph.D. Dissertation, Cambridge, MA: Harvard University, 1972. • O’Brien, J.E., Morris, J.C., Butler, J.N., Equilibria in aqueous solutions of chlorinated isocyanurate, Chapter 14 in Chemistry of Water Supply, Treatment, and Distribution, Alan J. Rubin editor, Ann Arbor Science, Ann Arbor MI, 1974, ISBN 0-250-4036-7. • Okhuysen PC, Chappell CL, Crabb JH, Sterling CR, DuPont HL. Virulence of three distinct Cryptosporidium parvum isolates for healthy adults. J Infect Dis 1999;180:1275--81. • Peeters, Appl. Environ. Microbiol.1989; 55(6): 1519-1522. • Rakestraw, L. F., Nelson, G. D., Flanery, D. M., Pabst, M., Gregos, E., Plumridge, A. M., Vattimo, R. M., A Comprehensive Study on The Microbicidal Properties of Stabilized and Unstabilized Chlorine and The Relationships of Other Chemical and Physical Variables in Public Swimming Pools; A Report of A Study Carried Out in Pinellas County, Florida, Summer/Fall, 1992, published November 1, 1994, available from Occidental Chemical Corporation. • Robinton ED et al. An evaluation of the inhibitory influence of cyanuric acid upon swimming pool disinfection. Am J Public Health. 1967 Feb;57(2):301-10. • Shields JM, et al. The effect of cyanuric acid on the disinfection rate of Cryptosporidium parvum in 20-ppm free chlorine. J Water Health. 2009 Mar;7(1):109-14. • Shields JM, Hill VR, Arrowood MJ, Beach MJ. Inactivation of Cryptosporidium parvum under chlorinated recreational water conditions. J Water Health 2008;6(4):513–20. • Warren IC et al. Swimming pool disinfection. Investigations on behalf of the Department of the Environment into the practice of disinfection of swimming pools during 1972 to 1975. Water Research Centre, Henly-on-Thames, England, 35 pp., Oct 1978. • Yamashita, T., Sakae, K., Ishihara, Y., Inoue, H., and Isomura, S. 1985. Influence of cyanuric acid on viricidal effect of chlorine and the comparative study in actual swimming pool waters. Kansenshogaku Zasshi, March 3, 1988, 62(3), 200-205. • Yamashita, Teruo; Sakae, Kenji; Ishihara, Yuichi; and Isomura, Shin, Microbiological and Chemical Analyses of Indoor Swimming Pools and Virucidal Effect of Chlorine in These Waters, 1990, Jap. J. Publ. Health, 37, 962-966. • Yoder, JS et al. 2012, MMWR 61(SS05); 1-12. • Zhou, L., Kassa, H., Tischler, M. L., Xiao, L., (2004) Host-adapted Cryptosporidium spp. In Canada Geese (Branta canadensis, App. Envir. Microbiol., 70(7), 4211-4215.