Risk Assessment and Characterization of Chloroform and Other Disinfection Byproducts

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1 Risk Assessment and Characterization of Chloroform and Other Disinfection Byproducts Jeffrey Sloan Chlorine Chemistry Council WCC Congress on Science Buenos Aires, Argentina

2 Overview History of chlorine and safe water What are disinfection byproducts (DBPs)? Do DBPs cause cancer or other health effects? EPA s risk assessment for chloroform How risk assessment informs decisions about drinking water safety

3 History of Chlorine Disinfection U.S. cities (Jersey City, Chicago) began continuous chlorination of drinking water in 1908 By 1918, over 1,000 U.S. cities used chlorination Chlorine considered a nearly ideal disinfectant Effective against most known pathogens Provides residual for distribution systems Suitable for range of water quality conditions Easily monitored and controlled Low cost Today, chlorine is still the disinfectant of choice

4 Virtually eliminated Virtually eliminated waterborne diseases such as cholera and typhoid in U.S.

5 Disinfection and Safe Water The filtration of drinking water plus the use of chlorine is probably the most significant public health advance of the millennium. - Life Magazine (1997) -

6 What are DBPs? DBPs form when a disinfectant reacts with natural organic material in water In 1973, U.S. EPA first identified a group of four byproducts (THMs) in chlorinated water Chloroform is most common of the four THMs Potential cancer risks led to first DBP limits (1979) Maximum THM level: 100ppb

7 Cancer Risk Animal data suggests THMs pose a potential cancer hazard Some human studies report higher cancer rates associated with chlorinated water More studies report bladder cancer than other types of cancer

8 Cancer Risk: Causal relationship not established Individual THMs are weak carcinogens Bladder cancer not seen in animal studies Human data is limited and inconsistent DBP exposure is not well characterized Elevated risks may be caused by other factors

9 Chloroform Risk Assessment Chloroform is most thoroughly studied DBP High dose given once daily causes cancer Initial liver damage leads to cancer Same daily dose given in drinking water does not cause cancer Without initial liver damage, no cancer risk Chloroform has threshold or safe level

10 What is U.S. EPA s Safe Level for Chloroform? Lowest dose causing any effect ~ 10 mg/kg/day EPA applies safety factors of 1,000 Safe dose for humans = 0.01 mg/kg/day Protective of cancer and non-cancer effects Significant margin of safety

11 What is a Safe Concentration of Chloroform in Drinking Water? Safe dose = 0.01 mg/kg/day EPA assumes: Adult weighs 70 kg Consumes 2 L water/day Gets 20% of chloroform exposure from drinking water Safe concentration = 70 ppb (No cancer risk)

12 *bromodichloromethane Reproductive and Developmental Health Effects Some studies have reported an association between DBPs and adverse effects on human reproductive health Higher rate of miscarriage reported in study of women in California Largest risk reported for one individual THM chemical (BDCM*)

13 *dibromoacetic acid Data Needed for Risk Assessment CC sponsored studies to further investigate otential reproductive/developmental effects Focus on two DBPs (BDCM and DBA*) Long term studies (including two-generation reproductive health studies) Exposure through drinking water Range of concentrations tested; lowest dose relatively close to human exposure

14 CCC Sponsored Toxicology Studies Conducted by an independent research laboratory Full compliance with U.S. EPA Guidelines Independently monitored Peer-reviewed by panel of experts (Science Advisory Group)

15 Publications: International Journal of Toxicology Developmental Toxicology Studies of BDCM in Rats and Rabbits (Christian et al., 2001) Two-Generation Reproductive Study of BDCM in Rats (Christian et al., 2002) Two-Generation Reproductive Study of DBA in Rats (Christian et al., 2002)

16 No Adverse Effect Levels BDCM General Toxicity: 50 ppm Developmental Toxicity: 450 ppm Reproductive Toxicity: 450 ppm No effects at doses 5, ,250 times higher than human exposure through drinking water

17 No Adverse Effect Levels DBA General Toxicity: 50 ppm Developmental Toxicity: 50 ppm Reproductive Toxicity: 50 ppm No effects at doses 45, ,00 times higher than human exposure through drinking water

18 CCC Sponsored Toxicology Studies: Conclusions Neither BDCM nor DBA should be identified as a risk to human reproductive performance or development when consumed in drinking water at ambient levels. - Christian et al

19 DBPs - Weight of the Science Potential risks are small and highly uncertain Cancer causation remains open question Weak evidence of reproductive/developmental effects Insufficient data for quantitative risk assessment All disinfectants produce DBPs More than 600 DBPs identified Alternative disinfectants produce high priority DBPs Little health data for unregulated DBPs

20 Updated U.S. Regulation of DBPs Further reduce DBP exposure Maximum THM level: 80 ppb Additional DBP limits (HAAs, bromate) May be achieved by removing organic material from source water (filtration) Rules also strengthen microbial protections Water systems continue to use chlorine

21 Conclusions: A Risk-Based Approach to Reduce DBPs DBPs are potential hazards, but pose little risk at low exposure levels Must consider risk tradeoffs of alternatives Safety, reliability, efficacy, and affordability All disinfectants form DBPs Disinfection remains top priority Microbial risks far greater than DBP risks