1.  Drinking-Water Standards  History  Key Definitions  How Standards are Developed  Current Issues Confronting Developers of Standards

2.  Water Quality First Linked to Disease  1854 - Cholera epidemic in London linked to Broad Street Pump  1887 - Typhoid (Lawrence, Mass.)  1892 - Cholera (Hamburg, Germany)  1908 - Jersey City, NJ first community to disinfect water with chlorine  1854 - Cholera epidemic in London linked to Broad Street Pump  1887 - Typhoid (Lawrence, Mass.)  1892 - Cholera (Hamburg, Germany)  1908 - Jersey City, NJ first community to disinfect water with chlorine

3.  Drinking Water Standards Development in U.S.  1914 - 1st Federal standards (applied only to interstate carriers)  U.S. Public Health Service Standards (revised 1925, 1946, 1956, 1962)  1974 - Federal Safe Drinking Water Act passed following EPA report of 66 potential carcinogens found in New Orleans water supply (act applies only to public supplies)

4.  1986 - Safe Drinking Water Act Amended  Public skeptical of EPA and water industry  Studies showed many systems with one or more toxic chemicals  Congress prescribes rigorous schedule for establishing standards  83 contaminants named for standards development  filtration of surface water supplies mandated  EPA directed to establish 25 new standards every three years

5.  Growth in Number of Drinking Water Standards

6.  Definitions  Primary drinking water contaminant - health-related, enforced  Secondary drinking water contaminant - non-health- related, not enforced

7.  Definitions  Maximum Contaminant Level Goal (MCLG) - A non-enforceable regulatory goal designed to prevent adverse human health effects and allow an adequate margin of safety (MCLG = 0 for any carcinogen)  Maximum Contaminant Level (MCL) - maximum permissible level of a contaminant in water delivered to any user of a public water system (set as close to MCLG as is technically and economically feasible)  Lifetime Health Advisory Level (HAL) - non-regulatory concentration of drinking water contaminant that is not expected to cause any adverse effects over a lifetime of exposure.

8.  Standards for Non-Carcinogens  Based on Dose/Response Studies  Assume a response “threshold” can be identified  Uses a “Safety Factor” approach to calculate the standard

9.  Dose/Response Testing Threshold or NOAEL (no observed adverse affect level) Dose Response

10.  Definitions  Reference Dose (RfD) - the daily exposure without deleterious effects over a lifetime  Drinking Water Equivalent Level (DWEL) - drinking water concentration assuming RfD for 70 kg adult is dissolved in 2 liters of water assumed to be consumed daily  Lifetime Health Advisory (HAL) - determined by applying relative source factor (generally 20% for organics, 10% for inorganics) to the DWEL

11.  Calculating Reference Dose  RfD(mg/kg/day) = NOAEL(mg/kg/day) / Safety Factor  Safety factor of 100 usually used  factor of 10 for human/animal response differences  factor of 10 for inter-individual response differences  additional safety factor of 10 applied if data are questionable

12.  Calculating DWEL & HAL HAL(mg/L) =DWEL(mg/L) X RSC Relative Source Factor Daily Water Consumption (2 L) DWEL(mg/L)= RfD(mg/kg/day) X Body Wt (kg) 20% for organics 10% for inorganics

13.  Example Calculation  NOAEL for Aldicarb = 0.125 mg/kg/day  RfD = NOAEL/Safety Factor = 0.125/100 = 0.00125 mg/kg/day  DWEL = [RfD X Body Wt.] / 2 Liters = [0.001 mg/kg/day X 70 kg] / 2 L = 0.035 mg/L  Lifetime HAL = DWEL X Source Factor = 0.035 mg/L X 0.2 = 0.007 mg/L

14.  Drinking Water Standards for Carcinogens  5 EPA Cancer Groups  A - Known human carcinogens  B - Probable human carcinogens  C - Possible human carcinogens  D - Not classifiable  E - No evidence of human carcinogenicity

15.  Drinking Water Standards for Carcinogens  Based on Dose/Response Studies  But assume that NO response threshold can be identified (ie any dose poses some risk)  Use mathematical models to extrapolate animal D/R data to the low risk levels considered acceptable for humans

16.  Why Assume No Theshold for Carcinogens ?  High natural incidence of tumors in all species makes threshold hard to define (requires large number of animal studies)  Practical doses that lead to identifiable numbers of excess tumors in small animal populations are much higher than doses of interest in minimizing cancer risk to humans

17.  D/R Modeling for Carcinogens  Several math models have been proposed...risk estimates from different models can vary by as much as 1,000,000 fold

18.  Drinking Water Standards for Carcinogens  D/R relationship generally treated as linear  risk = dose X constant  so if dose increases 10-fold... risk also increases 10-fold  EPA sets lifetime health advisories at 1 in 1- million risk level, but MCL’s often set at higher risk level due to technical or economic considerations

19.  Current Scientific Issues in Drinking Water Standards Development  Can cancer “thresholds” be identified?  How to set “standards” for mixtures of contaminants  Highly sensitive (and inexpensive) new water testing methods (ELISA) making pesticide testing more affordable  Establishing standards for new chemicals and chemical metabolites