Drinking-Water Standards

History Key Definitions How Standards are Developed Current Issues Confronting

Developers of Standards

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

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)

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

Growth in Number of Drinking Water Standards

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Assumes SDWA Reauthorization(failed in 1994)

Definitions

Primary drinking water contaminant - health-related, enforced

Secondary drinking water contaminant - non-health-related, not enforced

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.

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

Dose/Response Testing

Threshold or NOAEL(no observed adverse affect level)

Dose

Res

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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

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

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 organics10% for inorganics

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

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

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

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

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 foldModel Lifetime Risk

@ dose = 1 mg/kg/day

One - hit 6.0 X 10 -5

Linear Multistage(used by EPA)

6.0 X 10 -6

Multihit 4.4 X 10 -7

Weibull 1.7 X 10 -8

Probit 1.9 X 10 -10

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

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