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History and Development of Drinking Water Standards in the U.S.
(Text of a "Power Point" presentation)
==================================
Publication # : None - distributed in electronic format only
Author: Dr. Tom Glanville, Department of Agricultural and Biosystems
Engineering, Iowa State University
Date: March 1995
The following outlines the TEXT of slides prepared for a talk
on drinking water quality standards presented at the ISU Toxicology
Seminar on March 7, 1995.
To download the COMPLETE PRESENTATION (graphics and
text of slides in MICROSOFT "POWER POINT" FORMAT)
click on the companion "POWER POINT" file with the
same title as this file (located in the "POWER POINT"
subdirectory of the "WATER QUALITY" section of this server.)
Slide 1
Drinking-Water Standards
-History
-Key Definitions
-How Standards are Developed
-Current Issues Confronting Developers of Standards
Slide 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
Slide 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)
Slide 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
Slide 5
-Growth in Number of Drinking Water Standards
(Bar graph of number of enforced drinking water standards)
Slide 6
-Definitions
-Primary drinking water contaminant - health-related, enforced
-Secondary drinking water contaminant - non-health-related, not enforced
Slide 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.
Slide 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
Slide 9
-Dose/Response Testing
(diagram)
Slide 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
Slide 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
Slide 12
-Calculating DWEL & HAL
(formulae)
Slide 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
Slide 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
Slide 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
Slide 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
Slide 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
Slide 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
Slide 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
Slide 20
-Current Political Issues in Drinking Water Standards
Development
Public perceptions of risk generally do not agree with scientific risk
rankings (but standards development is often driven by public opinion)
-Estimated Costs of Implementing New Standards
-additional $34 million to implement pre-1986 standards
-additional $180 million to implement 1986 amendments
-additional $150 million per year after 1992
Slide 21
Current Political Issues in Drinking Water Standards
Development
-Public mistrust of EPA drinking water program
-400,000 cases of illness and 40 deaths caused by 1993 contamination of Milwaukee water
supply with cryptosporidium parasite
-quote from EPA senior official ..."what happened in Milwaukee is likely to happen again, but I can't predict where."
-Strong evidence of cancer risk associated with disinfection by-
products
Slide 22
-Current Political Issues in Drinking Water Standards
Development
-Recent EPA study showed more than 800 cities exceed "lead action level" set
by Safe Drinking Water Act
Natural Resources Defense Council report claims 90% of large public water systems in
U.S. continue to use technology developed before WW I
-2-year GAO report claims most states do not undertake the routine
inspections necessary to assure water supply safety **
Slide 23
-Additional Info Sources
-EPA Safe Drinking Water Hotline - 1-800-426-4791
-Internet gopher.epa.gov gopher.senate.gov
gopher.house.gov
-Drinking Water & Health series published by National Academy
Press
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