Water and Wastewater Calculation Manual

Public Water Supply 513

solution: Using Eq. (5.199), p ϭ 0.985, and AFI ϭ 0.606

Dosage 5 0.5 6.5 lb/d 3 0.985 3 0.606
MGD 3 8.34 lb/sMgal # mg/Ld

5 0.93mg/L

Example 5: A water plant uses 2.0 lb of sodium silicofluoride to fluoridate
160,000 gal water. What is the fluoride dosage?

solution:

Dosage 5 2.0 lb 3 0.985 3 0.606 3 0.606 3 106 mg/L
0.16 Mgal/d 3 8.34 lb/sMgal # mg/Ld

5 0.9 mg/L

Example 6: A water plant feeds 100 lb of hydrofluosilicic acid of 23%
purity during 5 days to fluoridate 0.437 MGD of water. Calculate the fluoride
dosage.

solution:

FR 5 100lb/5 d 5 20 lb/d

Dosage 5 sMGDd FR 3 p 3 AFI
3 8.34 lb/sMgal # mg/Ld

5 0.437 20 lb/d 3 0.23 3 0.792 (obtain AFIϭ 0.792
MGD 3 8.34 lb/sMgal # mg/Ld from Table 5.15)

5 1.0 mg/L

Example 7: A water system uses 1200 lb of 25% hydrofluosilicic acid in
treating 26 Mgal of water. The natural fluoride level in the water is 0.1 mg/L.
What is the final fluoride concentration in the finished water.

solution:

Plant dosage 5 26 3 1200 lb 3 0.25 3 0.792 mg/Ld
106gal 3 8.34 lb/sMgal #

5 1.1 mg/L

Final floride 5 s1.1 1 0.1d mg/L

5 1.2 mg/L

20 Health Risks

Human health risk is the probability that a given exposure or a series
of exposures may have or will damage the health of individuals exposed.
This section discusses the possible risk of drinking water, and assessing

514 Chapter 5

and managing risks by the public water suppliers through the rules and
guidelines of the US EPA. This section specifically covers assessing
and managing risks, radionuclides, and the value of health advisories
concerning drinking water.

20.1 Risk

Risk is the potential for realization of unwanted adverse consequences or
events. In general terms, human health risk is the probability of injury,
disease, or death under a given chemical or biological exposure or under
series of exposures. Risk may be expressed in quantitative term (zero to
one). In many cases, it can only be described as, high, low, or trivial.

We do not live in a risk-free world, but in a chemical world. There are
more than 65,000 chemicals produced, and they are increasing in
number every year. Through use and abuse, many of those chemical
products will end up in our environment—water, air, and land. These
chemicals include organics and inorganics that are used in industries
(including water treatment plants), pharmaceuticals, agricultures
(insecticides), home, personal cosmic purposes, etc. Even terrorism may
threaten our drinking water with chemical contamination.

Certain areas on the earth’s crest and rocks contain high levels of some
naturally occurring chemical elements, such as lead, mercury, fluoride,
and sulfur. In addition, radionuclides such as natural radium, Ra226,
Ra228; radon, Rn; uranium, U, etc.; and man-made radioactive sub-
stances occur throughout the world. Many contaminants may end up in
source waters. Trace amounts of these contaminants might be present
in the drinking water.

All human activities involve some degree of risk. Table 5.16 lists the
risks of some common activities. In addition, pathogen contamination in
food and drinking liquids poses risks. Waterborne disease outbreaks
(Giardia, Cryptosporidium, acute gastroenteritis, E. Coli, etc.) have
occurred in the past and can threaten at anytime (Hass, 2002; Lin, 2002).

Sand filtration, disinfection, and application of drinking water stan-
dards reduce waterborne diseases to protect public health. It was dis-
covered that DBPs result from the reaction of chlorine with natural
organic matter (NOM) in source water. The risk of carcinogenic DBPs
is a dilemma for water utilities. Alternative treatment measures and
microbial control have to be properly managed (see Section 19).

The term “safe,” in its common usage, means “without risk.” In tech-
nical terms, however, this common usage is misleading because science
cannot ascertain the conditions under which a given chemical exposure
is likely to be absolutely without a risk of any type.

Human health risk is the likelihood (or probability) that a given chem-
ical exposure or series of exposures may damage the health of exposed
individuals. Chemical risk assessment involves the complex analysis of

Public Water Supply 515

TABLE 5.16 Annual Risk of Death from Selected Common Human Activities

Activities Individual risk, per year Lifetime risk*
Automobile accident 1/4500 1/65
Lightening 1/2000,000
Coal mining 1/770 1/17
1/125 1/3
Accident 1/10,000 1/222
Black lung disease 1/13,000 1/186
Truck driving accident 1/83,000 1/130
Falls
Home accidents

Others 1/1,000,000
Smoking
Flying
Drinking diet soda
Living near nuclear power plant
Living in stone or brick building
Use of microwaves
Eating 100 charcoal broiled steaks

*Calculated based on 70-year lifetime and 45-year work exposure
SOURCE: US EPA, 1986; R. Begole, State Farm Insurance, personal communication

exposures that have taken place in the past, the adverse health effects
of which may or may not have already occurred. It also involves predic-
tion of the likely consequences of exposures that have not yet occurred.

20.2 Risk assessment

Risk assessment is a quantitative evaluation process of health or/and
environmental risks determining the potential risks associated with
exposure to a type of human hazard—physical, chemical, or biological.
There are four components to every (complete) risk assessment (US EPA,
1986):

1. Hazard identification:
■ Review and analyze toxic data (animal and human studies, and
negative epidemiological studies).
■ Weigh the evidence that a substance causes various toxic effects.
■ Evaluate whether toxic effects in one setting will occur in other
settings.

2. Dose-response evaluation:

■ Perform an estimate of the quantitative relationship between the
amount of exposure to a hazardous identified substance and the
extent of toxic injury or disease.

■ Extrapolate from high dose to low dose.
■ Extrapolate test animals to humans.

516 Chapter 5

3. Human exposure evaluation:

■ Investigate the inhalation, ingestion, and skin contact of a toxic
chemical.

■ Conduct case studies: how many people are exposed and through
which routes; what is the magnitude, duration, and time of exposure.

■ Perform epidemiological studies within different geographic areas.

4. Risk characterization:

■ Integrate the data and analyses of the above three evaluations to esti-
mate potential carcinogenic risk and noncarcinogenic health effects.

Example: In most public health evaluations, it is assumed that an individ-
ual adult or child consumes 2 or 1 L of water, respectively, each day through
all uses. The average body weights for a men, women, and children are
assumed to be 70 kg (154 lb), 50 kg (110 lb), and 10 kg (22 lb), respectively.
A toxic substance is present at 0.7 mg/L in water. Determine the daily dose
of the three groups for toxicological purposes.

solution:

Step 1. Calculate daily intake (DI) of toxic substance

For an adult

DI ϭ 0.7 mg/L ϫ 2 L/d
ϭ 1.4 mg/d

For a child

DI ϭ 0.7 mg/L ϫ 1 L/d
ϭ 0.7 mg/d

Step 2. Compute daily dose (DD) per unit weight

For a man

DD ϭ (1.4 mg/d)/70 kg
ϭ 0.02 mg/kg ⋅ d

For a woman

DD ϭ (1.4 mg/d)/50 kg
ϭ 0.028 mg/kg ⋅ d

For a child

DD ϭ (0.7 mg/d)/10 kg
ϭ 0.07 mg/kg ⋅ d

Note: A child gets the highest dose.

Public Water Supply 517

Dose-response models. The dose-response models for cancer death esti-
mation have been summarized (IUPAC, 1933; Klaassen, 2001). The
most frequently used ones are one-hit, Weibull, and multistage models
shown as follows:

One-hit (one-stage) model. The one-hit mechanistic model is based on the
somatic mutation theory in which only one hit of some minimum criti-
cal amount of a carcinogen at a cellular target for critical cellular inter-
action is required for a cell to be altered (become cancerous). The
probability statement for this model is

P(d) ϭ 1 Ϫ exp(Ϫbd ) (5.202)

where P(d) ϭ the probability of cancer death from a continuous dose
rate, unitless

b ϭ constant
d ϭ dose rate, ␮g/L
bd ϭ the number of hits occurring during a minute

Weibull model. The Weibull model is expressed as

P(d ) ϭ 1 Ϫ exp(Ϫ bdk ) (5.203)

where k ϭ critical number of hits for the toxic cellular response
Others are the same as the above.

Multistage model. Armitage and Doll (1957) developed a multistage model
for carcinogenesis that was based on these equations and on the hypoth-
esis that a series of ordered stages was required before a cell could undergo
mutation, initiation, transformation, and progression to form a tumor.
This relationship was generalized by Crump (1980) by maximizing the like-
lihood function over polynomials so that the probability statement is

P(d ) ϭ 1 Ϫ exp(Ϫ (b0 ϩ b1d1 ϩ b2d2 ϩ . . . . . . . . . ϩ bndk)) (5.204)

where P(d) ϭ the probability of cancer death from a continuous dose
rate, unitless

b’s ϭ constants, (mg/kg ⋅ d)–1
k ϭ the number of dose groups (biological stages)
d ϭ dose rate, ␮g/L

If the true value of b1 is replaced with b1* (the upper confidence limit
of b1), then a linearized multistage model can be derived where the expres-
sion is dominated by (bd*)d at low doses. The slope on this confidence

518 Chapter 5

interval, q1*, is used by US EPA for quantitative cancer assessment. To
obtain a(mn gu/pkpge⋅rd)9Ϫ51%) iscomnufildtiepnliceedibnytetrhveaal monournistko,ftehxepoqs1*urvea(lmueg/(krgis⋅kd/⌬).
dose in

Thus, the upper-bound estimate on risk R is calculated as

R ϭ q1* (mg/kg ⋅ d)Ϫ1 ϫ exposure (mg/kg ⋅ d) (5.205)

This relationship has been used to calculate a “virtually safe dose”
(VSD), which represents the lower 95% confidence limit on a dose that
gives an “acceptable level” of risk (e.g. upper confidence limit for 10Ϫ6
excess risk). The integrated risk information system (IRIS) developed
by the US EPA gives q* values for many environmental carcinogens
(US EPA, 2000a). Because both the q1* and VSD values are calculated
using 95% confidence intervals, the values are believed to represent
conservative, protective estimates.

The US EPA has utilized the linearized multistage model to calculate
“unit risk estimates” in which the upper confidence limit on increased
individual lifetime risk of cancer for 70-kg human, breathing 1 ␮g/m3 of
contaminated air or drinking 2 L/d of water containing 1 ppm (1 mg/L),
is estimated over a 70-year life span.

The human equivalent dosages are derived by multiplying the corre-
sponding animal dosages by (Wh/Wa)1/3. Where Wh and Wa are average
body weight of men and test animals, respectively.

When the response and human equivalent dose data are fit to the lin-
earized multistage model, the 95% upper limit on the largest linear
term is q 1*. Then,

q1* ϭ q1a* (Wh/Wa)1/3

To estimate the 95% lower level of dose concentration, d, corresponding
to a 95% confidence level of risk R,

then R ϭ 1 Ϫ exp(– dq1*) (5.206)
exp (– dq1*) ϭ 1 Ϫ R (5.207)
d (in mg/kg ⋅ d) ϭ (1/q1*) ϫ ln(1 Ϫ R)

To solve for d in ␮g/L with a 70-kg man drinking 2 L/d of water, a factor
is applied.

1 mg/kg ⋅ d ϭ1 mg/kg ⋅ d ϫ 1000 ␮g/mg ϫ 70 kg ÷ 2 L/d ϭ 35,000 ␮g/L
then

d (in ␮g/L) ϭ 35,000 ␮g(mg/kg ⋅ d)–1 ÷ q1*(mg/kg ⋅ d)Ϫ1 ϫ ln(1 Ϫ R) (5.208)

Public Water Supply 519

Example: The highest value do)fϪq1.1*Dfeotrearmdionsee-trheespcoonrrseessptounddyinfogrlvowineysltccholno--
ride in the diet is 2.3 (mg/kg ⋅
centration, d, when R is set as 10Ϫ4, 10Ϫ5, and 10Ϫ6.

solution: Using Eq. (5.208)
Step 1. Setting R ϭ 10Ϫ4

d (in ␮g/L) ϭ (Ϫ35,000/2.3) ϫ ln(1 Ϫ 10Ϫ4)
ϭ 6.09

Step 2. Setting R ϭ 10Ϫ5

d (in ␮g/L) ϭ (Ϫ35,000/2.3) ϫ ln(1 Ϫ 10Ϫ5)
ϭ 0.61

Step 3. Setting R ϭ 10Ϫ6

d (in ␮g/L) ϭ (Ϫ35,000/2.3) ϫ ln(1 Ϫ 10Ϫ6)
ϭ 0.061

Radionuclides in drinking water. Radionuclides may occur naturally
and may be man-made (about 200% in number more than natural
ones). Natural radionuclides in drinking water supplies include
radium (Ra-226 and Ra-228), radon (Rn-222), uranium (U-238), lead
(Pb-210), polonium (Po-210), and thorium (Th-230 and Th-232). They
omit one or more of the three types of nuclear radiation, i.e. alpha,
beta, and gamma rays in air, food, and drinking water. The radiation
attacks bone, red bone marrow, gonads, breast, kidney, lung, skin
(burn), etc. Most radionuclides have long decay half-lives. For exam-
ple, the half-lives for U-238 and Ra-228 are respectively of 4.5 ϫ 109
and 6.7 years. The radioactivity is expressed in curies (Ci). One curie
is the number of particles per second from one gram of radium. Dose
is the energy of a particle. One rad of dose is 100 ergs per gram of
energy deposited.

The MCLGs for radionuclides are set as zero. The MCLs for gross
alpha particle activity, combined with Ra-226 and Ra-228, and man-
made (approximately 200) radionuclides are 15 pCi/L, 5 pCi/L, and
4 millirem/yr. respectively. One pCi (pico Curie) is 10Ϫ12 Ci.

The drinking water equivalent level (DWEL, in pCi/L) for radionu-
clides is defined as (US EPA, 1986)

DWEL 5 sNOAELd sanimalfactor, f1dsBWd (5.209)
sUFdsWCdshumanfactor, f2d

520 Chapter 5

where NOAEL ϭ no observed adverse effect level
BW ϭ body weight, 70 kg for adult male
UF ϭ uncertainty factor, 10, 100, or 100
WC ϭ daily water consumption, 2L/d for adult

Example: Determine DWEL of natural uranium for a man.
Given: NOAEL ϭ 1 mg/kg ⋅ d, f1 ϭ 0.01, f2 ϭ 0.05, and UF ϭ 100.

solution: Usually, BW ϭ 70 kg and WC ϭ 2 L/d are used for assessing risks.
Using Eq. (5.209)

DWEL 5 sNOAELd sanimalfactor, f1dsBWd
sUFdsWCdshumanfactor, f2d

5 s1 mg/kg # dds0.01ds70 kgd
s100ds2 L/dds0.05d

5 0.07 mg/L 3 1000 ␮g/mg

5 70 ␮g/L

20.3 Risk management

Risk management is defined as decisions about whether an assessed risk
is sufficiently high to present a public health concern and about the
appropriate methods for control of a risk judged to be significant. In other
words, it is the process of deciding what to do about the problems.

Risk management involves the following:

■ find and decide the problems from risk assessment (type and concen-
tration of contaminants),

■ assume knowledge of health risks,
■ factor in the hydrology feasibility study and capital and operating

(site-specific) cost analyses,
■ decide and evaluate the measures (alternative control strategies) for

solving the problems,
■ reexamine exposure issues previously dealt with in risk assess-

ment, and
■ evaluate and monitor the results for the corrective measures for

meeting drinking water standards control strategies.

The basic categories of alternative control strategies may include source
control, treatment, combination of the above two, and short-term strate-
gies. The short-term control strategies are the use of bottled water, point-
of-use treatment (RO or ion exchange), or issuance of a boil water order.
The disadvantages of point-of-use units (in-home and workplace water
treatment) are maintenance upkeep problems and higher cost.

Public Water Supply 521

Some bottled waters have questionable water quality (although most
meet MCLs) and are not labeled as to sources and treatment processes.
In foreign countries and even in the United States, some are bottled from
the tap water (public drinking water systems).

Several best management practices for performing in the watershed
may be used for controlling raw water source to reduce or eliminate con-
taminants. Water supply utilities may locate new sources of supply. If
so, the new sources can be blended with or replace the existing water
source. Interceptor well(s) upstream of the source water may be used to
protect water supply wells. The wastewaters from the interceptor wells
need proper disposal or treatment.

If the contaminant source is a leaking storage tank, fix or remove the
tank; pump the well until contaminant levels drop, and then treat the
contaminated soil.

Treatment strategies. Treatment involves best available treatment tech-
niques to reduce contaminant to meet MCLs. Conventional treatment
processes combined with additional techniques can reduce contaminant
levels (Table 5.16; see US EPA, 1986):

a. Processes for inorganic removal

■ Conventional treatment
■ Lime softening
■ Iron exchange
■ Reverse osmosis

TABLE 5.16 Treatment Processes for Removal of Harmful Contaminants

Process Removes

Conventional As (V) at pH <7.5; Cd at pH > 8.5; Cr (III); Pb; Ag at
pH <8.0, pathogens, turbidity
Lime softening As ( V) at pH ϭ 10 – 10.8; Ba at pH ϭ 9.5 – 10.8 ; Cd;
Cr(III) at pH >10.5 ; Pb; Ag; F; V
Reverse osmosis All inorganics; commonly used for As (III), As(V); Ba, Cd,
Cr(III)’ Cr(VI); F, Pb, Hg, NO3, Se ( IV ), Se( VI ); Ag, Ra, U
Ion exchange, cation Ba, Cd, Cr(III), Ag, Ra
Ion exchange, anion As( V ), Cr( VI ); NO3, Se( IV ), Se( VI ), U
Activated carbon Volatile organics (benzene, vinyl chloride, carbon
tetrachloride, TCE, PCE, etc.), chlorinated aromatics (PCB,
Activated alumina dichlorobenzene), pesticides (aldicarb, chlordane, DBCP), DBP
Aeration As( V ), F, Se( IV)
Air stripping Volatile organics, Rn
Boiling Volatile organics, Rn
Membrane (nano-) Pathogens, bacterias
Pathogens, bacterias, DBP

522 Chapter 5

■ Activated alumina
■ Electrodialysis

b. Processes for organic removal

■ Conventional treatment
■ Aeration (diffused air, packed column, slate-tray)
■ Adsorption (granular or powder activated carbon, resins)
■ Oxidation (disinfection)
■ Reverse osmosis
■ Biodegradation
■ Boiling

The specific processes can be added to the existing treatment
processes. An excellent overview and case studies, including capital and
operating costs of the above processes used for risk management and
health advisories, are presented in the US EPA (1986).

Example 1: Based on lack of significant decrease in cholinesterase activity
in rats, the NOAEL for aldicarb sulfoxide in rats is 0.125 mg/kg ⋅ d. For HA
calculation purpose, EPA assumes:

Body weight, BW ϭ 70 kg for a man

BW ϭ 10 kg for a child

Daily water consumed, WC ϭ 2 L/d for man

WC ϭ 1 L/d for 10-kg child

Uncertainty factor, UF ϭ 100 for use with animal NOAEL

This example illustrates how the US EPA determines the HA numbers for
pesticide aldicarb.

solution:

Step 1. Calculate 1-day health advisory (HA)

For the 10-kg child: Using Eq. (5.13)

One-day HA 5 sNOAELd sBWd
sUFd sWCd

5 s0.125 mg/kg # dd s10 kgd
s100ds1 L/dd

5 0.012 mg/L or 12 ␮g/L

Step 2. Determine 10-day health advisory

Since aldicarb is metabolized and excreted rapidly (>90% in urine alone
in a 24-h period following a single dose), the 1- and 10-day HA values would

Public Water Supply 523

not be expected to differ to any extent. Therefore, the 10-day HA will be the
same as the 1-day HA (12 ␮g/L).

Step 3. Longer-term health advisory

For the 10-kg child:

Longer-term HA 5 s0.125 mg/kg # dd s10 kgd
s100d s1 L/dd

5 0.012 mg/L s12 ␮g/Ld

Step 4. Determine lifetime health advisory
a. Calculate RfD using Eq. (5.13a)

RfD* 5 NOAEL 5 0.125 mg/kg # d
UF 100

5 0.00125 mg/kg # d

*RRfD ϭ risk reference dose: estimate of daily exposure to the human
population that appears to be without appreciable risk of deleterious
noncarcinogenic effects over a lifetime of exposure.

The lifetime health advisory proposed above reflects the assumption
that 100 % of the exposure to aldicarb residues is via drinking water.
Since aldicarb is used on food crops, the potential exists for dietary
exposure also, lacking compound-specific data on actual relative source
contribution; it may be assumed that drinking water contributes 20%
of an adult’s daily exposure to aldicarb. The lifetime health advisory for
the 70-kg adult would be 9 ␮g/L, taking this relative source contribu-
tion into account.

Example 2: There are no suitable data available to estimate 1-day, 10-day,
and long-term health advisories. The study of the subacute exposure
to trichloroethylene (TTC) via inhalation 5 days a week for 14 weeks
by adult rats identified a LOAEL 55 ppm (300 mg/m3). Derive the DWEL
for TTC.

Solution:

Step 1: Determine total absorbed dose (TAD)

TAD 5 s300 mg/m3d s8 m3/dd s5/7d s0.3d 5 7.35 mg/kg # d
s70 kgd

where 300 mg/m3 ϭ LOAEL
8 m3/d ϭ volume of air inhaled during the exposure period

524 Chapter 5

5/7 ϭ conversion factor for adjusting from 5 d/week exposure
to a daily dose

0.3 ϭ ratio of the dose absorbed.
70 kg ϭ assumed weight of adult

Step 2: Determine RfD

Rfd 5 s7.35 mg/kg # dd 5 0.00735 mg/kg # d
s100ds10d

where 7.35 mg/kg ⋅ d ϭ TAD
100 ϭ uncertainty factor appropriate for use with data
from an animal study
10 ϭ uncertainty factor appropriate for use in conversion
of LOAFL to NOAEL

Step 3: Determine DWEL

DWEL 5 s0.00735 mg/kg # dds70 kgd 5 0.26 mg/L s260 ␮g/Ld
L/d

where 0.00735 mg/kg ⋅ d ϭ RRfD
70 kg ϭ assumed weight of protected individual
2 L /d ϭ assumed volume of water ingested by 70-kg
adult

The estimated excess cancer risk associated with lifetime exposure to
drinking water containing trichloroethylene at 260 ␮g/L is approxi-
mately 1 ϫ 10Ϫ4. This estimate represents the upper 90% confidence
limit from extrapolations prepared by EPA’s Carcinogen Assessment
Group using the linearized multistage model. The actual risk is unlikely
to exceed this value, but there is considerable uncertainty as to the
accuracy of risk calculated by using this methodology.

Example 3: A subchronic toxicity study of vinyl chloride monomer (VCM)
dissolved in soybean oil was administrated 6 days a week for 13 weeks, by
average to male and female wister rats. The NOAEL in the study was iden-
tified as 30 mg/kg ⋅ d.

Estimate the values of HA for VCM.

solution:

Step 1. Estimate 1-day HA

There are insufficient data for estimation of a 1-day HA. The 10-day HA is
proposed as a conservative estimate for a 1-day HA.

Public Water Supply 525

Step 2. Determine 10-day HA (as well as 1-day HA)
For a 10-kg child:

Ten-day HA 5 sNOAELd s6/7d sBWd
sUFd sWCd

5 s30 mg/kg # dds6/7ds10 kgd
s100d s1 L/dd

5 2.6 mg/L or 2600 ␮g/L

where 6/7 ϭ expansion of 6 d/week treatment in the study

to 7 d/week to represent daily exposure

Others ϭ as previous examples

Note: This HA is equivalent to 2.6 mg/d or 0.26 mg/kg ⋅ d.

Step 3. Determine the longer-term HA

Using Eq. (5.13),

for a child

Longer-term HA 5 s0.13 mg/kg # dds10 kgd
s100d s1L/dd

5 0.013 mg/L or 13 ␮g/kg # d

for an adult

Longer-term HA 5 s0.13 mg/kg # dds70 kgd
s100d s2 L/dd

5 0.046 mg/L or 46 ␮g/L

Note: This HA is equivalent to 92 ␮g/d or 1.3 ␮g/kg ⋅ d.

Step 4. Determine the lifetime HA

Because vinyl chloride is classified as a human carcinogen (Group A of US
EPA, Group 1 of International Agency for Research on Cancer), a lifetime HA
is not recommended.

References

Alley, E. R. 2000. Water Quality Control Handbook. New York: McGraw-Hill.
Allied Signal. 1970. Fluid systems, Reverse osmosis principals and applications. Allied

Signal: San Diego, California.
American Dental Association. 1980. Fluoridation facts. American Dental Association:

G21 Chicago, Illinois.