Environmental Engineering Reference
In-Depth Information
dosage, accumulation in the body over time, and effects beyond the teeth
(brain as well as bones) have not been resolved, although most authori-
ties believe that a moderate amount of fluoride ions (F
-
) in drinking water
contributes to good dental health. Fluoride is seldom found in appreciable
quantities of surface waters and appears in groundwater in only a few geo-
graphical regions, although it is sometimes found in a few types of igneous
or sedimentary rocks. Fluoride is toxic to humans in large quantities (the key
words here being “large quantities”) and is also toxic to some animals. Few
would argue that small concentrations of fluoride (about 1.0 mg/L in drink-
ing water) can be beneficial; however, when the concentration of fluorides in
untreated natural water supplies is excessive, either alternative water sup-
plies must be used or treatment to reduce the fluoride concentration must be
applied, because excessive amounts of fluoride cause mottled or discolored
teeth, a condition called
dental fluorosis.
.
The bottom line on fluoridation is that the widespread availability of fluo-
ride through water fluoridation, toothpaste, and other sources has resulted
in the steady decline of dental caries throughout the United States.
DID YoU KNoW?
Many communities choose to adjust the fluoride concentration in the
water supply to a level beneficial to reduce tooth decay and promote
good oral health. This practice is known as
community water fluorida-
tion
. Given the dramatic decline in tooth decay over the past 60 years,
the Centers for Disease Control and Prevention (CDC) named water
fluoridation one of the ten great public health interventions of the 20th
century (CDC, 2011).
Heavy Metals
Heavy metals are elements with atomic weights between 63.5 and 200.5 and
specific gravity greater than 4.0. Living organisms require trace amounts of
some heavy metals, including cobalt, copper, iron, manganese, molybdenum,
vanadium, strontium, and zinc. Excessive levels of essential metals, however,
can be detrimental to the organism. Non-essential heavy metals of particular
concern to surface water systems are cadmium, chromium, mercury, lead,
arsenic, and antimony. Heavy metals in water are classified as either non-
toxic or toxic. Only those metals that are harmful in relatively small amounts
are labeled toxic; other metals fall into the nontoxic group. In natural waters
(other than in groundwaters), sources of metals include dissolution from nat-
ural deposits and discharges of domestic, agricultural, or industrial wastes.
