Use of aluminium salts in drinking

AWWA Government Affairs: Use of Aluminum Salts in Drinking
Water Treatment (Approved April 11, 1997) To Be Published in AWWA MainStream
Executive Summary

Aluminum is the world’s most abundant metal; it makes up 7.9 percent of the earth's crust by
weight. Aluminum is typically found as a compound with other elements; it frequently occurs
naturally in water.
The use of aluminum salts in water treatment dates from the beginning of the twentieth century,
when aluminum sulfate (alum) began to be used as a coagulant for color and turbidity removal.
Aluminum salts used in the coagulation and sedimentation processes are an integral part of the
multibarrier approach to drinking water treatment. This approach protects the public from life-
threatening diseases, such as typhoid, cholera, and cryptosporidiosis. In addition, aluminum salts
make drinking water more palatable by clarifying the water and removing many impurities that
affect its color. Alum is the coagulant preferred by many water utility managers and operators
because of industry experience with alum, as well as its effectiveness, availability, purity, and
cost.
On average, the amount of aluminum in drinking water is about the same as the amount of
aluminum that occurs naturally in water sources. Aluminum compounds enter the body primarily
by ingestion of food; in addition, inhalation and dermal exposure can contribute to the total body
burden.
Based on studies conducted by the US Food and Drug Administration, total dietary intake of
aluminum is related to total food intake. It is estimated the average adult American consumes 20
to 40 mg of aluminum per day. Assuming concentrations of aluminum typically found in drinking
water, this source contributes approximately 1 percent of total daily consumption. In contrast, 90
percent of dietary aluminum exposure comes from FDA-approved food additives found in baked
goods, desserts, and cheeses. Medicines, including antacids and buffered aspirin, can contribute
up to 5,000 mg of aluminum. Individuals on antacid therapy commonly consume up to 3,000 mg
of aluminum per day and may do so for many years.
Since the 1970’s, various groups have voiced concern that long-term exposure to aluminum in
drinking water from the water treatment process may be a contributing factor in Alzheimer's
disease. To date, researchers have been unable to verify or refute these claims. Research results
are not sufficiently consistent or accurate to support concerns about aluminum in general or
aluminum in drinking water as causal agents for Alzheimer's disease. Evidence linking aluminum
with other neurological disorders is either limited or unavailable and does not justify strict
regulation of aluminum levels in drinking water.
Any discussion regarding aluminum-based coagulants should start with recognition of the proven
and valuable role of these coagulants in protecting public health while improving the aesthetic
characteristics of drinking water. Water utilities concerned with aluminum should regularly
monitor and voluntarily control aluminum residual. Three ways to control aluminum in drinking
water are optimizing the treatment process, reducing the usage of alum with coagulant aids, and
using a coagulant other than alum.
Background

The use of aluminum salts in drinking water treatment goes back several centuries, when it was
used to clari~ water drawn from muddy rivers and streams. Large-scale commercial use of
aluminum salts dates from the beginning of the twentieth century, when aluminum sulfate (alum)
began to be used as a coagulant for color and turbidity removal. Aluminum salts used in the
coagulation and sedimentation processes are an integral part of the multibarrier approach to
drinking water treatment. This approach protects the public from life-threatening diseases, such
as typhoid, cholera, and cryptosporidiosis. In addition, aluminum salts make drinking water more
palatable by clarifying the water and removing many impurities that affect its color. Alum is the
coagulant preferred by many water utility managers and operators because of industry experience
with alum as well as its effectiveness, availability, purity, and cost.
Since the 1970’s, various groups have voiced concern that longterm exposure to aluminum in
drinking water from the water treatment process may be a contributing factor or cause in
Alzheimer's disease. To date, researchers have been unable to verify or refute these claims.
Because no clear link between aluminum in drinking water and neurological disease has been
proved, aluminum is regulated for aesthetic reasons only. Because of uncertainties about its
health effects and for aesthetic reasons, many water providers monitor the amount of aluminum
in finished drinking water and take steps to control it.
Aluminum Exposure

Aluminum is the world’s most abundant metal; it makes up 7.9 percent of the earths crust by
weight. Aluminum is typically found in a compound with other elements; it frequently occurs
naturally in water. On average, the amount of aluminum in drinking water is about the same as
the amount of aluminum that occurs naturally in water sources. Aluminum compounds enter the
body primarily by ingestion of food; in addition, inhalation and dermal exposure can contribute
to the total body burden.
Based on studies conducted by the US Food and Drug Administration, total dietary intake of
aluminum is related to total food intake. It is estimated the average adult American consumes 20
to 40 mg of aluminum per day. Assuming concentrations of aluminum typically found in drinking
water, this source contributes approximately 1 percent of total daily consumption. In contrast, 90
percent of dietary aluminum exposure comes from FDA-approved food additives found in baked
goods, desserts, and cheeses. Medicines, including antacids and buffered aspirin, can contribute
up to 5,000 mg of aluminum. Individuals on antacid therapy commonly consume up to 3,000 mg
of aluminum per day and may do so for inany years.
Bioavailability

A question repeatedly asked is: Which forms or species of aluminum are most likely to be
absorbed in the digestive system and, therefore, most likely to cause an adverse health effect?
Bioavailability of aluminum is influenced by several factors. In addition to aluminum chemistry,
important factors include the low-pH environment of the stomach, the selective permeability of
the stomach lining, the dramatic change in pH and digestive conditions between the stomach and
the duodenum, and the chemical forms aluminum may take during transport across the intestinal
lining and in the blood plasma.
In the digestive process, the highly acid conditions of the stomach virtually guarantee that much
of the aluminum, regardless of how it is ingested, is converted to the same chemical form. As the
stomach contents pass through the duodenum into the intestines, the acid content is immediately
neutralized. This causes most of the aluminum to precipitate and become unavailable for uptake
or absorption by the body. Mass - balance investigations verify that more than 99.9 percent of
ingested aluminum is excreted through normal bowel function. What little aluminum the body
absorbs is eventually excreted in the urine.
Health Effects

Under certain conditions, aluminum can be part of a neurotoxic compound. The long-term
accumulation of aluminum in the bloodstream, a condition frequently suffered by kidney
dialysis patients, can result in severe encephalopathy, leading to dementia. Studies show that
aluminum injected into the brains of animals leads to the formation of amyloid protein deposits
and neurofibrillary tangles that are similar, though not identical, to those that appear in human
Alzheimer’s disease. Partly because of this similarity, it has been postulated that aluminum
is a contributing factor in Alzheimer’s disease. In addition, it has been suggested aluminum
is a contributing factor in several other neurological disorders, such as Parkinson's disease
and Down's syndrome.

To date, five major epidemiological studies have evaluated the relationship between drinking
water and Alzheimer's disease. Taken as a whole, the studies offer inconclusive and
contradictory results. Three of the studies report a positive association, but two establish no
meaningful relationship. Weakness in design and methodology plague each study, making
definitive conclusions difficult. The latter two studies, which were carried out on the largest
populations, seem to be of greatest value because they gathered more accurate exposure and
diagnostic information about the respective population bases than the other studies did. Overall,
the results do not support a relationship between aluminum in drinking water and Alzheimer’s
disease or any form of dementia. There is, however, a strong genetic component to several forms
of Alzheimer's disease.
In health-effects research, any systematic interpretation of data attempts to balance the evidence
of causality against statistical association: Is there cause and effect or simply coincidence? The
most widely accepted criteria for epidemiologic evaluation include strength of association,
consistency, specificity, temporality, biological gradient, plausibility, and coherence. To
establish causality, all of these criteria must be satisfied, in large part. In regard to aluminum and
neurological effects, few of the criteria are satisfied by the available evidence. There is not
sufficient consistency or accuracy to support concerns about aluminum in general or aluminum in
drinking water as causal agents for Alzheimer's disease. Evidence linking aluminum with other
neurological disorders is either limited or unavailable.

Does Aluminum Merit Regulation?

Though the role of aluminum in certain neurological disorders has not been proved,
research continues in an attempt to establish a possible link. The medical, academic, and
drinking water communities are conducting ongoing research about the health effects of
aluminum. Future research should address the extent and strength of any link, whether the
contribution of aluminum in drinking water is a significant portion of the total bioavailable
intake, and the possible beneficial effects of silicic acid or fluoride in reducing bioavailability.
Strict regulation of aluminum is not warranted until a health link can be confirmed to the
satisfaction of normal toxicological evaluation procedures used for demonstrably toxic
contaminants.
Potential Conflicts With Existing and Pending Regulations and Established Practice

Strict regulation of aluminum could adversely affect the ability of water utilities to deliver safe
and aesthetically pleasing drinking water. The US Environmental Protection Agency's Lead and
Copper Rule's target pH is substantially above the pH of minimum solubility for aluminum in
most coagulation processes. Under such conditions, to produce a low aluminum residual in
finished water, adequate settling and filtration must precede pH adjustment. The USEPA’s
pending Disinfection By-Products Rule, by requiring enhanced coagulation, will prompt many
water utilities to increase the amount of aluminum salts used in this process. Likewise, more
stringent regulation of arsenic may necessitate the use of treatment processes in which aluminum
salts are frequently cost-effective and chemically preferable. Though not required by regulation,
many utilities add fluoride to drinking water. Because aluminum forms strong soluble complexes
with fluoride, utilities that practice both coagulation and fluoridation must careflilly choose the
point of fluoride application to avoid increasing soluble aluminum levels.
In summary, existing and pending drinking water regulations, as well as established practice,
require various, sometimes competing, or even incompatible chemistry objectives. Any effort to
improve the quality of drinking water must consider the complex interplay of chemicals and
processes.
Strategies for Controlling Aluminum in Drinking Water

Although a link between aluminum in drinking water and adverse health effects has not
been definitively established, many water utilities and experts in the drinking water
community feel that it is prudent to regularly monitor and voluntarily control the level of
aluminum in drinking water. Many water utilities do this.
If the residual aluminum concentration exceeds the World Health Organization aesthetic
guidelines or the USEPA secondary water quality standards, water utilities should
investigate water treatment process improvements and costs for aluminum residual
reduction. An aluminum concentration of less than 0.2 mg/L has long been recommended
for aesthetic reasons and to minimize the color, turbidity, and postprecipitation in water
distribution systems.

Three ways to control aluminum in drinking water are optimizing the treatment process,
reducing the usage of alum with coagulant aids, and using a coagulant other than alum.

Optimizing the Treatment Process. Treatment plant operators control residual aluminum by
controlling the dose of the coagulant, manipulating pH to encourage flocculation, and
operating filters to remove turbidity effectively.
Coagulant residual monitors perform on-line chemical analyses of residual coagulant to indicate
whether something is affecting the coagulant dose. Adjusting the dose is one way to reduce the
amount of residual aluminum in finished water. Although coagulant residual monitors do not
directly determine whether an overfeed or underfeed occurs, they do provide a useful tool for
optimizing water treatment.
Likewise, zeta potential (a measurement of the particle charge strength surrounding colloidal
solids) is used to monitor and control the coagulant dose. Aluminum salts neutralize electric
charges and thereby facilitate floc formation. Streaming-current detectors operate on line to
measure the charged environment of the particle and colloid, and can also be used to adjust the
coagulant dosage accordingly.
Efficient flocculation is a key process in controlling residual aluminum. When added to water,
aluminum salts form a hydroxide floc, Al(OH)3, which is insoluble. The speed and efficiency of
this reaction is detennined partly by the pH of the water. Manipulating the water's pH to favor
the formation of hydroxide floc helps to ensure that much of the aluminum will be removed
in the form of floc during sedimentation and filtration.

Finally, operating filters to produce water with turbidity below the 0.1 -ntu range minimizes
the amount of aluminum floc particles in finished water.

Using Coagulant Aids. In some circumstances, coagulant aids such as activated silica,
polyelectrolytes, weighing agents, and absorbents can reduce alum usage.
Using Other Coagulants. Aluminum salts are not the only coagulant usetul to water treatment.
Iron salts are a notable alternative. Iron salts are used by about 20 percent of large water utilities
and by a smaller percentage of small and medium-sized utilities. The use of iron salts has been
increasing, albeit slowly, because of operational and water quality concerns associated with iron
salts.
Another alternative is polyaluminum chloride (PACl). Many surface water treatment plants
have started to use polyaluminum chloride instead of alum. Some of the reasons for this switch
are better cold-water performance by PACl, reduced sludge production, and less alkalinity
consumption. On a weight basis, PACl contains less aluminum than alum, but residual
aluminum is not necessarily dependent on the dosage used or the aluminum content of the
coagulant.
Conclusion

Concerns about a possible link between aluminum salts used in drinking water treatment to
neurological disorders are not sufficiently supported by available medical and scientific evidence
and do not justify strict regulation of aluminum levels in drinking water. Any discussion
regarding aluminum-based coagulants should start with recognition of the proven and valuable
role of these coagulants in protecting public health while improving the aesthetic characteristics
of drinking water. Water utilities concerned with aluminum should regularly monitor and
voluntarily control aluminum residual.
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1998 American Water Works Association.

Source: http://etienne.dal.free.fr/Bioforce/CD-ROM/doc/TESSI/Traitement_eau/ALSULPHA.pdf