General Information About Arsenic
Source
City of Los Angeles Water Services
Water Quality
ARSENIC
GENERAL INFORMATION
The current Interim Primary Standard for arsenic of 50 micrograms per liter (ug/L) in drinking water was established in 1976 to protect against skin cancer. This standard was scheduled for finalization with the other Phase II compounds in 1991. However, due to new evidence implicating arsenic in the development of other, more serious internal cancers, the Maximum Contaminant Level (MCL) for arsenic was delayed.
Epidemiological studies conducted in 1988 and 1990 on populations in Taiwan exposed to high levels of arsenic (300-800 ug/day) in drinking water show a higher than expected incidence of internal cancers of the liver, kidney, lung, and bladder, in addition to skin cancer. Researchers suspect that exposure to arsenic is responsible for the higher incidence, but genetics, nutrition, or other variables may also contribute to its development.
Arsenic is a difficult contaminant to study, because it does not induce cancer in laboratory animals. It has been shown, in fact, to be an essential nutrient in many animal species and may be an essential element in extremely small amounts for humans as well. In greater amounts however, arsenic is believed to be a potent carcinogen. Arsenic does not appear to induce cancer through the usual modes of initiation and/or promotion, but possibly through a late-stage process. The human body has some defenses against arsenic toxicity.
When amounts below 200-250 ug/day are ingested, the human body can detoxify arsenic by the addition of methyl groups. However, while this provides protection from toxic non-carcinogenic effects, it does not necessarily protect against carcinogenic effects. One hypothesis actually suggests that methyl groups used for arsenic detoxification are directed away from DNA synthesis, thereby causing chromosome damage and indirectly causing cancer. Further studies are needed, especially on U.S. populations.
THE REGULATION (draft)
The Environmental Protection Agency (EPA) has hinted at setting an MCL somewhere between 0.5 and 20 ug/L. To assess the risk associated with exposure to arsenic, EPA uses the linearized multistage model. Based on this model, a one in a million excess cancer risk level would be at 2 parts per trillion (0.002 ug/L). However, current commercial analytical technology cannot detect arsenic at levels below 2 ug/L.
The expected date of the rule is dependent on reauthorization of the Safe Drinking Water Act. Efforts to reauthorize the Safe Drinking Water Act in 1996, may include an arsenic regulatory schedule and changes to the standard setting process. Current draft legislative language would require EPA to finalize the rule by 2000. Drinking water associations, working with EPA hope to see an arsenic regulation based on “good science” which will be worthy of the investment customers may be asked to make.
IMPACT TO LADWP CUSTOMERS
Drinking
Water
The Los Angeles Aqueduct supply (LAA)
contains low levels of arsenic. The long-term
average arsenic level in this raw water
supply is 22 ug/L. After the water is blended
and treated, the level drops to an annual
average of 10 ug/L, well below the current
standard of 50 ug/L. The major contributing
source of arsenic is Hot Creek near Lake
Crowley. Mean annual flow from this creek is
22 cubic-feet per second (cfs), although
flows have ranged from 7 to 79 cfs. At the
new proposed levels, treatment to reduce
arsenic from the entire LAA supply (600 cfs)
will be quite costly. A treatment facility at
Hot Creek would be more cost-effective, but
siting a facility in such an
environmentally-sensitive area will be very
difficult.
In addition to the Hot Creek supply, Los Angeles Department of Water and Power (LADWP) anticipates that many local wells may require treatment. Historically, arsenic in the local well supply has been undetectable based on a detection limit of 10 ug/L. Currently, LADWP is in the process of monitoring all of its local wells using the newer detection limit of 2 ug/L. reatment. Only 2 of the more than 50 wells sampled to date have had detectable arsenic levels.
In addition, the Association of California Water Agencies has been conducting an occurrence evaluation of arsenic in California water supplies at the 0.5 ug/L level. This survey will provide the EPA with some concrete occurrence data which will also be used by ACWA to assess the inancial burden to the customers.
Ocean
Discharge
The Bureau of Sanitation is required under
the Clean Water Act to comply with an arsenic
ocean discharge standard of 12 ug/L per day.
The LADWP has been working with the Bureau of
Sanitation to help limit the amount of
arsenic in sewer discharge. One of the
interim operational changes currently being
evaluated is the addition of ferric chloride
and polymer at the Cottonwood Treatment
Plant, located north of Haiwee
Reservoir for arsenic reduction in the raw
water.
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