Arsenic has gotten a bad rap ever since the Frank Capra film Arsenic and Old Lace hit the big screen in 1944 (no, I don’t remember it, at least not all that well). It’s in the news with some regularity and almost never in a good light (see, for example, http://arsenic.news/). In reality, in addition to being scorned by the health community, it has some beneficial uses. We’ll explore the good and bad of arsenic below.
What is It?
We’re accustomed to thinking of arsenic (chemical symbol is As) as a metal, a not-quite-accurate description reinforced by its inclusion in the suite of eight “RCRA metals” – arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver. It’s really a metalloid – a solid chemical element with properties between those of metals and non-metals or a mix of both. The definition is rather vague, and some references list arsenic among the “non-metallic” elements. With no loss of exactness, Capra’s movie could just as easily have been called The Metalloid Murders. On second thought, no.
Occurrence in Nature and Regulation
Arsenic occurs naturally in over 200 mineral species, commonly combined with sulfur, especially as sulfides of iron, lead, and zinc. Every environmental consultant in Indiana with more than a month of experience knows that our state’s soil (and most other soil worldwide) contains a modest level of naturally occurring arsenic. Statistical studies at sites in northeast and western Indiana showed that natural arsenic concentrations in soil typically range from 2 to 15 milligrams per kilogram (mg/Kg) and average 7 to 8 mg/Kg. These stats are typical for soils and even sedimentary rocks in much of the Midwest. It’s infamy among consultants stems from the fact that arsenic occurs naturally at levels that commonly exceed Indiana’s residential migration-to-groundwater screening level (5.9 mg/Kg) and the direct contact screening level (9.5 mg/Kg), requiring that consultants prove to IDEM (over and over again) that the arsenic in soil at a site is due to nature rather than a contaminating activity.
Just as arsenic occurs naturally in soil, it’s also a natural constituent of groundwater as a result of its dissolution from minerals in soil and rock. The US EPA has set a Maximum Contaminant Level (MCL), or Drinking Water Standard, of 0.010 micrograms per liter (µg/L) in water designated for human consumption. In Indiana and many other parts of the Midwest, natural background levels of arsenic in groundwater commonly exceed the MCL, though levels vary widely. Arsenic exceedances in groundwater from private wells are more common than for public wells because the latter tend to be deeper and less affected by minerals leaching from soil and by surface activities.
Releases to the Environment
Historically, non-natural releases of arsenic to the environment have occurred through mining, smelting, coal combustion, and plating activities. Arsenic can also be released through a wide range of other beneficial industrial, commercial, and agricultural uses including strengthening alloys of copper and lead, manufacturing semiconductors, and leather tanning. In the past, arsenic has also been used to produce treated-wood products, herbicides, and insecticides, though many of these uses have or are being phased out. Oh yes, Mr. Capra’s movie also highlighted the use of arsenic to end the presumed suffering of lonely old bachelors.
Health Effects of Arsenic Exposure
Because it’s a natural part of the environment, low levels of arsenic occur in water, food, and even on particulates in air. Unfortunately, even small amounts of arsenic can be toxic to humans. The trivalent form (As+3) is much more toxic then its elemental (As0) or pentavalent (As+5) forms. The pentavalent form is the predominant species in water.
Ingestion (food and water) is the primary exposure route for most people. The symptoms and their seriousness depend on the level, frequency, and duration of exposure. In Arsenic and Old Lace, the Brewster sisters Abby and Martha clearly demonstrated the dire consequence of ingesting high levels of arsenic over a short time. At lower levels and/or for prolonged (chronic) contact periods, arsenic exposure can result in an interesting assortment of acute and chronic symptoms – general weakness, loss of hair, nose and gum bleeding, darkening of the skin, nausea and vomiting, warts on various parts of the body, decreased blood cell production, abnormal heart rhythm, reduced IQs in children, and the list goes on. Arsenic is also a known human carcinogen, and studies have linked its ingestion to increased risk of cancers of the skin, liver, bladder, and lungs.
Potential exposure to arsenic can often be managed or mitigated rather than actively remediated. Risk-management approaches include land-use restrictions (an institutional control) that prohibit residential development, agriculture, and groundwater use at a site. Common engineering controls are applying clean soil or other low-permeability materials over arsenic-impacted soil to prevent exposure and/or leaching to groundwater and calculating an exposure point concentration (EPC) for arsenic that focuses active remediation on small, localized areas while allowing most of a site to be used for restricted purposes. Active remediation of arsenic may include soil removal and disposal, in-place solidification and stabilization, or treating groundwater supplies using coagulation, softening, adsorption, ion exchange, or reverse osmosis processes.
Wilcox and Arsenic
Wilcox scientists have a wide range of experience in characterizing and evaluating both natural and anthropogenic occurrences of arsenic and other contaminants in the environment. Our specific experience includes sampling and analysis of soil, water, and air; statistical evaluations of natural (background) arsenic concentrations; calculation of exposure point concentrations for remediating arsenic-contaminated soil; specification of point-of-use and other treatment methods for reducing arsenic in potable water; and health-based assessments of arsenic exposure risk.
If you’d like assistance with assessing, managing, or mitigating risks related to arsenic or other contaminants or just have questions, please contact me at (317) 472-0999 or firstname.lastname@example.org.