Superfund Research Program
Low Dose Arsenic Exposures Related to Skin Cancer
Arsenic, a ubiquitous metalloid, is a known human carcinogen specifically linked to the occurrence of skin cancer at high levels of exposure. Most of the epidemiologic data regarding the relationship between drinking water arsenic and skin cancer come from research conducted in southwest Taiwan where well water concentrations of arsenic are as high as 1,220 parts per billion (ppb). These studies indicate an etiologic link between water arsenic and skin cancer. Risk assessments based on these and other data suggest that there may be effects below the current Maximum Contaminant Level (MCL) of 50 ppb.
Dartmouth College scientists including epidemiologists, biostatisticians, pathologists, chemists, and geologists are conducting wide-ranging studies to evaluate sources and levels of arsenic exposure in New Hampshire. Their goal is to provide the information required to evaluate carcinogenic risks due to arsenic exposure at levels commonly found the United States.
Part of their research involves investigating the geological source of arsenic found in New Hampshire's drinking water. They performed a geologic and spatial analysis using ground water samples collected from nearly 1,000 New Hampshire households and determined that domestic bedrock wells that are drilled deep into the underlying granite base generally have much higher arsenic levels than shallow surface wells. They have established that the high concentrations of arsenic found in the water from the deep wells correlate with presence of pegmatite dikes within the granitic bedrock, a geological formation common to many parts of New England.
This geologically-based model of arsenic distribution developed by this research has proven valuable to Dartmouth researchers conducting epidemiology studies. In addition, the New Hampshire Departments of Environmental Services and Health and Human Services staff have applied the information in a very practical way to address arsenic as a public health issue in their state. It is important to note federal regulations addressing the allowable levels of arsenic in drinking water do not apply to domestic wells (defined as those serving less than 15 households or 25 individuals). Dartmouth scientists estimate that 35-40% of the households in New Hampshire use private wells as their water source. Most of these wells have not been tested for arsenic.
To examine the relationship between arsenic exposure and incidence of skin cancers, Dartmouth scientists are conducting a case-control epidemiology study. They have studied about 900 New Hampshire residents who have had a non-melanoma skin cancer and are comparing their exposure histories to a random sample of the New Hampshire population. In order to study low dose arsenic exposure, the researchers needed new tools to precisely quantify exposure on an individual level:
- The Dartmouth scientists developed the technique to accurately measure very low arsenic concentrations in drinking water.
- These investigators have recently verified that toenail arsenic concentrations correlate well with concentrations of arsenic in water, indicating that this tissue is a useful biomarker of arsenic exposure.
This study is among the first to provide information regarding individual exposure to arsenic and risk of cancer in a geographically defined US population. The researchers determined arsenic exposure by evaluating the amount of arsenic accumulated in an individual's toenails and measuring the concentration of arsenic in the study participant's household drinking water supply. They determined that, in the study population, toenail arsenic concentrations were correlated with well water concentrations, especially among those with water concentrations above 1 ppb. Of the wells tested in this study, over 25% contain more than 2 ppb of arsenic; over 10% are above 10 ppb; and 2.5% are over 50 ppb. Case-control study results suggest that the arsenic dose-response relationship may begin to rise within the exposure range of the study population.
The New Hampshire-based study provides a unique opportunity to collect results directly applicable to the US population and helps identify those at greatest risk for arsenic-induced malignancies. Non-melanoma skin cancer is by far the most frequently occurring cancer in the US and recent studies indicate a dramatic increase in the incidence of these malignancies. Thus, the detection of even small increases in the relative risk of skin cancers in relation to arsenic exposure could have a major impact on the incidence of these malignancies.
In addition to conducting multidisciplinary studies concerning the implications of arsenic contamination of drinking water, Dartmouth Superfund Basic Research Program researchers are deeply involved in the development and support of the New Hampshire Arsenic Consortium. This Consortium brings together university scientists and the New Hampshire Departments of Environmental Services and Health and Human Services and the US Geological Survey. Formation of this group has led to increased communication among the agencies and has resulted in the design and undertaking of inter-agency projects to collect data to support risk assessments. The Arsenic Coalition has successfully raised the level of awareness of the issue of arsenic in drinking water, resulting in greater testing of private wells by the public and enhanced awareness of potential health impact.
For More Information Contact:
Margaret R Karagas
Geisel School of Medicine at Dartmouth Department of Epidemiology
7927 Rubin Building
Lebanon, New Hampshire 03756-1000
To learn more about this research, please refer to the following sources:
- Peters SC, Blum JD, Klaue B, Karagas MR. 1999. Arsenic occurrence in New Hampshire drinking water. Environ Sci Technol 33(9):1328-1333.
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