Epidemiological Data on Arsenic Ingestion and Skin Cancer

Based on this information, the dose level at which cancers first start to be seen from arsenic exposure is near the level at which the detoxification pathway is overwhelmed. Only epidemiological studies with arsenic concentrations in drinking water at or above 0.6 mg/L have reported incidence of skin cancers that increase with dose. The lowest estimated dose corresponding with positive studies of 0.011 mg/kg-day is slightly above the metabolic saturation threshold dose. This is solid evidence that arsenic does not act as a carcinogen in drinking water below this level. 

The regulatory impact of such an approach is shown in table 10.1. Under existing methods, the arsenic in drinking water concentration considered safe by the U.S. ERA is 0.045 mg/L. This is the concentration associated with a cancer risk of 1 in one million, assuming there is no threshold for cancer. Using the threshold approach, a concentration of arsenic in drinking water of 0.23 mg/L would be considered safe. In this case, the 0.23 mg/L concentration is the threshold for non-cancer effects. Although non-cancer effects can occur at levels below the threshold for cancer (re- 

Basis for Target Level Excess cancer risk = 1-ln-one-million Noncancer Hazard Quotient = 1 

Other types of cancer dose-relationships are also being identified for some chemicals. The U.S. ERA S new cancer risk assessment guidance is more flexible to allow use of these chemical-specific models in an effort to incorporate the best science into selection of safe concentrations. 

As we saw in chapter 7, toxicity factors used to evaluate non-cancer effects are primarily based on no-observed adverse effect levels (NOAELs) from animal studies. 

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Figure 10.2. Epidemiological Data on Arsenic Ingestion and Skin Cancer...

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