That is absolute BS.
If you want the truth, follow this link. Here is an excerpt which clearly shows that the NRC (which has NO National Academy of Science members) deliberately ignored science and forced adoption of the absurd and arbitrary 10 ppb limit.
Some scientists advocate use of mathematical models to predict cancer risk from these lower levels of arsenic exposure. The assumptions used in these models are critical.
The EPA's model assumes that any exposure to arsenic increases cancer risk and that cancer risk increases in a linear fashion with increasing exposure. Other models assume there is a "safe" level of exposure or are "sublinear" with increases in cancer risk that are negligible at low doses. Virtually all known toxicological processes follow a sublinear model.
Based on a variety of biochemical, toxicological and human study findings, the subcommittee stated in its report that only the sublinear models were plausible. But because subcommittee could not agree on which sublinear model was correct, the consensus forced by the NRC/EPA process — incredibly — was to opt for the EPA's linear model, the very model the arsenic subcommittee decided was wrong.
The linear model forced by the NRC process forces the adoption of the low standard because the effects at lower levels are artificially inflated. The correct model (the sublinear model) gives a realistic standard because the low level noneffect of arsenic is properly represented.
Because Steven Milloy calls almost any conclusion that he doesn't agree with "junk science", I don't necessarily agree with his conclusions.
For example, he writes this:
"For years the EPA has wanted to reduce the arsenic standard but was stymied by controversy over the relevant science. The EPA's own expert panel on arsenic concluded in 1997 that arsenic did not directly cause cancer. Available human data on U.S. populations doesn't indicate typical arsenic levels in drinking water cause cancer or other health effects — no doubt this is why the current arsenic standard is almost 60 years old."
What he doesn't say, and what both the NRC and EPA do say, is that the best study of the health effects of arsenic in drinking water was a study done in Taiwan. Milloy selectively chooses his debate ground in the above paragraph.
Having said that... it may very well be that the model is flawed. The NRC report, Arsenic in Drinking Water, does consider nonlinear dose-response models.
"Finally, we turn to some discussion of how the new EPA guidelines (EPA 1996) might apply in the present setting. If biological considerations suggest the presence of a nonlinear dose response, then the new guidelines would suggest specifying an appropriate model and using it to estimate low-dose risks. For example, the Poisson model could be used, in which case the model-based estimates in Table 10-11 might be adopted as the estimated risks at 10, 25, and 50 ppb. In the absence of a convincing biological argument for the use of a nonlinear model to predict risks at low doses, EPA generally recommends the use of a point-of-departure approach (EPA 1996). Basically, the idea is to estimate the dose corresponding to a low risk that is still high enough for the corresponding dose to be within the observable range of data. Risks at lower doses can be estimated by linear extrapolation from the point of departure."
They also say this in the discussion:
"The analyses presented in this chapter are based primarily on what is sometimes called a statistical approach to risk assessment. An argument can be made that the multistage Weibull model is derived for biological considerations; however, the philosophy behind statistical modeling is simply to describe the data using a flexible class of dose-response models that can accommodate a wide variety of shapes. In recent years, there has been a lot of interest in the development and application of more biologically based models that account for intake, metabolic pathways, and mode of action; in practice, the approach is rarely used because usually not enough is known about the mode of action for the compound in question. Arsenic certainly falls into that category. Use of biomarkers in the construction of dose-response models is a related idea that has generated a lot of interest in recent years. In practice, however, the data are generally not available to use that approach. Furthermore, statistical methods to incorporate biomarkers into dose-response models have not been developed. Research to develop such approaches would be extremely valuable."
So first you have to ignore Milloy's ad-hominem attacks on the qualifications of the report authors. So what does Milloy finally say about the models?
"The EPA's model assumes that any exposure to arsenic increases cancer risk and that cancer risk increases in a linear fashion with increasing exposure. Other models assume there is a "safe" level of exposure or are "sublinear" with increases in cancer risk that are negligible at low doses. Virtually all known toxicological processes follow a sublinear model."
The NRC report addresses this by saying that there is insufficient data to support the use of alternative models, even though they might be better. So when faced with what isn't known vs. what is known, in order to come to a conclusion it's preferable to base the conclusion on what is known.