Arsenic is a known environmental health hazard, linked to cancers and heart disease among other disorders. Regulators in the European Union and USA have set stringent limits on arsenic, but there remain a number of questions over the effects of the metal at low levels.

A new population-based study of cancer cases in New England¹ shows that there may be an increased risk of lung cancer arising from lower than permissible levels of arsenic. However, the results are hedged with caveats, and further research is needed to understand the biological mechanism by which arsenic affects lung function.

In contrast to studies focused on the ecology of arsenic, Julia Heck and colleagues took a broader epidemiological approach, and investigated 223 lung cancer cases in New Hampshire and Vermont. Heck, a former research fellow at the International Agency for Research on Cancer, based in Lyon, France, is now at the University of California, Los Angeles.

In the New England research, toenail clippings provided a biomarker for arsenic exposure, and personal health histories, diet and socio-economic factors were included in order to provide the kind of perspective lacking in previous studies of arsenic in drinking water.

Results from the study indicate that in populations exposed to relatively low levels of arsenic in drinking water, there is an increased risk of two types of lung cancer—small cell and squamous cell carcinomas—among subjects with higher arsenic concentrations in their toenails. But the relatively small sample size means that the findings should be interpreted with caution.

"Excess lung cancer risk in relation to arsenic exposure has been found in other studies, with higher levels of exposure," says epidemiologist Tony Fletcher at the London School of Hygiene and Tropical Medicine. "These new findings are interesting, but given the small study size the reported effect is uncertain, and therefore the findings need to be replicated."

With research into arsenic and cancer in general, it can be a challenge to disentangle health effects arising from exposure to arsenic compounds in drinking water, food, tobacco smoke and workplaces. "It is difficult to draw conclusions from these studies," the researchers write. "The mechanism of arsenic-related lung diseases and lung cancer may differ when arsenic is inhaled instead of ingested."

Unlike in previous work, the New England study includes detailed information on medical history, and, say the researchers, it avoids biases resulting from restricted access to potable water in some third world countries, and the increased availability of uncontaminated drinking water in more developed regions. Limitations of the study include the wide variation of arsenic levels in well water within small geographic areas, and the self-reporting of demographic and medical information by research subjects. That said, the latter is largely unavoidable in epidemiological studies.

The relevance of this latest research to the statutory control of arsenic levels is unclear, given the uncertainties involved and the already low limits established. In 1998, the EU adopted 10 parts per billion as a mandatory limit, and the Environmental Protection Agency followed suit in 2001, reducing the Maximum Contaminant Level from its previous 50ppb.

Is a maximum arsenic level of 10ppb too high? Possibly. But as Heck and colleagues make clear, further research is needed to better understand the effects of arsenic on the human body.

© 2009 Francis Sedgemore