Arsenic in California's Drinking Water:
An Update on Regulatory Activities

By Noah Chalfin

On March 7, California's Office of Environmental Health Hazard Assessment (OEHHA) released a draft document entitled "Public Health Goal for Arsenic in Drinking Water". The document's public comment period is open until May 2nd. Following the preliminary comment period, OEHHA will re-draft the document to incorporate suggestions and objections, and then release it for a second comment period, before issuing a final recommendation.

The Public Health Goal (PHG) is a technical report produced by OEHHA's Pesticide and Toxicology Section scientists. PHG's are an assessment of published toxicological data, with the aim of developing a human exposure level to a given water contaminant at which the public will be protected from adverse effects. Specifically, a PHG is the highest exposure level from which no acute or chronic health hazards are anticipated.

It is the charge of OEHHA (under the Safe Drinking Water Act of 1996) to provide these Public Health Goal risk assessments to the California Department of Health Services (DHS) for use in establishing primary drinking water standards (Maximum Contaminant Levels, or MCL's). While PHG's are calculated exclusively based on toxicological factors, the DHS must consider economic issues and technical feasibility in its derivation of enforceable drinking water standards. These standards must be set as practically close to the PHG as possible, so as to protect public health. Additionally, under federal law these levels must be at least as stringent as federal MCL's, if they exist.

In the current Public Health Goal document for arsenic, OEHHA found the most sensitive health endpoints for arsenic toxicity to be cancers of the lung and urinary bladder. This determination is based on epidemiological mortality studies from Taiwan, Chile and Argentina. Applying the California de minimis cancer risk level of one in a million, OEHHA toxicologists calculated the health protective concentration to be an almost infinitesimal level of 0.004 µg of arsenic per liter of drinking water (or 4 parts per trillion). For reference, one part-per-trillion is roughly equivalent to one drop in 25 million gallons!

Currently, the U.S. EPA has a much higher national drinking water standard of 0.05 mg/L (or 50.0 µg/L), a level which would allow 135 cancers in 10,000 chronically exposed people. EPA has proposed a revised standard of 10 µ g/L which, if upheld, will become effective in 2006. The EPA has also issued a health-based Maximum Contaminant Level Goal (MCLG) of zero, which is a non-enforceable recommendation analogous to the California Public Health Goal. While it may appear that the federal goal of zero falls much lower than the California PHG of 0.004 µg/L, note that arsenic cannot be detected in water at levels lower than 1.0 µg/L or 1,000 parts per trillion. Therefore, based on current analytical measurement techniques, it is unlikely that any regulatory body will approve an enforceable standard lower than detectable levels.

While acknowledging that the current OEHHA Public Health Goal will not appear in California statute any time soon, the new document serves an important purpose in terms of setting a precedent for protecting human health from the effects of arsenic. It identifies arsenic carcinogenicity as the most sensitive physiological endpoint (the effect seen at the lowest level of exposure), and alerts public health officials to just how many extra cancer deaths the levels present actually permit. Prior to this latest report, government bodies had generally regarded non-debilitating injuries to the skin, stomach and blood as the most sensitive indicators of arsenic toxicity. Because of the devastating impact of cancer in humans and its societal cost implications, this is a groundbreaking discovery.

While the task of incorporating the OEHHA PHG recommendation into law now rests in the hands of DHS, the release of this document signals an encouraging direction for the protection of California's public health. It can be expected that DHS will establish an MCL somewhere in the range of 1-10 µg/L for arsenic in drinking water. As the technology to detect lower levels of water contaminants develops, it is likely that the enforceable standards for remediation of these public health hazards will accordingly be lowered as well.