In a phone interview with The Chronicle, Rebecca Sutton – the principal investigator for the EWG study – said the goal of the sampling was not to try to characterize the water supply of any community over any period of time – only one sample was taken in each city. In Ann Arbor, that sample came from a residence.

The group found hexavalent chromium in 31 of the 36 samples collected. In 25 of those samples, the levels of hexavalent chromium were higher than a public health goal that has been proposed by the Office of Environmental Health Hazard Assessment (OEHHA) in California: 0.06 parts per billion (ppb).

Ann Arbor is among the communities that had a sample with a hexavalent chromium level higher than 0.06 ppb. The level in Ann Arbor’s sample was 0.21 ppb – roughly three times the proposed public health goal in California. [For a complete list of cities tested and their levels of hexavalent chromium – also known as chromium-6 – see the EWG report.]

So what’s at risk here? How did Ann Arbor wind up on the EWG’s list to test? And once Ann Arbor was on the list, how did EWG get a water sample to test?

Risk Assessment

A study conducted by the National Toxicology Progam in 2007 concluded that when ingested orally – as in drinking water – hexavalent chromium causes cancer in laboratory animals.

According to a summary by the Water Research Foundation (WRF), there is no national standard for maximum levels of hexavalent chromium. But the chemical is only one kind of chromium, and the total amount of chromium does have an established maximum contaminant load (MCL): 100 ppb. California’s MCL for total chromium is 50 ppb.

The WRF summary indicates that in September of 2010, the U.S. Environmental Protection Agency issued a draft risk assessment of hexavalent chromium addressing the health risk of ingesting it through drinking water. The EPA’s risk assessment process – which included a 60-day comment period from Sept. 30-Nov. 29, and a listening session on Nov. 18, 2010 – will be completed by the summer of 2011. From the WRF summary: “It is probable that this risk assessment will lead to a more stringent national standard for total or hexavalent chromium.”

The EWG’s Sutton, who holds a PhD in environmental chemistry from the University of California Berkeley, told The Chronicle that the results of the EWG study, which shows the widespread occurrence of hexavalent chromium across the country, should provide “good motivation” to California and federal authorities to keep moving forward on establishing safety standards for hexavalent chromium.

Why Ann Arbor?

The cities selected for the EWG study were either large, well-known cities or had a history of detecting total chromium in tests of their drinking water supply.

Sutton, a senior scientist for EWG, confirmed that the reason Ann Arbor was selected was its history of detecting any total chromium on some occasion in the past. In 2008, for example, the city reported the highest level of total chromium level detected at 2.1 ppb. [.pdf of Ann Arbor's 2008 Annual Report on Drinking Water] And two years before that, in 2006, the city measured a level of total chromium at 6.4 ppb. [.pdf of Ann Arbor's 2006 Annual Report on Drinking Water].

Those levels are well below the national standard for total chromium of 100 ppb, and also well under California’s standard of 50 ppb. In both reports for those years, detection of chromium is attributed to erosion of natural deposits.

Which Ann Arbor Water Was Tested?

City of Ann Arbor officials were initially unclear about the source of the sample used by EWG for their test. From the statement that city administrator Roger Fraser read aloud at Monday’s city council meeting: “It is unknown where EWG collected the water sample(s).”

In a phone interview on Tuesday with Molly Wade, the city’s water quality manager, Wade clarified that for regulatory purposes the state requires municipalities to conduct some tests at the water plant and others in the distribution system – at the tap. The city of Ann Arbor was not contacted to facilitate the collection of EWG’s sample at the city’s water plant, which is where the city’s the Annual Report on Drinking Water indicates the city monitors chromium.

Wade’s prior employment, before joining the city staff, included a 12-year period working for the Michigan Dept. of Natural Resources and Environment (MDNRE), which concluded as supervisor for drinking water, working out of the MDNRE’s Jackson office.

EWG’s Sutton explained that once Ann Arbor was on the list of cities to be included, EWG recruited a volunteer to submit a tap water sample. From the methodology section of the report:

EWG recruited water collectors via its staff and their contacts. Tap water samples were collected from unfiltered taps in homes or in public buildings such as hospitals, libraries and malls. Utility bills were typically reviewed to verify the water source of each sample.

All volunteers used a standardized sample collection protocol. Samplers ran the cold-water tap for two minutes to clear pipes of standing water and then collected approximately 100 mL of tap water in a 125 mL HDPE container. Samples were packed in coolers with chilled freezer packs and immediately shipped to the laboratory for analysis. With few exceptions, samples arrived within 24 hours of collection.

The samples were submitted to and analyzed by a California lab: Exova, an ISO/IEC 17025-accredited analytical laboratory. Sutton said that the samples sent to the lab were labeled with the name of the state in which a city was located, plus a designation number.

Implications for Safety of Ann Arbor’s Water

What if the eventual national standards for hexavalent chromium – which the EPA seems likely to develop sometime in 2011 – were to be set at California’s public health goal of 0.06 ppb? And what if the city of Ann Arbor’s water, in multiple samples over time taken at the water plant, showed the same level that EWG measured in the sample it collected for this recent study: 0.21 ppb?

How might the city make its water supply system comply with that hypothetical standard? The WRF summary indicates a variety of techniques that can be used to remove hexavalent chromium from water:

Anion exchange (both strong-base and weak-base), membrane filtration by nanofiltration and reverse osmosis, reduction followed by coagulation and precipitation, and adsorption can remove hexavalent chromium from drinking water.

In the meantime, EWG staffers are not contending that any of the cities’ water supply systems where they sampled are unsafe. In a phone conversation with EWG spokesperson Leeann Brown, she revealed to The Chronicle that she moved to Washington D.C. 20 years ago – from Ann Arbor. And when she visits Ann Arbor next week over the holidays, she won’t avoid drinking the tap water.