Hexavalent chromium, or Cr(VI), is almost constantly in the news lately. California’s Office of Environmental Health Hazard Assessment (OEHHA) has set a hotly contested Public Health Goal (PHG) of 0.020 ug/L, or 20 parts per trillion. Rep. Adam Schiff (D-CA) has introduced legislation into the U.S. House of Representatives to regulate Cr(VI), and Senator Barbara Boxer (D-CA) has introduced the companion legislation into the U.S. Senate. The U.S. Environmental Protection Agency (EPA) is re-reviewing the toxicological data for Cr(VI) after intense political and public pressure to regulate the chemical. But don’t confuse all of this frenzied activity with productivity, or even effective purpose.
The PHG setting process in California is a very rigorous one that takes into account the best available toxicological data in the scientific literature. OEHHA has identified the PHG level of 0.020 ug/L “as protective against all identified toxic effects from both oral and inhalation exposure to hexavalent chromium that may be present in drinking water.”(1) However, there is a great deal of debate among toxicologists that this PHG has been set much too low because of the methodology used in many of the studies OEHHA relied on. In contrast, there is almost no debate that almost any level of arsenic consumption can cause adverse health effects. The PHG in California has been set for arsenic at 0.004 ug/l, which is 4 parts per trillion, or 5 times lower than the PHG for Cr(VI). The EPA has a process similar to OEHHA’s for setting a Maximum Contaminant Level Goal (MCLG) which is analogous to the PHG. The MCLG that EPA has set for arsenic is 0 mg/L. “The International Agency for Research on Cancer (IARC) evaluated arsenic in 1980 and classified ‘arsenic and arsenic compounds’ in Group 1, which includes ‘chemicals and groups of chemicals, which are causally associated with cancer in humans.’ Arsenic is also known to be atherogenic, genotoxic, teratogenic, and may cause other adverse developmental effects in exposed children.’(2)
Setting PHG’s and MCLG’s is the first step in the regulatory process. These goals, along with other considerations such as Best Available Technologies (BAT) for treatment and what that treatment costs, are used to set the Maximum Contaminant Level (MCL), which is the regulatory level. The MCL for arsenic has been set at 10 ug/L, or 2,500 times higher than the PHG. Yet the political and public pressure is being applied to set the MCL for Cr(VI), a less toxic chemical by almost any measure, at or very near the PHG of 0.020 ug/L. The logic here is illusive to say the least.
I don’t think the MCL for arsenic should be lowered. There are too many small systems that can’t meet the MCL now, and many others can only meet it at great expense. That’s an expense that gets passed on to the consumer in a time when complaints about increasing water bills show up in the news a lot more frequently than news about Cr(VI). And I don’t think that the MCL for Cr(VI) should be set at or near the PHG. The same considerations that were used to set the MCL for arsenic 2,500 times higher than the PHG need to be applied to setting the MCL for Cr(VI). Water purity has to be balanced by water expense in providing an acceptable product to the public.
1) PUBLIC HEALTH GOALS FOR CHEMICALS IN DRINKING WATER, HEXAVALENT CHROMIUM (Cr VI), July 2011. http://oehha.ca.gov/water/phg/pdf/Cr6PHG072911.pdf
2) PUBLIC HEALTH GOALS FOR CHEMICALS IN DRINKING WATER, ARSENIC, April 2004.
http://oehha.ca.gov/water/phg/pdf/asfinal.pdf
Nice article Patrick. The only thing I might add is that USEPA sets their MCLG's for all known human carcinogens at zero. This actually makes much more sense than what OEHHA does where they can set a PHG (like arsenic or hex chrome) at a level that is not acheivable. This actually does a disservice to the public in their ability to understand the meaning of a PHG. Maybe someday we can get legislation to change the PHG format for carcinogens to equal what USEPA does.
ReplyDelete