There have been several assessments of research concerning the health effects of MTBE and other oxygenated fuels.16,17 Recently, results of a study of the movement of MTBE between tissues in human volunteers were published.18 U.S. EPA is currently updating its assessment of the health effects of MTBE.
There is uncertainty as to what levels of MTBE in drinking water cause a risk to public health.9 U.S. EPA has issued an advisory suggesting that drinking water should not contain MTBE in concentrations >20-40 |ag/L, based on taste and odor concerns, but has not issued a federal maximum contaminant level (MCL) for MTBE, which will be based on the ongoing U.S. EPA studies.1
In addition, 31 states have established standards, guidelines, advisory levels, or action levels (some based on the U.S. EPA advisory concentrations) for the maximum concentration of MTBE
allowable in drinking water. California Department of Health Services established a primary MCL of 13 |ag/L, corresponding to the de minimis cancer risk derived from animal studies and a secondary MCL of 5 |ag/L for taste and odor concerns.19 Forty-two states have established cleanup levels or guidelines (some site-specific) for MTBE in soil and groundwater. MTBE drinking water standards range from 5 to 240 ^g/L, with 90% of state standards <100 ^g/L. Soil cleanup levels range from 5 to 280,000 |^g/kg and groundwater cleanup levels range from 5 to 202,000 ^g/L, considering both potable and nonpotable uses for groundwater.10,20,21 More than 75% of the states have groundwater cleanup values <100 ^g/L.
Only limited information is available about the health risks of oxygenates other than MTBE. Fewer states have established standards and cleanup levels for these contaminants than for MTBE. Currently, there are no federal drinking water advisory or cleanup levels for these other fuel oxygenates. Several states have established, and some states have plans to establish, cleanup levels for other oxygenates.21 Table 24.1 summarizes the number of states that have cleanup levels for fuel oxygenates along with the range of cleanup levels established for each.
Analytical methods for petroleum hydrocarbons (usually BTEX) are well established and some of these protocols have been modified to include oxygenates as individual target compounds. Until recently, validated U.S. EPA analytical methods existed for only a few fuel oxygenates (specifically ethanol, methanol, and TBA). Methods that were developed for analysis of petroleum hydrocarbons in water samples may not be appropriate for fuel oxygenates for several reasons, such as analytical instruments may not routinely be calibrated for oxygenates, inappropriate methods may be used for sample analysis, detection limits (particularly for alcohols) may be higher than regulatory standards, or acid-catalyzed hydrolysis (breakdown) of ethers may occur during sample processing and analysis. In April 2003, U.S. EPA published a fact sheet20 that specifies steps that may be taken to address potential analytical problems with oxygenate analysis. U.S. EPA has found that using its approach consistently results in detection limits of 5 ^g/L or lower for MTBE, TBA, ETBE, TAME, TAEE, TAA, DIPE, and acetone.
Other researchers have provided additional information related to the methods used for the analysis of fuel oxygenates. The following references provide more detailed information about this subject.8,22,23
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