South Dakota Water Science Center
USGS IN YOUR STATE
USGS Water Science Centers are located in each state.
Fuel Oxygenates and Water Quality - Current Understanding of Sources, Occurrence in Natural Waters, Environmental Behavior, Fate, and SignificanceJohn S. Zogorski, A. Morduchowitz, A.L. Baehr, B.J. Bauman, D.L. Conrad, R.T. Drew, N.E. Korte, W.W. Lapham, and J.F. Pankow
U.S. Geological Survey, 1608 Mt. View Road, Rapid City, South Dakota 57702
Phone (605) 355-4560 ext. 214, Telecopier (605) 355-4523, firstname.lastname@example.org
EXECUTIVE SUMMARY AND RECOMMENDATIONS
Introduction and Scope
At the request of the U.S. Environmental Protection Agency (USEPA), the Office of Science and Technology Policy, Executive Office of the President, has coordinated an interagency assessment of the scientific basis and efficacy of the Nation's winter oxygenated gasoline program. This program mandates that compounds referred to as oxygenates be added to gasoline in select metropolitan areas across the United States to reduce the amount of carbon monoxide in the atmosphere in the winter. Many other areas of the United States have voluntarily chosen to use oxygenated fuels to abate air pollution and in severe ozone non-attainment areas reformulated gasoline is required. Fuel oxygenates are also used to enhance the octane of conventional gasoline - a practice that started in the late 1970's and continues today.
Methy tert-butyl ether (MTBE) is the most commonly used fuel oxygenate. The U.S. production was estimated to be 8.0 billion kilograms in 1995. Essentially all of MTBE produced is used for fuel oxygenation. Ethanol (EtOH) is the second most used oxygenate in gasoline blending. EtOH production in the U.S. was estimated to be 4.3 billion kilograms in 1994. No data are available to estimate the portion of this production used in gasoline. Gasoline in carbon monoxide non-attainment areas must contain no less than 2.7 percent oxygen by weight. By volume, this requirement for MTBE and EtOH corresponds to 14.8 and 7.3 percent, respectively. Oxygenates in limited commercial use include ethyl tert-butyl ether(ETBE), tert-amyl methyl ether (TAME), and diisopropyl ether (DIPE). Methanol (MeOH) is only being used as an oxygenate in a limited test program in California. Tert-butyl alcohol (TBA) has been added to gasoline in the past and is another potential fuel oxygenate, but is not currently produced for this purpose.
The purpose of this chapter is to address water-quality issues arising from the production, distribution, storage, and use of fuel oxygenates and their movement in the hydrologic cycle. It summarizes the scientific literature, data, and agency information on the sources, concentrations, behavior, and fate of fuel oxygenates, and their aqueous degradation products, in ground water and surface water. It also assesses the implications for drinking-water quality and aquatic life. Recommendations for further data-base compilation, monitoring, reporting of information, follow-up assessments, reports, and research efforts are also noted. Although the scope of this chapter is intended to cover all oxygenates and aqueous degradation products, little to no data and few scientific publications are available on the occurrence and behavior of oxygenates and their degradation products in ground water, surface water, and drinking water, except for MTBE. Some monitoring data are available for MTBE, however, these data sets are limited in scope.
Sources and Releases
Like hydrocarbon components of gasoline, fuel oxygenates are introduced to the environment during all phases of the petroleum fuel cycle, but the major sources of these compounds are likely associated with the distribution, storage, and use of oxygenated gasoline. Releases of gasoline containing oxygenates to the subsurface from, for example, underground storage tanks, pipelines, and refueling facilities provide point sources for entry of oxygenates as well as gasoline hydrocarbons into the hydrologic cycle. Urban and industrial runoff and wastewater discharges also represent potential sources of oxygenates to the environment. Water in contact with the spilled gasoline at the water table or in the unsaturated zone will solubilize oxygenates along with aromatic hydrocarbon constituents (e.g., benzene, toluene, ethylbenzene, and xylenes commonly referred to as BTEX). Such water can contain high oxygenate concentrations, for example, MTBE concentrations as high as 200,000 micrograms per liter, have been measured in ground water at a site of gasoline leakage.
Petroleum storage tanks represent the largest populations of potential point sources of alkyl ether oxygenates to natural waters. For example, in 1988 the USEPA estimated that there were about 2 million underground storage tanks (USTs) at over 700,000 facilities. In the last several years, USTs have been removed at many facilities, and the current EPA UST universe is an estimated 415,000 UST facilities (about 195,000 are service stations) with about 1.2 million tanks. USEPA's statistics show that slightly over 300,000 sites have been identified with contamination levels that require corrective action. Cleanup has been completed at about 130,000 of these sites. Because of the inherent difficulty in determining leak rates, leak durations, and the use of oxygenates in the released gasoline, it is difficult to develop a reliable estimate of past or current annual release of fuel oxygenates from these sources. USEPA and State requirements exist and require that USTs be fully upgraded to meet stringent release prevention and detection standards by December 1998. The concurrent improvement in the physical condition of USTs and release-detection capabilities, coupled with a reduction in the population of tanks, should contribute to a considerable reduction in the annual volume of oxygenated gasoline released to natural waters from this subset of point sources.
Estimated releases of MTBE, MeOH, and TBA during industrial activity are mostly to the atmosphere and are reported to the USEPA in annual Toxics Release Inventory (TRI) submissions by manufacturers. The release of MTBE to the environment is almost entirely associated with its production, distribution, storage, and use as a fuel oxygenate, whereas releases of MeOH and TBA occur from various other industrial and commercial uses. Industrial releases of other fuel oxygenates ETBE, TAME, DIPE, and most notably EtOH are not included in the TRI.
Annual estimates of exhaust emissions from vehicles, evaporative losses from gasoline stations and vehicles, and releases from storage tanks have not been reported in the scientific literature but are perceived to be important source of oxygenate (as well as other fuel components) release to the environment. Fuel oxygenates in the atmosphere, because of the dispersive effect of weather patterns and occurrence in precipitation, are considered a non-point source to the hydrologic cycle.
Occurrence in Air and Water and Significance to Drinking Water and Aquatic Life
The Clean Air Act, Clean Water Act, and Safe Drinking Water Act do not require the monitoring of fuel oxygenates in air, ground water, surface water, or drinking water. Therefore, comprehensive data to document the occurrence of fuel oxygenates in the major compartments of the hydrologic cycle across the Nation are not available from these programs.
MTBE and other fuel oxygenates are not included in routine ambient air monitoring done by local and State agencies. An exception is the State of California, which just recently began to monitor for MTBE and other volatile organic compounds (VOCs) in ambient air. Air-quality data have been collected for MTBE in six cities as part of special studies. These data are not sufficient to provide a national perspective, however, MTBE was found in urban air and the median concentrations within these urban areas ranged between 0.13 and 4.6 parts per billion by volume. Concentrations of MTBE in air near known sources of MTBE (gasoline stations, roadways, parking lots and garages, and so forth) are higher, and in many cases considerably higher than ambient urban air.
Little data exist on the occurrence of any of the fuel oxygenates in surface-water bodies including streams, rivers, lakes, and reservoirs. Similarly, little data exist on oxygenate occurrence for drinking water derived from surface water.
Storm water was sampled and analyzed for MTBE in 16 cities during 1991-95. These studies were completed by various U.S. Geological Survey (USGS) Districts to characterize storm-water runoff in cities with population exceeding 100,000. These projects were not specifically designed to determine the occurrence and sources of MTBE or other oxygenates, or other VOCs originating from gasoline. Northeastern States and California, high-use areas of MTBE oxygenated gasoline, were not sampled in the USGS studies. The compilations, however, do provide insight on the occurrence of MTBE in storm water in select cities. MTBE was detected in about 7 percent of 592 storm-water samples. When detected, concentrations ranged from 0.2 to 8.7 micrograms per liter, with a median of 1.5 micrograms per liter. Eighty-three percent of the detectable concentrations occurred during the winter season. Statistical evaluation comparing MTBE concentrations for samples collected during an April 1 to September 30 time period versus an October 1 to March 31 time period yielded statistically significant differences. MTBE was detected both in cities using oxygenated gasoline to abate carbon monoxide non-attainment and in cities presumed to have used MTBE in gasoline for octane enhancement.
Water-quality criteria for oxygenates to protect aquatic life have not been established. For the alkyl ether oxygenates, chronic aquatic toxicity data are lacking, and only limited information exists on acute toxicity and bioconcentration. Considerably more acute toxicity studies have been completed for EtOH and MeOH. The maximum concentration of MTBE detected in storm water reported above is about five orders of magnitude below the median lethal concentration for the most sensitive species investigated to date. More toxicity studies of aquatic animals and plants, bioaccumulation information, and ambient levels in surface water are needed before the significance of MTBE to aquatic life can be assessed.
Two data sets provide information on the occurrence of MTBE in ground water and drinking water derived from ground water. Limited or no data are available for any other fuel oxygenate. The first data set was collected as part of the USGS's National Water-Quality Assessment Program. MTBE was included on a list of analytes for ground-water samples collected in 20 major basins across the country during 1993-94. In addition, retrospective efforts of this Program have summarized MTBE occurrence data from a few State and regional ground-water assessment programs. The second data set was assembled during the preparation of this report as USEPA requested, through its 10 Regions, information on drinking-water programs that have analyzed for MTBE. In response to this request, data on the occurrence of MTBE in public drinking-water supplies derived from ground water were provided by seven States, and four States provided data on private wells. It is likely that a significant number of large water utilities monitor for constituents such as MTBE as part of routine scans for VOCs, therefore, additional information on MTBE occurrence may exist but could not be compiled in the timeframe of this assessment.
At least one detection of MTBE has occurred in ground water in 14 of 33 States surveyed. These 14 States are located throughout the United States. MTBE was detected in 5 percent of over 1,500 wells sampled. Most of the detections occur in shallow ground water in urban areas. Ninety-nine percent of the samples from wells screened in shallow ground water in agricultural areas did not have MTBE. About 98 percent of the wells screened in deeper aquifers or deeper parts of shallow aquifers did not have detections of MTBE, and of the remaining 2 percent that had detections of MTBE, the highest concentration reported was 7.9 micrograms per liter. The mechanism for occurrence in the deeper wells is unknown. MTBE's presence in drinking water for one or more utility was reported in six of the seven States that provided data for public water supplies derived from ground water, and MTBE was reported in all four of the States that provided data for private drinking-water wells.
Because only a few States have information on MTBE in drinking water, it is not possible in this preliminary assessment to describe MTBE concentrations in drinking water nationwide. A Federal drinking-water standard has not been established for MTBE, however, the USEPA has issued a draft lifetime health advisory of 20 to 200 micrograms per liter. The health advisory is expected to be revised in 1996. MTBE has been detected in 51 public drinking-water systems to date based on limited monitoring, however, when detected, the concentration of MTBE was generally low and nearly always below the lower limit of the current draft USEPA health advisory. This indicates that the consumption of drinking water was not a major route of exposure for these few systems. Additional MTBE monitoring data for drinking water are needed, from both the States which provided information for this preliminary assessment and from States that were unable to provide said information, before the significance of drinking water as a route of exposure can be assessed for the Nation.
In the past, routine monitoring of ground water at gasoline USTs has focused on BTEX compounds and, as such, little monitoring information is available for fuel oxygenates. Past and recent releases from UST, however, are perceived to be an important source for the entry of high concentrations of fuel oxygenates to ground water. A California Senate Advisory Committee has recently initiated a request to collect MTBE concentration data for ground water at UST sites. This information should be available during the second half of 1996, and it should be helpful in understanding MTBE water-quality concerns from USTs. At least 10 States have established an action level and/or clean-up level for MTBE at sites where gasoline releases have occurred and are being remediated. MTBE monitoring data may be available from these and other States, and this information would provide insights on the potential significance of oxygenate releases from USTs, as well as MTBE concentrations in ground water at these sites.
Studies have been conducted to establish taste and odor thresholds for oxygenates in water. These studies provide useful information regarding the potential impacts on the palatability of drinking water, and the ability for the public to detect MTBE-containing water before it is ingested. These studies indicate that the taste threshold for MTBE, ETBE, and TAME are 39 to 134, 47, and 128 micrograms per liter, respectively. Similarly, the odor detection threshold of MTBE, ETBE, and TAME in water are 45 to 95, 49, and 194 micrograms per liter, respectively. The above-noted taste and odor threshold values for MTBE fall in the range of the USEPA's draft health advisory.
Behavior and Fate of Fuel Oxygenates in the Hydrologic Cycle
Water in contact with spilled gasoline at the water table or in the unsaturated zone will solubilize oxygenates along with aromatic hydrocarbon constituents. Water that is equilibrated with an oxygenated fuel can contain very high concentrations of the oxygenate. For example, for a gasoline that is 10 percent by weight MTBE, the concentration of MTBE in water in chemical equilibrium with the gasoline at room temperature would be on the order of 5,000,000 micrograms per liter and the total BTEX hydrocarbon concentration would be on the order of 120,000 micrograms per liter. Ground-water MTBE concentrations as high as 200,000 micrograms per liter have been observed in wells near gasoline spills. The fact that measured concentrations are typically lower than solubility levels for gasoline oxygenated with MTBE is due either to dilution by uncontaminated water or depletion of MTBE from the gasoline source. Alcohol oxygenates could occur at high concentrations in water adjacent to spilled gasoline because of the high solubility of alcohols, however, there are no published studies that report alcohol concentrations in ground water from releases of oxygenated fuels.
While oxygenated gasolines can lead to high concentrations of fuel oxygenates in water, these concentrations are typically not high enough to increase either the water solubilities (co-solvent effect) or the transport rates of the BTEX compounds. Gasolines containing very high amounts of ethers and alcohols are capable of causing this effect, but such fuels are not in widespread use.
MTBE and other alkyl ether oxygenates are much less biodegradable than BTEX hydrocarbons in ground water. Furthermore, the alkyl ether oxygenates sorb only weakly to soil and aquifer materials, therefore, their transport by ground water will not be retarded to any significant extent. These factors explain why MTBE has been observed to persist at higher concentrations and advance ahead of BTEX plumes in ground water at gasoline spill sites. Conversely, EtOH would be expected to degrade much more rapidly than BTEX hydrocarbons, therefore, EtOH is not expected to persist much beyond the source area and the immediate contaminant plume at a gasoline spill site. It should be noted, however, that no data exist on the occurrence of EtOH in ground water to verify the hypothesis of EtOH's non-persistence and non-migration at spill sites.
Abiotic degradation processes including hydrolosis, direct photolosis, and indirect photolosis are not expected to significantly alter the concentration of MTBE in natural waters.
Because of their occurrence in the atmosphere, and favorable and rapid partitioning to water, fuel oxygenates will occur in precipitation in direct proportion to their concentrations in air. Changes in the ambient air concentration of MTBE, due to increased or decreased usage of oxygenated gasoline, for example, will affect the level of MTBE in precipitation. Cooler temperatures imply larger concentration of MTBE in precipitation for a given atmospheric concentration. Assuming a concentration of 1 part per billion by volume MTBE in the atmosphere, the concentration of MTBE in precipitation would increase almost tenfold, from about 0.2 to 1.5 micrograms per liter, if the temperature decreases from 20 to 0 degrees Celsius. Based on this range of proportionality and MTBE atmospheric concentration data collected in a few cities, precipitation for general urban atmospheres could contain sub-microgram per liter to about 3 micrograms per liter of MTBE. Theory predicts that precipitation concentrations will be higher near roadways, parking lots and garages, and gasoline stations that consistently experience higher air concentrations of MTBE. Available data suggest that the alkyl ether oxygenates have lifetimes in the atmosphere that range from 4 days to 2 weeks. The main degradation pathway seems to be reaction with hydroxyl radical to form tert-butyl formate. In summary, the atmospheric source of alkyl ether oxygenates in urban areas is believed to be continual, and results in low concentrations of MTBE in water relative to point sources such as USTs. The atmospheric source is also areally extensive due to the dispersive effect of weather patterns.
Precipitation inputs oxygenates directly to streams, rivers, lakes, and reservoirs as it falls on these surface-water bodies or enters surface water through overland runoff and storm-water drainage. While they are volatile from water, the alkyl ether oxygenates, such as MTBE, in large rivers and some streams will not be lost quickly by volatilization. Precipitation falling on land and recharging aquifers, together with diffusion of oxygenates from the atmosphere through the unsaturated zone, inputs oxygenates to shallow ground water. From shallow ground water it is possible that dissolved alkyl ether oxygenates will move deeper into an aquifer system toward wells and surface-water discharge areas. The concentration of an oxygenate in ground water along a particular flow path depends upon the age of ground water, that is its residence time in the aquifer from recharge location, and the rate of biodegradation reactions. Dissolved MTBE and other alkyl ether oxygenates would advance deeper into the aquifer system than BTEX compounds because they are less degradable than BTEX compounds, however, the significance of this deeper migration is uncertain because of the paucity of in-situ monitoring and degradation studies.
The chemical properties of oxygenates relative to BTEX compounds provide insight on the anticipated performance and costs of remediation techniques typically applied to remove BTEX at gasoline spill sites. The presence of MTBE and other alkyl ether oxygenates does not prevent the application of conventional (active) remedial methods (air stripping, carbon adsorption, and soil-vapor extraction) for fuel spills but it does raise the cost. For example, the alkyl ether oxygenates can be removed from water using aeration, but only with much higher air/water ratios than required for BTEX removal. The alcohol oxygenates cannot be removed from water by aeration in a cost-effective manner. Similarly, vacuum extraction and air-sparging techniques will be much less efficient for alkyl ether oxygenates than for BTEX, and infeasible for alcohol oxygenate remediation. The application of intrinsic (passive) bioremediation, an emerging, relatively inexpensive approach to the management of conventional gasoline spills, may be limited because of the slowness with which alkyl ether oxygenates are biodegraded and the tendency of these compounds to migrate from release sites. For contaminant plumes containing EtOH or MeOH, however, intrinsic bioremediation, or enhancements to in-situ bioremediation will remain effective.
This chapter has sought to provide an initial assessment of the water-quality consequences of the use of oxygenates in gasoline. The actions outlined in the specific recommendations given below will allow a more comprehensive understanding of those consequences. Specific recommendations are given for MTBE and the other alkyl ether oxygenates largely because of their extensive commercial use and their persistence in, and migration with ground water. Ethanol, the only alcohol currently in wide-scale commercial use as a gasoline oxygenate, is expected to undergo rapid biodegradation in ground water and surface water, except when concentrations are high enough to be toxic to microorganisms.
At the present time, sufficient monitoring data are not available in the Nation to characterize human exposure to the alkyl ether oxygenate compounds by the consumption of drinking water. Typical oxygenate concentrations are not known either for treated drinking waters, or for the surface- and ground-water sources of that drinking water, except for select States. Similarly, little information is available on either the concentrations of oxygenates in surface water to which aquatic animals and plants are typically exposed, or on the toxicities of those compounds to a broad range of aquatic species.
In order that resources directed to implement the recommendations outlined below be used wisely and efficiently, it is recommended that an ad hoc panel representing the public and private sectors develop a comprehensive and interdisciplinary monitoring, research, and assessment plan to determine the significance of the use of alkyl ether fuel oxygenates on drinking-water quality and aquatic life. The plan should identify lead agencies and organizations for various topics, and provide the necessary details which were beyond the scope of this initial assessment, such as: defining specific goals; establishing the timing and relative priority of research and monitoring needs; developing coordination between industry and various local, State, and Federal agencies; creating a national data base for analytical determinations; and selecting data sets for entry into the data base. Some components of the plan, such as monitoring and creating the national data base should be piloted for select cities and States to further work out details, such as common field sampling and analytical methods, and to make appropriate modifications if deemed necessary. Selecting cities and States that are actively engaged in monitoring for alkyl ether oxygenates in air and water would allow for the timely completion of the suggested pilot phase, with minimal additional expenditure.
Three broad recommendations are made based on this initial assessment:
1. Obtain more complete monitoring data and other information that would: (a) enable an exposure assessment for MTBE in drinking water, (b) characterize the relation between use of MTBE and other alkyl ether oxygenates in gasoline and water quality, and (c) identify and characterize major sources of MTBE to the environment.
2. Complete additional behavior and fate studies to expand current knowledge.
3. Complete aquatic toxicity tests to define the threat posed to aquatic life and establish, if warranted, a Federal water-quality criteria.
Completing the exposure assessment for MTBE in drinking water should be given priority. Monitoring of MTBE in drinking water for this purpose should initially be targeted to high MTBE use areas, and to those environmental settings that are otherwise thought to be most susceptible to contamination. State and Federal agencies and large public water utilities are encouraged to start voluntary monitoring of MTBE in drinking water immediately so that the drinking-water exposure assessment can be completed. Essential elements of each of the three recommendations are described below.
Better Characterize Ambient Concentrations, Oxygenated Gasoline Use, Sources to the Environment, and Relations Between Gasoline Use and Water Quality
--Add the alkyl ether oxygenates MTBE, ETBE, TAME, and DIPE to existing VOC analytical schedules and as USEPA routine target analytes for drinking water,wastewater, surface water, ground water, and remediation studies. This inclusion will provide considerable additional information on the occurrence of these oxygenates in water at little additional expense.
-- Create a national data base of analytical determinations of the alkyl ether oxygenates in air, and in ground, surface, and drinking waters. The data base should also include,for example, information on sampling dates, locations, detection limits, analytical method, quality control, and the reporting agency. Carefully selected monitoring data obtained by Federal, State, and local agencies should be reported for inclusion in the data base. The difficulty and limited success in compiling monitoring data from the States for this preliminary assessment illustrates the need for the recommended data base. The goal should be to assemble a data base that allows exposure assessments for the alkyl ether oxygenates in drinking water and for aquatic life in surface water. The USEPA in late 1970's and 1980's completed similar drinking-water assessments for other VOCs.
--Characterize the seasonal volumes of gasoline containing the alkyl ether oxygenates that are sold in the major regions and cities of the Nation. Such usage information is presently unavailable in any systematic form and at the necessary scale, and this lack of data prevents attempts to correlate water-quality data with actual seasonal use. Establishing relations between the use of MTBE (and other alkyl ether oxygenates) and the oxygenate's presence in ground water and surface water will enable the identification of those hydrologic and geologic settings that are most susceptible to contamination.
--Determine the annual releases of the alkyl ether oxygenates to air, land, and water from all sources (e.g., industrial releases, refueling losses, auto emissions, and storage-tank releases), both point and non-point in nature. Presently, estimates of this information are available only for MTBE, TBA, and MeOH, for some sources, and only for those industries which must file annual TRI reports. Precise estimates of annual releases will be difficult to make from currently available information but order-of-magnitude estimates should be made to identify major "data gaps" and to identify the primary source(s) of the alkyl ether oxygenates for air, surface water, ground water, and drinking water. Once characterized, the feasibility of further reducing these primary sources of fuel oxygenates to the environment should be determined.
--Annually review the information specified above and when adequate information is available, prepare interpretive report(s) on the water-quality consequences of the use of MTBE and other alkyl ether oxygenates. At a minimum, the reports(s) should cover: (1) exposure assessment for drinking water and aquatic life; (2) relation between oxygenated fuel usage and the seasonal occurrence of alkyl ether oxygenates in surface water, for various climatic and hydrogeologic settings, and (3) the significance of various sources of fuel oxygenates to air, surface water, ground water, and drinking water. The continued need to collect information on alkyl ether oxygenates should be re-assessed after the above-noted report(s) is completed.
Expand the Current Understanding of the Environmental Behavior and Fate of Alkyl Ether Oxygenates
--Characterize, via field monitoring in select cities and regions of the Nation, the occurrence, movement, and mass fluxes of alkyl ether oxygenates between ambient air, precipitation, surface water, the unsaturated zone, and shallow and deep ground water. This monitoring is needed to: (1) determine the significance of urban atmospheres as non-point sources of contamination of alkyl ether oxygenates to surface and groundwater; (2) identify climatic and hydrogeologic settings where movement of alkyl ether oxygenates in the hydrologic cycle will be of concern; and (3) evaluate the influence of drainage and storm-water management programs on contaminant movement. These studies should also determine the importance of overland runoff in altering the levels of alkyl ether oxygenates in urban streams and rivers, and in water recharged to shallow aquifers.
--Conduct additional laboratory and field research on the degradation of the alkyl ether oxygenates in the different compartments of the hydrologic cycle, under a variety of environmental conditions. Information is needed on degradationhalf-lives and pathways. It is especially important to clarify exactly how persistent the alkyl ether oxygenates can be in soil and ground water under a range of redox conditions, and to identify all of the important degradation products for possible monitoring and behavior/fate research. The potential for plants to uptake and otherwise alter the concentration of alkyl fuel oxygenates in the root zone should be determined.
--Conduct further theoretical modeling on the movement of the alkyl ether oxygenates from land surface to shallow ground water. This research should: (1) test the hypothesis that the frequent occurrence of MTBE in shallow urban ground water at low concentrations can be due to recharged precipitation or overland runoff; (2) identify the associated predominant transport mechanisms; and (3) provide insights on the climatic and hydrogeologic factors that favor such movement of alkyl ether oxygenates in the unsaturated zone.
Expand the Current Understanding of the Aquatic Toxicity of Alkyl Ether Oxygenates
Initiate studies of the chronic toxicity of alkyl ether oxygenates to a broad range of aquatic animals and plants indigenous to surface waters. Additional acute toxicity tests should also be completed for the same species. These studies are needed to: (1) define the extent of any threat posed by the alkyl ether oxygenates to aquatic life; and (2) collect sufficient information to form the basis of a Federal water-quality criteria, if warranted.
1996, Fuel oxygenates and water quality--Current understanding of sources, occurrence in natural waters, environmental behavior, fate and significance--Final report: Office of Science and Technology Policy, Executive Office of the President, 37 p. with attachments. [Also in Interagency assessment of oxygenated fuels--Fuel oxygenates and water quality: National Science and Technology Council, Washington, D.C., p. 2-1 to 2-80 plus appendices].