1999 Progress Report: Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft

EPA Grant Number: R825433C024
Subproject: this is subproject number 024 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
Investigators: Reuter, John E. , Allen, Brant C. , Goldman, Charles R.
Current Investigators: Reuter, John E. , Allen, Brant C. , Goldman, Charles R. , Jassby, Alan D.
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


To investigate sources, fate and transport of MTBE in surface water bodies used as drinking water sources.

Progress Summary:

Addition of fuel oxygenates to gasoline to enhance octane level, increase burning efficiency, and reduce the emission of atmospheric pollutants has become more common in recent years. The most frequently used fuel oxygenate is methyl tert-butyl ether (MTBE). As of 1992, urban areas classified as serious or moderate nonattainment for carbon monoxide (CO) under the 1990 Clean Air Act Amendments were required to sell oxygenated fuel containing a minimum of 2.7% oxygen by weight. For MTBE this would correspond to 14.8 percent by volume. In 1995 California's South Coast Region was using reformulated gasoline year round, and by June 1996 gasoline containing MTBE as the primary fuel oxygenate was at service stations state-wide.

Discovery of MTBE in groundwater, lakes and reservoirs used for drinking water has raised considerable concern among health officials and water suppliers. The U.S. Environmental Protection Agency has classified MTBE as a possible human carcinogen and has set a drinking water advisory at 20-40 µg.L-1 based on consumer acceptance. Recent legislation in California has established primary and secondary drinking water standards at 13 µg.L-1 and 5 µg.L-1 for public health and taste & odor, respectively. We have been involved in three projects; (1) study of sources, fate and transport of MTBE in the surface waters of Donner Lake, (2) MTBE emission into Lake Tahoe based on marine engine classification (e.g. 2-stroke vs. 4-stroke), and (3) survey of MTBE in surface, drinking water bodies, in California.

Despite recent policy decisions, few published studies exist on concentrations, sources and fate of MTBE in surface waters. The purpose of the Donner Lake study was to determine the (1) relative contribution of motorized watercraft as a source of MTBE, (2) its seasonal distribution, (3) loss from the water column, (4) extent of vertical transport, and (5) persistence between years; this work was done in Donner Lake, California, a multiple-use lake in the Sierra Nevada Mountains. MTBE measurements were made at 9 individual depths from surface to bottom on 16 dates. Recreational boating was the most important source of MTBE. Statistically, 86% of the change in MTBE was explained by variation in motorized watercraft use. Neither highway runoff nor precipitation contributed significantly. MTBE concentration ranged from <0.1 µg.L-1 to a high of 12 µg.L-1. Between July 1-7, 1997, MTBE content rose dramatically from 115 kg to 365 kg. By January, levels declined to a minimum of 15 kg suggesting little inter-annual persistence. The major loss of MTBE appeared to be volatilization at the air-water interface characterized by two distinct periods. During the boating season, MTBE decline was 1.2 kg.d-1 (193 day half-life). At the end of the boating season, MTBE loss increased to 8.1 kg.d-1 (14 day half-life). Thermal stratification acted to retard MTBE transport to deeper depths.

In response to the growing concern that the use of 2-stroke marine engines at Lake Tahoe was having a negative impact on lake water quality and aquatic life, we participated in a scientific study group to further investigate the magnitude of fuel pollution that was entering the lake from various types of watercraft. The group consisted of a variety of institutions with representatives from agencies, academia and other interest groups. The most important objectives of this group were to: (1) evaluate the transfer and fate of fuel-related hydrocarbons and emission constituents;(2) identify impacts of various classes of watercraft engines and other sources of contamination; (3) quantify the magnitude of all unburned fuels by type of watercraft engine and (4) assess hazards and risk to human health and aquatic life.
MTBE and BTEX compounds (benzene, toluene, ethylbenzene, xylene) were detected at a number of nearshore locations in Lake Tahoe and in other lakes in the Tahoe Basin which allow motorized watercraft. These compounds increased during motorized watercraft activity. In areas of high watercraft use (on the order of 50-100 marine engines in operation), concentrations of MTBE and benzene were found to exceed drinking water standards. The calculated mean values for MTBE and BTEX as monitored in the nearshore of Lake Tahoe did not exceed drinking water standards. On occasion, individual samples did exceed these standards. Concentrations at an open-water sampling station (mid-lake) were low and either near or below the reporting limit. Complete depth sampling from the surface to 450 m, gave no indication that MTBE or BTEX was either transporting to depth or accumulating in the lake. Concentrations dropped at the end of the summer boating season and was consistent with other studies. At no time did measured concentrations of MTBE or BTEX approach the US EPA criteria for protection of aquatic life.

Based on the volumes of fuel used by each class of engine as reported by the watercraft use study, and the calculated soluble fractions, carbureted 2-stroke engines contributed a disproportionate load of MTBE, benzene, and toluene to Lake Tahoe. Combining PWC and 2-stroke outboard classes to represent the 2-stroke carbureted engines, they contributed over 90% of the MTBE to Lake Tahoe, while only utilizing about 11-12% of the total fuel. Similarly these engine were responsible for over 70% of the benzene and 80% of the toluene deposited during the boating season. In contrast, the four-stroke inboard and inboard/outboard class consumed 87% of the fuel used by boating on Tahoe but was responsible for 8% of the estimate MTBE, 28% of the estimated benzene, and 17% of the estimated toluene loading to the lake. Estimated gallons of constituent load to Lake Tahoe during the 1998 boating season from 2-stroke engines was on the order of thousands of gallons of MTBE, hundreds of gallons of benzene, and ten's of hundreds of gallons of toluene.

The California Department of Health Services (DOHS) maintains a list of surface waterbodies used as drinking water sources. These include reservoirs, lakes and rivers. Of a state-wide total of 245 waterbodies used for drinking water, reservoirs are the most important in terms of both capacity and population served. MTBE monitoring data is not centralized and therefore, an extensive effort was made to contact the parties responsible for water quality or water supply for each individual source. Of the 245 identified waterbodies used for drinking water, we were able to obtain data for 105 (43%); no MTBE measurements were made at 38 (16%) of these waterbodies, and we received no response for 99 (40%).

State-wide, monitoring at 79, or 75%, of the 105 waterbodies with data consisted of 10 or less total samples; over 50% of the waterbodies tested had 5 or fewer individual samples. Far fewer waterbodies were sampled in larger numbers. Between 11-50 samples were taken at 13 waterbodies, 51-100 samples at 4 waterbodies, 101-150 samples at 2 waterbodies, and greater than 150 individual samples were taken at 6 waterbodies. Our understanding of the environmental fate and transport, and sources of MTBE is primarily based on those water bodies which were monitored extensively.

A total of 2,687 individual analyses for MTBE were available for this evaluation, and as noted, near all of these analyses were done at just 25 waterbodies. The majority of individual MTBE analyses were either below the analytical limit of detection (1,006 or 37%) or if measurable, less or equal to than 5 µg/L (1,134 or 42%). Combined, approximately 80% of the total number of MTBE analyses showed a concentration less than or equal to 5 µg/L. A total of 376 analyses were in the range of greater than 5 to 14 µg/L, with 151 analyses or approximately 5% exceeding 14 µg/L. Presented in a slightly different manner, and to avoid an undue influence of those six waterbodies which were extensively sampled, we tabulated the number of waterbodies with at least one measured concentration in excess of the detection limit, 5 µg/L and 14 µg/L. For these conditions, 59 (56%) of the 105 waterbodies did not contain measurable quantities of MTBE and the remaining 46 (44%) waterbodies were found to have MTBE greater than detection at least once. Of those waterbodies with detectable MTBE, 26 (25% of total number with data) were found to contain MTBE at levels greater than 5 µg/L at least once. A total of 12 waterbodies showed a MTBE concentration or greater than 14 µg/L in at least one sample.

Categorizing the 105 waterbodies for which MTBE data is available, on the basis of MTBE detection and the allowed use of motorized watercraft, the data strongly support the hypothesis that the use of watercraft is an important source of MTBE to lakes and reservoirs. For the 46 waterbodies which contained MTBE at concentrations above detection, 42 or 91% allowed motorized boating. Similarly, 46 or 78% of those waterbodies which did not allow motorized boating also did not contain measurable levels of MTBE. In the 4 waterbodies that contained MTBE at detectable concentration but which did not allow motorized boating, concentrations were low ranging from 0.6 to 2 µg/L. Of the 13 waterbodies with boating but no detectable MTBE, 7 were sampled in the winter when boating activity is significantly reduced.

Future Activities:

This series of research projects on MTBE has contributed to a number of policy decisions regarding MTBE, including banning of 2-stroke marine engines on Lake Tahoe and other waterbodies, and the call by Governor Gray Davis of California to phase-out the use of MTBE. We are currently analyzing samples taken in the summer of 1999 at lake Tahoe to determine if a drop in lake MTBE concentrations were detectable following the ban of 2-stroke engines. At this time, our MTBE work is largely complete. Working with colleagues from other institutions (Jim Oris - Miami University, Ohio and Glenn Miller - University of Nevada, Reno), we are planning to continue the study of PAH emission and possible aquatic toxicity in Lake Tahoe.

Supplemental Keywords:

RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Environmental Chemistry, Aquatic Ecosystem, Biochemistry, Environmental Monitoring, Ecology and Ecosystems, Drinking Water, fate and transport, ecosystem monitoring, watershed management, watersheds, human health effects, source water, MTBE, air pollution, aquatic ecosystems, environmental stress, water quality, ecosystem stress, hydrologic modeling, drinking water contaminants

Progress and Final Reports:

Original Abstract
2000 Progress Report
Final Report

Main Center Abstract and Reports:

R825433    EERC - Center for Ecological Health Research (Cal Davis)

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
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R825433C002 Sacramento River Watershed
R825433C003 Endocrine Disruption in Fish and Birds
R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
R825433C005 Fish Developmental Toxicity/Recruitment
R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
R825433C009 Modeling Ecosystems Under Combined Stress
R825433C010 Mercury Uptake by Fish
R825433C011 Clear Lake Watershed
R825433C012 The Role of Fishes as Transporters of Mercury
R825433C013 Wetlands Restoration
R825433C014 Wildlife Bioaccumulation and Effects
R825433C015 Microbiology of Mercury Methylation in Sediments
R825433C016 Hg and Fe Biogeochemistry
R825433C017 Water Motions and Material Transport
R825433C018 Economic Impacts of Multiple Stresses
R825433C019 The History of Anthropogenic Effects
R825433C020 Wetland Restoration
R825433C021 Sierra Nevada Watershed Project
R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
R825433C025 Regional Movement of Toxics
R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
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R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
R825433C035 Border Rivers Watershed
R825433C036 Toxicity Studies
R825433C037 Watershed Assessment
R825433C038 Microbiological Processes in Sediments
R825433C039 Analytical and Biomarkers Core
R825433C040 Organic Analysis
R825433C041 Inorganic Analysis
R825433C042 Immunoassay and Serum Markers
R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
R825433C045 Microbial Community Assays
R825433C046 Cumulative and Integrative Biochemical Indicators
R825433C047 Mercury and Iron Biogeochemistry
R825433C048 Transport and Fate Core
R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
R825433C053 Currents in Clear Lake
R825433C054 Data Integration and Decision Support Core
R825433C055 Spatial Patterns and Biodiversity
R825433C056 Modeling Transport in Aquatic Systems
R825433C057 Spatial and Temporal Trends in Water Quality
R825433C058 Time Series Analysis and Modeling Ecological Risk
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R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
R825433C064 Chlorinated Hydrocarbons
R825433C065 Sierra Ozone Studies
R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
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R825433C072 Molecular Monitoring of Microbial Populations
R825433C073 Aquatic - Rivers and Estuaries
R825433C074 Border Rivers - Toxicity Studies