Changes in geochemistry from the natural breakdown of petroleum hydrocarbons in groundwater promote mobilization of naturally occurring arsenic from aquifer sediments into groundwater. This geochemical change can result in potentially significant and overlooked arsenic groundwater contamination. Arsenic is a toxin and carcinogen linked to numerous forms of skin, bladder, and lung cancer. Of particular concern to public health is elevated arsenic in groundwater used for drinking water.
For the past 32 years a collaborative group of scientists have investigated the natural attenuation of a petroleum hydrocarbon spill in the shallow, glacial aquifer at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota. Scientists have found that the natural attenuation of petroleum hydrocarbons promotes a reduction of iron hydroxides, and they wondered if naturally occurring arsenic in the glacial aquifers in this area might be mobilized under these conditions. To address this question, for several years arsenic concentrations were measured in groundwater and sediment upgradient, within, and downgradient from the hydrocarbon plume.
Results from this field investigation reveal that arsenic concentrations in the hydrocarbon plume can reach 230 micrograms per liter (µg/L), or 23 times the current drinking water standard of 10 µg/L. Arsenic concentrations are below 10 µg/L upgradient and downgradient from the plume.
The scientists attributed the elevated arsenic in the hydrocarbon plume to a series of interrelated geochemical and biochemical processes. In hydrocarbon plumes, anoxic (low oxygen) conditions occur when microbes metabolize the carbon–rich petroleum and consume oxygen in the process. Once oxygen has been consumed, then iron hydroxides are used to metabolize the carbon, which can result in the release of iron and arsenic from the sediments to the groundwater. The migration of the iron–reducing zone and shifts in the biodegradability of the carbon sources within the hydrocarbon plume result in changes in the concentration and extent of the dissolved arsenic plume over time.
Results from this work also suggest that the arsenic released in the plume may reattach to aquifer sediments downgradient from the plume. This reattachment could be good news for limiting the extent of the arsenic contamination. However, this attachment process may be reversible, highlighting the need for long–term monitoring of arsenic and other chemicals that pose a water quality concern in areas associated with petroleum hydrocarbon leaks and spills.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and Hydrologic Research and Development Program, the Virginia Polytechnic Institute and State University, and the National Crude Oil Spill Fate and Natural Attenuation Research Site , a collaborative venture of the USGS, the Enbridge Energy Limited Partnership, the Minnesota Pollution Control Agency, and Beltrami County, Minnesota.
More Information
- National Crude OIl Spill Fate and Natural Attenuation Research Site
- Toxic Substances Hydrology Program Research Coordinator, Barbara A. Bekins, (USGS) Water Resources Mission Area
- Site Coordinator Jared T. Trost, (USGS) Upper Midwest Water Science Center
- For further details about naturally occurring arsenic in groundwater in the upper Midwest contact Melinda L. Erickson, (USGS) Upper Midwest Water Science Center
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Energy Integrated Science Team
National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota
Energy Integrated Science Team
Cyclical Mobilization and Attenuation of Naturally Occurring Arsenic in an Underground Petroleum Plume
Understanding Pathways of Unconventional Oil and Gas Produced Water Spills in the Environment
Crude Oil Contamination in the Shallow Subsurface
U.S. Geological Survey Identifies Crude-Oil Metabolites in Subsurface Plumes
Remote Sensing Provides a National View of Cyanobacteria Blooms
Ethanol-Containing Fuel Spills Enhanced Natural Trace Element Release from Sediments in an Experimental Setting
Pipeline Crude Oil Spill Still a Cleanup Challenge after 30 Years
Ground-Water Recharge Affects Fate of Petroleum Contaminant Plumes
- Overview
Changes in geochemistry from the natural breakdown of petroleum hydrocarbons in groundwater promote mobilization of naturally occurring arsenic from aquifer sediments into groundwater. This geochemical change can result in potentially significant and overlooked arsenic groundwater contamination. Arsenic is a toxin and carcinogen linked to numerous forms of skin, bladder, and lung cancer. Of particular concern to public health is elevated arsenic in groundwater used for drinking water.
Sources/Usage: Public Domain.A core sample was collected from the uppermost saturated portion of the sandy aquifer using the "freezing drive shoe" technology developed by USGS scientists at the National Crude Oil Spill Fate and Natural Attenuation Research Site. The freezing drive shoe enables nearly complete core recovery from saturated, sandy aquifers. Photo Credit: Jeanne B. Jaeschke, USGS For the past 32 years a collaborative group of scientists have investigated the natural attenuation of a petroleum hydrocarbon spill in the shallow, glacial aquifer at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota. Scientists have found that the natural attenuation of petroleum hydrocarbons promotes a reduction of iron hydroxides, and they wondered if naturally occurring arsenic in the glacial aquifers in this area might be mobilized under these conditions. To address this question, for several years arsenic concentrations were measured in groundwater and sediment upgradient, within, and downgradient from the hydrocarbon plume.
Results from this field investigation reveal that arsenic concentrations in the hydrocarbon plume can reach 230 micrograms per liter (µg/L), or 23 times the current drinking water standard of 10 µg/L. Arsenic concentrations are below 10 µg/L upgradient and downgradient from the plume.
The scientists attributed the elevated arsenic in the hydrocarbon plume to a series of interrelated geochemical and biochemical processes. In hydrocarbon plumes, anoxic (low oxygen) conditions occur when microbes metabolize the carbon–rich petroleum and consume oxygen in the process. Once oxygen has been consumed, then iron hydroxides are used to metabolize the carbon, which can result in the release of iron and arsenic from the sediments to the groundwater. The migration of the iron–reducing zone and shifts in the biodegradability of the carbon sources within the hydrocarbon plume result in changes in the concentration and extent of the dissolved arsenic plume over time.
Sources/Usage: Public Domain.A scientist completes anaerobic processing of sediment from selected core depths prior to geochemical analyses. Photo Credit: Melinda Erickson, USGS Results from this work also suggest that the arsenic released in the plume may reattach to aquifer sediments downgradient from the plume. This reattachment could be good news for limiting the extent of the arsenic contamination. However, this attachment process may be reversible, highlighting the need for long–term monitoring of arsenic and other chemicals that pose a water quality concern in areas associated with petroleum hydrocarbon leaks and spills.
This research was funded by the USGS Ecosystems Mission Area’s Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and Hydrologic Research and Development Program, the Virginia Polytechnic Institute and State University, and the National Crude Oil Spill Fate and Natural Attenuation Research Site , a collaborative venture of the USGS, the Enbridge Energy Limited Partnership, the Minnesota Pollution Control Agency, and Beltrami County, Minnesota.
More Information
- National Crude OIl Spill Fate and Natural Attenuation Research Site
- Toxic Substances Hydrology Program Research Coordinator, Barbara A. Bekins, (USGS) Water Resources Mission Area
- Site Coordinator Jared T. Trost, (USGS) Upper Midwest Water Science Center
- For further details about naturally occurring arsenic in groundwater in the upper Midwest contact Melinda L. Erickson, (USGS) Upper Midwest Water Science Center
- National Crude OIl Spill Fate and Natural Attenuation Research Site
- Science
USGS science related to this featured science activity.
Energy Integrated Science Team
The Energy Lifecycle Integrated Science Team focuses on the potential for contaminant exposures in the environment that might originate from energy resource activities including, extraction, production, transportation, storage, extraction, waste management and restoration. Perceived health risks to humans and other organisms will be distinguished from actual risks, if any. If actual risks are...National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota
The primary focus of the science team at the site is to improve the understanding of the mobilization, attenuation, transport, fate, potential health effects, and remediation of petroleum in the subsurface through collaborative research, peer-reviewed publications, presentations, data, and educational activities.Energy Integrated Science Team
The Energy Lifecycle Integrated Science Team focuses on the potential for contaminant exposures in the environment that might originate from energy resource activities including, extraction, production, transportation, storage, extraction, waste management and restoration. Perceived health risks to humans and other organisms will be distinguished from actual risks, if any. If actual risks are...Cyclical Mobilization and Attenuation of Naturally Occurring Arsenic in an Underground Petroleum Plume
Scientists found that naturally occurring arsenic in aquifer sediments was mobilized into groundwater and attenuated through reattachment to sediments within an underground petroleum plume. Understanding these patterns identifies anthropogenic factors that affect arsenic presence and magnitude in groundwater.Understanding Pathways of Unconventional Oil and Gas Produced Water Spills in the Environment
A new study measures the transport of chemicals associated with unconventional oil and gas (UOG) produced waters downstream from a pipeline leak in North Dakota. This work is part of a long-term study designed to understand chemical persistence in sediments and water and how those factors might be related to contaminant exposures and associated with adverse health effects, if any, on organisms.Crude Oil Contamination in the Shallow Subsurface
This investigation focuses on the long-term persistence in soils and groundwater of petroleum hydrocarbon spills, including crude oil and refined petroleum fuels. The study site near Bemidji, MN, is a laboratory for developing site assessment tools and understanding chemical changes affecting human and environmental health that occur during natural attenuation of petroleum hydrocarbons.U.S. Geological Survey Identifies Crude-Oil Metabolites in Subsurface Plumes
U.S. Geological Survey (USGS) scientists studying two subsurface crude-oil spill sites in Minnesota measured concentrations of oil breakdown products (metabolites) at greater concentrations than parent compound concentrations.Remote Sensing Provides a National View of Cyanobacteria Blooms
Four Federal agencies, including the U.S. Geological Survey (USGS), are collaborating to transform satellite data into information managers can use to protect ecological and human health from freshwater contaminated by harmful algal blooms.Ethanol-Containing Fuel Spills Enhanced Natural Trace Element Release from Sediments in an Experimental Setting
Experimental field research simulating hydrocarbon spills by researchers from the U.S. Geological Survey (USGS), Virginia Tech, and the University of St. Thomas showed that mixed ethanol and petroleum-based fuels increased the rate by which arsenic and other natural trace elements are released from aquifer sediments to groundwater when compared to petroleum-based fuels alone.Pipeline Crude Oil Spill Still a Cleanup Challenge after 30 Years
Research at a 1979 crude oil spill from a ruptured pipeline has exposed and helped to overcome many challenges facing an effective, cost-efficient cleanup of crude oil, U.S. Geological Survey (USGS) scientists have found. The environmental release of crude oil occurred near Bemidji, Minnesota.Ground-Water Recharge Affects Fate of Petroleum Contaminant Plumes
U.S. Geological Survey (USGS) scientists have discovered that rainwater recharging the water table above petroleum contamination plumes affects how plumes grow and the rate that petroleum products (in this case crude oil) degrade and weather in ground water. The amount of recharge affects the migration of oil in the subsurface, how chemicals dissolve from the oil into ground water, and the... - Publications
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