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.
Researchers conducted an intensive 2-month field experimental study to look at the mechanisms controlling arsenic and other trace element (nickel, chromium, and cobalt) releases from experimental fuel spills at the National Crude Oil Spill Fate and Natural Attenuation Research Site, near Bemidji, Minnesota. The researchers determined that the co-presence of ethanol and nitrate mixed with hydrocarbons had significant effects on the rates and timing of arsenic and other trace element releases to groundwater.
Because arsenic and other trace element releases are microbially controlled, the rate and extent of arsenic release depends, in part, on what the microbial community has available to metabolize as a food source. Researchers determined that when petroleum hydrocarbons were released in the subsurface (simulating a petroleum fuel spill), the microbial community metabolized these hydrocarbons and released iron at slow rates. As a result, arsenic associated with that iron was released to groundwater at slow rates and never exceeded 10 micrograms per liter (μg/L) (the U.S. Environmental Protection Agency drinking water standard) during the 2-month experiment; however, when ethanol (organic carbon source) was also added to the sediments (simulating a mixed ethanol-petroleum fuel spill), metabolism in the microbial community increased, and iron and arsenic were released to groundwater at higher concentrations due to elevated rates of biodegradation and iron reduction. The rapid release rates resulted in a maximum observed arsenic concentration of 99 μg/L, almost ten times the drinking water standard, in a short time period (5 days). The presence of ethanol also significantly decreased the timing of the onset of arsenic release, with the reaction beginning 23 hours after the start of the experiment with ethanol, compared to 189 hours without ethanol. The release to groundwater of other trace elements including nickel, chromium, and cobalt was observed at rates similar to arsenic.
To test the mechanics of how microorganisms release metals into groundwater, nitrate was added in some experiments. The release of arsenic and other trace elements was not observed in those experiments where nitrate was added because microorganisms preferentially use nitrate compared to iron, so any biodegradation in the presence of nitrate is coupled with the reduction of nitrate, not iron. As a result, iron remains in the aquifer sediments and arsenic remains adsorbed to iron, inhibiting its release to groundwater.
Results from this study highlight the importance of monitoring trace elements at fuel spill sites where organic contaminants might be biodegraded under iron-reducing conditions. These complex reactions can introduce new, unexpected types of contaminants that are not commonly monitored at organic-contaminant sites under current (2015) regulatory framework. Depending on the geochemical conditions and the nature of the organic matter, trace element concentrations in groundwater can exceed drinking water standards on short time frames (days), reinforcing the importance of screening the rapid changes in geochemistry following releases of organic carbon sources such as petroleum or ethanol.
Environmental Health Implications
Arsenic is a naturally occurring element and commonly exists in aquifer sediments adsorbed to iron hydroxides. When it remains attached to sediment, arsenic does not pose an immediate human health threat; however, changing geochemical conditions, such as those initiated by the introduction of organic carbon sources such as petroleum byproducts and ethanol, can release arsenic and other trace elements into groundwater to potentially toxic concentrations if the groundwater were to be used as a drinking water source or transported to streams where aquatic biota could be exposed. Arsenic is of particular concern because of its known toxicity and links to liver, bladder, and lung cancers.
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, University of St. Thomas, 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.
Below are other science projects associated with this project.
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
Natural Breakdown of Petroleum Results in Arsenic Mobilization in Groundwater
Pipeline Crude Oil Spill Still a Cleanup Challenge after 30 Years
Ground-Water Recharge Affects Fate of Petroleum Contaminant Plumes
Below are publications associated with this project.
Rates of As and trace-element mobilization caused by Fe reduction in mixed BTEX–ethanol experimental plumes
Below are news stories associated with this project.
- Overview
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.
A scientist collects a groundwater sample to analyze for arsenic and other chemicals from a well installed in a wetland at the National Crude Oil Spill Fate and Natural Attenuation Research Site, near Bemidji, Minnesota. Researchers collected samples over a two-month period to quantify rates of arsenic release from aquifer sediments as organic carbon in the form of petroleum byproducts and ethanol biodegraded in the aquifer. Photo credit: Jennifer McGuire, University of St. Thomas. Researchers conducted an intensive 2-month field experimental study to look at the mechanisms controlling arsenic and other trace element (nickel, chromium, and cobalt) releases from experimental fuel spills at the National Crude Oil Spill Fate and Natural Attenuation Research Site, near Bemidji, Minnesota. The researchers determined that the co-presence of ethanol and nitrate mixed with hydrocarbons had significant effects on the rates and timing of arsenic and other trace element releases to groundwater.
Because arsenic and other trace element releases are microbially controlled, the rate and extent of arsenic release depends, in part, on what the microbial community has available to metabolize as a food source. Researchers determined that when petroleum hydrocarbons were released in the subsurface (simulating a petroleum fuel spill), the microbial community metabolized these hydrocarbons and released iron at slow rates. As a result, arsenic associated with that iron was released to groundwater at slow rates and never exceeded 10 micrograms per liter (μg/L) (the U.S. Environmental Protection Agency drinking water standard) during the 2-month experiment; however, when ethanol (organic carbon source) was also added to the sediments (simulating a mixed ethanol-petroleum fuel spill), metabolism in the microbial community increased, and iron and arsenic were released to groundwater at higher concentrations due to elevated rates of biodegradation and iron reduction. The rapid release rates resulted in a maximum observed arsenic concentration of 99 μg/L, almost ten times the drinking water standard, in a short time period (5 days). The presence of ethanol also significantly decreased the timing of the onset of arsenic release, with the reaction beginning 23 hours after the start of the experiment with ethanol, compared to 189 hours without ethanol. The release to groundwater of other trace elements including nickel, chromium, and cobalt was observed at rates similar to arsenic.
To test the mechanics of how microorganisms release metals into groundwater, nitrate was added in some experiments. The release of arsenic and other trace elements was not observed in those experiments where nitrate was added because microorganisms preferentially use nitrate compared to iron, so any biodegradation in the presence of nitrate is coupled with the reduction of nitrate, not iron. As a result, iron remains in the aquifer sediments and arsenic remains adsorbed to iron, inhibiting its release to groundwater.
Results from this study highlight the importance of monitoring trace elements at fuel spill sites where organic contaminants might be biodegraded under iron-reducing conditions. These complex reactions can introduce new, unexpected types of contaminants that are not commonly monitored at organic-contaminant sites under current (2015) regulatory framework. Depending on the geochemical conditions and the nature of the organic matter, trace element concentrations in groundwater can exceed drinking water standards on short time frames (days), reinforcing the importance of screening the rapid changes in geochemistry following releases of organic carbon sources such as petroleum or ethanol.
Environmental Health Implications
Arsenic is a naturally occurring element and commonly exists in aquifer sediments adsorbed to iron hydroxides. When it remains attached to sediment, arsenic does not pose an immediate human health threat; however, changing geochemical conditions, such as those initiated by the introduction of organic carbon sources such as petroleum byproducts and ethanol, can release arsenic and other trace elements into groundwater to potentially toxic concentrations if the groundwater were to be used as a drinking water source or transported to streams where aquatic biota could be exposed. Arsenic is of particular concern because of its known toxicity and links to liver, bladder, and lung cancers.
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, University of St. Thomas, 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.
- Science
Below are other science projects associated with this project.
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.Natural Breakdown of Petroleum Results in Arsenic Mobilization in Groundwater
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...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
Below are publications associated with this project.
Rates of As and trace-element mobilization caused by Fe reduction in mixed BTEX–ethanol experimental plumes
Biodegradation of organic matter, including petroleum-based fuels and biofuels, can create undesired secondary water-quality effects. Trace elements, especially arsenic (As), have strong adsorption affinities for Fe(III) (oxyhydr)-oxides and can be released to groundwater during Fe-reducing biodegradation. We investigated the mobilization of naturally occurring As, cobalt (Co), chromium (Cr), andAuthorsBrady A. Ziegler, Jennifer T. McGuire, Isabelle M. Cozzarelli - News
Below are news stories associated with this project.