EVALUATION OF THE FATE AND 

TRANSPORT OF METHANOL 

IN THE ENVIRONMENT

Prepared For: American Methanol Institute 800 Connecticut Avenue, NW, Suite 620

 Washington, DC 20006

Prepared By: Malcolm Pirnie, Inc. 180 Grand Avenue, Suite 1000 

 Oakland, California 94612 

JANUARY 1999

3522-002 
Technical Memorandum i MALCOLM PIRNIE, INC. 

TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY .............................................................................................ES-1 

1.0 BACKGROUND .................................................................................................... 1 

 1.1 Purpose and Scope of Report........................................................................ 1 

 1.2 Introduction and History of Use ................................................................... 1 

 1.3 Methanol Production..................................................................................... 3 

 1.4 Chemical and Physical Properties................................................................. 4 

 1.5 Release Scenarios ......................................................................................... 5 

 1.6 Fate in the Environment ............................................................................... 7 

2.0 PARTITIONING OF METHANOL IN THE ENVIRONMENT........................... 9 

 2.1 Methanol Partitioning Between Environmental Compartments .................. 9 

 2.2 Air/Water Partitioning.................................................................................. 9 

 2.3 Soil/Water Partitioning................................................................................. 10 

 2.4 LNAPL Dissolution...................................................................................... 10 

 2.5 Comingling/Cosolvency Effects................................................................... 12 

3.0 FATE AND TRANSPORT OF METHANOL IN THE ENVIRONMENT........... 14 

 3.1 Soil and Groundwater Release ..................................................................... 14 

 3.1.1 Sources of Methanol in Soil and Groundwater.................................. 14 

 3.1.2 Losses of Methanol in Soil and Groundwater ................................... 15 

3.1.2.1 Biodegradation...................................................................... 15 

3.1.2.1.1 Presence of Indigenous Methanol-Degrading 

 Microbes ................................................................. 15 

 3.1.2.1.2 Availability of Electron Acceptors ......................... 17 

3.1.2.1.3 Availability of Nutrients ......................................... 18 

3.1.2.1.4 Adequate pH and Temperature Levels ................... 18 

3.1.2.1.5 Reports of Methanol Biodegradation Under 

 Various Redox Conditions...................................... 19 

 3.1.2.2 Adsorption............................................................................ 22 

 3.1.2.3 Volatilization from Groundwater ......................................... 22 

 3.2 Surface Water ............................................................................................... 23 

 3.2.1 Sources of Methanol in Surface Water .............................................. 23 

 3.2.2 Losses of Methanol in Surface Water................................................ 23 

 3.2.2.1 Biodegradation...................................................................... 24 

3.2.2.2 Abiotic Degradation.............................................................. 24 

3.2.2.3 Bioaccumulation ................................................................... 25 

3.2.2.4 Volatilization ........................................................................ 25 

3.3 Methanol / BTEX Comingled Plumes .......................................................... 26 

3.4 Conclusions................................................................................................... 27 

 

4.0 METHANOL ADDITIVES .................................................................................... 28 

4.1 Purpose and Background of Additives ......................................................... 28 

4.2 Fate and Transport of Three Known Additives............................................ 28 
Technical Memorandum ii MALCOLM PIRNIE, INC.

4.2.1 Luminosity........................................................................................... 28 

4.2.2 Taste .................................................................................................... 29 

4.2.3 Colorant............................................................................................... 31 

 4.3 Conclusion .................................................................................................... 32 

5.0 REMEDIATION AND TREATMENT................................................................. 33 

 5.1 Remediation for Methanol ........................................................................... 33 

 5.2 Impetus for Drinking Water Treatment........................................................ 33 

 5.3 Air Stripping................................................................................................. 34 

 5.4 Activated Carbon.......................................................................................... 34 

 5.5 Advanced Oxidation..................................................................................... 35 

 5.6 Membranes ................................................................................................... 36 

 5.7 Biological Treatment (Biologically Activated Filters)................................. 36 

 5.8 Conclusions .................................................................................................. 37 

6.0 METHANOL TOXICOLOGY............................................................................... 38 

 6.1 Health Effects of Methanol ......................................................................... 38 

6.1.1 Inhalation............................................................................................ 38 

6.1.2 Ingestion ............................................................................................. 40 

6.1.3 Dermal Exposure................................................................................ 40 

 6.2 Aquatic Toxicity........................................................................................... 41 

 6.2.1 Toxicity of Methanol to Microbial Populations ................................ 42 

7.0 FUTURE RESEARCH NEEDS ............................................................................. 43 

8.0 CONCLUSIONS..................................................................................................... 45 

8.1 Fate and Transport ......................................................................................... 45 

8.2 Methanol Additives........................................................................................ 45 

8.3 Remediation and Treatment.......................................................................... 46 

 8.4 Human and Aquatic Toxicity........................................................................ 46 

9.0 ACKNOWLEDGEMENTS.................................................................................... 48 

 

10.0 REFERENCES ........................................................................................................ 49 

LIST OF TABLES 

Table 

No. Description Page 
Technical Memorandum iii MALCOLM PIRNIE, INC.

1-1 Global Methanol Capacity and Demand............................................................ 3 

1-2 A Summary of Physical and Chemical Properties of Methanol, 

 Gasoline (BTEX), and Benzene......................................................................... 5 

1-3 Estimated Releases of Methanol for the United States...................................... 6 

1-4 Estimated Half-Lives of Methanol in the Environment..................................... 7 

2-1 Effects of Methanol on Aqueous BTEX Solubility ........................................... 13 

3-1 Selected Types of Aerobic and Anaerobic Respiration Involved In Microbial 

 Metabolism of Organic Matter .......................................................................... 16 

3-2 Comparative Rate Constants for Anaerobic and Aerobic Degradation............. 19 

3-3 Comparative Values of Octanol-Water Coefficients and 

 Bioconcentration Factors ................................................................................... 25 

4-1 Select Chemical and Physical Properties of Potential Luminosity Additives ... 29 

4-2 Select Chemical and Physical Properties of Bitterant Additives....................... 30 

4-3 Select Chemical and Physical Properties of Colorant Additives....................... 31 

6-1 Hazard Summary .............................................................................................. 38 

6-2 Methanol Toxicity Exposure Limits.................................................................. 39 

6-3 Lethal Doses of Methanol in Rats and Rabbits.................................................. 40 

6-4 Reported Median Lethal and Median Effective Concentrations for Methanol. 41 

6-5 Biological Effects of Methanol on Various Microorganisms as Measured 

 by the Toxicity Threshold from a cell Multiplication Inhibition Test............... 42 

LIST OF FIGURES 

Figure 

No. Description Page 

3-1 Methane Oxidation Pathway of Methanotrophic microorganisms.................... 16 
Technical Memorandum ES-1 MALCOLM PIRNIE, INC. 

EXECUTIVE SUMMARY 

The purpose of this report is to summarize the existing information regarding methanol—

its fate and transport in the environment and potential impacts, if any, on human health and the 

environment. Pure methanol (M100) which is expected to be used in fuel cell vehicles is the 

primary focus of this study, as opposed to the currently available gasoline-methanol fuel mixture 

which consists of 15 percent gasoline and 85 percent methanol (M85). A thorough literature 

review was conducted with over 100 documents reviewed as part of this study. Because neither 

the Clean Air Act (CAA), Clean Water Act (CWA), nor the Safe Drinking Water Act (SDWA) 

require methanol monitoring, a national database on occurrence of methanol in the environment 

is not available for evaluation. Therefore, results from laboratory and field studies documented 

in the literature and computer modeling were used to assess the fate and transport of methanol in 

the environment. A more complete summary of the findings of this study is presented in the 

following detailed report. This executive summary provides an overview of these findings. 

BACKGROUND

Methanol has been a widely used industrial chemical since the 1800s. Methanol is 

produced from steam reformed natural gas and carbon dioxide using a copper-based catalyst. 

Current uses of methanol include use as a feed stock for a variety of widely used organic 

chemicals, including formaldehyde, acetic acid, chloromethane, and methyl tert-butyl ether 

(MTBE). It is also used as a solvent in paint strippers, paints, carburetor cleaners, plastics, 

plywood, and automobile windshield washer solutions. Since 1965, methanol has been used in 

the U.S. as a fuel in certain vehicles (e.g., race cars), either as M100 or M85. Flexible fuel 

vehicles (FFVs)—vehicles capable of using either conventional gasoline, M85, or any 

combination of the two fuels—were developed by Ford Motor Company in 1978. A program 

funded by the California Energy Commission in conjunction with several oil companies 

provided the initial refueling infrastructure. FFVs were produced primarily to reduce the U.S. 

dependency on crude oil and for their ability to reduce carbon monoxide and ozone forming 

emissions. 

For a number of reasons, including an insufficient network of M85 fueling facilities, 

methanol FFVs have not become widespread. Therefore, other clean burning vehicles will be 
Technical Memorandum ES-2 MALCOLM PIRNIE, INC.

required to achieve even lower emission standards likely to be established in the future. 

Recently, researchers have turned from alternatively-fueled internal combustion engines to fuel 

cell technology. In 1994, Georgetown University introduced the first liquid-fueled fuel cell 

vehicle which derived its energy by reacting hydrogen and oxygen in the fuel cell. In 1999, the 

world’s largest automakers are all working to commercialize fuel cell vehicles. Due to the liquid 

properties of methanol at room temperature, ambient pressure, the high hydrogen to carbon ratio, 

and the relatively low combustion temperature, methanol is considered an ideal hydrogen carrier 

for fuel cell vehicles. The continuing development of fuel cell vehicles is driven by the 

projected low cost, environmental consumer benefits, and regulations in California, New York, 

Massachusetts, and other areas which require 10 percent of the Model Year 2003 vehicles to be 

Zero Emission Vehicles (ZEV) and by concerns over global warming. Consequently, there is a 

significant economic incentive to develop and market fuel cell vehicles which are expected to 

appear in large quantities worldwide by 2004. 

Methanol production worldwide is expected to increase to meet the anticipated future 

demand. In the U.S., annual methanol production 

has risen consistently over the last ten years, with 

17 plants currently producing approximately 2.25 

billion gallons of methanol per year (see Table ES1). Currently the U.S. imports 25 percent of its 

total demand, principally from Canada. In 1993, 

approximately 12 million gallons of methanol were 

used as a direct fuel, either M100 or M85 for FFVs 

in California, and another 212 million gallons were 

used in other fuels and fuel additives. The American Methanol Institute (AMI) estimates that by 

the year 2010, methanol demand for fuel cell vehicles alone may reach 882 million gallons per 

year, which would be 8 percent of the current (1998) world capacity. 

POTENTIAL FOR RELEASE OF METHANOL TO THE ENVIRONMENT 

The expected exponential growth in the demand for methanol will result in increased 

transportation by barge and rail, as well as an increased number of storage and distribution 

facilities. Given this expected increase in production, transportation, storage, and use of 

TABLE ES-1 

Global Methanol Capacity and Demand 

(1997) 

Entity % of 

Capacity 

% of 

Demand 

North America 35 36 

Asia/Pacific 17 22 

Western Europe 11 22 

South America 11 4 

Other 26 16 

Adapted from http://www.chemweek.com, 1998
Technical Memorandum ES-3 MALCOLM PIRNIE, INC.

methanol, the potential for accidental releases to the environment will increase. In 1992, 

methanol ranked third amongst all chemicals reportedly released by industry to the environment 

as noted in annual Toxics Release Inventory (TRI) reports required by the U.S. Environmental 

Protection Agency (USEPA). As shown in 

Table ES-2, U.S. methanol releases are 

primarily to the atmosphere; however, 

approximately 20% of the methanol is 

directly discharged to the soil, groundwater, 

or surface water (total mass released 

represents approximately 1% of the total 

mass of methanol produced). 

Three conceptual release models or 

scenarios were considered as part of this 

study. These include: tank truck or rail car release, barge release, and release from underground 

storage tanks (USTs) at a refueling facility. A release from a tank truck or rail car could take 

place in a variety of settings. A rail tank car accident could potentially release up to 34,500 

gallons of methanol. In addition to transport of methanol in the U.S. by rail, the U.S. obtains 

some of its methanol demand from overseas, all of which is transported by ships or barges. 

Thus, releases to ocean, estuary, or river environments are possible. A typical barge tanker 

carries 45,000 tons of product (13.6 million gallons) and in 1999, a 96,000 ton (29.1 million 

gallons) vessel will be introduced for dedicated methanol transport. The third release scenario 

involves methanol losses at a fueling or storage facility from an UST. A typical UST could 

allow a fuel release into the subsurface at a rate of 0.5 gallons per minute (gpm) before the leak 

detection devices are activated. Although continuous releases of this size are uncommon, the 

potential for significant methanol losses from USTs cannot be overlooked. 

Because the CAA, CWA, and SDWA do not require monitoring of methanol in 

groundwater, surface water, or the atmosphere, national monitoring data sets on methanol 

occurrence in air or water are not available. However, the behavior of methanol within 

environmental compartments—soil, air, surface water, and ground water—can be predicted 

based on its chemical and physical properties. Methanol is a clear, colorless, volatile liquid with 

a faint alcohol-like odor, though it is difficult to detect in the air at low concentrations (<10 part 

TABLE ES-2 

Estimated Releases of Methanol for the United 

States 

Reported 

Release to: 

1992a 

(million 

lbs/year) 

1993b

(million 

lbs/year) 

Atmosphere 195 171.8 

Underground 

Injection 

27 27.9 

Land 3.3 1.72 

Water 16.4 10 

Total releases 251.7 211.4 

a

USEPA, 1994a. bZogorski et al., 1997. 
Technical Memorandum ES-4 MALCOLM PIRNIE, INC.

per million by volume (ppmv)). Methanol is the simplest alcohol, having only one carbon atom, 

and is capable of being completely mixed in water. It easily dissolves in other alcohols and 

chlorinated hydrocarbons, but has limited solubility in diesel fuel, vegetables oils, and aliphatic 

hydrocarbons. The chemical and physical properties of methanol have been used to describe the 

fate and transport of methanol in the environment in the event that an accidental release were to 

occur. 

FATE AND TRANSPORT 

Although methanol occurs 

naturally in the environment as a 

result of various biological processes 

in vegetation, microorganisms, and 

other living species, a large release of 

concentrated methanol to ground 

water, surface water, or soil has the 

potential to adversely impact the 

affected environment. Once released, 

the half-life of methanol (the time 

required for 50% reduction in the 

mass released or present) depends on 

numerous factors including: the nature of the release, quantity of the release, and physical, 

chemical and microbiological characteristics of the impacted media. Table ES-3 is a summary of 

the estimates of the range of probable methanol half-lives in various environmental media as 

documented from various reports, in comparison with the probable half-lives of benzene, a 

common gasoline constituent. Based on these data, regardless of the release scenario, methanol 

appears unlikely to accumulate in the groundwater, surface water, air, or soil. 

The physical and chemical properties of methanol help to further define the fate and 

transport of this chemical in the various environmental media in the context of each of the 

conceptual release scenarios. The dominant mechanisms of methanol loss from subsurface soil 

and groundwater are expected to be biodegradation and advection (dispersion and diffusion) with 

little loss from adsorption on soils due to its high solubility and low retardation factor. In 

TABLE ES-3 

Estimated Half-Lives of Methanol and Benzene in the 

Environment

Environmental Medium 

Methanol 

Half-life 

(days) 

Benzene 

Half-life 

(days) 

Soil 

(Based upon unacclimated grab 

sample of aerobic/water suspension 

from groundwater aquifers)

1 - 7 5 - 16 

Air 

(Based on photooxidation half-life)

3 - 30 2 - 20 

Surface water 

(Based upon unacclimated aqueous 

aerobic biodegradation)

1 - 7 5 - 16 

Groundwater 

(Based upon unacclimated grab 

sample of aerobic/water suspension 

from groundwater aquifers)

1 - 7 10 - 730 

Adapted from Howard et al. (1991). 
Technical Memorandum ES-5 MALCOLM PIRNIE, INC.

surface water, the infinite solubility of methanol will result in rapid wave-, wind-, and tideenhanced dilution to low concentrations (< 1%). Once concentrations have been diluted below 

toxic levels the dominant mechanism of methanol loss is expected to be biodegradation. 

Compared to other loss mechanisms identified, including volatilization and chemical 

degradation, biodegradation is expected to be the dominant process controlling the fate of 

methanol in the soil, groundwater, and surface water environments. In addition, the 

biodegradation of methanol can occur under both aerobic (oxygen present) and anaerobic 

(oxygen absent) conditions. 

Therefore, following any of the three conceptual release scenarios presented, methanol is 

not likely to persist in soil or water due to its rapid biodegradation. Methanol is miscible in 

water and consequently will dissolve quickly and be diluted to low concentrations in the event of 

a surface water spill. In groundwater, methanol concentrations are highly dependent on the 

nature and the magnitude of the release, but will likely fall to low concentrations once complete 

dissolution has occurred. In both surface and ground waters, methanol will likely be easily 

biodegraded under a wide range of possible water quality conditions. 

Relative to conventional gasoline and diesel fuel (and many of their constituent elements 

such as benzene), methanol is a safer and more environmentally benign fuel. Thus, hazards 

caused by gasoline releases will be more serious than those due to methanol releases, and these 

hazards will persist longer in the environment. 

TREATMENT

Following a release of methanol to the subsurface as a result of any of the three release 

scenarios, remediation of soil and ground water may be required if natural biodegradation is not 

sufficient to meet potential clean up standards in a reasonable time frame. Methanol will quickly 

biodegrade and, therefore, natural attenuation is likely to be an effective and inexpensive 

remediation strategy for both soil and water. If biodegradation is not sufficient to meet cleanup 

objectives and an alternative remediation strategy is required, the high vapor pressure of 

methanol suggests that soil vapor extraction will effectively remove any residual methanol from 

the soil. Once extracted from the subsurface, the methanol vapors can be biodegraded using 

appropriate technologies such as vapor phase biofilters. 

It is unlikely that elevated levels of methanol will persist in either groundwater or surface 
Technical Memorandum ES-6 MALCOLM PIRNIE, INC.

water due to the rapid rate of biodegradation. However, if drinking water sources experienced a 

methanol release, treatment would likely be required before distribution to the public. Most 

treatment technologies that remove gasoline components from water, including air stripping and 

granular activated carbon, are not effective at removing methanol due to its low volatility and 

high solubility. Reverse osmosis or nanofiltration are also ineffective at removing methanol 

because of its small size and low molecular weight. 

 Advance oxidation processes such as ozonation with ultraviolet light are expected to be 

effective, but the feasibility and cost of treatment is site specific. Biological treatment processes 

are effective at removing methanol from drinking water, and are increasingly being accepted by 

the drinking water community for drinking water applications. However, biological treatment in 

drinking water applications is still not extensively used and, therefore, would require broader 

regulatory acceptance. In conclusion, in the unlikely event that methanol contaminates source 

waters, methanol can be removed in both a remediation and drinking water treatment context 

using biological processes. However, the effectiveness, cost and public acceptance will be site 

specific. 

HUMAN AND AQUATIC TOXICITY

Methanol’s properties and toxicity are well understood. According to the extensive 

literature reviewed for this study, methanol is neither mutagenic nor carcinogenic. Human 

exposure to methanol can occur via the inhalation, ingestion, or dermal contact pathways. 

Inhalation of methanol vapors can cause irritation of the mucus membranes, dizziness, nausea, 

headaches, and blurred vision if exposure at high levels occurs. While inhalation is the most 

common route of exposure to the body, ingestion represents the most serious acute health hazard 

due to the much higher volume of methanol which can be ingested relative to the volume which 

can be inhaled. The effects of ingestion follow the same pattern described for inhalation. With 

respect to dermal contact, methanol readily absorbs into the dermal layer with repeated exposure 

causing eczema, redness, and scaling. However, the current evidence shows that acute toxic 

effects on humans and some animals from methanol only occur at high doses (> 10 mg/l). The 

U.S. Department of Energy considers gasoline to be “overall” more hazardous to human health 

than neat (i.e., pure) methanol. 

Methanol is significantly less toxic to marine life than crude oil or gasoline, and many of 
Technical Memorandum ES-7 MALCOLM PIRNIE, INC.

the effects of short term exposure are temporary and reversible. The Office of Pollution 

Prevention and Toxics indicated that methanol is essentially non-toxic to the four aquatic fish 

species that were tested. A large methanol spill into a surface water would have some immediate 

impacts to the biota in the direct vicinity of the spill. However, because of its properties (i.e., 

methanol readily mixes with water and evaporates quickly in the atmosphere) methanol would 

rapidly dissipate into the environment, and within fairly short distances from the spill would 

reach levels where biodegradation would rapidly occur. 

RECOMMENDED RESEARCH 

The detailed report which follows this executive summary contains a comprehensive 

evaluation of the fate and transport of methanol in the environment. As previously stated and 

supported by this comprehensive evaluation, if methanol is released into the soil, groundwater or 

surface water, it will rapidly biodegrade. However, there are several fate and transport issues 

where available literature is incomplete and additional research is warranted to fill apparent data 

and information gaps. Three areas of future research are recommended: 

• Similar to other fuels, methanol may contain additives to address performance, pollution, or 

health issues. If additives are required, a thorough evaluation of the fate and transport of 

these additives is recommended. 

• The literature reviewed for the comprehensive report suggests that methanol will rapidly 

degrade once released into soil, groundwater, or surface water. However, if high 

concentrations of methanol exist near the point of release, the concentration of methanol may 

be toxic to microorganisms in the immediate area resulting in limited or no biodegradation. 

An analysis of methanol releases that have occurred at methanol fueling areas, storage areas, 

production locations, or during transport should be conducted to verify that methanol does 

behave as predicted. 

• The fate and transport of a methanol plume that becomes commingled with a gasoline plume 

is briefly addressed in this report; however, there remain several uncertainties. The effect of 

the presence of methanol on the fate and transport of conventional gasoline plumes needs to 
Technical Memorandum ES-8 MALCOLM PIRNIE, INC.

be better understood, including an evaluation of methanol impacts on the solubility and 

biodegradation rates of benzene and other gasoline constituents. 
Technical Memorandum MALCOLM PIRNIE, INC. 1

1.0 BACKGROUND 

1.1 Purpose and Scope of Report 

 One of the main industrial strategies for reducing carbon emissions to the atmosphere 

from mobile sources is the development of near zero emissions vehicles, such as those powered 

by fuel cells. Use of these vehicles is expected to increase dramatically over the next decade 

and beyond. One promising technology for fuel cell powered vehicles is the use of methanol as 

the fuel source. 

 As fuel cell powered vehicles proliferate, dramatic increases in worldwide use of 

methanol are anticipated. Increased use of methanol as a fuel source will increase the potential 

for releases of methanol to the environment during production, transport, storage, distribution 

and consumption. As a consequence, questions regarding the potential impacts of unintentional 

methanol releases to the environment, its subsequent transport and fate, and its possible impacts 

on human health and the environment can be expected. 

 The purpose of this study, requested by the American Methanol Institute, is to summarize 

existing knowledge on the fate and transport of methanol in the environment, and to identify 

potential impacts, if any, on human health and the environment. This report will focus primarily 

on fate and transport issues arising from the use of pure methanol as expected in fuel cell 

vehicles, also known as M100, as opposed to the currently available gasoline-methanol fuel 

mixture, which consists of 85 percent methanol and 15 percent gasoline (M85). Available 

literature will be reviewed on: 1) fate and transport processes that can affect the distribution of 

methanol in the environment; 2) fate and transport of methanol in the context of potential release 

scenarios; 3) human and aquatic toxicity of methanol; and 4) treatment processes for removing 

methanol from soil or water. In addition, available information will be reviewed on the 

characteristics of additives that may be considered for use in methanol. Finally, data gaps will 

be identified and research needs recommended as appropriate to reduce uncertainties regarding 

the fate and transport of methanol. 

1.2 Introduction and History of Use 

 Methanol is a widely used industrial chemical that has been in commercial use since the 

1800’s. Methanol is produced from steam reformed natural gas and carbon dioxide using a 
Technical Memorandum MALCOLM PIRNIE, INC. 2

copper-based catalyst. Current uses of methanol include a feed stock for formaldehyde, acetic 

acid, chloromethane, and methyl tert-butyl ether (MTBE), and a solvent in paint strippers, paints, 

carburetor cleaners, plastics, plywood, and car windshield washer fluids. 

Since 1965, methanol has been used as a fuel in certain vehicles, either as a pure 

compound (M100) or as a mixture of methanol and conventional gasoline, in an 85/15 mix, 

(M85). For example, methanol has been used as a fuel source in Indy race cars for more than 30 

years (CEC, 1998). In 1987, the first prototype flexible fuel vehicles (i.e., vehicles capable of 

running on conventional gasoline, M85, or any combination of the two fuels) were developed by 

Ford Motor Company (CEC, 1998). A program funded by the California Energy Commission in 

conjunction with several oil companies provided the initial refueling infrastructure. Emerging 

from this program, Ford built 2,500 Taurus FFVs (2,137 in California) in 1993 (CEC, 1998). 

FFVs were primarily produced because they could decrease the nation’s dependency on crude 

oil and because of their ability to reduce carbon monoxide and ozone forming emissions to levels 

below those mandated by the Clean Air Act Amendments (CAAA) of 1990. 

California currently leads the nation in the number of operating FFVs (light and heavy 

duty): 10,000 light duty FFVs and 485 heavy duty FFVs as of 1994 (CEC, 1994) and 

approximately 15,000 light duty FFVs in 1998. To facilitate these FFVs, California installed 

over 110 public and private methanol fueling facilities; however, this network is not sufficient to 

supply M85 conveniently to all individual consumers requiring fuel (http: www.energy.ca.gov/). 

For this reason and others, methanol FFVs have not become widespread and are no longer being 

produced; the advantages and disadvantages of FFVs have not been investigated in this report. 

In recent years, researchers have turned from alternatively-fueled internal combustion 

engines to fuel cell technology. Georgetown University introduced the first liquid-powered fuel 

cell vehicle in 1994. A fuel cell combines hydrogen and oxygen electrochemically to form 

water, electricity, and heat. The purpose of any fuel in a fuel cell vehicle is to serve as a source 

of hydrogen. Due to the liquid properties of methanol at room temperature, and ambient 

pressure, the high hydrogen to carbon ratio, and the relatively low combustion temperature, 

methanol is considered an ideal hydrogen carrier for fuel cell vehicles (Nowell, 1998). The 

continuing development of fuel cell vehicles by several auto manufacturers is driven by the 

projected low cost of the vehicles and regulations in California, New York, Massachusetts, and 

other states which require 10% of the Model Year 2003 vehicles to be Zero Emission Vehicles 
Technical Memorandum MALCOLM PIRNIE, INC. 3

(ZEV). A ZEV is a vehicle which does not emit carbon monoxide, volatile organic compounds 

(VOC), non-methane organic gases (NMOG), formaldehyde, nitrous oxides (NOx), or 

particulate matter. Methanol-powered vehicles will only receive a partial emissions credit (i.e., a 

0.7 credit where a ZEV credit of 1 implies no emissions) (CARB, 1998) because there are some 

evaporative emissions associated with the use of methanol fuel falling in the category of NMOG; 

however, running emissions of all chemicals except carbon dioxide and water vapor are 

substantially reduced. Consequently, there is significant economic and environmental incentives 

to develop and market fuel cell vehicles which are expected to appear in large quantities 

worldwide by 2004 (Nowell, 1998). 

1.3 Methanol Production 

 Methanol is produced in 17 plants across 

the United States, which accounted for 35% of the 

total global methanol production capacity in 1997 

(see Table 1-1). The total annual production of 

methanol in the US has risen consistently over the 

last ten years and continues to grow as a result of 

methanol’s use in the manufacture of MTBE, a 

widely used gasoline oxygenate. Due to the demand for methanol from MTBE manufacturers, 

methanol prices reached a peak in 1994. Since then, capacity has been steadily added and 

demand from MTBE manufacturers has decreased resulting in a significant drop in methanol 

prices. Approximately 1.3 billion gallons of methanol were produced in the U.S. in 1992, 2.2 

billion gallons in 1995, and 2.25 billion gallons in 1998. In 1993, approximately 12 million 

gallons of methanol were used as a direct fuel, as either M100 or M85, for FFVs in California, 

while another 212 million gallons were used in other fuels (e.g., Indy race car) and to produce 

fuel additives (MTBE). 

 The American Methanol Institute (AMI) estimates that by the year 2010, methanol 

demand for fuel cell vehicles could reach 882 million gallons per year, which is 8% of current 

(1998) world capacity. By 2020, AMI estimates that this demand may increase to 135% of 

current world capacity (Nowell, 1998). This exponential growth in the methanol industry will 

result in increased transportation by barge and train, as well as an increased number of storage 

TABLE 1-1 

Global Methanol Capacity and Demand 

(1997) 

Entity % of 

Capacity 

% of 

Demand 

North America 35 36 

Asia/Pacific 17 22 

Western Europe 11 22 

South America 11 4 

Other 26 16 

Adapted from http://www.chemweek.com, 1998
Technical Memorandum MALCOLM PIRNIE, INC. 4

and distribution facilities. 

1.4 Chemical and Physical Properties 

 The behavior of an organic chemical within environmental compartments—air, 

groundwater, surface water, and soil—can be predicted by that compound’s chemical and 

physical properties. Methanol is a clear, colorless, volatile liquid with a faint alcohol-like odor, 

though it is difficult to detect at concentrations below 10 ppm. Methanol is the simplest of the 

alcohols, having only one carbon atom, and is completely miscible in water. Methanol easily 

dissolves in other alcohols and chlorinated hydrocarbons, but has limited solubility in diesel fuel, 

vegetable oils, and aliphatic hydrocarbons (USDOE, 1991). The properties of methanol are 

compared to the properties of conventional gasoline in Table 1-2. Benzene is included in the 

Table as a representative gasoline constituent where the properties of gasoline are not available. 

Many of these properties will be referred to throughout the text to describe the fate and transport 

of methanol in the environment. 
Technical Memorandum MALCOLM PIRNIE, INC. 5

Table 1-2 

A Summary of Physical and Chemical Properties of Methanol, Gasoline (BTEX), and Benzene 

Physical and chemical properties Methanol Gasoline Benzene 

Molecular weight [g/mole] 32.04 ~100 (c) 78.11 (c) 

Elemental composition by weight 

% Oxygen 

% Carbon 

% Hydrogen 

50% 

37.5% 

12.5% 

(mix of C4 to 

C14 

hydrocarbons) 

0% 

92% 

8% 

Specific gravity 0.7915 @ 60°F (f) 0.72-0.78 (c) 0.88(c) 

Boiling point [°C] 64.7 27-225 (b) 80.1(c) 

Water solubility [mg/L] miscible 100-200(c) 1,780 

Vapor pressure 

[mm Hg] (@ 25°C) 

[psi] (@ 100°F) (e) 

126 

4.63 

-- 

7-15 

76, 95 (c) 

-- 

Heat of combustion [kJ/kg] (b) 19,930 43,030 --- 

Henry’s Law constant [atm m3 g-1 mole-1] 4.55 x 10-6 

4.42 x 10-6(c) 

--- 5.43 x 10-3 

(c) 

Henry’s Law constant [-] @ 25 oC 1.087 x 10-4 --- 0.22 

Liquid Dispersion Coefficient @ [m2/s] 

25o

C 

1.65 x 10-9 --- 9.95 x 10-10

Log Koc 0.921 

0.44 (c) 

--- 1.8-1.99 

1.50-2.16 (c) 

Log Kow -0.77 

-0.75(c) 

--- 2.13 

1.56-2.15 (c) 

Flammability Limits (b): 

 Lower (LFL) 

 Volume percent 

 Temperature (°C) 

6.0 

7 

1.4 

-43 

--- 

 Upper (UFL) 

 Volume percent 

 Temperature (°C) 

36.5 

43 

7.6 

-30 to-12 

--- 

Flash Point (°C) 12°C (54°F) (a) -43 (°F) --- 

Vapor Density @ 1 atm; 10 oC (b) 1.4 2-5 3.4 

(a) Merck Index, 1989; (b) Machiele, 1989; (c)Zogorski et al., 1997; (d) Bauman, 1989; (e) USDOE, 1991; 

1.5 Release Scenarios 

In 1992, methanol ranked third among all chemicals reportedly released by industry to 

the environment as noted in annual Toxics Release Inventory (TRI)—reports required by the 

U.S. Environmental Protection Agency (USEPA) (USEPA OPPT, 1994). These releases are 

primarily from glue manufacturers, MTBE formulators, pulp and paper manufacturers, and other 

chemical producers (AMI, 1998). As shown in Table 1-3, US methanol releases in 1992 and 
Technical Memorandum MALCOLM PIRNIE, INC. 6

1993 were primarily to the atmosphere; however, approximately 20% of the methanol is directly 

discharged to soil, groundwater or surface water. The total volume of methanol released to the 

environment represents approximately 1% of the total production volume. The Clean Air Act 

(CAA), Clean Water Act (CWA), and Safe Drinking Water Act (SDWA) do not require 

monitoring of methanol in surface water, groundwater, or the atmosphere. Thus, national 

monitoring data sets and information on methanol occurrence in air or water are not available 

(Zogorski et al., 1997). 

 Given the limited data on releases and 

occurrences of methanol, this report will 

evaluate the fate and transport of methanol in 

soil and water in the context of three 

methanol release scenarios. The three 

scenarios are as follows: 

Scenario 1: Tank truck or rail car release. 

Currently, the most of the imported methanol 

to the U.S. is transported by rail car from Canada. A release from a rail car or tank truck could 

take place in a variety of settings, including the desert, the coast, or near a drinking water source. 

A tank car may release as much as 34,500 gallons of methanol (Perry et al., 1984). 

Approximately 1,400 truckloads are delivered each year throughout California (CEC, 1994). 

Scenario 2: Barge release. Ocean and river releases could occur since the U.S. imports some 

methanol from overseas by barge or ship. A typical ship carries 45,000 tons (13.6 million 

gallons) of product, and in 1999, a 96,000 ton (29.1 million gallons) vessel for methanol 

transport will be introduced. 

Scenario 3: Storage / Fueling facility Release. The third conceptual scenario involves the 

release of methanol at a fueling or storage facility. Currently, a gasoline underground storage 

tank (UST) can release fuel into the subsurface at a leak rate as high as 0.5 gpm before the leak 

detection devices are activated; methanol USTs are expected to have a similar detection 

sensitivity. Consequently, it is conceivable that methanol releases will occur at methanol fueling 

TABLE 1-3 

Estimated Releases of Methanol in the United 

States 

Reported 

Release to: 

1992a 

(million 

lbs/year) 

1993b

(million 

lbs/year) 

Atmosphere 195 171.8 

Underground 

Injection 

27 27.9 

Land 3.3 1.72 

Water 16.4 10 

Total releases 251.7 211.4 

a

USEPA, 1994a. bZogorski et al., 1997. 
Technical Memorandum MALCOLM PIRNIE, INC. 7

facilities at a rate similar to gasoline UST releases. If methanol USTs are located at a gasoline 

dispensing location, subsurface methanol releases may encounter existing gasoline contaminant 

plumes. The 1998 federal UST upgrade requirements will significantly reduce the number of 

new releases; however, impacts of methanol releases on the fate of existing plumes needs to be 

considered. This scenario represents an important potential route of methanol release to 

groundwater. 

1.6 Fate in the Environment 

 Methanol occurs naturally in the environment due to various biological processes in 

vegetation, microorganisms, and other living species (ENVIRON, 1996). However, a large 

release of methanol to the surface water, soil, or groundwater has the potential to adversely 

impact the surrounding environment. 

 Once released into surface waters or the subsurface environment, the fate of methanol 

depends on numerous environmental 

factors including: the nature and 

quantity of the release, and physical, 

chemical and biological characteristics 

of the impacted media. Various 

reports summarize estimates of 

possible methanol half-lives (the time 

required for 50% reduction in 

concentration) (see Table 1-4) in 

various environmental media. In the 

atmosphere, methanol will be photooxidized relatively quickly; the halflife ranges between 3 and 30 days. In 

soil or groundwater, rapid biodegradation is expected with the half-life ranging from 1 to 7 days. 

Finally, in surface water following a pure methanol spill, methanol is expected to disappear 

quickly; half-lives are reported between 1 and 7 days. The half lives are compared to reported 

half lives for benzene to illustrate the relatively rapid degradation of methanol. 

 Based on data summarized in Table 1-4, regardless of the release scenario, methanol 

TABLE 1-4 

Estimated Half-Lives of Methanol and Benzene 

in the Environment 

Environmental Medium Methanol 

Half-life 

(days) 

Benzene

Half-life 

(days) 

Soil 

(Based upon unacclimated grab 

sample of aerobic/water suspension 

from groundwater aquifers)

1- 7 5 - 16 

Air 

(Based on photooxidation half-life)

3 - 30 2 - 20 

Surface water 

(Based upon unacclimated aqueous 

aerobic biodegradation)

1 - 7 5 - 16 

Groundwater 

(Based upon unacclimated grab 

sample of aerobic/water suspension 

from groundwater aquifers)

1 - 7 10 - 730 

Adapted from Howard et al. (1991). 
Technical Memorandum MALCOLM PIRNIE, INC. 8

appears unlikely to accumulate in the soil, air, surface water, or groundwater. However, it is 

unclear whether these reported rates were developed under realistic field conditions. 

Consequently, these values represent generic order-of-magnitude half-lives and should be used 

with caution for a site-specific assessment of the fate and transport of methanol. In Section 3, 

these rates will be further evaluated as a function of specific hydrogeologic (subsurface), and 

limnologic (lake) conditions. 
Technical Memorandum MALCOLM PIRNIE, INC. 9

2.0 PARTITIONING OF METHANOL 

IN THE ENVIRONMENT 

2.1 Methanol Partitioning Between Environmental Compartments 

 The purpose of this section is to describe the equilibrium partitioning of methanol 

between air, water, and soil phases. Partitioning is directly related to the physiochemical 

properties of methanol including solubility, vapor pressure and adsorptivity and the physical and 

chemical characteristics of the environmental compartment. 

 When any chemical is released to an environment consisting of more than one medium 

(e.g., air and water), the chemical will tend to distribute itself between these two phases, a process 

that has been well described by the science of chemical thermodynamics (see e.g., Thibodeaux, 

1996; Schwarzenbach et al., 1993). In an enclosed system, the concentrations of the chemical in 

each phase can be predicted assuming that an equilibrium is achieved. In an open system, which 

is undergoing dynamic changes, continual transfer between phases is likely. The rate of these 

changes is important for predicting the fate and transport of the chemical of interest. For 

purposes of this analysis, however, the simple equilibrium model provides a basis for assessing 

the relative distribution of a compound such as methanol between environmental media. 

2.2 Air/Water Partitioning 

The air/water equilibrium partitioning behavior of methanol can be predicted using 

Henry’s Law when methanol concentrations are less than 100,000 ppm (i.e., less than 10% by 

weight). The Henry’s Law constant represents the ratio of a contaminant’s concentration in the 

air to its concentration in the water at equilibrium. A compound with a dimensionless Henry’s 

Law constant less than 0.05 will partition strongly from the gas phase into the water phase when 

contaminated air is brought into contact with clean water (Zogorski et al., 1997). The value of 

Henry’s Law constant for methanol given in Table 3-6 is 1.09 x 10-4 [-] at 25o

C. Since this value 

is quite low, atmospheric methanol will partition into water droplets. Conversely, methanol in 

water bodies is likely to remain in the aqueous phase. Therefore, once in water, methanol will be 

difficult to remove by volatilization. 
Technical Memorandum MALCOLM PIRNIE, INC. 10

2.3 Soil/Water Partitioning 

 The soil/water partition coefficient, Kd, specifies the equilibrium ratio of a contaminant’s 

concentration in/on the solid phase to that in the aqueous phase, thus, determining the 

distribution of a chemical between soil and water. In addition, the Kd value can be used to 

estimate the rate of movement of a chemical in groundwater compared to the rate of groundwater 

flow. For non-ionic organic compounds such as methanol, Kd values are a function of the 

organic carbon content of the soil (foc) and the organic carbon based partition coefficient (Koc

[L/kg]). It can be shown that Kd = Koc • foc (Schwarzenbach et al., 1993). Values of foc are sitedependent and are typically low in most subsurface environments (on the order of 0.5% or foc = 

0.005) (Zogorski et al., 1997). Koc values for methanol are low (~8) (Table 1-2) relative to 

values of other gasoline oxygenates (~12 for MTBE) and aromatics (~100 for benzene). 

Consequently, in a soil/water environment, methanol will be present primarily in the water 

phase. 

 For the listed Koc values, it can be shown that retardation due to adsorption will be 

negligible (Wood et al., 1990; Zogorski et al., 1997). The retardation factor for methanol and 

other short-chain alcohols is usually one. Thus, dissolved methanol will migrate at the velocity 

of groundwater except in soils with organic carbon fraction greater than 10 percent (i.e., for foc = 

0.1 the Kd is approximately 0.8 signifying nearly equivalent concentrations of methanol adsorbed 

on soil and dissolved in water). Consequently, methanol will generally travel through the 

groundwater at rates significantly higher than constituents in gasoline, including benzene, 

toluene, ethylbenzene, or xylenes (BTEX). However, due to rapid dissolution and 

biodegradation, ultimate methanol plume lengths will likely be shorter than BTEX plumes. 

2.4 Methanol Dissolution 

 The dissolution of methanol into groundwater involves dissolution from a pure methanol 

pool (M100). Under this scenario, methanol is likely to leach quickly from the release area into 

the groundwater. For gasoline releases, the aqueous concentrations of gasoline hydrocarbons 

and ether oxygenates in contact with water can be estimated from the hydrocarbon’s solubility in 

water multiplied by its mole fraction in the gasoline (maximum theoretical solubility of MTBE = 

48,000 ppm x 11% by volume = 5,280 ppm) (Poulsen et al., 1992). However, because methanol 

is completely miscible in water, this relation breaks down and the concentration must be 
Technical Memorandum MALCOLM PIRNIE, INC. 11

estimated based on presumed mixing conditions using a fuel/groundwater mixing ratio and a 

dilution factor. 

 Assuming that subsurface mixing ratios are between 10 and 100, the maximum range of 

methanol concentrations would be 0.9% to 9.1% by volume (7,000 to 70,000 ppm by mass) for a 

M100 release. However, these high concentrations will only occur in the immediate vicinity of 

pure methanol releases. Much lower concentrations are anticipated further from the source due 

to methanol plume dilution. 

 Alternatively, the concentration of methanol in the groundwater can be approximated by 

taking the ratio of the release flow rate and the groundwater velocity and assuming a source area 

width and vertical mixing ratio. For example, if methanol is released from an underground 

storage tank at approximately 0.5 gpm, and groundwater is moving at 1 ft/day, the source area 

width is 1 meter and the vertical mixing ratio is 10 to 100, the resulting methanol concentration 

in the groundwater will be between 70 ppm and 700 ppm. These concentrations would be much 

larger in the immediate vicinity of a catastrophic underground storage tank release (i.e., complete 

tank failure) or barge release. However, in most cases, the infinite solubility of methanol will 

cause methanol concentrations to rapidly decrease as a result of mixing, dispersion, and 

diffusion. 

 Poulsen et al. (1992) evaluated the rate of dissolution of methanol from a M85 into water. 

Poulsen et al. (1992) experimentally determined that approximately 99% of the methanol would 

leach into the water phase in the time required for three volumes of water, each equal to the 

initial gasoline volume, to move past the gasoline. They concluded that this would result in a 

short discrete plume. 

 The rate of methanol dissolution into the subsurface following a release is similar to the 

rate of ethanol dissolution because methanol and ethanol have similar properties. Heermann and 

Powers (1997 & 1998) studied the partitioning behavior of ethanol and BTEX compounds from 

an ethanol-blended gasoline. According to Heermann (1998), the aqueous concentration of 

ethanol due to dissolution of ethanol-blended gasolines is dependent on the concentration of 

ethanol in the gasoline and on mass transfer limitations in subsurface systems. Heermann 

showed that when the concentration of ethanol was 10% (by volume) in a gasoline, greater than 

99% of the ethanol partitioned into the water phase. Heermann did not quantify the time 

required for dissolution but determined that it is limited by the rate of ethanol liquid molecular 
Technical Memorandum MALCOLM PIRNIE, INC. 12

diffusion to the gasoline/groundwater boundary which may result in longer dissolution times (> 

1 year). 

 In conclusion, pure methanol will quickly dissolve into the groundwater and disperse at a 

rate directly proportional to the velocity of the local groundwater. All of the methanol present in 

an M85 gasoline will likely be released into the groundwater, but the time for complete 

dissolution is site specific. It is unlikely that either M85 or M100 will exhibit a slow dissolution 

time (>1 year) because of the large quantities of methanol in contact with the water phase, 

methanol’s infinite solubility in water, and methanol’s affinity for the water relative to soil, thus, 

reducing the effects of diffusion-controlled dissolution. However, the time required for 

dissolution is highly dependent on the source area shape and the types of soils in the subsurface. 

Therefore, if methanol enters a low permeable soil horizon with minimal groundwater contact, 

dissolution could proceed slowly. 

2.5 Commingling/Cosolvency Effects 

 Cosolvency is a chemical-phenomenon whereby one chemical dissolved in water 

increases the aqueous solubility of a second chemical. For example, BTEX compounds tend to 

be more soluble in concentrated aqueous methanol solutions than in water alone. This 

preferential solubility is referred to as the cosolubility effect. The possibility of enhanced 

aqueous solubility of BTEX due to a neat or pure methanol plume that encounters existing 

subsurface BTEX contamination is an issue for methanol releases from underground storage 

tanks at existing gasoline stations (Scenario 3) (Donbaldson et al., 1993). 

 The majority of studies on the effects of methanol cosolvency have focused on increased 

BTEX solubility within methanol/gasoline mixtures such as M85. Results show that M85 

releases into the subsurface may produce high concentrations of aqueous methanol as well as 

elevated aqueous BTEX concentrations near the front of the plume. However, the BTEX 

distribution in the plume will change as a function of the aqueous/gasoline phase volume ratios 

(Poulsen et al., 1992; Chen et al., 1997; Beck, 1991). In 1991, the American Petroleum Institute 

published a study that evaluated the effect of methanol on the cosolubility of BTEX compounds 

for M85 (Barker, et al., 1990). API concluded that for aqueous methanol concentrations below 

8.5% (v/v) (i.e., about a 10-fold dilution factor), BTEX solubility was not increased. As the 

concentration of methanol increased from 8% to 25%, the BTEX solubility increased linearly 
Technical Memorandum MALCOLM PIRNIE, INC. 13

with the methanol concentration. Above a 25% (v/v) 

concentration of methanol, the BTEX solubility increased 

exponentially with the methanol concentration (see Table 

2-1). In conclusion, the magnitude of BTEX cosolubility 

is controlled by the concentration of the methanol plume 

at the point of BTEX/methanol plume interaction which is 

a function of the dilution factor (Barker, et al., 1991). 

 Cosolvency experimentation with M85 was also 

conducted at the Canadian Forces Base in Borden, 

Ontario. Similar to previous studies, the Borden study concluded that for methanol 

concentrations below 0.7% (i.e., 7,000 ppm), there was no distinguishable change in the mobility 

or solubility of the BTEX components. However, this study concluded that enhanced mobility 

will likely occur for methanol concentrations greater than 25% (i.e., 250,000 ppm) (Barker, et al, 

1990; Hubbard et al., 1994). While these concentrations are unlikely in the plume area, they can 

be anticipated in the source area of an M100 or M85 plume with a low dilution factor. 

TABLE 2-1 

Effects of Methanol on 

Aqueous BTEX Solubility 

Equilibrium 

Methanol 

Conc. 

Observed 

BTEX 

Solubility 

(ppm) 

8% 120 

17% 174 

44% 933 

(Barker, et al., 1990)
Technical Memorandum MALCOLM PIRNIE, INC. 14

3.0 FATE AND TRANSPORT OF METHANOL 

IN THE ENVIRONMENT 

 The chemical and physical properties of methanol are described in Section 1 and Section 2 

and summarized in Table 1-3. The following three subsections discuss the fate and transport of 

methanol following a release, as presented in the three scenarios, namely: 1) tank truck or rail car 

spill to soil and/or groundwater; 2) barge spill to surface water; and 3) underground storage tank 

release to soil and groundwater. Each subsection further describes the sources of methanol into 

the respective environmental compartment and the ensuing loss mechanisms from that 

compartment. 

3.1 Soil and/or Groundwater Release 

Very few data sets are available on reported levels of methanol in aquatic systems and 

subsurface environments in the United States. The apparent lack of monitoring for methanol, 

particularly in aqueous systems, is likely a result of (1) the level of difficulty associated with 

methanol analysis in the water phase, (2) its short half-life due to its high biodegradation 

potential and (3) the lack of governmental monitoring requirements and control mandates for 

groundwater, surface water and drinking water (Clean Water Act, Safe Drinking Water Act). 

3.1.1 Sources of Methanol in Soil and Groundwater 

 There are several processes related to the use of methanol as a fuel which would be 

directly responsible for methanol releases to soil and groundwater. The dominant sources are 

those discussed in Scenarios 1 and 3—release from a tank truck or rail car and release from an 

underground methanol storage tank. Precipitation may also serve as a transport mechanism 

which introduces methanol into the subsurface by infiltration through the unsaturated zone. 

Precipitation, however, has been shown to be a minor source of contaminant transport into the 

soil and groundwater for other highly water-soluble chemicals, such as MTBE, (Zogorski et al., 

1997) and is therefore expected to be a minor contributing source of methanol into groundwater. 

3.1.2 Losses of Methanol from Soil and Groundwater 
Technical Memorandum MALCOLM PIRNIE, INC. 15

 As a result of its high solubility, low retardation factor and ease of biodegradability, the 

dominant mechanisms of methanol loss from subsurface soil and groundwater are expected to be 

biodegradation and advection (i.e., transport from the source area by groundwater flow), with 

little loss due to adsorption. 

3.1.2.1 Biodegradation 

 In general, microorganisms have been shown to play a prominent role in 

governing the fate of fuel hydrocarbons in subsurface aquatic and soil systems (NRC, 

1993). When environmental conditions are amenable to microbial activity, aerobic 

microbial populations oxidize organic contaminants and consume oxygen in the process. 

Once the localized area has been depleted of the oxygen necessary for aerobic 

respiration, anaerobic conditions develop and anaerobic biodegradation proceeds. While 

it is well established in the scientific literature that methanol will biodegrade readily in 

the subsurface under both aerobic and anaerobic conditions, three factors are required for 

successful methanol biodegradation: the presence of indigenous methanol-degrading 

microbial populations, the availability of electron acceptors and nutrients, and adequate 

pH and temperature levels. 

3.1.2.1.1 Presence of Indigenous Methanol-Degrading Microbes 

 Methanol is widely produced in nature by anaerobic microorganisms responsible 

for complex aromatic hydrocarbon biodegradation (Heijthuijsen and Hansen, 1990; 

Oremland et al., 1982). As a result, methanol molecules are ubiquitous in nature. 

Furthermore, due to methanol’s high solubility in water, methanol molecules are 

bioavailable to microorganisms which can utilize them as a source of carbon and energy. 

A wide distribution of methanol-degraders in the environment can therefore be expected 

(Brock and Madigan, 1991). 

 

Systematics of methanol oxidation: Methylotrophs, organisms that can grow using only 

one-carbon compounds such as methanol, are known to use both methane and methanol 

as their sole carbon and energy source under both aerobic and microaerobic (low oxygen) 

conditions (Brock and Madigan, 1991). Methylotrophs are of commercial interest in the 
Technical Memorandum MALCOLM PIRNIE, INC. 16

bacterial metabolism of C1 compounds (Heijthuijsen and Hansen, 1990; Komagata, 

1990). Consequently, a large number of methanol-utilizing bacteria have been isolated 

from a wide variety of natural sources, and most of these isolates have been identified as 

aerobic, Gram-negative bacteria (Komagata, 1990). 

CH4 CH3OH HCHO HCOOH CO2

NADH 

+ H+

NAD+

O2 H2O

MMO

PQQ PQQH2 NADH 

+ H+

NAD+

H2O

NADH 

+ H+

NAD+

Cells

Figure 3-1. Methane oxidation pathway of methanotrophic microorganisms. 

 Adapted from (Chang, 1995). 

 Methanol is also an intermediate of the methane oxidation pathway used by 

methanotrophic organisms (see Figure 3-1); methanotrophs are ubiquitous in nature. 

Methanotrophs oxidize methane to methanol by the enzyme methane monooxygenase. 

Methanol is then oxidized to 

formaldehyde by methanol 

dehydrogenase (Lehninger et 

al., 1993; Smeraldi et al., 

1994) which is then 

assimilated into cell material 

by the activity of either of 

two pathways, one involving 

the formation of the amino 

acid serine and the other 

proceeding through the 

synthesis of sugars (Prescott 

et al. 1996). 

3.1.2.1.2 Availability of Electron Acceptors 

 Microorganisms obtain energy by transferring electrons from electron donors (in 

Table 3-1 

Selected types of aerobic and anaerobic respiration 

involved in microbial metabolism of organic matter 

Process Electron 

Acceptor

Metabolic 

Products 

Relative 

Potential 

Energy 

Aerobic 

Respiration 

O2 CO2, H2O High 

Denitrification NO3- CO2, N2 

Iron reduction Fe3+ CO2, Fe2+ 

Sulfate 

reduction 

SO4

2- CO2, H2S 

Methanogenesis CO2 CO2, CH4 Low 

Taken from Suflita and Sewell (1991)
Technical Memorandum MALCOLM PIRNIE, INC. 17

this case, methanol) to electron acceptors. Electron acceptors are compounds that have a 

lower oxidization state than electron donors and they include molecular oxygen, nitrate, 

Fe(III), sulfate and carbon dioxide. The most energetically favored mechanism by which 

microorganisms oxidize organic compounds is aerobic metabolism (i.e., the use of 

oxygen as the electron acceptor) (see Table 3-1). 

 The presence of oxygen is a requirement for obligate aerobic microorganisms. 

Facultative aerobic and anaerobic microorganisms are able to use other electron 

acceptors when oxygen is not available. Oxygen is usually present in and around 

groundwater recharge areas as a result of infiltrating rainwater. When oxygen is not 

available, the following electron acceptors are preferentially utilized by microbes in the 

order shown: nitrate > Fe(III) > sulfate > carbon dioxide (Brock and Madigan, 1991). 

The redox potential (i.e., available electron acceptors) in subsurface environments is 

highly site-dependent. 

 Methanol biodegradation has been shown to take place under both aerobic 

(oxygen as the electron acceptor) and anaerobic (all electron acceptors besides oxygen) 

conditions. The aerobic biodegradation of methanol is the most energetically favored 

mechanism for methanol-degraders and leads to the mineralization of methanol. 

 Microbial growth on methanol with nitrate as the electron acceptor by 

facultatively anaerobic nitrate-reducing bacteria is the second most energetically favored 

mode of methanol metabolism (Metcalf and Eddy, Inc., 1979). There are over 100 

wastewater treatment plants in the United States that currently use methanol as a carbon 

source to remove nitrate (NO3

-

) from water by anaerobic denitrification. Other modes of 

anaerobic biodegradation of methanol have been studied extensively, resulting in the 

identification of at least 11 species of methanogenic bacteria that can grow on methanol 

(Brock and Madigan, 1991). 

Other types of anaerobic metabolism include acidogenesis (resulting in the 

production of acetate or butyrate) (Florencio et al., 1995) and sulfidogenesis 

(Heijthuijsen and Hansen, 1990). The ability of sulfate-reducing bacteria to oxidize 

methanol was rarely reported in early studies (Esnault et al., 1988; Ward and Winfrey, 

1985). However, in the past few years, evidence has accumulated which suggests that 

sulfate-reducing bacteria are involved in anaerobic degradation of methanol in sediments, 
Technical Memorandum MALCOLM PIRNIE, INC. 18

particularly in marine environments. Sulfidogenic methanol-utilizing microorganisms 

have been shown to oxidize methanol by reducing sulfate to hydrogen sulfide 

(Heijthuijsen and Hansen, 1990). Finally, some methanol-degrading strains have been 

shown to utilize hydrogen (Heijthuijsen and Hansen, 1990). 

3.1.2.1.3 Availability of Nutrients 

 Most microorganisms require life-sustaining growth factors such as nitrogen and 

phosphorus for cell growth. In general, microbial growth in most sub-soils is not limited 

by nitrogen and phosphorus as long as the contaminant concentrations are in the sub ppm 

range (Tiedje, 1993). As stated previously, for M100 releases into the subsurface, 

methanol concentrations will often exceed 1 ppm, resulting in potentially nutrient-limited 

conditions. However, as methanol is advected away from the source area, concentrations 

will decrease and microbial activity is not likely to be nutrient-limited. 

3.1.2.1.4 Adequate pH and Temperature Levels 

 Most microorganisms grow best in a relatively narrow pH range around neutrality 

(6 to 8) (LaGrega et al., 1994). The characteristic range of pH’s found in groundwater 

systems (5 to 9) generally reflects the buffering capacity of the framework carbonate or 

silicate minerals that make up groundwater aquifers (Chapelle, 1992; King et al., 1992). 

This range of pH values in aquifers is unlikely to pose a significant problem for the 

biodegradation of methanol by indigenous subsurface microorganisms since most of the 

methanol-utilizing bacteria which have been isolated from natural sources have been 

shown to grow in the neutral pH range (Komagata, 1990). Even if the pH of groundwater 

were to deviate significantly from the neutral pH range, some strains of methanolutilizing microorganisms have been shown to prefer acidic pH values ranging from 2.0 to 

5.5, while others have been shown to prefer alkaline pH values of 7.0 to 9.5 (Komagata, 

1990). 

 The temperature of an environment is also an important factor for the growth and 

activity of microorganisms. Metabolism of subsurface populations accelerates with 

increased temperatures up to an optimum value at which growth is maximized. Most of 

the bacteria present in subsurface environments operate most effectively between a 
Technical Memorandum MALCOLM PIRNIE, INC. 19

temperature range of 20°C to 40°C. This is the range of many natural environments 

(Chapelle, 1992) since subsurface temperatures within 100 meters of the surface are 

typically within 2°C of the mean annual surface temperature. Temperature should 

therefore not pose a significant problem for the biodegradation of methanol by 

indigenous subsurface microorganisms even at temperatures as lows as 10oC. 

3.1.2.1.5 Reports of Methanol Biodegradation Under Various Redox 

Conditions 

 Simple alcohols such as methanol and ethanol can be degraded in both aerobic 

and anaerobic environments at rates much faster than gasoline components, such as 

benzene (see Table 3-2). It is important to note in Table 3-2 the difference between 

laboratory-derived and field-derived degradation rates. Laboratory rates are often higher 

(an order of magnitude or more) than field-derived rates due to a combination of elevated 

laboratory temperature and a larger microbial density in the laboratory growth medium. 

For example, note that all the reported benzene rates are laboratory-derived and, thus, 

likely represent faster degradation rates than would be observed in the field. 

Only large concentrations (>100,000 ppm) of alcohols are generally considered to 

Table 3-2 

Comparative Rate Constants for Anaerobic and Aerobic Degradation 

 

Anaerobic Pseudo First 

Order Rate Constant 

Aerobic Pseudo 

First Order Rate 

Constant 

Compound Electron 

Acceptor 

Range of Rates 

(day-1) 

Range of Rates 

(day-1) 

Ethanol NO3

-

Fe3+

SO4

-2

0.53 (1)(11)

0.17 (1) (11) 

0.1 (1) (11) 

0.23 (1) (11) 

0.35 (1) (11)

Methanol NO3

-

SO4

-2 

Anaerobic 

Methanogenic 

0.0051-0.88 (3) (11) 

0.016-0.34 (3) (11) 

0.0059-0.017 (7) (11) 

0.030 (8) (11), 0.35 (9) (11)

0.019 (4) (12) 

0.011 (10) (12)

Benzene NO3

-

Fe3+

SO4

-2

Methanogenic 

General 

0.0095-0.045 (3) (11) 

0.0065-0.024 (3) (11)

0.0022-0.047 (3) (11)

0.0039-0.052 (3) (11)

0.0062-0.00096 (5) (13) 

0.043 (5) (11) 

0.14 (5) (11)

1) Estimated from Corseuil and Alvarez 1996b; Corseuil et al. 1996c and 1998; 2) Suflita et. al., 1993; 

3) Aronson et. al., 1997; 4) Hubbard et al, 1994; 5) Rathbun, 1998; 6) Barker et. al., 1998; 7) Novak et. 

al., 1985; 8) Bagley and Gossett, 1995; 9) Florencia et al., 1995; 10) Barker et al., 1990; 11) 

Determined in a laboratory; 12) Determined from field data; 13) Estimated from first principles.
Technical Memorandum MALCOLM PIRNIE, INC. 20

be toxic to most microorganisms and are therefore not biodegradable (Brusseau, 1993; 

Hunt et al, 1997a,b). High concentrations of methanol may occur near pure methanol 

spills and may inhibit microbial activity near the source; however, these concentrations 

will become more dilute with time and with increasing distance from the source 

(Katsumata and Kastenburg, 1996). 

The biodegradation of methanol has been measured both in the field and in 

laboratory studies. In an extensive field study at the CFB Borden site in Canada, the fate 

and persistence of an M85 fuel was investigated in an aerobic shallow sandy aquifer 

(Barker et al., 1990). The average concentration of methanol introduced into the aquifer 

was 7030 ppm. By day 476 of the experiment, about 99% of the methanol was degraded 

(see Table 3-2 for the effective first order degradation rate). Insufficient oxygen was 

present in the plume to account for the removal of all the methanol; the researchers 

therefore concluded that the methanol degraded first aerobically then anaerobically 

(Hubbard et al., 1994). 

 In a laboratory study, methanol biodegradation was investigated in soils from 

three different subsurface sites under various redox conditions (Novak et al., 1985). The 

first site was aerobic and also had high nitrate levels; the second site was anoxic and had 

low nitrate but high sulfate concentrations; and the third site was anoxic and had low 

nitrate and sulfate levels. Rapid biodegradation took place in the microcosms at the first 

site from both the saturated (4.19 to 4.55 ppm/day) and unsaturated zones (4.44 to 5.15 

ppm/day) although the amount of methanol added was sufficient to create anaerobic 

conditions. Rapid methanol biodegradation was also observed in the microcosms from 

the saturated zone of the second site (1.33 to 3.18 ppm/day) and the third sites (1.0 to 2 

ppm/day). This study concluded that methanol concentrations up to 1,000 ppm were 

removed in less than a year at temperatures of 10 to 11°C and at pH range of 4.5 to 7.8. 

Methanol was found to be readily biodegradable in all subsurface soils examined, with 

biodegradation proceeding more rapidly in the saturated region. This research suggests 

that methanol contamination in groundwater is unlikely to persist for lengthy periods of 

time because of its susceptibility to biodegradation under both aerobic and anaerobic 

conditions. 

 In another laboratory study, Suflita and Mormile (1993) measured acclimation 
Technical Memorandum MALCOLM PIRNIE, INC. 21

periods (periods before degradation proceeded) and biodegradation rates of methanol and 

various other alcohols and fuel oxygenates in anaerobic aquifer slurries at organic 

concentrations of 50 ppm. These researchers reported a methanol acclimation period of 5 

days, the shortest among the alcohols tested (the other alcohols being ethanol, 2-propanol 

and tert-butanol), as well as an anaerobic methanol biodegradation rate of 7.4 ± 0.7 

ppm/day. In a later study, these researchers investigated methanol biodegradation under 

a range of redox conditions (Mormile et al., 1994). Under nitrate reducing conditions, 

methanol was degraded with stoichiometric amounts of nitrate consumed. However, 

under sulfate reducing conditions the researchers concluded that the sulfate reducing 

bacteria were not utilizing the methanol. Generally speaking, high concentrations of 

methanol are not used by sulfate-reducing bacteria to an ecologically significant extent. 

However, sulfate reducers have been found to contribute to methanol depletion in other 

studies, and at least four species of sulfate-reducing bacteria have been isolated that can 

utilize methanol (Nanninga and Gottschal, 1986; Esnault et al., 1988). 

 Other laboratory studies have reported the biodegradation of methanol under 

various redox conditions and by microorganisms from diverse environments. For 

example, the methanogenic degradation of methanol was demonstrated for an enrichment 

culture derived from an anaerobic digester as well as for a pure culture. The rates of 

methanol degradation by the enrichment and pure cultures without acclimation periods 

were reported to be 1.92 and 1.37 ppm/minute (extrapolated from Figures 2 and 6B, 

respectively) (Bagley and Gossett, 1995). Fitch et al. (1996) also grew methanolutilizing cultures in a chemostat culture at methanol concentrations of 1500 to 2700 ppm 

and found the cell yield of methanol-grown cells to be consistent with what has 

previously been reported for methanotrophs. Florencio et al. (1993) investigated the 

anaerobic biodegradation of methanol at a range of pH values by a culture derived from 

an anaerobic granular sludge reactor used to treat alcohol distillery wastewater. Florencio 

et al. (1995) monitored the anaerobic removal of methanol by methanogens and 

acetogens in upflow anaerobic sludge blanket reactors. Results from these studies 

showed that methylotrophic methanogens dominated in a broad pH range (4.2 to 7.2) 

while significant acetogenesis occurred in the presence of high methanol concentrations. 

Finally, Beeman and Suflita (1987) measured methanol biodegradation in microcosms 
Technical Memorandum MALCOLM PIRNIE, INC. 22

from a shallow anoxic aquifer underlying a municipal landfill in Oklahoma. By 

recovering 70 to 100% of the methane produced during methanogenesis, they were able 

to demonstrate that methanogenesis of methanol was occurring. 

3.1.2.2 Adsorption 

 Another methanol loss mechanism from the groundwater is adsorption to soil 

materials. However, adsorption will not contribute significantly to the loss of methanol 

from the environment due to the rapid rates of biodegradation in soil and groundwater 

and vaporization from dry soils. Little adsorption is expected for compounds such as 

methanol because of its polarity, low KD values, and miscibility as discussed previously. 

3.1.2.3 Volatilization from Groundwater and Vaporization from Soil

Methanol’s high solubility and low Henry’s constant are expected to result in 

minimal methanol losses from groundwater due to volatilization or off-gassing. 

However, in the soil, methanol will vaporize from the residual phase or source area under 

low soil moisture conditions (ENVIRON, 1996). Vaporization will occur much quicker 

for M100 fuels than conventional gasoline due to the high vapor pressure of methanol. 

This may result in migration of methanol away from the source area due to vapor phase, 

diffusion driven transport. Despite the potential for lateral distribution of methanol in the 

subsurface, analytical soil samples often do not contain detectable levels of methanol 

near an M85 spill. This is likely due to the mass loss from vapor phase microbial 

degradation of methanol (Beck, 1991).

3.2 Surface Water 

3.2.1 Sources of Methanol in Surface Water 

 The potential dominant source of methanol in surface water is the direct release of neat 

methanol into a surface water body following accidental release or catastrophic failure during 

transport, such as is outlined in Scenario 2. Nonpoint sources of methanol include precipitation 

from the atmosphere, which is not expected to be significant, as noted earlier. 
Technical Memorandum MALCOLM PIRNIE, INC. 23

3.2.2 Losses of Methanol in Surface Water 

 The processes that contribute to methanol losses from surface water bodies include 

biodegradation, abiotic degradation, volatilization and bioaccumulation. As with groundwater, 

the dominant loss mechanism in surface waters is expected to be biodegradation. Methanol 

concentrations in the vicinity of a surface water release will rapidly decrease due to advection, 

dispersion, and diffusion. Due to methanol’s infinite solubility in water, an M100 release in 

open water, as discussed in Scenario 2, will disperse to non-toxic levels (< 1%) at a rate much 

faster than a parallel gasoline release. The rate of dispersion is directly proportional to the 

amount of mixing in the aquatic environment. Tidal flows combined with wind-induced wave 

action will cause a large methanol spill to rapidly disperse to levels below toxic thresholds. The 

effect of wave action on the speed of contaminant mixing in surface waters has been measured 

extensively for gasoline components following release from recreational vehicles (Malcolm 

Pirnie, 1998). In all cases measured, gasoline components quickly mixed throughout the upper 

layer of the surface water bodies; methanol is even more soluble in water than most gasoline 

components and will, consequently, mix even more rapidly. 

To verify these predictions, several computer simulations were done to model the 

advective dispersion of methanol away from a source area (Machiele, 1989). The first 

hypothetical simulation revealed that a 10,000 ton methanol release in the open sea would reach 

a concentration of 0.36% within an hour of the spill. The second hypothetical simulation of a 

spill at a rate of 10,000 liters/hr from a coastal pier exhibited a concentration of less than 1 

percent at the spill site within 2 hours and to 0.13 percent within 3 hours after the spill ceased. 

3.2.2.1 Biodegradation 

 The dominant process responsible for removal of methanol in surface water 

bodies is biodegradation. The reported half-life of methanol in surface waters under 

aerobic conditions is short and has been reported to be as low as 24 hours (see Table 3-2) 

(Howard et al., 1991). 

 In flowing water bodies, wind- or current-enhanced mixing maintains dissolved 

oxygen concentrations at a level sufficient to support aerobic microbial processes. Even 

in oxygen-limited environments such as the bottom layers of stratified lakes, anaerobic 
Technical Memorandum MALCOLM PIRNIE, INC. 24

biodegradation is expected to proceed at rapid rates; the reported half-life for methanol 

biodegradation under anaerobic conditions ranges from 1 to 5 days (Howard et al., 1991). 

Additionally, the nutrient supply in rivers and lakes is generally not expected to restrict 

the rate of methanol metabolism because the required nutrient supplies are constantly 

recharged by runoff (Alexander, 1994). However, high concentrations of methanol 

resulting from a large spill in an enclosed area will deplete the surface water of oxygen 

required to sustain aquatic life. 

3.2.2.2 Abiotic Degradation 

Abiotic degradation (i.e., non-biological or chemical) reactions are not likely to 

contribute significantly to methanol removal from surface water bodies. Hydrolysis 

reactions usually transform compounds into more polar products; methanol is a very 

polar molecule and is stable in water. Photolysis involves the transformation of a 

compound as a consequence of its direct absorption of light. Methanol does not adsorb 

light in the visible spectrum and long wavelength UV. It does adsorb very short 

wavelength UV, which is present in negligible amounts in solar radiation. In addition, 

methanol can be naturally oxidized by hydroxyl radicals formed in the water by the 

photolysis of nitrate, nitrite, and hydrogen peroxide resulting from reactions with excited 

humic materials or from the reaction of H2O2 with Fe(II) (Schwarzenbach et al., 1993). 

Thus, naturally occurring photooxidation of methanol via direct or indirect oxidation is 

possible; however, these reactions are slow and, thus, not expected to be significant in 

surface waters. 

3.2.2.3 Bioaccumulation 
Technical Memorandum MALCOLM PIRNIE, INC. 25

 The bioaccumulation of fuel hydrocarbons and certain additives has been studied 

extensively (e.g. Brault et al., 1994). As 

shown by various studies, uptake and 

elimination of organic pollutants in 

freshwater fish and invertebrates may occur 

through gill membranes, the efficiency of 

which depends on blood proteins and the 

hydrophobicity of the compounds. 

Bioaccumulation in aquatic organisms is 

expressed by bioconcentration factors, BCF 

(Streit, 1994). To our knowledge, no studies 

have been reported for methanol bioaccumulation. However, octanol-water coefficients 

(Kow) and bioconcentration factors for methanol and other oxygenates have been reported 

(see Table 3-3). Octanol-water coefficients may be used as an indicator for 

bioaccumulation potential and are widely used as a descriptor of hydrophobicity (Mackay 

et al., 1992). In conclusion, methanol is expected to bioaccumulate slightly less than 

ethanol, and significantly less than benzene and most other more hydrophobic 

constituents in gasoline. Regardless, small quantities of methanol introduced into 

mammals as a result of bioaccumulation from methanol fuel releases can be rapidly 

metabolized, negating any long term effect. 

3.2.2.4 Volatilization 

 Volatilization is not a primary source of loss for methanol since methanol has a 

low air/water partition coefficient and the rate of biodegradation most likely exceeds the 

rate of volatilization. In the environment, methanol has similar properties to ethanol and, 

therefore, the volatilization rate of ethanol from surface waters can be used to describe 

the relative volatilization rate of methanol. In a recent study, the volatilization rates for 

several oxygenates and gasoline constituents were calculated based on their chemical 

properties for various lake conditions (Malcolm Pirnie, 1998). Under typical California 

lake conditions (temperature = 20o

C; wind speed > 5 mph; epilimnion ~ 20 feet), ethanol 

was predicted to volatilize almost five times slower than BTEX compounds. Under these 

Table 3-3 

Comparative values of octanol-water 

coefficients and bioconcentration factors 

Compound Log Kow Log BCF 

Methanol -0.82 (1)

-0.77 (1) 

-0.16 (2)

-0.31 (2)

-2.09 (1)

Ethanol -0.32 (1)

-0.31 (1) 

-0.75 (2)

-1.63 (1)

Benzene 2.13 (2)

1.56 - 2.15 (2)

6.8 (3)

(1) Mackay et al., 1992; (2) Zogorski et al., 1997; 

(3) RSP, 1994 
Technical Memorandum MALCOLM PIRNIE, INC. 26

conditions and ignoring biotic reactions, benzene has a half-life of approximately 9 days; 

whereas, ethanol has a half-life of approximately 40 days. Using the model and the 

conditions discussed above, methanol has a predicted half-life of approximately 60 days. 

In another evaluation, the half-life of methanol in a river and a pond were modeled to be 

approximately 4.8 days and 51.7 days, respectively; however, this model included other 

transport mechanisms besides volatilization (USEPA OPPT, 1994). In conclusion, 

despite the slow volatilization and minimal adsorption, methanol will not persist in 

surface waters due to its intrinsic tendency to be degraded quickly. 

3.3 Methanol / BTEX Commingled Plumes 

 BTEX compounds are the most toxic group of hydrocarbons in gasoline. Naturally 

occurring biodegradation controls the persistence of these compounds in the subsurface 

environment. High concentrations of alcohols and ether oxygenates can potentially impede the 

biodegradation of BTEX (Salanitro, 1993). Alcohols will be biodegraded in preference to BTEX 

and can therefore consume the oxygen required for BTEX biodegradation. Alcohols can also be 

toxic or inhibitory to subsurface populations of BTEX-degraders at elevated concentrations 

(Barker et al, 1990). 

 Information on the effect of methanol on the biodegradation of BTEX in the field is 

available from the Borden site study in Canada. Three gasolines (M85, 15% MTBE, and base 

gasoline) were allowed to migrate in an aquifer (Barker et al., 1990). By day 476 most of the 

methanol was degraded, but BTEX compounds in the methanol plume were at higher relative 

concentrations than in the MTBE and non-oxygenated plumes. These data suggest that methanol 

may have slowed BTEX biodegradation rates compared to BTEX biodegradation in MTBEcontaining and oxygenate-free groundwater. Laboratory experiments found no significant 

biodegradation of BTEX in the presence of 7000 ppm methanol but some BTEX biodegradation 

was noted when the methanol concentration was only 1000 ppm. It was concluded that the 

mechanism for greater BTEX persistence in the presence of methanol is the initial inhibition of 

BTEX biodegradation by toxic methanol concentrations followed by inhibition due to the 

removal of oxygen by preferred methanol biodegradation. Such results are particularly 

important in assessing the fate of benzene, a known carcinogen (Dean, 1985) and the most 

recalcitrant monoaromatic under anaerobic conditions. 
Technical Memorandum MALCOLM PIRNIE, INC. 27

 In another laboratory microcosm study, the biodegradation of BTEX was reportedly 

impaired at 1.4% (14,000 ppm) methanol and was completely inhibited at higher methanol levels 

(Novak et al., 1985). In conclusion, the biodegradation rate of BTEX compounds in a gasoline 

plume that has become commingled with a methanol plume (Scenario 3) could be significantly 

retarded in the presence of high methanol concentrations. This reduction in BTEX 

biodegradation could effectively increase the length of BTEX plumes. A complete evaluation of 

this effective plume elongation has not been completed for this evaluation, but is likely to be a 

function of the distance between the methanol leaking UST (LUST) and the petroleum LUST 

and the placement of the two USTs relative to groundwater movement. 

3.4 Conclusions 

 Applying the hazard assessment guidelines from USEPA’s Office of Pollution Prevention 

and Toxics, a recent study concluded that methanol is not persistent in the environment because 

it readily degrades in air, soil and water, and has no persistent degradation intermediates 

(ENVIRON, 1996). In the event of a catastrophic methanol spill, methanol will rapidly dilute to 

low concentrations (< 1%) and subsequently quickly biodegrade. If clean-up measures are 

implemented, they must be instituted at a much faster pace compared to petroleum spills in order 

to capture the methanol plume prior to significant dilution. However, the relative speed of 

methanol’s biodegradation is expected to result in natural cleanup times that are faster than the 

active cleanup times for methanol or gasoline releases. 
Technical Memorandum MALCOLM PIRNIE, INC. 28

4.0 METHANOL ADDITIVES 

4.1 Purpose and Background of Additives 

 Methanol is a demonstrated alternative to gasoline and other fossil-based fuels; however, 

most evaluations of potential environmental impacts due to releases of methanol have focused 

primarily on fate of methanol and circumvented any potential ancillary impacts. Similar to other 

fuels, methanol may require the use of additives to address performance, pollution, or health 

issues. 

Although it is currently unknown whether additives will be required for wide-spread use 

of methanol fuel, several potential safety concerns regarding methanol use as a fuel source have 

been identified based on its chemical and physical properties. Several investigations, conducted 

in the eighties and early nineties, identified the known safety, health, and environmental issues 

associated with methanol and developed a list of potential additives to address these concerns 

(Machiele, 1989, 1990). Manufacturers are currently focusing their additive investigation and 

testing efforts on luminosity (the ability to see a burning flame), taste (to prevent ingestion), and 

color. Investigation efforts focus on evaluating the need for these additives, identifying the most 

suitable compound, determining their impact on fuel cell efficiency, if any, and documenting 

their effectiveness at addressing certain human health and safety issues. Therefore, it is useful to 

evaluate the physical characteristics of the additives themselves and how these additives could 

impact soil, air, or groundwater following a methanol fuel release. 

4.2 Fate and Transport of Three Known Additives

This section provides a brief summary of the fate and transport of the leading candidate 

compounds for additives and the potential environmental impacts of these compounds if released 

into the environment. 

4.2.1 Luminosity

Several types of compounds have been identified to increase the luminosity of methanol, 

including: hydrocarbon mixtures, aromatics, aliphatics, olefins, other alcohols, ethers, metal 

organic salts, and alcohol soluble organic dyes. In tests conducted by Southwest Research 

Institute and California Air Resources Board (Fanick, 1990), toluene (>4% volume) and two 
Technical Memorandum MALCOLM PIRNIE, INC. 29

proprietary alcohol-soluble solids (MO and AO) provided the most promising results. For 

example, by varying the toluene content from 4% to 10%, the luminosity increases 10 to 100 

times. Select chemical and physical properties of these potential luminosity additives are 

presented in Table 4-1. 

In general, the fate and transport of toluene and hexane is well understood based on their 

physiochemical properties. 

They have a relatively high 

vapor pressure, are readily 

biodegraded under aerobic 

conditions, and exhibit 

more retardation than 

methanol due to their lower 

solubility and higher soil 

partition coefficient. Given 

the proprietary nature of 

MO and AO, the potential 

fate and transport 

characteristics of these 

compounds could not be evaluated. 

4.2.2 Taste

Studies conducted by Lawless and Hammer (Lawless, 1983) demonstrated that addition 

of a bitterant reduces accidental ingestion of a product. Another study, conducted by C. Bering, 

J. Griffiths and J. Wild in the early 1980s (Bering et al., 1982), concluded that the average 

volume of liquids containing a bitterant, that would be ingested is less than one teaspoon. The 

potential health concerns at elevated levels of methanol has prompted the consideration of 

bitterants to prevent ingestion of methanol containing fuels. 

A possible bitterant candidate is Denatonium Benzoate, or Bitrex, which has become a 

widely used defensive measure to prevent ingestion of products from several industries, 

including: 

Alcohol: Denatured alcohols 

Table 4-1 

 Select Chemical and Physical and Properties of Potential Luminosity 

Additives 

Parameter AO/ MO Toluene Hexane 

Chemical Name PROP phenyl 

methane 

n-Hexane, 

dipropyl 

Molecular Formula PROP C7H8 C6H14

Molecular Weight (g/mol) PROP 92.14 86.18 

Specific Gravity PROP 0.867 0.6548 

Boiling Point (oC) PROP 110.6 -95 

log Kow (-) PROP 2.73 4.11 

Henry’s Constant (-) PROP 0.272 0.130 

Solubility (water) (mg/L @ 

20 o

C) 

PROP 526 9.47 

Vapor Pressure (atm) PROP 26.31 4.89 

Appearance PROP colorless, liquid w/ aromatic 

odor 

Note: UNK - Unknown or not available information 

PROP - Proprietary materials, chemical data not available.
Technical Memorandum MALCOLM PIRNIE, INC. 30

Medical Products: Medical wipes, nail-biting deterrents, rubbing alcohol 

Agricultural Products: pesticides, plant nutrients 

Automotive Products: Anti-Freeze, brake fluid, polishes 

Household Products: Cleaners, disinfectants 

Bitrex can be detected at 10 ppb and is noticeably bitter at concentrations greater than 50 

ppb. Common applications of Bitrex range from 6 ppm up to 100 ppm. Anonymous research 

disclosures indicate that concentrations as low as 1 ppm Bitrex reduced ingestion of detergent 

by children by over 75%. The appropriate quantity of 

Bitrex is case-specific and is dependent upon the 

viscosity and existing taste of each product. Preliminary 

estimates indicate that 10 ppm of Bitrex by volume in 

M100 would be sufficient to prevent ingestion of 

methanol. Select chemical and physical properties for 

Bitrex are listed in Table 4-2 below. 

According to Material Safety Data Sheets and 

Bitrex Information Sheets provided by the Macfarlan 

Smith distributor, Bitrex is generally stable at neutral pH 

values for up to two years (Bitrex, 1998). Although no 

transformation of Bitrex has been observed in acidic 

conditions, under alkaline conditions it is converted to an 

hydroxide salt. Chemical or physical variations will not 

affect the performance of Bitrex since the bitter quality is 

imparted by the denatonium cation which remains in 

solution. 

The solubility of Bitrex in solvents such as 

methanol and water can be attributed to its polarity; 

conversely Bitrex is relatively insoluble in petroleum 

based solvents. The solubility and octanol-water partition coefficient of Bitrex indicate that it 

would be less soluble in water than methanol. The fate and transport of Bitrex in the 

environment, specifically, the biodegradability, retardation, and bioaccumulation is not well 

understood. However, the manufacturers of Bitrex report a biodegradation half life, derived 

Table 4-2 

Select Chemical and Physical and 

Properties of Bitterant Additives 

Parameter Bitrex/ 

Denatonium 

Benzoate 

Molecular 

Formula 

C28H34N2O3

Molecular Weight 

(g/mol) 

446.5 

Specific Gravity 1.12 

Boiling Point UNK 

log Kow (-) 0.9 

Henry’s Constant UNK 

Solubility (water) 

(mg/L @ 20 o

C) 

45,000 

Solubility 

(methanol) (mg/L 

@ 20 o

C) 

690,000 

Vapor Pressure 

(atm) 

UNK 

Appearance white granules 

Note: UNK - Unknown or not available 

information 

Source: MSDS, Macfarlan Smith Data Sheet
Technical Memorandum MALCOLM PIRNIE, INC. 31

under laboratory conditions and temperature of about 20oC, of approximately 45 days (Bitrex, 

1998). 

4.2.3 Colorant

Methanol is a relatively colorless liquid compared with gasoline which has an orange 

hue. To visually distinguish methanol from gasoline and other liquids, colorant additives may be 

required for its wide-spread use. 

Studies conducted in 1994 by Japanese researchers have identified a food additive, Acid 

Blue 9 that would apparently provide an 

adequate, identifiable color to methanol at a 

concentration of 1 ppm (Yutaka and 

Kasamatsu, 1998). The studies evaluated 

twenty-three (23) dyes to distinguish neat 

methanol from other liquids and to minimize 

the potential performance impacts of adding 

dyes to methanol. Dyes were evaluated based 

on tests for health impacts, quality 

deterioration, performance impacts and 

economic factors including cost and 

availability (Yutaka and Kasamatsu, 1998). 

Acid Blue 9 is typically used as a 

non-toxic food dye. It is also relatively inert 

and does not cause chemical reactions with other materials. However, the reactivity of Acid 

Blue 9 within a fuel cell vehicle has not been tested. Specific chemical and physical parameters 

for Acid Blue 9 are not available. However, some general characteristics were drawn from the 

evaluation report (see Table 4-3). 

Based on the limited chemical and physical compound information available, the actual 

fate and transport of Acid Blue 9 could not be evaluated. 

4.3 Conclusion

 There are several potential additives that may be used in methanol fuel, however, the fate 

and transport of these additives in the environment is not well understood. This is primarily a 

Table 4-3

Select Chemical and Physical and Properties of 

Colorant Additives 

Parameter Acid Blue 9 

Chemical Class Triphenyl-methane 

(Non-halogenated) 

Molecular Formula C37H43N4O9 S3Na2

Molecular Weight 

(g/mol) 

829.72 

Specific Gravity UNK 

Boiling Point UNK 

log Kow (-) 0.9 

Henry’s Constant UNK 

Solubility (water) (mg/L 

@ 20 o

C) 

miscible in water 

Solubility (methanol) 

(mg/L @ 20 o

C) 

UNK 

Vapor Pressure (atm) UNK 

Appearance Bright greenish blue 

Note: UNK - Unknown or not available information
Technical Memorandum MALCOLM PIRNIE, INC. 32

result of the proprietary nature of these additives and their complex chemical structure. Based 

on the projected widespread usage of methanol in the future and the possible widespread usage 

of these or other additives, a detailed evaluation of the fate and transport of potential additives is 

warranted. 
Technical Memorandum MALCOLM PIRNIE, INC. 33

5.0 REMEDIATION AND TREATMENT 

5.1 Remediation of Methanol 

 Following a release of methanol to the subsurface as a result of the release scenarios 

discussed in Section 1, remediation may be required if the spill is in a high-risk area (i.e., 

potential receptors are nearby). Methanol will quickly biodegrade as discussed in Section 3 and, 

therefore, natural attenuation is likely to be an effective and inexpensive remediation strategy in 

most soil, groundwater, and surface water scenarios. However, if a methanol plume becomes 

commingled with a gasoline plume, rapid biodegradation of methanol may deplete the 

surrounding soil and groundwater of electron acceptors and nutrients required for the 

biodegradation of gasoline. Therefore, a successful natural attenuation strategy for all 

contaminating constituents may require that the natural environment be enhanced with the 

addition of oxygen, nutrients, or other amendments to facilitate biodegradation of other gasoline 

constituents. 

 If methanol is released to a subsurface environment with low microbial activity and/or 

deep groundwater, there may not be sufficient microbial activity to completely degrade the 

released methanol. Consequently, an alternative remediation strategy is required. Under such 

circumstances, the high vapor pressure of methanol suggests that soil vapor extraction will 

effectively remove residual methanol from the soil. Once extracted from the subsurface, the 

methanol vapors can be biodegraded using vapor phase biofilters. In summary, the remediation 

of methanol from soil and groundwater is not expected to pose insurmountable technical 

challenges due to it tendency to quickly biodegrade. 

5.2 Impetus for Drinking Water Treatment

While it is unlikely that elevated levels of methanol will persist in groundwater due to the 

rapid rate of biodegradation, neat methanol releases near drinking water supply wells could 

impact a water supply source. Unlike certain gasoline additives, the taste and odor threshold 

concentration for methanol is high, ranging from 10 ppm to 20,000 ppm in air (USEPA, 1994a). 

Alternatively, in order for any toxic symptoms to occur, drinking water concentrations would 

have to exceed roughly 9,200 ppm (Machiele, 1989). Based on the groundwater measurements 

that have been obtained, and an estimated ‘worst-case scenario’ model for methanol release into 
Technical Memorandum MALCOLM PIRNIE, INC. 34

groundwater, it is highly unlikely that methanol concentrations will exceed the toxicity level in 

drinking water supply wells, assuming the methanol source is a sufficient distance from the 

supply well. Similarly, the U.S. Department of Energy released a report which refers to the 

unlikely possibility of toxic contamination (defined as concentrations greater than 1,000 ppm) in 

drinking water. (USDOE, 1991). 

Regardless, it is likely that drinking water sources containing elevated levels of methanol 

will require treatment before it is delivered to the public. There are several treatment options 

including: air stripping, activated carbon, advanced oxidation, membrane filtration, or 

biologically activated filters. Each of these treatment technologies is discussed briefly below. 

5.3 Air Stripping 

 The effectiveness of air stripping for removing a contaminant from water is a direct 

function of that contaminants Henry’s constant. As the Henry’s constant increases, the 

contaminant is more readily removed from water. Typically, chemicals with a dimensionless 

Henry’s constant below 0.005 (20o

C) are not amenable to removal by air stripping (Roberts, 

1995). Consequently, conventional air stripping can not be used to remove methanol (H[-] 

<0.00011) from drinking water. However, increases in the water temperature will increase the 

Henry’s constant, which will allow use of stripping for removing methanol. This process, known 

as steam stripping has been used to remove alcohols from industrial waste waters, and could 

conceivable be used to remove methanol from drinking water. However, high costs 

(>$5.00/1,000 gallons) are required to raise the temperature of water from 10o

C to 40oC which 

will likely limit the acceptability and feasibility of this technology for removal of methanol from 

drinking water. 

5.4 Activated Carbon 

The effectiveness of activated carbon for removing a contaminant from water is a direct 

function of that contaminant’s soil/water partition coefficient (Kd). As discussed earlier, 

methanol has a very low soil/water partition coefficient due to its high polarity and, hence, 

solubility. Therefore, methanol will not adsorb strongly to granular activated carbon (GAC) or 

other adsorbents when present in water. The ineffectiveness of adsorption is also demonstrated 

by noting the magnitude of the Freundlich isotherm constants for methanol. While it was not 
Technical Memorandum MALCOLM PIRNIE, INC. 35

possible to locate any isotherms for methanol, isotherms for ethanol and acetone are likely 

surrogates for methanol’s adsorptivity. The Freundlich isotherm constants for ethanol and 

acetone range from 0.0 to 14 [mg/g(L/mg)^1/n] (Crittenden et al., 1997). Compared to benzene 

which adsorbs relatively well (isotherm constant range from ~20 to 117 [mg/g(L/mg)^1/n]), 

ethanol and acetone have a very small equilibrium adsorption coefficient (Crittenden et al., 

1997). Thus, adsorption processes, such as GAC have limited application for methanol removal 

from water. 

5.5 Advanced Oxidation 

The factors that control the effectiveness of advanced oxidation for removing 

contaminants from water include type of oxidation process, the water quality, contact time, and 

contaminant oxidation potential. Advanced oxidation treatment becomes most competitive for 

chemicals, such as methanol, that neither readily volatilize from water (H < 0.005 [-]) nor are 

easily adsorbed onto carbon. Calgon, a major vendor of advanced oxidation processes (AOP) 

verified that methanol treatment in drinking water is achievable, but electrical energy 

consumption per order of magnitude methanol reduction (EE/O) values and, thus, feasibility will 

vary according to influent concentrations and water quality (Reko, 1998). This vendor stated 

that if influent concentrations of methanol are 100 ppm, 1,000 ppm, and 10,000 ppm, the 

corresponding EE/Os will be 20, 100, and 500, respectively. These EE/O values imply that 20 

kilowatt hours are required to lower methanol from 100 ppm to 10 ppm for every 1000 gallons of 

treated water, or an energy cost of approximately $2/1000 gallons. Actual costs are potentially 

lower than this because methanol levels in water supply sources will likely not exceed 10 ppm. 

 Compared to MTBE treatment, methanol treatment will require twice as much electricity, 

which results in higher treatment costs. Unit costs also rise with a decrease in system size. In a 

recent study by Malcolm Pirnie on treatment costs associated with removal of MTBE from 

drinking water, the cost to remove MTBE from drinking water may be as low as $0.50/1,000 

gallons for a large scale treatment system (6,000 gpm) and as high as $1.50/1,000 gallon for a 

smaller scale treatment system (60 gpm). It is also possible, and in some cases more feasible, to 

combine UV/oxidation technology with other treatment technologies (particularly biological 

treatment), as a finishing process to treat the last 5-10% of methanol contamination. Finally, 

AOP technologies can cause oxidation by-product formation which must be considered on a site 
Technical Memorandum MALCOLM PIRNIE, INC. 36

specific basis. Thus, the suitability of AOP for removal of methanol requires site specific pilot 

studies to resolve treatment cost and by-product formation issues. 

5.6 Membranes

Reverse osmosis or nanofiltration membranes can be used to remove some organic 

compounds from water. These processes remove organic molecules by size exclusion. 

However, because methanol is similar to water in its small size and low molecular weight, 

membranes will not typically be effective. A major vendor of reverse osmosis membranes 

reports that methanol removal using this technology will likely be less then 20%. 

Comparatively, they stated that larger alcohols such as isopropyl alcohol (with five carbon 

atoms) can be removed by membranes up to levels of 98%. 

5.7 Biological Treatment (Biologically Activated Filters) 

 Methanol in drinking water supplies can be treated effectively through biological 

treatment. The type of technology used depends on the anticipated influent concentrations. For 

influent methanol levels of 1 ppm, a slow sand filter should provide the required microbial 

activity for successful treatment for drinking water. Higher influent levels (on the order of 100 - 

1000 ppm) would require treatment in a biologically activated filter (BAF) with counter air flow. 

Design of a BAF for methanol treatment would require pilot studies to determine the optimum 

design capacity and appropriate operating conditions for the desired methanol removal 

efficiency. 

 In 1997, the University of Colorado at Boulder completed a pilot project for removal of 

nitrate in a biological process that utilizes indigenous bacteria (Scott, 1997). The pilot plant 

consists of towers containing layers of bacteria that reduce the nitrates to nitrogen. The simple, 

low maintenance system produced an effluent which met the federal and state drinking water 

standards for nitrate. Methanol could also be removed in a similar process. 

 Upton et al. (1993) evaluated a wastewater treatment process which combines a tertiary 

solids removal sand filter with denitrification. Methanol was used as the carbon source required 

for growth and cell metabolism of the heterotrophic bacteria. Theoretically, reduction of one 

gram of nitrate (NO3

−

) to nitrogen gas requires 1.9 grams of methanol; however, pilot studies 

with a 1,000 m3

/d filter showed methanol consumption on the order of 4.4 g methanol / g nitrate. 
Technical Memorandum MALCOLM PIRNIE, INC. 37

 Drinking water purveyors are often reluctant to use BAFs due to the potential for 

microbial activity in the treated effluent water. Federal law mandates the disinfection of all 

groundwater used as drinking water, regardless of the groundwater quality. Disinfection with 

chlorine or ozone following the BAF may reduce the purveyors’ concerns over microbial levels 

in the treated water. Although this treatment option is conceptually feasible with moderate costs, 

there will be resistance on the part of water utilities because of inherent limitations of biological 

processes in drinking water treatment. Consequently, the use of BAFs to remove methanol from 

drinking water will likely be limited. 

5.8 Conclusion

 In conclusion, conventional drinking water treatment technologies used for removal of 

organic compounds (air stripping and activated carbon) are not effective for removal of 

methanol. Advanced oxidation processes have been proven for methanol treatment, but may be 

cost prohibitive, and must be analyzed on a site by site basis. Alternatively, biologically 

activated filters represent a cost-effective proven technology to remove methanol from drinking 

water, though this technology may be limited by treated water quality concerns of water 

purveyors. Very little field site documentation is available due to the fact that methanol has not 

been reported as a contaminant in drinking water sources. The most promising technologies for 

methanol removal in drinking water applications are some form of biological treatment and 

advanced oxidation either separately or in combination.
Technical Memorandum MALCOLM PIRNIE, INC. 38

6.0 METHANOL TOXICOLOGY 

6.1 Health Effects of Methanol 

Methanol’s properties and toxicity are well understood. Human exposure to methanol 

can occur via the inhalation, ingestion, or dermal contact pathways. Identified human illnesses 

associated with methanol exposure include organic solvent poisoning, systemic acidosis, optic 

nerve damage and central nervous system (CNS) effects. 

 Though often considered to be 

more toxic than gasoline, methanol’s 

occupational Threshold Limit Value (TLV) 

is only slightly lower than that of gasoline 

(a TLV of 200 ppm versus gasoline’s 300 

ppm). Table 6-1 contrasts the hazards 

associated with M100 (100 percent 

methanol used in fuel cells) versus 

gasoline fuels. In 1991, the U.S. 

Department of Energy reported that 

overall, gasoline is considered to be more 

hazardous to human health than neat 

methanol (USDOE, 1991). 

6.1.1 Inhalation

 Inhalation of methanol vapors is 

the most frequent type of exposure. 

Exposure to fuel vapor sources can be 

attributed to exhaust emissions, vehicle 

refueling emissions, and emissions from 

spills and uncovered fuel. Acute methanol 

inhalation toxicity does not appear to be a 

problem for drivers or service station 

attendants exposed to methanol vapors during refueling and under a wide range of traffic 

conditions (HEI, 1987). Measured exposure levels were well less than methanol’s 8-hour TLV 

(200 ppm) and the highest exposure duration was determined to be approximately 15 minutes. 

TABLE 6-1 

HAZARD SUMMARYa

M100 Gasoline 

Flammability 

 Ease of Occurrence 

 Open & Restricted 

 Areas 

 Enclosed Spaces 

4 

8 (2-4) b

9 

2 

 Relative Hazard if Fire 

 Fire Severity 

 Ease of Extinguishing 

 Flame Visibility 

3 

7 

8 

10 

10 

1 

Toxicity 

 Inhalation-Low Conc. 

 Toxicity 

 Ease of Occurrence 

3 

10 

10 

10 

 Inhalation - High Conc. 

 Toxicity 

 Ease of Occurrence 

10 

3 

10 

4 

 Skin Contact. 

 Toxicity 

 Ease of Occurrence 

9 

3 

8 

3 

 Ingestion 

 Toxicity 

 Ease of Occurrence 

10 

8(2) c

10 

3 

Table adapted from Machiele, 1998; a 1-No concern. 2 to 3 = Low 

Level concern. 4 to 6 = moderate concern. 7 to 8 = high-level 

concern. 9 to 10 = extreme hazard. b

 Numbers in parenthesis 

reflect hazard reductions resulting from design changes. C Number 

in parenthesis incorporates the lowered likelihood of ingestion due 

to the presence of additives.
Technical Memorandum MALCOLM PIRNIE, INC. 39

The calculated dosage based on worst-case methanol inhalation exposures of 150 ppm for 15 

minutes results in a maximum dose of 0.6 mg/kg body weight. This analysis assumes a 70 kg 

person breathing at twice the resting rate where 60 percent of the inhaled vapor is absorbed into 

the body. A body burden of 0.6 mg/kg is similar to the amount created through normal fruit, 

vegetable and alcoholic beverage intake (0.3-1.1 mg/kg/day) (Machiele, 1988) and is 500 times 

less than methanol’s minimum lethal dose. Most methanol related activities result in much lower 

inhalation exposures and related body burden. 

 Chronic inhalation exposure to methanol of greater than 200 parts per million has 

resulted in irritation to the mucus membranes, dizziness, nausea, headaches and blurred vision. 

Generally, there are no overt health problems associated with low-level exposures (USDOE, 

1991). EPA’s Office of Air Quality Planning and Standards has evaluated methanol for chronic 

toxicity and has given it a composite score of 7 (where scores range from 1 to 100, with 100 

being the most toxic). 

The American Conference of Governmental Industrial Hygienist (ACGIH) has 

established an 8-hour time weighted average threshold limit value (TLV) of 200 ppm for worker 

exposure to methanol. Threshold limit values refer to airborne concentrations of substances and 

represent conditions under which it is believed that nearly all workers may be repeatedly 

exposed daily, for a working 

lifetime, without adverse health 

effects. Exposure to airborne 

methanol concentrations greater 

than the National Institute for 

Occupational Safety and Health 

(NIOSH) Immediately Dangerous to 

Life or Health (IDLH) value of 6,000 ppm represents a condition under which workers may not 

be able to escape without loss of life or irreversible health effects. A summary of relevant 

airborne methanol occupational exposure limits is presented in Table 6-2. 

 

6.1.2 Ingestion 

Inhalation exposure is the most common route of entrance into the body; however, 

TABLE 6-2 

Methanol Toxicity Exposure Limits (1) 

Occupational Work 

Standard -TWA a

8 hr workday 200 ppm 

(OSHA, ACGIH) 

TLV-STEL b 15 minute 

exposure 

250 ppm 

IDLH c immediate 6,000 ppm 

1) Festa, 1996. a) Time Weighted Average. b) Short Term 

Exposure Limit. c) Immediately Dangerous to Life or Health. 
Technical Memorandum MALCOLM PIRNIE, INC. 40

ingestion represents the most serious route of exposure. Methanol ingestion exposure typically 

could occur as a result of intentional drinking, unintentional drinking during siphoning, or 

unintentional drinking due to ignorance of the potential consequences. The toxicity effects of 

ingestion follow the same pattern described above for inhalation. The ingestion threshold for 

toxic effects can be as little as 6 to 18 ml (USDOE, 1991; Machiele, 1989). There is a wide 

disparity in these toxic levels based on the natural variability in the recipients ability to 

metabolize methanol. 

Observed human lethal dosages via ingestion range from 15 to 250 grams (Wimer, et al., 

1983). However, only a few documented cases are found in the literature and almost all of the 

cases predate 1920. In a review of the actual case evidence in medical literature for methanol 

toxicity at low ingested doses (30 ml or less) Kopinski (1993) concludes that the published 

literature on actual methanol ingestion cases does not support a minimum lethal adult dose of 

less than 30 ml (approximately 24 grams). Areas of uncertainty in analyzing these cases 

included the potential for synergistic effects due to other constituents in ingested drinks and the 

difficulty in obtaining reliable dose estimates. LD50 (i.e., the lethal dose affecting 50 percent of 

a test population) data points for methanol ingestion in animals are presented in Table 6-3. 

Table 6-3 

Lethal Doses of Methanol and Benzene in Animal Studies 

LD50 Methanol Benzene 

Oral-rat—mg/kg 

Oral-mouse—mg/kg 

Oral-monkey—mg/kg 

Dermal-rabbit—ml/kg 

Inhalation-rat—ppm 

5,600-13,000a

, 12,800b

9,000b

7,000b

20a,b

64,000a

4,894c

4,700c

9,980c

a MSDS, 1996. b Exxon, 1991. c MSDS, 1987

6.1.3 Dermal Exposure

 There are many possible instances in which people come in contact with vehicle fuels. 

Generally, exposure through spillage or use of a solvent will cause only mild effects on the skin 

(defatting or a mild dermatitis). Methanol readily adsorbs into the dermal layer at a rate of 0.2 

mg/cm2 per minute (Machiele, 1988). Repeated exposure may cause eczema, redness, and 

scaling. Methanol’s more serious toxic effects described previously are only a threat in the event 
Technical Memorandum MALCOLM PIRNIE, INC. 41

of excessive absorption. Thus, momentary contact is not a large concern (USEPA, 1994a). 

6.2 Aquatic Toxicity

 High concentrations of methanol are toxic to most plants and animals. In the event of a 

large, concentrated spill from a tanker ship, the acute effects of methanol exposure would result 

in damage to biota in the immediate spill area. 

 The USEPA Office of Pollution Prevention and Toxics (1994a) reported on the 

sensitivity to methanol for several aquatic species. This study reported values of median lethal 

concentrations, LC50, and median effective concentrations, EC50, for methanol (Table 6-4). LC50

is the estimated concentration that is expected to be lethal to 50% of the test animals or plants, 

and EC50 is the estimated concentration that is expected to cause an effect other than death to 

50% of the test animals or plants (non-lethal effects include changes in behavior, growth, 

immobilization, reproduction and equilibrium). 

Table 6-4 

Reported Median Lethal and Median 

Effective Concentrations for Methanol and Benzene 

Test animal or plant Methanol 

LC50

(mg/L) 

Methanol 

EC50

(mg/L) 

Benzene 

LC50 / EC50

(mg/L) (3)

Pimephales promelas 

(Fathead Minnow) 

28,100 

(96 hrs) (1)

NA 15 

(96 hrs) 

Oncorhynchus mykiss 

(Rainbow trout) 

20,100 

(96 hrs) (1)

13,000-13,200 

(EQU) (216 hrs) (2)

5 

Alburnus alburnus 

(Bleak) 

>28,000 

(96 hrs) (1)

NA NA 

Lepomis macrochirus 

(Bluegil) 

15,400 

(48 hrs) (1)

16,000-16,100 

(EQU) (216 hrs) (2)

22 

Cyprinus carpio 

(Common carp) 

28,000 

(48 hrs) (1)

NA NA 

Carassius auratus 

(goldfish) 

1,700 

(48 hrs) (1)

NA 34 

Anabaena 

(blue green algae) 

NA 2.57-3.13% 

(10-14 days) (1)

growth inhibition 

NA 

(1) USEPA, 1994a; (2) Zogorski et al., 1997; (3) USEPA, 1980; NA = Not Available. 

The results of this study indicated that methanol is essentially non-toxic to the species 

tested. Based on an in-depth review of the toxicity and environmental distinctions between 
Technical Memorandum MALCOLM PIRNIE, INC. 42

methanol and conventional fuels, Machiele concludes that in general, methanol is significantly 

less toxic to marine life than petroleum fuels, and that many of the effects of short term exposure 

are temporary and reversible (Machiele, 1989). Water quality criteria for methanol to protect 

aquatic life have not yet been established by the EPA.

6.2.1 Toxicity of Methanol to Microbial Populations 

 In general, high concentrations of alcohol (10 to 15%) are considered to be toxic to most 

microorganisms (Brusseau, 1993; Ingram and Buttke, 1984). A number of studies have been 

conducted to evaluate the effect of methanol on subsurface microbial populations. In a 

laboratory study, methanol up to a concentration of 1,000 mg/L was found to biodegrade in soil 

microcosms from three different sites with no apparent toxicity to the microorganisms (Novak et 

al., 1985). In another laboratory study, the presence of 19% methanol caused a 10,000 fold 

decrease in the microbial population of aquifer material (Butler et al., 1992). These researchers 

suggested that methanol from an M85 plume may adversely affect the indigenous microbiota’s 

ability to contribute to attenuation of petroleum hydrocarbon contaminants in situ. 

 Verschueren (1983) reviewed the biological effect of methanol and reported that 

methanol has been reported to impact sludge digestion at a concentration of 800 mg/L and NH3

oxidation (50% inhibition) in Nitrosomonas at a concentration of 160 mg/L. Toxicity thresholds 

for other microorganisms are reported in Table 6-5. 

Table 6-5 

Biological effects of methanol on various microorganisms as measured by the toxicity threshold

from a cell multiplication inhibition test 

Microorganism Toxicity threshold 

(cell multiplication inhibition test) 

Bacteria (Pseudomonas putida) 6600 mg/L 

Algae (Microcystis aeruginosa) 530 mg/L 

Green algae (Scenedesmus quadricauda) 8000 mg/L 

Protozoa (Entosiphon sulcatum) >10,000 mg/L 

Protozoa (Uronema parduczi Chatton Lwoff) >10,000 mg/L 

from a cell multiplication inhibition test.; Adapted from Verschueren (1983).
Technical Memorandum MALCOLM PIRNIE, INC. 43

7.0 FUTURE RESEARCH NEEDS 

 This report contains a comprehensive evaluation of the fate and transport of methanol in 

the environment. As noted, there are several areas where the available literature is not sufficient 

to address all fate and transport issues associated with unintentional releases of methanol to the 

soil, groundwater, or surface water. Based on the review provided in this report, the following 

research suggestions are recommended: 

1) As discussed in Section 5, the selection of methanol additives, if needed, may significantly 

alter the risk posed by methanol releases into the environment. As the need for additives and 

their possible choices are evaluated, the fate and transport of the additives will need to be 

addressed as part of the evaluation process. 

2) The literature reviewed for this report suggests that methanol will rapidly degrade once 

introduced to the subsurface. However, high concentrations of methanol near the source may 

be toxic to microorganisms resulting in limited or no source area biodegradation. 

Consequently, an analysis of methanol releases that have occurred at methanol fueling areas, 

storage areas, production locations, or during transportation would serve to verify that 

methanol does not significantly accumulate in the environment, nor does it pose a threat to 

drinking water resources. 

3) The fate and transport of a methanol plume that may become commingled with a gasoline 

plume is briefly discussed in section 3 of this report; however, there remain several 

uncertainties. The effect of methanol on the fate and transport of BTEX plumes needs to be 

better understood. In addition, if the BTEX biodegradation rate is reduced, the effect of this 

reduced rate on increases in BTEX plume lengths should be further evaluated. 

4) If any of the above studies indicate that methanol or methanol additives may persist in the 

subsurface, an evaluation should be completed to determine the best technology for 

remediation and treatment of these compounds. The chosen technology should address 

removal of these compounds in the source area, plume area, or at the drinking water source 
Technical Memorandum MALCOLM PIRNIE, INC. 44

well. For drinking water applications, it should be determined whether the selected 

technology, or a combination of technologies, meets the requirements posed by the drinking 

water community with respect to process reliability and regulatory approval. 
Technical Memorandum MALCOLM PIRNIE, INC. 45

8.0 CONCLUSIONS 

8.1 Fate and Transport 

 The fate and transport of methanol released into the environment has been evaluated in 

the context of three conceptual release scenarios: 1) a rail car or tank truck spill during transport; 

2) an ocean or river spill during transport; and 3) an underground storage tank release at a 

methanol dispensing location. In each of these scenarios, methanol is unlikely to persistent in 

any of the environmental compartments due to its rapid biodegradation. Methanol is miscible in 

water, and will consequently dissolve and dilute to very low concentrations in the event of a 

surface water spill (Scenario 2). Similarly, groundwater methanol concentrations are highly 

dependent on the nature and magnitude of the release, but will likely fall to low concentrations 

once complete dissolution has occurred. In both of these scenarios, the low concentrations of 

methanol will likely be easily biodegraded under a wide range of geochemical conditions. 

 Biodegradation is the primary process for methanol removal from the environment. 

Relative to gasoline, methanol is safer and more environmentally benign. Hazards incurred by 

gasoline releases are greater than those of methanol releases, and will persist much longer in the 

environment (USDOE, 1991). 

8.2 Methanol Additives 

It is currently unknown whether additives will be required for wide-spread use in 

methanol fuel. Because of several potential safety concerns over the use of methanol as a fuel 

source the need for additives must be evaluated. Manufacturers are currently focusing their 

additive investigation and testing efforts on three chemical or physical characteristics of 

methanol: luminosity, taste, and color. 

For each category, there may exist a set of candidate chemicals which addresses the 

stated problem. However, often these chemicals are proprietary in nature, such that the chemical 

properties are not published. Consequently, a detailed analysis of the fate and transport of these 

additives was not possible. 

8.3 Remediation and Treatment 
Technical Memorandum MALCOLM PIRNIE, INC. 46

Most treatment technologies that are commonly used to remove gasoline components 

from water (e.g., air stripping, granular activated carbon) are not effective for removing 

methanol from water due to the high solubility and low Henry’s constant relative to other 

gasoline components. In the majority of remediation cases, the inability of these technologies to 

remove methanol from water is inconsequential because biodegradation of methanol in the soil, 

groundwater, and surface water will readily occur. If methanol were to impact drinking water 

sources, advanced oxidation processes have been proven, though the feasibility and costs of the 

treatment are very site specific. Biological treatment processes are effective at removing 

methanol from water, and are increasingly being used to polish the effluent from advanced 

oxidation processes. However, biological treatment in drinking water applications is still not 

extensively used and, therefore, would require regulatory acceptance. In conclusion, methanol 

can be removed in both a remediation and drinking water treatment context using biological 

degradation; however, the effectiveness, cost and public acceptability will be site specific. 

8.4 Human and Aquatic Toxicity 

 Methanol’s properties and toxicity are well understood, and the ocular toxicity and 

metabolic acidosis that are effects of acute high doses of methanol are well-known. Methanol is 

neither mutagenic, nor carcinogenic. While methanol produces toxic effects on humans and 

animals, the current evidence suggests that these effects only occur at high doses (Festa, 1996). 

While methanol is often considered to be more toxic than gasoline, the threshold limit value 

(TLV) for methanol vapor is only slightly lower than that for gasoline; and the U.S. Department 

of Energy considers gasoline to be ‘overall’ more hazardous to health than neat methanol. 

 Methanol is significantly less toxic to marine life than petroleum fuels, and many of the 

effects of short term exposure are temporary and reversible. Based on the reported values of 

median lethal and effective concentrations for methanol, the Office of Pollution Prevention and 

Toxics indicated that methanol is essentially non-toxic to the four aquatic fish species that were 

tested. However, a surface water spill of methanol could result in the depletion of oxygen which 

would prove to be toxic to local fish species. Methanol has a negligible bioaccumulation 

potential and is relatively non-toxic to ecological receptors. While the aquatic toxicity of 

methanol is high, toxic concentrations could be observed near a LUST source area or after a pure 

product methanol spill; this concentrations will likely quickly dissipate. Thus, in most cases, 
Technical Memorandum MALCOLM PIRNIE, INC. 47

methanol concentrations will be benign to surrounding organisms, but in extreme circumstances, 

methanol could prove toxic to indigenous microbes or aquatic life. 

 In conclusion, the fate and transport of methanol in the environment is well understood. 

Methanol spills to the soil, groundwater, and surface water will quickly biodegrade under both 

aerobic and anaerobic conditions and, consequently, methanol is not expected to persist. 

Methanol exhibits a lower toxicity to both humans and indigenous microbes then conventional 

gasoline. Therefore, based on this analysis, methanol appears to be a more environmentally 

benign fuel compared to conventional gasoline. 
Technical Memorandum MALCOLM PIRNIE, INC. 48

9.0 ACKNOWLEDGEMENTS 

 This research was performed at the request of American Methanol Institute (AMI) under 

the direction of Michael Kavanaugh, Ph.D., P.E., Vice-President of Malcolm Pirnie, Inc. 

Andrew Stocking from Malcolm Pirnie, Inc. was the Project Manager, and Karen Pappas of 

Malcolm Pirnie, Inc. was the Project Engineer. Literature review and analysis for 

biodegradation were provided by Rula Deeb (Ph.D. Candidate, University of California, 

Berkeley). Please address correspondence or questions to Dr. Michael Kavanaugh or Andrew 

Stocking at: 

MALCOLM PIRNIE, INC.

180 Grand Ave., Suite 1000 

Oakland, California 94612 

(510) 451-8900 Tel. 

(510) 451-8904 Fax 

astocking@pirnie.com 
Technical Memorandum MALCOLM PIRNIE, INC. 49

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Technical Memorandum MALCOLM PIRNIE, INC. 50

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intrinsic bioremediation of BTX plumes in Brazil. Hazardous Waste & Hazardous 

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