Environmental Issues

Methanol: Environmental Issues

The following describes what processes occur following a release of Methanol on land, in water and underground.

  1. Tanker truck or railway tank spill. Methanol released to soil and/or groundwater.
  2. Barge spill. Methanol released to surface water.
  3. Underground storage tank leak. Methanol released to soil and groundwater.

Presence of Indigenous Methanol-Degrading Microbes

Methanol is widely produced in nature by anaerobic microorganisms responsible for complex aromatic hydrocarbon biodegradation (Heijthuijsen & Hansen, 1990; Oremland et al., 1982). As a result, Methanol molecules are ubiquitous in nature. Furthermore, due to its 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 & Madigan, 1991).

Systematics of Methanol oxidation: Methylotrophs (example: Methylococcus capsulatus), organisms that can grow using only single-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 & Madigan, 1991). Methylotrophs are of commercial interest in the bacterial metabolism of C1. 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.

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.

Losses of Methanol in Surface Water

The processes that contribute to Methanol losses from surface water bodies include Biodegradation, a biotic 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 much faster rate 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. 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 adjective 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.

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 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.

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.

Conclusions

Applying the hazard assessment guidelines from the 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 (Malcolm Pirnie Inc., 1999). 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.

Various reports summarize estimates of possible Methanol half-lives (the time required for 50% reduction in concentration) (see Table 1-4) in different environmental media. In the atmosphere, Methanol will be photo-oxidized relatively quickly; the half-life 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 reports of half-lives for Benzene to illustrate the relatively rapid degradation of Methanol.

Estimated half-ife of Methanol and Benzene in the environment (Howard et al., 1992)

Environmental medium

Methanol half-life (days)

Benzene half-life (days)

Soil 1-7 5-16
Air 3-30 2-20
Surface water 1-7 5-16
Groundwater 1-7 10-730

References

  • Alexander, C.M.O. 1994. Trace-Element Distributions within Ordinary Chondrite Chondrules – Implications for Chondrule Formation Conditions and Precursors. Geochimica et Cosmochimica Acta, 58 (16):3, 451-3,467
  • Brock, T.D. and M.T. Madigan. 1991. Biology of Microorganisms (6th edition). Englewood Cliffs, NJ: Prentice-Hall.
  • Heijthuijsen J.H.F.G., and T. A. Hansen. 1990. C1 Metabolism in Anaerobic Non-Methanogenic Bacteria. In: G.A. Codd, L. Dijkhuizen and F.R. Tabita (eds.), Autotrophic Microbiology and One-Carbon Metabolism (pp. 163-193). Dordrecht, Boston, London: Kluwer Academic Publishers.
  • Howard et al., 1992. Handbook of Environmental Degradation Rates. Chelsea, MI: Lewis Publishers.
  • Howard, P.H., Boethling, R.S., Jarvis, W.F., Meylan, W.M., and E. M. Michalenko. 1991. In: H. T. Printup (ed.), Handbook of Environmental Degradation Rates. Chelsea, MI: Lewis Publishers.
  • Machiele, P.A. 1989. A Perspective on the Flammability, Toxicity, and Environmental Safety Distinctions Between Methanol and Conventional Fuels. Prepared for the American Institute of Chemical Engineers. U.S. Environmental Protection Agency. Ann Arbor, MI.
  • Malcolm Pirnie, Inc. 1999. Evaluation of the Fate and Transport of Methanol in the Environment. Prepared for the American Methanol Institute, 800 Connecticut Ave., NW, Suite 620, Washington, D.C. 20006.
  • Oremland, R.S., L. Marsh, and D.J. Des Marais. 1982. Methanogenesis in Big Soda Lake, Nevada: An Alkaline, Moderately Hypersaline Desert Lake. Applied Environmental Microbiology, 43: 462 – 468.
  • Malcolm Pirnie, Inc. 1999. Evaluation of the Fate and Transport of Methanol in the Environment. Prepared for the American Methanol Institute.