Marine Ventures International, Inc. (MVI) conducted desktop studies to address the issue of the ecotoxicological effects of methanol discharged in produced water from two platforms in the eastern Mediterranean Sea.  Oil and gas operators sometimes inject methanol into pipelines to prevent methane hydrate formation and to dissolve hydrates in producing oil and gas wells, platform and subsea hydrocarbon systems. 

Hydrate formation inhibits flow within oil and gas pipelines. The primary use of methanol in gas and condensate production is to inhibit the accumulation of hydrate in flowlines containing a mixture of natural gas, waste gases, gas condensate, and formation water (produced water).  Prior to discharging of the produced water to surface waters adjacent to the platforms, it generally treated to remove hydrocarbons.  Methanol, however, is not completely removed during the treatment process. About 50% of the methanol remains in the discharged produced water, and the rest vaporizes into the gas phase.

The primary concern was the potential effects of these discharges on organisms living in the vicinity of the two platforms.  There are limited scientific data on the acute and chronic toxicity of methanol to freshwater and marine plants and animals.  MVI compiled and evaluated these data to estimate the predicted no-effect concentration (PNEC) of methanol in seawater. Different species of marine plants and animals vary widely in their sensitivity to short- and long-term exposure to methanol in seawater.   MVI analyzed the relative sensitivities and ecological effects of exposure to methanol at concentrations at or below the PNEC, at several environmentally realistic concentrations above the PNEC value, and for different lengths of time. The toxicity and ecological effects data were similarly assessed relative to predicted environmental fates and persistence estimates for methanol under oceanographic conditions at the platforms.

Results of the studies indicated that the methanol in the produced water plume from the platforms will disperse rapidly through dilution, biodegradation, and evaporation by at least 100,000-fold within 100 meters (325 feet) of the discharge. Because produced water plumes from these platforms are buoyant and the methanol is rapidly lost, it is unlikely that methanol will sink to the seafloor. Thus, the only organisms that may be exposed to methanol reside in the upper approximately 50 meters (165 feet) of the water column. Given the predicted concentrations of methanol at the end of the discharge pipe, the toxicity of methanol to marine organisms living in the upper water column and on the upper portions of the platform legs is very low.  The studies determined there is no ecological risk from the methanol discharges to the biological communities living in the near-surface waters around the two eastern Mediterranean Sea platforms.