Much Ado: How Big Is the Problem of Hydrolysis of Methyl Tertiary Butyl Ether (MtBE) to Form Tertiary Butyl Alcohol (tBA)?

Abstract

Groundwater contaminated by the gasoline additive methyl tertiary butyl ether (MtBE) is also frequently impacted by tertiary butyl alcohol (tBA). The USEPA recently sponsored a study that discusses the possibility of hydrolysis of MtBE to form tBA during analytical procedures. This finding is important because it suggests that existing tBA data may not accurately depict tBA or MtBE concentrations in groundwater. This article discusses the mechanism and kinetics of MtBE hydrolysis, then presents three case studies of analytical results from sites in California, USA. Although these case studies are limited in scope, the data do not support the occurrence of the hydrolysis of MtBE to form tBA due to acid preservation of groundwater samples. At a minimum, this suggests that MtBE hydrolysis may not be as pervasive a problem as suggested in USEPA's study; therefore, concerns about the validity of historical tBA data may not be warranted. The reason for this result may be simple: there are two necessary factors that promote hydrolysis: low pH and high temperature (above 40°C). Although the static headspace analysis method used to obtain the data in the White et al. study may require heating to achieve adequate sensitivity, many laboratories perform purge-and-trap analyses without heating. Under those conditions, hydrolysis may not occur. However, it may be prudent to preserve samples with alkaline preservatives, to eschew high temperatures during the analysis of groundwater samples, or to neutralize the sample pH before heating.