Methyl tert-butyl ether (MTBE), a synthetic chemical used as a fuel additive, has been detected more frequently in the environment than previously. In this study, we examine the effects of MTBE (up to 100 mg/L) and its primary metabolite tertbutyl alcohol (TBA) (up to 1,400 mg/L) on the hatch rate and larval development of the African catfish Clarias gariepinus. Exposure to higher MTBE concentrations resulted in deformed eyes, mouthparts, and spinal cord and in increased larval mortality. Methyl tert-butyl ether exposure had no significant impact on egg viability, whereas TBA induced a decline of hatch rate. The MTBE can be regarded as a pollutant with toxicological effects on catfish larvae at concentrations above 50 mg/L. Although such concentrations greatly surpass present-day concentrations found in surface water (0.088 mg/L), concentrations up to 200 mg/L have been detected in groundwater.

Eleven soil samples (contaminated and non-contaminated top soils and aquifers) from seven different locations in Belgium were examined in lab-scale batch microcosms simulating in situ conditions for their indigenous capacity to biodegrade methyl tert-butyl ether (MTBE). The effect of implementing nutrients or additional oxygen and of the presence of co-contaminants on MTBE degradation was investigated. All soils showed rapid degradation of benzene. On the other hand, only one site, historically contaminated with oxygenated fuel, provided soil samples showing relatively fast MTBE biodegradation. These soil samples originated from four different depths from the vadose and saturated zone. MTBE degradation kinetics differed between the samples of the saturated and non-saturated zone and depended on the implemented conditions. MTBE-biodegradation in the samples from the non-saturated zone started after a very short lag-phase (<7 days), while long lag-phases (up to 270 days) were obtained with the other samples. Addition of extra nutrients stimulated MTBE degradation kinetics in microcosms containing the saturated soil samples while inhibiting effects were seen in the case of non-saturated soil samples. In contrast, implementing dissolved oxygen concentrations of 9.5 and 11.5 mg l(-1) led to lower degradation kinetics compared to 8 mg l(-1) in microcosms containing saturated soil samples, while stimulating effects were seen with the non-saturated soil samples. Addition of an extra carbon source like benzene or propane did increase in general the MTBE first order degradation rate constant. Differences in the eubacterial community composition between these depth samples were confirmed based on denaturing gradient gel electrophoresis (DGGE) patterns of PCR-amplified 16S rRNA gene fragments. The results of the presented study indicate that an aerobic MTBE biodegradation potential is not omnipresent in Belgian sub-soils.

Biodegradation of methyl tert-butyl ether (MTBE) in aquifer material was studied during slurry enrichments (batch-systems) simulating in situ conditions. Soil samples taken at 4 different depths at a gasoline-contaminated site were used and the microbial population of each soil sample was separately enriched. The MTBE-degradation kinetics and the community dynamics as a response to different implemented in situ important parameters (e.g. additions of nutrients, addition of extra oxygen and presence of co-contaminants) were determined and compared between the different depths. In all enrichments the MTBE-biodegradation capacity was active for more than 600 days. PCR-DGGE fingerprints revealed that addition of extra nutrients or benzene did not lead to significant changes in the eubacterial population. No differences could also be observed between the community composition of the enrichment conditions after 1 year of incubation at different oxygen concentrations (8, 9.5 and 11.5 mg/l DO). In contrast, adding propane did induce differences in band intensity of the fingerprint. A different eubacterial community was observed at the 4 different examined depths.

A lab scale study has been set-up to evaluate the possibilities of an inoculated bioreactor for the on-site treatment of MTBE-contaminated groundwater. Activated carbon was inoculated with two different MTBE-degrading cultures, an axenic strain (Rubrivivax sp. PM-1) and an MTBE-degrading enrichment culture. Based on batch experiments the cultures were found to degrade MTBE in the presence of the activated carbon. Column-experiments have been started to evaluate MTBE-degradation in a continuous system. Oxygen uptake was detected in the inoculated column as well as in the non-inoculated column. Based on the available preliminary data it is difficult to make a distinction between sorption and degradation of MTBE. Formation of TBA indicates that at least a part of the MTBE is removed by biodegradadation.

MTBE has only recently being used as an octane enhancer in gasoline in Europe and is considered as a more recent groundwater contaminant on this continent. In this study we examined if during the recent contamination history, European MTBE contaminated aquifers had developed MTBE degrading microbial communities. Different MTBE contaminated and non-contaminated aquifers and soils were tested for their intrinsic biodegradation potential. The role of the oxygen concentration, the availability of nutrients and the influence of the presence of a co-contaminant like benzene on the MTBE biodegradation capabilities of the indigenous microorganisms were examined. All studied soil samples showed degradation of benzene under all tested conditions. On the other hand only one aquifer showed the capacity to degrade MTBE as demonstrated by the disappearance of MTBE and the production of TBA, the main degradation product of MTBE.