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MTBE was effectively biodegraded under oxidizing environmental conditions in the presence of an acclimated mixed culture isolated from a petrochemical biotreater. MC-1 (Gram-positive coccus), MC-2 (Acinetobacter lwoffii) and MC-3 (Bacillus sp.) were present in the culture medium, with MC-1 being the predominant organism. The presence of other easily assimilated carbon sources in the culture medium influenced MTBE biodegradation. In batch studies, 62–73% MTBE was biodegraded in 144–192 hours at an initial concentration of 100 ppm as the sole carbon source, with the ORP ranging from 191–274 mv, and at a temperature of 29°C. The overall K rate constants and the specific k rate constants were evaluated using a first order rate equation. Mean values determined were 1.79×10-1 day-1 and 1.66×10-2 day-1/(mg/L cell mass), respectively. Continuous upflow fixed biofilm reactor studies were performed at retention times of 0.25, 0.5, and 1 day at an initial MTBE concentration of 150 ppm. Results indicated that approximately 53% MTBE was biodegraded for the 0.25 day retention time and 70% for both the 0.5 and 1.0 day retention times. Three kinetic models were evaluated for all experimental retention times. These included: Model I (Eckenfelder); Model II (Arvin) and Model III (first-order biphasic). Results indicated that model III yielded the highest and most consistent correlation coefficients for all retention times evaluated.

The prevalence of heavy metal pollution and mobility of both Pb and Cd was investigated in street dust samples from the Metropolitan Area of Monterrey (MAM) in northern Mexico. Street dust samples from 30 selected sites were analysed for their content of Zn, Cd, Pb, Cr and Ni after digestion according to U.S. EPA Method 3051. Multivariate analysis including correlation coefficient analysis, Principal Component Analysis and Cluster Analysis was used to analyse the data and identify possible sources of these heavy metals. Compared with background values, elevated concentrations of Pb (300 mg kg(-1)), Cd (7.6 mg kg(-1)) and Cr (78 mg kg(-1)) were observed in street dust of MAM. Based on multivariate statistical approaches, the studied elements were classified in three main sources: (1) Cr, Ni and Zn mainly derived from industrial activities; (2) Cd originating from traffic-related activities; and (3) Pb associated with vehicular emissions. A sequential extraction procedure using the Tessier method was applied to evaluate the mobility of Pb and Cd in street dust. The majority of Pb was associated with the residual fraction followed by the carbonate fraction. The majority of Cd was associated with the residual fraction. These results indicated that the mobility was higher in Pb (26%) compared with Cd (11%), posing a potential risk to the environment.

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