Xylene biodegradable

Otenio, M.H., Lopes da Silva, M.T, OUveiia Marques M.L., Roseiro, J.C., Bidoia, E.D. 2005. Benzene toluene and xylene biodegradation by Pseudomonas putida CCMI 852. Braz. J. Microbiol. 36 (3) 258-261. 

The xylenes are mildly toxic. They ate mild skin irritants, and skin protection and the cannister-type masks are recommended. The oral LD q value for rats is 4300 ppm. The STEL for humans is 150 ppm. Xylenes show only mild toxicity to fish, and the threshold limit for crop damage is 800—2400 ppm. Biodegradation with activated seed is slow, and sewage digestion is impaired by 0.1% concentrations. In the event of a spih, oil-skimming equipment, adsorbent foam, and charcoal maybe used for cleanup. 

Enrichment factors during the anaerobic degradation of o-xylene, m-xylene, m-cresol, and p-cresol by pure cultures of sulfate-reducing bacteria that use the fumarate pathway ranged from -1.5 to -3.9 ppm (Morasch et al. 2004). It was therefore proposed that this could be applied to evaluating in situ bioremediation of contaminants that use this pathway for biodegradation. 

Morgan P, ST Lewis, RJ Watkinson (1993) Biodegradation of benzene, toluene, ethylbenzene and xylenes in gas-condensate-contaminated water. Environ Pollut 82 181-190. 

Fig. 4.21 gives mean values for some organic substances in the Glatt infiltration system. The figure illustrates that tetrachlorethylene is not eliminated during the infiltration process. In the case of 1,4-dichlorbenzene and 1,3-dimethylbenzene (m-xylene) elimination occurs but this elimination is caused by biodegradation. 

Benzoic acid, a common food preservative, may be a suitable substrate to achieve biostimulation. It is a relatively inexpensive, harmless aromatic compound that has been previously used in analogue enrichment1 schemes to enhance biodegradation of the aromatic herbicide, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) [336]. Benzoate ion is also an intermediate in the toluene pathway and it can induce related enzymes involved in the degradation of toluene and m-and p-xylenes [336]. In addition, the anionic nature of benzoic acid would minimize its retardation and facilitate its distribution when injected into an... 

Accordingly, Alvarez et al. [28] used flow-through aquifer columns to evaluate the efficacy of using benzoate ion (from sodium benzoate) as a biostimulatory substrate to enhance the aerobic biodegradation of benzene, toluene, and o-xylene (i.e., BTX), fed continuously at low concentrations. They reported the following key points ... 

DO-IT has been used at several sites to treat benzene, toluene, ethyl benzene, and xylene (BTEX), methyl ferf-butyl ether (MTBE), and total petroleum hydrocarbons (TPH). According to the vendor, this technology may also be applied or modified to clean up any aerobically biodegradable contaminants in soil. 

WST claims that the technology treats soil (in situ) and potentially treats natural sediment (in situ). The developer claims that WST Bioblends biodegrade benzene, ethylene, toluene, and xylene (BETX) volatile aromatic hydrocarbons. 

The musks make a good case study for illustrating biodegradability rules of thumb and their application in molecular design for non-persistence. Musk xylene appears... 

Biodegradation can be accelerated in a prepared bed reactor with forced aeration. These reactors (Figure 1.2) are used at many Superfund sites for bioremediation of PAHs and BTEX (benzene, toluene, ethylbenzene, and xylene) (Alexander, 1994). This method, with recirculating leachate, was used to reduce the average total petroleum hydrocarbon concentration in a diesel-contaminated soil from 6200 mg/kg dry soil to 280 mg/kg in approximately 7 weeks (Reynolds et al., 1994). A bed reactor with forced aeration was also used to treat 115 000 m3 of soil contaminated with bunker C fuel oil (Compeau, Mahaffey Patras, 1991) and 23 000 m3 of soil contaminated with gasoline and fuel oil (Block, Clark Bishop, 1990). 

Table 3.5. Summary of results from reports on the anaerobic biodegradation of the xylenes... 

When aquifers were amended with nitrate in order to stimulate biodegradation, the results were generally consistent with those obtained in laboratory investigations. In a field injection experiment at Seal Beach, California, Ball et al. (1994) demonstrated complete removal of w-xylene and the m-,/-xylene fraction decreased significantly in parallel bioreactor experiments. A Canadian study showed a decrease in m- and /-xylene of 14% and 15%, respectively, over aim flowpath in the Borden aquifer (Barbara et al., 1992). Very little degradation was observed beyond that point, presumably due to the availability of preferred electron donors in the landfill leachate impacted aquifer. 

As with nitrate, the anaerobic biodegradation of m- and /-xylene could also be linked with the reduction of sulfate at a rate of about 1 /M/day. Edwards et al. (1992) demonstrated the sulfate-dependent degradation of all three xylene isomers. Interestingly, the xylenes were not degraded until toluene was almost depleted. 

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