| Description |
Endocrine disruption in aquatic animals caused by treated wastewater effluent has been extensively studied. Endocrine disruption describes the alteration of normal endocrine functions due to exposure by endocrine disrupting chemicals (EDCs). Estrogenic activity was frequently detected in wastewater treatment effluent, fresh water, or sedimentation due to incomplete degradation of EDCs in the wastewater treatment facilities. These endocrine disruptors can be degraded by microorganisms but at time scales of a few days to a hundred days. Biological processes only can degrade EDCs to a limited degree as indicated in treatment plant mass balance studies. Microorganisms utilize oxidation enzymes to breakdown EDCs to lower toxic level products during wastewater treatment, while metal and drug resistance proteins interact with the biodegradation process by exporting chemicals out of the cell. This mechanism reduces EDCs' availability and contact time with oxidation enzyme, resulting higher extracellular contaminant concentrations. The objective of this research is to find out if drug resistant proteins contribute EDCs' biopersistence and lack of EDCs biodegradation in wastewater treatment. The substrates of drug resistant proteins were selected among various estrogenic chemicals including natural and synthetic estrogens, phytoestrogens, plasticizers, flame retardants, and nonionic surfactants. Besides steroids, the synthetic estrogen 17α-ethynylestradiol, phytoestrogens of nonylphenol, octylphenol, and plasticizer bisphenol-A are substrates of the major multidrug resistant proteins AcrAB-TolC in E. coli and MexAB-OprM in Pseudomonas aeruginosa. As endocrine disruptors enter the bacterium, they are exported from the cell, limiting their contact time with oxidizing enzymes. The enzyme oxygenase was employed in this study to remove these endocrine disruptors. The results showed that toluene dioxygenase degrades bisphenol-A efficiently. Both multidrug resistant and oxygenase genes were transformed into E. coli, and batch bioreactors were used to determine the biodegradation ability. The presence of a drug resistant protein reduced the degradation rate of bisphenol-A to 0.146 hours-1 from the rate of 0.184 hours-1 without a resistant protein. To find out which proteins function at environmentally relevant concentrations found in wastewater treatment plants and surface water, efflux and oxidation gene induction was measured. In E. coli, hormone-resistant genes acrB and yhiV and peroxidase katE were expressed the greatest; in Pseudomonas, ring cleavage oxygenases and certain drug-resistant genes were up-regulated in the presence of EDCs. To apply this study for water reclamation and wastewater treatment plants, the bacteria population was monitored, and endocrine disrupting chemicals analysis was performed. Biological treatment only removed 75% of E2 (17β-estradiol) equivalent estrogenic activity in the Central Valley Water Reclamation Facility in Salt Lake City, Utah. Meanwhile, drug resistant bacteria were detected in the effluent of this wastewater treatment plant after all treatment processes, including UV disinfection. |
