Recalcitrant

RDX and HMX are rather more recalcitrant, especially under aerobic conditions, but there are promising indications that biodegradation can occur under some conditions, especially composting (67). Several strains of bacteria able to use RDX (and Triazine) as a sole source of nitrogen for growth have recentiy been isolated, and this is an area where rapid progress is being made. 

Electroporation. When bacteria are exposed to an electric field a number of physical and biochemical changes occur. The bacterial membrane becomes polarized at low electric field. When the membrane potential reaches a critical value of 200—300 mV, areas of reversible local disorganization and transient breakdown occur resulting in a permeable membrane. This results in both molecular influx and efflux. The nature of the membrane disturbance is not clearly understood but bacteria, yeast, and fungi are capable of DNA uptake (see Yeasts). This method, called electroporation, has been used to transform a variety of bacterial and yeast strains that are recalcitrant to other methods (2). Apparatus for electroporation is commercially available, and constant improvements in the design are being made. 

CometaboHsm refers to situations where a compound caimot be biodegraded effectively unless another food source is available. The recalcitrant compound, such as TCE, does not provide the energy to allow the microorganisms to grow and thrive. When another food source is available such as... 

It has been found that partial oxidation is satisfactoiy as a pre-treatment to biological or carbon adsorption treatment. Partial oxidation often seems to make recalcitrant organics easier to degrade biologically and easier to adsorb. 

Xenobiotic Compound foreign to biological systems. Often refers to human-made compounds that are resistant or recalcitrant to biodegradation and decomposition. 

Isotretinoin COOH Topical 0.05% cream Oral 0.251.0 mg/kg/ d Cystic acne, recalcitrant nodular acne Rosacea gram-negative folliculitis pyoderma faciale hidradenitis suppurativa cancer prevention... 

Acitretine ch3o x x Oral 0.25-1.0 mg/kg/d Psoriasis (erythrodermic, pustular, and severe recalcitrant) Palmoplantar keratoderma pustulosis palmoplantaris, icthyosis, Darier s disease, pityriasis rubra pilaris, lichen ruber planus... 

Combinations of retinoids with ultraviolet A or B radiation (and other drugs). For example, RePUVA-therapy (retinoids and psoralen and UVA combination) is currently one of the most effective regimens for recalcitrant severe psoriasis. 

A positive feedback between vegetation and atmospheric CO2 will occur if biomass declines. This will happen to the extent that climatic warming causes increased water stress, either through decreased precipitation or increased evap-otransporation, particularly on soils of low water-holding capacity. Decreases in soil nutrient availability, either directly caused by drought or indirectly caused by replacement with taxa with more recalcitrant litter, may further decrease the net release of carbon from the biosphere to the atmosphere. Positive feedback will also arise if the current standing biomass of trees is replaced by small trees, shrubs, and herbs that store less carbon. 

This drug has proved to be very recalcitrant, as it by-passes sewage treatment. Common WWTP influent concentrations are in the order of magnitude of several hundreds of nanograms per liter [5, 8, 13, 19, 20]. 

Many authors reported poor elimination of antiepileptic drug carbamazepine [6,13,17,49, 54]. Pharmacokinetic data indicate that only 1-2% of carbamazepine is excreted unmetabolized. However, glucuronide conjugates of carbamazepine can presumably be cleaved in the sewage, and thus increase its environmental concentrations [51]. This is confirmed by its high ubiquity in the enviromnent at concentration levels of several hundred nanograms per liter in different surface waters. Due to its recalcitrant nature, it can be used as anthropogeiuc marker for the contamination of aquatic environment. 

Huling SG, Pope DF, Matthews JE, et al. 1995. Wood preserving waste-contaminated soil Treatment and toxicity response. In Hinchee RE et al., ed. Bioremediation of recalcitrant organics. Columbus, OH Battell Press, 101-109. 

Most beneficial in treating recalcitrant melasma and post-inflammatory hyperpigmentation... 

Fig. 10.2. a Patient with recalcitrant melasma unresponsive to glycolic acid or salicylic acid peels, b Responded to combination salicylic acid/TCA peeling... 

There is minimal published data on the use of combination peeling protocols in deeply pigmented skin (Fitzpatrick skin types IV-Vl). The author has reported the efficacy of combination peeling with salicylic acid 20 and 30% in combination with 10% TCA for recalcitrant melasma patients. This peeling regimen was well tolerated with minimal side effects in darker racial ethnic groups (see Salicylic acid/TCA peel section). 

Fig. 16.3. a Severe recalcitrant post-inflammatory hyperpigmentation secondary to acne excorians. b After a series of four salicylic acid 20 and 30% peels and 10% hydroquinone cream... 

The refractory nature of some pollutants, notably, persistent polyhalogenated compounds, has raised problems of bioremediation of contaminated sites (e.g., sediments and dumping sites). There has been interest in the identification, or the production by genetic manipulation, of strains of microorganisms that can metabolically degrade recalcitrant molecules. For example, there are bacterial strains that can reductively dechlorinate PCBs under anaerobic conditions. 

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