Microbial Reductive Transformation of Pentachloronitrobenzene under Methanogenic Conditions

Abstract

The reductive transformation of pentachloronitrobenzene (PCNB), an organochlorine fungicide, was investigated with a mixed, methanogenic culture developed from a contaminated estuarine sediment. Batch assays performed with this enrichment culture resulted in the biotransformation of PCNB to pentachloroaniline (PCA), which was then sequentially dechlorinated as follows: PCA --> 2,3,4,5- and 2,3,5,6-tetrachloroaniline (TeCA) --> 2,4,5- and 2,3,5-trichloroaniline (TrCA) --> 2,4-, 2,5-, and 3,5-dichloroaniline (DCA) --> 3- and 4-chloroaniline (CA) (low levels). Glucose fermentation, methanogenesis, and dechlorination were not inhibited at an initial PCNB concentration up to 40 microM, which is 27 times higher than its aqueous solubility. The addition of 25 mM 2-bromoethanesulfonate (BES) to the PCNB-amended culture resulted in the complete inhibition of methanogenesis, but the biotransformation of PCNB to PCA and its sequential dechlorination pathway were not affected. The addition of sodium azide (200 mg/L) to the PCNB-amended culture resulted in complete inhibition of methanogenesis, but did not inhibit the transformation of PCNB to PCA; however, PCA dechlorination was not observed. PCNB was also abiotically transformed to PCA in autoclaved culture media but at much lower rates as compared to the biotic assays. In contrast, the rate of PCNB to PCA transformation in autoclaved culture controls was similar to the rates observed in the azide-amended culture and the active enrichment culture, indicating that biotically derived reductants facilitated the observed transformation of PCNB to PCA. Dechlorination of PCA was not observed in any of the abiotic controls. These findings have significant environmental implications in terms of the fate and transport of PCNB, PCA, and its dechlorination products in subsurface systems.

Effect of shocked nitrobenzene concentrations on the operational performance of anaerobic sequential batch reactor

“…As a result, the NB reduction process was energetically replenished. This finding was similar to that of a previous study, which found that SBR performance can be quickly recovered from a threefold shock in the influent nitrophenols concentration after the addition of sufficient carbon sources .…”

“…Previous studies have also reported that the influent NB concentrations and loading rates could influence NB removals by the applied anaerobic reactors such as ABR, AMBR, and CSTR reactors ; and that the measured IC 50 was always below 50 mg L −1 , indicating the heavy toxicity of NB under shocked influent concentration and this in turn decreased the NB removals in this study. Apart from NB reduction, a previous study also suggested that the nitro group associated compounds such as pentachloronitrobenzene (PCNB) could also inhibit the biological activities in dechlorinating pentachloroaniline (PCA) .…”

Energy and Nutrient Recovery from Sewage Sludge and Manure via Anaerobic Digestion with Hydrothermal Pretreatment

“…Total gas production was measured by displacement of an acidified brine solution (10% NaCl w/v and 2% H 2 SO 4 v/v) in graduated burets. The gas composition was determined by gas chromatography with thermal conductivity as previously reported. , …”

Development of an HPLC method for determination of pentachloronitrobenzene, hexachlorobenzene and their possible metabolites

“…PCNB degradation intermediates viz; pentachloroaniline (PeCA), tetrachloroaniline (TeCA), trichloroaniline (TCA) and dichloroaniline (DCA) from anaerobic enriched soil sample have been identified by HPLC with the retention time 3.532, 5.375, 4.121, 6.951 min and UV-absorption spectra 246.9, 308.5, 248.1, 221.1 nm (Figure 1). There are few reports on degradation of PCNB by anaerobic mixed culture via reductive dechlorination under anaerobic condition [22,25]. Similarly, HCB degradation intermediates from anaerobic enrichment were identified as pentachlorobenzene (PeCB), tetrachlorobenzene (TeCB), trichlorobenzene (TCB) and dichlorobenzene (DCB) with the retention time 16.31, 9.746, 12.06, 4.976 min and UV-absorption spectra 287.1, 229.3, 268.2, 284.8 nm (Figure 2).…”

“…Therefore, there has been an increase in effort to remove PCNB, HCB and their possible intermediates from the environment either by abiological or biological means during the past decades. The biotransformation products of PCNB include pentachloroaniline (PeCA), tetrachloroaniline (TeCA), trichloroaniline (TCA), dichloroaniline (DCA), chloroaniline (CA), pentachlorophenol (PCP), pentachlorothiophenol, pentachlorothioanisole and pentachloromethyl-phenyl sulfoxide [22-25]. The biotransformation products of HCB are pentachlorobenzene (PeCB), tetrachlorobenzene (TeCB), trichlorobenzene (TCB), dichlorobenzene (DCB), pentachlorophenol (PCP), tetrachlorohydroquinone (TeCH) and dichlorohydroquinone (DiCH) [14-16].…”