Biodegradation of HCB under anaerobic conditions

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1-2- Biodegradation of HCB[1]

1-2-1- Degradation of HCB under anaerobic condition:

In the past decade, the usage of HCB prohibited in many country but HCB has been found as hazardous pollutants in many places worldwide. Biodegradation of HCB is possible in environmental under anaerobic conditions such as sodium, groundwater and soil but the progress is very slowly (Beurskens and others, 1992; Chang and others, 1997). Some reports documented about biodegradation in sediments (Chen and others, 2002; Chen and others, 2004; Hirano and others, 2007; Pavlostathis and Prytula, 2000; Prytula and Pavlostathis, 1996), soil (Watanabe and Yoshikawa, 2008). Degradation of CLD[2] in anaerobic sewage sludge was reported by (Fathepure and others, 1988), The authors observed greater than 90% pesticide removal after 3 weeks. The only Three strains of bacteria capability of degrading Hexachlorobenzene via reductive dechlorination have been isolated (Taş and others, 2011), that including Dehalobium chlorocoercia DF-1 (Wu and others, 2002), Dehalococcoides ethenogenes strain 195 and Dehalococcoides sp. strain CBDB1and (Adrian and others, 2000; Fennell and others, 2004; Taş, 2009; Taş and others, 2009).

1-2-2- Metabolites and Mechanism of Anaerobic Dechlorination

Anaerobic degradation reductive dechlorination of HCB was first reported in 1987 (Fathepure and others, 1988). So far, the pathway that is known for the microbial degradation of HCB under anaerobic canditions by coupling reductive dehalogenation to electron transport (Beurskens and others, 1994; Chen and others, 2000; Hirano and others, 2007; TaÅŸ and others, 2011). Chlorinated aromatics can serve as electron acceptors (Fathepure and others, 1988). Reductive dechlorination pathways is shown in figure 1 and HCB were dechlorinated via 1,2,3,5-and 1,2,4,5-tetrachIorobenzene (TeCB), 1,3,5- and 1,2,4-TCB , 1,2,4-TCB[3] and 1,3-DCB[4] . they are final dechlorination products (Beurskens and others, 1992; Boyd and others, 1987; Fathepure and others, 1988; Holliger and others, 1992).

1-3- Biodegradation of DDT[5]

1-3-1- Degradation of DDT under anaerobic condition:

DDT was the first synthetic insecticide. Nowadays, use of this persistent organic pollutants is prohibited in most countries, but still DDT is ubiquitous in the environment all (Purnomo and others, 2011; Sudharshan and others, 2012). DDT can be biodegradation or mineralized by multistep processes in both aerobic and anaerobic condition. For example sediments capibilty of utilizing persistent pesticides and degradation even mineralized by aerobic and anaerobic degradation (Fang and others, 2014). Thus far, species within the genera Pseudomonas (Chacko and Lockwood, 1967; Kamanavalli and Ninnekar, 2004), Sphingomonas (Chacko and Lockwood, 1967; Fang and others, 2014), Desulfomonile tiedjei (DeWeerd and others, 1990) and Eubacterium limosum (ATCC 8486) is isolated from the human intestine (Yim and others, 2008), and Alcaligenes denitrificans (Ahuja and Kumar, 2003)‎ have been found to metabolize DDT. (Corona-Cruz and others, 1999), reported anaerobic coupled with aerobic biodegradation of DDT and maximum DDT degradation of 84.4 %.

1-3-2- Metabolites and Mechanism of Anaerobic Dechlorination

Biodegradation pathway of DDT is multistep process in anaerobic environment, involving reductive dechlorination, dioxygenation, hydrogenation, hydroxylation, decarboxylation, hydrolysis (a major transformation pathway in soil and water in the presence of H2O, H+, and OH¯ ), and meta-ring cleavage reactions. Biodegradation pathway of DDT is multistep process in anaerobic environment involving reductive dechlorination such as three degradation step (DDT→DDD,DDE[6]), hydrogenation, dioxygenation, hydroxylation, decarboxylation and meta-ring cleavage reactions(Rangachary and others, 2012). That is different from the degradation pathways for anaerobic biodegradation but high-order metabolites such as DDA, DDOH[7] and DDNU (Aislabie and others, 1997). (Wedemeyer, 1967), reported first metabolic pathways for DDT by aerobacter aerogenes that shown at the bottom:

DDT → DDD[8] →DDMU[9] →DDMS[10] → DDNU[11] → DDA[12] → DBP[13], or DDT → DDE.

Researches were lack of information about DDT degradation. Later, (Planche and others, 1979) indicted DDE could be degraded to DDMU by a microcosm under anaerobic sediments.biodegradation pathway in sediment shown on figure 2. DDT and its metabolites in the sediment:

DDT →DDD → DDMS and DDE → DDMU (Li and others, 2010; Quensen and others, 2001; Sudharshan and others, 2012) and the relative transformation rates of DDT, DDE, and DDD is DDT>DDD>DDE (Huang and others, 2001), so DDD was the major biodegradation product of DDT under anaerobic environments (Mwangi and others, 2010; Yu and others, 2011). DDT metabolic reports in human intestinal gut by (Yim and others, 2008), that Eubacterium limosum transformed DDT completely to DDD and used DDT as electron donors.

1-4- Biodegradation of heptachlor

1-4-1- Degradation of heptachlor under anaerobic condition

Heptachlor used as insecticide. Heptachlor is mostly persistent in environment (Sakai and others, 2008). Under anaerobic conditions, heptachlor is showed only limited conversion (Hill and McCarty, 1967). The data available on this substance indicate that heptachlor is degraded for more than several years in soil (Lichtenstein and others, 1970; Mahugija, 2014; Miles and others, 1969). (Sethunathan and Yoshida, 1973), this paper is a research about Clostridium sp. that isolated from flooded soil for degradation γ-BHC and heptachlor.

1-4-2- Metabolites and Mechanism of Anaerobic Dechlorination

It is not readily biodegraded but it is transformed biologically in both situations aerobic and anaerobic, mainly to the stable heptachlor epoxide (Lichtenstein and others, 1970). (Hayashi and others, 2013) , have reported that heptachlor was degraded a small amount to heptachlor epoxide in soil. Figure3 shown this degradation pathway.

1-5- Biodegradation of endrin and dieldrin

1-5-1-Degradation of endrin and dieldrin under anaerobic condition

Of the year 1960s began studies on biodegradation of endrin and dieldrin that more researches were reported about the aerobic biodegradation (Matsumoto and others, 2009). Biodegradation of dieldrin and endrin was reviewed in 2007 and 1982 (Lal and Saxena, 1982; Matsumoto and others, 2009). (GOWDA and Sethunathan, 1977), studied that endrin proceeded under anaerobic conditions in three soils by radiotracer technique. Thay have reported anaerobic microbial strains could degrade various types of POPs such as ,heptachlor, dieldrin, aldrin, endrin and HCB. These strains isolated from PCB-contaminated sediment. (Baczynski and others, 2004), reported that methanogenic granular sludge could dechlorination of cyclodiene pesticides such as dieldrin and endrin.(Baczynski and others, 2004), studied methanogenic granular sludge with purpose dechlorinate dieldrin and endrin. Biodegradation studies under anaerobic conditions are summarized in Table 2.

1-5-2- Metabolites and Mechanism of Anaerobic Dechlorination

Deldrin has simple mechanism reported by (Maule and others, 1987) that is the deletion of the chlorine atom from chlorinated hydrocarbon. (Chiu and others, 2005), reported cleaving the epoxide ring by a mechanism of epoxide reduction by anaerobic enrichment culture obtained from river sediment. So, they are the Transformation of deldrin to aldrin then aldrin is converted to two syn- and anti-monodechlorodieldrin metabolites by epoxide reduction. Researches show only two monochlorinated metabolites of endrin under anaerobic transformation so it can say bacteria have a catalyzed role in reductive dehalogenation (Matsumoto and others, 2009).

1-6- Biodegradation of lindane and HCH-isomers

1-6-1-Degradation of lindane and HCH-isomers under anaerobic condition

Lindane and the other HCH isomers have been used in agriculture as a pesticide. There are little knowledge about anaerobic HCH degradation. It has not been reporte on the anaerobic biodegradation of the ε –HCH (Lal and others, 2010). While the four HCH isomers can degrade under anaerobic conditions .Thus far, species within the genera Dehalobacter (Doesburg and others, 2005), Clostridium spp (Jagnow and others, 1977; MacRae and others, 1969), Bacillus circulans and Bacillus Brevis (Gupta and others, 2000) and two Desulfovibrio species (Boyle and others, 1999), Citrobacter (such as ,C. butyricum, C. pasteurianum and Citrobacter freundii) (Heritage and MacRae, 1977; Heritage and Rae, 1977), Desulfococcus (Elango and others, 2011) and Desulfobacter curvatus (Badea and others, 2009) have been found to metabolize the lindane and HCH-isomers.

(Van Eekert and others, 1998), have studied, capable of degrading beta-HCH by methanogenic granular sludges from upflow anaerobic sludge blanket (UASB) reactors fed. A number of studies have utilized for degradation isomer-HCH of anaerobic mixed bacterial culture such as (Kohnen and others, 1975) that mixed culture consisting of Bacilli. Mixed culture Clostridia and C. butyricum, C. pasteurianum and Citrobacter freundii. Thay are shown degradation rate in the following order γ-HCH > α-HCH > β-HCH = δ-HCH (Jagnow and others, 1977). (Pesce and Wunderlin, 2004) isolated bacteria from sediment and have used in aerobic mixed bacterial culture including Bosea thiooxidans and Sphingobacterium paucimobilis, degraded HCH after 3 days.

1-6-2- Metabolites and Mechanism of anaerobic Dechlorination

the mechanism of biotransformation of HCH-isomer and lindane under anaerobic condition is explained with detection of intermediates substance of the presumed pathway. According to papers and reports, intermediates of HCH such as TeCCHs[14], PeCCHs[15] , PCCHa[16] (Buser and Mueller, 1995). (Tsukano and Kobayashi, 1972), abserved TeCCH flooded rice field soils treated with lindan but this intermediates was not found in soils treated with sodium azide or in soils without lindane treatment. suggested two degradation pathway for HCH isomers under anaerobic conditions, Based upon identify the intermediates material

gama-, alfa-HCH → PCCHa (with a dechlorination) → 1,2-DCB[17] → 1,3-DCB→ finally CB

for β- and δ-HCH → TeCCH → 1,2,3-TCB → 1,2-DCB → 1,4-DCB → CB[18]

The other Simpler pathway for the reductive dehalogenation of HCH is:

HCH → TeCCH → dichlorocyclohexadiene ( DCCH) → finally benzene (Doesburg and others, 2005; Lal and others, 2010). Most papers of anaerobic degradation reported the accumulation of benzene and chlorobenzene (Buser and Mueller, 1995; Middeldorp and others, 1996; Zhu and others, 2005).

that Figure3 shown this pathways.

1-7- Biodegradation of Methoxychlor

1-7-1-Degradation of Methoxychlor under anaerobic condition

Methoxychlor [1,1,1-trichloro-2,2-bis(p-methoxyphenyl) ethane] is a hazardous substance and stable for this reason, is one of POPs. Methoxychlor have a half-life < less than 28 days under anaerobic conditions in sediments also in soils. (Satsuma and Masuda, 2012), this paper to studied seven bacteria that ability to dechlorinate methoxychlor in aerobic and anaerobic conditions. This seven environmental bacterial species including: Enterobacter amnigenus, Aeromonas hydrophila, Bacillus subtilis,Klebsiella terrigena, Mycobacterium obuense, Acinetobacter calcoaceticus, and Achromobacter. Biodegradation studies of OCPs under anaerobic conditions are summarized in Table 2.

1-7-2- Metabolites and Mechanism of anaerobic Dechlorination

Microbial species and pathway dechlorination of methoxychlor in the environment are not well-known or there are few reports (Castro and Yoshida, 1971; Masuda and others, 2011b). Enterobacter aerogenes were capable of degrading methoxychlor to DMDD [19] under anaerobic conditions (Mendel and Walton, 1966). Eubacterium limosum is a bacteria from human intestine that has been able degrades of methoxychlor to 1,1-dichloro-2,2-bis(pmethoxyphenyl) ethane (methoxydichlor) (Yim and others, 2008). Also, K. pneumoniae converts methoxychlor to [1,1-dichloro-2,2-bis(4-methoxyphenyl)ethane, de-Cl-MXC] (Baarschers and others, 1982).

[1] hexachlorobenzene (HCB)

[2] Chlordane (CLD)

[3] -trichlorobenzene (TCB)

[4] 1,3-dichlorobenzene (1,3-DCB)

[5] 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)

[6] 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (DDE)

[7] 2,2-bis(p-chlorophenyl)ethanol (DDOH)

[8] 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (DDD)

[9] 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (DDMU)

[10] 1-chloro-2,2-bis-(p-chlorophenyl)ethane (DDMS)

[11] 2,2-bis(p-chlorophenyl)ethylene (DDNU)

[12] 2,2-bis(p-chlorophenyl)acetic acid (DDA)

[13] 4,4-dichlorobenzophenone (DBP)

[14] tetrachlorocyclohexenes (TeCCHs)

[15] pentachlorocyclohexenes (PeCCHs)

[16] pentachlorocyclohexanes (PCCHa)

[17] dichlorobenzene (DCB )

[18] Chlorobenzene

[19] bis(p-methoxyphenyl)-1,1–dichloroethane (DMDD)