2.3. Effects of polychlorinated biphenyls (PCBs) on human health

PCB mixtures have been associated with cancer incidents in animals from long time back [17, 28, 29]. PCBs were found to induce liver tumors, thyroid adenomas, intestinal metaplasia, and adenocarcinomas in rats and mice [29]. Exposure to some environmental chemicals such as DDT and PCBs has been associated with a drop in sperm count, breast cancer, testicular cancer, and hypospadias, which are all associated with endocrine disruption caused by these chemicals [30]. This comes as a result of some PCB congeners being able to occupy thyroid receptors, thus interrupting their action [17, 30].

PCBs accumulate in the fats of organisms and get passed on from one organism to the other in food chains [31, 32], thus causing bioaccumulation. They get entry into the human body and animals through the skin, lungs, and gastrointestinal tract [13]. PCBs then get distributed to various parts of the body via blood and accumulate in different tissues [31, 33]. The effects of PCBs on humans depend on age, sex, and part of the body affected by chemicals [13]. The liver, as the major organ for removal of toxins in the body, is usually highly affected by PCBs [13, 29]. Humans become exposed to PCBs through consumption of contaminated fish, meat, and dairy products [28] and also through grains grown in PCB contaminated soils [13, 28]. PCBs have been isolated from human milk and serum [31, 34] and have been found to have effects on breastfed children leading to low IQ and endocrine-related ailments [28, 31, 34]. Some studies have shown an increase in cancer mortality in workers exposed to PCBs [13].

#### 2.4. Biodegradation

Biodegradation is the metabolic ability of microorganisms to transform or mineralize organic contaminants into less harmful, non-hazardous substances, which are integrated into natural biochemical cycles [27, 35]. Specific bacteria having bio-degradative potential for various chemical substances in wastewater as well as raw water may be used to treat water [35] for purposes of safe recycling. Bacteria, unlike other organisms, have the ability to interact better with man-made and naturally occurring compounds, which result in such compounds being changed structurally and eventually degraded [35]. This is in a way a better cleanup strategy that can be used in the cleanup of wastewater as it is environment friendly [35]. Use of mixed population of microbes is usually recommended as it has been seen to yield faster results as the two different microbes attack different parts through different mechanisms resulting in effective breakdown of the toxic compound [21, 33]. This activity also creates a condition of cometabolism [33].

PCBs may not be readily biodegradable, but studies have shown that some bacteria species such as Vibrio cholera, Acinetobacter 1woffnii, Aeromonas hydrophila, Pseudomonas aeruginosa, Pseudomonas putida, Rhodococcus sp., Bacillus sp., and Burkholderia sp. have the ability to breakdown these compounds, although it is through a very long route [11, 13, 21, 36, 37, 51]. This may be achieved through co-metabolism and mineralization [8, 35]. They use of a metabolic pathway similar in all these bacteria, which comprise four steps catalyzed by enzymes BphA, BphB, BphC, and BphD [37]. The pathway, according to Petric et al., is initiated by insertion of two oxygen atoms at the carbon positions 2, 3 of one aromatic ring [37]. This is followed by dehydrogenation meta-cleavage and hydrolysis forming a 5-carbon compound [37]. The process follows a biphenyl catabolic pathway [37].

#### 2.5. Biodegradation of xenobiotic compounds

environment through various human activities [24]. Water has become a widely used environmental matrix for monitoring POPs [20, 25, 26], although most studies on PCBs have been

The destruction of PCBs by chemical, thermal, and biochemical processes is extremely difficult and presents the risk of generating extremely toxic dibenzodioxins and dibenzofurans through

PCB mixtures have been associated with cancer incidents in animals from long time back [17, 28, 29]. PCBs were found to induce liver tumors, thyroid adenomas, intestinal metaplasia, and adenocarcinomas in rats and mice [29]. Exposure to some environmental chemicals such as DDT and PCBs has been associated with a drop in sperm count, breast cancer, testicular cancer, and hypospadias, which are all associated with endocrine disruption caused by these chemicals [30]. This comes as a result of some PCB congeners being able to occupy thyroid

PCBs accumulate in the fats of organisms and get passed on from one organism to the other in food chains [31, 32], thus causing bioaccumulation. They get entry into the human body and animals through the skin, lungs, and gastrointestinal tract [13]. PCBs then get distributed to various parts of the body via blood and accumulate in different tissues [31, 33]. The effects of PCBs on humans depend on age, sex, and part of the body affected by chemicals [13]. The liver, as the major organ for removal of toxins in the body, is usually highly affected by PCBs [13, 29]. Humans become exposed to PCBs through consumption of contaminated fish, meat, and dairy products [28] and also through grains grown in PCB contaminated soils [13, 28]. PCBs have been isolated from human milk and serum [31, 34] and have been found to have effects on breastfed children leading to low IQ and endocrine-related ailments [28, 31, 34]. Some studies

Biodegradation is the metabolic ability of microorganisms to transform or mineralize organic contaminants into less harmful, non-hazardous substances, which are integrated into natural biochemical cycles [27, 35]. Specific bacteria having bio-degradative potential for various chemical substances in wastewater as well as raw water may be used to treat water [35] for purposes of safe recycling. Bacteria, unlike other organisms, have the ability to interact better with man-made and naturally occurring compounds, which result in such compounds being changed structurally and eventually degraded [35]. This is in a way a better cleanup strategy that can be used in the cleanup of wastewater as it is environment friendly [35]. Use of mixed population of microbes is usually recommended as it has been seen to yield faster results as the two different microbes attack different parts through different mechanisms resulting in effective breakdown of the toxic compound [21, 33]. This activity also creates a condition of co-

have shown an increase in cancer mortality in workers exposed to PCBs [13].

carried out on contaminated soils than water [27].

receptors, thus interrupting their action [17, 30].

2.3. Effects of polychlorinated biphenyls (PCBs) on human health

partial oxidation [12, 16, 27].

142 Wastewater and Water Quality

2.4. Biodegradation

metabolism [33].

According to Heider and Rabus, xenobiotic compound due to its recalcitrant nature is hard to break down [38]. The recalcitrant nature of these compounds is a result of the complexity of its chemical composition [8]. Breakdown of these compounds occurs when enzymes act on certain groups present in the compound [38]. The halocarbons, for example, the halogen group, are targeted, with enzymes such as oxygenases playing a major role in their breakdown [8]. The enzymes target the bonds such as ester-, amide-, or ether bonds present in the compounds leading to break down of these compounds [39, 40]. The enzymes may target the aliphatic chains and in aromatic compounds, the aromatic components may be targeted [40]. The mode of attack as well as the site depends primarily on the action of enzyme, its concentration, and favorable conditions [40]. According to Abor-Amer [40], the xenobiotics do not act as a source of energy to microbes and as a result, they are not degraded while the presence of a suitable substrate induces its breakdown [39]. These substrates are known as co-metabolites, and the process of degradation is known asco-metabolism [39]. Gratuitous metabolism is another process in which xenobiotics serve as substrates and are acted upon to release energy [8].

The processes described cannot be achieved through the use of Moringa oleifera in treating wastewater to remove PCBs. It is evident from literature that the removal of these compounds using plant protein has not been fully studied [52]. Plant protein has been found to be slightly efficient with the reduction of fecal coliforms and other bacteria [41, 42], which has made Moringa treatment to be applicable. The use of Moringa oleifera seed powder in water treatment plants has been found to target mainly microorganisms, thus reducing turbidity [43]. Although this mode of water treatment has been used, especially in rural areas of the developing countries, synthetic polymers, aluminum sulfate, ferric chloride, and poly aluminum chlorides used together with this powder have been reported to be unsafe [41, 43, 44]. The action of Moringa oleifera seed powder has been reported to be based on the ability of the protein contained in the seeds to be able to form coagulants, which reduce water turbidity by acting on coliforms [45]. The bacteria found to be mainly involved in biodegradation of POPs and PCBs have been found mostly not to be coliforms [11, 13]. After treating water with Moringa seed powder, 10<sup>1</sup> –105 of bacteria is left [45]. Taking into cognizance that Moringa is a tree, sustainability of tree growth and productivity, which relies on environmental conditions, may not be viable. This will therefore affect production and maintenance of the Moringa tree species, given the global warming and related environmental problems. Growing of bacteria indoors is quite sustainable, when compared to growth of plants although Lea argues that propagation is affordable [44].

of anhydrous sodium sulfate mixed with a PCB-containing solvent to remove residual water. The extract was concentrated to 1.5 ml using a rotary evaporator Stuart RE300DB, LASEC, South Africa and filtered with 0.45 μm PTFE syringe filters. Extracts were analyzed by high performance liquid chromatography (HPLC) UFLC Shimadzu using a florescence detector pump RF-20A and system gold column C18 (CTO-20A). The excitation level was set at 254 nm, emission level at 390 nm. The mobile phase used was a mixture of acetonitrile and water (80:20) as described by Roy et al. [46]. Data analysis was computed using real-time analysis. All chemicals used were of HPLC grade supplied by Sigma Aldrich through

The Role of Bacteria on the Breakdown of Recalcitrant Polychlorinated Biphenyls (PCBs) Compounds in Wastewater

http://dx.doi.org/10.5772/intechopen.75400

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Samples of wastewater from the Notwane Sewage Treatment Plant were used in this study to find out the degree of biodegradation of PCBs in wastewater un-inoculated and inoculated with the test organism. Spectral changes (a shift in wavelength (λmax) in nm), detected using the UVvisible spectrophotometer, were used as an indication that the compounds were broken down into new products. The results of the wavemax (λmax) nm obtained are presented in Figure 2.

The results shown by chromatogram indicated that there was a shift in λmax from 224 to 270 nm in 0 h of incubation to 96 h of incubation at 30C on a rotary shaker in the dark. These results were obtained using a Cary 300 UV-visible spectrophotometer at a wavelength range of 200–800 nm. The results were an indication that isolates Pseudomonas aeruginosa was able to degrade Aroclor 1260 into chlorobenzoates and derivatives, which have wavelength ranging

Figure 2. Spectral changes of PCB degradation in water inoculated with isolate Pseudomonas aeruginosa.

Lehlabile Scientific, South Africa.

4.1. Degradation of PCBs by Pseudomonas aeruginosa

from 244 to 270 nm, hence the shift in wavelength.

4. Results
