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Bioremediation for Sustainable Environmental Cleanup

PAHs released from the industries into the marine ecosystems are the main source of

contaminated marine ecosystems, whereas PAHs in the air are mainly from two sources which

include stationary (e.g., industrial production including power plant, coking plant, boiler and

waste incinerator and residential combustion like smoking, cooking, etc.) and mobile sources (e.g.,

exhausts from railways, motor vehicle, aircraft, etc.). PAHs in food (or the food cycle) is a major

health concern (Premnath et al. 2021). PAHs in the soil through the precipitation is carried to the

surface/groundwater and incorporated into crops, which after human consumption is accumulated

in human and other organisms via the food chain (Wang et al. 2018).

In terrestrial environment, PAHs are covered by the SOM (Soil Organic Matter) and soil

minerals due to their hydrophobic, lipophilic and semi volatile properties resulting in their decreased

degradation by microorganisms and finally their accumulation into the soil in large quantities

(Mazarji et al. 2021). Due to the carcinogenic toxicity of PAHs, there are strict regulations to limit

their release into the natural sources (Chatzimichail et al. 2021).

Out of 100 detected PAHs (parent and alkylated derivatives) 16 are listed in Clean Water

Act, 1972 (United States of America) which are presented in Table 5.1, whereas eight are listed

by European Commission (2013) due to their potential risk to mankind and ecological well-being

(Table 5.2) (Ofori et al. 2021).

Table 5.1. List of 16 PAHs under Clean Water Act, 1972 (USEPA 2014).

1. Chrysene

9. Napthalene

2. Acenaphthylene

10. Benzo[b]fluoranthene

3. Acenaphthene

11. Benzo[k]fluoranthene

4. Phenanthrene

12. Benzo[a]pyrene

5. Anthracene

13. Benzo[a]anthracene

6. Fluoranthene

14. Dibenz [a,h]anthracene

7. Fluorene

15. Benzo[g,h,i]perylene

8. Pyrene

16. Indo[1,2,3-cd] pyrene

Table 5.2. List of 8 PAHs under Water Framework Directive (European Commission 2013).

1. Napthalene

5. Anthracene

2. Benzo[b]fluoranthene

6. Fluoranthene

3. Benzo[k]fluoranthene

7. Indeno [1,2,3-cd]

4. Benzo[a]pyrene

8. Benzo[g,h,i]perylene

5.2.1 Sources of PAHs in Soil

PAHs are mainly produced when there is incomplete combustion of coal, wood, gas, oil and

garbage. Petroleum product spillage and various domestic and industrial activities are known to

produce PAHs (Singh and Haritash 2019). PAHs can be released in the environment and can be

found dispersed in soil, air and water (Wang et al. 2018, Singh and Haritash 2019). Since PAHs are

hydrophobic and lipophilic in nature, soil remains a vital sink for PAHs. There are studies which

report that about 90% of PAHs can be stored in soil (Wang et al. 2018). When water contaminated

with PAHs is used to irrigate soil, it also acts as a source of PAHs in soil (Tsibart and Gennadiev

2013). PAHs can also be incorporated in crops through soil (containing PAHs) which can result in

accumulation of PAHs in human and other organisms through food chains (Wang et al. 2018). There

is thus, a dire need to monitor the concentration of PAHs in soils. Sources of PAHs in soil can be

mainly classified into two categories: (1) Natural sources; (2) Anthropogenic sources (Tsibart and

Gennadiev 2013). Natural sources of PAH refer to various cosmic, geological and biological factors

which favor the formation of PAHs (Tsibart and Gennadiev 2013). On the other hand, anthropogenic

sources of PAHs include various human activities which contribute to the production of PAHs in

soil. Production of cement, aluminium, asphalt, creosote and various petrochemical industries come

under anthropogenic sources of PAHs in soil.