PAHs in Terrestrial Environment and their Phytoremediation 69

Based on the origin of production of PAHs, sources of PAHs can be categorized into three types,

i.e., pyrogenic, petrogenic and biogenic. Pyrogenic PAHs are produced when there is incomplete

combustion of fossil fuels at very high temperatures under anaerobic conditions. Petrogenic PAHs

are mainly present in crude and refined petroleum. These PAHs enter the soil during storage,

transport and leakage from oil refineries. Biogenic PAHs are produced by microorganisms, algae,

phytoplanktons and plants (Abdel-Shafy and Mansour 2016).

5.2.2 Effects of PAHs in Terrestrial Ecosystem

PAHs polluted soil can cause various health implications in humans and in other organisms (Abdel-

Shafy and Mansour 2016). Many PAHs are mutagenic and carcinogenic in nature. They act as

immunotoxins to various living organisms including microorganisms. Contamination of soil by

PAHs can affect the population and activity of microorganisms living in the soil (Singh and Haritash

2019). Overall microbial diversity in soil can also be affected as PAHs may have toxic effects

towards the microorganisms. When soil is highly contaminated with PAHs some adverse effects can

be seen such as tumors in invertebrate animals. High concentrations of PAHs in soil can also affect

development, immunity and reproduction of animals inhabiting that area. PAHs can be absorbed

by mammals through dermal contact with PAHs polluted soil (Tsibart and Gennadiev 2013). PAHs

can be absorbed by plants via roots and then transported to other parts of the plants. However,

phytotoxicity induced due to PAHs is of rare occurrence. PAHs can also enter food chain through

accumulation in plants. Water run-off from PAHs contaminated soils into the water bodies can cause

exposure of PAHs to seafood and fishes (Abdel-Shafy and Mansour 2016). In some studies, it is

reported that long term exposure of skin to PAHs causes skin cancer in animals.

Thus high levels of PAHs can prove fatal for various terrestrial animals. PAHs can leach from

soil and can contaminate underground water. Bathing with groundwater contaminated with PAHs

can cause skin problems. Dermal contact with soil contaminated with PAHs can cause redness of

skin, peeling or blistering. The health effects caused due to exposure of PAHs depend on the:

i. Quantity of PAHs entering the body

ii. Duration of exposure to PAHs

iii. Response of body to PAHs

Some tests are available to check the presence of PAHs in blood and urine. These tests cannot

predict the potential side effects of PAHs that entered the body. Cancer is the far most alarming side

effect of PAHs present in soil. Many PAHs present in soil are slightly mutagenic in-vitro but their

derivatives can be potent mutagens. The various effects of PAHs in terrestrial ecosystems are given

in Figure 5.1.

Effects of

PAH in soil

Acts as mutagens

and cause cancer

Affects aquatic life

Affects population and

activity of microorganisms

Water pollution through

surface run off from

polluted soil into

waterbodies

Acts as

immunotoxins

Phytotoxicity

Cause skin problems

and

Figure 5.1. Overview of effects of PAHs in soil.