Contaminants’ characteristics, behavior, and their fate

Due to their toxicity, persistence, and noil-biodegradable namre, trace metals containing mercury, arsenic, lead, cadmium, copper, zinc, nickel, chromium, and organic pollutants in soil and water have drawn considerable attention worldwide (Yang et al. 2009). These contaminants in the environment may accumulate in aquatic flora, fauna, and microorganisms, which may enter the food chain and consequently appear in humans (Varol 2011, Shukla et al. 2012). These contaminants may be anthropogenic as well as natural in origin. To prevent environmental pollution, especially soil and water, and to improve the ecosystem’s health, it is essential to thoroughly understand the contamination characteristics of pollutants in ecological segments and target their potential sources (Sakan et al. 2009, Shukla et al. 2014).

Petroleum and other hydrocarbons are a complicated mixture composed mainly of carbon and hydrogen, in which most of the alkanes are determined to be narcotic and irritant, and most of PAHs have substantial toxicity, carcinogenicity, teratogenicity, and mutagenicity (Kao et al. 2008, Shukla et al. 2014). Many oil pollutants in the water cause severe pollution to the water ecosystems and are detrimental to the health of living creatures and human bodies (Zhang et al. 2003).

Once contaminants are in soils, where they go and how quickly they travel depends on several factors. Few organic pollutants can undergo chemical modifications or degrade into products that may be toxic than the original compound (Garrison et al. 2000, Newman and Reynolds 2004). The chemical elements which cannot break down, but then characteristics may change, can be quickly taken up by plants or animals. Many contaminants vary in their tendency to end up in water held in the soil or in the underlying groundwater (by leaching through the land), volatilize (evaporate) into the air, and bind tightly to the soil (Shayler et al. 2009).

Biological and physico-chemical processes usually bound the presence of organic contaminants in soils. It includes sorption-desorption, volatilization, and bio-chemical degradation, uptake by plants, run-off, and leaching (Mamy et al. 2005). The pattern (horizontally and vertically) of organic pollutants in soils depends on their action and degradation. Movement and degradation of organic contaminants, in him, depend on three common factors: (i) Chemical and biological properties of the pollutant, (ii) hydraulic properties of the soil, and (iii) weather conditions. Movement of the organic pollutants can be due to diffusion and mass flow (Mamy et al. 2005, Todorovic 2009).

Bioremediation also requires minimal effort and can often be carried out on-site, usually without causing a significant separation of normal activities. That also reduces the need to transport loads of waste off-site and potential risks to human health and environment that can arise during transportation (NAP 1993, Slianna 2012). It is also a cost-effective process as it costs less than the other conventional methods that are used for cleaning up of hazardous waste. It also helps in the destruction of the pollutants; many of the dangerous compounds can be transformed into harmless products. It does not use any hazardous chemicals (NAP 1993).

Bioremediation is excellent for biodegrading organic pollutants. Common examples of organic contaminants that respond to bioremediation include petroleum hydrocarbons (PAHs), nou-clilorinated chemicals (e.g., acetone), wood treatment chemicals (e.g., creosote and pentachloropheuol (PCP), certain chlorinated aromatic compounds (e.g., chlorobenzenes and biphenyls) and certain chlorinated aliphatic compounds (e.g., trichloroetheue (TCE)) (USEPA 2001a). Inorganic contaminants such as heavy metals from acid mine drams (AMD) are often treated using bioremediation techniques (NAP 1993, Slianna and Reddy 2004). Table 1 below shows the behavior of pollutants.

Table 1. Behavior of contaminants.