**Author details**

Knowledge on the fate of heavy metals in soil–plant system is of great importance as that helps in predicting food quality especially in popular crops. Highest concentrations of heavy metals were recorded in the topmost layer of soils (Yedilar *et al*.,1994) and they reported that concen‐ trations in rice leaves and grains were lower than values observed in rice roots in China.

Composted sludge has high content of organic carbon which has the capacity of absorb‐ ing organic pollutants in soil thereby reducing their solubility as demonstrated by several authors (Hernandez-Soriano et al.,2007; Stevens-Garmons et al.,2012). In addition, organic carbon inputs might enhance the soil buffer capacity. The application of slightly acidic sewage (6.3), will also affect the mobility and bioavailability of metals present in soils. The evolution of heavy metal distributions and bioavailability depended not only on total metal concentration but also on other properties such as pH, organic matter decomposition and dissolved organic carbon (Miaomiao *et al*.,2009) and they reported that composting systems decreased soil pH, soil organic matter and dissolved carbon. Their results varied between sewage sludge and swine waste. In some studies conducted in China, soil pH, soil organic matter and clay content were used to predict phytoavailability of Cadmium in paddy soils,stating that pH negatively correlated with cadmium cont of soils (Krebs et al.,1998). Martinez and Motto, (2000) reported that solubility availability, mobility and toxicity of heavy metals to plants increases as pH decreases. In a study at Suwon, Korea. Kim *et al*. (2009) remarked that translocation of heavy metals depended more on the variety of crop

Polluted soils and soil-related natural resources can be decontaminated using living organisms including plant species classified as hyperaccumulators. Besides several microbial species can be used in bioremediation process since they can perform and efficient biodegradation activities. Efficacy in microbial degradation as well as microbial growth and activity are readily affected by edaphic characteristics like aeration, pH, temperature, and moisture. Bioremedia‐ tion ensures a minimum impact on the ecosystem, minimizing the presence of potentially toxic by-products after the process.. There are *ex situ* and *in situ* methods of bioremediation; but, most *in situ* bioremediation techniques are generally the most desirable options due to costeffectiveness and limited impact since they can be performed in situ; avoiding excavation and transport of contaminants. The *in situ*technique proves more affordable in rural communities with higher prevalence of poverty. The main drawback is associated with long-term character of bioremediation. However, most bioremediation techniques are constrained by high specificity of operation, long period of degradation and lack of acceptable endpoints of treatment. Further research is needed to overcome the time constraint of bioremediation processes as well and to increase the spectrum of activity of microbial species to address a

variety of wastes that are currently generated and entering the soil..

rather on soil physicochemical properties.

354 Environmental Risk Assessment of Soil Contamination

**7. Conclusion**

Emmanuel Uzoma Onweremadu\*

Address all correspondence to: uzomaonweremadu@yahoo.com

Department Of Soil Science and Technology, Federal University Of Technology, Owerri, Nigeria
