Soil plays crucial and strategic life-supporting roles as man and many other living organisms depend directly or indirectly on if for food and shelter. In spite of this fact, the soil is constantly subjected to various forms of abuse, including heavy metals pollution. The ecological destructive effect, high cost, and intensive labour requirement associated with ex situ physico-chemical remediation methods make the search for in situ remediation techniques inevitable. This paper gives an update on the remediation techniques that can be carried out in situ. Included in the review are more recent biological remediation methods, like vermiremediation, which are especially eco-friendly, cost effective, and sustainable.

Soil contamination from heavy metals and polycyclic aromatic hydrocarbons (PAHs) from dumpsite, automobile mechanic workshop and metal scrap sites pose human and ecological health risks. This study assesses the levels of heavy metals and PAHs in soils from these sites and their effects on the DNA yield and fragmentation of native plants around there. The DNA yield and fragmentation were compared to those obtained from non-polluted sites (control). DNA of the plants species, Musa acuminata (banana), Jatropha curcas (Barbados nut), Carica papaya (pawpaw), Axonopus compressus (carpet grass), Sida acuta (wireweed), and Eleucine indica (crabgrass grass) for polluted sites and control were analyzed using Gel electrophoresis. Soil heavy metals; copper (Cu), zinc (Zn), lead (Pb) and chromium (Cr) were evaluated from dumpsite, metal area and mechanic workshop using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Polycyclic aromatic hydrocarbons were also determined from soils of the polluted sites using the GC/MS spectrophotometry. The result obtained from the DNA analysis showed that DNA yield and fragmentation of the polluted plants had higher indices than the controls which shows that heavy metals and polycyclic aromatic hydrocarbons affect the DNA of the plants. The effects of the pollutants on DNA of polluted plants had more smearing in their tissue than non-polluted plants. Heavy metals evaluation showed that zinc level was the highest in all the study sites; dumpsite, metal area and mechanic workshop (5.146 mg/kg, 2.709 mg/kg and 1.990 mg/kg respectively) than the control (p<0.05). Chromium was the least present (0.022 mg/kg, 0.018 mg/kg and 0.002 mg/kg respectively). The results of this study indicate that dumpsite, mechanic workshop and metal scrap sites are potential sources of PAH and toxic metal, which can pose serious human health and ecological risks.

Previous researches have shown the presence of heavy metals (HMs) such as lead (Pb) at different levels in Olusosun dumpsite, Lagos. This study aimed at finding out if the anatomical differences found in Luffa cyclindrical and Amaranthus viridis grown on the dumpsite is an indication of the HMs and also determine the distribution of HMs on the dumpsite. The results showed the HMs detected in the dumpsite soil at three spots were significantly higher than the control (p=0.5). The concentrations of HMs were in sequence for soils A: Pb>Zn=Cr>Fe>Cu>Ni. Spot B: Fe>Cr>Pb>Zn>Cu>Ni, spot C: Fe>Pb>Cr>Zn>Cu>Ni and Control: Pb>Fe>Zn>Cu>Ni. All the HMs detected at the three spots and control were below the World Health Organization (WHO) and Dutch pollutant standard level, except for (Zn) which was at the exact limit (50.000Mg/kg). The plants obtained from both the dumpsite and control sites didn't show marked visible morphological changes. However, anatomical changes in the leaves epidermis such as irregular shape of the epidermis, absence of trichomes and decrease in quality and stomata size were all witnessed in the dumpsite plant as against the control. Hence, it is likely that all detected differences in the epidermal structures of the test plant grown on dumpsite soil were caused by the high level of HMs present in the dumpsites and therefore suggested that, changes in epidermal structures of L. cyclindrical and A. viridis grown on Olusosun dumpsite soils is an indication of HMs such as Zn and Pb present.