Assessment of Some Heavy Metals as Contaminants in Petroleum Contaminated Soils of Eleme, Port Harcourt Nigeria
Abstract
Samples from petroleum contaminated soil of Eleme, Port Harcourt and from non petroleum contaminated soil, Awka, Nigeria serving as control were analyzed for heavy metals. The results of the analysis showed that the metals concentrations in mg/kg were Ni <0.05- 2.05, Cr 0.005- 0.37, Cd <0.005- 0.008, Zn 0.14 – 2.87 Pb <0.02- 0.19 Fe 12.32- 29.11, Mn < 0.008- 0.036, Se <0.001, as <0.001, and V <0.001. Majority of the metal concentrations were above those of the control. Though the values obtained did not exceed soil quality standards stipulated in the Environmental Management Regulations, 2007, the toxic metals could accumulate to a threatening level over a period of time. Food poisoning, occupational hazards and various disorders emanate from heavy load of toxic metals in our environment.
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Introduction
Environmental pollution may result from industrial and commercial activities when substances resulting from these activities enter the environment and attain levels which may cause discomfort and / or harm to man and his environment (Udosen et al, 1990). From the point of view of environmental pollution, metals may be broadly classified into three categories namely, non-toxic but accessible, toxic but non-accessible and toxic and accessible .It is the third category that has attracted more attention from the point of view of environmental pollution and public health (Dara, 2008).
The toxic metals occur in very small quantities in the earth’s crust (less than 1000ppm) and hence are called “trace metals”. These are further arbitrarily subdivided on the basis of their densities. Those having densities below 5g/cm3 are called light metals and those with densities above 5g/cm3 are designated as heavy metals (Dara, 2008; Santra, 2005). The main threats to human health from heavy metal (HM) are associated with exposure to cadmium, lead, mercury and arsenic but additionally, there are other 19 elements known as heavy metals: antimony, bismuth, cerium, chromium, cobalt, copper, gallium, gold, iron, manganese, nickel, platinum, silver, tellurium, thalium, tin, uranium, vanadium and zinc (Fernandez-lugueno et al.,2013). Some heavy metals are essential for living organisms but high concentrations or accumulation in a physiological system is detrimental or injurious to health especially where such metals are found above maximum allowable levels (Hough et al., 1982; Nigerian Industrial Standard (NIS), 1983). Large amounts of any of them may cause acute or chronic toxicity referred to as poisoning (Kabata-Pendras and Mucherjee, 2007).Heavy metals accumulate in topsoil and at larger concentrations can poison important soil microbial groups, crops and food (Chaudri, 2001). In areas with high concentrations, metallic contamination of food and water probably led to the poisonings (Gilman et al., 1975). A disaster resulting from heavy metal contamination was the minamata disease in Japan caused by methyl mercury poisoning (Christian et al, 1974). The mercury poison was through food chain build-up which occurred in Japan’s minamata bay which received industrial waste containing mercury compounds.
Conclusion
In order of decreasing magnitude, the average heavy metal content in the top soil samples are as follows: Fe (12.32-29.11)> Zn (0.14-2.87)>Ni (<0.05- 2.05)> Cr (<0.005-0.37)>Pb (<0.02-0.19)>Mn(<0.008-0.036)>Cd(<0.005-0.008)>V(<0.001), As(<0.001) and Se(<0.001). Majority of the metal concentrations were higher than control except Ni in samples A, C, D, E, F, Cr in sample B, Pb in sample A, Fe in sample B, Mn in samples A, D and E. All vanadium and arsenic concentrations fell below or equal to the detection limit. The average concentration of all the metals were compared with soil quality standards stipulated in the Environmental Management Regulations, 2007 and the results show that they were all within the standards. However, they could accumulate to a threatening level over a period of time (Gilman, 1975; Adejumobi, 2005).