Evaluation of Heavy Metal Pollution in the Suame Industrial Area, Kumasi, Ghana.

Background
Heavy metal pollution in industrial and residential areas in cities has become a public health issue in Ghana. Anecdotal evidence suggests that most industrial areas have elevated levels of heavy metals in soil. As a result of poor zoning and unregulated activities, large sections of seemingly industrial areas are also used as residential areas. There have been no studies on the levels of heavy metal contamination in such mixed activity locations.


Objectives
The study was undertaken to identify possible heavy metals and their concentrations in soil samples collected from the Suame Industrial Area, Kumasi, Ghana.


Methods
Soil samples were collected, processed and the concentration of copper (Cu), lead (Pb), zinc (Zn), cobalt (Co) and chromium (Cr) were analyzed using X-ray fluorescence (XRF).


Results
The concentration of all metals exceeded the threshold limit values (TLV). They also exceeded the European Soil Bureau Network (ESBN) maximum allowable limits (MAL), and are therefore considered to be pollutants. The results, expressed as mean concentration±standard deviation mg/kg (percent above TLV) were Pb: 414.83±159.38 mg/kg (418.9%), Cr: 264.84±189.15 mg/kg (353.1%), Co: 68.15±34.12 mg/kg (227.2%), Cu: 265.82±80.53 mg/kg (354.4%) and Zn: 3,215.84±4,074.54 mg/kg (1,607.9%). Furthermore, the concentrations of Pb and Co exceeded the United States Environmental Protection Agency (USEPA) residential soil regional screening levels (RSLs).


Conclusions
The elevated metal concentrations found in the present study demonstrate that the site is heavily polluted with Pb, Co and Cr. This is attributed to unregulated activities at the site; therefore, measures should be put in place to ameliorate the effects of potential heavy metal toxicity to workers, local residents and the environment. Re-zoning of activities and clear demarcation of residential and industrial areas is advocated.

Heavy metal pollution of soil samples from some of these localities is of great concern because of the dangers posed to workers, inhabitants and the environment. The high levels of metals recorded at these areas are alarmingly high. Therefore, the inhabitants, including children and the numerous workers who reside and work in these polluted environments, are at serious risk of heavy metals toxicity and greater awareness of this issue is needed. 1 It has been estimated that 20% of the total burden of disease in the developing world is due to environmental pollution. 2 Therefore, raising awareness and increasing efforts to reduce the risk of pollution, including heavy metal pollution, would further decrease the burden of disease, and as a consequence, improve the well-being of the population and hence increase productivity. Heavy metals are almost everywhere in the environment, as a result of both anthropogenic and natural activities, and humans are exposed to them through various pathways. 3,4 Heavy metal accumulation in soils and plants is of increasing concern due to the potential human health risks as Zinc this accumulation leads to food chain contamination. 5 It is believed that the concentrations of these metals released into the ecosystem may lead to geoaccumulation, bio-accumulation, and bio-magnification. 6 There have been many studies of soil pollution using different techniques, including magnetic susceptibility measurement, atomic absorption spectrophotometry, and neutron activation analysis. 7-10 In this report, we quantitatively assessed the levels of copper (Cu), lead (Pb), zinc (Zn), cobalt (Co) and chromium (Cr) contamination in an area which functions both as an industrial and residential area in Suame, Kumasi, Ghana. This report is also intended to raise awareness of the issue of heavy metal contamination and to encourage regulation and creation of control measures by the country's Environmental Protection Agency. These measures could be in the form of zoning and clear demarcation or re-designation of activities, and construction of enclosures around the study area. Further, the separate collection and disposal of waste from industrial and domestic sources is strongly advocated.

Study Site
The Suame Industrial Area is an integral part of Kumasi in the Ashanti Region, Ghana. It is popularly known as "Magazine". The soil type in the area is mainly sandy soil. It lies at latitude 06 o 43'21.26" N and longitude -1 o 38'40.19'' W. The area sees many forms of industrial use, such as car body part repair, auto mechanic shops, metal fabrication workshops (smelting, molding, welding), manufacturing of corn (cereal grains), mill parts and whole machines, and manufacture of aluminum and silver utensils. Also present are blacksmiths, carpenters, and car paint sprayers. Suame is also known for vigorous commercial activities including trading in all kinds of automobile spare parts, building materials and electrical appliances. Food and drinking bars are also located within the area. In addition, Suame also serves as a settlement area to some inhabitants of Kumasi and is densely populated.
A cursory look suggests that the soils are heavily polluted; there is very little vegetation, and the soil appears barren (Figure 1a, b), dark brown to black in some places, and there are patches where industrial wastes such as grease, automobile engine oil, tires and pieces of rusty metal have been discarded.
In other areas, domestic refuse can be seen strewn about.

Sample Collection
Soil samples were taken from the surface of the soil at 0-10 cm depth with the aid of a core sampler. In all, 20 samples were collected; 12 samples (three replicates from each sampling spot) were collected along a specified transect at intervals of 5 m, covering a total distance of 60 m. The transect was chosen alongside one of the longest walkways at the study site ( Figure 1c). The remaining eight samples were taken at a random distance from the transect. However, as there were no clearly demarcated zones for residential, commercial or industrial activity, these samples were not treated separately. For instance, some artisans live in the same premises used as work places. In other areas, food is prepared, sold and eaten in the open, under trees next to a 'workshop' (Figure 1d). Children could also be seen playing in some work areas ( Figure 1e). Therefore, the soil samples were treated as a composite rather than separately. The week and bagged. The bagged samples were then sent to the Geological Survey Department, Accra where the elemental analysis was performed. The samples were ground into powered form using a sieve shaker (Fritsch sieve, Fritsch Gmbh, Idar-Oberstein, Germany). The sieve shaker is a four-chamber sieve machine with decreasing pore sizes samples were bagged and labelled for easy identification.

Sample Processing
Samples were later air-dried for one Research which works within a time frame. This can be easily reset depending on the quantity and level of smoothness required. Only samples with sizes smaller than the sieve (125 µm) were extracted into the lower chamber, resulting in fine samples. The milled samples were bagged and labeled and readied for elemental analysis.
Four grams of the milled soil samples were measured into a sample cup with an inner diameter of 28 mm with the aid of a chemical balance, and then homogenized with 0.9 g of Hoechst wax C (Merck Millipore, Darmstadt, Germany). Two small pebbles were added to help with thorough mixing and further grinding of the sieved sample with the wax. The sample container was then covered and placed in a mill machine (Mill MM 200, Retsch GmbH, Haan, Germany), where the mixture was sufficiently mixed into a very uniform state. The period for the milling process was set to approximately three minutes. Subsequently, the pebbles were removed from the sample container using a spatula. The resulting sample was poured into a die and covered. The die was then placed in a press machine and pelleted under a weight of 5 tons. The pellets were

Results
The results showed that the concentrations of the heavy metals Cu, Pb, Zn, Co and Cr were all very high in the soil (  Figure 4, the

Figure 4 -Concentration (mg/kg) plotted against separation distance (m) for Cobalt
Research concentration of Co dropped initially from 79 mg/kg to 65 mg/kg at 5 m, increased to a maximum of 136 mg/ kg, then dropping to 38 mg/kg, which was constant up to a distance of 30 m. It decreased to 56 mg/kg at 55 m. The least polluting metal based on the percentage above the TLV was Co, 227.3% at a distance of 25 m. The concentration of Co was the lowest of all the metals studied, indicating minimal use of Co in this area.
The concentration of Cu in soil in the study area ranged from 120 to 410 mg/kg, exceeding the threshold concentration value of 75 mg/kg for Cu. As shown in Figure 5, the initial concentration of Cu was 200 mg/ kg. It then rose to 320 mg/kg up to a distance of 15 m and then to a minimum concentration of about 120 mg/kg at 20 m. There was a sharp rise in concentration to 410 mg/kg at 25 m. From this point there was no consistency in the concentrations up to about 23 mg/kg at 45 m, then increasing gradually to a concentration of 290 mg/kg at 55 m.
The concentration of Zn was slightly above the threshold limit value of 200 mg/kg as shown in Figure 6. The initial concentration of Zn was about 6,200 mg/kg, then dropping to 600 mg/kg at a distance of 5 m. There was also an increase in concentration of about 7,800 mg/kg at 10 m and then dropping to 5,000 mg/kg. The maximum concentration was recorded as 13,400 mg/kg at a distance of 20 m. It then dropped slowly to 600 mg/ kg. The most polluting metal based on the percentage above the TLV was Zn, 1607.9% at a distance of 25 m. Zn is used to galvanize iron and steel which is used for automobile bodies and in car battery repair. These activities in the area presumably resulted in the high concentrations of Zn.
The soil heavy metal concentrations were compared with the RSLs for residential and industrial land use and the USEPA limits ( Table 2). Two metals, Pb and Co, exceeded the residential limits by 4.7% and 196.5%, respectively, but they did not exceed the industrial limits. There is an RSL value for (hexavalent chromium (CrVI) = 0.3 mg/kg), but not for total chromium. However, CrVI was not measured in soil in this study. Chromium is used to harden steel, and in the manufacture of steel for utensils, roofing sheets, car frames, window frames etc., to prevent rusting.
In addition, chromium plating is used to give a polished finish to many steel products such car and truck parts and furniture. In contrast, the mean concentration of Cu and Zn were below both the USEPA residential and industrial soil RSLs. The results of the present analysis

Figure 6 -Concentration (mg/kg) plotted against separation distance (m) for zinc
Research are a cause for concern because of the excessively high metal concentrations compared with their TLVs. Each analyzed heavy metal had a concentration above its threshold limit value, indicating the presence of pollution in the study area. This is directly attributable to the activities conducted in this area. For instance, Zn, Pb, and Cu are released into the environment due to improper disposal of car batteries and leakage of diesel and engine oil from vehicles. Similarly, paint spraying of car parts, metal fabrication, and the burning of waste materials like car tires, plastics, etc. also release metal pollutants into the atmosphere which are then deposited. These heavy metals have adverse effects on the human population in the area, other living organisms and the environment.

Conclusion
From the results of the present study, it is evident that heavy metals are present in considerably high concentrations in the soil in the Suame industrial area. Industrial activities should also be monitored to include safe collection and disposal of industrial and domestic wastes.
We aim to raise awareness of heavy metal contamination and to encourage creation of effective regulation and control measures including zoning and clear demarcation, regulation of industrial activities and erection of enclosures around work areas. In addition, safe and separate collection and disposal of waste from both industrial and domestic sources is advocated.