The use of spent engine oil, tyres, refuse etc in the singeing of cow skin is a common sight in many local abattoirs in Nigeria. This research work analyzed the heavy metal content in cow skin proceed using different methods from two Area Councils of the FCT. Metals like Mn, Ni, Fe, Cd, Pb and Zn were determined using AAS. From the results obtained, the heavy metal concentrations (mg/kg) in processed cow skins in Gwagwalada and Kuje Area Councils are in the range of Pb (0.1172-0.2656), Cd (BDL), Ni (BDL), Mn (0.8934-0.9526), Fe (13.3735-18.5128) and Zn (3.0142-5.9430) in scrapped (S_c) cow skins, Pb (BDL-1.0973), Cd (BDL) Ni (BDL), Mn (1.3005-1.6724), Fe (21.1975-25.0922) and Zn (2.3903-7.6962) in singed (S_n) cow skins and Pb (BDL-0.1471), Cd (BDL), Ni (BDL), Mn (0.2204-1.4261), Fe (11.2719-24.1805) and Zn (0.8110-7.1082) in singed and then washed (S_W) cow skins.

Heavy metals are metallic chemicals with a relatively high density that are toxic, persistent and hazardous to human health at low concentrations [1]. These include mercury (Hg), lead (Pb), copper (Cu), cadmium (Cd), arsenic (As), chromium (Cr), thallium (TI), manganese (Mn), zinc (Zn), and nickel (Ni) [2]. Some of these metals (Fe, Mn, Cu and Zn) are essential for metabolism in their lower concentrations [3]. As, Cd, Cr, Co, Pb, Ni, and Zn are the most common heavy metals potentially hazardous to human health [4]. However, cadmium and lead have more significant side effects on human health since they are easily accessible through the food chain [5].

The World Health Organization (WHO) has identified food contamination as a problem facing humanity today [6]. This include problem include heavy metal contamination in meat, which is of great concern for both food safety and human health because of the toxic nature of these metals at relatively low concentrations [7]. Consumption of unsafe amount of heavy metals in food may lead to the disruption of biological and biochemical processes in the human body [8] causing various disorders that are characterized by gastrointestinal disorders, stomatitis, tremors, diarrhea, hemoglobinuria, paralysis, vomiting, convulsions, and depression [9]. Similarly, heavy metals have the ability to disrupt metabolic activity and genetic makeup, or to affect embryonic or fetal development [10].

In FCT-Abuja as in most part of Africa singeing with scrap tyre, spent engine oil, polystyrene, refuse and firewood have become a major method of removing the hair on the skin of slaughtered cattles and goats. These disturbing methods are worrying since they can introduce different contaminants into the meat, thereby rendering it unsafe for human consumption [11].

This work is aimed at investigating the possible heavy metals contaminating cow skins processed in Gwagwalada and Kuje Area Councils of Federal Capital Territory.

Experimental Methods
Cow skins from already slaughtered cows were collected from abattoirs in two Area Councils of the Federal Capital Territory.

Seven cows were randomly selected for the sampling in each Area Council; three samples were collected from each cow making a total of 21 samples per Area Council. The three samples collected from each cow were processed using deferent method, viz: scrapped (unsinged), singed and singed and then washed. The processed cow skins were put in the oven at temperature of 105°c to get their moisture content. Singeing of the cow skin was carried out using different materials like fire wood, fuel with refuse, spent engine oil, charcoal, tyre etc while scrapping was done using hot water and razor blade/knife.

Moisture Content
This was done by weighing 5 g of the sample into a crucible, placed in an oven and heated for 5 hours at constant temperature of 105°C. The sample was then removed and put rapidly into a desiccator in order to prevent more moisture uptake from atmosphere. The sample was cooled to constant mass and reweighed. This was done in triplicate. The difference in the mass constitutes the amount of moisture content of the adsorbent in percentage.
W₂-W₃
W₂-W₁              1
W₁ = Mass of empty crucible
W₂ = Initial mass of crucible with sample
W₃ = Final mass of crucible with sample
Ash Content
10 grams of the samples were put in a muffle furnace at a temperature of 530OC for four hours thirty minutes; allowed to cool in a desiccator and weighed; the percentage ash was calculated using the formula below
% ash (wet) =   weight of crucible and ash-weight of crucible            x 100
                              weight of crucible and sample-weight of crucible                             2

Sample Preparation
The Ash was dissolved in 2cm³ of HNO₃ and made up to 50 cm³ with distilled de-ionized water.

Elemental Analysis of the Sample
Pb, Cd, Ni, Mn, Fe and Zn in cow skins processed by different methods were determined using atomic absorption spectrophotometry (AAS).
Standard Working Solution
The Stocks were severally diluted to obtained standard working solution. All solutions were prepared using distilled de-ionized water. All the salts used were of analytical grade.

Statistical Analysis
All data were subjected to two ways analysis of variance (ANOVA) without replicate.

From the results obtained, it is evident that the singed samples contain more heavy metals. This may be due to the technique of singeing where spent engine oil, refuse, tyres etc are used as the singeing agent where there is high possibility of direct contact between the skin and metal stripes in the tyres. This may be the reason for higher metal concentrations in singed samples.

Table 2 revealed that the higher the ash content, the higher the heavy metal concentration in the samples. The highest concentration of lead was observed in cow skins singed in Kuje Area Council (1.0973mg/kg), which is far above permissible limit. This might be due to the substances (tyre, spent engine oil, polystyrene, refuse etc) used in singeing off the hair from the cow skins.

In Kuje Area Council for example lead content in the singed sample is 1.0973 mg/kg and 0.1471 mg/kg for the singed and washed sample indicating a massive 87% drop in lead concentration when the singed skin was washed.

Lead would become toxic if it is consumed in the amount which exceed threshold and can cause acute and chronic poisoning. It causes about 10% of intellectual disability of otherwise unknown cause and can result in behavioral problems. Some effects are permanent [12]. Lead is known to induce reduced cognitive development and intellectual performance in children and increases blood pressure and cardiovascular disease in adult. It is also evident that the singeing did not introduce lead into the sample from Gwagwalada. The scrapped sample from Gwagwalada contain the highest lead dose, this amount may have been introduced into the sample through other sources while the scrapped sample in Kuje contain the least lead dose as expected. Apart from the Sn and SW samples from Gwagwalada, The levels of lead far exceeded the maximum permissible level (MPL) of 0.01 mg/kg [13]. Cadmium and nickel concentrations in all the samples are below detection limit (BDL) in both Area Councils.

Nickel and Cadmium in all the samples are below detection limit. Manganese is an important element for human health, essential for development, metabolism and antioxidant system. Nevertheless, excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal, death and symptoms similar to Parkinson’s diseases [14]. The highest manganese in the sample was found in singed sample in Kuje Area Council which is within the permissible limit for age 9 and above.

Zinc is an essential trace metal with very low toxicity in human [15-16]. Symptoms of high doses of zinc are nausea, vomiting, pains, crams and diarrhea. Even though iron is an essential metal, excess of it can pose a health risk, human body has no regulated physiological means of excreting iron. Only small amount of iron are lost daily due to mucosal and skin epithelial cell sloughing. So controlled iron level is primarily accomplished by regulating uptake [17]. The highest concentration of iron in the sample is 25.0922mg/kg.

Finally, in singed animal skin, it is believed that heavy metals accumulate both on surface and in the skin in way that washing can remove the surface metals making washing an important operation in animal skin treatment

Mean results of processed cow skins in the area councils of Federal Capital Territory revealed that the contaminants were in the range Fe > Zn > Mn > Pb. Anova analysis also revealed (p>0.05) meaning that there was significant difference between the heavy metal concentration in the processed cow skins in the two Area Councils. Conclusively, the singed washed skin in Gwagwalada was safer for consumption than that of Kuje because of the absence of Pb, Ni and Cd. It is therefore recommended that government should ensure safe methods of processing the skin at the abattoir in all Area Councils as this will reduce bioaccumulation of the toxic metals in the animal skin.