HEAVY METAL CONTENT OF AGRICULTURAL SOILS AT PINDIGA, AKKO LOCAL GOVERNMENT AREA OF GOMBE STATE, NIGERIA

Ogidi A. Ogidi, Danja B.A., Sanusi K.A. Hammashi H. Lodma, Nathaniel Sunday Samuel, Abdurrahman Abubakar, And Nasiru Aminu Rano. Department of Chemical Sciences, Federal University of Kashere, Gombe state, Nigeria. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 03 September 2018 Final Accepted: 05 October 2018 Published: November 2018

In this study the heavy metals (Cd, Cr, Fe, Pb and Zn) content of agricultural soils at Pindiga area of Akko logal government area of Gombe state was determined using atomic absorption spectrophotometer to ascertain the level of heavy metal present the agricultural soils in the area.

Study Site
Pindiga is a settlement in Ako L.G.A, Gombe state, Nigeria and located on lat 9°59'0" N and 10°56'0"E. It is located at an elevation of 523m above sea level.
Sample matrix/ sample codes Ten soil samples was collected at each sample site and mixed into a composite representative sample for each sample site (Ogidi, 2015).

Sample collection, preservation and pretreatment
The soil samples were collected from soil surface (0 -20cm depth) at ten different spots with the help of stainless steel spoon and made into a composite sample. The soil samples were placed into a nitric acid treated polythene bag to prevent metals from adhering to the containers and then transported to the laboratory where they were air dried for about 3days then oven-dried to constant weight at 105 , disaggregated in a ceramic pestle and mortar, ground to powder and sieved, (Kisamo, 2003, Ndimele andJimoh, 2011).

Sample digestion
Soil samples were digested with 15mL of concentrated acid mixtures (5mL conc.HClO 4 , 15mL conc.HNO 3, and 10mL conc. H 2 SO 4 ) was poured into the 100mL beaker containing the soil sample (1g), covered with watch glasses, and heated over a water bath in a fume cupboard until the digestion was complete. The content of the beaker was then diluted to 100mL with de-ionized water and transferred to dispersing bottles for heavy metal analysis (Ndimele andJimoh, 2011, Wufen, et al., 2009).

Apparatus/ reagents
All glass ware, including sample bottles, burette, and pipettes used were washed cleaned and rinsed with HNO 3 , followed by distilled water to avoid errors arising from contamination. All reagents used were of analytical grade (APHA, 1985;Ademoroti, 1996).

Physio-Chemical Parameters Determined
Physio-chemical parameters of samples determined in the course of study are as follows

Determination of pH
The pH of the soil samples was measured using a kelilong portable electronic pH meter (KL-009 (1)). Just before the pH meter was used it was standardized with three buffer solutions of different pH values to serve as check for proper instrument response. Buffers with pH values of 2,7and 12 were used, About 20g air-dry tailing sample was mixed with 100mL of distilled water and in a 250mL volumetric flask, shaken for 1 hour and the pH measured (Miller and Kissel, 2010).

Determination of Moisture content determination
About 4g of sample was weighed into a previously weighed crucible, and then transferred into an oven set at 105 to dry to constant weight for 24 hours overnight. At the end of the 24 hours, the crucible plus sample was removed from the oven and transferred to desiccators, cooled for ten minutes and weighed. The moisture content of the sample was thus determined as below (Ogidi, 2015) Where, weight of empty crucible = W 0 230 Weight of crucible + sample = W 1 Weight of crucible + oven dried sample = W 3 .

Method of Analysis
The method of analysis used in determining heavy metals content of samples is the atomic absorption spectrophotometric (AAS) method, due to its accessibility, specificity, wide range of application, low detection limit, and cost effectiveness (Ademoroti, 1996). The heavy metal content of the samples where determined using an atomic absorption spectrometer (AAS), Perkin Elmer 400ASS.

Statistical Analysis
The minimum, maximum, range, mean, and standard deviation, as well as the student t-test values of the concentrations of heavy metals in soil were determined. Microsoft excel (windows 2007), were employed in statistical analysis.

Physio-Chemical Parameters of Samples pH of Soils
The pH of soil sample at Pidinga ranged from 5.1 to 6.6. The maximum pH value was at model farm and the minimum value was at Garin Jauro. the pH of soils at Pindiga where moderately acidic and similar to the pH range of soils used for irrigation farming at the banks of River Benue at Makurdi, Central Nigeria reported by Ogidi, (2015) , but higher than the mean value (3.1) at dump sites at Makurdi metropolis reported by Agber and Tsaku, (2013). The mean pH values of soils in this study is higher than the minimum value (5.4) and lower than the maximum value (9.8) for cultivated soils close to Ashaka cement factory at Gombe, Eastern Nigeria reported by Buba et al., (2016). The pH of soils in this study is favorable for the growth of food crops. Heavy metal ions are more mobile in acidic conditions; heavy metals are freely available and absorbed by plants from the soil at this condition (Sherene, 2010)

Moisture Content of Soils
The moisture content of soils at Pindiga ranged from 17.1% to 58.0%. The maximum moisture content of soil was at Sumbe and the minimum was at Garin Dawa. The mean percentage (%) moisture content of soils in the study was more than the value range of 3.1-4.6 % for soils around dump sites at Makurdi, Central Nigeria reported by Agber and Tsaku (2013), this could be due to the absorption and accumulation of water in soils at pidinga during the wet season since study was conducted during the wet season.
also higher than the maximum value 0.551 mg/kg at Mwazan Region in Tanzania reported by Kisamo, (2003), but less than the recommended limit for soil (85 mg/kg) set by USEPA. Cd has no essential to the health of humans and animal, at higher concentrations in organisms above the recommended limits it is toxic (Ogidi, 2015).  (Ogidi, 2015).

Iron
Iron in agricultural soils in this study has a mean concentration of 21.31 mg/Kg and this falls within the range (13.14 -27.01 mg/Kg) for irrigated soils in Gombe state, Nigeria reported by Babangida et al., (2017). was greater than the maximum value 2.79 mg/kg at Mwazan Region in Tanzania reported by Kisamo, (2003), but less than the mean concentration of Fe in soil (746± 245 mg/kg) for soils at Makurdi, North Central Nigeria reported by Ogidi, (2015). Extreme concentrations of ion in soils can create mineral nutrient imbalance through antagonistic effects on the uptake of certain essential metals like K and Zn (Sahrawat, 2015).

Lead
The concentration of Pb in soils has a mean value of 36. 10 2015), but less than the recommended limit for soils set by USEPA. Excess Pb content of soils above regulatory limits create serious health hazards to both humans and animals due to its ability to bio-accumulate in soft tissues creating organ and tissue failures (Ogidi, 2015).

Zinc
Zn content of soils in this study has a mean value of 0.20 mg/Kg which is less than the value range (

Conclusion:-
The study indicates that the pH of soils at study areas from Ako LGA, Gombe state, Eastern Nigeria is moderately acidic, and this pH value is good enough for agricultural activities by enhancing the availability and mobility of mineral nutrients in the soil. The moisture content of the soils also encourages the growth of microorganisms in the soils and also aid in soil mobility of nutrients within the soil. The study shows the presence of heavy metals in agricultural soils at study sites at levels below the regulatory limits set by WHO and USEPA. From the mean concentration of heavy metals, Zn has the lowest concentration while Fe had the highest concentrations in the soils, but Cd and Pb which are non-essential and highly toxic above the permissible limits have concentrations below the regulatory limits. Thus the soils are safe for cultivation of food crops since they are free of heavy metal contaminations.

Recommendations
Heavy metals poisoning is of great concern to man and the environment, thus there is need to monitor the heavy metals content of soils on regular bases. The government needs to enforce regulations against the illegal dumping of refuse, metallic waste, agrochemicals and other harmful substances into the environment. The application of green pesticides in place of conventional synthetic and persistent agrochemicals should be promoted and encouraged. There is also a need for assessing the heavy metals content of soils before food crops are cultivated on them so as to avoid bio-absorption of toxic levels of heavy metals by food crops from the soil.