Impact of Mining and Agriculture on Metal Concentrations in Soil and Food Crops in Selected Local Government Areas of Nasarawa State, Nigeria

ABSTRACT

The total concentration of Cd, Co, Cu, Mn, Ni, Pb and Zn were detemlined in the soil and plant materials from some selected local government areas of Nassarawa state, Nigeria. The modified USEPA- 3050 method of HNOr HCI04 - H202 was used in the preparation of soil sample for total deternlination whilst the plant materials were digested with HN03 -H202. The CaCh. DTPA extraction method was used in the determination of the concentration of bio available metals in soil samples. The flame atomic absorption spectrometry was used in the determination of metals in the soil and plant digests. A precision of 8.5, 6.1, 4.5, 3.1, 2.4, 1 .2, and 2.5, percents were obtained for Zn, M,n, Cd, Cu, Co, Pb and Ni respectively, for soil samples; whilst plant sample materials gave precisions of 4.2, 3 .2, 4.5, 3.3, 1 .7, 2.9 and 3 .2 percents respectively, for Zn, Mn, Cd, Cu, Co, Pb and Ni. Quality assurance of the digestion method for trace metal determination in soil was carried out by a recovery study and the analysis of Certified Reference Material (CRM); SD- M 2/TM ; Pacific Ocean soil sediment sample (1 990). Percent recoveries of 89- 96% were obtain for most metals. The range of metals (mgkg- 1 ) in the reference soil materials were 71.8 - 76, 1 1 65- 1 200, 27.0 -37. 9, 0.09 -0. 1 5, 1 2.8- 14. 1, 21.4 24.6 and 49.5 - 57.2 for Zn, Mn, Cu, Cd, Co, Pb and Ni respectively and these were in agreement with the Certified Values as show by the student t- test.The soils were slightly ac idic with the pH ranging from 5.9 - 6.7 in study area and the percent organic c arbon varied from 1 .20 - 1.53% The total metal levels in the soils (mkkg- 1 ) v varied from 1 5 .0 - 84.0, 1 60.0- 342.0, 4 1 .0-76.0, 1 .0-2.83, 0.1-0.4, 4.10-9.16 and 13.0 -39.0 for Zn, Mn, Cu, Cd, Co, Pb and Ni, respectively. The percent bio available metals in the soil ranged from 1 1-15, 10 -15, 15 -20, 7- 1 0, 5-10, 5- 10 and 2-4, for Zn, Mn, Cd, Co and Ni respectively, in (mgkg-1 ) The concentration of metals in plant material (mgkg-1 ) were 1. 18 -9.3 (4. 1 3) for Zn; 6.4 -40. 0(1 8.25) for Mn; 0. 1 -0.7 (0.24) for Cd;l .8-6.8 (3 .78) for Cu; 0.10-0.98 (0.42) for Ni. Pb; 0.1-0.80 (0.36) and 0.0 1- 0.03 (0.02) for Co. Generally, mining and agticultural activities were suspected to be the major contributors of metals in the study area. The average concentrations of Zn, Mn, Cu, Cd, Co, Pb and Ni obtained in the study area for soil and food crops were compared with other regional studies, country standards and quality guidelines to evaluate their risk significance and quality assessments specified for the protection of human health. These levels compared favourably with results fi:om other regional studies, country standards, as well WHO/F AO benchmarks for soil and food quality standards . That the concentrations of metals in this study were lower than quality guidelines for agriculture, residential and commercial purposes indicate that there is currently no threat to human health in the use of the soil and consumption of food crops in these areas.