Assessment and Distribution of Metal Pollutants in Fadama Soils along River Ngadda and Alau Dam in Maiduguri, Borno State, Nigeria

Elemental metal pollutants concentration levels and their distribution in soils obtained from farmlands
along the bank of river Ngadda and Alau dam in Maiduguri, Borno State, and North-East of Nigeria is
presented. The study was aimed at determining the levels of contamination of soils with metal
pollutants used for fadama farming along the bank of river Ngadda and Alau dam with the objectives
of assessing the contamination levels of the soils with metal pollutants from the various farmlands at
the various sampled sites of study, and the distribution of the various metal pollutant in the various
sampled sites. Soil samples were collected from thirteen different sites on the farmlands along the
bank of the river and the dam. The samples were analyzed using Instrumental Neutron Activation
Analysis (INAA) and the result obtained indicate that the concentration level of some of the elements
determined were above maximum allowable concentration (MAC) value while some below the (MAC)
values for example the concentration range for Cr was (16 ± 2 – 47 ±3) ppm, Sb was (0.18 ± 0.04 –
14.2 ± 7) ppm, Zn was (21.8 ± 4 – 145 ± 7) ppm and the maximum values for these ranges exceed
the (MAC) value recommended for Agricultural soils while the concentration ranges for As was (0.46 ±
0.12 – 1.0 ± 0.2)ppm, Co was (1.6 ± 0.3 – 5.3 ± 0.4) ppm, Vn was (14.6 ± 2.32 – 29 ± 2) ppm with the
maximum value for these ranges being below the MAC values given by some countries. The elements
obtained from samples collected from different study areas along the bank of river Ngadda and Alau
dam were analyzed for similarity distribution of the study area using mathematical tool of cluster
analysis technique employing hierarchical procedure and using WARD’s method. The result obtained
produce a dendrogram consisting of two clusters comprising of six and seven sites with percentage
similarity of 96.5% and 90.8% respectively with one site as an outlier. It is recommended that since
some of the trace metals namely Cr, Sb, and Zn assessed in the fadama soils indicates
concentrations above the MAC values, they can posed negative health implications to consumers of
food which were cultivated on soils from the study area, therefore there is the need to condition the
soils before using it for farming so as to make it suitable for food crop farming. From the results
obtained from this and presented, it can be clearly observed that the concentrations of some of the
toxic trace elements analyzed and determined in this research were found to be above the MAC
values given by some countries for soils to be used for agricultural purposes while others were within
the range of the MAC values and some were below the limit given by some countries. However, even
for soil samples that were having concentration below the MAC values since the soils were used for
agricultural purposes it will be of great importance that such studies and investigations on such soils
be carried out periodically so as to ascertain and monitor the levels of this metal toxicants and where
the level of metal pollutants were above the MAC values there is the need to conditioned the soils so
as to remedy the concentration of the pollutants before using the soils for agricultural purposes since
the plants may absorb these metal toxicants and it will accumulate above threshold level thereby
causing negative effect on the use of the soils.