Abuja Journal of Agriculture and Environment (AJAE)

INFLUENCE OF TREATED WASTEWATER ON TRACE AND HEAVY METALS IN SOILS OF WUPA, ABUJA, Nigeria
Author(s): Ogwueleka, T.C., Abba A. Simon and Barnabas I. Musa
Volume/Issue: Volume 2 , Issue 1 (2022)

ABSTRACT:

The soils adjoining a sewage treatment Plant in Abuja were studied to assess the influence of treated wastewater on accumulation of some trace and heavy metals in the soil. Soil samples were collected from five locations in the entire area (four locations along the main canal conveying the treated waste water into the Wupa River and a location 50 m away from the canal to serve as a control site). Samples were collected and analysed for particle size distribution and some selected chemical properties as well as some trace and heavy metals following standard laboratory procedures. The soils were generally sandy loam in texture with high proportion of sand and low clay fraction. The sand content ranged from 642 to 772 g/kg while clay ranged from 47 to 61 g/kg. Soil pH was ranging from 5.58 to 6.29 fitting the soil into the range of moderately acidic to slightly acidic. Electrical conductivity ranged from 0.963 to 4.30 dScm-1.Exchangeable cations were generally low; however, exchangeable acidity was influenced by soil’s contact with treated wastewater since the lowest value of 9.63 was recorded from the control site. The distribution of trace and heavy metals showed that there was an increase in the concentration of the trace and heavy metals in the soils as lowest values were only observed in the control site. However, the range of values observed for the trace and heavy metals were within permissible environmentally safe limits except for Ni which was higher than the permissible safe limit for plants. Fe ranged from 23.22 to 415.40 mg/kg, Mn ranged from 19.36 to 157.97 mg/kg, Cu ranged from 0.59 to 2.92 mg/kg while Zn ranged from 2.21 to8.87 mg/kg. For the heavy metals, Cr ranged from 12.69 to 29.77 mg/kg, while Ni ranged from 16.94 to25.53 mg/kg. Cadmium in all the samples was below detectable limits. It was concluded that there is need for adoption of improved sewage treatment processes that will eliminate toxic metals such as NI, Cr, Zn and Mn among others. There is need for further study on the quality of treated wastewater discharged into the Wupa River where it eventually ends up as part of irrigation water in the area. Fish from the Wupa River and vegetables grown from the area should be studied for bioaccumulation of heavy metals.

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