Ecological risk assessment of heavy metal exposure to River Sauna as irrigation water source in Kano State, Nigeria

Abstract

The indiscriminate discharge of both domestic and wastewater have a great impact on the quality of water in River Sauna. This assess the quality of the water used for urban agriculture and ecological risk assessments of some heavy metals exposure in River Sauna as irrigation water source in Kano metropolis, Nigeria. Water samples were collected from different sites at distances of 0, 250, and 500 meters from points of discharge. The collected samples were analysed for physicochemical properties and heavy metals in the laboratory using standard methods. The results showed that amongst all the different sources evaluated, the industrial waste water had the highest pH, electrical conductivity and total dissolved solids of 8.26, 4.87 dSm^-1 and 2.89 gL^-1 respectively. Higher electrical conductivity (EC), residual sodium carbonate (RSC) and chlorides were observed both in industrial and domestic discharge sites. There is a high potential of salinity and environmental toxicity with the continued discharge of waste water from both industry and homes. The results also indicated a highly significant difference (P<.001) in the concentration of Ca, Mg and Na at varying distances within the sampling sites. The value of computed degree of contamination and pollution load index were observed to be <7 and <1 in all sampling sites respectively. The abundance of the heavy metals was in the order of Cu > Ni > Cd > Pb > Cr and below the WHO permissible limit for surface water, except for Cd, which recorded 0.015 mgl^-1 in the industrial discharge site and thus necessary treatments and precautions should be put in place to minimize the impacts.