Determination of heavy metals and nutrients in rivers Naka and Irigu, Chuka using aas uv/visible spectrophotometry

Abstract

Levels of concentration of heavy metals (lead, cadmium, arsenic and mercury) and nutrients in rivers Naka and Irigu were determined in the first three months (January, February and March , 2013 ) and variation downstream compared. Lead and cadmium were determined using A tomic A bsorption S pectrosc opy (AAS) . Hydride generation method was used to determine concentration of arsenic while that of mercury was determined using cold vapour technique. Calorimetric methods were used to determine levels of nitrates and phosphates . Concentration levels of le ad, cadmium and arsenic were found to be beyond the permissible levels stipulated by National Environment Management Authority ( NEMA ) and World Health Organisation ( WHO ) drinking water specifications. Lead had the highest concentration with a range of 0.05 37±0.103 parts per million ( ppm ) to 0.765±0.782 ppm followed by cadmium with a concentration range of 0.035 ± 0.006ppm t o 0.24±0.0084 ppm in both rivers Naka and Irigu . The high concentration levels of lead in River Naka could be attributed to disposal of wastes directly into the river from Chuka Town due to poor drainage systems. Mercury was found to be below the detection limit. On the other hand, phosphate had a concentration rang e of 8.31 ±0.429 ppm to 10.33±0.189 ppm. T his was above the specified level of 2.2ppm in drinking water according to NEMA . Only nitrate was below the recommended levels of 50 ppm and 45 ppm NEMA and WHO guidelines respectively for drinking water.