Levels of Physicochemical Parameters and Polycyclic Aromatic Hydrocarbons in Water, Soils and Sediments from a Section of River Nzoia, Kakamega County-Kenya.

Abstract

Water pollution is an overbearing environmental challenge due to increasing anthropogenic activities from industrial, agricultural and domestic fronts. While data on the water quality such as heavy metals and physico-chemical parameters is enormous, that onpolycyclic aromatic hydrocarbons(PAHs) presents a research gap. The 16 priority polycyclic aromatic hydrocarbons in the environment have increasingly become a health risk as a result of anthropogenic activities. The study was undertaken to determine the levels of 16 priority PAHs in water, soil and sediment from a section of river Nzoia during wet and dry season. The PAHs have been identified by various regional and international agencies as persistent pollutants because of their high toxicity, carcinogenicity and mutagenicity. River Nzoia is located in a region dominated by agricultural and industrial activities. The river receives chemical pollutants from agricultural farms within the river catchment areas and wastewater discharge from Mumias Sugar Company, Nzoia Sugar Company, West Kenya Sugar Company and Webuye paper mill. Since the river water is used for domestic use within the catchment area and beyond, it is important chemical pollutants are monitored regularly. The aim of the study was to determine seasonal variation of physico-chemical parameters (pH, total dissolved solids, conductivity and temperature) and the levels of PAHs in water, soil and sediment from selected parts of River Nzoia (Mumias bridge, Torofu bridge and Waterfall site) during the wet and dry seasons. The physico-chemical parameters were measured in situ while GC-MS Agilent 7890A was used for identification and quantification of PAHs.The physico-chemical parameters gave levels that were within the maximum allowed limit set by WHO and USEPA, but with significant differences between the wet and dry seasons (p<0.005).The levels of PAHs varied from one sampling point to another across the three matrices.In water, PAHs levels ranged from 0.046±0.006 - 0.092±0.003 ng/L (wet season) and 0.026±0.003- 0.046±0.011 ng/L (dry season), with the former being significantly higher (p<0.005). In sediment, the range was 4.21±1.19 - 8.94±3.33 ng/g (wet season) and 5.53±0.33 - 8.36±2.17 ng/g (dry season) with the latter being significantly higher (p<0.005). In soil, levels ranged from 2.45±0.57 - 8.42±0.05 ng/g (wet season) and 2.59±0.89 - 9.74±1.97 ng/g (dry season), with the former being significantly higher (p<0.005).Benzo(a)anthracene and dibenzo(a,h)anthracene were found in all matrices in both seasons.It is also worth noting that phenanthrene, acenaphthylene and benzo(a)pyrene were not detected in all sampling points during both seasons across the three matrices. Higher concentrations of PAHs were recorded during the wet season than dry season although the levels were below the maximum limits by WHO of 50 ng/L and 4 mg/kg in water and soil/sediments respectively.Though the levels were within the acceptable limits by WHO continuous monitoring on levels of PAHs is needed to further determine their trend in their levels since they are considered as persistent pollutants.