Assessment of New Persistent Organic Pollutants-pesticides in Air and Soil Samples From Sites in Nairobi and Mount Kenya

Abstract

Persistent organic pollutants (POPs) are compounds of great concern because of the adverse effects they have on humans, wildlife and the environment. They are toxic and have a tendency to accumulate in the food chains. They are also capable of persisting in the environment for a long time, migrating in air, water, soil and sediments. The result is wide spread distribution of POPs in the atmosphere. This study was undertaken to determine the spatial distribution, temporal and seasonal variations of the new persistent organic pollutants-organochlorine pesticides in air and soil in Nairobi and Mt. Kenya areas. Four out of the ten new Persistent Organic pollutants (new POPs) and some of their isomers and metabolites were analysed in air and soil samples from Industrial area, Dandora dumpsite, Kabete and Mt. Kenya. Air samples, collected using passive samplers and soil samples collected using Auger samplers were sampled on quarterly basis between July 2012 and April 2013. The identification and quantification of the new POPs- pesticides was done using a gas chromatographic system (Agilent 6890N) in combination with an auto sampler (Agilent 7683 Series injector), and an electron capture detector (Agilent μECD). The new POPs that were detected include; α-HCH, β-HCH, γ-HCH (lindane), α- endosulfan, β-endosulfan and Endosulfan sulfate. The residue levels of the new POPs were lower at the Mt. Kenya and Kabete sites than at the Dandora and Industrial area sites. The sum of the concentrations of the aerial new POPs (Σnew POP) ranged between 3.4643 ng/M3 and 14.3746 ng/M3 at the Dandora site; 4.1236 ng/M3 and 5.6328 ng/M3 at the Kabete site; 7.5279 ng/M3 and 11.4572 ng/M3 at the Industrial area site; and 0.6874 ng/M3 and 1.3336 ng/M3 at the Mt. Kenya site. The levels of the new POPs in air increased while the levels of the new POPs in soil decreased during the warm-dry season signifying the effect of volatilization from soil when temperatures are high. The sum of the concentrations of the new POPs in soil ranged between 10.93ng/kg and 230.48 ng/kg at the Dandora site; 17.06 ng/kg and 29.05 ng/kg at Kabete site; 19.65 ng/kg and 78.41ng/kg at Industrial area; and 1.71 ng/kg and15.02 ng/kg at the Mt. Kenya site. The concentrations of the new POPs in soil declined during the warm-dry season at all the four sites. At the Dandora site, the concentrations declined from 230.48 ng/kg to10.93 ng/kg; from 29.05 ng/kg to28.77 ng/kg at the Kabete site; from 78.41 ng/kg to 52.18 ng/kg at the Industrial area; and 15.02 ng/kg to5.76 ng/kg at the Mt. Kenya site. The average residue levels of the new POPs analysed in air at the four sites revealed that the one with the highest average level was β-HCH (7.6434 ng/M3) while α-HCH had the lowest residue level in air of the new POPs of 0.0358 ng/M3. The residue levels of the new POPs in air and soil were generally high at the Dandora and Industrial area sites. This indicates that industrial activities such as Tetra-Pac, general plastics, Phillips industries waste and stock piles are the main sources of the new POPs in Nairobi. The high concentration level poses a health risk to residents of Dandora and Industrial area workers. The levels of the new POPs were higher in air than in soil at the four sites during all the three sampling sessions. At the Kabete site, the average levels of the new POPs in air were 4.8504 ng/M3and 24.96 ng/kg in soil. This trend was repeated at the other sites; 8.8684 ng/M3 in air and 97.70 ng/kg in soil at the Dandora site; 1.0583ng/M3 in air and 7.49 ng/kg in soil at the Mt. Kenya site; 9.0152 ng/M3and 50.08 ng/kg at the Industrial area site. The Pearson‟s correlation coefficients as determined for the seasonal levels of the new POPs present in air were positive at all the sites and were negative at some sites for soil. The inter-matrix correlation was very weak at the Kabete site (p=0.043)