Determination Of Chemical And Microbiological Contaminants In Soils, Water And Kales (Brassica Oleracea) From Selected Sites In Eastern Nairobi Metropolitan

Abstract

This study investigated the extent of pesticides residues, heavy metals and microbial contaminants in Kales, water and soils from Nairobi metropolitan. Samples were collected from six sites within Nairobi Metropolitan area namely, Kitengela, Mlolongo and Athi River farms and open air markets, covering the wet and dry months between July 2015 and February 2016. Pesticide residues were extracted using organic solvents and analyzed using Gas Chromatography equipped with electron capture detector, whereas heavy metals were analyzed using Atomic Absorption spectrometer. The microbial contaminants were analyzed using 3M kit. Percentage recoveries for pesticides ranged from 70.00-114.83%, whereas the detection limits ranged between 1.12 ng/L to 3.6 ng/L. The pesticides concentration in kales ranged from BDL to 322.55±9.64 μg/kg. p,p’-DDD was the highest detected pesticide during the month of February 2016 from Kitengela market. Soil pesticides concentration ranged from 0.001 to 170.53±3.03 μg/kg, with α-endosulphan recording the highest concentration in soil from Mavoko market. Pesticides residues in water ranged from 0.001 to 3.53±0.02 μg/L, with aldrin recording the highest concentration in February, 2016 from Mlolongo farm irrigation water. Heavy metals concentrations in kales ranged from <0.01 to 0.74±0.00 mg/kg. Lead was the highest heavy metal detected in vegetables from Mlolongo farm. Concentrations of heavy metals in water ranged from <0.01 to 0.16±0.01 mg/L. Copper was the highest heavy metal detected in Kitengela farm water. Heavy metal in soil ranged from <0.01 to 1.03±0.08 mg/kg, zinc was the highest heavy metal detected in Kitengela market soil samples. E-coli concentration ranged from 0 to 13±2 cfu/L. The highest levels in kales were measured in samples from Mlolongo market during the month of December 2015. Soil E-coli concentrations ranged from 0 to 145±8 cfu/g detected in soils from Kitengela farm. The concentrations in water ranged from 4 to 89 cfu/ml, with the highest levels measured in water samples from Mlolongo farm irrigation water. Coliform concentrations in vegetables ranged from 8±2 to 353±19 cfu/g, with the highest detected in samples from Mlolongo market in the month of December 2015. For soil, the coliform concentration ranged from 1±0 to 3,214±284cfu/g and the highest detected was from vi Mlolongo market during the month of February 2016. For water, the concentration ranged from 81±3 to 3,797±119 cfu/ml, with the highest detected in water from Mlolongo farm in the month of February 2016. The results showed that organochlorine pesticides such as aldrin, dieldrin, endrin, heptachlor, DDT and its metabolites are still present in samples from Nairobi metropolitan. The presence of high levels of lead, E. coli and total coliform in vegetables should be taken seriously by public health sector, and also the kales should not be consumed raw since they expose people to dangers caused by the contaminants.