Assessment of the Concentrations and Distribution of Selected Polybrominated Diphenyl Ethers in Nairobi River Drainage Basin and Their Photocatalytic Degradation Pathways

Abstract

Polybrominated diphenyl ethers are linked to adverse health effects that include thyroid hormone disruption, neuro-developmental deficit, abnormal pregnancy, and potential carcinogens. This study was aimed at assessing the levels and spatial distribution of selected polybrominated diphenyl ethers in water, sediments, soil and air of Nairobi River basin. The study also investigated the photo-catalytic degradation of BDEs 28, 85 and 183. Water, sediments, soil and air samples were collected, extracted, cleaned and analysed for brominated diphenyl ethers using gas chromatography coupled with mass spectrometer. Nitrogen doped titanium oxide catalyst was prepared by sol-gel method, characterized and its photo catalytic activity tested using methylene blue and methylene red. The mean concentration of PBDEs in water ranged from ≤0.001 to 72.89±6.15 ng/L, river sediments ranged between 134.70±3.07 to 24,386.13±207.22 ng/kg, soil ranged between 16.46±1.99 to 30,561.35±145.57 ng/kg and air samples ranged from ≤0.001 to 152.72±3.19 pg/m3. Nitrogen was successfully doped into titanium oxide matrix and caused visible light response. The synthesized nitrogen doped titanium oxide degraded both methylene blue and methyl red. The photo-catalyst degraded methylene blue up to 96.7% at pH 7.0. Nitrogen doped titanium oxide nanoparticles synthesized and characterized degraded BDEs 28, 85 and 183 through stepwise debromination. The debromination efficiency by nitrogen doped titanium oxide was about 96.70%, 70.54% and 67.57% for BDEs 28, 85 and 183 respectively in 120 minutes. The calculated degradation half-life of BDEs 28, 85 and 183 were 70.01, 65.39 and 20.81 minutes respectively. The data shows anthropogenic contamination of Nairobi River by polybrominated diphenyl ethers, suggesting a potential risk to aquatic organisms that inhabit the river. The use of the water for irrigating vegetables and watering livestock also poses a potential health risk due to contamination across the food chain. This study is the first of its kind to assess the levels of polybrominated diphenyl ethers in Nairobi River basin and the photo catalytic degradation of polybrominated diphenyl ethers in tropical environment. The information obtained from this study forms a baseline data on the levels of polybrominated diphenyl ethers in Kenya and methods to enhance removal of polybrominated diphenyl ethers from the environment. The information will also be used by policy formulators to make decisions concerning the use of polybrominated diphenyl ethers.