Demonstrating PM2.5 and road-side dust pollution by heavy metals along Thika superhighway in Kenya, sub-Saharan Africa

E G Maina; A N Gachanja; M J Gatari; H Price

doi:10.1007/s10661-018-6629-z

Demonstrating PM_2.5 and road-side dust pollution by heavy metals along Thika superhighway in Kenya, sub-Saharan Africa

Environ Monit Assess. 2018 Mar 27;190(4):251. doi: 10.1007/s10661-018-6629-z.

Authors

E G Maina¹, A N Gachanja², M J Gatari³, H Price⁴

Affiliations

¹ Department of Chemistry, Jomo Kenyatta University of Agriculture and Technology, P.O. Box, 62000-00200, Nairobi, Kenya. gachuie2@gmail.com.
² Department of Chemistry, Jomo Kenyatta University of Agriculture and Technology, P.O. Box, 62000-00200, Nairobi, Kenya.
³ Institute of Nuclear Science and Technology, College of Architecture and Engineering, University of Nairobi, P.O. Box 30197, G.P.O., Nairobi, Kenya.
⁴ School of Natural Sciences, University of Stirling, Stirling, UK.

PMID: 29582158
DOI: 10.1007/s10661-018-6629-z

Abstract

This study assessed the level of heavy metal in roadside dust and PM_2.5 mass concentrations along Thika superhighway in Kenya. Thika superhighway is one of the busiest roads in Kenya, linking Thika town with Nairobi. Triplicate road dust samples collected from 12 locations were analysed for lead (Pb), chromium (Cr), cadmium (Cd), nickel (Ni), zinc (Zn), and copper (Cu) using atomic absorption spectrophotometry (AAS). PM_2.5 samples were collected on pre-weighed Teflon filters using a BGI personal sampler and the filters were then reweighed. The ranges of metal concentrations were 39-101 μg/g for Cu, 95-262 μg/g for Zn, 9-28 μg/g for Cd, 14-24 μg/g for Ni, 13-30 μg/g for Cr, and 20-80 μg/g for Pb. The concentrations of heavy metals were generally highly correlated, indicating a common anthropogenic source of the pollutants. The results showed that the majority of the measured heavy metals were above the background concentration, and in particular, Cd, Pb, and Zn levels indicated moderate to high contamination. Though not directly comparable due to different sampling timeframes (8 h in this study and 24 h for guideline values), PM_2.5 for all sites exceeds the daily WHO PM_2.5 guidelines of 25 μg/m³. This poses a health risk to people using and working close to Thika superhighway, for example, local residents, traffic police, street vendors, and people operating small businesses. PM_2.5 levels were higher for sites closer to Nairobi which could be attributed to increased vehicular traffic towards Nairobi from Thika. This study provides some evidence of the air pollution problem arising from vehicular traffic in developing parts of the world and gives an indication of the potential health impacts. It also highlights the need for source apportionment studies to determine contributions of anthropogenic emissions to air pollution, as well as long-term sampling studies that can be used to fully understand spatiotemporal patterns in air pollution within developing regions.

Keywords: Africa; Air pollution; Atomic absorption spectrophotometer; Contamination factor; Geo-accumulation; Health; Heavy metals; PM2.5; Roadside dust; Vehicular emission.

MeSH terms

Air Pollutants / analysis*
Air Pollution / analysis
Air Pollution / statistics & numerical data
Cadmium / analysis
Chromium / analysis
Copper / analysis
Dust / analysis
Environmental Monitoring / methods
Kenya
Metals, Heavy / analysis*
Nickel / analysis
Particulate Matter / analysis*
Spectrophotometry, Atomic
Zinc / analysis

Substances

Air Pollutants
Dust
Metals, Heavy
Particulate Matter
Cadmium
Chromium
Copper
Nickel
Zinc