Assessment of airborne particulate matter around cement industries in Athi river, Machakos county, Kenya.

Abstract

Particulate matter (PM) of 10 micron (μm) or less in diameter, (PM10) is a component of inhalable dust. These particles are indicators of air pollution and one of the major human health and environmental concern. Their harmful health effects, ranges from minor irritation to chronic infections in the respiratory system. Furthermore, their toxicities depend on the chemical composition. The PM10 levels vary greatly due to the influence of meteorological factors and their removal from the atmosphere is most challenging especially when they consist of secondary particles. There has been health concern among communities over possible exposure to elevated levels of PM10 of the cement industries. The study was therefore conducted to assess PM10 levels around the cement industries in Athi River Municipality, Machakos County in Kenya. The PM10 levels were collected from five sites in the morning and afternoon for three hours at each site, for three consecutive days during the rainy (April-June and in October) and dry (January-March and in September) seasons of 2019. They were collected using a 47 mm polytetrafluoroethylene filter membrane fitted in an air sampler (Model: Ecotec microvolt-1100). All filter membranes were conditioned for 24-hours prior to pre-weighing and post-weighing using unibloc shimadzu AUW220D analytical balance. Meteorological measurements were further recorded during collection of PM10 levels. The analysis of PM10 levels and elemental composition were carried out using the gravimetric and energy dispersive X-ray fluorescence (EDXRF) techniques, respectively. The results showed that mean ± standard deviation (SD) PM10 levels ranged from 43.2±10.7 to 592.6±133.5 μg/m3 across the five sites regardless of the period of the day and the season. In descending order, the industrial site “A” had mean PM10 level (μg/m3) of 592.6±133.5 and 271.6±46.6; industrial site “B” had 401.2±70.1 and 216.0±28.3; commercial site had 370.4±49.0 and 160.5±38.6; residential areas “B” had 333.3±37.1 and 179.0±10.7 and “A” had 246.9±21.4 and 129.6±18.5 in the morning and afternoon, respectively during the dry season. During the rainy season, similar trends were observed with industrial site “A” having a mean PM10 level (μg/m3) of 302.5±56.6 and 166.7±37.1; industrial site “B” had 277.8±32.1 and 154.3±28.3; commercial site had 246.9±46.6 and 86.4±21.4 residential areas “B” had 197.5±38.5 and 74.1±18.5 and “A” had 111.1±18.5 and 43.2±10.7, in the morning and afternoon, respectively. The study showed that industrial sites had the highest PM10 levels, followed by the commercial sites and the least levels were from residential sites. The substantial PM10 levels in these sites were mainly attributable to emissions from cement industries. The levels were significantly higher (p< 0.05) in the morning than afternoons in both seasons and considerably high (p < 0.05) during the dry compared to the rainy season. The meteorological factors had a high influence (p < 0.05) on these levels where, negative correlations of R= -0.752 and R= -0.783 were observed between wind speed and temperature, respectively, and PM10 levels during the dry season. Conversely, a positive correlation of R = 0.906 was obtained between relative humidity and PM10 levels. Similar trend in the correlation values of R = -0.374, R = -0.506 and R = 0.826 were observed between wind speed, temperature and relative humidity, respectively, and PM10 levels in the rainy season. The mean PM10 values for residential site ‘’B” situated downwind of the cement industries were also consistently high notwithstanding the period of the day and season when compared to those of the residential site “A” situated upwind. The PM10 levels at the five sites had variations in the percentage composition of Cu, Sb, Si, Al, Ca, Fe, Zn, Cr, Pb, Cd and Ni. Nonetheless, Si, Cd, Al, Ca and Fe, components of cement, were prominent elements detected across these sampling sites irrespective of the seasons. The high levels of PM10 with toxic components found in this study implies that suitable interventions and policies should be put in place to control these levels and safeguard human health and environment.