Indoor settled harmattan dusts at seven sampling stations from the University of Agriculture Makurdi were collected between November, 2014 to March, 2015 (five months) using the wipe sampling methodology. Gravimetric measurement of the dust samples from all the sample locations revealed that dust loading within the institution during the period of assessment ranges from 4.475 - 6.533 g/m 2. Masses of indoor settled dust were expectedly higher along high traffic, untarred roads and construction sites as well as in older buildings than others during the period of this study. AAS analysis of the dust samples shows that heavy metal concentrations (mg/kg dry weight) throughout the sampling stations during the period of investigation range from 0.2372 - 0.7152 for Cu, 293.6 - 884.9 for Fe, 4.265 - 68.55 for Mn and 4.239 - 42.53 for Zn. The concentrations of all the metals investigated were found to be lower when compared with related values in literature and were within acceptable limits during the period of this study. Pearson correlation matrix also shows positive correlation between the possible metal pairs at 95% level of confidence, indicating a similar source which may be from anthropogenic activities within and outside the area.
The Harmattan is a cold-dry and dusty trade wind, blowing over the West African sub region. This northeasterly wind blows from the Sahara Desert into the Gulf of Guinea between the end of November and the Middle of March (winter) [
The air is particularly dry and desiccating when the Harmattan blows over the region. Dust according to Adekola and Dosumu [
Many studies on settled dust have focused on elemental concentrations and source identification [
Considerable attention has been paid to the study of metal pollution in city air, residential house dusts, roadside dusts and soils. However, there is little concern of the presence of these metallic pollutants in indoor dust in public offices. Since there are limited data on dust contamination in offices, this study is important and timely. The aim of this work was to determine the concentrations of heavy metals indoors by examining dust from selected offices of the Federal University of Agriculture Makurdi, Nigeria. The information obtained will form the basis that can be used for planning and management strategies to achieve a better environmental quality in the University, as well as serve as baseline for further studies in the area.
Makurdi town is the headquarters of Makurdi Local Government Area and capital of Benue State, generally known as the “Food Basket” of Nigeria. The town is located between latitude 7˚38'N - 7˚50'N, and longitude 8˚24'E and 8˚38'E with a total area of 200 km2. It is situated in the Benue valley in the North Central region of Nigeria with population of 500,791 people. It is traversed by the second largest river in the country, the River Benue (
University of Agriculture Makurdi (UAM) is located in Makurdi and it occupies an arable land area of 8048 hectares. The University is made up of nine (9) Colleges and thirty nine (39) Departments spread throughout its North Core and South core campuses. Several agricultural activities take place within the institution with the application of modern technologies such as the use of tractors, fertilizers, herbicides and pesticides of different sorts. This as well as the heavy traffic witnessed on daily basis contributes to the presence of substantial amount of heavy metals within the indoor environment of the institution.
Reagents of analytical grades procured from Sigma Aldrich, USA were utilized in this study without further treatments.
The wipe sampling methodology was employed in this study for the collection of indoor settled dust. Dust wipe samples were collected according to the American Society for Testing and Material, ASTM E1728 protocol [
[
Ashless filter paper (Whatman no 42) was used as the wipe material in this study. The researcher selected filter paper out of many brands of wipes available, because filter papers completely digest in acid and they contain very low background concentrations of the metals under study. Filter papers were weighed before and after sampling using electronic analytical balance. This was to determine the level of dust loading in different sampling sites. Before weighing, the samples were equilibrated in desiccators at 20˚C - 30˚C in a humidity controlled room for 24 h [
In this study, sampling of indoor settled dust was conducted between the months of November, 2014 and March, 2015 (five months) representing the dry harmattan season when there is high prevalence of dust in the study area. Outdoor settled dust samples were also collected from the vicinities of sampled College buildings during the same period to serve as control. Twenty one offices (three from each of the seven buildings housing the nine Colleges of the University) were selected at random for this study. A total of 210 wipe samples of indoor settled dust were collected from office desks (900 cm2) and ceiling fan blades (100 cm2 each) not previously rusted. While a total of 30 samples of outdoor settled dust was collected from three locations A, B and C within the vicinities of the sampled College buildings during the same period to serve as control. In each College building sampled, one field blank tissue paper was exposed to all handling procedures used for the samples with the exception that no surface was wiped [
College Building | Sample Code | Coordinate | Control Code | Coordinate |
---|---|---|---|---|
Sciences | SC1, SC2, SC3 | latitude 7˚45'N, longitude 8˚37'E and Altitude 143.0 meters | A | latitude 7˚45'N, longitude 8˚37'E and Altitude 129.0 meters |
Veterinary Medicine | VM1, VM2, VM3 | latitude 7˚45'N, longitude 8˚37'E and Altitude 125.0 meters | A | latitude 7˚45'N, longitude 8˚37'E and Altitude 129.0 meters |
Food Technology | FT1, FT2, FT3, | latitude 7˚47'N, longitude 8˚37'E and Altitude 122.0 meters | B | latitude 7˚47'N, longitude 8˚37'E and Altitude 119.0 meters |
Engineering | EN1, EN2, EN3 | latitude 7˚47'N, longitude 8˚37'E and Altitude 134.0 meters | B | latitude 7˚47'N, longitude 8˚37'E and Altitude 119.0 meters |
Agronomy | AG1, AG2, AG3 | latitude 7˚47'N, longitude 8˚36'E and Altitude 116.0 meters | B | latitude 7˚47'N, longitude 8˚37'E and Altitude 119.0 meters |
Agric Econ & Extension | AE1, AE2, AE3 | latitude 7˚47'N, longitude 8˚37'E and Altitude 1126.0 meters | B | latitude 7˚47'N, longitude 8˚37'E and Altitude 119.0 meters |
Animal Science | AS1, AS2, AS3 | latitude 7˚48'N, longitude 8˚37'E and Altitude 137.0 meters | C | latitude 7˚48'N, longitude 8˚37'E and Altitude 128.0 meters |
The surface concentration (loading) of dust loading in each office was found by subtracting the initial mass of filter paper (before sampling) from the final mass of filter paper (after sampling) using electronic analytical balance. Dust loading for each sample location was obtained using the following mathematical expression:
where DL = Dust Loading (g/m2), M1 and M2 are the initial and final masses (grams) of filter paper respectively and A represents the area (m2) of surface wiped.
Dust wipe filter papers from each container were digested in concentrated analytical grade HNO3 on hot plate. After digestion, the contents in the beaker, upon cooling was then transferred quantitatively into a 50 mL volumetric flask and brought to volume with de-ionized water, filtered through ashless filter paper (Whatman no 42) and stored in polypropylene bottles prior to heavy metals analysis. 0.5 g of dust samples from each of the control sites as well as the blank samples were also digested following similar procedure. The Digests were then examined for the concentrations of Cu, Fe, Mn and Zn using Atomic Absorption Spectrophotometer (Shimadzu AA-6300).
The experimental data collected in this research work are presented as tables as mean along with their standard deviations and bar charts.
Smaller particles of dust find their way into the lungs and depending on the size get deposited therein causing respiratory problems [
The results of heavy metal concentration for each of the seven sample locations including the control sites from November, 2014-March, 2015 are presented with graphical plots in Figures 2-5. Pearson Correlation matrix showing the relationship (at 0.05 level of significance) between the metals under study is depicted in
Copper: Cu is an essential element in our diet but at elevated doses, it causes anaemia, liver and kidney damages, stomach and intestinal irritation. Excessive intake of Cu may also result in death with symptoms such as hypertension, coma and jaundice [
Sample Location | Total Dust (g) | Total Area (m2) | Dust Loading (g/m2) |
---|---|---|---|
SC | 0.621 ± 0.001 | 0.120 | 5.175 |
VM | 0.537 ± 0.033 | 0.120 | 4.475 |
FT | 0.569 ± 0.024 | 0.120 | 4.742 |
EN | 0.784 ± 0.033 | 0.120 | 6.533 |
AG | 0.682 ± 0.008 | 0.120 | 5.683 |
AE | 0.623 ± 0.061 | 0.120 | 5.192 |
AS | 0.626 ± 0.060 | 0.120 | 5.217 |
SD = Standard Deviation.
Element | Cu | Fe | Mn | Zn |
---|---|---|---|---|
Cu | 1 | 0.818* | 0.806* | 0.670 |
Fe | 0.818* | 1 | 0.630 | 0.712 |
Mn | 0.806* | 0.630 | 1 | 0.352 |
Zn | 0.670 | 0.712 | 0.352 | 1 |
*Correlation is significant at the 0.05 level (2-tailed).
Author | Heavy Metal Concentration | Study Area | |||
---|---|---|---|---|---|
Cu | Fe | Mn | Zn | ||
Current Study | 0.2372 - 0.7152 | 293.6 - 884.9 | 4.265 - 68.55 | 4.239 - 42.53 | University of Agriculture Makurdi |
Yap et al. [ | 87.50 - 442.0 | 3445 - 3852 | NA | 439.0 - 880.0 | Selangor School, Malaysia |
Chattopadhyay et al., [ | 147.0 | NA | NA | 657.0 | Sydney, Australia |
Mgbamena and Onwukeme [ | 12.75 - 34.75 | 2701 - 2798 | 87.50 - 124.5 | 160.0 - 161.0 | Aba, Nigeria |
Ibrahim et al., [ | 0.860 - 3.120 | 1111 - 2436 | 10.03 - 24.99 | NA | Amber Province, Iraq |
Adekola and Dosumu [ | 0.510 | 40.60 | NA | NA | University of Ilorin, Nigeria |
NA = Not Applicable, ND = Not Detected.
area ranges from 0.2372 - 0.7152 mg/kg. The highest concentration was recorded at the College of Engineering (EN) while the lowest concentration of Cu was recorded at the College of Animal Science (AS) as depicted in
Iron: Fe is an abundant element in the earth crust [
Manganese: Mn is an essential nutrient element for both plants and animals. However, very high concentration of Mn could be dangerous. The concentration of Mn determined in all the sites within the period of assessment ranges from 4.265 - 68.55 mg/kg, with the highest value recorded at the College of Sciences (SC) while the lowest concentration of Mn was recorded at the College of Animal Science (AS) as depicted in
Zinc: Zn is one of the most common elements in the earth crust. It is found in air, soil and water. Zn attaches to dust particles in air which settles as Zn dust particles. Zn is an essential element in our diet, insufficient amount of it can cause health problems and too much of it can be harmful. According to Mafuyai et al. [
All the metals investigated (Cu, Fe, Mn and Zn), were found to be below the maximum permissible limits of heavy metals in dust as reported by Ibrahim et al. [
The Pearson correlation matrix for heavy metal concentration in studied samples as shown in
The maximum values for all the metals reported in the present study are lower when compared with those reported by Yap et al. [
The masses of indoor settled harmattan dust within the University of Agriculture Makurdi were higher along high traffic, untarred roads and construction sites as well as in older buildings than others during the period of this study, indoor dust loading was in order of VM < FT < SC < AE < AS < AG < EN. However, within the period of this research, dust loading in all the College buildings was below SANS (South African National Standard) threshold limit of 18 g/m2/month Similarly, the results of this study show that Cu, Fe, Mn and Zn were detected in indoor settled dust samples investigated within the University of Agriculture Makurdi in order of Cu < Mn < Zn < Fe. The concentrations of these metals were compared with reported values from some popular cities and institutions around the world. The results indicated that the metals were of lower concentrations than reported literature values. This indicates that heavy metals in dust are higher in more industrialized and densely populated cities than otherwise. Similar case may also exist in areas where buildings are located close to roads and construction sites. All the investigated metals in the present study showed concentrations within acceptable limits. However, indoor settled dust can be drastically reduced by frequent wet mopping and vacuuming, also by minimizing the use of windows during the harmattan season.
Ishaq S. Eneji,Itodo U. Adams,Kadili A. Julius, (2015) Assessment of Heavy Metals in Indoor Settled Harmattan Dust from the University of Agriculture Makurdi, Nigeria. Open Journal of Air Pollution,04,198-207. doi: 10.4236/ojap.2015.44017