Air pollution research has gained a lot of prominences worldwide in recent times, because of the increased level of anthropogenic activities and climatic change arising from the quest for industrialization in all cities of the world. It is one of the major causes of deterioration in human health conditions as the breathing of safe air is important just as safe water or food ( Akolkar et al., 2015). Particulates matter is known to be one of the most threatening atmospheric pollutants on human health conditions, together with sulfur dioxide, nitrogen dioxide, and ozone ( WHO, 2016). Fine Particulate (PM_2.5 and PM₁₀) being of special concern. These particulates are emitted from a variety of sources, mainly from traffic and industrial production, as well as by natural sources like desert dust outbreaks, forest fires and dust resuspension by wind ( Karagulian et al., 2015).Exposures to fine particulates are linked to decreased lung function and increased respiratory symptoms such as airways irritation, coughing, or difficulty breathing and possibly worsen COVID-19 symptoms (Carretero-Peña et al., 2019). Therefore, monitoring fine particulates pollution and controlling their emission levels in the surrounding air have become one of the major concerns of environmental protection agencies and public health protection organizations.

It has been reported by many researchers that anthropogenic activities are a major cause of heavy metals and fine particulates matter contaminants in the air (Kasassi et al., 2008; Zhang et al., 2010). Industrial operations in developed and developing countries are known to contribute greatly to anthropogenic air pollution with particulate matter and the gaseous pollutants been released mostly at levels that constitute environmental nuisance (Tyovenda et al., 2016; Hadlocon et al., 2015). Ambient air pollution by heavy metals is a universal problem because most of the metals are inextinguishable and can pose serious risks to human health, plants, animals, ecosystems, or other media (Khan et al., 2008; Zeireini et al., 2005; Shinggu et al., 2010; Abah et al., 2020).

Lopez et al. (2005) reported that anthropogenic activities releasing fine particulates and heavy metals into the air contribute about 4% - 8% of deaths annually in the world that has linked to air pollution. Constituents of air pollution may be organic, inorganic, or a combination of both with heavy metals contents which continuously contaminates the ambient air for many decades, even after they are no longer being emitted into the atmosphere. The effects of this pollution not only degrade the quality of air, water, and food crops but are also detrimental to human health and animals (Dong et al., 2011; Anietie & Labunmi, 2015; Abah et al., 2020). Unlike other pollutants, heavy metals can go unnoticed while building in air or soil at concentrations that are toxic to living things (Taghipour et al., 2013; Melaku et al., 2008). Toxicity signs for each heavy metal vary; for instance, Cu, As, Pb, Hg, Al poisoning, and Zn are known to cause gastrointestinal disorders, stomatitis, tremor, diarrhea, ataxia, paralysis, hemoglobinuria, vomiting and convulsion, pneumonia, and depression (Singh et al., 2010).

Lin et al. (2016) reported that excessive intake of Pb into the human body can damage the nervous, skeletal, endocrine, enzymatic, circulatory, and immune systems. Cadmium intake can cause chronic effects such as lung cancer, kidney dysfunction, prostatic proliferative lesions, pulmonary adenocarcinomas, prostatic proliferative lesions, and bone fractures (Brevik et al., 2015).

In recent years, Northern Nigerian major cities have witnessed rapid population growth of humans, and increased rate of industrial activities with the resultant increase in fine particulate levels and heavy metals degrading the air quality.

Unfortunately, these cities and industries have no capacity and facilities to combat air pollution from the source thus, all industrial emissions are deposited into the air leaving nature to take its cause. These may result to enhance levels of particulate matter and heavy metals loading in the immediate vicinity and the resulting consequences on the biological system. Despite this, no comprehensive data has been published on the fine particulate and heavy metals pollution status of the immediate industrial vicinities in northern Nigeria. Thus, this study focuses on assessing the current pollution status of environmentally concerned fine particulate (PM2.5&10) and heavy metals in the ambient air within the vicinity of some selected northern Nigeria industries to gauge the values with set regulatory standards. It is hoped that the study will provide baseline data for continuous monitoring of the impact of fine particulate and the heavy metals content of the immediate industrial environment and hence, useful in recommending precautionary measures that could limit the exposure of the people living and working close to the industrial area to particulate and metal pollutants.

The results of the monthly mean particulates matter (PM2.5 and PM10) measured from the industrial sites between September 2018-August 2019 is computed together with the toxicity potential using Equations ((1), (2)) from all the sites and presented in Table 2, we used the World Health Organization (WHO) permissible limit of 25.0 µg∙m−3 and 50.0 µg∙m−3 for PM2.5 and PM10 respectively. While the results of the heavy metals concentrations were given in part per million (ppm) by AAS but were converted to mg∙m−3 using Equation (7) and presented in Table 3 along with their respective toxicity potentials.

1   mg ⋅ m − 3 = 0.041   ppm × m i (7)

where m i is the molecular weight of the metal (i) in g∙mol⁻¹ and 0.041 is the conversion factor at standard temperature (Tyovenda et al., 2016).

As can be seen in Table 2 and Figures 2-4, the month of December and January

Note: TP that are harmful to human are indicated with bold figures.

had the highest mean concentrations of PM_2.5 and PM₁₀ in the Grand Cereals industry, Jos with toxicity potentials in December, January, February, and April exceeding unity and thus posing potential threats to the lives of the people living and working in the site. In the Jhako industry, higher concentrations of PM_2.5 were captured in March and February with TP values exceeding unity while PM₁₀ had concentrations in December, January, February, March, and April more than the set standard of 50.0 µg∙m⁻³. However, in the Terytex industry, the results were promising as concentrations of PM_2.5 and PM₁₀ exceeded the set standard of 25.0 µg∙m⁻³ and 50.0 µg∙m⁻³ in December and January only. Higher concentrations PM_2.5 and PM₁₀ with toxicity potentials exceeding one occurred consistently in almost all the three sites in December 2018-April 2019. The reason for this may not be farfetched from the fact that within these periods of the study, the rain was reduced, washout was also reduced and resuspension of dust was enhanced by the harmattan. On average the receptors of the Grand Cereals industry, Jos are more susceptible to respiratory infections like asthma, chronic bronchitis, benign, airways irritation, coughing or difficulty breathing, and aggravation of tuberculosis/COVID-19 symptoms (Lopez et al., 2005; WHO, 2020).

The correlations between the PM2.5 and PM10 concentrations in the industrial site determine using equation 3 were positive and very strong with R ranging from 0.7 - 0.9. This means that these particulates originate from similar anthropogenic sources from the industrial vicinities. The correlation was stronger at the Grand Cereals industry, Jos with the coefficient of determination R2 = 0.88, followed by the Terytex industry, Kano with R2 = 0.69.

The results of Table 3 and Figure 5 showed that of the eight heavy metals (Ni, Co, Cu, Pb, Cd, Cr, Mn, and Zn) analyzed in all the sites only Nickel, Lead and Cadmium that had values in the ambient air exceeding the set standard by WHO/EU in Terytex industry, Kano and Grand Cereals, Jos. The shaded area of Figure 5 and Table 3 showed that the Concentration Ni was highest in the Terytex industry followed by Grand Cereals, Jhako has the highest concentrations of copper, followed by Grand cereals with Grand Cereals recording higher concentrations of Pb, Cd, Cr, Mn, and Zinc. Diseases like diarrhea, gastrointestinal disorders, tremor, stomatitis, hemoglobinuria, paralysis, ataxia, vomiting and convulsion, depression, and pneumonia may be prevalent within these industrial areas (Taghipour et al., 2013). Other effects of inhaling heavy metals in the air like neurotoxic, or even carcinogenic, mutagenic, or teratogenic may also occur (Singh et al., 2010). For example, workers that inhale excessive Pb were reported by Lin et al. (2016) to suffer damages of the nervous, skeletal, endocrine, enzymatic, circulatory, and immune system. While chronic effects of inhaling Cd include lung cancer, kidney dysfunction, hypertension, pulmonary adenocarcinomas, prostatic proliferative lesions, and bone fractures (Brevik et al., 2015; Kamani et al., 2014; Mafuyai et al., 2014). Exposure to enhanced levels of Nickel may results in Ni dermatitis consisting of itching of the fingers, hands, and forearms also Lu et al. (2010) reported that exposure high levels of nickel compounds cause

Note: Numbers bolded with * indicates toxicity potential that are harmful to human.

Figure 5. Variation of heavy metals concentrations in ambient air in the industrial sites.

intestinal disorders, convulsions, and asphyxia. Repeated exposure can cause sleeplessness, headache, dizziness, weakness, poor memory, tightness in the chest, loss of hair, loss of libido. Lung and nasal cancers have also been reported from exposure to nickel refinery dust and nickel sub sulfide (US Environmental Protection Agency, 1999).

Month/Year

From the results of a two-way correlation analysis carried out on the heavy metals concentrations in the three sites using Equations (4)-(6), it was found that the highest correlation R = 0.99 was observed for site i, k with site j, i and j, k recording R = 0.45 each respectively. The multiple results as tested by Equations (4)-(6) gives a strong correlation with R = 0.83 in all the cases respectively. These strong correlations indicate the interdependence of these metal pairs and could be attributed to the presence of these metals in similar sources (i.e. industrial operations, the exhaust of power plants, emissions from folk lifters, emission stacks, and dust generated from the processing of industrial raw materials as well as vehicular emissions).

The concentration levels of fine particulates (PM2.5 and PM10) and eight heavy metals (Ni, Co, Cu, Pb, Cd, Cr, Mn, and Zn) and their toxicity levels in ambient air collected from three industrial sites in northern Nigeria has been examined in this study. The monthly mean concentrations levels of (PM2.5 and PM10) captured during the dry season months of December, January, February, and April in Grand Cereals industry, Jos and Jhako Technology, Kaduna exceeded the regulatory limit value of 25.0 µg∙m−3 and 50.0 µg∙m−3 as set by WHO for PM2.5 and PM10 respectively.

However, in the Terytex industry, the results were promising as concentrations of PM2.5 and PM10 exceeded the set standard of 25.0 µg∙m−3 and 50.0 µg∙m−3 in December and January only. Higher concentrations PM2.5 and PM10 with toxicity potentials exceeding one occurred consistently in almost all the three sites in December 2018-April 2019. The reason for this is because, during these periods of the study, the rain was reduced, washout was also reduced and resuspension of dust was enhanced by the harmattan. The correlation between the PM2.5 and PM10 concentrations in the industrial site was positive and very strong with R ranging from 0.7 - 0.9. This means that these particulates originate from similar anthropogenic sources from the industrial vicinities.

The study also reported varying concentrations of the eight heavy metals (Ni, Co, Cu, Pb, Cd, Cr, Mn, and Zn) analyzed in all the sites with only Nickel, Lead, and Cadmium concentrations in the ambient air exceeding the set standard by WHO/EU in Terytex industry, Kano and Grand Cereals, Jos. At all the industrial areas sampled, cadmium recorded the highest toxicity potential of 4.20, in the Grand Cereals industry, Jos while Co concentrations were below detection levels by AAS in all the sites studied. The inter-elemental multiple correlation coefficients of the heavy metals in the three sites revealed a very strong correlation (R > 0.8) and high positive correlation were observed for any of the two pairs with R ranging from 0.5 to 1.0. These means common sources of anthropogenic inputs contributed to the heavy metals recorded from the industrial areas. We suggested that for cleaner air quality, these industries install electrostatic precipitators to combat fine particulates emission from their stack and also recommended a proper legislative framework to regulate and control industrial fugitive emissions to protect northern Nigeria air shed.

We appreciate the cooperation and kindness of Eng. Aondowase Kwaza, the Manager of Jhako Technologies, Kaduna, Eng. David Dafeng of Grand Cereals, Jos, and Eng. Haruna Abubakar of Terytex industry, Kano for granting us access to carry out this study within their industrial premises.

The authors declare no conflicts of interest regarding the publication of this paper.