Air pollution is the introduction/emission of harmful solid or gaseous substances into the atmosphere, which are capable of inducing adverse effects to all forms of biodiversity including man and his valuable possessions. Harmful substances that impair air quality include Carbon monoxide, Oxides of Nitrogen and Sulphur, Hydrogen Sulphide, Methane, Ammonia, suspended particulates etc. Air pollution results from both anthropogenic and lithogenic activities 1, however anthropogenic impacts and their sources are more influential compared to lithogenic impacts 1. As a result of poor and inappropriate management of Municipal solid waste, most cities are faced with serious health and environmental problems 2.

High concentration of individual pollutant gases or their synergy with others 3, could have adverse human and environmental effects. Inhalation of these gases is one of the commonest means of exposure. Accumulation of pollutants in the human body through inhalation of air is an important route 4. Hydrogen Sulphide is basically responsible for the foul smell associated with dumpsites. According to Rim-Rukeh 5, it can be sensitive at concentration as little as 0.11 – 0.33 ppb, with flammability at highest and lowest concentrations of 44% and 4% respectively. Furthermore, it is colourless and denser than normal air, and has a characteristic property of an objectionable odour like rotten-egg, at a very minute concentration 5. Emission of H₂S occurs when putrefying microbes decompose biomass under anaerobic conditions.

It was reported by the International Panel on Climate Change (IPCC) that, besides emissions from fossil fuel combustion, methane emission from landfills account for 3 - 19% of the anthropogenic sources and global warming 67. Another aspect of air pollution is Suspended Particulate Matter (SPM). Air pollution is largely linked to high rates of distress and mortalities resulting from respiratory and cardiovascular ailments 891011, with the emission of some basic pollutant gases (NOX, SOX and CO) from most municipalities indicated as major contributors 11.

The research by Akinremi 12, has indicated a correlation between the rates of pollution, mortality and life expectancy. The adverse effects posed by air pollution cannot be overemphasized. Some signs and symptoms are wheezing, coughing, as well as exacerbation of already existing diseases like asthma. It can cause or promote other major health problems like heart disease, stroke and lung cancer etc. It is also worthy of note that when putrefying organism act on biomass from waste stream they enhance the release of pollutant gases 13, like methane, ammonia and hydrogen sulphide 1. The broad spectrum of harmful effects on man and his environment traceable to gaseous air pollution demands a greater commitment to the development of environmental policies and strategies to manage the challenge posed by the emission of hydrogen sulphide from dumpsites in Yenagoa metropolis effectively.

As presented in Figure 1, the mean background trending of Hydrogen Sulphide (H₂S) ranges from 1.35 - 8.89 ppm, with lower levels in dry season compared to wet season. It is noteworthy that the second station of the central dumpsite (CDS 2), recorded the highest mean value in wet season, compared to dry season value of Akenpai station indicating the lowest level of H₂S gas. Furthermore, it was noteworthy that the mean level of H₂S was below detection limit for both wet and dry seasons in the control stations (Figure 1).

The spatial variation of H₂S level amongst the dumpsite stations is presented in Figure 2. Results showed that H₂S level was low, apart from the two stations of the central dumpsite. Notwithstanding the level of H₂S ranged from 1.40 - 14.34 ppm. In addition, the control station recorded values below detection limit (0.01 ppm), compared to values in other stations (Figure 2). Based on seasonal variations (Figure 3), the levels of H₂S ranged from 1.88 – 4.43 ppm with highest and lowest values in the months of April and March respectively (Figure 3).

Table 1 presents the seasonal health risk assessment on the levels of H2S associated with the dumpsites in all stations. The health risk assessment was based on two scenarios, which were the median mean scenario (MMS), and the Geometric Mean Scenario (GMS). Based on the MMS, the levels of H2S in Akenpai (LA) station were moderate in both seasons; and also safe in both seasons based on the GMS. In the Etegwe station (LB), the MMS indicated that H2S level was moderate in dry season, but unsafe for sensitive group in during the wet season. However, based on the GMS H2S levels were safe in dry season and moderate in wet season (Table 1). The level of H2S in Opolo station (LC) was unsafe for sensitive group in dry season, and moderate in wet season based on the MMS. In the same vein, moderate condition was observed in both seasons based on the GMS. In Kpansia market (LD), the GMS, showed that H2S was safe in the dry season and moderate in the wet season. Comparatively, based on the MMS H2S levels were moderate in both seasons. Furthermore, in the two stations of the central dumpsites (LE and LF), the levels of H2S were hazardous in both seasons and scenarios, except for the GMS in station 1 during wet season which had an unhealthy condition (Table 1).

Hydrogen Sulphide emissions associated with dumpsites in Port-Harcourt were reported as 0.19 mg/m314. In Delta State, it ranged from 3.4 - 7.7 ppm 5. Zaria Metropolis in Kaduna State, results showed that H₂S levels ranged from 0.00135 ppm - 0.0315 ppm in dry season, and 0.0005 ppm - 0.0037 ppm in wet season 15. In Nekede, it was reported that morning and evening emissions of H₂S from dumpsites range from 0.80 ppm – 0.84 ppm and 0.79 ppm – 0.82 ppm respectively 16.

Beside the environmental hazard associated to H₂S, Health hazard have also been reported. According to the Occupational Safety and Head Administration 17, exposure to H₂S at low concentration can cause nasal, eye, throat, respiratory tract irritation and exacerbate conditions of sensitive groups like asthmatic patient. Exposure to moderate emission can result to severe eye and respiratory impairment including coughing, dyspnea, headache, dizziness, nausea, vomiting, staggering and excitability 1718. High level exposure to H₂S have been documented to cause rapid grave health problems including; shock, convulsions, suffocation, extremely rapid unconsciousness, coma and death 17. Large volume of H₂S emanate from dumpsite 1, and the need to mitigate their envisaged adverse consequences have become necessary.

This research investigated the level of H₂S associated with MSWs dumpsites in Yenagoa metropolis. Results showed significant levels of H₂S, especially from the central dumpsites (LE and LF). Meanwhile, H₂S level was below detection limit in the control station (LX). Consequent upon our findings, the level of H₂S may be on the rise due to a rise of anthropogenic activities together with poor management of waste stream. The emission of H₂S may pose grave environmental threats due to its greenhouse effects. Consequently, the sequestration of H₂S has become necessary. We therefore recommend the gasification of H₂S for power generation, as a waste to wealth policy. In addition, dumping of wastes close to public places should be prohibited following the provision modern or sanitary landfills. Furthermore, effective legislations and policies should be enacted to ensure the reduction, reuse and recycling of waste stream.