Effects of Seasonal Variation on Air Quality and Microbial Composition around Sawmilling Sites in South East Nigeria

Background: The demand for wood and wood products for use in construction and building has resulted in a surge in sawmilling activities especially in Nigeria with resultant incessant emissions into the environment.

Aims: This study was therefore aimed at investigating the air quality status and microbial composition of air around two different sawmill facilities.

Place and Duration of Study: This study was carried out within sawmilling sites at the Ahiaeke and Okigwe Timber markets in Abia and Imo states of Nigeria respective during the dry and rainy seasons.

Methodology: Air quality determination was done in–situ using hand held environmental sensor meters (HANNA Air Monitors, Rhodes Island, USA). Bacterial and fungal concentration (cfu/m3) in the air of saw-mill sites were evaluated by passive air sampler. Petri dishes containing nutrient agar, MacConkey and Sabouraud dextrose agar were exposed at intervals of 10 minutes, 20 minutes and 30 minutes at four designated points as 0m, 50m, 100m and 500m (control).

Results: Seasonal trends were observed in the levels of air pollutants from both sites in this study. PM2.5 and PM10 were at the peaks during the dry season at both sites (Ahiaeke and Okigwe) reaching 134ppm and 275ppm respectively for Ahiaeke whilst it was 39ppm and 65ppm respectively for Okigwe at ground level (0m). There was a continual decline in the values observed for H2S and CH4 as the distances decreased at both sites during dry seasons at 100m while at 500m (control) nothing was detected. It was determined that sampling times of 10minutes yielded countable bacterial growth of 7.4cfu/m3 and 6.2cfu/m3 at the 0m and 50m distances respectively at the Ahiaeke site. A sampling time of 30minutes yielded increased bacterial load of 9.9cfu/m3 and 8.4cfu/m3 at the 0m and 50m distances respectively at same site. A similar trend was observed for total bacterial, coliform and fungal counts at the Okigwe site. Nucleotide sequences of bacterial 16S rRNA gene fragments retrieved from bacterial isolates in this study were deposited in the GenBank nucleotide sequence database under accession nos. MK621199, MK621103, MK621201, MK640631, MK640622, MK640625, MK640623, MK640628, MK640630, MK621201, MK643270, MK621195, MK640785, MK640842 and MK640843 for the bacterial isolate whereas the fungal isolates were deposited with MK621199, MK621202, MK640642 and MK640638.

Conclusion: The results obtained in this study are not only useful in providing information on the prevailing air quality but also justify the need for epidemiological research in the area to ascertain the level of impact of continuous gaseous emission from the sawmill on the pollution of the sites.