Tree Species as Biomonitors of Air Pollution around a Scrap Metal Recycling Factory in Southwest Nigeria: Implications for Greenbelt Development

Trees are biomonitors and sinks for air pollutants but better sinking ability comes from trees with high tolerance for air pollution. Consequently, this study investigated the Air Pollution Tolerance Index (APTI) and Anticipated Performance Index (API) of six dominant tree species around a scrap metal recycling factory in Ile-Ife, Southwest Nigeria. Biochemical and physiological parameters such as the relative water content, total chlorophyll, leaf extract pH and ascorbic acid content of the leaves of the selected tree species were determined and used to compute the APTI. The biological and socio-economic characters of each tree species were equally examined to determine the API. The APTI of the selected tree species during the dry season was in the N. laevis (11.8) > A. boonei (11.2) > S. siamea (11.0) > B. micrantha (10.8) > T. orientalis (10.6) > T. grandis (9.6). According to the API grading, N. laevis and A. boonei were classified as "good" (62.5% each) tree species for greenbelt development for both dry and wet seasons, while T. orientalis was also classified as a "good" (62.5% each) tree species for greenbelt development for the wet season only. Native tree species such as N. laevis, A. boonei and T. orientalis exhibited better tolerance to gaseous pollutants and are recommended for biomonitoring environmental health and greenbelt establishment.