Seasonal variability of heavy metal content in the atmosphere of Ketu-Mile 12 Area of Lagos - State, south -western Nigeria using Polytrichum juniperinum as biomonitor

Abstract

This research reports the seasonal variability results of some heavy metals (Zn, Pb, Cr, Ni and Cu) present in Ketu-Mile 12 area, Lagos - State using moss plant (Polytrichum juniperinum) as a bioindicator. The samples of the Moss specie were collected randomly for wet (March - August, 2017) and dry seasons(September, 2016 - February, 2017) at ten different locations at Ketu-Mile 12 area, between 2 - 2.5 m high from unplastered buildings. The samples were properly cleaned from all the debris then weighed and digested with a mixture of HN0₃ and H₂O₂ for 35 min. The concentrations of the five heavy metals were determined using Atomic Absorption Spectrophotometer (AAS). Results showed that Zinc (Zn) was the most abundant in all the sites while the least abundant is Cadmium (Cd) during the wet and dry season. During the dry season, the most polluted site was Ketu garage (2.0536mg/L) while Iyana school (0.2614mg/I) was the least polluted site. Similarly, Mile 12 Market(3.4303mg/L) was the most polluted site during the wet season while Kosofe (0.5358mg/L) was least polluted site. The average concentrations of the heavy metals at Ketu-Mile 12 during the dry and wet seasons and percentage concentration of the heavy metals were as follows respectively: Zn(3.5411mg/I;80.1%),Pb(0.1696mg/I;3.9%), Cd(0.0116mg/I; 0.3%), Ni (0.1374mg/I; 3.2%) and Cu(0.5080mg/I; 11.6%) and during the wet season were Zn(7.2496mg/I;72.1%), Pb(0.5373mg/I;5.3%), Cd(0.0442mg/I; 0.5%), Ni(0.2289mg/I; 2.3%) and Cu(1.9925mg/I;19.8%). The sequence of bioaccumulation and distribution followed the pattern : Zn > Pb > Cu > Ni > Cd. Therefore, it was clearly seen that the heavy metal concentration during the wet season was greater than that during the dry season. There was a significant difference in the level of each heavy metal in the atmosphere of Ketu -Mile 12 (P < 0.05). The concentration of some of the heavy metals present were greater than the Federal Ministry of Environment of Nigeria (FME) and World Health Organization (WHO) threshold limiting values suggesting that the study area was polluted.

Keywords: Anthropogenic, bioaccumulation, bioindicator, concentrations, pollution, spectrophotometer