Monitoring of Environmental Trace Elements in the Industrial-Urbanized Zone of East Algiers by Means of Epiphytic Lichens and Tree Bark

In eastern Algiers (Algeria), a passive biomonitoring research was conducted in the urban-industrial area of Reghaia. To use the ubiquitous olive tree bark in large-scale biomonitoring of trace metal air pollution, we evaluated its bioaccumulation efficiency in a comparative study with the epiphytic lichen Xanthoria parietina. With the use of the effective, non-destructive multi-element approach known as X-ray fluorescence analysis (XRF), the amounts of 12 trace elements in samples of lichen and tree bark were effectively measured. The results revealed that both biomonitors displayed a consistent pattern of element accumulation, and the correlation between average concentrations exhibited substantial agreement, despite tree bark performing somewhat better than lichen. To distinguish between the accumulation rates of elements by lichens and tree bark, the contamination factor (CF) was calculated. Overall, CFs varied considerably depending on the elements assessed and the sampling sites, the highest values for Cd being found in Xanthoria parietina and Olea europaea bark, at 256 and 294.5 respectively.  In order to identify where the trace elements under investigation originated from, enrichment factors were also determined. The results obtained suggest contamination of anthropogenic origin for As, Br, Cu, Pb, Cd and Zn, generated from road traffic, industrial activities, and agricultural practices, in contrast to Al, Cr, Fe, Mn, Ti, and V, which are believed to have lithogenic origins. These findings reveal extreme metal pollution in the Reghaia region, and demonstrate that the bark of Olea. europaea can be as reliable a bioindicator as lichens for assessing levels of atmospheric pollution by trace elements in urban and industrial areas, where harsh environmental conditions can lead to the scarcity or even disappearance of lichens.