ACCUMULATION OF AIRBORNE TRACE METALS IN MOSSES: A BIOMONITORING STUDY

Abstract

The mosses; resembled as the common ancestor of terrestrial plants, have a better suitability to monitor atmospheric depositions as they obtain nutrients needed for their vital processes from both wet and dry deposition and they do not have real roots. The weakly developed cuticle of the mosses is promoted the trace metal uptake from the atmosphere. Thus, this study aimed to assess the suitability of inhabitant mosses in Avissawella city area to accumulate airborne trace metals. Mosses were collected along three transects covering the city area and the reference moss samples were collected from nearby pristine area. All the samples were collected from tree barks and above 1.5 m from the ground. The collected samples were cleaned, oven dried, powdered, acid digested, and analyzed for Mn, Fe, Ni, Cu, Zn, Cd and Pb by Atomic Absorption Spectroscopy. At the each and every step, care was taken to avoid any of metal contamination from used materials and equipments. The obtained results from two sample t test implied a significant difference (p value ≤ 0.05) between the mean trace metal concentration in mosses collected from city and from reference area. Corresponding mean trace metal concentrations (µgg-1) for each trace metal in city and reference area are respectively as; Mn: 6.48 ± 0.47, 2.464 ± 0.14, Fe: 1788 ± 173, 247.9 ± 11, Ni: 10.14 ± 0.47, 5.83 ± 0.24, Cu: 9.30 ± 0.76, 3.764 ± 0.12, Zn: 537 ± 42, 160.4 ± 9.7, Cd: 3.231 ± 0.054, 2.456 ± 0.035, Pb: 65.4 ± 3.9, 24.38 ± .0. Accordingly, the indigenous mosses in the city area have accumulated more amounts of all the trace metals when comparing with their reference samples. Thus indicate the city air is contaminated with mentioned trace elements and the major causes for the elevated levels of trace metals in air at city area are the automobile exhausts and the industrial emissions. Further the ratios of the contamination were calculated and this was used to map the level of contamination as a spatial distribution patterns with ArcGIS 10.4. Moss biomonitoring is a reliable method which can be implemented as a continuous biological monitoring method to evaluate the level of airborne trace metals in urban environs.