In vitro and in vivo assessment of antimicrobial, enzymatic, and antifouling properties of self-potent lichen symbiotic bacteria.

This study aimed to comprehensively assess the antimicrobial, antifouling, and antibiofilm-forming potential of lichen symbiotic bacteria against marine fouling bacterial strains. A total of 50 lichen-associated bacteria (LAB) isolates were successfully characterized and evaluated for their effectiveness in mitigating biofouling caused by various marine biofoulers. Through a battery of biological assays encompassing enzymatic, antagonistic, antimicrobial, and antifouling assays, 15 LAB isolates were identified based on their antagonist activities. Notably, the strain LAB4 exhibited remarkable performance across all bioassays, demonstrating its proficiency as an antifouling agent. The production of crude LAB extracts was successfully scaled up using a large-scale fermentor and further optimized. Additionally, a phylogenetic analysis of the isolated strain Bacillus proteolyticus D65's 16S ribosomal RNA gene revealed a high query coverage and percentage identity of 92.62% (accession no. MK883171.1). In conclusion, the lichen bacterial symbiotic isolate B. proteolyticus exhibited significant in vitro and in vivo inhibition of foulants. This study highlights the potential of lichens as a valuable source of yet unexplored bacteria. The bacterial consortium associated with Parmotrema sp. holds promise in combatting biofouling, which poses a substantial threat to the maritime industries and their economic stability.

Atmospheric pollution by potentially toxic elements: measurement and risk assessment using lichen transplants.

The lichen Usnea articulata collected from an unpolluted area was exposed for 6 months at 26 sites for the sample chosenusing a stratified random design, and the content of potentially toxic elements (PTEs) including As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sn, V, and Zn, was assessed using ICP-MS. The health risk for both adults and children was then calculated using the PTEs concentrations. The results showed that despite the hostile urban conditions, transplanted lichens depicted clear deposition patterns of airborne PTEs, mostly associated with industrial sites, where As and other elements showed remarkably high values. The cumulative hazard index was below the risk threshold, both for adults and children. For the entire population (particularly children) residing in areas surrounding industrial sites, As and Cr appeared to be potentially carcinogenic elements.

Use of new Indices for the Assessment of Air Quality in the Safi Region (Morocco) using Lichen Biomonitoring of Air Contamination by Trace Elements.

This study aims to use environmental indices as complementary tools to other air quality biomonitoring techniques. The concentrations of trace elements Hg, Se, V, Mo, and Ba were analyzed by ICP-MS in four lichens: Xanthoria calcicola, Xanthoria parietina, Ramalina pollinaria, and Ramalina lacera. To assess the contamination of lichens by trace elements, different environmental indices were calculated: Contamination Index (Ic), Contamination Factor (CF), Pollution Load Index (PLI) and Enrichment Factor (EF). The results revealed that the genus Ramalina has a low tolerance to polymetallic pollution with a PLI not exceeding 0.44. The genus Xanthoria seems more resistant to polymetallic pollution with a maximum PLI of 2.58. The calculation of the enrichment factor revealed a very strong enrichment of the lichens in Mo, Hg and Se with a maximum content in Ba which reflects a strong metallic contamination of various origins especially in the urban and industrial areas of the region.

Assessment of Cytotoxic/Antitumour Potential and in silico Study of Salazinic Acid Isolated from Parmotrema concurrens.

INTRODUCTION: Despite numerous scientific advances, cancer continues to be one of the main causes of death in the world. This situation has driven the search for promising molecules. Lichen substances have been widely described for their pharmacological potential. OBJECTIVE: The present study evaluated the antitumour potential of a depsidone isolated from Parmotrema concurrens- salazinic acid (SAL) - through in vitro, in vivo and in silico studies. METHODS: The molecule was isolated from the acetonic extract of the lichen and recrystallized in acetone. The macrophage J774, sarcoma-180 and MDA-MB-231 cell lines were used for the MTT cytotoxicity assay. The antitumor assay used a murine model (Swiss albino mice) with sarcoma-180. The animals were treated for seven consecutive days with doses of SAL (25 and 50 mg/kg) and 5-fluorouracil (20 mg/kg). RESULTS: Its purity was determined using high-performance liquid chromatography (94%), and its structure was confirmed by H1 and C13 nuclear magnetic resonance. SAL was not considered toxic to cancer cell lines, showing cell viability rates of 79.49 ± 4.15% and 86.88 ± 1.02% for sarcoma-180 and MDA-MB-231, respectively. The tumour inhibition rate was greater than 80% in the animals treated with SAL and 65% for those that received 5-fluorouracil. Simulations of molecular dynamics to estimate the flexibility of the interactions between human thymidylate synthase and derivatives of SAL and 5-fluorouracil revealed that SAL exhibited greater enzymatic interaction capacity, with highly favourable energy, compared to 5-fluorouracil. CONCLUSION: The present results demonstrate the potential of salazinic acid as a tumour inhibition agent.

High spatial resolution assessment of air quality in urban centres using lichen carbon, nitrogen and sulfur contents and stable-isotope-ratio signatures.

Air pollution and poor air quality is impacting human health globally and is a major cause of respiratory and cardiovascular disease and damage to human organ systems. Automated air quality monitoring stations continuously record airborne pollutant concentrations, but are restricted in number, costly to maintain and cannot document all spatial variability of airborne pollutants. Biomonitors, such as lichens, are commonly used as an inexpensive alternative to assess the degree of pollution and monitor air quality. However, only a few studies combined lichen carbon, nitrogen and sulfur contents, with their stable-isotope-ratio signatures (δ13C, δ15N and δ34S values) to assess spatial variability of air quality and to 'fingerprint' potential pollution sources. In this study, a high-spatial resolution lichen biomonitoring approach (using Xanthoria parietina and Physcia spp.) was applied to the City of Manchester (UK), the centre of the urban conurbation Greater Manchester, including considerations of its urban characteristics (e.g., building heights and traffic statistics), to investigate finer spatial detail urban air quality. Lichen wt% N and δ15N signatures, combined with lichen nitrate (NO3-) and ammonium (NH4+) concentrations, suggest a complex mixture of airborne NOx and NHx compounds across Manchester. In contrast, lichen S wt%, combined with δ34S strongly suggest anthropogenic sulfur sources, whereas C wt% and δ13C signatures were not considered reliable indicators of atmospheric carbon emissions. Manchester's urban attributes were found to influence lichen pollutant loadings, suggesting deteriorated air quality in proximity to highly trafficked roads and densely built-up areas. Lichen elemental contents and stable-isotope-ratio signatures can be used to identify areas of poor air quality, particularly at locations not covered by automated air quality measurement stations. Therefore, lichen biomonitoring approaches provide a beneficial method to supplement automated monitoring stations and also to assess finer spatial variability of urban air quality.

Winter condition variability decreases the economic sustainability of reindeer husbandry.

Wild and semidomesticated reindeer are one of the key species in Arctic and subarctic areas, and their population dynamics are closely tied to winter conditions. Difficult snow conditions have been found to decrease the calving success and survivability of reindeer, but the economic effects of variation in winter conditions on reindeer husbandry have not been studied. In this study, we combine state-of-the-art economic-ecological modeling with the analysis of annual reindeer management reports from Finland. These contain local knowledge of herding communities. We quantify the occurrence probabilities of different types of winters from annual management reports and analyze the effects of this variation in winter conditions on reindeer husbandry using an age- and sex-structured bioeconomic reindeer-lichen model. Our results show that difficult winters decrease the net revenues of reindeer husbandry. However, they also protect lichen pastures from grazing, thereby increasing future net revenues. Nonetheless, our solutions show that the variability of winter conditions overall decrease the net income of herders compared to constant winter conditions. Low lichen biomass appears to make reindeer management more sensitive to the effects of difficult winter conditions. We also found that it is economically sensible to use supplementary feeding during difficult winters, but the net revenues still decrease compared to average winters because of the high feeding costs. Overall, our analysis suggests that the increasing variability of winter conditions due to climate change will decrease net revenues in reindeer husbandry. This decrease will still occur even if the most extreme effects of climate change do not occur. This study shows that combining a state-of-the-art bioeconomic model and practitioner knowledge can bring compatible insights, ideas, results, and a bottom-up perspective to the discussion.

Air Quality Assessment by the Determination of Trace Elements in Lichens (Xanthoria calcicola) in an Industrial Area (Sicily, Italy).

This study provides data on variation in the content of metals and metalloids measured in the lichens (Xanthoria calcicola Oxner) collected in the Syracusan petrochemical complex (Sicily, Italy) which is considered one of the largest in Europe. Concentrations of eighteen trace elements measured in the lichens that were collected from 49 different points were analyzed using an inductively coupled plasma (ICP-MS) device. The concentrations of the typical elements of industrial emissions (As, Cr, Ni, and V) highlight the environmental criticality that exists in the study area. The interpretation of the data in terms of multi-element statistical analysis (FA) and enrichment factor (EFs) proved to be particularly useful in identifying several sources that contribute to the presence of trace elements in the atmospheric particulate between anthropogenic emissions and geogenic emissions. The results of this study reveal the versatility of the lichen species Xanthoria calcicola Oxner in the search for trace elements in highly anthropized environments, so the approach followed in this study can also be applied to other industrial contexts.

Antiangiogenic properties of lichen secondary metabolites.

Lichens are symbiotic organisms which are composed fungi and algae and/or cyanobacteria. They produce a variety of characteristic secondary metabolites. Such substances have various biological properties including antimicrobial, antiviral, and antitumor activities. Angiogenesis, the growth of new vessels from pre-existing vessels, contributes to numerous diseases including cancer, arthritis, atherosclerosis, infectious, and immune disorders. Antiangiogenic therapy is a promising approach for the treatment of such diseases by inhibiting the new vessel formation. Technological advances have led to the development of various antiangiogenic agents and have made possible antiangiogenic therapy in many diseases associated with angiogenesis. Some lichens and their metabolites are used in the drug industry, but many have not yet been tested for their antiangiogenic effects. The cytotoxic and angiogenic capacities of lichen-derived small molecules have been demonstrated in vivo and in vitro experiments. Therefore, some of them may be used as antiangiogenic agents in the future. The secondary compounds of lichen whose antiangiogenic effect has been studied in the literature are usnic acid, barbatolic acid, vulpinic acid, olivetoric acid, emodin, secalonic acid D, and parietin. In this article, we review the antiangiogenic effects and cellular targets of these lichen-derived metabolites.

Assessment of air pollution at the indoor environment of a shooting range using lichens as biomonitors.

The aim of the study was to examine the changes in ecophysiological parameters and accumulation of heavy metals in lichens transplanted to a shooting-range environment. Thalli of the epiphytic lichen were transplanted from an unpolluted site to a shooting range. Chlorophyll a fluorescence, thiobarbituric acid reactive substances (TBARS), and damage to cell membranes in the lichen Evernia prunastri and Ramalina farinacea thalli were determined after 3 months exposure period indoors in a shooting range. The concentrations of some heavy metals including cadmium, copper, iron, manganese, nickel, lead, antimony, and zinc were measured in lichens as indicators of the levels of air pollution in the studied environment. Thalli of the lichens transplanted to the shooting-range environment showed stress symptoms where the presence of metal pollutants produced a loss of integrity of lichen cell membranes and induced oxidative stress as evidenced by increased levels of TBARS. The response of lichens transplanted to indoors of shooting range demonstrated a significant accumulation of Pb indicating potential increased metal exposure and consequent adverse health effects.

Nickel spreading assessment in New Caledonia by lichen biomonitoring coupled to air mass history.

Lichen biomonitoring and air mass trajectories were used to study the influence of mining activities in the atmospheric dispersion of metallic elements to assess the exposure of the population to dust emitted by mining activities. A map of forward trajectory densities from open mine surfaces throughout New Caledonia was computed and allowed to identify three preferred wind directions (trade wind, bent trade winds and oceanic winds) that could arise in mining particles dispersion all over New Caledonia. Areas where an air quality monitoring would be advisable to evaluate the exposure of the population to the Nickel dusts have been identified. Lichens collected around the industrial mining site KNS and in North Provence of New Caledonia were analysed for their Ni, Co, Cr, Zn and Ti contents. Backward trajectories were simulated from the lichen sampling point using FLEXTRA fed with ECMWF meteorological data, and densities of trajectories having overflown a mine were calculated. Ratio metal/Ti was then plotted as a function of air mass trajectory densities having overflown open pits. A positive correlation between trajectory densities and titanium-normalized metal in lichen for Ni, Co, Cr was highlighted, indicating that mining is a source of dispersion of these metals. For Zn, which is a tracer of fossil fuel or biomass (wood) combustion activity, no correlation was found. Graphical abstract.

Searching for lichen indicator species: the application of self-organizing maps in air quality assessment-a case study from Balkan area (Serbia).

The subject of this paper is the possibility of using self-organizing map (SOM) in the biomonitoring studies. We used lichens as biomonitors to indicate different degrees of air quality. This research included all of 88 lichen species that was collected at 75 investigated points. These lichen species showed the different responses to air pollution. The air quality was assessed by IAP (index of atmospheric pollution) values. The IAP values were calculated for all of investigated points on the territory of four natural and one urban ecosystem. Calculated IAP values were in range of 10 to 75. On the basis of the lichen data and IAP values, we have employed SOM analysis that distinguished three clusters (A, B, and C). It presented lichen indicator species for each cluster: 16 species for cluster A, 18 species for cluster B, and two species for cluster C. This paper presents a useful method to find indicator species.

Recalibration and validation of the Swiss lichen bioindication methods for air quality assessment.

The aim of this study was to recalibrate the Swiss lichen bioindication methods, developed and calibrated with air pollution data 30 years ago. Since then, levels of air pollution have considerably decreased, and the mix of pollutants has changed due to successful emission control in Switzerland and neighboring countries. In particular, there has been a change from a sulfur- and acid-dominated to a more nitrogen-dominated pollution mix of NH3/NOx and ozone, resulting in increased pH levels. This allowed a recolonization and change in abundance and composition of the epiphytic lichen vegetation, indicating an improved air quality in Switzerland. The existing indices of atmospheric pollution or purity IAP18 and IAPBR developed 30 years ago showed good longitudinal correlations with air pollutant levels until the end of the last century, but a growing drift was observed in some regions over the last 15 years. This called for a method recalibration with more recent air pollution data. Data from a total of 7178 trees from 22 Swiss regions grouped into 1331 homogenous plots and covering the period 1994 to 2017 were averaged by year within plots. Three pollutant-specific lichen indices were newly established, one for primary pollutants (NO2, PM10, SO2), one for ozone (AOT40f), and one for ammonia (NH3). These pollutant-specific lichen indices were derived from linear regression models with lichen variables and a linear time trend variable as predictors, using time-dependent coefficients. Parameters were selected using the Lasso method. The primary pollutant lichen index showed a coefficient of determination R2 of 0.86 in the model with NO2, PM10, and SO2 as predictor variables, whereas corresponding models with other predictor variables (i.e., NH3, AOT40f, and meteorological variables) were of considerably lower fit. Regionalized lichen models for three larger Swiss regions revealed even better results, compared with the unified Swiss models. The best regionalized ozone and ammonia lichen indices reached an R2 of 0.88 and 0.71, respectively.

Forest health effects due to atmospheric deposition: Findings from long-term forest health monitoring in the Athabasca Oil Sands Region.

Oil sands developments release acidifying compounds (SO2 and NO2) with the potential for acidifying deposition and impacts to forest health. This article integrates the findings presented in the Oil Sands Forest Health Special Issue, which reports on the results of 20 years of forest health monitoring, and addresses the key questions asked by WBEA's Forest Health Monitoring (FHM) Program: 1) is there evidence of deposition affecting the environment?, 2) have there been changes in deposition or effects over time?, 3) do acid deposition levels require management intervention?, 4) what are major sources of deposited substances? and 5) how can the program be improved? Deposition of sulphur, nitrogen, base cations (BC), polycyclic aromatic compounds and trace elements decline exponentially with distance from sources. There is little evidence for acidification effects on forest soils or on understory plant communities or tree growth, but there is evidence of nitrogen accumulation in jack pine needles and fertilization effects on understory plant communities. Sulphur, BC and trace metal concentrations in lichens increased between 2008 and 2014. Source apportionment studies suggest fugitive dust in proximity to mining is a primary source of BC, trace element and organic compound deposition, and BC deposition may be neutralizing acidifying deposition. Sulphur accumulation in soils and nitrogen effects on vegetation may indicate early stages of acidification. Deposition estimates for sites close to emissions sources exceed proposed regulatory trigger levels, suggesting a detailed assessment of acidification risk close to the emission sources is warranted. However, there is no evidence of widespread acidification as suggested by recent modeling studies, likely due to high BC deposition. FHM Program evolution should include continued integration with modeling approaches, ongoing collection and assessment of monitoring data and testing for change over time, and addition of monitoring sites to fill gaps in regional coverage.

Air quality assessment in different environmental scenarios by the determination of typical heavy metals and Persistent Organic Pollutants in native lichen Xanthoria parietina.

The study was aimed to evaluate the ability of native lichen Xanthoria (X.) parietina to biomonitor and bioaccumulate some heavy metals (As, Cd, Co, Cr, Ni, Pb), PAHs, PCDDs, PCDFs, PCBs and PBDEs and to evaluate the use of the native X. parietina as a multi-tracer tool for scenarios characterized by different anthropogenic pressures. Samples of native X. parietina were collected in six different sites (two green, two residential and two industrial areas, respectively) and analyzed for the target compounds. The results show that X. parietina was a useful tool for the biomonitoring of air quality in the selected areas, and was able to bioaccumulate all the studied metals and POPs. In particular, the total concentrations dry weight (dw) ranged between 8.1 and 103.4 mg kg-1 for metals, from 113 × 103 to 183 × 103 ng kg-1 for PAHs, from 868 to 7685 ng kg-1 for PCBs, from 14.3 to 113.8 ng kg-1 for PCDDs/Fs (∑TEq = 0.9-7.1), and from 194 to 554 ng kg-1 for PBDEs. Besides, in general, the levels of analytes recovered in the different samples of lichen show an increasing trend from green to industrial sites, especially for PCBs (mean values equal to 1218, 4253 and 7192 ng kg-1 respectively for green, residential and industrial areas). The statistical approach, based on Pearson's correlation and principal component analysis tests, showed that one of the industrial sites was well-separated from the others, that resulted grouped due to some similarities.

Assessment of Pb2+ removal capacity of lichen (Evernia prunastri): application of adsorption kinetic, isotherm models, and thermodynamics.

Biological materials play a significant role in the treatment of heavy metal-contaminated soil and wastewater. In this study, the Pb2+ biosorption potential of lichen Evernia prunastri, extensively available at a forest in Bilecik-Turkey, was investigated at batch-scale level. The optimal conditions were determined and the adsorption isotherms, kinetics, and thermodynamic calculations were also done. In order to have detailed knowledge about metal biosorption, SEM, FTIR, and BET analyses were carried out before and after the biosorption process. The optimal pH was found pH 4 and the maximum metal uptake capacity was found as 0.067 mol kg-1. The results of this study indicate that the lichen was effectively applied to the removal of Pb2+ process as an inexpensive biosorbent from industrial wastewater.

Lichens as a spatial record of metal air pollution in the industrialized city of Huelva (SW Spain).

Huelva is a highly industrialized city in SW Spain hosting, among others, a Cu smelter, a phosphate fertilizer plant, a power plant, and oil refineries. This study aims to evaluate metal concentrations in lichens as bioindicators of atmospheric pollution in the impacted urban areas. Xanthoria parietina species from Huelva and nearby villages, as well as reference samples from remote, non-contaminated urban areas, were analyzed for trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, Sr, As, Cd, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Er, Tm, Yb, Lu, Pb, Th, U) using Inductively Coupled Plasma-Mass Spectrometry; and for major elements (Ca, K, Mg, P, and S) by Inductively Coupled Plasma-Optical Emission Spectrometry after acid digestion. The metal composition of X. parietina exhibits spatial distribution patterns with extremely elevated concentrations (Co, Ni, Cu, Zn, As, Cd, Sb, Ba, Pb, U, and S) in the surroundings of the industrial estates to <1 km distance. Mean concentrations were significantly lower in the urban areas >1 km from the pollution sources. However, air pollution persists in the urban areas up to 4 km away, as the mean concentrations of Cu, Zn, As, Cd, Sb and S remained considerably elevated in comparison to the reference samples. Though rigorous source apportionment analysis was not the aim of this study, a good positive correlation of our results with metal abundances in ambient particulate matter and in pollution sources points to the Cu smelter as the main source of pollution. Hence, the severe air pollution affecting Huelva and nearby urban areas may be considered a serious health risk to local residents.

Lichen as a Biomonitor for Vehicular Emission of Metals: A Risk Assessment of Lichen Consumption by the Sichuan Snub-Nosed Monkey (Rhinopithecus roxellana).

Two lichen species, Usnea aciculifera and Usnea luridorufa, were used as biomonitors for the deposition of traffic-related metals in China's Shennongjia National Nature Reserve. The suitability of the two lichen species for use as biomonitors was compared. The health threat to the Sichuan snub-nosed (aka golden) monkey (Rhinopithecus roxellana) from consuming lichen with elevated metal concentrations due to vehicular traffic was then assessed. Lichens, with large surface areas and neither roots nor stomata, efficiently absorb both particulate and gaseous air pollutants. The resulting data was used to assess the effect of heavy metal accumulation on the lichens as well as the health risk imposed on the monkeys as lichen is a primary food source. Lichen samples were collected in the core area of the reserve at three locations of varying traffic intensity. A forth site in the reserve, with no proximate traffic, was used as the control. Results show: (1) lichen from high traffic sites has significantly higher concentrations of Fe, Cd, Pb Zn, and Cr than lichen collected from the control site; (2) vehicular traffic is the primary source of metals in lichen; (3) U. luridorufa collected at high traffic sites displayed decreased photosynthetic efficiency, an indication of stress; (4) intake of Cd and Pb from vehicle emissions in the Shennongjia National Nature Reserve could adversely affect snub-nosed monkey health. This research advances the science of biomonitoring, contributes to environmental protection efforts in China's nature reserves and helps improve food safety for Sichuan snub-nosed monkey, a national treasure of China.

BtM, a Low-cost Open-source Datalogger to Estimate the Water Content of Nonvascular Cryptogams.

Communities of nonvascular cryptogams, such as mosses or lichens, are an important part of the Earth's biodiversity, contributing to the regulation of the carbon and nitrogen cycles in many ecosystems. Being poikilohydric organisms, they do not actively control their internal water content and need a humid environment to activate their metabolism. Therefore, studying water relationships of nonvascular cryptogams is crucial to understand both their diversity patterns and their functions in the ecosystems. We present the BtM datalogger, a low-cost open-source platform for the study of the water content of nonvascular cryptogams. The datalogger is designed to measure ambient temperature, humidity, and conductance from up to eight samples simultaneously. We provide a design for a printed circuit board (PCB), a detailed protocol to assemble the components, and the required source code. All this makes the assembly of the BtM datalogger accessible to any research group, even to those without previous specialized knowledge. Therefore, the design presented here has the potential to help popularize the use of this type of device among ecologists and field biologists.

Assessment of air pollution by mercury in South African provinces using lichens Parmelia caperata as bioindicators.

Large-scale assessment of atmospheric air pollution by mercury (Hg) using lichen Parmelia caperata as biological indicator was undertaken using samples from five provinces of South Africa collected between 2013 and 2017. Analysis of lichens provides time-integrated data, which correspond to the mean Hg concentration in air at a specific location over a long time period. Determination of Hg in lichens was carried out by direct thermal decomposition of samples using a Zeeman-effect atomic absorption spectrometer, thereby requiring no chemical pretreatment. The lowest mercury concentration of 60 ± 8.0 ng g-1 (n = 45) was measured in lichens from Limpopo province. This value was accepted as a background Hg concentration in SA lichens. The Hg in lichens from northern parts of Mpumalanga province varied from 72 ± 9.0 to 100 ± 17 ng g-1 (n = 45), while in southern parts of the province, where 11 coal-fired electrical power stations are located, values ranged from 139 ± 7.0 to 183 ± 10 ng g-1 (n = 28). The highest Hg concentration, 218 ± 21 ng g-1 (n = 10), was found in lichens from Secunda, Mpumalanga province. It could be traced to the possible Hg emission during thermal treatment of coal at the largest SA industrial plant that transforms coal into liquid fuels. In Pretoria and Johannesburg, cities in Gauteng province, Hg in lichens was between 110 and 162 ng g-1 (n = 48). Based on the results of measurements, the equation connecting Hg concentration in lichens with Hg concentration in air has been derived. It was used for the calculation of atmospheric Hg concentration in South African provinces. Calculated values (0.8-1.45 ng m-3) were found to be within statistical summary of mean atmospheric Hg in remote places (1.70 ± 0.17 ng m-3), and in other locations (1.5-3.0 ng m-3) lower than in impacted areas of the world (5.20 ± 3.47 ng m-3).

Use of corticolous lichens for the assessment of ambient air quality along rural-urban ecosystems of tropics: a study in Sri Lanka.

Monitoring of air quality using lichens as bioindicators on the basis of lichen diversity and frequency is limited along rural-urban ecosystems in tropics. This study attempted to assess and correlate the use of corticolous lichens with atmospheric SO2 and NO2 in such an ecosystem in Sabaragamuwa Province in Sri Lanka. Nine sampling locations, each having three subsampling sites with 162 Mangifera indica and Cocos nucifera trees, were selected for the study. The coverage and frequency of lichens found on selected trees were recorded by 400-cm2 grids and identified using taxonomic keys. SO2 and NO2 levels at each site were determined by "Ogawa" passive air samplers. Data of lichen diversity were used to formulate the index of atmospheric purity (IAP). The environmental parameters related to lichen colonization were measured using standard methods. Data were analyzed using MINITAB 17. The mapping of spatial distribution of lichens and air pollutants were done using inverse distance weighting surface interpolation of geographical information system based on IAP values. A negative correlation was observed between IAP and SO2 and NO2 levels. The presence of the genus Pyxine in almost all urban sites indicated that it could be used as a reliable pollutant tolerant indicator in urban ecosystems. In addition, the index-based mapping techniques could be used successfully to see the effect of atmospheric pollution in urban ecosystems. These results conclude that corticolous lichens have the potential to be used as bioindicators of air quality monitoring along rural-urban ecosystems of tropics.