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Guia Morelli. La Pira 4, Firenze, Italy. Capponi 3r, Firenze, Italy. This article belongs to the Collection Environmental Risk Assessment. For a better graphical comparison, the values for barks were divided by four. At sites where more than one lichen species was present, the fit was calculated considering the average of values.
In the present study, mercury Hg concentrations were investigated in lichens Flavoparmelia caperata L. Hale, Parmelia saxatilis L. were integrated with Hg concentrations in tree barks and literature data of gaseous Hg levels determined by passive air samplers PASs in the same area. The ultimate goal was to compare obtained by the three monitoring techniques to evaluate potential mismatches.
Mercury concentration was lower than in Pinus nigra barks at the same site. There was a moderate correlation between Hg in lichen and Hg in bark, suggesting similar mechanisms of Hg uptake and residence times. The differences occurred because a PASs collected gaseous Hg, whereas lichens and barks also picked up particulate Hg, and b lichens and bark had a dynamic exchange with the atmosphere.
Lichen, bark, and PAS outline different and complementary aspects of airborne Hg content and efficient monitoring programs in contaminated areas would benefit from the integration of data from different techniques. Keywords: biomonitoring; airborne pollutants; particulate Hg; lichens; tree barks; passive air samplers; mining area biomonitoring ; airborne pollutants ; particulate Hg ; lichens ; tree barks ; passive air samplers ; mining area. Introduction Mercury Hg is a widespread contaminant of much concern due to its high toxicity, persistence, and accumulating behavior in the environment [ 1 ].
In the reduced form Hg 0Hg displays long residence times in the atmosphere and a consequent ability to be transported over long distances, making it a global scale pollutant [ 2 ]. Now more than ever, the coming into force of the Minamata convention requires the proper monitoring of airborne Hg contents in order to reduce Hg anthropogenic emissions. An effective estimation of environmental and human health risks to Hg exposure depends on the development of reliable, low cost, easy-to-use monitoring networks [ 3 ].
These methods are excellent to characterize point sources [ 6 ]. However, they lack spatial resolution and provide only short-term information on Hg contamination [ 67 ]. Biomonitoring is the assessment of gradient of pollutants in naturally occurring living biological material [ 8 ]. Among wildlife, mammals, birds, fish, and most recently snakes have been employed as biomarkers for Hg [ 9 ]. In plants, Hg especially accumulates in lichens, algae and mosses, and in higher plants. The employment of Hg concentrations in lichens and mosses in situ or after transplantation is a long-established practice for Hg monitoring [ 101112131415 ].
Recently, the use of higher plant tissues e. In addition to the determination of total Hg in plant tissues, some studies also investigate the adverse effects such as alteration in transpiration and photosynthesis, imbalance in carbohydrate metabolism and production of secondary stresses on the growth and metabolism of plants [ 18 ]. A recently developed technique for Hg monitoring is represented by manufactured passive air samplers PASswhere a bituminous coal-derived, sulfur-impregnated, activated carbon is employed as sorbent for Hg species [ 19 ].
Passive sampling, either by employing living organisms or manmade products, is a more sustainable and ecologically relevant approach to monitor Hg for longer periods of time [ 202122 ] and allows a better detection of nonpoint sources of Hg and better spatial resolution [ 67 ]. The different monitoring techniques, relying on different processes, do not necessarily give compatible.
Hence, several attempts have been made to evaluate the reliability and comparability of technical and biological methods to monitor Hg in the atmosphere [ 8 ], as well as the interchangeability of substrata. For example, epiphytic lichens in mining areas were found to accumulate more Hg than mosses due to differences in morphology and ecophysiology [ 2324 ]. This has led some authors to conclude that the best monitoring programs are achieved using more than one substratum [ 25 ]. To date, studies comparing Hg contents in tree barks and epiphytic lichens collected at the same sites are not abundant [ 26272829 ] and have been mostly conducted in areas with low concentrations of Hg in air.
Additionally, no studies have compared lichens and tree barks with the new recently developed PAS system. To fill this gap, epiphytic lichens and tree barks Pinus nigra J. Arnold were investigated for Hg concentrations in the Monte Amiata area Tuscany, Italya regional possibly global scale hotspot for Hg because of the presence of a large abandoned mining and smelting district. These data were compared with the gaseous Hg concentrations obtained by PASs on the same area.
The comparison was based on a limited dataset and should be regarded as preliminary. However, it sets the ground for an optimal, and possibly complementary, use of the different techniques in monitoring programs. Mercury mining and smelting operated in the area from toalthough the main production occurred from to [ 31 ].
The environmental legacy of this extensive Hg mining and metallurgy has been the subject of many studies see [ 30 ] for a partial reference list. Lichen sampling was performed concurrently with tree bark sampling at 10 sites Figure 1 in Julymaking reference to grids established for deployment of PASs [ 6 ]: a closer-spaced grid near ASSM Abbadia grid; sites identified by lowercase a and a progressivee.
Having ly decided to sample Pinus nigra trees to be consistent with the study of [ 16 ]the site choice was conditioned by the presence of this species, making efforts to select trees as close as possible to a PAS deployment site. We obtained samples of Flavoparmelia caperata L.
It was only possible to collect more than one lichen species at some sites. We estimated that at each site, the lichen samples, the tree sampled for bark, and the next PAS were all within a maximum 20 m distance usually less. Collected lichen samples were identified in the field and subsequently verified in the laboratory using a dissecting microscope. The nomenclature of lichens followed [ 33 ].
For Hg concentrations, we decided to use the whole lichen thallus of each sample in order to compare the long-term accumulation performance of the two substrates lichens and barks. Lichen thalli were airdried and carefully cleaned under a dissecting microscope. Then, the lichen material was manually shredded into small pieces and homogenized using a ceramic mortar to obtain three replicates of about 40 mg for each collected species in each site.
The local gaseous elemental Hg concentrations GEM in the air were taken from [ 6 ]. A description of the analytical and computation methods and a description of PAS have been provided by the authors of [ 6 ] and [ 19 ], respectively. As reported by the authors of [ 6 ], deployment times were different for the Amiata and the Abbadia grids. We did not know the specific value of GEM at the moment of bark and lichen sampling. However, the range of values in the time interval including our sampling was fairly narrow. Therefore, they can be assumed to be representative of conditions at sampling time, at least as an order of magnitude see further discussion.
Table 1 summarizes, for each site, the Hg contents dry weight in soil, lichens, and Pinus nigra barks, and the range of elemental Hg concentrations in air estimated from PAS data. For the reasons explained by the authors of [ 32 ], for barks, the Hg concentration was the mean of the four samples taken at cm above ground.
For the three sites a13, a21, and a49where more than one lichen species was collected, we did not observe a consistent order of enrichment by species. For example, at each of the three sites, a different species exhibited the highest Hg content X. Mercury contents of both X. For P. In a bivariate plot Figure 2Hg concentrations in lichens and barks appear positively correlated.
For gaseous Hg concentrations, the highest values were observed at site a49, which was located close to the mine Figure 1 b.
Mercury concentrations in lichens were the same order of magnitude as those ly reported for lichen species in the Monte Amiata area [ 34353637 ]. Specifically, for X. Notably, these authors analyzed only the outermost part of the lichens. Those authors also showed a decrease of Hg contents lichen with distance from ASSM similar to our data compare Figure 3 in [ 34 ] with our Figure 3. Mercury content in lichen showed a good correlation with local Hg soil content, which is consistent with reports [ 35 ].
Working on a slightly larger bark sample set, a statistically ificant correlation was established between Hg contents in barks and soil [ 32 ]. The comparison of lichen and bark data showed that the Hg scavenging efficiency per mass unit was generally higher for barks.
By contrast, in other studies dealing with different lichen and plant speciesHg contents were found to be higher in lichens than in tree barks [ 26272829 ]. At present, the mechanism regulating Hg uptake by lichens or bark is unknown. However, the fairly good correlation between the contents in the two matrices suggests that uptake mechanisms may be largely similar. Both substrates may take up Hg as gaseous species mostly Hg 0 and as particulate matter. There is no comparable knowledge of transformations occurring in Hg speciation in bark, but preliminary have showed a certain degree of Hg binding with organic functional groups mainly thiols [ 40 ].
Both lichens and barks show a dynamic exchange with the atmosphere, i.
In general, however, the released Hg is only a small fraction of that taken up. For instance, the authors of [ 32 ] observed a negligible release of Hg by Pinus nigra bark upon 24 h of batch reaction with deionized water. The residence time of the metal in lichen was estimated to be in the order of a few years references in [ 39 ]. For bark, there are no data, but a weak correlation between Hg bark content and tree age tens of years was observed [ 32 ], suggesting that the residence time may be ificantly shorter than tree age i. By contrast, PASs rapidly and irreversibly trap only gaseous Hg compounds.
The upper limit of the uptake capacity of the carbon sorbent is very high, and it was certainly not exceeded during the deployment at ASSM [ 6 ]. This exchange makes lichen not very reliable indicators of Hg concentrations in air [ 39 ]; c some of the concentrations obtained with PAS referred to time period of one week only, and the specific wind and temperature conditions prevailing during one of the week-long sampling periods July may not be reflective of the long-term average conditions [ 6 ]; d the time period reflected by the different types of samples was not the same.Sex dating Abbadia San Salvatore
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Monitoring of Airborne Mercury: Comparison of Different Techniques in the Monte Amiata District, Southern Tuscany, Italy