Monitoring air pollution close to a cement plant and in a multi-source industrial area through tree-ring analysis.

Thirty-two trace elements were examined in the tree rings of downy oak to evaluate the pollution levels close to a cement plant isolated in a rural context and an industrial area where multiple sources of air pollution are or were present. Tree cores were collected from trees growing 1 km from both the cement plant and the industrial area that are located 8 km from each other. The analysis of the trace elements was performed on annual tree rings from 1990 to 2016 using laser ablation inductively coupled plasma mass spectrometry. Trace elements Cs, Mg, Mn, S and Zn reflected the emission history of the cement plant. Their values have increased since early 2000s, when the cement plant started its activity. However, the lack of significant trends of pollutants in the tree rings from the industrial area and the possible effect of translocation and volatility of some elements left open questions. The very weak changes of the other trace elements in the period 1990-2016 suggest those elements do not mark any additional effect of the industrial activity on the background pollution. The results confirm that downy oak trees growing close to isolated industrial plants must be considered a pollution forest archive accessible through dendrochemistry.

Preserving air pollution forest archives accessible through dendrochemistry.

Plants are continuously exposed to human air pollution, absorbing pollutants in their tissues. Trees can store pollutants in wood, in the annual growth rings, retaining traces of pollutants in the environment. Information on past pollution events are archived by trees, which dendrochemistry, a dendrochronological science combined with chemistry, is able to access. Many authors have suggested that trees could complement the conventional environmental monitoring: a forest archive of pollution events. However, the implications of trees occurrence in polluted areas on planning and management have not yet been discussed. In this article, we investigate whether forest archives exist and whether they should be integrated into the network of existing monitoring stations. We use a case study, the Veneto region of Italy, one of the most polluted areas in Europe, to examine the occurrence of trees around 28 industrial plants retrieved from a European pollution register. We propose planning actions to develop the latent potential of these forest archives for environmental monitoring, which society may benefit. We follow three steps: (a) assessing the cover and composition of tree canopies around the industrial plants, (b) inventorying the existing artificial air monitoring stations in order to discover whether pollutants around the industrial plants are already monitored, (c) assessing land use patterns in order to identify which are the receptors of air pollution and enhance the forest archive in the future. These spatial analyses are conducted in a 1-km radius buffer with the industrial plant as the centre. Results show that forest archives are available, with cover and composition suitable for dendrochemistry studies. Artificial monitoring stations are too far from industrial plants or have been installed recently, unable to provide historical data. Trees are an alternative source of pollution data. Receptors of air pollution include a diversity of urban, rural and agricultural lands, where forest archives can be managed and conserved through a variety of actions. Environmental protection agencies should value these trees, preserving them and accessing the records held in this forest archive. Similar inventories must be promoted in other industrialised regions of the world even at larger scales. Studies like this one should also be incorporated into landscape or urban planning processes.