Magnetic monitoring of pollution in the urban area of Tandil city using lichens as biomonitors

DÉBORA C. MARIÉ; MARCOS A. E. CHAPARRO; MARÍA A. IRURZUN; JUAN M. LAVORNIA; HARALD H. BÖHNEL; CLAUDIA MARINELLI; ROSANA CEPEDA; ANA M. SINITO

Congreso; XXVII Reunión Científica de la Asociación Argentina de Geofísicos y Geodestas; 2014

A biomonitor is an organism which has a reaction thatcan be identified against different adverse influences if there is analteration of the environment, for example, pollution. Some biological speciesare unable to adapt ecology or genetically to the altered environmental condition,hence its absence is an indicator of problems (Hawksworth and Hill, 1984; Nimiset al, 2002).Lichens are known to be sensitive to various pollutantsand are considered a good biological indicator of air quality. Thus they arewidely used in environmental studies, and recently, in magnetic monitoring (Chaparro et al., 2013).This study focuses on the use of lichen specie (Parmotrema pilosum) as biomonitor of pollutionand presents a detailed study of magnetic parameters to assess the urban areaof Tandil City (Argentina). The main sources of pollution in the urban area arethe vehicular traffic and metallurgical industries. The sampling design was a stratified random sampling;it proposed a total of 671 trees for sampling. A total of 180 samples oflichens on the bark tree were collected and studied from the selected sites.Magnetic susceptibility, magnetic hysteresis loops, anhystereticand isothermal remanent magnetization and thermomagnetic measurements were usedto determine the magnetic properties of lichen samples. The vegetation materialwas measured in laboratories from Argentina (IFAS, UNCPBA) and México (CGEO,UNAM).The magnetic mineralogy shows a predominance ofmagnetite like-phase. The Day?s plot shows that the samples are located in pseudo-singledomain(PSD) region and the thermomagnetic studies (curves M(T)) suggestsmagnetite as the main magnetic carrier.Concentration and magnetic grain size dependent parameterswere computed in 2-D contour maps as can be observed in Fig 1.These representations allow us todifferentiate polluted and low-polluted areas. The distribution of magneticvalues shows the areas with high vehicular and metallurgical industryinfluence.Magnetic grain size estimations indicate cleardifferences between sample sites: presence of fine particles (high χARM/χ)in sites with low vehicular traffic or park areas, while sites affected bypollution (high vehicular traffic or metallurgical industry influence) arecharacterized by coarser magnetic grain sizes (low χARM/χ).Statistical analysis used Spatial AutocorrelationAnalysis (Index of Moran) and Analysis Multivariate of Variance (MANOVA).  Two study areas was tested:central (inside Buzón, del Valle, Cabildo, Lopez de Osornio Avenues), andperiphery (outside marked Avenues).For spatialdependence of the magnetic variables, neighborwas defined as: each tree is neighbor ofitself; of those belonging to the same blockand those belonging to the opposite sidewalks. For the central area, the HCRvariable presents a high correlation but less than 0.7; this implies a slightspatial dependence. The periphery area HCR and SIRM/c, show a high and significant spatial correlation. Forboth areas, the others variables has positive spatial auto-correlation, thisshows a smooth tendency to cluster spatially.Multivariateanalysis results show significant differences between the two areas; thecentral, presents lower values of ARM, cARMand SIRM than periphery. In contrast, HCR, SIRM/cand cARM/c,show low values for samples of the periphery.