Magnetic techniques applied to study the accumulation time period of urban/industrial dust in lichens

ANA M. SINITO; DÉBORA C. MARIÉ; MARCOS A. E. CHAPARRO

Congreso; 26th International Union of Geodesy and Geophysics; 2015

This study assesses the accumulation time period of urban/industrial dustin the lichen Parmotrema Pillosum, using different magnetic parameters. Thestudy was carried out in Tandil City (37º19.5?S; 59º08.3?W), Argentina. Weselected a control (without or with low pollution load) site for collectinglichens to transplant. Such lichens were prepared and transplanted in variousselected sites inside the urban area. These sites are affected by differentpollutant emission sources (vehicle traffic and metallurgical factories).Twelve samples for each site were prepared and simultaneously transplanted inorder to make monthly collections.Magnetic susceptibility (X), anhysteretic and isothermal magnetizations(ARM, IRM) were measured. Also, associated parameters were used, such as kFD%,XARM, HCR, S-ratio, SIRM/X and XARM/X. Inaddition, deposited particles onto the lichen surface were observed by scanningelectron microscopy (SEM) and analyzed by x-ray energy dispersive spectroscopy(EDS).The analysis of the set of parameters indicates the predominance offerromagnetic minerals, like (titano)magnetite. The King´s plot indicates amajority of fine magnetic grains (less than 0.1 mm).There is a general trend of increase for parameters related to magneticconcentration, though a slight decrease is observed after rainy periods,apparently due to a washing effect of surface particles. The magnetic grainsize dependent parameters decrease with time while magnetic concentrationincreases, suggesting that higher magnetic concentrations are associated withthe accumulation of coarser magnetic grains.SEM and EDS indicate higher Fe content and the presence of spherulesproduced by industrial activity near the collection sites.