Relevant Magnetic Parameters and Heavy Metals From Relatively Polluted Stream Sediments – Vertical and Longitudinal Distribution Along A Cross-City Stream In Buenos Aires Province, Argentina

M.A.E. CHAPARRO; J.C. BIDEGAIN; A.M. SINITO; S.S. JURADO; C.S.G. GOGORZA

Studia geophysica et geodaetica

StudiaGeo s.r.o.

Lugar: Praga; Año: 2004 vol. 48 p. 615 - 636

0039-3169

ABSTRACTPrevious magnetic and geochemical studies of stream sediments in the Northeast ofBuenos Aires Province, in the Greater La Plata area, have revealed a high level of traceelements, especially lead and zinc. Continuing these preliminary works, new samplingsites were considered in order to improve and increase the magnetic mapping of this area.This part of the study focuses especially on the magnetic properties of sediments from across-city stream. Such stream receives a variable pollutant load from urban, industrialand diffuse sources.Concentration-dependent magnetic parameters, magnetic carriers (para, anti andferrimagnetic) and their features (e.g. softer or harder magnetic carrier, grain sizedistribution, etc.) have been calculated using magnetic measurements. According tomagnetic parameters and heavy metal loads two main distinctive groups of sedimentcoresare distinguished. The vertical distribution of sediments reveals a recentanthropogenic influence, possibly, belonging to the last 20-40 years.Four out of all the magnetic parameters (magnetic susceptibility, anhysteric remanentmagnetisation, S-ratio and κARM/κ) were chosen in order to investigate their relationshipwith contents of heavy metals. In all the cases, good positive correlations were obtainedusing linear regression. However, more significant correlation factors were achieved forgrain size and magnetic feature-dependent parameters (κARM/κ and S-ratio) than formagnetic concentration-dependent parameters. Therefore, the κARM/κ and the S-ratioseem to be the most relevant magnetic parameters to describe the vertical andlongitudinal distribution of heavy metals present in these stream sediments. The nonsignificantrelationship between heavy metals and concentration-dependent parameterscould be explained taking into account the discrimination of the two distinctive groups.The group belonging to the Coastal Plain shows a clear linear trend between heavymetals and magnetic susceptibility and anhysteric remanent magnetisation.Keywords: ferrimagnetic minerals, heavy metals, environmental pollution, rockmagnetism, magnetite, stream sediments