Occurrence and characteristics of iron-bearing minerals in surface road dusts: a case study in the coastal areas of southern Fujian, China

Abstract

Changes in the magnetic phase, magnetic concentration, and/or magnetic grain-sized of dust-bound iron-bearing minerals depend on both lithogenic components and anthropogenic inputs. Knowledge of the magnetic properties of road dusts in various road ecosystems is of paramount importance to control dust pollution for the benefit of the environment and human health. The magnetic characteristics of road dusts, collected in the coastal areas of southern Fujian, China, were determined via magnetic measurements, X-ray diffraction analysis, Mossbauer spectroscopy (MS), and scanning electron microscopy with integrated energy-dispersive X-ray spectrometry. Analyses of the temperature dependence of magnetization, backfield demagnetization, and hysteresis loops suggested that the main magnetic carriers in road dusts were low-coercivity minerals with minimal antiferromagnetic phases derived from anthropognic sources. The coefficients of variation for χLF, SIRM, and χARM were 53.46%, 50.98%, and 58.56%, respectively. Samples with high values of χLF had a high ratio of iron ions in the octahedral B and tetrahedral A sites in magnetite. The most common iron oxides in the dust-bound iron-bearing minerals were non-stoichiometric magnetite, hematite, and possibly metallic iron. Elevated concentrations of trace metals (e.g., Cd, Cr, Co, and V) in the dust-bound iron-bearing minerals partially confirmed the coexistence of magnetic minerals and trace metals in the road dusts. Analysis of the spatial characteristics of magnetic concentration–related parameters will be useful in accurately documenting and tracking levels of pollution.