Distribution of selected heavy metals in sediments of the Agueda river (Central Portugal).
The state of river water deterioration in the Agueda hydrographic basin, mostly in the western part, partly reflects the high rate of housing and industrial development in this area in recent years. The streams have acted as a sink for organic and inorganic loads from several origins: domestic and industrial sewage and agricultural waste. The contents of the heavy metals Cr, Cd, Ni, Cu, Pb, and Zn were studied by sequential chemical extraction of the principal geochemical phases of streambed sediments, in the <63 microm fraction, in order to assess their potential availability to the environment, investigating the metal concentrations, assemblages, and trends. The granulometric and mineralogical characteristics of this sediment fraction were also studied. This study revealed clear pollution by Cr, Cd, Ni, Cu, Zn, and Pb, as a result from both natural and anthropogenic origins. The chemical transport of metals appears to be essentially by the following geochemical phases, in decreasing order of significance: (exchangeable + carbonates) >> (organics) >> (Mn and Fe oxides and hydroxides). The (exchangeable + carbonate) phase plays an important part in the fixation of Cu, Ni, Zn, and Cd. The organic phase is important in the fixation of Cr, Pb, and also Cu and Ni. Analyzing the metal contents in the residual fraction, we conclude that Zn and Cd are the most mobile, and Cr and Pb are less mobile than Cu and Ni. The proximity of the pollutant sources and the timing of the influx of contaminated material control the distribution of the contaminant-related sediments locally and on the network scale.
dos Reis
Anabela Ribeiro
AR
Departamento de Geologia, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. anarreis@utad.pt
Parker
Andrew
A
Carter
Joy
J
Ferreira
Martim Portugal
MP
D001682:Biological Availability; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry*; D019216:Metals, Heavy / Q000032:analysis*; D011174:Portugal; D045483:Rivers; D014873:Water Pollutants / Q000032:analysis*
D019216:Metals, Heavy; D014873:Water Pollutants