Nature Of Suspended Particulate Matter Research Articles

Nature of suspended particulate matter and concentrations of heavy metals in sediment in the southern part of Lake Victoria, East Africa

The concentrations of metals in bottom sediment in the Tanzanian waters of Lake Victoria and the nature of suspended particulate matter (SPM) were analysed. The objective of the study was to compare levels of metals in sediment from different locations and to establish their sources. Metal concentrations were higher in sediment in locations within urban catchments. There were significant differences between sites for concentrations of Cu, Cr, Zn, Hg and Pb in sediment. Mercury concentration was higher in Nungwe Bay sediment compared to other areas, and Cr was higher in Magu Bay, while Cu, Pb and Zn were higher in Mwanza Gulf. Watershed characteristics such as urbanisation, and lake characteristics such as algal biomass, influence the nature of SPM, and hence the concentration of metals in the sediment. The potential to distinguish between different origins of metals in the lake, if the sources of SPM are well construed, is demonstrated.

Mercury in the Lot–Garonne River system (France): Sources, fluxes and anthropogenic component

Dissolved and particulate Hg fluxes in the Lot–Garonne–Gironde fluvial-estuarine system were obtained from observation of daily discharge and suspended particulate matter (SPM) concentrations. In addition to the measurements of the total dissolved (<0.45 μm) and particulate Hg (>0.45 μm), called HgT D and HgT P respectively, the dissolved inorganic Hg species (HgR D) were determined monthly. Geochemical background values for HgT P in sediments and SPM were similar to crustal values and to typical concentrations in SPM of non-contaminated river systems, respectively. The Riou Mort watershed already known as the origin of important historical polymetallic (e.g., Cd, Zn) pollution was identified as an important Hg point source. In the downstream Lot River, Hg concentrations were clearly higher than those in other moderately contaminated systems. The mean relative contribution of HgR D to HgT D in the Lot River and in the Garonne River was close to 25% and 50%, respectively, and showed no correlation with water discharge or SPM concentration. Depending on the origin and nature of SPM, HgT P concentrations were correlated or not with particulate organic C (POC). Maximum HgT P concentrations were measured in samples containing low POC concentrations and were attributed to sediment resuspension. In contrast, high POC concentrations (6–17%) during algal blooms were associated with low/moderate HgT P concentrations (<0.5 mg kg −1) at different sites, suggesting that Hg concentrations in fluvial phytoplankton may be limited by bioavailability of dissolved Hg and/or physiologically controlled Hg accumulation. Mercury was mostly (up to 98%) transported in the particulate phase with estimated annual Hg fluxes at the outlet of the Lot River system ranging from 35 to 530 kg a −1 for the past decade. The minimum anthropogenic component (58–84% of total Hg fluxes) could not be explained by present Riou Mort point source contributions, suggesting important Hg release from contaminated sediment as a major source and from downstream point sources (e.g., coal-fired power plants and/or metal processing industries). HgT P concentrations and fluxes were strongly related to hydrologic variations and were clearly increased by riverbed dredging during lock construction. Therefore, the estimated Hg stocks in the Lot River sediment (5–13 tons) represent an important potential Hg source for the downstream fluvial-estuarine system.

Use of macroalgae as biological indicators of heavy metal pollution in Thermaikos Gulf, Greece.

Heavy metal concentrations in macroalgae are used to monitor the level of bioavailable metals in estuarine and sea shore areas. Macroalgae correspond to the characteristics for bioindicators, since they provide a time-integrated picture of the bioavailable pollutants (Phillips, 1977). Macroalgae have a relatively longlife span, they can offer an environmental picture over extensive periods of time and occur abundantly along the seashore (Phillips et al. 1986, Levine 1984, Fytianos et al. 1997). Different species are usually used to monitor metal concentrations in various geographical areas, according to heavy taxonomic distribution (Ho, 1990, Stratis et al. 1996). Algae accumulate metals by means of a two-stage process, consisting first of a rapid, reversible physico-chemical process of adsorption on the exterior surface, and then of a slower metabolically regulated intracellular uptake (Garnham et al. 1992). Consequently, metal concentrations are greatly dependent both on external factors which affect metal interactions with the cell wall (pH, salinity, inorganic and organic complexing molecules) and on physico-chemical parameters which control the metabolic rate (temperature, light, oxygen and nutrients). Since metal binding on the external wall is a continuous process during the life-span of algae, older tissues usually contain higher amounts of many metals (Shimshock et al. 1992, Barreiro et al. 1993). Algae bind only free metal ions, the concentrations of which depend on the nature of suspended particulate matter. This, in turn, consists of both inorganic and organic complexes (Martin et al., 1994). Only a few benthic algae satisfy all requirements for successful metal monitoring, due to virtually continuous seasonal and geographical distribution in estuaries, tolerance to large salinity variations and resistance to high pollution concentrations (Edwards, 1972). The macroalgae most extensively used for monitoring heavy metal contamination of water belong to the genera Fucus, Enteromorpha, Laminaria and Ulva. The studies of Shiber and Washburn (1978), Sawidis and Voulgaropoulos (1986) and Ho (1990) support the existence of a direct relationship, between metal concentrations in water and in the tissues of U. lactuca. These macroalgae assimilate dissolved nutrients during their growth and released them almost completely in superficial sediment during their mineralization, this later process follows the almost complete disappearance of macroalgae and continues throughout winter (Sfriso et al., 1988). Few areas in Greece are considered to be polluted by heavy metals and in most of them, studies have been made in order to define the level of metal accumulation in the soft tissues of different organisms (Vasilikiotis et al., 1983; Catsiki et al. 1991).