Distribution of Heavy Metals and Their Concentrations in the Surface Sediments - Literature review Example

This review of literature focuses on the distribution of heavy metals and their concentrations in the surface sediments -- a subject matter that is of particular interest to environmental chemists (Unnikrishnan & Nair, 2004). Far from being merely academic in end and use, a study of surface sediments and the heavy metals that are trapped and collected in them (Harikumar, Nasir & Rahman, 2009, pp. 225) is handy in providing information on changing ecology of particular environments (Cohen, 2003). Being the largest single non-point source pollutant (see Soil in our Streams, [n.d.]), sediments are increasingly used to assess human impact on the aquatic environment (Bryan & Langston, 1992; Daskalakis & O’Connor, 1995), and are sensitive indicators of quality of life in bodies of water (Harikumar, Nasi & Rahman, 2009, pp. 225). Too, they proffer invaluable data on the behavior of metals (Belluci et al., 2003; Bertolotto et al., 2003; Borretzen & Salbu, 2002; Lee & Cundy, 2001; Weis, Callaway & Gersberg, 2001). Chiaradia et al. (1997) studied the particulates that were present in roof cavities of houses in the Illawara region (NSW, Australia) and the lagoon in the area that acts as a natural sink for particulate matters. They did a microscopic investigation employing X-ray fluorescence (spectrometry) (Jenkins, 1999) and stable lead isotopic analyses (OECD-NEA, 2000, pp. 101-104). All investigated houses yielded in excess of 250 µg g-1 lead – which was indicative of a historic record of lead pollution. Houses that are close to a copper smelter contained higher (>2500µg g-1) lead concentrations. The isotopic composition in the dust – i.e.,206Pb/204Pb – was relatively constant at 17.0. The lead concentration in the lagoon that they investigated was found to have one (1) natural and four (4) anthropogenic contributories. The natural source consists of Permian rocks cropping out in the catchment area had a 206Pb/204Pb of ~18.7 isotopic composition. The anthropogenic sources are an old disbanded base-metal smelter (206Pb/204Pb of ~16.2-16.3), the copper smelter (206Pb/204Pb ~17.9), gasoline-derived lead (206Pb/204Pb ~ 16.4-16.5), and industries utilizing coal (206Pb/204Pb ~18.9). The researchers concluded that for the last five decades, atmospheric fall out of lead-bearing particulate matter was the dominant pathway for addition of lead to the lagoon and the dwellings in the region of Illawara. Lottermoser (1998) investigated heavy metal concentrations in such bodies of water as the Hunter River, which runs through a heavily industrialized and thickly populated area, and the Newcastle Harbor and the Throsby Creek found in urbanized but lightly industrialized areas. He wrote that the element concentrations of silver, arsenic, cadmium, chromium, copper, mercury, nickel, lead, antimony and zinc within the Hunter River ae notably one order of magnitude higher than the upstream background values. Similarly high concentrations were detected from sediments of the Newcastle Harbor and Throsby Creek, which are accounted for by atmospheric deposition of lead additives from petrol and subsequent lead transport by road run off waters into the local drainage system and anthropogenic sources of heavy metal and metalloid contamination especially in sample sites close to sewage outlets. MacFarlene & Booth (2001) monitored the Cowan and Berowra Creeks, and ascertained the presence of anthropogenic contaminants such as copper, lead, zinc, phosphorous and nitrogen. According to them, the heavy metal concentrations were still below sediment guideline values for biological effects. However, they sounded off the need to closely monitor the future impacts of the presence of heavy metals in these sites. Liaghati, Preda, & Cox (2003) examined samples from Bells Creek in southeast Queensland, a non-industrialized coastal plain limited to small settlements and agricultural land. A total of ninety-nine samples were analyzed for chromium, vanadium, nickel, copper, zinc, lead, arsenic, iron, manganese and aluminum. A comparison between metal concentration within the area and mean heavy metal content of standard sandstone showed that except for manganese, all other metals showed elevated levels throughout the catchment. But, the elevation of levels was established to be natural when metal concentrations were compared to parent bedrock and a normalization procedure (Covelli & Fontolan, 1997) was applied to the data set. In general note, thus, Liaghati, Preda & Cox (2003) posit that geochemistry and mineralogy of the samples manifest the effect of both natural and anthropogenic inputs to the catchment. Harikumar, Nasir & Rahman (2009) examined five sediment cores from the fresh water region of the Vembanad Lake, the largest estuarine ecosystem in Kerala, India for their trace element contents. They determined the average concentration of iron, manganese, nickel, copper, zinc, cadmium, lead, mercury and chromium in the samples they had collected using gravity type corer, digested with a mixture of nitric acid and perchloric acid and analyzed by atomic absorption spectrophotometry (Jones, 2001, pp. 266-267). They reported that heavy metals such as iron (varying from 25.55g/kg to 82.37g/kg), manganese (281.67mg/kg to 1311mg/kg), copper (16.73mg/kg to 56.13mg/kg), nickel (36.53 to 74.47mg/kg) and zinc (103.39 to 305.29mg.kg) are richly deposited towards the surface of the core sediment samples collected from the center of the lake. Lead (0.61 to 80.03mg/kg), cadmium (0.07 to 2mg/kg) and mercury (highest concentration was 1.6mg/kg) were uniformly distributed throughout the core. Likewise, they evaluated the quality of the sediments based on sediment quality guidelines, pollution load index, sum of toxic units and with effect range low/effect range median and threshold effect level/probably effect level values of Environmental Protection Agency guidelines. Finally, their study determined the degree of contamination of each stations in the lake – which they claimed to point towards the fact that Vembanad Lake is facing serious pollution with increased rate of deposition of heavy metals. Birch & Taylor (1999) tried to identify the main sources of heavy metals to Port Jackson in Sydney (Australia) and the potential biological significance of high contaminant concentrations over the areas of the estuary by studying both fluvial and estuarine sedimentary heavy metals. They collected 1,700 superficial samples – the largest regionally compatible estuarine database in the country – from Port Jackson using either a polycarbonate corer operated from a boat or a stainless steel box corer. With these samples, eight (8) metals – i.e., copper, cobalt, cadmium, iron, manganese, nickel, lead and zinc – were analyzed using a 2:1 HClO4/HNO3 digestion (see Shaibur et al., 2010) and a Perkin Elmer (model 3000) Flame Atomic Absorption Spectrometer (FAAS) (see Tao et al., 2003). Of these eight (8) heavy metals, though, only three (3) – i.e., cooper, lead and zinc – were focused on after the other five (5) elements showed declining trend in concentration from the upper reaches of the estuary towards the estuary mouth. The concentration of copper in the superficial sediment is the highest (>200µg g-1); the lead and the zinc concentrations are almost the same (1000µg g-1). These findings simply confirmed what has previously been established – that is, that Port Jackson has indeed one of highest level of heavy metal concentrations of any estuary in Australia (see Birch 1995; Birch 1996). Still in Port Jackson, Hatje et al. (2003) ascertained the moderate concentration of cadmium, nickel, manganese, cobalt and zinc. They placed the mean concentrations of the four elements at 0.04±0.02µg/l (cadmium), 0.86±0.40µg/l (nickel), 20.0±25µg/l (manganese) and 6.47±2.0µg/l (zinc). Cobalt, with its concentration at 1.68±0.37µg/l, was slightly exceeding the recommended values. These concentrations were determined after samples were taken in winter and summer seasons at low slack water, during dry, low-flow conditions (representing the typical (saline) state of the estuary). The (surface) samples were then collected in pre-cleaned polyethylene bottles with caps. The bottles containing the samples were then sealed inside two polyethylene bags for transportation to the laboratory. In the laboratory, the cadmium, nickel, cobalt and zinc were made to pass through a 0.45µm filter, and analyzed by a modified dithiocarbamate-complexation (see Magnusson & Westerlund, 1981). The major alteration that the researchers introduced in their process was the use of a combined sodium bicarbonate buffer/ammonium pyrrolidine dithiocarbamate (APDC) regent (Lemos, da Franca & Moreira, 2007) and 1.1.1 trichloroethane as the extraction solvent (Michulec & Wardencki, 2006) in lieu of Freon (Ibrahim & Suffet, 1988). The sample aliquouts (200ml) were buffered to pH 5-6 by addition of the combined reagent and extracted with two 10ml portions of triochloroethane. The extracts were combined and the metals back-extracted into 1ml Merck suprapur concentrated nitric acid. The back extracts were diluted to a final volume of 10ml by addition of 9ml of deionised water. Cadmium was finally analyzed by GFAAS (Perkin Elmer 4100ZL) (see Cabon, 2005), using Zeeman-effect background correction (Fernandez, Myers & Slavin, 1980). Copper, nickel and zinc were analyzed by ICP-AES (Spectro Flame-EOP) (Wang, et al. 1999). Manganese was analyzed directly by ICP-AES (Spectro Flame-EOP) using salinity-matched standards. Each batch of extraction was analyzed with aliquots of CASS-4 (Yang, et al. 2004) to ensure analytical accuracy. Hatje et al. (2003) write that their research has given information concerning the contemporaneous distribution of dissolved trace metals in the Port Jackson, and (after confirming the findings of the previous studies) has provided a data set against which long-term contamination may be assessed. This is interesting to note as this counters van der Berg (1993) who held that there is no universal pattern of trace metal behavior in estuaries on account of variances in environmental factors such as hydrodynamic residence times, mixing patterns and transport processes (see also Camusso et al., 1997). The concentration of heavy metals is not only notable in bodies of water. Manta et al. (2002) measured 70 top soil samples from green areas and parks in Palermo, Italy to determine the concentrations of vanadium, manganese, cadmium, zinc, nickel, chromium, cobalt, lead, mercury, and antimony. Mineralogy, physic-chemical parameters and major element contents of these top-soil samples were determined yielding the specific result that the lead, zinc, copper, and mercury concentrations (202, 138, 63 and 0.68 mg kg-1 respectively) were higher than in unpolluted soils in Sicily (44, 122, 34 and 0.07 mg kg-1). The ensuing basic and multivariate statistical analyses (cluster analysis and principal component analysis) that were performed to reduce the multi-dimensional space of variables and samples provided the results demonstrating that lead, zinc, copper, antimony and mercury were of anthropic pollution, and manganese, nickel, cobalt, chromium, vanadium and cadmium were from parent materials. Conclusively, the researchers pointed to vehicle traffic as the main source of pollution to urban top soils in Palermo. Lamb et al. (2009) investigated the pore-water content and speciation of the heavy metals – copper, zinc, cadmium and lead – in a range of uncontaminated and long-term contaminated soils so as to establish their potential bio-accessibility to soil biota, plants and humans. Their analysis has found the copper concentration to be higher in contaminated soils than in uncontaminated soils. However, zinc, cadmium and lead were not generally found at elevated levels in the pore-water but in a single contaminated soil. The researchers were led to realize that a long period of ageing and soil weathering may have led to a substantial reduction in heavy metal concentrations in the pore-water of contaminated soils. Kachenko & Singh (2004) focused on the concentration of cadmium, copper, lead and zinc in the soils and vegetables in the vicinities of the ports of Kembla and Boolaroo. The soil samples were collected at depths of 0-30 and 60-90cm, air-dried and sieved to obtain Read More