Spatial analysis of trace element contamination in sediments of Tamiraparani estuary, southeast coast of India

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Abstract

The impact of industrial effluents on the Tamiraparani estuary was investigated by determining the degree of trace element contamination in the estuarine sediments. Surface samples were taken from 30 locations covering the entire estuary. Grain size and trace element (Ni, Pb, Co, Cu, Zn, Cd, Mn, Fe, Al) variations were analysed, and enrichment factors (EF) as well as geo-accumulation indices (Igeo) calculated to understand the contamination level of the study area. A geographical information system (GIS) mapping technique was employed to highlight the spatial distribution patterns of trace elements in the estuarine sediments. Vulnerability maps prepared from the Igeo values revealed that the estuary is extremely contaminated with Cd and moderately contaminated with Zn and Pb. The sources of these metals are associated with nearby chemical plants and harbour activities. The cumulative effect of anthropogenic activities has led to a serious threat to the whole estuarine environment.

Graphical abstract

Highlights

► Trace elements in Tamiraparani estuarine sediment were analysed. ► The sediments are highly enriched with cadmium, Zinc and Lead. ► Spatial distributions of trace elements are mapped within the estuary. ► IDW algorithm was used to model the spatial distribution. ► EF and Igeo values reveal that the estuary is polluted by anthropogenic activity.

Introduction

Coastal marine environments are known to receive huge amounts of chemicals and are considered among the most sensitive areas for the accumulation of noxious compounds. The environmental quality of coastal ecosystems is an issue of growing international attention (Förstner, 1983). Contamination of estuarine sediments by trace elements is a world-wide problem and sediments represent one of the ultimate sinks for heavy metals discharged into the aquatic environment (Gibbs, 1977, Luoma and Bryan, 1981). The trace element content in the estuarine sediments reflects the range of chemical, oceanographic and geological controls on their distribution. Such controls include the composition of the sedimentary detritus, the partition of the trace elements between the solid and solution and the post-depositional conditions in bottom sediments (Calvert and Pedersen, 1993, Friske and Coker, 1995, Querol et al., 1997).

A geochemical study of trace elements like Cu, Pb, Co, Cr, Ni, Zn, and Cd could provides a hydrogeochemical framework for assessing the sources and mechanism of metal input, enrichment, and distribution in sediments (Arakel and Hongjun, 1992). Such studies on estuarine sediments have assumed greater awareness in view of catastrophic events of Cd and Pb poisoning (Padmalal et al., 1997).

The enhanced preservation of organic matter in fine-grained sediments can lead to trace metal enrichment in their authigenic phase either through complexation reactions or by increasing sorptive capacity of the sediments (Alberic et al., 2000). However, depending on the depositional environment, sediments can be a source or sink for trace metals. However, trace elements need not necessarily be fixed to the sediment, as recycling can occur by biological, chemical, and physical processes (Adams et al., 1992, Rees et al., 1996, Das et al., 1995, Lee et al., 2003).

Spatial survey of sediment-metal contents, as well as the comparison of these elements to non-polluted sediments (background values) is a key step to understand the transport and deposition of the contaminant trace elements in coastal aquatic systems (Chester and Voutsinou, 1981, Alexander et al., 1993, Delgado et al., 2010, Nobi et al., 2010).

The measurement of trace element contents and distribution in the marine environment leads to a better understanding of their behaviour and is important for detecting sources of pollution (Förstner and Wittman, 1979). To date, no data pertaining to the trace element composition of the sediments in the Tamiraparani estuary have been available. Moreover, the influence of anthropogenic factors (chemical plants, port activities) has raised the question as to whether this estuary is facing any serious threat from trace element contamination. Hence, the present study has been initiated to evaluate the geochemical factors that affect the spatial distribution of trace elements, including possible anthropogenic factors, in Tamiraparani estuarine sediments through GIS techniques.

Section snippets

Study area

The Tamiraparani estuary lies within the latitudes 8° 40′ to 8° 35′ N and longitudes 78° 10′ to 78° 13′ E off the Tuticorin coast near the Gulf of Mannar (Fig. 1). The study area falls into the Survey of India Toposheet No. 58L/2. The estuary has a length of 5 km from west to east (station 13 to 18) and 10 km from north to south (station 25 to 7). It has a mean water depth of 5 m. It is bounded by the Tuticorin harbour in the north and the Dhrangadara Chemical Plant (DCW) in the south and is

Sediment sampling and analysis

The geographical locations of the sampling sites were recorded using a hand-held GPS (Garmin eTrex,) for GIS analysis (Fig. 1). Sediment samples were collected using a stainless steel van Veen grab. Two samples, one for geochemical analysis and the other for grain-size analysis, were collected at each station. The samples for geochemical analysis were packed in thick polyethylene bags and tagged. For laboratory analysis, the samples were dried in a hot-air oven at 40 °C before being powdered

Results and discussion

The descriptive statistics of the trace elements (Ni, Pb, Co, Cr, Cu, Zn, Cd, Mn, Fe and Al) in the sediment samples are shown in Table 1. The highest values are presented by elements such as Zn, Pb, Cu, and Mn which have mean values exceeding 50 ppm, whereas Ni, Co, Cr, and Cd are found to occur in lower values. Significant variations are noted in elements like Mn, Zn, Cu, and Pb which have mean values of 668.5, 198.6, 40.19, and 26.16 ppm respectively. In addition, some elements have mean

Conclusion

A quantitative geochemical analysis of the surface sediments of the Tamiraparani estuary was carried out. The enhanced preservation of organic carbon in fine-grained sediments has led to contamination of trace metals due to the preferential adsorption of metal scavenging phases like Fe/Mn hydrolysates in view of the larger grain surface areas provided by the fine sediments (Förstner, 1983, Usero Garcia et al., 1997, Thuy et al., 2000, Bradl, 2004). However, most of the trace elements do not

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