Elsevier

Environmental Pollution

Volume 219, December 2016, Pages 1077-1091
Environmental Pollution

Comparison of pollution indices for the assessment of heavy metal in Brisbane River sediment

https://doi.org/10.1016/j.envpol.2016.09.008Get rights and content

Highlights

  • In-depth investigation of heavy metal pollution of river sediments.

  • Current pollution indices found to provide poor indication of risk.

  • A modified ecological Index (MRI) is proposed.

  • MRI provides an improved method for assessing ecological risk.

Abstract

Estuarine environment is complex and receives different contaminants from numerous sources that are persistent, bioaccumulative and toxic. The distribution, source, contamination and ecological risk status of heavy metals in sediment of Brisbane River, Australia were investigated. Sediment samples were analysed for major and minor elements using LA-ICP-MS. Principal component analysis and cluster analysis identified three main sources of metals in the samples: marine sand intrusion, mixed lithogenic and sand intrusion as well as transport related. To overcome inherent deficiencies in using a single index, a range of sediment quality indices, including contamination factor, enrichment factor, index of geo-accumulation, modified degree of contamination, pollution index and modified pollution index were utilised to ascertain the sediment quality. Generally, the sediment is deemed to be “slightly” to “heavily” polluted. A further comparison with the Australian Sediment Quality Guidelines indicated that Ag, Cr, Cu, Ni, Pb and Zn had the potential to rarely cause biological effects while Hg could frequently cause biological effects. Application of potential ecological risk index (RI) revealed that the sediment poses moderate to considerable ecological risk. However, RI could not account for the complex sediment behaviour because it uses a simple contamination factor. Consequently, a modified ecological risk index (MRI) employing enrichment factor is proposed. This provides a more reliable understanding of whole sediment behaviour and classified the ecological risk of the sediment as moderate to very high. The results demonstrate the need for further investigation into heavy metal speciation and bioavailability in the sediment to ascertain the degree of toxicity.

Introduction

Globally, disproportionately large human populations live near waterways and they extensively modify riparian zones, resulting in significant threat to water quality and river health. Worldwide deterioration of water quality arises from both natural and anthropogenic processes including soil erosion, mining, agricultural, industrial, transportation and energy production related activities (Chung et al., 2015, Li et al., 2014). These activities generate pollutants such as heavy metals, which eventually find their way into rivers and streams through weathering, disposal of effluents, runoff and leachates, as well as atmospheric deposition (Mucha et al., 2003). After their introduction into the aquatic ecosystem, most metals are attached to fine-grained particulates and, as a result of settling, accumulate in bottom sediments (Farkas et al., 2007), where they may cause adverse biological effects even though water quality criteria are not exceeded (NRC, 1989, Bibi et al., 2007). Heavy metals are ubiquitous environmental pollutants, which are persistent, non-biodegradable, toxic and bio-accumulative in the aquatic ecosystem (Arnason and Fletcher, 2003, Li et al., 2014). They have drawn wide attention due to their negative effects on human and ecosystem health (Brady et al., 2014a). Consequently, their concentrations, distribution, fate, impact and sources in the environment have attracted global interest and these are areas of ongoing research (Iqbal and Shah, 2014, Brady et al., 2014a, Brady et al., 2014b Sekabira et al., 2012, Singovszka et al., 2015, Vaezi et al., 2015).

The accumulation of metals in the sediment poses a long term threat to water bodies and other parts of the environment. Therefore, there is a need for sediment quality indicators to assess the risks of contamination and toxicity posed by metals in the aquatic environment. This has led to the development of many sediment quality indicators such as contamination factor, enrichment factor, index of geo-accumulation (I-geo), (modified) degree of contamination (Cd or mCd), (modified) pollution index (PI or MPI) and sediment quality guidelines (Muller, 1969, Tomlinson et al., 1980, Qingjie et al., 2008, Brady et al., 2015, Vidal and Bay, 2005). However, these sediment quality indicators either define a qualitative threshold or focus on ecological risk assessment of a single metal. Yet heavy metal pollution in the environment generally occurs in the form of complex mixtures. The synergistic effects of metal pollution rather than an individual metal effect may be of greater concern. The potential adverse risks due to hazardous chemicals (such as heavy metals) in the same medium can be assumed to be cumulative in worse case scenarios (Neff et al., 2005). Consequently, the potential ecological risk index (RI) developed by Hakanson (1980), which evaluates the combined pollution risk of an aquatic system through a toxic-response factor is well suited for assessing ecological risk posed by heavy metals in the environment. Nonetheless, RI is computed using a simple contamination factor. This could possibly introduce error in the assessment of risk pose by a complex environment like an estuary where sedimentation with significant input from creeks is a common occurrence (Brady et al., 2015). Contamination factor does not take the lithogenic and sedimentary inputs of the element of interest into account. In contrast, enrichment factor, which can normalise the impact of terrestrial sedimentary inputs, could provide more useful information and offer a more realistic estimate of the real ecological risk.

The area under study, the Brisbane River estuary, is the largest and most highly urbanised river system in south east of Queensland. The river catchment supports a large population (in excess of one million) and is currently experiencing rapid population growth (ABS, 2015). The catchment is characterised by sub-tropical weather with discrete wet summer (November to May) and dry winter (April to October) seasons (Eyre et al., 1998). The area is also categorised by a physio-geographic stratification along a hydrological gradient from lower to upper catchment, varying urbanization and distinct land uses. Historically, the river has received large amounts of treated sewage effluent with the lower reaches receiving effluent from eight wastewater treatment plants. The area is tidal and flood prone with eleven (11) major floods recorded since 1840. Elevated concentrations of metals in the sediment have been documented (Cox and Preda, 2005, Mackey and Mackay, 1996, Mackey et al., 1992). However, there is lack of information on the quality of the sediment after the recent significant floods in January 2011 and 2013.

The aim of the study was to use sediment quality indicators, including contamination factor, enrichment factor, index of geo-accumulation, modified degree of contamination, modified pollution index, Australian New Zealand sediment quality guidelines and potential ecological risk index to assess the ecological state of the river sediment. This will provide a tool for key stakeholders, including catchment managers, government, and the public in relation to action to protect aquatic biota and wildlife. Also, we propose a modified potential ecological risk index (MRI) which uses enrichment factor instead of contamination factor. This should account for the non-conservative sediment behaviour and natural variations in the sediment resulting in proper identification of anthropogenic contamination. Moreover, the generic outcomes of this study are expected to provide essential guidance for monitoring and regulation of heavy metals in urban waterways worldwide.

Section snippets

Sample collection

The study was conducted in 2014–2015 to cover the different land-use types and various urbanization levels of the river. Twenty two sites spanning Latitude 27°32′20.81″S to 27°22′39.37″S and Longitude 152°51′1.55″E to 153° 9′40.86″E were sampled (Fig. 1). The sites can be grouped into four physio-geographical strata namely: rural (SP1-SP3, which is mostly forestland), residential (SP4-SP12, moderately to highly residential, park and bushlands), commercial (SP13-SP18, highly urbanised,

Analytical performance of the method of analysis

The performance of the LA-ICP-MS method had been detailed in Duodu et al. (2015). However, due to the initial poor recovery of Cr, a simple excel equation was developed from the average Cr concentration of PACS-2 using GBW07312, MESS-3 and STSD-1 as calibration standards. This gave Cr recovery of 100.3%. Table 3 gives the measured against certified values of some metals in PACS-2 employing GBW07312, MESS-3 and STSD-1 as calibration standards. There was good agreement between the measured and

Conclusion

The concentrations of major and trace metals (determined with LA-ICP-MS) in Brisbane River sediment are presented in this study. The distribution characteristics show that most of the metals analysed were fairly stable across the sampling sites and between sampling periods. The variation patterns of elements in the sediment were found to be strongly dependent on their sources. Three sources of metals: marine sand intrusion, mixed lithogenic and sand intrusion as well as transport-related

Acknowledgement

The authors are thankful to Queensland University of Technology and Ghana Atomic Energy Commission for providing scholarship and study leave, respectively, for Godfred Odame Duodu to undertake this study. Our sincere gratitude goes to the Institute of Future Environments (QUT), which operates the Central Analytical Research Facility where the data reported in this paper was derived. Access to CARF is supported by generous funding from the Science and Engineering Faculty (QUT). Lastly, we

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