Elsevier

Environmental Technology & Innovation

Volume 8, November 2017, Pages 126-131
Environmental Technology & Innovation

Enrichment, contamination and geo-accumulation factors for assessing arsenic contamination in sediment of a Tropical Open Lagoon, Southwest Nigeria

https://doi.org/10.1016/j.eti.2017.06.006Get rights and content

Abstract

The presence of toxic heavy metals and metalloids in aquatic environments constitutes a major risk and there is an urgent need for continuous monitoring of such pollutants. This study assesses the concentrations of arsenic (As) in surface sediments from 15 locations on the Lagos Lagoon, Nigeria during the wet and dry seasons to determine the degree of contamination. The results showed that the mean total As concentration in sediment (2.44 mg kg1 dry weight) did not exceed the Canadian Interim Sediment Quality Guideline (CISQG) value of 7.24 mg kg1 dry weight during the wet and dry seasons. Based on the Sediment Quality Guidelines (SQGs) of the United States Environmental Protection Agency (USEPA) and ecological risk assessment using the enrichment factor (EF), contamination factor (CF) and geo-accumulation index (Igeo), the study’s results indicate two things: firstly, low to moderate and significant levels of enrichment from As; and secondly, low to moderate degree of contamination in Lagos Lagoon during the study period.

Introduction

Arsenic (As) has emerged as an important worldwide problem due to the associated health risks and is now recognized as a notorious poison as well as a human carcinogenic and teratogenic agent ATSDR (2007), Ravenscroft et al. (2009). Unregulated human activities and industrial processes such as copper smelting, mining and coal burning contribute to high levels of As in the environment. These high As levels from anthropogenic sources are usually associated with certain fertilizers, drugs, insecticides, wood preservatives, herbicides, pesticide application and other animal-feeding operations (Mandal and Suzuki, 2002). High concentrations of As in marine sediments can lead to acute and chronic toxicity in marine organisms via ingestion of particulate matter (As associated with particles), through membrane-facilitated transport or passive diffusion (As dissolved in water) (Bhattacharya et al., 2007). A recent study investigated the distributions of As and other metals such as iron (Fe) and manganese (Mn) in the sediments of two pristine areas (Crab and Spartina) in the Patos Lagoon Estuary, Brazil. It was reported that concentrations of As in sediments of Crab and Spartina areas ranged up to 33 mg kg1 and 24 mg kg1, respectively (Costa et al. 2016). Another study reported that the concentration of As in sediments from Emet Stream, Turkey was 14.51–3317.1 mg kg1 (Benzer, 2016).

It has been reported that Lagos Lagoon contains elevated concentrations of heavy metals in environmental and biological media Ajagbe et al. (2012), Chukwu (2006), Ladigbolu and Balogun (2011). A previous study reported that levels of heavy metals discharged into drains/canals/streams and subsequently into Lagos Lagoon were as follows: Fe – 161,718 kg, Mn – 205,989 kg, Co – 15,683 kg, Zn – 7026 kg, Cr – 5285 kg, Pb – 2259 kg, Ni – 6124 kg, Cd – 538 kg and Hg – 278 kg per annum (Oyewo, 1998). Ekaete et al. (2015) also reported that heavy metal concentrations in Lagos Lagoon sediments had the following ranges: Ni (Bdl-17.55 mg kg1), Mn (12.5–1180.25 mg kg1), Pb (Bdl-27.04 mg kg1), Zn (Bdl-543.33 mg kg1), Cu (Bdl-35.55 mg kg1), Cr (Bdl-220.53 mg kg1) and Fe (832.64–19722.80 mg kg1). Another recent analysis on the Lagos lagoon sediment extracts reported that they exhibit teratogenic, embryogenic, and genotoxic properties with some of the pollutants suspected of being potential human carcinogens (Sogbanmu et al., 2016). Despite the numerous pollution studies and sediment toxicity in Lagos Lagoon, reports focusing on As concentrations as a major global concern are generally limited. Considering the increasing anthropogenic sources of coastal pollution and the previous report of Aderinola et al. (2009) which recorded As concentration in the sediment of Lagos lagoon as 0.083 mg kg1, it is crucial to continuously monitor the As concentration alongside other contaminants in the sediments of Lagos Lagoon, Nigeria. The objective is to understand the current contamination scenario. Furthermore, although the assessments of drinking water and dietary exposure remain a major concern for As exposure, aquatic sediments as sinks represent a continuous exposure route for aquatic biota and this means that regular ecological risk assessments are required.

Ecological risk indices such as enrichment factor (EF), contamination factor (CF) and geo-accumulation index (Igeo) have been conveniently employed as diagnostic tools by a number of researchers Abrahim and Parker (2008), Likuku et al. (2013), Nowrouzi and Pourkhabbaz (2014) for assessing the pollution status of metals (Pb, Cd, Ni, Fe, Cu, Mn, Co and Zn) contaminated sediments. The main objectives of this study are to assess the degree of As contamination in the sediments of Lagos Lagoon and the ecological risk associated with the obtained levels of As using the EF, CF and Igeo.

Section snippets

Site description and sediment sampling

Sampling was carried out at Lagos Lagoon which is situated between latitudes 06°26–06°36N and longitudes 003°23-003°40E. It is an area where a wealth of human and transportation activities take place daily including unregulated discharge of effluents, sewage and solid wastes Adeniyi et al. (2008), Nubi et al. (2008). The study area and sampling locations of sediments in Lagos lagoon are presented in Fig. 1. Approximately 1 kg sediment samples were obtained using Van-Veen grab sampler during

Concentrations of As in sediments

The analytical results of As in Montana soil indicate that the differences between certified (107.0 ± 5, mg kg1) and measured results (103.3 ± 0.6 mg kg1) were less than 5% (recovery 96.5%). Concentrations of As were found in the 0.27–7.97 mg kg1range from Lagos Lagoon sediments (average: 2.38 and 2.47 mg kg1; median: 1.8 and 2.04 mg kg1 for wet and dry seasons, respectively). The observed mean contents of As revealed no consistent upward or downward trend. In fact, they fell within the

Conclusion

Lagos Lagoon was found to accumulate As in varying and sometimes very low but measurable concentrations throughout the study. Statistically, the concentrations of As in sediments were normally distributed throughout the analysis period. The SQGs, EF, CF and Igeo indicate that sediments were unpolluted to being moderately enriched by As. The present study did not include the bioavailable forms of sediment-bound toxic metals, which could be included in future studies.

Acknowledgments

We extend our thanks for the laboratory support offered by the Centerfor Environmental Risk Assessment and Remediation (CERAR), Mawson Lakes Campus of the University of South Australia, Adelaide. The first author is grateful to the CRC CARE , Australia for the financial support which enabled her to conduct an analysis of samples in Australia as part of her Ph.D. study.

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      The determination of the proportion of natural and anthropogenic sources of metals in sediments is essential. Pollution can be eventually assessed by isotopic analyzes (Gao et al., 2008; Han et al., 2015; Xu et al., 2017; Zaborska, 2014), but due to high costs and time consuming, classic indexes are generally used (Table 1): degree of contamination (Cd) (Abrahim & Parker, 2008; Hakanson, 1980), modified degree of contamination (mCd), contamination factor (CF) and Pollution Load Index (PLI) (Kalender & Çiçek Uçar, 2013; Pejman et al., 2015; Peña-Icart et al., 2016; Saeedi & Jamshidi-Zanjani, 2015; Tomlinson et al., 1980), geoaccumulation index (Igeo) (Abrahim & Parker, 2008; Aiman et al., 2016; Han et al., 2017; Hanif et al., 2016; Hasan et al., 2013; Kalender & Çiçek Uçar, 2013; Muller, 1969; Peña-Icart et al., 2016; Usese et al., 2017; Wang et al., 2015; Zahra et al., 2014; Zhang et al., 2009; Zhiyuan et al., 2011), enrichment factor (EF) (Abrahim & Parker, 2008; Aiman et al., 2016; Hanif et al., 2016; Hasan et al., 2013; Kalender & Çiçek Uçar, 2013; Kaushik et al., 2009; Peña-Icart et al., 2016; Qi et al., 2010; Sinex & Helz, 1981; Usese et al., 2017; Wang et al., 2015; Zahra et al., 2014; Zhang et al., 2009) and potential ecological risk index (PERI) (Aiman et al., 2016; Hakanson, 1980; Han et al., 2017; Pejman et al., 2015; Saeedi & Jamshidi-Zanjani, 2015; Wang et al., 2015; Zhang et al., 2016). These indices are based on a comparison between the concentration measured in the sample and the concentration in a reference sample (natural background).

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