Marine Pollution Bulletin 89 (2014) 435–443

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Marine Pollution Bulletin

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Baseline

Metal contamination of estuarine intertidal sediments of Moreton Bay,Australia

http://dx.doi.org/10.1016/j.marpolbul.2014.10.0020025-326X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +61 7 3365 2176.E-mail address: g.morelli@uq.edu.au (G. Morelli).

Guia Morelli a,⇑, Massimo Gasparon a,b

a School of Earth Sciences, The University of Queensland, St Lucia, Qld 4072, Australiab The Australian National Centre for Groundwater Research and Training, Australia

a r t i c l e i n f o a b s t r a c t

Article history:Available online 22 October 2014

Keywords:Heavy metals contaminationExchangeable metals fractionSurficial sedimentsEstuariesMoreton Bay

Trace element concentrations in surface intertidal sediments were analyzed to assess the level of contam-ination along the western side of Moreton Bay (Australia). The environmental risks posed by metals wereevaluated using sediment quality guidelines, the Risk Assessment Code (RAC) and enrichment relative tobackground levels. Chromium, Ni, and Cu are the main contributors to sediment pollution. Sediments arealso enriched in Zn, Cd and Pb by 1.5–3 times the regional background. Zinc, Cd and Co may pose high tovery high risk to the aquatic biota due to their potential bioavailability, while Ni, As, Cu, Pb and Cr maypose medium risk at some of the investigated sites. Results emphasize the importance of using differentmethods for the assessment of sediment pollution at an estuarine site.

� 2014 Elsevier Ltd. All rights reserved.

Estuarine and marine embayments are important componentsof the complex and dynamic coastal watersheds as they supportdifferent habitats and provide significant economic benefits. Heavymetals used in all kinds of human activities are one of the mainecosystem threats for estuarine waters, and are often associatedwith sediments transported from the catchments (e.g.MacDonald et al., 1996; Forstner, 2008). Anthropogenic metalsare bound to sediments by particle surface absorption, ionexchange, co-precipitation, and complexation with organic matter(Tessier and Campbell, 1987; Passos et al., 2010). In intertidal areasdisturbance of sediments may change the bio-geochemical condi-tions (redox potential, pH and salinity) facilitating metal desorp-tion and/or remobilization (e.g. Tessier and Campbell, 1987;Förstner and Kersten, 1988; Morrisey et al., 2000; Swales et al.,2002; Coynel et al., 2007; Hill et al., 2013). Some of the sedi-ments-bound metals can be released to the water column becom-ing bioavailable and potentially toxic to marine organisms (Tessierand Campbell, 1987; Lacerda et al., 1992; Sahuquillo et al., 2003;Santana et al., 2007; Gao et al., 2010; Hooda, 2010). Sedimentsand marine sedimentary particulate matter can thus be eithersinks or sources of contaminants for the aquatic ecosystem(Gibbs, 1993; Förstner, 2008; Förstner and Salomons, 2008;Tessier et al., 2011; Hill et al., 2013). A complete assessment ofthe anthropogenic metal contribution to the environment shouldtake into account both the total and the exchangeable metal

concentration (Tessier et al., 1979; Rauret, 1998; Sahuquilloet al., 2003; Passos et al., 2010).

Moreton Bay in southeast Queensland (27�S, 153�E) is a semi-enclosed embayment (�125 km from north to south) separatedfrom the Pacific Ocean by a chain of three sand islands (Fig. 1).The region is one of Australia’s largest estuarine systems compris-ing five major river catchments (total area of 21,220 km2), withthe Brisbane River catchment being the most developed and themost impacted by the State’s capital, Brisbane (Dennison andAbal, 1999; Douglas et al., 2003). The bay is a popular tourist desti-nation and a commercial gateway to the Brisbane port for touristand commercial ships. Part of Moreton Bay is a marine park estab-lished to protect its high biodiversity (dugongs, marine turtles, greynurse sharks, dolphins, and other aquatic fauna), and some of thecoastal wetlands are listed as wetlands of international importance(Ramsar Wetlands Convention, 1971). The area is experiencing themost rapid urbanization in Australia and the wide-scale catchmentmodifications have led to deterioration of the bay water andsediment quality (increased sediment runoff, sewage discharge,increased nutrient and contaminant fluxes into the bay – Clark,1998; Dennison and Abal, 1999; Cox and Preda, 2005; Morelliet al., 2012). To date, very few studies have explored metal concen-trations in the bay’s sediments and their potential toxicity to resi-dent organisms (Burton et al., 2005; Cox and Preda, 2005; Morelliet al., 2012; Brady et al. 2014). Most of the western coast of MoretonBay is characterized by shallow, muddy, intertidal flats borderedwith mangroves and subjected to sediment deposition from the riv-ers and marine sand from the ocean. In many areas the intertidal

436 G. Morelli, M. Gasparon / Marine Pollution Bulletin 89 (2014) 435–443

flats are often disturbed by anthropogenic activities (e.g. dredgingto maintain navigational channels, walking and fishing) and by nat-ural disturbance (physical or biological sediment mixing). The aimsof the investigations reported in this paper were to measure theconcentrations of heavy metals (V, Cr, Co, Ni, Cu, Zn, As, Cd, andPb) in the surficial intertidal sediments of Moreton Bay, establishtheir exchangeable fraction to assess their potential bioavailability,and evaluate their enrichment relative to natural background lev-els. Finally, various guidelines and risk assessment codes were usedto assess the quality of the sediments and the impact of metals onthe local biota.

A total of 15 surface sediments (0–15 cm) were collected inMoreton Bay intertidal areas (Fig. 1) by hand pushing aluminumpipes (1–2 m long and 15 cm in diameter) into the sediments.The sediment cores were extracted after sealing the top of the corewith a test plug to avoid core loss during recovery. The top10–15 cm of each core were then sliced at about 2–3 cm intervals(depending on sediment characteristics) and stored at 4 �C untilanalysis. The remaining core lengths were used for other studies.

Sediments grain-size was measured using a Malvern Mastersiz-er laser particle analyzer with a measuring range between 0.03 and2000 lm. Textural classification of the sediment samples wasbased on the relative percentage of the different fractions (clay<4 lm, 4–63 lm silt, and >63 lm sand). The loss on ignition(LOI) method was used to estimate total organic matter, whichwas expressed as a percentage of dry weight after heating 0.2 gof sediment to 550 �C for 4 h (Heiri et al., 2001). For chemical anal-yses, all the samples were oven dried at 60 �C for 24 h prior to siev-ing through a 1 mm nylon mesh screen. One part of the passingfraction was used for extraction analysis without any further

Fig. 1. Map of Moreton Bay and location of the sampling sites.

treatment, while the other was powdered with an agate mortarprior to total digestion. Analyses were carried out in a clean labo-ratory (Class 1000). All lab ware used for sample treatment wasacid-cleaned prior to being used (boiling with HNO3 1:1) andrinsed several times with ultra pure water.

Total metal concentrations were determined by total digestion.Aliquots of 0.1 g of powdered sediments were digested over a hotplate in screw-top Teflon beakers after several steps of heatingand evaporation using a combination of ultrapure acids (HNO3 +HF, HCl, and HNO3) until complete dissolution. Analytical qualitycontrol was monitored by simultaneous analyses of internationalcertified reference materials (AGV-2 Andesite Standard [USGS];and MESS-3 Beaufort Sea Standard [National Research Council,Canada]), analytical blanks and sample replicates. Detection limitswere three orders of magnitude lower than metal concentrationsin the samples. Results were generally within 95% of certified val-ues. Relative standard deviations (RSD) were <2% for all metals inAGV-2 and <4% for all metals in MESS-3 except Cd and Zn (12%and 10% RSDs respectively). Recoveries for MESS-3 were 95–100%for all metals except Zn (86%), Cd (119%) and Pb (104%), whilethose for AGV-2 were around 98–102%.

The exchangeable fraction of metals was determined by apply-ing the first step of the BCR sequential extraction procedure(Quevauviller et al., 1997). The acetic acid extraction solution(0.11 mol/l) was prepared from stock distilled glacial acetic acid(17.2 mol/l). Approximately 40 ml of the extraction solution wereadded to 1 g of sediment in a 50 ml polypropylene centrifuge tube.After 16 h shaking at room temperature, samples were centrifugedat 3000 rpm for 20 min and the supernatant decanted and stored inclean centrifuge tubes at 4 �C until required for analysis.Laboratory blanks, procedural blanks and replicates were analyzedduring each batch of extractions. Quality control was performed byanalyzing the certified material BCR-701 (SM&T). Good agreementwas found with the certified values for Ni, Zn and Pb (RSD <1%) aswell as for Cu and Cd (RSD <5%). Reproducibility was typically <10%RSD. An Inductively Coupled Plasma–Mass Spectrometry (ThermoX7) was used to determine V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb.Major elements (Al, Fe, Mn and Ca) were analyzed by InductivelyCoupled Plasma Optical Emission Spectroscopy (Perkin–ElmerOptima 8300).

Gran size, LOI and total heavy metal concentrations at each siteare shown in Table 1 along with the summary of their statisticalparameters. Grain size was highly variable across the bay withmud (silt + clay) ranging between 1% and 95% and sand between8% and 97%. Mud was prevalent (>50%) in Deception Bay (G37and G34), the Pine River (G6) and South Moreton Bay. Sand(>90%) formed most of Bramble Bay intertidal areas (G16, G26,G24), and in Waterloo Bay sediments were a mixture of sand andmud. Organic matter expressed as LOI (%) varied from 0.6% to12.6%. The highest content of organic matter was found at sitesG5 and G31 in South Moreton Bay, while the lowest content wasfound in sediments in Bramble Bay. Total element concentrationsranged from 1 to 7.9 wt% for Al; 11.3 to 117.7 mg/kg for V; 11.5to 116.0 mg/kg for Cr; 11.3 to 109.6 mg/kg for Zn; 3.2–37.7mg/kg for Pb; 3.5–36.2 mg/kg for Ni; 2.9–30.1 mg/kg for Cu;2.4–20.3 mg/kg for Co; 2.7–18.5 mg/kg for As; 0.02 mg/kg to belowdetection limit for Cd. Higher concentrations of heavy metals werefound in Deception Bay, the Pine River and in South Moreton Bay.The positive and high kurtosis for Cd and Pb highlighted thepresence of peaks of those metals in some of the sediments.

The spatial variability of the exchangeable metal fraction of Zn,Co, Pb, Ni, Cu, and As is shown in Fig. 2. The highest concentrationof Zn (57.4 mg/kg) was found at site G34. Bramble Bay and the PineRiver sediments were characterized by moderately high Zn con-centrations (�10–18 mg/kg). In Bramble Bay, Co and Ni were alsohigh compared to the other Moreton Bay sites. The lowest

Table 1Total average, maximum, minimum and median metal concentrations (in mg/kg for trace metals and wt% for Al, Ca, Fe and Mn), grain size fractions (wt%) and LOI (wt%) in intertidal sediments of Moreton Bay. The concentrations of theupper continental crust-UCC (Taylor and McLennan, 1985) and the average of Moreton Bay background (Morelli et al., 2012) are also shown.

Location Clay Silt Sand LOI V Cr Co Ni Cu Zn As Cd Pb Al Ca Fe Mn

G37 13 54 33 Mean 5.1 70.7 58.6 9.9 17.9 13.7 41.7 13.4 0.103 10.4 4.0 0.7 2.6 0.022Max 6.5 77.6 66.6 11.0 20.3 15.1 45.9 14.3 0.119 11.5 4.4 0.8 2.8 0.024Min 4.1 54.9 45.0 8.4 12.6 10.5 35.2 12.9 0.094 8.8 3.1 0.6 2.2 0.019Median 4.9 75.2 61.5 10.1 19.3 14.6 42.8 13.2 0.100 10.7 4.3 0.7 2.7 0.022

G34 15 59 26 Mean 7.9 81.9 82.1 14.3 25.0 22.9 70.3 13.8 0.128 17.7 5.6 0.9 3.6 0.052Max 9.8 117.7 116.0 20.3 36.2 30.1 103.0 18.5 0.192 24.4 7.8 1.2 5.1 0.076Min 6.1 28.2 28.2 5.4 7.6 7.7 21.2 7.4 0.075 8.5 1.7 0.3 1.1 0.014Median 7.9 90.9 92.0 15.8 28.2 27.0 78.6 14.6 0.123 19.0 6.3 1.1 4.1 0.059

G9 6 21 73 Mean 1.6 34.2 33.7 7.4 10.2 9.6 35.1 7.8 0.055 9.0 2.8 0.4 1.4 0.020Max 1.8 90.9 92.0 15.8 28.2 27.0 78.6 14.6 0.123 19.0 6.3 1.1 4.1 0.059Min 1.3 11.3 12.4 3.7 4.1 2.9 15.7 5.0 0.029 4.5 1.2 0.1 0.4 0.005Median 1.6 17.27 15.2 5.1 4.3 4.2 23.0 5.8 0.034 6.2 1.8 0.2 0.6 0.008

G6 20 72 8 Mean 5.2 92.9 86.9 15.9 24.4 20.7 87.4 11.2 0.117 18.6 6.1 1.1 3.8 0.038Max 5.6 95.0 88.9 16.4 25.1 21.5 93.3 11.2 0.120 21.2 6.3 1.2 3.9 0.039Min 5.0 89.0 82.7 15.2 23.1 19.5 81.2 11.1 0.113 16.4 5.9 1.1 3.7 0.037Median 5.2 93.9 88.0 16.0 24.6 21.0 87.5 11.2 0.118 18.4 6.0 1.1 3.7 0.038

G24 1 2 97 Mean 1.9 74.7 49.1 19.4 16.4 8.2 53.7 10.0 0.058 10.5 5.8 1.5 2.8 0.054Max 2.0 85.2 60.6 19.8 17.0 9.0 57.0 10.2 0.067 10.7 6.0 1.7 3.1 0.060Min 1.6 60.0 36.3 18.8 16.0 7.1 51.3 9.9 0.045 10.3 5.6 1.4 2.6 0.046Median 2.0 76.7 49.7 19.5 16.4 8.4 53.3 9.9 0.060 10.4 5.8 1.5 2.8 0.054

G26 1 8 91 Mean 1.3 54.8 34.5 13.1 11.8 7.2 45.2 6.6 0.058 10.2 5.7 1.4 2.1 0.033Max 2.2 58.2 36.7 14.0 12.4 8.3 47.8 7.1 0.074 10.4 5.9 1.4 2.2 0.037Min 0.6 47.6 30.7 12.0 10.7 6.5 41.8 6.2 0.050 9.8 5.4 1.3 1.9 0.030Median 1.3 56.7 35.4 13.1 12.0 7.0 45.6 6.6 0.055 10.3 5.8 1.4 2.1 0.033

G16 1 3 97 Mean 1.9 51.6 35.2 13.0 10.9 5.9 45.8 7.3 0.052 9.8 5.9 1.6 1.9 0.033Max 2.3 57.3 41.5 13.3 11.5 7.1 49.5 7.7 0.058 10.2 6.2 1.7 2.1 0.040Min 1.6 45.5 30.2 12.7 10.3 5.0 41.4 6.9 0.043 9.2 5.5 1.4 1.7 0.029Median 1.3 51.73 34.6 13.0 10.9 5.8 46.1 7.3 0.1 9.9 5.9 1.6 1.9 0.033

G14 8 25 68 Mean 4.2 56.0 45.8 14.8 16.4 12.6 61.8 10.5 0.075 12.4 4.6 0.9 2.5 0.024Max 6.5 57.2 49.1 15.5 17.0 13.8 63.8 11.0 0.080 12.5 4.7 1.0 2.6 0.025Min 3.2 52.8 42.0 14.2 15.4 11.2 60.7 10.0 0.072 12.3 4.5 0.9 2.3 0.023Median 3.5 57.06 46.1 14.7 16.6 12.6 61.4 10.4 0.1 12.5 4.6 1.0 2.6 0.024

G21 5 17 78 Mean 2.6 15.0 13.4 2.8 4.2 5.8 14.8 3.4 0.037 5.0 1.5 0.1 0.5 0.003Max 3.1 18.2 17.9 3.4 5.1 7.3 19.4 3.8 0.073 5.6 1.7 0.2 0.7 0.004Min 2.1 12.6 11.5 2.5 3.5 4.7 11.3 2.9 0.019 4.5 1.2 0.1 0.4 0.002Median 2.6 14.6 12.1 2.7 4.0 5.7 14.3 3.4 0.028 5.0 1.5 0.1 0.5 0.003

G23 8 33 60 Mean 2.7 36.6 35.4 6.6 10.3 10.6 25.5 6.5 0.051 7.8 2.7 0.4 1.4 0.011Max 3.6 41.9 38.7 7.1 11.8 11.3 28.7 8.0 0.058 8.2 3.1 0.4 1.7 0.013Min 1.5 33.2 32.2 6.2 9.1 10.0 23.6 4.9 0.040 7.3 2.5 0.4 1.2 0.010Median 2.9 41.9 38.7 7.1 11.8 11.3 28.7 8.0 0.058 8.2 3.1 0.4 1.7 0.013

G31 12 57 31 Mean 10.1 77.6 79.7 11.5 22.1 16.0 63.5 15.7 0.159 20.0 5.9 0.7 3.9 0.023Max 11.3 83.3 82.0 12.9 24.6 18.9 83.2 16.8 0.301 37.7 6.6 0.8 4.2 0.025Min 8.9 74.5 77.0 10.6 20.8 13.9 52.6 15.2 0.088 10.8 5.6 0.6 3.7 0.019Median 2.9 76.3 79.9 11.3 21.4 15.7 59.0 15.4 0.122 15.7 5.8 0.6 3.8 0.023

G32 17 41 43 Mean 3.6 47.8 41.4 9.0 14.5 10.9 39.5 5.7 0.041 7.5 3.7 0.4 1.9 0.013Max 5.1 57.3 45.4 11.4 17.0 14.2 45.5 7.8 0.046 8.6 4.4 0.5 2.3 0.014Min 1.9 40.3 38.0 6.9 10.7 9.1 32.2 4.1 0.037 6.7 2.9 0.4 1.4 0.010Median 3.7 46.7 41.2 8.8 15.1 10.1 40.1 5.5 0.042 7.5 3.7 0.5 1.9 0.014

(continued on next page)

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438 G. Morelli, M. Gasparon / Marine Pollution Bulletin 89 (2014) 435–443

exchangeable metal concentrations were found in south MoretonBay far from any close contamination source, with the exceptionof site G5 where high concentrations of Zn, Cr and Co (�19, 3,3.0 and 2.6 mg/kg) were noted as well as of Cd (0.67 mg/kg). Leadconcentrations were <1 mg/kg with the exception of site G34(2.4 mg/kg) and G24 (2.6 mg/kg).

Grain size variability is known to control the geochemicalbehaviour of heavy metals in sediments since fine particles arethe most chemically active components of sediments due to theirpotential to bind higher proportions of metals (Loring, 1991; Gaoand Chen, 2012). Many studies on estuarine contamination haveoften focused in analyzing metal content of the <0.063 mm fractionof sediments (e.g. Förstner, 1989; Irvine and Birch, 1998; Birchet al., 2001; Forstener and Salomons, 2008). Our study investigatedmetals in the sediment fraction <1 mm, after grain size resultsshowed that within this range sediments had high variability andmud was not predominant along the bay. The analyzed metalconcentrations were, therefore, generally representative of thebulk intertidal sediments. Total metal concentrations strongly cor-related with each other and with Al (r = 0.63–0.90) suggesting thatthey are associated with Al-silicates and predominantly derivedfrom geological sources. The low correlation between exchange-able metal fraction and Al and mud suggest that the fine sedimentfraction is not the principal scavenger for the more mobile metals,and metal distribution cannot be simply interpreted as a functionof grain size. For example, Co, which is the most mobile amongthe metals analyzed, had negative correlation with mud(r = �0.04). Similarly, exchangeable Zn and Ni concentrations atsite G24 (mainly formed by sandy sediments) were relatively highcompared to other sites dominated by mud. Vanadium, Cu, Asand Cd accumulation was closely related to organic matter(r = 0.47–0.55), considered a stressor in coastal ecosystems (Valdeset al., 2005), deriving from natural sources and also from organic-rich waste (sewage, effluent from food processing farms, and fishfarms).

Metals in the exchangeable fraction can become easily bioavail-able following small changes in environmental conditions (Tessieret al., 1979; Soares et al., 1999; Sahuquillo et al., 2003; Passos et al.,2010). Potential metal bioavailability was calculated in this studyas the percentage of the exchangeable fraction relative to the totalmetal concentration in the sample providing a method to assessthe risk posed to the benthic fauna by heavy metals (Tessieret al., 1979). The extractability percentages of the average andmaximum values for metals at each site (Fig. 3) revealed that Cdand Zn were the most mobile (33% and 29% of these metals areassociated with the exchangeable fraction), followed by Co (25%),Ni (13%) and As, Cu and Pb (7–10%). Exchangeable Fe variedbetween 1% and 8.3%, with a high value of 9.3% at site G14. The bio-availability of Fe and Mn was monitored because of their tendencyto form iron oxides and hydroxides and thus act as potential scav-engers for other heavy metals (Siegel, 2002). In summary, averagemetal concentrations in the exchangeable fraction decreased in thefollowing order: Zn > Co > V > Ni > Cu > Cr > Pb > As > Cd. Whencompared to the total metal concentrations, potential metalbioavailability decreased in the following order: Cd > Zn > Co >Ni > As > Cu > Pb > V > Cr. The high bioavailability of Zn, Cd, andCo in Bramble Bay and in Deception Bay (at G9) proved that sandysediments are capable of bonding high concentrations of metals.

The most common way to quantify the anthropogenic contribu-tion to the metal fraction in sediments is to compare measuredmetal concentrations with uncontaminated background levels rep-resenting the natural geochemical concentrations (Salomon andForstner, 1984; Matschullat et al., 2000; Reimann et al., 2005;Reimann and Garrett, 2005; Gasparon et al., 2007). Enrichmentfactors (EFs) are calculated as the ratio between each metal ofinterest and Al, divided by the concentrations of the same metal

Fig. 2. Spatial distribution of the extracted metal fractions in Moreton Bay. Cadmium is not shown in the graphs as it is <0.05 mg/kg at all sites with the exception of G5(Cd = 0.47–0.57 mg/kg). Four surface samples were analyzed for each core, and each bar refers to the metal concentration at a different depth interval (from left to right: 0–3 cm, 4–7 cm, 8–10 cm and 11–15 cm).

G. Morelli, M. Gasparon / Marine Pollution Bulletin 89 (2014) 435–443 439

and Al in the background: EF = (met/Al)sample/(met/Al)background.Normalization of metal concentrations against Al accounts forthe sample variability due to heterogeneous sediment types, grainsizes and mineralogy (Loring and Rantala, 1992). EFs are oftendetermined using average crustal abundances (such as the uppercontinental crust – UCC concentrations, e.g. Hu et al., 2013; Gaoand Li, 2012) as natural background values, especially where localbackground values cannot be established. However local regionalbaseline values calculated from the least impacted sedimentsavailable in the target area should be used where possible to obtainthe most realistic data (Rubio et al., 2000; Burton et al., 2005). Inthis study, EFs of Pb, Zn, Cu, Co, Ni, Cd, Cr and As were determinedusing existing geochemical background concentrations (Table 1)for the Moreton Bay’s sediments (Morelli et al., 2012). In generalEF � 1–1.5 indicate that the selected metal is mostly sourced bycrustal materials, EF = 1.5–3 denotes moderate enrichment inanthropogenic metals, while EF = 3–5 implies moderate to severeenrichment and the need for further investigation (Zhang andLiu, 2002; Vreca and Dolenec, 2005; Wang et al., 2007). The exam-ined sediments were moderately enriched in Zn, Cd, Pb, and Cu(EF > 1.5 and <3) across all sites in Deception Bay (G37, G34, G9),at the mouth of the Pine River (G6) in Bramble Bay, in Waterloo

Bay (G21 and G23), and in South Moreton Bay (G4 and G5). EF val-ues of As (EF �1.5) in Deception Bay (G37) and in South MoretonBay (G4) indicated minimal anthropogenic contribution. Incontrast, EF values for V, Co, Ni and Cr were lower than 1.5 at allsites, suggesting very small to negligible anthropogenic contribu-tion. Chromium was only moderately enriched at site G4. The goodpositive correlations between Mn and As (r = 0.68), V (r = 0.84) andCr (r = 0.64) further suggest that enrichments in these metals arepartly inherited from the local source rocks and depositionalprocesses. Vanadium and Cr are the dominant metals sourced frombedrock in sediments from the Pumicestone Passage area (Predaand Cox, 2002), and the relatively high concentrations of As inDeception Bay were associated with manganese rich clay (Bradyet al., 2014). High concentrations of Mn were also found on thetidal flats of Deception Bay (Preda and Cox, 2002). When comparedwith UCC concentrations (Taylor and McLennan, 1985) sedimentsshowed moderate enrichment (EF = 1.5–3) for Zn (at G6, G14, G4,G5), V, Cr, Co and Ni (at most sites), moderate to severe enrichment(EF > 3) for Cr (at G37, G34, G6 and G31), V (at G4), Ni (at G31 andG4) and Cd (at G4) and significant enrichment for As (EF = 4–10) atall sites and for Cr and Cd (EF > 5) at sites G4 and G5. It would beincorrect, however, to interpret these elevated EF values as

Fig. 3. Extractability (%) for the (a) average and (b) maximum concentrations of metals at the sampling sites.

440 G. Morelli, M. Gasparon / Marine Pollution Bulletin 89 (2014) 435–443

evidence for human impact, because the crystalline UCC is stronglydepleted in elements typically associated with terrigenous marinesediments and organic matter, such as As and Cd. Therefore theelevated UCC-normalized EF values simply indicate the selectionof non-representative background material for the normalization.

The environmental risk caused by elevated metal concentrationsin the sediments, irrespective of their natural or anthropogenic ori-gin, is assessed by established guideline values (Hubner et al.,2009). Sediment quality guidelines (SQGs) indicate threshold val-ues for metal concentrations in sediments and waters to respondto management regulations for the protection of natural ecosys-tems (Perin et al., 1985; MacDonald et al., 1996, 2000; ANZECCand ARMCANZ, 2000; Jain, 2004; Passos et al., 2010). Australianand New Zealand Guidelines for Fresh and Marine Water Quality(ANZECC and ARMCANZ, 2000) provide a range of metal concentra-tions in sediments defined by low interim sediment qualityguidelines (ISQG-L) and high interim sediment quality guidelines(ISQG-H). ISQG-L is a threshold level triggering the requirementfor additional environmental investigation: metals < ISQG-L repre-sent a minimal effect range, with no adverse biologic effects,metals P ISQG-L indicate biological effects may occur occasionally.Concentrations P ISQG-H denote that sediments are likely to havea biological impact for the ecosystem (ANZECC and ARMCANZ,

2000). None of the metals analyzed in this work was found to beabove the ISQG-H (Table 2). The ISQG-Ls were exceeded for Crand Ni at site G34, G6, G9, G31, G29, G4 and G5.

Metal contamination was also assessed against, one of the mostwidely-used sediment quality guidelines (MacDonald et al., 1996,2000). This SQGs are based on threshold concentrations (TEL)and probable effect levels (PEL) defining three ranges of chemicalconcentrations with regard to biological effects: <TEL (adverseeffect rare), TEL–PEL (adverse effects occasional), >PEL (adverseeffect frequent). Although caution is needed when using SQGsbecause the investigated sediments should be geologically/geo-chemically similar to the reference sediments (USEPA, 1989), theTEL/PEL – based SQGs show a very high degree of comparability(Hubner et al., 2009). All metal concentrations were below thePEL thresholds at all sites. The TEL values were exceeded by Crand Ni (at most of the sites), by Cu (at G34, G9, G6), Pb (at G31),and As (at G37, G34, G9, G6, G24, G14, G31 and G5), implying thatadverse consequences to biota may occasionally occur in mostparts of the bay.

Our results were also compared with Reference Median Range(RMR) for metals occurring naturally in Queensland estuarine sed-iments (Moss and Costanzo, 1998). These guidelines providebenchmarks for comparison with data from sites affected by

Table 2List of sites exceeding sediment quality guidelines ANZECC and ARMCANZ (2000) (mean values), SQG (MacDonald et al., 1996) (mean values) and Reference Median Range forQLD (Moss and Costanzo, 1998) (median values). The dash (–) indicates no SQG exceedance. Refer to Table 1 for mean and median values for each element at each site.

Element ANZECC/ARMCANZ (2000) SQG (MacDonald et al., 1996) Reference Median Range for QLD estuarine sediments (Moss and Costanzo, 1998)

ISQG-L ISQG-H TEL PEL RMR-low RMR-median RMR-high

Benchmark value 80 370 52.3 160.4 30 60 95

G34 G37 G4 G37 G26 G31 G5 G37 G4Cr G6 – G34 G5 – G34 G16 G29 G34 –

G6 G6 G14 G32 G6G31 G24 G23 G4 G31

Benchmark value 65 270 18.7 108.2 5 17 23

G34 G37 G26 G23 G5 G34 G34Cu – – G6 – G34 G16 G31 G6

G6 G14 G29G24 G21 G32

Benchmark value 21 52 15.9 42.8 5 10 23

G34 G37 G14 G37 G24 G23 G4 G37 G26 G31 G34Ni G6 – G34 G31 – G34 G26 G31 G5 G34 G16 G32 G6

G31 G6 G5 G9 G16 G29 G6 G14 G29G24 G6 G14 G32 G24 G23 G5

Benchmark value 50 220 30.2 112.2 5 5 13

G37 G24 G21 G32 G37 G24 G21 G32 G34Pb – – – – G34 G26 G23 G5 G34 G26 G23 G5 G6

G9 G16 G31 G9 G16 G31 G31G6 G14 G29 G6 G14 G29

Benchmark value 200 410 124 271 5 5 13

G37 G24 G14 G5 G34Zn – – – – G34 G26 G31 G6 –

G6 G16 G32 G5

Benchmark value 20 70 7.24 41.6 n/a n/a n/a

G37 G6 G14As – – G34 G24 G31 –

G9 G16 G5

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contamination (Moss and Costanzo, 1998). No contamination isdeemed to have occurred where median concentrations are closeto the median values defined by the RMR, while concentrationsclose to or above the high RMR values suggest that sedimentscould be affected by some degree of contamination and the needfor additional analyses before any conclusions can be reached(Moss and Costanzo, 1998). Nickel, Pb and Cu concentrations wereabove the RMR high values at three sites (G34, G6 and G31), indi-cating some contamination has occurred. The RMR median valueswere exceeded by Pb at all sites (except G4), Cu (at G34 and G6),and Zn (at G34, G6, G5). It should be noted here that Moss andCostanzo (1998) derived their RMR values solely from the<0.63 lm sediment fraction. Since this particular fraction istypically enriched in trace elements compared with the coarsefractions, it may be concluded that the bulk sediments (<1 mm)analyzed during the present study exceeded RMR benchmarkvalues for metals at all sites examined.

The risk associated with metal presence in aquatic system isdetermined also by how strongly metals bind to sediments, amechanism that controls their potential bioavailability and move-ment into aquatic food chains. Concentrations of exchangeablemetals were assessed against the available Risk Assessment Code(RAC), a set of criteria that identify the risk posed to the aquaticenvironment by the most labile metal fraction under natural con-ditions (Perin et al., 1985; Jain, 2004). Following these criteria, sed-iments are considered to be safe if their exchangeable metalfraction is <1% of the total metal load. Values of 1–10% are of lowenvironmental risk, whereas 11–30% indicates medium risk, 31–50% high risk, and values >50% represent very high risk to the envi-ronment (Perin et al., 1985; Jain, 2004; Passos et al., 2010). For allthe investigated sediments Cr, Ni, Cu, As and Pb were within the

low risk category (Fig. 3), while Co, Zn and Cd fell into the mediumrisk category at almost all the sites and into the high to very highrisk in some instances (Zn at G34 and Cd at sites G24 and G5).Maximum levels of Cu, Pb, Ni and As may also pose medium envi-ronmental risk. To the best of our knowledge, this study is the firstassessment of potential metal bioavailability in the western inter-tidal sediments of Moreton Bay.

Using the SQGs approach, Moreton Bay intertidal sedimentswere classified as moderately contaminated with Cr and Ni, withmoderate Cu and As contamination occurring at some sites. Insome areas Pb and Zn were also determined to be moderatelyenriched when weighed against Moreton Bay background levelsand the Queensland RMR values. Interestingly, neither elementexceeded the SQG benchmarks adopted here. In contrast, Cr andNi, which exceeded the SQGs values, were not enriched comparedto Moreton Bay background values. The highest concentrations ofmetals along Moreton Bay intertidal areas were found in DeceptionBay (sites G34 and G37), at the mouth of the Pine River (G6) and inSouth Moreton Bay (G31, G4 and G5). Previous work (Burton et al.,2005; Cox and Preda, 2005) on Moreton Bay sediments establishedthat Pb, Cd, Zn and Ni exceed the ISQG-L (ANZECC and ARMCANZ,2000) values close to urban storm water drainage, municipal solidwaste landfill sites and especially along the Brisbane River. Rela-tively high Cu levels around marinas and mooring facilities havealso been attributed to the use of Cu-based antifouling paints(Warnken et al., 2004; Leon and Warnken, 2008). Chromium, Cu,Ni and As in Deception Bay (sites G34, G37 and G9) may be asso-ciated with contaminant flow from the Pumicestone Passage tothe Redcliffe Peninsula and from the Caboolture River to the southside of the bay (Brady et al., 2014). However, the absence of aspecific point source (except for the port of Brisbane area) suggests

442 G. Morelli, M. Gasparon / Marine Pollution Bulletin 89 (2014) 435–443

that the main contribution to the contaminant load is derived fromurbanization of the catchment area and the associated sewage anddomestic waste discharge (As), industrial run off, urban stormwaters, wash off from urban surfaces (e.g., roads and roofs), recre-ational and industrial marinas (Cu, Ni), agriculture and fertilizers(Cd, Cr, Cu) and combustion of fossil fuel (Pb, Zn, Ni). The resultsof this study also suggest that while Zn, Cd and Co concentrationsdo not exceed conventional SQGs, or demonstrate any significantenrichment in the bay, they may pose moderate to high risk ofadverse health effects to aquatic biota in some areas, e.g., BrambleBay. Elevated concentrations of exchangeable metals were found atsites where mud is not predominant (G9, G24 or G21), highlightingthe importance of analyzing bulk sediments (as opposed to onlythe fine sediment fraction), since sandy sediments may also beenriched in exchangeable metals. At the studied sites, changes inthe environmental conditions induced by the complex coastalhydrodynamic (tidal exchange, flood events, storms or resuspen-sion of sediments by human and natural activities) control themobilization of heavy metals adsorbed onto sediment particles.Exceedance of sediment quality guidelines is not necessarily dueto human impact, and may be inherited from the local geologicalbackground and depositional settings. Therefore care must betaken when using sediment quality guidelines to assess the extentof human impact, and guidelines should always be applied with anunderstanding of the environmental situation and consideringtheir limitations (Buchman, 1999; Hubner et al., 2009; Yanget al., 2012). The results generated in this study provide a usefulbaseline of total and exchangeable metal concentrations for futureestuarine management (e.g. dredging for building/maintenance ofnavigational channels, control of fishing and recreational activities)in the region.

Acknowledgments

The authors would like to thank The University of Queensland(International Postgraduate Research Scholarship to G. Morelli)and the Australian National Centre for Groundwater Researchand Training (Program 3) for financial support and Sunny Hu forassistance with the geochemical analyses. The suggestions madeby an anonymous reviewer to an early version of this manuscripthave contributed to its final revision and are gratefullyacknowledged.

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