Assessment of trace metal contamination and bioavailability in an Environmental Protection Area: Guaxindiba estuarine system (Guanabara Bay, Rio de Janeiro Brazil)

Journal Pre-proof Assessment of trace metal contamination and bioavailability in an Environmental Protection Area: Guaxindiba estuarine system (Guanabara Bay, Rio de Janeiro Brazil) Michele Fernandes, Estefan Monteiro da Fonseca, Leonardo da Silva Lima, Susanna Eleonora Sichel, Jessica de Freitas Delgado, Thulio Righeti Correa, Valquiria Maria de Carvalho Aguiar, José Antonio Baptista Neto

PII: DOI: Reference:

S2352-4855(19)30421-9 https://doi.org/10.1016/j.rsma.2020.101143 RSMA 101143

To appear in:

Regional Studies in Marine Science

Received date : 6 June 2019 Revised date : 3 February 2020 Accepted date : 3 February 2020 Please cite this article as: M. Fernandes, E.M. Fonseca, L.S. Lima et al., Assessment of trace metal contamination and bioavailability in an Environmental Protection Area: Guaxindiba estuarine system (Guanabara Bay, Rio de Janeiro Brazil). Regional Studies in Marine Science (2020), doi: https://doi.org/10.1016/j.rsma.2020.101143. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2020 Published by Elsevier B.V.

Journal Pre-proof Assessment of trace metal contamination and bioavailability in an Environmental

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Protection Area: Guaxindiba estuarine system (Guanabara Bay, Rio de Janeiro,

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Brazil)

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Michele Fernandes, Estefan Monteiro da Fonseca; Leonardo da Silva Lima; Susanna

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Eleonora Sichel; Jessica de Freitas Delgado; Thulio Righeti Correa, Valquiria Maria de

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Carvalho Aguiara, José Antonio Baptista Neto

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Departamento de Geologia e Geofísica/LAGEMAR – Universidade Federal Fluminense-Brazil - Av. Litorânea

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s/nº - 24210-340-Gragoatá, Niterói, RJ, Brasil.

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[email protected] (55) (21)26295910

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Abstract

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Guaxindiba River, located inside an Environmental Protected Area (EPA) inside Guanabara

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Bay, was evaluated concerning trace metals and arsenic. A total of 7 sediment cores up to

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80 cm were extracted along the river and in the channel that connects Guaxindiba and

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Caceribu rivers. No natural enrichment from bottom to top was observed, suggesting a

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constant mobilization of the sedimentary column along the Guaxindiba River. Results

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showed elevated concentrations of Zn (175.77-321.01 mg.kg-1) and Ni (27.71-108.39 mg.kg-

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severely enriched in Ni (EF >10) and Cu (EF>5). No enrichment was observed for As. The

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evaluation of bioavailability through the Risk Assessment Code (RAC), however, revealed

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medium risk for Zn and Ni, which exhibited high concentrations, and low risk for sediments

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severely enriched in Cu. Despite exhibiting minor enrichment and low concentrations, under

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PEL, the RAC revealed high risk for Cd, for bioavailability. Overall, the Guaxindiba River

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proved to be contaminated by recent pollution, in spite of its localization inside an EPA.

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Keywords: sediments; trace metals; bioavailability; estuaries; EPA Guapimirim,

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Guaxindiba River

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) surpassing the probable effect levels (PEL) reference values. Sediments were considered

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1. Introduction

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Estuaries are dynamic, complex and unique environments, and are considered the most

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productive marine ecosystems in the world (Chapman and Wang, 2001; Hossain, et al,

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2019). They are the transition zone between the continents and the ocean and are constantly

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subjected to morphodynamic alterations driven by continental and marine processes

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(Pritchard, 1967, Dalrymple, 2006). These environments attract urbanization and the

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negative consequences that come along with it, especially the contamination of water and

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sediments, which can affect local biota. They are the ultimate sinks for anthropogenic 1

Journal Pre-proof pollutants, with a wide variety of contaminants implied in environmental disturbances

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(Ducrotoy, 2010; Pan & Wang, 2011). The role of estuarine sediments as sinks for chemical

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pollutants is well established in several studies that describe the role of this compartment as

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a geological record (Abuchacra et al., 2015; Aguiar et al., 2018), allowing the evaluation of

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anthropogenic inputs over time (Chatterjee et al., 2007; Veerasingam et al., 2015). The study

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of sediment cores is an excellent approach to evaluate the effects of anthropogenic

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influences on depositional environments, as well as natural processes.

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Among urban contaminants, trace metals pose one of the most deleterious threats that

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reach coastal areas (Baptista Neto et al., 2006). These elements are extremely persistent in

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the environment and can be bioaccumulated and concentrated in the upper levels of the food

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chain. Trace metals are potentially damaging to ecosystem health, interfering with the

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physiology and ecology of marine organisms (Udofia et al., 2009). It is known that the

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distribution, mobility and bioavailability of trace metals are highly variable in different

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aquatic environments (Fonseca et al., 2014) and it follows that the particular dynamics of

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such elements in sediments are directly influenced by their fractionation (e.g. metal

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carbonates, oxides, sulfides, organometallic compounds) rather than by their total

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concentration (Okoro et al., 2012). Total metal concentration does not provide information

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concerning bioavailability, toxicity or mobility. The amount of bioavailable metal in

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sediments for aquatic organisms drives toxicity; therefore, it is possible that a contaminated

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sediment has a large concentration of trace metals but does not manifest toxic effects on

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biota. For this reason the evaluation of trace metal fractionation within the sediment has

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fundamental importance in determining remobilization potential (Abollino, et al., 2011;

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Canuto et al., 2013).

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Low hydrodynamic energy prevails in the Guanabara Bay where the deposition of fine

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sediments associated with estuarine processes predominate. In the northeast sector there is

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an extensive fluviomarine flat that comprises an area of environmental preservation

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denominated EPA de Guapimirim, considered the biggest remaining mangrove forest of

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Guanabara Bay (Baptista Neto et al., 2006; Soares-Gomes, et al. 2016). Guaxindiba River is

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located in this preservation area and its upper course receives domestic and industrial

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wastewater discharge, mainly from São Gonçalo city (Fonseca et al., 2014). Its lower course

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and mouth are surrounded by a remaining area of mangrove (Porto et al., 2014). Despite the

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discharge of pollutants received by the Guaxindiba River, this is an important area for

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artisanal fishing (Ferreira et al., 2011). However, the high level of pollutants directly

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impacts the fishing communities that depend on fish and invertebrates (Maranho et al.,

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2009). Finally, there is uncertainty about the capacity of this river to trap pollutants for long

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periods since its drainage basin has an extremely steep geomorphology, resulting in large

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sediment remobilization during rainfall events in the wet season. Dredging is also a strong

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factor influencing sediment remobilization in the Guaxindiba river. The aim of the present study was to assess trace metal contamination and potential

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bioavailability of these elements along the main channel of the Guaxindiba River, and to

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characterize trace metal export during the strong summer rain flushing events.

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2. Study Area

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Located in the northeast area of Guanabara Bay, the Guapimirim Environmental

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Protected Area (EPA) covers 14,000 ha of mangroves, marine area, farms and urban

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concentrations in the cities of São Gonçalo, Itaboraí, Magé and Guapimirim. The

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Guaxindiba River is part of this EPA, contributing with water and sediment inputs into the

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Guanabara Bay. The area consists of a flat-lying coastal plain with quaternary sediments,

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mainly clays and silts with interbedded sands (Catanzaro et al., 2004, Baptista Neto et al.,

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2006). The Guaxindiba River receives domestic and industrial sewage, resulting in a high

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degree of deterioration (Fonseca et al., 2014). It is also commonly used as a dumping spot

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for a significant part of the population not served by public urban sewage system.

Previous studies of the Guaxindiba River by Aguiar et al. (2011), Fonseca et al. (2014)

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and Abuchacra (2018) revealed anthropogenic impacts at this area. Aguiar et al. (2011)

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evaluated the water column of the Guaxindiba River and found extreme elevated

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concentrations of nutrients along with hypoxia, characterizing severe eutrophication in this

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area. Fonseca et al. (2014) studied the contamination levels of the Guaxindiba River

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sediments for organic compounds and trace metals. According to the Eh data, near the

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bottom, the conditions are reductive. Fine particles predominated in most of the stations,

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between 51.4 and 96.8% of silt and clay, characterizing a low hydrodynamic environment.

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High levels of salinity were registered throughout the water column of the entire Guaxindiba

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River (29.0 to 31.0), suggesting that the supply of freshwater in the environment is low and

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there is a long range salt wedge. It has been suggested that the main hydrodynamic force

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acting on the study area is the tide. Fonseca et al. (2014) confirmed this information through

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the tide station installation. Results did not indicate any discrepancy between the river level

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and values recorded in Rio de Janeiro Harbour, also located inside Guanabara Bay. The

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study revealed a very impacted environment. The results of the total organic carbon and

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particle size analysis indicated favorable conditions for the contaminant deposition, with

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Journal Pre-proof high concentrations of organic matter. The study conducted by Abuchacra (2018) confirmed

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the influence of domestic effluents and fertilizers in the EPA of Guapimirim, especially in

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the Guaxindiba mangrove area.

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3. Materials and methods

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3.1.Sampling Seven sampling stations were situated along the margins of the Guaxindiba estuarine

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environment (Fig. 1). Water variables, pH, dissolved oxygen (DO) and oxidation potential

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(Eh) were measured near the bottom with a YSI® probe. For sediment sampling, PVC cores

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were manually inserted into bottom sediments up to 1 m. Sediment cores were transported to

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the laboratory and opened vertically. Each core was sub-sampled into 20 cm aliquots. All

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the cores were located along the Guaxindiba River, except for core 7, which was located in

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an artificial channel connecting the Guaxindiba and Caceribu rivers.

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Figure 1: Guaxindiba River and sampled stations.

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3.2.Laboratory Analysis Particle size analysis was performed using a Malvern 2600LC laser analyzer after removal of organic matter through loss on ignition and carbonate with HCl 10%. Total organic carbon (TOC), total nitrogen (TN) and sulfur (S) were determined in

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samples previously treated with HCL 10% (v/v) to eliminate carbonates. Samples were read

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on a Perkin Elmer CHNS/O Analyser 2400. For the determination of total trace metal

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concentrations and As, 0.5 g of each sample was weighed and digested with 15.0 ml of

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HNO3. After 12 h, samples were heated at 160°C for 4 h. The extraction proceeded with the

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addition of 8.0 ml of hydrogen peroxide 30% (v/v) and subsequent heating at 160 C for 30

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more minutes. Samples were then filtered through 0.45µm membranes and diluted to

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100 mL in a volumetric flask. Sample blanks and a reference sediment WQB-1 from the

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National Laboratory for Environmental Testing, (Burlington, CA) were also analyzed at

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regular intervals to monitor quality control. Mercury analysis was performed according to

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USEPA method 7471 (USEPA, 1997). The quality of the analytical results was controlled

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by the use of an analytical blank.

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Digested samples were determined using a Perkin Elmer Model 4100 atomic absorption spectrophotometer.

Cores 3 and 5 at depths of 0-20 and 60-80 cm were chosen for the sequential

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extraction analysis. The fractionation of trace metals was performed using BCR procedure

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(Community Bureau of Reference), with BCR 701 as reference material (Ure et al., 1993;

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Passos et al. 2010; Passos et al. 2011; Canuto et al. 2013, Aguiar et al., 2018). The analysis

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was performed using 0.5 g of sample, maintaining the proportion of sample to volume of

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reagent, following the original method of a total mass of 1.0 g (Pessoa, 2011, Aguiar et al.,

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2018). The accuracy of the analytical procedure was assessed using the certified reference

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material BCR 701. The extraction procedure involves three steps:

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Step 1: Exchangeable fraction (F1-soluble in acid or metals bounded to carbonates). Metals

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were extracted through mechanical shaking with 20 ml of acetic acid 0.11 M for 16 h,

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followed by centrifugation to separate the extract.

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Step 2: Reducible fraction (F2-metals bounded to Fe and Mn oxides). Metals were extracted

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through mechanical shaking with 20 ml of hydroxylammonium chloride (pH 1.5) for 16 h,

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followed by centrifugation to separate the extract.

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Step 3: Oxidizable fraction (F3-metals bounded to organic matter and sulfides). Metals were

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extracted with 5 ml of H2O2 8.8 M, and left for 1 h at room temperature followed by heating

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in a water bath at 85oC. Then the sample was treated with another 5 ml of H2O2 8.8 M and

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Journal Pre-proof was left to dry at 85oC for 1 h. After cooling, 25 ml of ammonium acetate 1 M was added to

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the sample followed by mechanical shaking for 16 h, and centrifugation to separate the

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extract.

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In between the steps, the samples were washed with 15 ml of Milli-Q water, mechanically

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shaken for 15 minutes and centrifuged to extract the supernatant. All reagents used were

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analytical grade. The trace metals in each extract were determined using a flame atomic

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absorption spectrometer (FAAS) with an AA Analyst 800-Perkin Elmer.

The residual concentration was calculated by the difference from the total obtained

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sediment concentration (TC):

R = TC –(F1+F2+F3)

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3.3.Indexes

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3.3.1.

Risk Assesment Code

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The Risk Assesment Code (RAC) was used to evaluate ecological risk, considering

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the percentage of metal in the first extraction (exchangeable/soluble in acid). The ecological

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risk is classified as: (i) no risk (<1%); (ii) low risk (1-10%); (iii) medium risk (11-30%); (iv)

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high risk (31-50%) and (v) very high risk (>50%) (Canuto et al., 2013, Aguiar et al., 2018).

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3.3.2.

Enrichment Factor

In order to assess sediment contamination, enrichment factors (EF) were calculated.

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To reduce grain size and mineralogical effects on metal variability and to identify possible

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anomalous metal concentrations, geochemical normalization of the metal data to a

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conservative element, should be applied. Fe concentrations have been used for normalization

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purposes (Ho et al., 2012). The enrichment factor (EF) (Ergin et al., 1991) for each element

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was calculated as:

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𝐸𝐸𝐸𝐸 =

𝑇𝑇𝑇𝑇𝑇𝑇

𝑋𝑋𝑋𝑋 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑋𝑋𝑋𝑋𝑋𝑋𝑋𝑋

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where:

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EF = Enrichment factor,

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TMc =Measured trace metal concentration (mg.kg-1),

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Xc = Measured normalizing element concentration. Fe was used as normalizer (mg.kg-1),

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TMref = Trace metal concentration in local background, average shale or upper crust

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(mg.kg-1),

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Xref = Normalizing element concentration in background and upper crust values. In the

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present study, Fe was used for normalization. EF values around 1.0 indicate that the element in the sediment originated

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predominantly from lithogenous material, whereas EF values higher than 1.0 indicate that

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the element is of anthropogenic origin. The degree of enrichment is given by EF ranges as

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follows: EF < 1-no enrichment;1
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5
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severe enrichment and EF > 50-extremely severe enrichment.

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Data was evaluated statistically using a Spearman analysis to check the significance

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of the correlation between the variables and Kruskall-Wallis to test the significance of the

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differences between cores. Analyses were performed with Statistica 7.0®.

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4. Results and Discussion

Reducing conditions of the Guaxindiba bottom waters revealed highly negative Eh

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values (Fig. 2). Low oxygenation of bottom waters was found at every station, with the

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exception of C3. Hypoxia (DO<2.00 mg/l) was found at upper stations C1 and C2 and also

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at C6 (Fig. 2). Dissolved oxygen levels under 5 mg.l-1 indicates the beginning of biological

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stress, and hypoxia is a symptom of eutrophication, especially in shallow waters that can

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lead to the reduction of demersal fish stocks, migration of benthic animals and even the

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complete disappearance of marine organisms. Eutrophication alters living resources and

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habitat carrying capacity (Yin et al., 2004; Dodds, 2006). Results at certain stations (C1, C2

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and C6) corroborated the findings of Aguiar et al. (2011) that found DO values between 0

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and 2.32 mg.l-1 at the Guaxindiba waters, indicating anoxia and hypoxia in this river.

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Figure 2: pH, dissolved oxygen (DO) and oxidation potential (Eh) at bottom waters of the Guaxindiba River.

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Journal Pre-proof Trace metal distribution as well as organic matter in sediments are essentially

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controlled by the presence of fine particles, among other factors (Yao et al., 2015). In the

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present study, fine particles were predominant in every station. The sum of silt and clay

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ranged between 77 and 99% (Fig. 3). Grain size results of Guaxindiba reveal the potential of

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the river to retain contaminants and organic matter and characterized it as a low

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hydrodynamic environment (Yao et al., 2015). The present study corroborated the findings

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of Fonseca et al. (2014) of silt and clay between 51.4 and 96.8% in Guaxindiba bottom

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sediments. Additionally, Porto et al. 2014, described the predominance of fine particles

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(over 90%), in the same area.

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Figure 3: Results of grain size analysis for sediment cores.

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Overall, TOC was quite elevated (Fig. 4), varying between 3.16 and 8.07%. Core 1

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had the lowest concentrations among the stations. A noticeable increase was found in cores

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2 and 7 from 20 cm towards the top. Total nitrogen followed the pattern of TOC, with core 1

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having the lowest concentrations and a remarkable increase from bottom to top in cores 2

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and 7. Core 4 also showed an increase in TN concentrations towards the top. C/N varied

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between 8.66 to 13.61, characterizing organic matter of mixed origin tending to marine, with

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the exception of the top of core 3, in which C/N (13.61) revealed organic matter of mixed

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origin (Bader, 1955). Core 1 had the lowest concentrations of S, following the pattern of

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TOC and C/N. Most C/S values ranged from 1.62 to 5.01, revealing a reducing environment

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(Borrego et al., 1998), corroborating the results of Eh from bottom water. The only

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exception was the bottom of core 1, with C/S value of 7.49, characterizing an oxidizing

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environment. From the point of view of elemental analysis, the area of core 1 at the upper

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river seems to be the least impacted by domestic input along Guaxindiba. TOC and TN

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results were in accordance with the findings of Abuchacra (2018) for Guaxindiba, who

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registered ranges of 3.61-6.94% and 0.30-0.53% for total organic carbon and nitrogen,

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respectively.

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Figure 4: Results of total organic carbon (TOC), total nitrogen (TN) and sulfur (S) for cores

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C1 to C7 at Guaxindiba River.

Overall no metal profile showed a typical superficial enrichment, with the exception

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of Cd, suggesting a continuous remobilization of local sediment resulting from chronic

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events such as seasonal rains as well as the steep morphology effects (Fig. 5). Dredging

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operations at the study area are also a strong factor to be considered in sediments

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remobilization.

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The effects of pollution in aquatic systems are usually reflected by benthic

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organisms, since they can integrate recent pollution recorded in the sediments and different

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kinds of pollutants (Okbah et al., 2014). Sediment quality guidelines have been developed

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over the last decades in order to evaluate pollution effects on benthic fauna. Some of the

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most used sediment guidelines are Threshold Effect Level (TEL) and Probable Effect Level

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(PEL) (MacDonald et al., 1996, Long and MacDonald, 1998, Okbah et al., 2014). TEL

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corresponds to concentrations under which adverse biological effects rarely occur and PEL

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accounts for concentrations above which biological adverse effects are frequently observed.

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Zinc concentrations exceeded threshold levels (124 mg.kg-1) in every core along the

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Guaxindiba River. Highest values, above PEL (271 mg.kg-1) were found at C1

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(284.58 mg.kg-1) and C3 (321.01 mg.kg-1) at the upper river (Fig. 1) both having a very

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similar vertical distribution. C5 and C6, down the river, presented the lowest concentrations

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and very little vertical variation. Copper concentrations were higher than TEL (18.7 mg.kg-1) 11

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114.27 mg.kg-1. Core 7 is located in the artificial Cangurupi channel, so, it receives

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contributions from both rivers (Caceribu and Guaxindiba), depending on the tide (Fig. 1).

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Cu concentrations in the cores presented a very similar distribution to Zn profiles, for C2,

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C4, C5 and C6 with the last two, closer to the river mouth having the lowest Cu

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concentrations and small vertical variations (Fig. 5).

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For Ni, concentrations along every core, except C5, exceeded PEL (42.8 mg.kg-1).

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Nevertheless, Ni values in C5 were all above the TEL (15.9 mg.kg-1). Cores located in the

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upper river presented the highest concentrations, 155.23 mg.kg-1 at the bottom of C2 and

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158.39 mg.kg-1 at 60 cm in C3. Cores closer to the mouth (C5 and C6) exhibited the lowest

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Ni values (Fig. 5).

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Lead concentrations did not surpass the PEL (112 mg.kg-1) in any of the cores,

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however, the TEL (30.2 mg.kg-1) was exceeded in every core, with the exception of the ones

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located down the river C5 and C6, which also had little variation from bottom to top. The

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highest Pb concentrations were found at the bottom of C3 (47.11 mg.kg-1) and in the middle

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of C2 (58.37 mg.kg-1).

Chromium concentrations were under the TEL (52.3 mg.kg-1) and vertical profiles

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exhibited little variation from top to bottom. Compared to the other trace metals results

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presented so far, Cr showed a striking difference, in the sense that concentrations in the

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cores increased from the upper river towards the mouth (Fig. 5). This may suggest a

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different source for Cr. The highest Cr concentration was found at the top of C5 (50.11

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mg.kg-1.). Cadmium concentrations were fairly low in all cores, however, the TEL (0.7

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mg.kg-1) was exceeded at C1, C4 and C7, and the last two sites were under the direct

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influence of the Caceribu River. The highest Cd values were found at C4 (0.85 and

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0.95 mg.kg-1) at surface and 20 cm, respectively.

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Arsenic concentrations remained under the TEL (7.24 mg.kg-1), in every core and

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had a vertical and longitudinal gradient very similar to Cr, with core concentrations

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increasing from head to mouth. The highest concentration of As (7.10 mg.kg-1) was found in

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C6 at 40 cm.

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Mercury concentrations surpassed the TEL (0.13 mg.kg-1) in all the cores, and the

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PEL (0.70 mg.kg-1) was exceeded in C3 with concentrations of 0.93 mg.kg-1 at 20 cm and

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0.76 mg.kg-1 at 40 cm. The longitudinal gradient for Hg in the cores is similar to the ones

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exhibited by most metals in this study, with cores closer to the mouth (C5 and C6) having

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smaller concentrations, and higher values in the upper river. 12

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Figure 5: Vertical profile of zinc, copper, nickel, lead, chromium, cadmium, arsenic and mercury for cores C1 to C7 at the Guaxindiba river.

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The similarities among vertical profiles of Zn, Cu, Ni, Pb and Hg, with cores closer

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to the River mouth having the lowest concentrations suggests a common source for these

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elements, and Spearman analysis reinforces this hypothesis, through direct and significant

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correlation between them (Tab. 1). In the case of the afore mentioned elements, the

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anthropogenic input may arise from the upper estuary, especially in the area of C1 to C3.

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The influence of Caceribu waters on C4 must be also considered, because during ebb tide, 13

Journal Pre-proof its waters flow towards Guaxindiba. It should be noted, however, that concentrations of

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trace metals found in bottom sediments from Guaxindiba were considered higher than the

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ones found in Caceribu, in a study conducted by Porto et al. (2014). As and Cr, which had

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similar vertical profiles, and an increasing longitudinal gradient towards the river mouth

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seem to have a common origin, which is confirmed by a high and significant direct

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correlation between them. The Guaxindiba river crosses the second biggest city in the state

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of Rio de Janeiro, São Gonçalo. This city has no sewage treatment at all, and the Guaxindiba

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River receives domestic and industrial effluents along its course, which could be an effective

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source of trace metals.

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It is well established that organic matter is an important controller of trace metals

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retention in sediments. However, in the present study only Cr, As and Cd had a significant

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correlation with total organic carbon (Tab. 1), indicating that this may be the main

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geochemical carrier for these elements in the Guaxindiba River.

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A Kruskall-Wallis analysis revealed significant differences for trace metals among

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the 7 cores, except for Cd (Tab. 2), confirming the differences observed in the raw data,

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especially for Zn, Cu, Pb, Ni, which had smaller concentrations closer to the mouth of

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Guaxindiba. As for arsenic and chromium, the longitudinal differences in relation to the

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other elements were noticeable.

Table 1: Spearman correlation (p<0.05) for trace metals, arsenic, total organic carbon, total nitrogen and total sulfur (significant correlations in bold). Cr

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1.00

-0.53 1.00

Cu

Zn

As

-0.74 0.43 1.00

-0.60 0.47 0.85 1.00

Pb

0.95 -0.49 -0.76 -0.61 1.00

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Cr Ni Cu Zn As Pb Hg Cd TOC TN TS

Ni

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-0.64 0.74 0.43 0.44 -0.58 1.00

Hg

-0.53 0.89 0.45 0.49 -0.47 0.61 1.00

Cd

-0.04 -0.30 0.37 0.42 0.00 -0.21 -0.23 1.00

TOC

0.61 -0.56 -0.39 -0.28 0.63 -0.86 -0.53 0.41 1.00

TN

0.55 -0.59 -0.32 -0.17 0.56 -0.82 -0.52 0.52 0.92 1.00

S 0.52 0.00 -0.31 -0.11 0.51 -0.47 -0.02 -0.01 0.51 0.38 1.00

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Table 2: Results of Kruskall-Wallis (p<0.05) for cores C1 to C7. Variable

p

Cr Ni Cu Zn As Pb Hg Cd TOC TN S

0.0001 0.0002 0.0003 0.0003 0.0002 0.0019 0.0006 0.2630 0.0192 0.0300 0.0114

lP repro of

317

Table 3 shows that concentrations of Cr, Cu, Cd and Pb were similar to the values

320

encountered by Fonseca et al. (2014) and Porto et al. (2014) for the Guaxindiba River.

321

Levels of Ni and Zn, however, were higher than the ones from previous studies. In

322

comparison to Guanabara Bay (Aguiar et al., 2016), where the river discharges,

323

concentrations of trace metals were much lower, with the exception of Ni, which was more

324

elevated in the Guaxindiba River, suggesting a strong anthropogenic input of this element in

325

the upper river. Trace metal concentrations found in the Guaxindiba River were also similar

326

to the ones encountered in the industrially polluted system of Santos-S. Vicente (Hortellani

327

et al., 2008), even for Hg, with the exception of Ni, which was much higher in the study

328

area. Trace metals concentrations found in the present study were also comparable to the

329

moderately polluted Mandovi estuary (Veerasingam et al., 2015), impacted by mining

330

activities, while Guaxindiba had a much higher Zn concentration. Mean concentrations of

331

trace metals in Guaxindiba also surpassed the values found by Chatterjee et al. (2007) in the

332

Hugli estuary (India) that receives anthropogenic inputs mainly from industrial origin.

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15

Journal Pre-proof Table 3: Values of trace metals in sediments (mg.kg-1) from tropical and subtropical estuaries around the world. Cr

Ni

Cu

Zn

As

Cd

Pb

Hg

This study

23.7350.11

27.71158.39

32.1877.23

175.77321.01

2.12– 7.1

0.330.95

25.6158.37

0.190.93

**This study

39

72.86

48.27

224.61

5.04

0.52

34.06

0.33

**Hugli Estuary (India) Chatterjee et al. (2007)

78.5

49.6

38

180

-

Estuarine System of Santos/S. Vicente (Brasil) (Hortellani et al., 2008)

<5-97.5

1.3-44.2

-

6-312

-

<0.50.98

Vembanada wetland system Harikumar et al. (2009)

-

36.5374.47

16.7356.13

103.39305.29

-

0.07-2

**Guaxindiba river (Fonseca et al., 2014)

29

22

15.0

99

-

0.03

19.3

-

**Guaxindiba river (Porto et al., 2014)

31.8

44.6

66.6

161.2

-

0.6

34.6

-

Mandovi Estuary (India) Veerasingam et al. (2015)

145.89150.42

-

39.2357.23

57.7-71.15

-

-

22.6222.8

-

Guanabara bay (Aguiar et al., 2016)

18-297

11-41

18-423

23-698

-

-

18-287

-

**Guaxindiba riverbackground (Abuchacra, 2018)

29.4

12.6

8.6

92.1

-

-

18.3

-

Average Shale (Turekian and Wedephol, 1961)

90

68

45

95

13

0.3

20

0.4

*Thresholf effect level (TEL) *Probable Effect level (PEL)

336

lP repro of

Localization

rna

334 335

33.4

-

<2-204.8

<0.030.92 -

52.3

15.9

18.7

124

7.24

0.7

30.2

0.13

160

42.8

108

271

41.6

4.21

112

0.70

*Mac Donald et al. (1996); **mean values

The anthropogenic increase in the sediment cores in the Guaxindiba River was

338

evaluated through the use of enrichment factors (EF). Through the determination of metal

339

concentration along a 3 m core in the Guaxindiba mangrove, Abuchacra (2018) established

340

local background values for Zn, Pb, Cu, Ni and Cr (Tab. 3), which were used for the

341

calculation of EF in the present study. For As, Hg and Cd the concentrations of average

342

shale by Turekian and Wedephol (1961) were used as backgrounds. The normalization of

343

data was made with Fe concentrations obtained from this study.

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344

Figure 6 presents the results of EF for trace metals and arsenic for the Guaxindiba

345

River. Zinc had minor enrichment in every core, except for C1 and C3 at 20 cm, considered 16

Journal Pre-proof 346

moderately enriched. Overall EF for Zn was uniform from bottom to top, and only C4 had a

347

slightly increase in EF towards the top. For Cu cores exhibited moderate enrichment (C5 and C6) and moderate severe

349

enrichment (C1, C2, C3, C4, C7). A small increase in EF from bottom to top was observed

350

for C3 and C7 but, despite that, the enrichment classification remained.

lP repro of

348

351

Variation of EF was observed for Ni. C6 was uniform from bottom to top and

352

classified as minor enrichment. C5 had a similar profile for EF, except for the top where the

353

sample was considered to have moderate enrichment. At C2 and C3, the EF increased from

354

top to bottom, changing the classification from moderate severe enrichment to severe

355

enrichment. At C4 the same increase was observed towards the bottom that was classified as

356

moderate severe enrichment.

Concerning Pb, cores were classified as minor enrichment, except for C2 at 40 cm,

358

being classified as moderate enrichment. Sediments also had minor enrichment in Cr in all

359

the cores. The same was observed for Hg in C1, C4, C5 and C6. As for C2, C3 and C7 the

360

Hg enrichment was considered minor. Among the elements studied, As was the only one

361

that showed no enrichment (Fig. 6).

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17

362 363 364

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Figure 6: Enrichment factors for zinc, copper, nickel, lead, chromium, cadmium, arsenic and mercury for cores C1 to C7 at the Guaxindiba River.

18

Journal Pre-proof Considering that metal enrichment in the study area has an anthropogenic origin, Cu

366

and Ni are the elements of most concern, since they had EF ranging from moderately severe

367

enrichment to severe enrichment. Nevertheless, total concentrations of trace metals do not

368

establish the real bioavailability potential. Analyzing different forms and species of a

369

particular metal gives a clearer idea about its potential accumulation, bioavailability and

370

mobility (Passos et.al. 2010). Thus labile metal complexes (with fast dissociation rate

371

constants) can therefore be used to estimate bioavailability of metals (Chakraborty et al.,

372

2014). The BCR extraction technique allows for the evaluation of metals’ bioavailability,

373

and also distinguishes elements of anthropogenic origin, from those of lithogenic origin

374

(Canuto et al., 2013, Aguiar et al., 2018). The bonding of metals from anthropogenic origin

375

usually occurs with the first three extractable fractions (F1-F3). The residual fraction (R)

376

contains primary and secondary minerals originated from natural geological formations, and

377

metals are still bonded to their crystalline structure, preventing these elements from

378

becoming bioavailable in a short period of time (Passos et al. 2010, García-Ordiales et al.

379

2016).

lP repro of

365

380

As far as bioavailability is concerned, the RAC (Risk Assessment Code) uses the

381

percentage of metal that is bonded to carbonates and presents a higher risk to biota, since

382

this is the weaker bond with sediments (Bacon and Davidson 2008; Canuto et al. 2013; De

383

Andrade Passos et al. 2011; Ikem and Adisa 2011, Aguiar et al., 2018).

In the present study, two cores were chosen to apply the BCR extraction, C3, in the

385

upper river directly under the influence of anthropogenic input, and C5, closer to the river

386

mouth and Guanabara bay salt wedge.

rna

384

Many sequential extraction approaches, including the BCR technique, have been

388

used to obtain information about the distribution of Pb in sediments (Yuan, 2004; Nemati et

389

al., 2011; Yang et al., 2012) and other matrices, such as soil (Kierczak et al., 2008; Favas et

390

al., 2011). In the present study, Pb showed a greater affinity for the reducible fraction (F2),

391

especially in C3, with over 70% of lead concentrations in F2 at the top of the core (Fig. 7).

392

In C5, concentrations in the reducible (F2) and residual (R) fractions were very close, over

393

40% in each one, except for the bottom, with 38% of Pb in R. The elevated concentrations

394

of Pb in the reducible fraction (F2) suggests that Fe-Mn oxides are involved in trapping this

395

element at pH values above 7 (Kassir et al., 2012). The highest percentage of Pb found in

396

the non-residual phase (F1-F3) suggests that Pb is potentially bioavailable in the studied

397

area. Diaz-de Alba et al. (2011) found similar results for Pb in regions impacted by human

398

activities, with concentrations that were mostly found in the labile fraction (F1). Compared

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19

Journal Pre-proof to metals from natural origin, metals that come from anthropogenic input are more weakly

400

associated with the sediments. These elements may be released back to the aqueous phase

401

with changes in the physical and chemical conditions of the environment. The RAC for Pb

402

indicated no risk in both cores since less than 1% of the metal was bonded to the more

403

readily available soluble fraction (F1).

lP repro of

399

404

Copper was present in high concentration associated with the oxidizable fractions

405

(F3) in both cores, however, at C3 the metal showed higher affinity for F3. The decreasing

406

distribution among all fractions in C3 (top and bottom) was: oxidizable>residual > reducible

407

>

408

residual>oxidizable>reducible>soluble. Results show organic matter as a carrier for Cu in

409

the upper river, probably due to domestic anthropogenic input. Copper has a high affinity for

410

the soluble organic fraction (Wally et al., 2013) and can also bond to various forms of

411

organic matter by complexation. Copper concentrations in C3 presented low ecological risk

412

and no risk in C5 according to RAC results.

soluble

(Fig.

7).

At

C5,

the

decreasing

fractionation

order

was:

For Zn, the fractionation decreasing order was the same for C3 and C5:

414

residual>soluble>reducible>oxidizable (Fig. 7). More than 50% of Zn was concentrated in

415

the residual fraction (R), representing a lithogenic contribution and, therefore, not

416

bioavailable. The amount of Zn in the bioavailable fractions (F1-F3) was more concentrated

417

in the first fraction (F1), which covers metals that are exchangeable or associated with

418

carbonate forms and affected by pH changes. For Zn, the RAC established medium risk for

419

C3 and C5, with higher values in the core from the upper river.

rna

413

420

The dominant phase for Cr was the residual fraction (R), which accounted for more

421

than 70% in the present study at both cores. Metals associated with the residual fraction are

422

likely to be incorporated in alumino-silicate minerals (Wally et al., 2013), and are not

423

usually

424

residual>oxidizable>reducible>soluble (Fig. 7). The percentage of Cr in the soluble fraction

425

was insignificant in all the samples. According to the RAC, Cr concentrations offered no

426

ecological risk in both cores concerning the more readily available fraction (F1).

The

decreasing

content

distribution

for

Cr

was

Jou

bioavailable.

427

Nickel distribution along the sediment fractions was quite different for C3 and C5,

428

however, Ni was predominant in the residual fraction (R), with a higher percentage in C5

429

(Fig. 7). C3 had higher concentrations of Ni in the reducible (F2) and soluble fractions (F1)

430

compared to C5. The decreasing distribution of Ni in C5 was the same for top and bottom:

431

residual>oxidizable>reducible>soluble. The RAC values for Ni, established medium risk for

432

concentrations in C3 and low risk at C5. 20

Journal Pre-proof Cadmium levels were elevated in the soluble phase (F1), on the other hand,

434

concentrations in the oxidizable fraction (F3) were the lowest in both cores (Fig, 7). Low

435

levels of Cd in the organic matter and sulfides can be due to the low adsorption constant and

436

labile complex with organic matter (Baron et al., 1990). Cadmium is an element of

437

environmental concern element. Indeed, among the metals extracted with BCR technique,

438

cadmium presented the greatest concern, since the RAC results established high ecological

439

risk for Cd values in C3 and medium risk in C5. Despite its low concentrations cadmium

440

presented elevated bioavailability to biota.

lP repro of

433

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441

21

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Figure 7: BCR results for zinc, copper, nickel, lead, chromium and cadmium.

rna

442

Considering the bioavailability, it was clear that concentrations of Ni, Zn and Cd in the

444

upper river at C3, presented higher risks as established by the RAC. The fact that

445

concentrations of organic material (TOC) were very elevated at both cores, did not help to

446

trap the elements in the oxidizable fractions with the exception of Cu.

447

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443

5. Conclusions

The results obtained clarified the potential impact of dredging operations or natural

448 449

events, which are capable of mobilizing bottom sediments.

450

The water column clearly demonstrated signs of eutrophication, with hypoxia in the

451

upper river and also near the mouth, as well as a reducing environment identified by Eh

452

values.

453

Results of trace metals analysis indicated the presence of elevated concentrations

454

especially for Ni, Zn and Hg. All these elements surpassed the concentrations of probable 22

Journal Pre-proof 455

effect level and showed a higher contamination level in the upper river, tending to decrease

456

towards the mouth. The same distribution pattern was observed for Hg. The vertical profiles

457

of trace metals and arsenic did not exhibit a marked enrichment from bottom to top,

458

suggesting a constant mobilization of the sediments from the river bed. Enrichment factors revealed minor enrichment for Pb and Cr, and no enrichment for

460

As. For the other elements, sediments were found to be severely enriched in Ni and Cu.

461

Despite elevated concentrations for Zn, sediments at Guaxindiba were classified as of minor

462

enrichment for this element. Hg also presented minor enrichment at certain locations in the

463

upper river and no enrichment for the rest of the samples. Nevertheless, it is important to

464

point out that these indexes can only be considered suggestive. Their results can vary

465

depending on local conditions and the average shale or upper crust values used for

466

normalization.

lP repro of

459

467

The partitioning of sediment-associated elements as given by the sequential

468

extraction and risk assessment code results revealed an elevated bioavailability for Cd,

469

despite the fact that total concentration of this element did not exceed the PEL in any

470

sample. Even so, the Cd concentration bonded to the soluble fraction is concerning. Zn and

471

Ni, on the other hand, presented very elevated concentrations along Guaxindiba resulting in

472

medium risk in terms of bioavailability to biota, especially in the upper river.

Overall, results showed that the Guaxindiba bottom sediments have an elevated

474

anthropogenic input in terms of organic matter and trace elements, especially in the upper

475

course of the river. This poses a question of how well this river is being cared for since it is

476

located inside an official Enviromental Protection Area. Bioavailability of these elements is

477

linked mainly to the soluble fraction of sediments, the one bonded to carbonates, and in this

478

sense, Cd was the only metal that offered an elevated risk to biota.

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479

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23

Journal Pre-proof 480 481 482

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Abuchacra, P. F. F. 2018. Reconstituição Ambiental da Planície Costeira do Nordeste da Baía de Guanabara (RJ) a partir do Holoceno Médio e Novas Contribuições ao Debate do Antropoceno. Thesis. Departamento de Geografia. Universidade Federal Fluminense, 216p.

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