Butyltins and PAHs contamination of surface sediments from coastal areas under influence of Mar del Plata port

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Butyltins and PAHs contamination of surface sediments from coastal areas under influence of Mar del Plata port

Abstract

The distribution of butyltins (BTs) and polycyclic aromatic hydrocarbons (PAHs) in surface sediments adjacent sandy beaches of Mar del Plata port, Argentina, was studied to assess whether this port is an important source of contamination to the surrounding intertidal environments. Within the port, TBT concentrations ranged from 24.2 to 150 ng Sn g-1 and the concentrations of PAHs (18) varied between 199 and 17,173 ng g-1. PAHs were detected at low concentrations in all beach sediments, whereas TBT concentrations reached 10.9 ng Sn g-1. Although the distribution of both BTs and PAHs indicate that the port is not an important source of contamination for surrounding beaches, the very low TOC content and the coarse grain size of the beaches sediments could partially explain their low contaminant levels. Our results indicate a reduction in TBT levels in Mar del Plata port after the instauration of national and international TBT restrictions.

Keywords: port pollution; intertidal sediments; BTs; PAHs.

1. Introduction

Marine ports are important contaminant sources for coastal environments, contributing to inputs of polycyclic aromatic hydrocarbons (PAHs), metals, antifouling biocides, and plastic debris (Darbra et al. 2005). Port facilities are often situated in estuaries, bays or artificial enclosed systems where circulation is limited and thus sediments can contain high concentrations of contaminants (Chen and Chen 2011) such that benthic communities are degraded (Martínez-Lladó et al. 2007). Of special concern in such areas are butyltin compounds from antifouling paints and PAHs (Delucchi et al. 2011; Ünlü et al. 2013). However, there have been few studies of these contaminants in sandy beaches compared with the large number that have measured inorganic trace-elements (Nagarajan et al. 2013) or oil spills (Veiga et al. 2010). Sandy beaches shelter a wide variety of invertebrates and are important to humans since they provide diverse ecosystem services and support recreational activities (Schlacher et al. 2008).

Butyltins (BTs) and polycyclic aromatic hydrocarbons (PAHs) are discharged into marine systems from many port activities. Tributyltin (TBT) has been used since the 1960´s as a biocide in antifouling paints. Due to its high environmental persistence, toxicity and endocrine disruptor potential, the International Marine Organization (IMO) banned the use of TBT-based antifouling paints in September 2008. PAHs are organic contaminants that reach the aquatic environment following the high-temperature combustion of organic matter, petroleum spills or natural diagenetic processes (Srogi 2007). The carcinogenic and mutagenic properties associated with some PAHs (Nisbet and LaGoy 1992) justifies their inclusion in European Union and US EPA priority pollutant lists.

Mar del Plata port (MDPP) is a relatively small port (1,400,000 m2), yet holds ~60% of the Argentinian fishing fleet and is one of the most important shipyards in Argentina. It is surrounded by several sandy and rocky beaches in which many intertidal benthic communities can be found and human recreational activities take place. Both BTs and PAHs have been detected in surface sediments in Mar del Plata port (Goldberg et al. 2004; Cledón et al. 2006; Bigatti et al. 2009; De Waisbaum et al. 2010; Albano et al. 2013). However, PAHs have never been measured in beaches near Mar del Plata port and although TBT levels have been reported in one beach, there are no data on TBT concentrations since its banning in 2008. Thus, it is important to update information about BTs levels in Mar del Plata port in order to verify the effectiveness of local and international regulations since this area was identified as a hot spot of TBT contamination in South America (Castro et al. 2012a).

In this context, the present study evaluated the spatial distribution of BTs and PAHs in areas under the influence of Mar del Plata port in order to assess whether the port represents a significant source of contamination to the surrounding intertidal environments. Considering the predominant coastal current direction in the area (south-north), the hypothesis of a contamination gradient from Mar del Plata port towards tourist beaches was appraised.

2. Materials and methods

2.1 Sampling and sample preparation:

Surface sediments (upper 5 cm) were collected using a stainless steel Van-Veen grab at 9 sites during December 2012. Five of these points were sampled inside Mar del Plata port (S1-S5), 3 in beaches to the north (Popular (P), Alfonsina (A) and Constitución C)) and 1 at a beach to the south (Punta Mogotes (PM)) of MDPP (Fig. 1). Since sand predominated in beach sediments, 9 sediment samples were taken randomly at each site, then mixed and sieved in situ using a 120 µm mesh to make two single composite samples of 100 to 200 g wet weight. In the laboratory, sediments were dried in an oven at 45 °C until constant weight and then stored at -20 °C for subsequent analysis. The concentration of total organic carbon (%TOC) in all sediment samples were determined by an elemental analyser (CHNS Perkin Elmer 2400 Series II) after decarbonation in a desiccator containing HCl (37%).

2.2. Butyltin analysis:

Butyltins levels were analyzed according Castro et al. (2012b). Briefly, 5 g of dried sediments were extrated by sonification in tropolone solution (0.05% w/v) in methanol, the extracts were then derivatized using 2 ml of n-pentyl magnesium bromide in diethyl ether solution (2 M), according to Morabito et al. (2000) and again extracted with 3 x 5 mL of hexane. A cleanup was then performed using a silica-gel column (3.5 g) eluted with 15 mL of hexane/toluene (1:1). Finally, the solution was added of 100 ng of tetrabutyltin solution (internal standard). Extracts were analyzed by gas chromatography using a Perkin Elmer Clarus 500MS equipped with mass spectrometer detector. The analytical curves were made using the matrix addiction technique and quantification limits (LQ) were 2, 3 and 3 ng Sn g-1 for TBT, DBT and MBT respectively. The quality assurance and quality control was based on regular analyses of blanks, spiked matrices and certified reference material (PACS-2 / National Research Council of Canada, Ottawa, Canada). Results obtained for the PACS-2 (TBT - 852 ± 47 ng Sn g-1; DBT - 1035 ± 35ng Sn g-1 and MBT - 557 ± 38 ng Sn g-1) were in good agreement with the certified (TBT – 890 ± 105 ng Sn g-1 and DBT - 1047 ± 64 ng Sn g-1) and reported values (MBT - 600 ng Sn g-1). The samples recoveries were between 79% and 98% and RSD (relative standard deviation) below 20% (IUPAC, 2002).In order to assess the degree of TBT degradation and to predict if the contamination in coastal areas of Mar del Plata is recent or not, the butyltin degradation index (BDI) was calculated based on the following equation: Butyltin degradation Index (BDI) = [MBT] + [DBT] / [TBT] (Díez et al. 2006). Old TBT inputs are normally associated with values of BDI > 1.

2.3. Polycyclic aromatic hydrocarbon analyses:

The analytical procedure is described in Niencheski & Fillmann (2006). An exact mass of dried sediments (15 g) was spiked with p-Terphenyl-D14 a surrogate standards and then Soxhlet-extracted with n-hexane/dichloromethane (1:1) for 12 h. The extract was concentrated down to 1 mL using a BÜCHI Syncore® Polyvap R-24 system parallel evaporator and activated copper was added to remove any sulfur. Then, the extract was fractionated into aliphatic (AHC) and polyaromatic (PAH) hydrocarbons by liquid chromatography adsorption using a column of silica gel (6 g) and neutral aluminum oxide (8 g). The identification was based on the retention time and mass spectra. Analyte quantification was performed comparing the sample results with standard curves built using deuteron d8-naphthalene, d10-acenaphthylene, d10-phenanthrene, d12-chrysene and d12-perylene for PAH (Sigma Aldrich, Sao Paulo, SP, Brazil). Both processes were performed at the Laboratory of Organic Contaminants and Ecotoxicology of the Universidade Federal do Rio Grande (Rio Grande, RS, Brazil) using gas chromatography (Perkin Elmer® Clarus 500 – GC-MS) equipped with a mass spectrophotometry detector (CG-EM). All chemicals used were analysis of residues grade and the quantification limit was 0.125 ng L-1.

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