Migration of pentachlorophenol in artificial and natural sediments of Puck Bay

The study area included 7 sites located in the outer part of Puck Bay, one site located in the shallowest place of Puck Lagoon (ZP 1) and one located outside the Bay (ZP 7) (Fig. 1). The selection of marine sediment sampling sites in Puck Bay was based on the organic carbon content data (Uścinowicz 2011) as well as characteristics of the Bay bottom. The study also included samples of bottom sediments collected near the quays of the Port of Gdynia.

Samples of bottom sediments were collected using a Van Veen grab during the cruises on board r/v “Oceanograf 2” in 2012 (November) − the Port of Gdynia and in 2013 (June) − Puck Bay. Prior to the analysis, sediment samples were stored in a freezer at a temperature of -21°C, and then air-dried (Wang et al. 2003; Ganeshjeevan et al. 2007; Padilla − Sánchez et al. 2010), sieved (particles larger than 2 mm were removed) and homogenized in a porcelain mortar.

The analysis of sediment grain composition in samples from Puck Bay and the Port of Gdynia was conducted using a sieve analysis (Myślińska 2001; Pempkowiak et al. 2005). Characteristics of bottom sediments were described with the GRADISTAT 5.11 beta program.

All the bottom sediment samples were prepared for PCP analysis by 24 h extraction in a Soxhlet apparatus or 40 minutes in an ultrasonic bath of 10 g to 20 g dry sediment (fraction φ< 2.00 mm) with the solution of methanol: Milli-Q water (4:1) and addition of 10% triethylamine. The extracts were cleaned by solid phase extraction (SPE) using Clean-Up C-18 CUC18 (6 cm³ 500 mg^-1) columns as described (with minor changes) in Lewandowski et al. (2014). The HPLC analysis was performed using a DIONEX apparatus and the chromatographic conditions were as follows: the thermostat temperature 25°C, the UV-VIS detector (wavelength λ = 254 nm), the chromatography column Hypersil GOLD (250 mm × 4.6 mm × 5 μm), mobile phases: eluent (B) acetonitrile and eluent (A) Milli-Q water, the flow rate 1.0 cm³ min^-1, gradient elution: 5% B for one and a half minute, then B was gradually increased to a maximum of 95% at the nineteenth and a half minute, this gradient was maintained for one and a half minute and returned to the 5% B gradient within the last minutes of the analysis.

Methanol, Milli-Q water, triethylamine, acetonitrile were of HPLC grade purchased from Avantor Performance Materials (POCH). The linearity of the applied analytical method, based on 6 points, was calculated by Pearson’s correlation analysis (correlation coefficient r = 0.995). The recovery of each extraction method was determined by adding a defined amount of PCPaq standard (Supelco). The obtained recovery value for extraction in an ultrasonic bath was 75% and 92% for extraction in a Soxhlet apparatus. The limit of quantification (LOQ) for pentachlorophenol analysis was 2.9 ng g^-1 d.w. and the limit of detection (LOD) was 1.0 ng g^-1 d.w.

Figure 1

Sediment (fraction φ< 2.00 mm) toxicity was investigated using the Basic Solid Phase Test in accordance with the procedure provided by the producer Azur Environmental Ltd. (Azur Environmental 1998, ASTM 2004). The determined toxicity can be expressed as 30 min EC₅₀ values (%) which correspond to the effective concentration of a xenobiotic (solid or liquid) causing a 50% decrease in light emission. Another parameters to express the toxicity are toxicity units (TU), which are an inverse of EC₅₀ to facilitate the interpretation of the obtained results, where a higher value of TU means higher toxicity, contrary to EC₅₀ values which decrease as toxicity increases (Salizzato et al. 1998; Coya et al. 2000; Mamindy-Pajany et al. 2012; Witt el al. 2014; Lewandowski et al. 2014; Kobusińska et. al 2014).

The content of organic carbon (TOC) was determined in sediment samples using a Vario TOC analyzer at the Department of Marine Chemistry and Environmental Protection, in accordance with the recommended methodology (Parsons et al. 1985). Details of the analysis (with minor changes), validation and quality parameters are described in Lewandowski et al. (2014). The TOC value in samples is given in % of sediment dry weight (equals mg g^-1 d.w.). Additionally, the content of organic matter expressed as a loss on ignition (LOI) was analyzed (Ciborowski 2010).

Based on the grain size composition, the sediment type (Table 1) and the percentage content of selected fractions were determined. For the purpose of this publication, only the fraction with a diameter bellow 0.0625 mm is presented in Table 2 a) and b) as the most important in terms of PCP sorption. The bottom sediments from Puck Bay ZP: 3, 4, 5, 6 and 7 are characterized by a high percentage (ranging from 67.0 to 74.3%) of the silt-clay fraction. In other samples (ZP: 1, 2, 8 and 9) collected near the shore, a similar percentage content of this fraction (0.3-9.4%) was determined as in the harbor sediments. Based on the interpretation of statistical analysis (GRADISTAT 5.11 beta program) of the grain size distribution in sediments from the Port of Gdynia, the following was determined: all the collected material was poorly sorted, the main fraction was sand (89-98%) and the silt-clay fraction represented a small admixture (1-11%) (Table 2 b). On the one hand, these values are similar to the data presented in the SMOCS project report (Sapota et al. 2012), but on the other hand, they are much lower than those presented by Radke et al. (2012). The differences show how strongly the environment of harbor sediments can be disturbed.

The TOC concentrations in the sediments from Puck Bay and the Port of Gdynia varied in a wide range (Table 2 a and b). Lower values (0.09-0.52 and 0.31-1.52, respectively) were obtained for sandy sediments collected from shallow coastal areas (samples ZP 1, 2, 8 and 9) or those located in the vicinity of the main harbor canal (French Quay 1, 2; Indian Quay 1 and Polish Quay 3) (Fig. 1). Significant amounts of TOC (3.55-5.46 and 3.04-7.01, respectively) were determined for sediments collected from greater depths (samples ZP 3, 4, 5, 6 and 7) or further off the main harbor canal (Presidential Basin, Indian Quay 2, 3 and Polish Quay 1, 2) in the Port of Gdynia. The highest value of total organic carbon (7.41%) was determined in sediments from the Presidential Basin of the Port of Gdynia, which is probably related to the contamination with oil compounds (Uścinowicz 2011).

The low organic carbon content in sandy coastal sediments is not the effect of low intensity of carbon release into the bottom sediments but the result of rapid circulation of matter (Huettel et al. 1998). A regional and seasonal difference in organic carbon content occurs alike in areas of shallow and deepwater sediments (Uścinowicz 2011). In Puck Bay, there are areas with a relatively high TOC content (Table 3). The process of pre-sedimentation of the carbon-rich organic matter occurs there through its transportation by rivers and production in the basin as a result of intensive supply of biogenic salts. The distribution of TOC concentration depends on the seabed topography and the related circulation of currents (Uścinowicz 2011). A positive correlation was determined for Puck Bay and the Port of Gdynia between the content of total organic matter expressed as LOI and TOC content (r = 0.98). According to the above data, the increased accumulation of PCP can be expected in sediment collected from sites ZP 3, 4, 5, 6, 7, and part of the quays located further away from the main channel of the Port of Gdynia.

The overall toxicity was an additional parameter measured and used in the assessment of the analyzed sediments. The influence of bottom sediment samples (NaCl extracts) on vital functions of Vibrio fischeri bacteria expressed as values of toxicity units (TU) is presented in Table 2 a and b. The toxic effect (values above 25 TU, according to Sawicki et al. 2007) was determined for sediment samples from Puck Bay, in which the content of the silt-clay fraction (>70%) and TOC (>3.5%) was significant. Sandy sediments of Puck Bay showed no acute toxicity. Bottom sediments collected close to the quays of the Port of Gdynia (at which regular dredging works are carried out) and analyzed for the content of PCBs, PAHs and metals did not show strong toxicity either (TU<25). Nonetheless, the analysis of samples from Indian 2, 3 and Polish 1 quays revealed a low-toxic (between 10 and 25 TU) effect on bacteria. Reference samples from the Presidential Basin (not tested regularly), which contained the largest amounts of TOC and the fine fraction (<0.0625 mm) were described as strongly toxic (TU>100). In some publications (Łukawska-Matuszewska et al. 2009), a strong correlation between high values of TU and the content of fine fraction (<0.0625 mm) was explained by adsorption of Vibrio fischeri on sediment grains. This thesis is confirmed or disproved after the correlation between the toxicity and the content of total carbon (TC) is determined. The low value of the correlation coefficient means that the sediment granulation affects the toxicity value. In this study, the effect of organic contaminants was observed for sediment samples collected in the Port of Gdynia and Puck Bay, because values of toxicity were strongly correlated (r = 0.90 and r = 0.94, respectively) with TOC content, which is 80-90% of the TC mass (Niemirycz 2007).

PCP was determined in the surface bottom sediments of Puck Bay and the Port of Gdynia in varying concentration (Table 4). These are the first data on the concentration of the researched compound in these areas. The values of PCP concentration in sediment samples from Puck Bay ranged from <LOD to 230.1 ± 20.8 ng g^-1 expressed in sediment dry weight. The highest concentration of PCP was determined in the sediments collected from the deeper area of Puck Bay (Table 1). An exception was the sample of sediment collected at site ZP 3, the value of which was below the limit of detection, even though it was collected from a considerable depth and contained a significant amount of TOC and the fraction <0.0625 mm. Sample ZP 7 (collected out of Puck Bay) was characterized by the highest degree of contamination with PCP (230.1 ± 20.8 ng g^-1 d.w.) and a lower value of TOC. The PCP concentration in this region is significantly above the accepted limit for the Baltic Sea, i.e. 25 ng g^-1 d.w. recognized as Predicted No Effect Concentration (PNEC) (Muir & Deluge 1999). Compared to the other study sites of Puck Bay, site ZP 7 is located (about 2 km to the east) within the closest proximity to the Gdynia dumping site − a storage place for dredged spoil coming from port channels and basins.

The range of PCP concentrations determined in bottom sediments of the Port of Gdynia − from <LOD to 25.0 ± 3.6 ng g^-1 d.w. − is similar to that determined in the Port of Gdańsk, i.e. from <LOD to 12.4 ng g^-1 d.w. (Lewandowski et al. 2014). This indicates a similar contribution of PCP sources in these areas. It should be pointed out that the Port of Gdańsk is located in the estuary of the Dead Vistula, i.e. an arm of the Vistula, which can transport PCP to harbor waters. Dmitruk et al. (2008) analyzed samples of bottom sediments collected at the 800^th km (Cracov), the 405^th km (Warsaw) and the 13^th km (Gdańsk) of the Vistula. The average concentration of PCP was 1.2 ng g^-1 d.w. It appears from the above data that the Vistula River (through the Dead Vistula) has a minor impact on PCP concentration in the Port of Gdańsk. Despite low concentrations of PCP in sediments of the harbor, which represents a dynamic environment strongly affecting the surface layer of bottom sediments, it should be kept in mind that this material is removed to the sea as dredged spoil. This operation may result in higher availability of PCP in the marine environment. Dredged spoil is analyzed for a number of substances considered as toxic, but not PCP, even though some characteristics of POPs were confirmed for this compound (Borysiewicz 2008; Subramanian 2010; United Nations Environment Programme 2015). The content of fine fraction (<0.0625 mm), total organic carbon and mechanical mixing of sediments close to the studied quays had a major impact on the differences in PCP concentrations in bottom sediments of Puck Bay (natural environment) and the Port of Gdynia (anthropogenic environment). The obtained range of PCP concentration in Puck Bay was similar to that presented in the above-mentioned publications and other papers on the content of PCP in sediments of other regions of the Baltic Sea, Europe (15-200 ng g^-1 d.w. Muir & Eduljee 1999) or the nearby North Sea (26.5-200 ng g^-1 d.w. Eurochlor 1999).

Due to the coastline structure in Puck Bay and Puck Lagoon, the authors of this paper assume that the value of PCP concentrations may be affected by the Vistula and the bottom currents. These two areas are separated by the Rybitwia Shoal which causes the formation of different circulation systems in each of them. In Puck Bay, vectors of currents also induce the formation of circulation dominated by currents moving in a clockwise direction. The average currents flow within its coastal waters in the northern directions near Gdynia and Rybitwia Shoal and to the east, near the Hel Peninsula.

Long-term observations of bottom currents in Puck Bay gave rise to the conclusion that there is a current (upwelling type) opposite to the surface current with an average speed of 4 cm s^-1 flowing into the Rybitwia Shoal (Nowacki 1993b). The speed of bottom currents increases with increasing salinity and decreasing depth. The coastline structure in Puck Bay and its exposure to the wind result in a varying speed of the currents and the associated flows, depending on the wind direction (south, south-east). The vectors of currents in Puck Lagoon indicate the existence of two systems of circulation, resulting from the existence of the two major morphological forms. The average vectors of currents in Puck Bay prove the dominance of the inflow and transport of waters in the direction of Puck Bay (Nowacki 1993b). The incoming waters from the Gulf of Gdańsk into Puck Bay are characterized mainly by higher salinity. Sometimes, however, these waters are a mixture of seawater and the Vistula waters, which results in the reduced salinity (Nowacki 1993c).

The highest concentration of PCP in bottom sediments of the Gdańsk Basin was obtained for site ZP 7, which is located to the east of the Gdynia dumping site. Based on the conducted studies, it seems that the material stored at the dumping site may be spread by the bottom currents into areas where accumulation processes occur. Interdisciplinary research, including hydrodynamic modeling, will confirm the hypothesis. Based on the maps of surface currents (Fig. 2) and salinity, generated by the Ecohydrodynamic Model of the Gulf of Gdańsk ( http://model.ocean.univ.gda.pl/, University of Gdańsk), it can be concluded that the waters of the Vistula in certain months (June − September) have a strong impact on the outer part (north-eastern) of Puck Bay and a weaker effect on its inner part. Consequently, the freshwater mixes with saltwater, which can lead to faster sedimentation of matter.

Figure 2