Persistence of polycyclic aromatic hydrocarbons in sediments in the deeper area of the Northern Adriatic Sea (Mediterranean Sea)

Persistence of polycyclic aromatic hydrocarbons in sediments in the deeper area of the Northern Adriatic Sea (Mediterranean Sea)

Chemosphere 90 (2013) 1839–1846 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere...

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Chemosphere 90 (2013) 1839–1846

Contents lists available at SciVerse ScienceDirect

Chemosphere journal homepage: www.elsevier.com/locate/chemosphere

Persistence of polycyclic aromatic hydrocarbons in sediments in the deeper area of the Northern Adriatic Sea (Mediterranean Sea) Mauro Marini ⇑, Emanuela Frapiccini National Research Council (CNR), Institute of Marine Science (ISMAR), Largo Fiera della Pesca, 2, 60125 Ancona, Italy

h i g h l i g h t s " PAHs are discharged in the Northern Adriatic Sea by numerous rivers of the Po Valley. " Po Valley is a very important area for the impact of human activity. " Behaviour of PAHs in the coastal belt and deeper areas of the Northern Adriatic Sea. " Several environmental factors affect PAH degradation. " Batch degradation tests have been conducted to examine the persistence of PAHs.

a r t i c l e

i n f o

Article history: Received 18 June 2012 Received in revised form 21 September 2012 Accepted 22 September 2012 Available online 3 November 2012 Keywords: PAHs Deep Adriatic Sea Marine sediments Persistence

a b s t r a c t The Po Valley is the most important agricultural and industrial area of Adriatic basin. In this area there are several rivers which transport polycyclic aromatic hydrocarbons (PAHs) into the sea via suspended particulate matter. This study describes the persistence of PAHs in the deep and coastal sediments of the Northern Adriatic. Different environmental conditions were studied: salinity, temperature, sunlight, sediment particle size and organic matter in sediment. The average conditions in the deep areas of the Northern Adriatic are: salinity higher than 37, temperature lower than 11 °C, darkness and clayey sediments with a high organic matter content. These conditions increase the persistence of the PAHs in the deep area of the Northern Adriatic. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are an important class of organic compounds with two or more fused aromatic rings that persist in soils and sediments. They are ubiquitous organic pollutants with relatively low water solubility inversely proportional to their number of aromatic rings, a low dissolution rate and strong adsorption to the soil or sediments (Walker, 1936; Karickhoff et al., 1979; Cerniglia, 1993). The largest release of PAHs is due to the incomplete combustion of organic compounds during the course of industrial processes and other human activities, such as the processing of coal and crude oil, the combustion of natural gas, including that for heating, the combustion of refuse, traffic, cooking and tobacco smoking, as well as in natural processes such as carbonisation and forest fires (Walker, 1936; Laflamme and Hites, 1978). The key point for describing the environmental fate of PAHs is the study of the their persistence. The deposition of suspended par⇑ Corresponding author. Tel.: +39 71 2078840; fax: +39 71 55313. E-mail address: [email protected] (M. Marini). 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.09.080

ticulates transported by rivers may have an increasing effect in the accumulation of PAH compounds in sediment, further to their hydrophobicity and their recalcitrance. Thus, PAH deposited in sediment tends to be persistent and may accumulate in higher concentrations (Wilson and Jones, 1993). Microbial transformation and photolysis are regarded as two important processes for the removal of PAH from aquatic environments (Yuan et al., 2001); other possible fates are volatilisation, photooxidation, chemical oxidation, bioaccumulation and adsorption (Park et al., 1990). Because of their persistence in the environment and their genotoxicity sixteen PAHs have been identified as priority pollutants by the US Environmental Protection Agency (US EPA) and are monitored routinely (Perkin Elmer Corporation, 1993; Yuan et al., 2000) This study focuses on the Northern Adriatic Sea, a relatively shallow sub-basin of the Adriatic Sea (max depth 75 m) characterised by the presence of several rivers and by anthropogenic activities (De Lazzari et al., 2004). The distribution and source of PAH pollution has been widely studied in the various areas of the Adriatic Sea (Hamilton, 1989; Dujmov et al., 1994; Notar et al., 2001; Magi et al., 2002; Bihari et al., 2007). The main areas polluted by

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PAHs of pyrolytic origin are located in proximity to anthropogenic activity, industrial and port areas and rivers mouths (30– 527 ng g1 dry wt., Guzzella and De Paolis, 1994). The Po river, with a mean flow rate of 1.496 m3 s1 (Cozzi and Giani, 2011), is the longest Adriatic river and the largest in terms of streamflow, with additional contributions from many smaller Apennine rivers. The middle-lower Po flows east some 350 km in the Pianura Padana (Po Valley), characterised by high density of population, it is a very important agricultural region and the industrial heart of Northern Italy (Fuzzi et al., 1996; Pirrone et al., 2005; Castellarin et al., 2011). The biogeochemical processes of the Northern and Western Adriatic Sea are clearly more influenced by river runoff and flooding (Campanelli et al., 2004; Marini et al., 2008; Boldrin et al., 2009). The advance of the flood waters was marked by the arrival of large amounts of debris as well as by the increase of current speed and direction and by the significant decrease in salinity (Campanelli et al., 2011). The Adriatic ecosystem is strongly influenced by the quality and amount of river sediments, due to morphological and to hydrodynamic and seasonal circulation patterns. It is crucial to follow the transport pathways of riverine-derived particulate matter from the different continental regions and to identify their accumulation areas on the shelf (Ravaioli et al., 2003). Brambati et al. (1983) and Ravaioli et al. (2003), described the transportation and deposition of sediment in the Northwestern Adriatic by comparing it with the general circulation of the Adriatic sea according to Artegiani et al. (1997). The persistence of PAHs in marine sediments is governed by a wide variety of abiotic and biotic factors which include temperature, pH, sediment type, oxygen, water availability, nutrients, depth, salinity, diffusion, microbial adaptations, bioavailability, physico-chemical properties of the PAH and seasonal factors (Shiaris, 1989; Cerniglia, 1993). Wang et al. (2001), have demonstrated the strong positive correlations between PAH concentrations and organic matter associated with different size fractions in the sediments and that the organic matter and black carbon plays the most important role in adsorption of PAHs in marine sediments (Ahn et al., 2008). Several batch degradation tests have been conducted in the laboratory, to examine the persistence of PAHs in marine sediment collected in the deeper area of the Northern Adriatic Sea. The first objective was to observe the behaviour of PAHs once they are discharged into the sea by rivers. The second objective was to determine the persistence of PAHs once discharged into the deep sea, in relation to some factors that affect their degradation: organic matter, the type and size of the sediment and the temperature and sunlight.

A is strongly influenced by the contribution of fresh water that flows along the western Adriatic coast. In the site A three sediment samples were collected to determinate the degradation of PAHs at two different conditions of salinity (37 and 20). Sites B and C are located along the midline that bisects the Adriatic Sea longitudinally. These sites differ by particle size and organic matter. Site B and site C are classified as sandy and silty-clay, respectively, according to the classification by Shepard (1954) and as described by Ravaioli et al (2003), De Lazzari et al (2004). Site B has a lower percentage of organic matter than site C: 1.4 and 3.39, respectively. These two sites were chosen to study the persistence of PAHs in deep sediments and as the particle size and organic matter influence behaviour of PAHs, to vary some environmental conditions, such as temperature (6/18 °C) and sunlight (light/dark). Six sediment samples were collected from site B and five sediment samples were collected from site C.

2. Materials and methods

dC ¼ KC dt C ¼ C 0 eKt

2.1. Study area and samples The geographical locations of the sampling sites are shown in Fig. 1. The characteristics of the marine sediments collected in the three areas of the Adriatic Sea are described in Table 1. The marine sediments used in this study were collected from three locations: site A (the western Adriatic coast close to Ravenna), site B (situated 60 km offshore from the coast of Pesaro) and site C (situated 50 km offshore from the coast of Ancona). Site A is a coastal area of the Northern Adriatic influenced by river water from the Po Valley. It is affected by the general hydrodynamics of the basin through the introduction of low salinity water at its western boundary and by sedimentation from the Apennine rivers, to which is added the sedimentation from the Po river (Artegiani et al., 1997). Consequently, the salinity of site

2.2. Preparation of the samples and PAH extraction Marine sediment samples were collected with a box corer (5 cm depth), gross vegetable material and animal remains or shell residues were eliminated and the samples were homogenised and stored at 18 °C prior to chemical analysis. Sixteen US EPA priority pollution were used in this study for batch degradation test. For PAH extraction 10.0 g of wet sediment was weighed with an analytical balance. The sediment samples were then extracted three times with 20 mL methylene chloride by ultrasonication (BRANSONIC 1510E-MT) for 15 min. Methylene chloride was then removed by rotary evaporation, at a temperature of 37 °C). The extract was recovered with acetonitrile (0.5 mL) for further chromatographic separation. 2.3. Degradation parameters and chemical analyses Marine sediment samples collected at sites B and C were stored in closed jars of transparent glass and in the presence of oxygen, at different laboratory conditions: 6 °C and dark; 18 °C and sunlight. A different salt concentration (37 and 20) was added to samples of marine sediment collected at site A, which were stored at room temperature. The study of the persistence of PAHs in marine sediments was carried out by evaluating the loss of 50% of the initial concentration (C0) of the contaminant, that of the half-life. The half-life is also used to determine the persistence of other organic compounds (e.g. pesticides; Trevisan et al., 1995; Businelli et al., 2000). The PAH degradation data collected during this project fit well with first order rate constant (Yuan et al., 2001; Hinga, 2003), which complies with the following kinetics law:

ð1Þ

For the calculation of the half-life, t is equal to t1/2 and CC0 is equal to 1 : 2

t1=2 ¼

ln 2 K deg

K deg ¼

ln 2 t1=2

ð2Þ

ð3Þ

where t1/2 (d) is the half-life, C0 (lg g1, dry wt.) is the initial PAH concentration at time t0, C (lg g1, dry wt.) is the PAH concentration at time t1/2 and Kdeg (d1) is the degradation rate constant which expresses the speed with which the reaction proceeds.

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Fig. 1. Map of Adriatic Sea, geographic localisation of the sampling sites (Schlitzer, 2004).

Table 1 Characteristics of the site A, site B and site C of the North Adriatic Sea. Sample location

Abbreviation

n

Bottom (m)

Sanda

Silta

Claya

Organic mattera

Salinityb

Temperature (°C)b

P

Coast of Ravenna Offshore Northern Adriatic Offshore Northern Adriatic

A B C

3 6 5

<10 60 76

57.4 79.8 7.9

31.0 12.2 34.9

11.6 8.0 57.2

n.i. 1.4 3.39

20–36 >37 >37

8–25 <11 <11

48.89 7.16 108.00

PAHs (ng g1 d. w.)c

n, number of sediment samples. n.i., no information. a Values are in% dry weight. b In bottom, (Artegiani et al., 1997; Marini et al., 2002). c In this study.

A standard PAH solution (EPA 610 PAH Mix), purchased from Supelco, Bellefonte, PA, USA, was used as inoculum for the batch degradation test. An appropriate dilution of the standard solution EPA 610 in the ratio 1:50 was prepared with dichloromethane. Standard solution (1:1) contains a mixture of sixteen priority PAHs, with a known concentration: naphthalene (964 ng g1), acenaphthylene (1936 ng g1), acenaphthene (955 ng g1), fluorene

phenanthrene (96.6 ng g1), anthracene (194.2 ng g1), (97.0 ng g1), fluoranthene (194.2 ng g1), pyrene (94.0 ng g1), chrysene (96.8 ng g1), benz[a]anthracene (97.2 ng g1), benzo[b]fluoranthene (194.5 ng g1), benzo[k]fluoranthene (96.5 ng g1), benzo[a]pyrene (91.0 ng g1), dibenz[a,h]anthracene (192.8 ng g1), indeno[1,2,3-cd]pyrene (100.4 ng g1) and benzo[ghi]perylene (193.4 ng g1). The collected sediments (about

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200 g) were spiked with a diluted standard PAHs solution (2 mL). The degradation rates were studied for period of 50 d. The extractions were conducted in exactly time periods (0, 1, 3, 7, 9, 12, 14, 21 and 50 d, after inoculation). The PAHs were analysed with high-performance liquid chromatograph (HPLC) (Ultimate3000, Dionex). A mixture of PAHs was separated on a 4.6  150 mm analytical reverse-phase column C16 3 lm 120 Å. Eluting PAHs were detected with a fluorescence detector (RF2000, Dionex). Acenaphthylene cannot be analysed with fluorescence detection, so it is analysed with a PDA-100 Photodiode Array Detector. A mixture of acetonitrile and water, distilled and further purified by a Mill-Q system (Millipore, Billerica, MA, USA), was used as the mobile phase, delivered with a gradient program at 1.5 mL min1 (IOC-UNESCO, 1982). PAH concentration was determined by HPLC. The wet weight of each sample of marine sediment was corrected to the dry weight, after the determination of the percentage of humidity in the sediment samples. Each concentration was expressed on a dry-weight basis. Calibration solutions were prepared by serial dilutions from a standard PAH solution (EPA 610 PAH Mix). 2.4. Recovery tests Most papers (Marvin et al., 1992; Sun et al., 1998) reported that ultrasonic methods were suitable for the extraction of PAHs from soils and sediments. In particular, the comparison between ultrasonic and ‘‘traditional’’ methods (i.e., Soxhlet extraction, mechanical shaking) showed no significant differences in the extraction efficiency at low levels of pollution (Song et al., 2002; De Luca et al., 2004). Recovery rates were obtained for each individual PAH on wet sediment and two sediment samples certified for PAH: IAEA code 408 and IAEA code 383, purchased from the International Atomic Energy Agency, Vienna, Austria. These samples were extracted and analysed following the same procedure as the sediments. The PAHs were grouped according to the number of rings (Notar et al., 2001). In this study the recovery rates were higher in the wet than in the dry sediments. Recovery values obtained ranged from 58.99% to 111.00%. In the sediment samples certified for PAH, recovery values obtained ranged from 53.21% to 87.83% and from 60.86% to 81.81%, respectively for IAEA – 383 and IAEA – 408 (Table 2). 3. Results PAHs reach the Adriatic Sea mainly from the rivers of the Po Valley, adsorbed by organic particles and clays due to their chemical and physical characteristics (Means et al., 1980). Once they are adsorbed within the sediments, they are transported to the deepest part of the basin by currents (Brambati et al., 1983; Curzi and Tomadin, 1987). For this reason, studies have been carried out to measure the persistence of PAHs in ratio to the salinity of marine coastal sediments (Fig. 1, site A), as affected by saline gradients, and their persistence in the deep sediments of the open sea. The half-life and the degradation rate constant of each PAH were calculated in order to evaluate the persistence of PAHs. The PAHs analysed in this study were divided into four groups according to the number of their aromatic rings. Two–three rings include naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene; four rings include fluoranthene, pyrene, chrysene, benz[a]anthracene; five rings include benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene; six rings include indeno[1,2,3-cd]pyrene and benzo[ghi]perylene (Notar et al., 2001).

3.1. Half-life of the PAH in relation to salinity The results obtained from the three coastal sediment samples, collected in the vicinity of site A, have shown that high salinity values (superior or equal to 37) slow down the degradation of PAH molecules (Fig. 2.). Molecules that have shown greater sensitivity to changes in salinity had a higher molecular weight. All PAHs at a salinity of 37 persist longer than salinity of 20: that is 28.01% (two, three rings PAH), 40.28% (four rings PAH) 53.65% (five rings PAH) e 34.39% (six rings PAH). 3.2. Half-life of the PAH in relation to temperature and sunlight Given that PAH behaviour varies according to the salinity gradient, the second objective of this study was to observe the persistence of PAHs in the deep marine sediments of the Adriatic sea (Fig. 1, site B and site C) where salinity is superior or equal to 37 (Artegiani et al., 1997). These sediments are characterised by different particle sizes and varying organic content (Table 1). At both sites the half-lives and the degradationrate constant of each PAH were determined in relation to the conditions imposed by temperature and sunlight. The half-lives for each PAH were grouped according to the number of aromatic rings. The half-lives calculated for site B (Table 3), at 18 °C and with sunlight, vary between a minimum of 5.9 d (four rings PAH), to a maximum of 12.3 d (six rings PAH). However, at 6 °C with dark, the half-lives vary from a minimum of 8.5 d (four rings PAH), to a maximum of 12.0 d (five rings PAH). At site C (Table 4), at 18 °C and sunlight, the half-lives vary from a minimum of 6.3 d for PAH with two, three rings, to a maximum of 17.6 d for PAH with six rings. However, at 6 °C with the absence of light, the half-lives vary from a minimum of 10.5 d for PAHs with four rings, to a maximum of 19.1 d for PAHs with five rings. 3.3. Half-life of the PAH in relation to particle size and organic matter Sites B and C have a different sediment typology and a different percentage of organic matter (Table 1). From the batch degradation tests carried out, the four groups of PAH had high half-lives in the deep sediments of site C, which are clayey and rich in organic matter (Fig. 3). The compounds which displayed a greater difference between the two sites are those with a higher molecular weight. In particular, the PAHs with five rings increase their half-lives more at site C than at site B. That is, 78.07% and 71.30%, at a temperature of 18 °C in sunlight and at 6 °C in darkness, respectively. The PAH with three rings, being more volatile compounds, have shown a lot of variability between the two sites. That is, 3.83% and 26.19%, at a temperature of 18 °C in sunlight and at 6 °C in darkness, respectively. 4. Discussion and conclusions Given the lack of literature on the persistence of the PAHs in deep sea (Bouloubassi et al., 2006; Shao et al., 2010), the collected data are useful for describing the behaviour of PAHs in the deep sediments of the Northern Adriatic Sea. In these areas the PAHs are adsorbed in the organic particles of the sediment and are transported by the numerous rivers of the Po Valley (Brambati et al., 1983; Artegiani et al., 1997; Ravaioli et al., 2003). The PAH are more available for biodegradation when they are in the aqueous phase of the sediment. This is because at the water– sediment interface the PAHs are more degraded (Xia and Wang, 2008). The increase in salinity, which the hydrocarbons experience when thrown into the sea from the rivers causes a mass transfer of PAHs in the sorbed phase rather than the aqueous phase,

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Rings

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene

2 3 3 3 3 3

Average 2–3 rings Fluoranthene Pyrene Chrysene Benz[a]anthracene

Recovery (%) IAEA 383

Recovery (%) IAEA 408

40.59 ± 0.75 60.17 ± 7.15 63.48 ± 5.74 62.40 ± 8.76 67.52 ± 0.94 59.78 ± 24.38

64.74 54.71 41.48 90.19 n.i. 52.90

n.i. n.i. n.i. n.i. 76.10 87.53

4 4 4 4

58.99 ± 7.95 82.99 ± 1.90 77.47 ± 0.21 93.41 ± 7.93 110.26 ± 16.75

60.80 89.66 53.18 55.10 58.29

81.81 65.44 86.85 78.87 50.83

Average four rings Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Dibenz[a,h]anthracene

5 5 5 5

91.03 ± 6.70 96.59 ± 3.73 96.58 ± 14.24 104.92 ± 14.51 89.60 ± 4.18

64.05 53.88 46.31 47.58 65.06

70.50 51.00 n.i. 58.51 73.09

Average five rings Indeno[1,2,3-cd]pyrene Benzo[ghi]perylene

6 6

96.92 ± 9.16 116.55 ± 6.83 105.45 ± 0.14

53.21 92.55 83.10

60.86 62.00 60.54

111.00 ± 3.84

87.83

61.27

Average six rings *

Recovery (%) Wet sed*

Mean ± standard deviation, n = 2; n.i., not included in International Atomic Energy Agency, Vienna, Austria.

Fig. 2. The half-life of the four PAH groups calculated at site A in different salinity conditions: 37 and 20. Error bars represent standard deviation (SD, n = 3); p > 0.05.

increasing the constant distribution with a higher persistence of PAHs in the sediment (Wild and Jones, 1993). Means (1995), have demonstrated that as salinity was increased, there was an increase in the slope of the sorption isotherm, indicating that the binding of the pyrene molecule to the sediment organic carbon increased. In this study, this has been observed especially in the PAHs of high molecular weight, where the changes in salinity have a greater influence on the solubility of such molecules (Fig. 2). In particular, those with five rings at a salinity of 37 persist longer than at a salinity of 20, that is by 53.65%. While, the lightest two, three ring molecules registered a smaller difference of 28.01%. Even though this study does not investigate the causes of the higher persistence of PAHs at low temperatures and in the absence of sunlight, it might be assumed that this is the result of two main factors. First of all, the biodegradation of organic compounds is facilitated by the presence of environmental conditions favourable to microorganisms (Cerniglia, 1993; Hinga, 2003). Quan et al. (2009), have demonstrated the metabolic activity of the microorganisms was inhibited at a low temperature. Furthermore, the temperature could potentially affect the sorption rate (Wu and Gschwend, 1986). When the temperature decreases, the solubility

subsequently decreases and thus the bioavailability of the PAHs and the biodegradation decrease (Whitehouse, 1984; Eriksson et al., 2003). Another factor that could have contributed to a greater persistence of the PAHs in darkness was the absence of photodegradation. PAHs degraded at slightly higher rates when high light intensities were used (King et al., 2004; Saeed et al., 2011). In the deep sediments of the Northern Adriatic Sea the average annual temperatures oscillate between 10 °C and 11 °C, while the salinity is superior or equal to 37 (Artegiani et al., 1997; Boldrin et al., 2009). In these areas investigated, with the exception of indeno[1,2,3-cd]pyrene and of benzo[ghi]perylene, all the molecules showed a greater persistence at a lower temperature (6 °C) and in darkness (Tables 3 and 4). The molecules which were most sensitive to changes in temperature and sunlight were those with a lower molecular weight (two, three rings), whose persistence at sites B and C increased by 64.62% and 107.15%, respectively. Furthermore, in these areas the persistence of the PAHs in the sediments increases as a result of a low penetration of light which is due to low water transparency (Precali et al., 2005). The persistence and bioavailability of PAHs in the marine environment depend on the physical and chemical characteristics of the PAH as well as the composition and chemical characteristics of the sediment. Organic matter in sediment is known to be involved in PAH sequestrations (Means et al., 1980). The sediments with high levels of organic matter have a strong affinity to hydrophobic compounds, such as PAHs, in comparison with sediments with low levels of organic matter (MacRae and Hall, 1998; Xia and Wang, 2008). Furthermore, the PAHs are mainly adsorbed in the small particles (clay), which have a greater capacity for adsorption because of their greater specific surface area (Xia and Wang, 2008). Hinga (2003) showed that sediments with higher total organic carbon have lower oxygen concentration and may also provide more sites within the organic matrix where lower molecular weight PAHs are sequestered and less subject to microbial degradation. Magi et al. (2002), confirm these data in two coastal areas of the Northern Adriatic Sea. In the current study this result was confirmed in the deep sea sediments of the Northern Adriatic Sea for the PAHs. Indeed, the persistence of PAHs is greater in the clayey sediments at site C, where the organic matter is 3.39%. The PAHs with a higher molecular weight have a greater affinity

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Table 3 Half-life (t1/2), rate degradation constant (Kdeg) and correlation coefficient (r) for each PAHs in the site B. p > 0.01. PAHs site B

T 18 °C, sunlight t1/2 (d)

a

Kdeg (d

T 6 °C, dark 1

)

18 °C, sunlight in relation to 6 °C, dark (%) 1

r

t1/2 (d)

Kdeg (d

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene

5.9 6.5 5.5 5.6 7.4 6.1

0.12 0.11 0.13 0.12 0.09 0.11

0.91 0.93 0.91 0.91 0.89 0.91

12.7 13.0 8.2 9.5 9.3 8.1

0.05 0.05 0.09 0.07 0.07 0.09

)

r 0.93 0.91 0.93 0.95 0.94 0.91

115.44 98.04 48.35 69.18 25.10 31.59

Average 2–3 rings Fluoranthene Pyrene Chrysene Benz[a]anthracene

6.2 6.1 6.0 5.6 5.6

0.11 0.11 0.12 0.12 0.12

0.92 0.87 0.87 0.89

10.1 8.9 10.4 7.7 7.0

0.07 0.08 0.07 0.09 0.10

0.90 0.89 0.85a 0.91

64.62 45.26 74.17 35.73 24.77

Average four rings Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Dibenz[a,h]anthracene

5.8 7.4 8.5 9.6 8.0

0.12 0.09 0.08 0.07 0.09

0.91 0.89 0.91 0.82a

8.5 8.5 10.1 14.1 15.3

0.08 0.08 0.07 0.05 0.05

0.89 0.90 0.93 0.82a

44.98 15.64 20.06 47.14 91.61

Average five rings Indeno[1,2,3-cd]pyrene Benzo[ghi]perylene

8.4 11.2 13.4

0.08 0.06 0.05

0.90 0.77a

12.0 10.4 12.9

0.06 0.07 0.05

0.95 0.87

43.61 7.06 3.35

Average six rings

12.3

0.06

11.7

0.06

5.20

p > 0.05.

Table 4 Half-life (t1/2), rate degradation constant (Kdeg) and correlation coefficient (r) for each PAHs in the site C. p > 0.01. PAHs Site C

T 6 °C, dark 1

18 °C, sunlight in relation to 6 °C, dark (%) 1

t1/2 (d)

Kdeg (d

r

t1/2 (d)

Kdeg (d

5.3 3.9 11.8 – 5.9 4.6

0.13 0.18 0.06 – 0.12 0.15

0.87 0.85a 0.77 – 0.85a 0.88

13.4 10.3 18.8 – 8.9 9.7

0.05 0.07 0.04 – 0.08 0.07

0.84a 0.88 0.85a – 0.96 0.84a

151.55 163.20 59.08 – 50.00 111.94

6.3 7.5 9.6 7.7 7.3

0.13 0.09 0.07 0.09 0.09

0.87 0.81a 0.83a 0.89

12.2 – 10.5 13.4 7.6

0.06 – 0.07 0.05 0.09

0.95 0.91 0.92 0.94

107.15 – 9.23 74.90 3.50

Average four rings Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Dibenz[a,h]anthracene

8.0 16.0 14.4 13.4 13.2

0.09 0.04 0.05 0.05 0.05

0.88 0.91 0.92 0.84a

10.5 20.5 20.8 20.3 14.9

0.07 0.03 0.03 0.03 0.05

0.96 0.78a 0.87 0.90

29.21 28.40 44.01 51.46 12.66

Average five rings Indeno[1,2,3-cd]pyrene Benzo[ghi]perylene

14.2 17.4 17.9

0.05 0.04 0.04

0.86 0.78a

19.1 17.4 16.9

0.04 0.04 0.04

0.78a 0.83a

34.13 0.25 5.60

Average six rings

17.6

0.04

17.1

0.04

Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Average 2–3 rings Fluoranthene Pyrene Chrysene Benz[a]anthracene

a

T 18 °C, sunlight )

)

r

2.67

p > 0.05.

to organic matter. The ratio of the half-life of five ring PAHs in site C to that of site B is 78.07% and 73.90%, respectively, when the temperature is 18 °C and there is light and 6 °C and in darkness (Fig. 3). The PAHs with two and three rings with a values of 3.83% and 25.36%, demonstrated lower values at a temperature of 18 °C and sunlight and of 6 °C in darkness, respectively. In agreement with MacRae and Hall (1998), the smaller and more soluble PAHs were degraded faster than the larger, less soluble compounds. In these degradation trials a growth directly proportional to the half-life was observed in relation to the number of rings, especially at a temperature of 18 °C and in the presence of sunlight. In the marine environment, the behaviour of PAHs is the result of the interplay between the sources of the PAHs, the physico-

chemical properties of the individual compounds, water and sediment movement, and field conditions (King et al., 2004). In conclusion, it has been possible to measure the parameters of PAH persistence in the deep sediments of the Northern Adriatic, an area that is important for its impact on humans. Once the PAHs reach the Adriatic Sea from the rivers, they become less bioavailable in the deep clayey sediments and are transported by sea currents to very specific areas of the Adriatic where they accumulate. The bioavailability of PAHs in the sea is also limited due to the different saline concentration which increases the phenomena of sediment adsorption. The oceanographic conditions, low temperature and darkness, favour the greater persistence of PAHs in deep Northern Adriatic sediments.

M. Marini, E. Frapiccini / Chemosphere 90 (2013) 1839–1846

Fig. 3. Half-life of the four PAH groups calculated at sites B and C at a temperature of 18 °C and in sunlight and at a temperature of 6 °C and darkness.

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