Estimation of Polycyclic Aromatic Hydrocarbons pollution, risk assessment and loads into Mediterranean Sea from Volturno River, Southern Italy.

Background: This study reports the data on the contamination caused by polycyclic aromatic hydrocarbons (PAHs) drained into the Volturno River and its environmental impact on the Tyrrhenian Sea (Central Mediterranean Sea). One of the key aims of this study is to use the PAHs as indicators of pollution, by identifying the main sources from which these pollutants originate. Also, the ecosystem health risk and the seasonal and spatial distribution of PAHs in samples of water and sediment was assessed. The 16 PAHs identied by the USEPA as priority pollutants were determined in the water dissolved phase, suspended particulate matter and sediments collected from 10 sites in four seasons. Results: A multidimensional statistical approach was used to identify three pollution composite indicators. Contaminant discharges of PAHs into the sea were calculated in about 3.158,2 kg/year showing that this river should account as one of the main contribution sources of PAHs to the Tyrrhenian Sea. Total concentrations of PAHs varied in ranges 434.8 to 872.1 ng g -1 and 256.7 to 1686.3 ng L -1 in sediment samples and in water (total of water dissolved phase and suspended particulate matter), respectively. Conclusion: The statistical results indicated that the PAHs mainly had a pyrolytic source and the rainy season was the most polluted time. The toxic equivalent concentration (TEQ) of carcinogenic PAHs was 130.3 to 302.1 ngTEQ g -1 , implying that the Volturno River basin presents a denite carcinogenic risk. PCA analyse of PAHs Tyrrhenian principal component analysis on a dataset obtained on dissolved and suspended particulate PAHs (Naphthalene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz(a)anthracene, Chrysene, uoranthene, Benzo(k)uoranthene, Benzo(g,h,j)perylene, Indeno(1,2,3,c,d)pyrene, Dibenz(a,h)anthracene and for BaP 80%, suggesting that adverse effects might occasionally occur. The concentrations of individual PAHs do not exceed their respective ERM values, but the ERL values exceeded for Flu in 30%, Ace in 70% and DahA for all samples. The results indicated that in certain sites PAHs may have been found and the environmental integrity was at risk of PAHs in the sediments from the Volturno River and Estuary.

idea of the evolution of the pollution downriver and nine points were sampled in the continental shelf around the Volturno mouth in order to estimate the impact of the Volturno River pollution on the Mediterranean Sea environment. The rst three sites to undergo sampling were 500mt away from the Volturno Estuary, further sampling was executed on three locations 1000mt away from the river mouth and, lastly, the nal three samples were gathered 1500mt away ( Fig. 1). Sampling coordinates are stated in Table 1. Table 1 Description of the sampling sites and concentration of PAHs in the water dissolved phase (DP), suspended particulate matter (SPM) and the sediments of the Volturno River, Southern Italy. In each sampling site two amber bottles of water (consisting of 2.5 litres) were collected and brought back to the laboratory while refrigerated (4 °C). Samples of surface sediment (0-5 cm) were gathered through a grab sampler (Van Veen Bodemhappe 2 L capacity) and conserved in aluminum box. Sediments samples were refrigerated all through transfer to the laboratory and preserved at -20 °C until analysis.
The procedure employed for extraction and cleanup has been published before and opportunely modi ed [22]. Water samples were shortly ltered through a GF/F glass ber lter (47 mm x 0.7 µm; Whatman, Maidstone, UK) which had been previously kiln-red at 400 °C overnight. Filters (suspended particulate matter, SPM) were preserved at -20 °C in the dark until analysis. The portion of pollutants passing through the lter (DP, dissolved phase) was extracted in the same day of sampling (3-6 h from sampling) after being conserved at 4 °C in the darkness.
The dissolved phase was examined by liquid-liquid extraction procedure. One 2 L separatory funnel was loaded with water sample and was spiked with a surrogate solution of benzo[a]pyrene-d12 and indeno [1,2,3-cd] pyrene-d12 in methanol obtaining a nal concentration in water of 10 ng L − 1 . Have been added 50 mL of dichloromethane (VWR, Radnor, Pennsylvania, USA) to the 2 L separatory funnel and it was extracted the sample by stirring the funnel for 3 minutes with periodic venting to discharge excess pressure. The organic layer was left to rest to separate from the water phase for a minimum of 5 minutes. If the emulsion interface between layers was more than one-third the volume of the solvent layer, has been added a few mL of saturated sodium chloride solution, has been shaken and waited a few minutes. At the end of the last ltration the sample has been connected to the rotary evaporator and concentrate to 2 mL. The extract has been transferred to a 4 mL vial and evaporate until dry under a gentle nitrogen ow. To continue by adding 0.5 mL of hexane with internal standard chrysene-d12.
Sediments were oven dried at 60 °C and sieved at 250 µm. Then, 5 g of sediment were spiked with the surrogate mixture (10 ng of benzo[a]pyrene-d12 and indeno[1,2,3-cd] pyrene-d12 ) and extracted three times by sonication using 15 mL of dichloromethane/methanol (1:1) (VWR) for 15 min. After centrifuging, the organic extract has been analyzed in the same way than the water samples.

Instrumental analysis
PAHs were quanti ed by GC-MS QP2010 Plus Shimadzu (Kyoto, Japan), equipped with a AOC-20i Shimadzu (Kyoto, Japan) autosampler, operating in the electron impact mode at 70 eV. A Rxi 5Sil MS capillary column (5% phenyl 95% dimethylpolysiloxane) (30 m, 0.25 mm ID and 0.10 µm of lm thickness) was used. The column temperature was programmed as follows: rst, heated to 60 °C and held for 2 min; ramped to 200 at 25 °C min − 1 ; then ramped to 270 at 10 °C min − 1 and held for 6 min; and nally ramped to 310 at 25 °C min − 1 and held for 10 min. Helium was used as carrier gas. The injection port temperature was 300 °C and it was operated in pulsed splitless mode. Acquisition was carried out in the single ion monitoring mode (SIM) using two characteristic ions for each target analyte. Target analytes were identi ed and veri ed by comparing retention times of the samples with standards and using the characteristic ions and their ratio for each target analyte. Furthermore, for the higher concentrated samples, the identi cation of target analytes was con rmed in full-scan mode (m/z range from 60 to 350) and were quanti ed using the internal using the characteristic ions and their ratio for each target analyte.

Quality assurance and quality control
The limit of detection (LOD) and limit of quanti cation (LOQ) were calculated as having signal-to-noise ratios of above 3 and 10, respectively, by ve replicate analyses. The mean surrogate recoveries in the dissolved phase were 92.8 ± 5.2% for benzo[a]pyrene-d 12

Statistical analysis and calculation of PAHs inputs
The analysis of the data was performed with the statistical software SPSS, version 14.01 for Windows (SPSS Inc., Chicago, IL, USA). All data were presented as the mean ± Standard Deviation (SD). The level of signi cance was set at p ≤ 0.05.
The method used to estimate the annual contaminant discharges (F annual ) was based on the UNEP guidelines [24] and has been widely accepted [25][26][27]. A ow-averaged mean concentration (C aw ) was calculated for the available data, which was corrected by the total water discharge in the sampled period. The equations used were the following: where C i and Q i are the instantaneous concentration and water ow discharge, calculated by means of a daily averaged water ow, respectively for each sampling event. Q T represents the total river discharge for the period considered (November 2017 -July 2018), calculated by adding the monthly averaged water ow [28,29,30]. River ow data was collected from the register of the Autorità di Bacino Nazionale dei Fiumi Liri-Garigliano e Volturno to http://www.ildistrettoidrogra codellappenninomeridionale.it (Abruzzo, Basilicata, Calabria, Campania, Lazio, Molise, Puglia Government for the Environment).
Furthermore, to study the temporal contaminant discharge variation, C i and Q i were considered for each campaign and expressed as kg/year.
Principal component analysis (PCA) is a useful technique that allows to reduce the dimensionality of a data set (sample) by nding a new set of variables, smaller than the original set of variables, that nonetheless retains most of the sample's information [31,32], like the sample's variation, originated from the correlations between the initial variables. It tries to preserve the essential parts that have more variation of the data and remove the non-essential parts with fewer variation. These new variables, called principal components (PCs), are not correlated, and are ordered by the fraction of the entirety of the information each retains. There are three main methods used in order to determine the optimal number of components [33,34,35] in a principal component model (Amount of explained variance, Cattell's scree test and Kaiser's eigenvalue greater than 1.0 rule). In order to enhance the interpretation of the results of the PCA, it is possible to rotate the axes to reduce the dimensions or cover the maximum variation. Rotation is done so that the rst axis contains as much variation as possible, the second axis contains as much of the remaining variation and so on. Change of coordinates used in principal component analysis (PCA) is known as Varimax rotation. It maximizes the sum of the variances of the squared loadings as all the coe cients will be either large or near zero, with few intermediate values.
The goal is to associate each variable to at most one factor. The interpretation of the results of the PCA will be simpli ed. In order to analyse in depth the pollution of PAHs affecting the Volturno River and its environmental impact on the Tyrrhenian Sea, principal component analysis has been conducted on a dataset obtained on dissolved phase and suspended particulate matter. In each analysis, 17 PAHs (Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz(a)anthracene, Chrysene, Benzo(b) uoranthene, Benzo(k) uoranthene, Benzo(a)pyrene, Benzo(g,h,j)perylene, Indeno(1,2,3,c,d)pyrene, Dibenz(a,h)anthracene and Perylene) have been taken into account.

PAHs concentrations in water dissolved phase
The concentrations in the water dissolved phase (DP) of total PAHs detected at 10 locations of the Volturno River and its Estuary, during the four campaigns, compositional pro les of PAH in the dissolved phase, which indicate that 2-and 3-ring PAHs were abundant in all sampling sites, representing on average over 62% of all PAHs. In addition, the suspected carcinogenic 5-6-ring PAHs was present in low concentrations, accounting for only 17% of total PAHs. The prevalence of low molecular weight PAHs (2-3-ring) in the water could be explained by their high water solubility and relatively high vapor pressures [36,37,38]. Compared with the water of polluted rivers in other parts of the world (Table 2), the concentration of ΣPAHs in the the Volturno River dissolved phase (64.3-1429.1 ng L − 1 ) was much higher than those found in the Xijiang River, China by Deng et al. [39], in the Yellow River (China) by Li et al. [40], in the Songhua River (China) by Ma et al. [41], in the Wyre River, England by Moeckel et al. [42], in the Elbe and Weser Rivers, Germany by Siemers et al. [43], in the Marseilles coastal area, France by Guigue et al. [44] and in the Tiber River (Italy) by Patrolecco et al. [45] and Montuori et al. [22]; these levels were however lower than those found in the Daliao River, China by et al. [46], in the Yellow River (China) by Zhao et al. [47], in the Songhua River (China) by Zhao et al. [48], in the Daliao River estuary (China) by Zheng et al. [49], in the Gomti River, India by Malik et al. [50], in the Cauca River, Colombia by Sarria-Villa et al. [8], in the Almendares River, Cuba by Santana et al. [51] and in the Buffalo River estuary, South Africa by Adeniji et al. [52]. Based on these results, the levels of PAHs in the dissolved phase in the Volturno River are comparable to those found in the Henan Reach of Yellow River, China by Sun et al. [53], in the Gulf of Tunis, Tunisia by Mzoughi and Chouba [54], in the Danube River, Hungary by Nagy et al. [55] and in the Sarno River by Montuori and Triassi [22].  show that 4-, 5-, 6-ring PAHs were abundant at most sampling sites, accounting for 25%, 20%, and 12% of ΣPAHs in SPMs, respectively.
The proportion of high molecular weight PAHs increased to 57%, much above than in dissolved samples, where it was 38%. The results indicated that high molecular weight PAHs were preferentially sorbed by the particulate matter due to its high hydrophobicity and hardly biodegraded, in agreement with the PAHs partition theory [45,54,47]. In fact, the partition coe cients (Kp, de ned as the ratio of the concentration of a chemical associated with SPM to that in the DP: Kp = C SPM /C DP ) showed an increasing trend of high-ring compounds in their SPM partitioning (average value of 0.80, 0.96 and 1.00 respectively for 4-, 5-, 6ring PAHs).
Compared with other polluted rivers in the world (Table 2), PAHs in SPMs from the Volturno River were much higher than those detected in the Xijiang River and Yellow River, China by Deng et al. [39] and Li et al. [40] respectively, in the Henan Reach of Yellow River (China) by Sun et al. [53], in the Songhua River (China) by Ma et al. [41], in the Yellow River (China) by Zhao et al. [47], in the Gulf of Mexico, Mexico by Adhikari et al. [21] and in the Gulf of Tunis, Tunisia by Mzoughi and Chouba [54], but lower than those found in the Daliao River estuary, China by Guo et al and Zheng et al. [46,49] respectively and in the Sarno River by Montuori and Triassi [22].

PAHs concentrations in sediments
The concentrations of total PAHs in sediment samples are illustrated in Table 1 ). As to the compositional pro les of PAH in sediments at each sampling sites, 4-and 5-ring PAHs were abundant at most sites, accounting for 37% and 40% of ΣPAHs in sediments, respectively. Low molecular weight PAHs were gradually decrease by diluation due to their relatively high water solubility and easier degradation. Therefore, high molecular weight PAHs could easily reach the sediment due to their low vapour pressure, low water solubility and more refractory behavior; thus, they were more resistant to degradation [56,57,38].
In comparison with polluted rivers in other parts of the world (  [30], and in the Sarno River by Montuori and Triassi [22]. The concentration of ΣPAHs in the samples of sediment from the Volturno River and river mouth was inferior than the concentration found in the Daliao River, China by Guo et al. [46], in the Caspian sea coast, India by Yancheshmeh et al. [68], in the Ba n Bay, Canada by Foster et al. [69], in the Cocó and Ceará Rivers, Brazil by Cavalcante et al. [70], in the Bahia Blanca Estuary, Argentina by Oliva et al. [10], in the Cauca River, Colombia by Sarria-Villa et al. [8], in the Buffalo River Estuary, South Africa by Adeniji et al. [52], in the Ammer River, Germany by Liu et al. [9], in the Portimão Harbor, Portugal by Bebianno et al. [71], in the Gulf of Tunis, Tunisia by Mzoughi and Chouba [54], in Durance River and Huveaune River, France by Kanzari et al. [72,73] and in the Iberian coast and Ría de Arousa, Spain by Leòn et al. [74] and Perèz-Fernàndez et al. [6] respectively and in the Gulf of Trieste, Italy by Bajt [75]. The low concentrations of PAHs in sediments may be due to the high content of sand and low TOC contents (1.1-9.5 mg g − 1 , mean 5.1). Figure 2 showed the relationship between %TOC with the ΣPAHs in the sediment samples. As results showed, a positive linear regression exists between total PAH concentration and TOC data in sediments (r = 0.97, p < 0.01) as indicated by many other studies [46,53,8].

PAHs seasonal and spatial distribution in DP, SPM and sediment samples
The concentrations of total PAHs in DP, SPM and sediment samples of the Volturno River at different sampling sites are illustrated in Table 1. The results show that the ratio of the concentration of ΣPAHs in DP samples to that in SPM was higher than one in all sites (average 2.5; SD ± 1.5). These results lead us to consider that the total amount of PAHs in DP samples was more abundant than in SPM samples for each site and season. These data were also con rmed by the analysis of the ratio of the individual PAHs, and it was possible to observe the same trend obtained from the reports of the sums.
Even the total amount of PAHs in SPM samples was more abundant than in sediment samples for each sampling site. In fact, the ratio of the concentration of ΣPAHs in sediment samples (ng g − 1 ) to that in the SPM samples (expressed in ng g − 1 ) was less than 1 in all sampling sites (average 0.014; range 0.006-0.022; SD ± 0.006). In particular, the results indicate that PAHs concentrations in DP were low during the wet season oods (February) and high during the dry season (July). The seasonal variation of PAHs concentrations was depending to the hydrological conditions, which could cause dilution ratio variations.
Therefore, a high river ow rate resulted in a higher dilution ratio in the wet season oods caused a decrease in the PAHs concentration in both the Volturno River and its estuary. In July, the concentrations of total PAHs in SPM samples were lowest in all sampling sites. The results could be explained by the ow decrease during the dry season that a greater stagnation of SPM determining the transfer of the more polar PAHs from SPM to DP. Based on these results, it can be concluded that the load and relocate of PAHs between different phases in each sampling site of the Volturno were related to a variation in the ow during rainy and dry seasons. Therefore, high concentration of PAHs in SPMs but moderate in sediment indicated that the contamination of PAHs in Volturno River and Estuary might be caused by fresh input of PAHs.
In order to evaluate the huge input of PAHs drained from storm water runoff, tributary in ow, wastewater treatment plant and industrial e uent discharge, agricultural runoff, atmospheric deposition, dredged material disposal, the total load of PAHs into the Tyrrhenian Sea was calculated. The total PAHs loads contribution to the Tyrrhenian Sea from the Volturno River is calculated in about 3.158,2 kg/year.
The spatial distribution of PAHs in DP, SPM and sediment samples from the Volturno River and its estuary were studied by comparing the concentrations of ΣPAHs in different sampling sites in dry and rainy seasons, respectively (Fig. 3). Indeed, the level of contamination of PAHs in the water clearly decrease from Sea, PAHs concentrations range in general from very high in the vicinity of the river out ows to very low in offshore areas (Fig. 3). At 500 m of river out ow, the concentration of PAHs were close to those of the Volturno mouth (Fig. 3). The concentrations at the sampling sites then decreased at 1000mt and more at 1500mt of the river out ows. Particularly, at the Volturno mouth the PAHs loads move into the Tyrrhenian sea southward (Fig. 3). As can be seen from the data obtained, the trend concentrations shows a decreasing movement from the mouth towards 1500mt at sea. This can depend both on the ow of the river which varies according to the season, and on the diluting effect of the sea.

Source identi cation
To investigate the origin of PAHs and identify separately petrogenic from pyrolytic inputs, chemical pro ling and different diagnostic ratios on isomeric relations were used: An/(An + Phe), Fl/(Fl + Pyr), BaA/(BaA + Chr) and InP/(InP + BghiP) [13,76]. The rst group is from pyrolytic sources, which includes combustion of fossil fuels, vehicles using gasoline or diesel fuel, waste incineration and coke production, carbon black, coal tar pitch, asphalt and petroleum cracking. The second group is from petrogenic sources, which include crude oil and petrochemicals (gasoline, diesel fuel, kerosene and lubricating oil). Finally, apart from pyrolytic or petrogenic source, PAHs can be formed during diagenetic processes, i.e. the formation of sediments from organic material [6]. Each source (i.e. pyrolytic, petrogenic and diagenetic) gives rise to typical PAH patterns. In general, combustion products are dominated by relatively high molecular weight (HMW) compounds with four or more condensed aromatic rings, whereas bi-and tricyclic aromatic compounds (LMW) are more abundant in fossil fuels, which are, moreover, dominated by alkylated derivatives [9,10,11].
The ratio study re ected a prevailing pattern of pyrolytic inputs of PAHs in the Volturno River and its estuary. In fact, the results showed that An/(An + Phe) ratio was 0.1 in DP, SPM and sediments (mean 0.42, 0.40 and 0.47, respectively), which attributed the origin of PAHs to pyrogenic sources. Furthermore, Fl/(Fl + Pyr) ratios can distinguish petroleum input from combustion processes and discriminate among such sources [13,77]. For Fl/(Fl + Pyr), low ratios (< 0.40) indicate petroleum, intermediate ratios (0.40-0.50) of liquid fossil fuel combustion, whereas ratios > 0.50 are characteristic of grass, wood, or coal combustion. In the Volturno River and Estuary, ratio Fl/(Fl + Pyr) 0.5 was found to water, particulate matter and sediments, indicating a variable impact urban tra c emissions and from biomass burning (Fig. 4a). Ratio BaA/(BaA + Chr) 0.35 was found in water and in sediments, which suggests vehicular emissions; and similar behavior it is observed for ratio InP/(InP + BghiP) 0.35, which indicates combustion sources (Fig. 4b). Finally, the LMW/HMW ratio was relatively low (< 1 for most sites), suggesting a pyrolytic origin of PAHs at these sites (mean 0.85; range 0.09-2.99). PAHs may transport and deposit into the river over time. In addition to these inputs, some other sources such as the roads on both sides of the river and along the coast, the runoff containing street dust, and municipal wastewater, result in the pattern of pyrolytic origins of PAHs contamination in the area. About that, no other rivers in the area adjacent to that of the Volturno River has been considered with regard to the evaluation of the PAHs and for this reason valid comparisons can't currently be made. However, some rivers have been taken into consideration for the evaluation of the PAHs, even if they are at greater distances from Volturno River [22,78,30].
The Volturno atland is a heavy industrial area, with many heavily polluting factories. In additions in the Campania Region has resulted in the widely documented illegal disposal of urban, toxic and industrial wastes. The industrial wastes enriched with combustion-derived PAHs are directly discharged into the Volturno River. The emission of atmospheric particles from factories, also cause serious air pollution, and the particulate-associated PAHs may transport and deposit into the river. In addition to these inputs, some other sources such as the roads on both sides of the river and along the coast, the runoff containing street dust, and municipal wastewater, result in the pattern of pyrolytic origins of PAHs contamination in the area.
In addition to pyrolytic and petrogenic sources, Per is also produced by in situ degradation of biogenic precursors [12,76,6]. Indeed, Per is probably the most important diagenetic PAHs encountered in sedimentary environments and, thus, a high abundance of Per relative to other PAHs can indicate an important natural origin of the compound. Per has been frequently associated with inputs from rivers and estuaries [12,68,79]. In fact, it has been suggested that concentrations of Per above 10% of the total penta-aromatic isomers indicate a probable diagenetic input, whereas those in which Per accounts for less than 10% indicate a probable pyrolytic origin of the compound. In the present study, the concentrations of Per detected in all sediment samples were very low (range 4.3-15.5 ng g − 1 ) and contributed less than 2% to the penta-aromatic isomers, indicating a pyrolytic origin of these compounds.

A composite indicator for water pollution
In order to formalize a Water Pollution Composite Indicator (WP-CI) we analysis at the same time Dissolved phase (DP) and Suspended Particulate phase (SPM) samples collected from 10 sites ("Sou1", "500N2", "1000N3", "1500N4", "500C5", "1000C6", "1500C7", "500S8", "1000S9", "1500S10") during the months of April, July, November and February. The correlation matrix points out sets of correlated variables and only the rst seven highest eigenvalue are larger than one. However, the rst two components explain the 60,0% (32,6% and 27,4%, respectively) of the total variance. The PCA for this dataset pointed out a clear distinction of the pollution of the two phases and allowed us to de ne two SCIs (Speci c Composite Indicator). In fact, the rst factor is characterized by the presence of PAHs belonging to SPM and we named it "SPM-Composite Indicator"; the second factor is de ned by the PAHs of the DP, the second factor is called "DP -Composite Indicator". Looking at the plot of the rst two principal components, and making a correlation between sites and seasons we observe that the pollution from SPM is higher in February, in the sites 500N2, 1000C6, 1500C7, 1000S9, however DP pollution is higher in July at sites 1500C7 e 1500S10 (Fig. 5a and 5b). For each SCI is possible to rank the 40 statistical units and nally it is possible to observe the nal ranking based on the WP-CI (Table 3). The site that has a lower rate of global pollution in all seasons of the year is the 4, followed by 3 and then 7. However, just in reference to site 7 there is an irregular behavior of the two parties. In fact, while in November both SPM and DP appear to have a low level of pollution, in other seasons the two components have contrasting behavior. The most polluted months are February and April especially for the SPM component, on the contrary, the least polluted months are July and November, in particular for the SPM component. The month of February, instead, has a tendency to lower pollution for the DP, on the contrary, July and April are the months most polluted. Based on these results, it can be con rmed that the load and relocate of PAHs between different phases in each sampling site of the Volturno were related to a variation in the ow during rainy and dry seasons. Table 3 Rankings based on SCIs and WP-CI according to these thresholds, (1): normalized score > 0:60, (2): normalized score > 0:30 and < 0:60, (3): normalized score < 0:30.

Risk assessment
To evaluate the potential adverse effects caused by PAHs in the Volturno River were used the sediment quality guidelines (SQGs) values developed by [80] and by [81]. Sediment quality guidelines (SQGs) are an important tool for the assessment of contamination in marine and estuarine sediments. Two sets of SQGs, including the ERL/ERM and the TEL/PEL values, were applied in this study to assess the toxic effects of individual PAHs in sediments. These sets are de ned as: i) effect range low (ERL)/effect range median (ERM) and ii) the threshold effect level (TEL)/probable effect level (PEL). ERLs and TELs represent chemical concentrations below which the probability of toxicity and other effects are rare. Differently, the ERMs and PELs represent mid-range above which adverse effects would occur frequently. ERLs-ERMs and TELs-PELs represent a possible-effects range, within which negative effects would occasionally occur [61,82].
In the Volturno River, not all PAHs concentrations in sediment samples were below the TEL and ERL values, but the concentrations were signi cantly lower than the PEL and ERM values (Table 4). , our data showed that the mean values of BaP and BkF + BbF concentration in the Volturno River (63.9 and 41.2 ng L − 1 , respectively) were higher than the EQS values (50 and 30 ng L − 1 , respectively), and mean value of BghiP + InP values (67.4 ng L − 1 ) was signi cantly higher than the EQS value of 2 ng L − 1 , showing that the environmental integrity of the river watercourse was at risk. Also RQ (Risk Quotient), the ratio between the Measured Environmental Concentration (MEC) and the Predicted No Effect Concentrations (PNECs), has been calculated. OSPAR Commission, the mechanism by which 15 Governments and the EU cooperate to protect the marine environment of the North-East Atlantic, established a list of PNECs for several substances, including PAHs. In particular, in OSPAR Agreement 2014-05, in Table 2, Sect. 5, PNECs values were reported for single PAHs. According to these values, we calculated ratio between single MEC and PNEC for single PAHs. As result, we obtained, both for water (sum of DP + SPM) and sediment, an RQ > 1 for most compounds, con rming that the environmental integrity of the river watercourse was at risk.

Conclusions
This research is part of a larger project which brings forth fundamental data on the frequency, distribution and likely sources of PAHs in the Volturno River and its input into the Tyrrhenian Sea (Central Mediterranean Sea), Southern Italy. Low molecular weight PAHs were abundantly present in water samples, while in sediment samples the predominant class were high molecular weight PAHs. The concentration levels of PAHs in DP, SPM and sediment phases were remarkably different amongst sampling sites. Contaminant discharges of PAHs into the sea showed that this river should account as one of the main contribution sources of PAHs to the Central Mediterranean Sea. A Water Pollution Composite Indicator (WP-CI) and individual diagnostic PAHs ratio revealed that the main PAHs source was pyrolytic and suggested that the majority of this pollution derived for the most part from vehicle tra c and combustion processes. Regarding the risk assessment, even if the concentration of many single PAHs in a number of stations were above ERL and/or TEL (and below ERM and/or PEL), which would on occasion yield negative environmental consequences, the EC-EQS (European Commission -Environmental Quality Standards) and the RQ (Risk Quotient) indicated that the integrity of this area is possibly at risk. Thus, the Volturno River waters should be continuously kept under monitor as PAHs could lead to negative consequences on its aquatic ecosystems and organisms.

Figure 1
Map of the study area and sampling sites in the Volturno River and Estuary, Southern Italy.

Figure 2
Relationship between TOC (%) and ΣPAHs in the sediment samples of the Volturno River.

Figure 3
Spatial and temporal concentration of PAHs in the water dissolved phase (DP, ng L-1), suspended particulate matter (SPM, ng L-1) and sediments (ng g-1 dry wt) of the Volturno River and Estuary, Southern Italy.