Vertical fluxes of polycyclic aromatic hydrocarbons and organochlorine compounds in the western Alboran Sea (southwestern Mediterranean)

ELSEVIER

Marine Chemistry

52 ( 1996) 75-86

Vertical fluxes of polycyclic aromatic hydrocarbons and organochlorine compounds in the western Alboran Sea ( southwestern Mediterranean) Jordi Dachs a, Josep M. Bayona a7*, Scott W. Fowler b, Juan-Carlos Miquel b, Joan Albaig6s a a Department of Environmental Chemistry, C.I.D.-C.S.I.C.,

Jordi Gironu 18. E-08034, Barcelona, Spain b IAEA Marine Environment Laboratory, P.O. Box 800, MC-98012, Monaco, Monaco

Received7 June 1995;accepted 1 November 1995

Abstract Time-series samples of sinking particles were collected in the Alboran Sea with sediment traps moored at three water column depths (250, 500 and 750 m) between February and May 1992. The samples were analyzed for individual polychlorobiphenyl congeners (i.e. PCBs IUPAC no.: 28, 52, 101, 118, 153, 138 and 180), chlorinated pesticides (DDE and Lindane) and individual polycyclic aromatic hydrocarbons (PAHs; 3-6 aromatic rings). Average concentrations of PCB and total PAHs were 78.9 ng g-’ (range: 27.3-212) as Clophen A40 equivalents and 1176 ng g-’ (range: 104-2780), respectively. The l,l-dichloro-2,2-bis( p-chlorophenyl)ethene (4,4’-DDE) and 1,2,3,4,5,6-hexachlorocyclohexane (-y-HCH) were the only chlorinated pesticides identified throughout the sampling period, with respective concentrations of 6.6 ng g- ’ (range l.l- 15) and 16.8 ng g-’ (range 5.4-48). Corresponding fluxes of PCBs (as Clophen A40 equivalents) and PAHs were 15.1 ng m-2 d-’ (range: 6.9-24.9) and 225 ng m-* d- ’ (range: 15-625). Contaminant fluxes were analyzed with other collective fluxes obtained from the same samples (i.e. fecal pellets, mass and organic carbon); while higher molecular weight PAHs (MW > 228 daltons) exhibited a strong correlation with the mass fluxes (r* = 90.7%, p < 0.001, n = 18), the lower molecular weight compounds (MW < 202 daltons) covaried with organic carbon and fecal pellet fluxes ( r2 = 76.4%, p < 0.001, n = 18). The ZPCB fluxes covaried with organic carbon, and fecal pellet fluxes and depth (r* = 97.6%, p < 0.001, n = 9). The 4$-DDE only covaried with fluxes of organic carbon (r2 = 85.87%, p < 0.001) and y-HCH with the fecal pellets fluxes and depth (r2 = 85.2% and p = 0.001, n = 9). Comparison with similar data from the northwestern Mediterranean and other oceans suggests that the Alboran Sea is a relatively clean environment primarily due to its relative remoteness from input terrigenous sources.

1. Introduction Direct measurements of particle-associated contaminant flux using sediment traps are of primary

* Corresponding author. Fax: 34-3-204 59 04. 0304-4203/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0304-4203(95)00084-4

importance for estimating residence times and transport rates of anthropogenic compounds in aquatic environments (Baker et al., 1991; Fowler, 1991). Studies carried out during the last two decades have shown that large, rapidly sinking particles, although scarce, account for a significant portion of the total flux of organic contaminants (Elder and Fowler,

J. Dachs et al./ Marine Chemistry 52 (1996) 75-86

76

1977; Osterroht and Smetacek, 1980; Bums and Villeneuve, 1983; Bums et al., 1985; Fowler and Knauer, 1986; Broman et al., 1988; Fowler et al., 1990; Lipiatou et al., 1993). Thus, biological or physico-chemical mediated processes leading to the formation of large, fast sinking aggregates are key factors controlling the fate of pollutants in the sea. However, knowledge of the adsorption-desorption processes of organic contaminants with sinking particles as well as their biotic and abiotic transformations are aspects which require further study. To date sediment trap experiments designed to measure PAH and PCB fluxes in the Mediterranean have only been conducted in the northwestern region (Bums and Villeneuve, 1983; Bums et al., 1985; Fowler et al., 1990; Lipiatou et al., 1993). Consequently, the present work focused on the southwestem basin, an area with a unique hydrographic regime (Font, 1987) and characterized by a high primary productivity driven by physical processes (Lohrenz et al., 1988; Videau et al., 1994). In the present sediment trap fluxes of study, time-series organochlorine compounds (i.e. PCBs, 4,4’-DDE, and y-HCH) and polycyclic aromatic hydrocarbons (PAHs) were measured in the Alboran Sea (southwestern Mediterranean) at three water column depths (250,500 and 750 m) during a 3-month experiment.

Ir

n

Fluxes and concentrations of the different chemical compounds were analyzed by multiple linear regression using other bulk parameters such as total particle mass, organic carbon, fecal pellets and depth in order to obtain further insight into the particle-compound associations.

2. Materials and methods 2.1. Site description The Alboran Sea, with a surface area of roughly 5.4 X lo4 km’, is the most western portion of the Mediterranean Sea situated between Spain and the north African coast (Fig. 1). Thermohaline differences between the Atlantic and Mediterranean lead to a large exchange of water through the Gibraltar Strait with a net positive inflow towards the Mediterranean which compensates the evaporative losses. The water inflow results in an anticyclonic gyre in the western Alboran Sea which displays great variability in extent, shape, strength and location on time scales of days to months (Millot, 1987). This anticyclonic gyre leads to the formation of upwelling off the Spanish coast which increases the productivity of the area (Estrada et al., 1989). Vertical CTD profiles

SPAIN

36’

Fig. 1. Study area in the Alboran Sea showing the location of the sediment trap mooring.

J. Dachs et al. /Marine

show that the Atlantic water mass (< 37%0) flows into the Mediterranean in the upper 150 m of the water column. Consequently, all the trap collection depths were within the Mediterranean water mass (200-600 m, intermediate and > 600 m, deep water). Urban effluents of primary treated sewage from coastal cities, tourist resorts and agricultural activities (Fig. 1) are the major point sources of pollution in the western Alboran Sea because there are no significant river discharges into the entire Alboran basin. Moreover, atmospheric deposition is believed to be the major transport route of pollutants in the region (UNEP/WHO, 1992). In addition, the area is subjected to heavy maritime traffic. 2.2. Sampling A mooring with three sediment traps at 250, 500 and 750 m was deployed in the Alboran Sea (36 04.8’ N, 04 14.1 W) at ca. 1200 m water column depth during the R/V Valdiuia EROS-2000 cruise in 1992 (Fig. 1). Particles were collected using a programmable time-series sediment trap (Technicap PPS3, Cap d’Ai1, France) equipped with a six cup PTFE collector. Sequential samples of 15 days duration each were obtained from February 27 to May 27, 1992. The cylindro-conical sediment trap dimensions are 0.125 m2 of surface area and an aspect ratio (height/diameter) of 2.5. A 2% buffered formaldehyde solution was used as sample preservative. Details for sample preparation and organic carbon measurements have been described previously (Miquel et al., 1994). Upon recovery of the trap moorings, the wet samples were transferred to acid washed vials and stored at 4°C in the dark until they were processed in the laboratory. The particulate material was first wet sieved through a l-mm nylon mesh to remove large plankton which frequently entered into the traps. Samples were then examined under a dissecting microscope and any swimmers noted were removed by hand-picking (Michaels et al., 1990). The remaining sample was desalted and freeze-dried for later analyses. 2.3. Analytical procedures Aliquots of freeze-dried particulate material (50100 mg) were spiked with octachloronaphthalene

Chemistry 52 (1996) 75-86

77

and perdeuterated pyrene as analyte surrogates, and were extracted (3 times) with 5 ml of dichloromethane-methanol (2: 1) by sonication. Organic extracts were fractionated by column chromatography (5 X 20 mm> using 2 g alumina, previously activated at 120°C. Two separated fractions were collected: (I) 6 ml of n-hexane (PCBs), (II) 5 ml of 2:l dichloromethane-n-hexane (DDE, lindane, PAHs). Elemental sulphur was removed from both fractions (I and II> by an activated powdered copper treatment. 2.4. Instrumental

analysis

Fractions I and II were analyzed in a 5890 Hewlett-Packard GC (Palo Alto, USA) equipped with an ECD detector. Samples were injected in the splitless injection mode at 280°C and detector temperature was held at 310°C. A fused silica capillary column of 30 m X 0.25 mm i.d. coated with 0.25 pm of DB-5 was used. Helium was the carrier gas supplied at 30 cm s- ’ . PAHs were analyzed by GC-MS in a MD 800 apparatus (Fisons, Milan, Italy) using a SIM acquisition programme under electron impact ionization (70 eV energy) containing the following diagnostic ions: 178, 192, 206, 184, 198, 212, 202, 226, 228, 252, 276 and 278. Dwell time was approximately 70 ms. Other analytical conditions were similar to those described above for the GC-ECD analysis. Total, organic and inorganic carbon were determined as described elsewhere (Miquel et al., 1994). 2.5. Quantitation Quantitation was performed by the external standard procedure. The calibration mixture contained the analyte surrogates spiked in the sample and all the target analytes in the case of the organochlorine compounds and 14 PAHs which are included in the U.S. E.P.A. priority pollutant list. Recoveries of spiked samples according with the standard addition procedure were higher than 80% and the RSD was below 15% (N = 3). Procedural blanks and control samples were processed in the same manner as real samples and they were below 5% of the abundance of analytes. Results were corrected for recovery.

J. Dachs et al. /Marine

78

3. Results and discussion 3.1. Mass fluxes of bulk parameters During late winter-early spring 1992, average downward mass fluxes at 250, 500 and 750 m water column depth in the western Alboran Sea were 235, 169, and 197 mg m-* d- ‘, respectively (Table 1). These particulate fluxes are some of the highest reported for the open western Mediterranean. For example, fluxes along the Nice-Corsica transect of 178 mg m-* d- ’ at 200 m (Marty et al., 1994, period February-July) and of 111 and 22 mg rnv2 d-’ at 20 and 1000 m, respectively (Miquel et al., 1994, period January-December) were lower than those measured in the Alboran Sea. Peinert and Miquel (1994) working in the eastern Alboran Sea measured spring fluxes from 20 to 390 mg m-* d-’ in the upper 300 m of the frontal area. Likewise, the organic carbon fluxes measured in our study (15.618.2 mgC m-* d-i) were similar to or higher than those reported for the northwestern Mediterranean (Marty et al., 1994; Miquel et al., 1994). Peinert and Miquel (1994) also found high POC fluxes in the Eastern Alboran Sea (mean of 30.2 mg m-* d- ’ at 100 m depth). Only measurements made on the slope in the Gulf of Lions exhibited higher fluxes of organic carbon (92.7 mg m-* d- ‘, Buscail et al., 1990) than in the Alboran Sea. Consequently, the Alboran Sea can be viewed as an area of relative high productivity in the Mediterranean which is probably related to its peculiar, seasonally-driven hydrographic characteristics (Font, 1987; Videau et al., 1994). Organic carbon accounted for 65% of the total carbon (Table l), which suggests the presence

Chemistry 52 (1996) 75-86

of a small contribution of cocolithophorids that are often responsible for most of the inorganic carbon flux in other seas (Honjo, 1982). Carbonate fluxes decreased with depth as has been previously reported in different areas (Wakeham et al., 1980; Matsueda and Handa, 1986; Miquel et al., 1994). Conversely, mass, total fecal pellet, total carbon, organic carbon and nitrogen fluxes were fairly constant throughout the water column. The somewhat higher mean mass flux (197 mg m-* d-l) at 750 m compared to the average flux at 500 m was due to a pulse of enhanced particle flux (605 mg m-* d- ‘> at 750 m that took place during the period 13 to 28 March. This pulse was coupled to a major flux of primary particles through 250 m which occurred approximately 15 days earlier. Zooplankton fecal pellets were a principal component of the particles sampled at 500 and 750 m during that period and their presence suggests that strong grazing activity in the overlying waters was occurring during March (Fowler et al., in prep.). 3.2. Sources of organic contaminants 3.2.1. Organochlorine compounds The average distribution pattern of PCBs at 250 m

depth with maximum abundances of congeners IUPAC no. 52, 118 and 153 is characteristic of Clophen Am-A54 mixtures (Schulz et al., 1989) (Fig. 2B). The distribution of the individual PCB congeners in sinking particles is closer to the dissolved than to that found in the suspended particulate matter, which is enriched in the highly-chlorinated, substituted congeners (IUPAC nos. 118, 153 and 138) (Valls et al., 1990; Tolosa, 1993). The congener distribution is

Table 1 Average daily fluxes (mg m-* d- ‘1 measured with sediment traps in the Alboran Sea, 27 February-27 May, 1992 Trap depth

Mass flux Total carbon Organic carbon Carbonate Total fecal mass Nitrogen a Ranges given in parentheses.

250

500

750

234(153-510) ’ 23.3 (12-39) 15.6 (7-24) 7.7 (5-14) 4.6 2.7 (1.3-4.4)

169 (57-254) 24.5 (8-74) 18.2 (6-62) 6.3 (2- 12) 6.5 2.5 (1.0-7.9)

197 (58-605) 23.6 (5-71) 17.8 (S-52) 5.8 (l-19) 6.8 3.1 (0.7-10.5)

J. Dnchs et al./Marine

Chemistry 52 (1996175-86

similar to that reported in settling particles from the Lake Superior (Baker et al., 1991). Taking into consideration the magnitude of organic contaminant concentrations and their partitioning behaviour, Baker et al. (1991) concluded that rapidly sinking particles are solids that have acquired the organic contaminants through food-chain transfer processes. On the other hand, the PCB distribution in all particles collected at the site showed an enrichment in the lesser chlorinated congeners. Such a distribution is the likely result of a chlorination-dependent fraction-

79

ation process which occurs during the seaward transport of the PCB compounds. According to their phase association, the lesser chlorinated congeners are those which are more mobile and, thus, are transported further from the source (Bidleman, 1988). A similar trend has been noted in sediment transects collected from the northwestern Mediterranean basin (Tolosa, 1993). The relative remoteness of the Alboran Sea sampling site from land-based sources of PCBs is consistent with the PCB congener distribution we found in the sinking particles.

PAH

0

0

B

Ph

CP-Ph DBT CP-DBT FL Ant. Cl-DBT Cl-Ph

5r~-~-.~-^

Cr

Pv

. BaA

BFI

Pei BePv BaPy

PC6

I

DDE

I1250

500

Lindane

0

750m I

Fig. 2. Individual average contaminant concentrations (ng/g) in sedimenting particles from different water column depths (250, 500 and 750 m). (A) PAHs. Compound identification is as follows: Ph, phenanthrene; C,-Ph, methylphenantbrenes; C,-Ph, dimethylphenauthrenes; Ant, anthracene; DBT, dibenzothiophene; C ,-DBT, methyldibenzothiophenes; C,-DBT, dimethyldibenzothiophenes; Fl, fluoranthene; Py, pyrene; BaA, benz[a]authracene; Cr, chrysene; BFl, total benzofluoranthene isomers; BePy, benzdelpyrene; BaPy, benzda]pyrene; Per, petylene and(B) PCB congeners (IUPAC nos. 28, 52, 101, 118, 153, 138 and 180). DDE and lindane.

80

J. Dachs et al. /Marine

Lindane (y-HCH) and 4,4’-DDE were the only organochlorine pesticides identified in all the samples analyzed. The occurrence of y-HCH as a major HCH isomer is consistent with the usage of lindane ( > 99%) in the region rather than benzene hexachloride (BHC) which is a multicomponent mixture used elsewhere in the northern Europe (65-70% CX-HCH and 12-16% y-HCH, Ballschmiter and Wittlinger, 1991). The predominance of 4$-DDE over the parent pesticide (4,4’-DDT) indicates a lack of recent inputs of diphenylethane pesticides, the prevalence of oxic conditions in the water column (Wolfe et al., 19771, and the absence of long-range transport in the region. Likewise, during 1985-86 in the LacazeDuthiers canyon in the northwestern Mediterranean, 4,4’-DDT was also identified, however, its main metabolites (DDE and DDD) were more prominent than the parent pesticide (Fowler et al., 1990). 3.2.2. PAHs The PAH distribution, with maximum concentrations of phenanthrene and dibenzothiophene and remarkably high concentrations of their mono- and dialkyl-substituted homologs (Fig. 2A), is characteristic of the prevalent sources of fossil fuel PAHs (Sporstol et al., 1983). Indeed, the high concentration of pyrene relative to fluoranthene, chrysene-triphenylene and bem$a]anthracene is further evidence supporting the prevalence of fossil fuel PAHs in the region. Nevertheless, pyrolytic PAHs (i.e. benzofluo ranthenes and benzopyrene isomers) are also present but at concentrations one order of magnitude lower than fossil fuel PAHs. Furthermore, the low concentration of perylene is consistent with the pyrolytic origin of this compound (Venkatesan, 1988). 3.3. Concentration of contaminants 3.3.1. Organochlorine compounds Levels of PCBs (as Clophen A40 equivalents) in the Alboran Sea (Fig. 2B) are higher than the concentrations measured in a sediment trap samples from coastal waters in the Ligurian Sea at 80 m depth (Tolosa, 1993). Earlier studies carried out at the same site off Monaco indicate a decrease of at least one order of magnitude in concentrations during the last two decades (12-620 ng g-‘, Fowler et al., 1979). These data from the coastal Ligurian Sea

Chemistry 52 (1996) 75-86

reflect the effectiveness of the regulations in the usage of PCBs and is particularly apparent in the reduction of contaminant concentrations in marine particles near the PCB terrestrial source. However, due to the stability of these compounds, their concentrations in particles are still high in more remote areas such the Alboran Sea. The higher concentrations of PCBs measured at 3200 m in the Sargasso Sea during 1978-1980 than those found in our 1992 study in the Alboran Sea are consistent with a temporal decline in PCB concentrations in sinking particles in open sea regions. Similarly, the 4,4’-DDE concentrations found in the Alboran Sea were higher than those measured in the Ligurian Sea (2.4-5.5 rig/g;; Tolosa, 1993) where 4$-DDE predominates over the parent pesticide. Lindane concentrations found in the Alboran Sea were consistently higher than the previous reported values for the northwestern Mediterranean (Bums et al., 1985; Fowler et al., 1990). The higher lindane concentrations present in the southwestern Mediterranean could be accounted for by a greater usage in the agricultural areas surrounding the Alboran Sea. 3.3.2. PAHs Total average particulate PAH concentrations in the Alboran Sea (0.10-2.8 pug g-i, Fig. 2A) are consistently lower than values recently found in the coastal Ligurian Sea (l-12 pg/g, Raoux et al., 1995) and along a transect from Nice to Corsica (0.5-4.07 lug/g, Lipiatou et al., 1993). The concentrations measured in our study are similar to those reported for pristine areas such as Dabob Bay, USA (Prahl and Carpenter, 1979) and lower than more polluted waters such as the Stockholm archipelago (Broman et al., 1988) and Puget Sound, USA (Bates et al., 1984). Consequently, the Alboran Sea appears to be a rather pristine environment as concerns PAH-related compounds. 3.4. Contaminant fluxes 3.4.1. Organochlorine compounds Average fluxes of the organochlorine compounds are shown in Fig. 3A. Average fluxes of PCBs (as Clophen A40 equivalents) through 250, 500 and 750 m in the water column were of 11.8, 13.1 and 18.5 ng m-* d-l, res pectively. These average values are

J. Dachs et a/./Marine

Cl-Ph

0

’

6

0.8 b

Ant.

I

Chemistry 52 (1996) 75-86

Cl-DBT

FI.

0aA

81

BFI

BaPy

PCB

(

0.6

B ?0.4 3.2 0

28

52

101

118

153

138

180

DDE

Linda

Fig. 3. Average fluxes (ng m-* d- ’ ) a t different depths (‘250, 500 and 750 m) of (A) PAHs and (B) individual lindane. For compound identification please see Fig. 2 legend.

higher than deep water fluxes reported for the Sargasso Sea (Table 2) and lower than or similar to those found in the Lacaze-Duthiers Canyon (Table Table 2 Selected fluxes (ng m-* Sampling

d- ‘) of organochlorinated

site

Sargasso Sea Lacaze-Duthiers Tongue of Ocean Ligurian Sea (W. Kiel Bight (Baltic

canyon (Bahamas) Medit.) Sea)

PCB congenem,

21, and offshore Monaco (Table 2), and similar to those in the Tongue of the Ocean off the Bahamas (Table 2). Fluxes of PCBs in the western Baltic Sea

contaminants

PCBs ’

DDE

?HCH

References

4.4 146 13.4 n.r. 186

n.r. 2.2 n.r. 3.6 103

n.r. 9.9 nr. 2.5 512

Knap et al., 1986 Fowler et al., 1990 Harvey and Steinhauer, 1976 Bums et al., 1985 Osterroht and Smetacek, 1980

n.r.: not reported. a Total PCBs reported as Aroclor equivalents.

DDE and

J. Dachs et al./Marine

82

Chemistry 52 (1996) 75-86

(Table 2) were 4 orders of magnitude higher than the western Alboran Sea. Consequently, the fluxes in the Alboran Sea are most likely characteristic of more pristine environments remote from pollution sources. Atmospheric deposition appears to be the predominant input of PCBs into the Alboran Sea. In fact, combined dry and wet deposition for the northwestem Mediterranean basin were estimated to be 62.7 ng me2 yr- ’ (Villeneuve and Cattini, 1986). Unfortunately, no comparable data are available at present for the southern basin, but atmospheric input is expected to be lower due to its greater distance from land-based sources of pollution. Fluxes of the major chlorinated pesticides are also shown at Fig. 3B. These fluxes were lower than those reported for the Lacaze-Duthiers Canyon during 1985-1986 (Table 2) and comparable to those which have been measured in the Ligurian Sea (Table 2). Correlation was examined between the fluxes of organochlorine compounds and fluxes of bulk parameters (mass, organic carbon and fecal pellets) and the sediment trap depth (Table 3). The regression factor (r2> was dependent upon the class of compounds, however, it was higher than 85% (n = 9) at a confidence level (p> of 99.99% considering organic carbon and fecal pellet fluxes as well as depth. The covariability of organic carbon and total PCB fluxes with depth for three sampling periods is shown in Fig. 4A. Mass fluxes were not correlated with any of the organochlorine compounds examined. In con-

organic carbon fluxes were closely correlated with fluxes of the organochlorine compounds according to relative, i.e. the higher the hydrophobicity of the organochlorine compound, the stronger the correlation between the two parameters. However, lindane, the compound with the lowest hydrophobicity (log Kow = 3.961, did not covary with the organic carbon flux. PCBs and 4$-DDE with a higher hydrophobicity (log Kow 5.5-7.2) exhibited a significant correlation (Table 3). Knap et al. (1986) have also reported a significant correlation between PCB fluxes and organic carbon content of sinking particles collected in the Sargasso Sea south-east of Bermuda. Fecal pellet fluxes were negatively correlated with fluxes of PCBs and y-HCH, whereas no correlation was found with DDE. Although fecal material was abundant in the traps (3.4 X 10e3 to 2.0 X lo4 fecal pellets me2 d-l), their overall contribution to the mass flux was only 0.6 to 9% (Fowler et al., in prep). This relative contribution is much lower than those reported for other areas of the NW Mediterranean Sea (Miquel et al., 1994) and could, at least partly, explain the negative correlation between ‘yHCH and PCB fluxes and the flux of fecal pellets. This observation is particularly surprising since the important role of fecal pellets in the transport of PCBs to the deep ocean has been well documented (Elder and Fowler, 1977). Furthermore, fecal pellet fluxes apparently were not closely related to DDE fluxes, however, organic carbon content in particles

Table 3 Parametric coefficients and variable contribution of contaminants and bulk oarameters

(%I obtained by multiple linear regression

Contaminant

class

PCBs 4,$-DDE Lindane Total PAH Fossil PAHs ’ Pyrolytic PAHs e

to the overall regression

trast,

cm)

log Kow il

Mass

Organic carbon

Fecal pellets

Depth

5.5-1.2 5.7 3.96 4.6-6.2 N.A. 4.5-6.2

N.S. N.S. N.S. 0.732 (88.3%) N.S. 0.252 (90.7%)

0.076 b (49.2%) ’ 0.02 (85.9%) N.S. 3.75 (2.4%) 4.54 (27.3%) -0.31 (1.7%)

-0.151 (27.8%) N.S. - 0.089 (26.8%) N.S. 4.25 (49.1%) N.S.

0.023 (20.6%) N.S. 0.043 (58.4%) N.S. N.S. N.S.

N.S.: not significant, N.A.: not available. a Data sources: Mackay et al., 1992; Ballschmiter and Wittlinger, 1991; Dunnivant and Elzerman, 1988. b Parametric coefficients of multiple linear regression equation. ’ Contribution of the variable to the total regression in percentage. d Sum of methylphenanthrenes, dimethylphenanthrenes, methyldibenzothiophenes and dimethyldibcnzothiophenes. e Sum of anthracene, fluoranthene, benz(a)anthracene, ~benzofluranthenes, Ebenzopyrenes and perylene.

analysis between fluxes

r2

P (%)

97.6 85.9 85.2 90.7 76.4 92.3

0.00 0.00 0.00 0.00 0.00 0.00

J. Da&

et al./

Marine

Chemistry

exhibited a higher correlation with DDE than with PCBs. In addition, fluxes of PCBs and lindane were positively correlated with the water column depth (Table 3). ,2

0

Org.

C.dFlux(mz-2

d-’ )

48

80

.A_-

52 (1996)

75-86

83

3.4.2. PAHs Fluxes of individual PAHs at different water column depths are displayed in Fig. 3A. Total fluxes were 0.22-0.24 pg m-’ d- ‘, and are lower than

A

250

,-:_: 250: 7

3

a

/I

cgm 8

PO P(

. . --. .-_ . .

750

750

0

0.1

0.2

0.5

0

0.6

1.4

PcE%ux (ng $id.,)

PAH Fl$ug II%% ) Mass Flux (g t+ d-’ )

0

.

.

Or& C. Flu;Jmg rn:l-l)

10

7

5.6

5.

60

B 250

2 5500

+

8

*

750

: 0

0.1

0.2

F,:(ug

0.5

rib-l

0.6

1.4

0

5.6

0

12

tit )

Org. Ck4Flux(rngza

7

PCE%JX (ng 13 d-l )

PAH ) Mass Flux (g ma d” )

46

60

Y----l

0

0~~ C. Flu;Jmg rn:;‘)

10

5.

60

C 250

750 __.

I 0.1

0

0.5

0.2

0.6

PAH Ffi (g rn”jel ) Mass Flux (g mr d-1)

[A PAH flux

-x MassFlux m Org.C. Flux1

0

1.4

2.6

4.2

5.6

-I 7

PCB Flux (ng me2d-l ) 1f

PC8 flux

m Org.C. Flux]

Fig. 4. Mass, organic carbon, PAH and PCB fluxes with depth during three sampling periods in 1992 (A: March 13-28; B: April 12-27; C: May 12-27). Fluxes of the remaining sampling periods are not shown here because PCB concentrations were below the detection limit (ca.

I ng g-’ dry wt.).

84

J. Dachs et al./Marine

those reported for 200 m in the northwestern Mediterranean (0.67-0.91 pg m-* d- ‘, Lipiatou et al., 1993) and at 80 m in the Ligurian Sea (0.12-10 pg me2 d- ‘, Rao ux et al., 1995). In comparison, fluxes reported for the Stockholm archipelago (Baltic Proper) are higher ranging from 0.15 to 1.l pg rn-’ d- ’ (Broman et al., 1988). Accordingly, PAH fluxes in the Alboran Sea could be considered as typical background values for the western Mediterranean basin. Crimalt et al. (1988) have estimated atmospheric depositional fluxes for the Alboran Sea ranging from 5 to 28 ng m-* d- ’ (dry plus wet deposition) from aerosol samples collected at sea level. Taking into consideration the lower atmospheric depositional fluxes of PAHs than those found in sinking particles in the water column, and the prevalence of pyrolytic over fossil fuel PAHs, in the aerosol contaminated particles sinking through the water column could be attributed to an alternative source of PAHs. It is likely that accidental oil spills and tanker ballast operations could be the main source of the fossil fuel hydrocarbons measured in the samples. Fluxes of total PAHs were correlated with organic carbon (Table 3) however the correlation with mass flux showed greater significance. Fig. 4B shows the covariability between organic carbon and mass fluxes with depth. In order to obtain further insight into the mechanism of transport, correlation analyses were performed according to the molecular weight of PAHs. While the low molecular weight PAHs were correlated with organic carbon and fecal pellet fluxes, the pyrolytic compounds covaried with mass and organic carbon fluxes. These results are consistent with the particulate characteristics of pyrolytic-derived PAHs. On the other hand, the fossil fuel PAHs are mostly associated with the dissolved phase, and could be scavenged by organic rich particles such as fecal pellets which are known conveyors of organic contaminants to the deep sea. Our findings on particulate-associated organic contaminants reflect the importance of the routes of transport and phase association in the fate of PAHs, PCBs and chlorinated pesticides in the southwestern Mediterranean, a region which is characterized by a high particle fluxes. However, further research is needed in order to fully understand the water column and bentbic layer processes which affect the ultimate fate of these trace contaminants.

Chemistry 52 (1996) 75-86

4. Conclusion Concentration and fluxes of high priority, organic contaminants in sinking particles collected in the Alboran Sea are characteristic of a rather pristine environment due to the relative remoteness of this region from pollution sources. Whereas atmospheric fallout is the most likely source of pyrolytic PAHs and PCBs in the region, oil spills and deballasting could account for the fossil fuel PAHs measured in the particles. The prominence of 4,4’-DDE over the parent pesticide (DDT) is consistent with the lack of recent inputs of diphenylethane pesticides in the region. On the other hand, the relatively high abundance of lindane ( y-HCH) reflects a pattern of recent usage in the riparian countries.

Acknowledgements

Financial support was obtained from the CEC STEP and MAST Programmes under EROS-2000 (Contracts EV4VOlllF and MAST-0016-C(EBD)) and the Spanish Plan for Research (Grant NAT 93-0693). One of us (J.D.) is indebted to the C.S.I.C. for a predoctoral fellowship. The crew of the R/V Vuldiuiu and J. La Rosa are thanked for their help in collecting the samples, and J.L. Teyssie for his assistance with sample preparation. The IAEA Marine Environment Laboratory operates under a bipartite agreement between the International Atomic Energy Agency and the Government of the Principality of Monaco.

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