Toxicity evaluation of produced formation waters after filtration treatment

doi:10.4236/ns.2010.21005

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Vol.2, No.1, 33-40 (2010) Natural Science

http://dx.doi.org/10.4236/ns.2010.21005

Toxicity evaluation of produced formation waters after

filtration treatment

Loredana Manfra, Chiara Maggi, Jessica Bianchi, Michela Mannozzi, Olga Faraponova, Livia

Mariani, Fulvio Onorati, Andrea Tornambè, Claudia Virno Lamberti, Erika Magaletti

ISPRA, Advanced Institute for Environmental Protection and Research, Rome, Italy; [email protected]

Received 19 June 2009; revised 24 July 2009; accepted 28 July 2009.

ABSTRACT

During the last years many authors have char-

acterized the produced formation waters (PFWs)

with respect to chemical compounds and toxic-

ity. Most of data are related to PFWs collected on

offshore platform after treatment process. The

available results showed that the particulate

phase had an influence on PFW toxicity. As-

suming the toxicity of PFWs treated on platform,

the aim of this paper is to study the toxicity of

these PFWs after a further filtration treatment

carried out in laboratory. For this purpose PFWs

were sampled from three natural gas platforms

located in the Adriatic Sea (Italy) below treat-

ment system. The eco-toxicological bioassays

have been conducted on test-organisms be-

longing to different trophic levels such as bac-

teria, algae, crustaceans and fishes. The PFWs

resulted toxic according to an overall assess-

ment obtained through the bioassays. Further-

more, it has been possible to identify the spe-

cies that were more sensitive to the tested PFWs,

namely Tigriopus fulvus, Dicentrarchus labrax

and Vibrio fischeri. Besides, a chemical char-

acterization was reported related to the con-

taminants present in the PFWs to go with

eco-toxicological assessment. Barium, zinc and

manganese showed the most concentrations

among the metals and the lower molecular

weight components were common among the

organic compounds. Some differences among

PFWs were observed both for toxicity and

chemical composition. The highest toxicity was

recorded in PFWs (PFW1 and PFW2) containing

the highest concentrations of some metals (Ba,

Mn and Zn) and/or BTEX.

Keywords: Adriatic Sea (Italy); Offshore Platforms;

Natural Gas Production Fields; Produced Formation

Waters; Toxicity Assessment; Bacterium (Vibrio

Fischeri); Algae (Dunaliella Tertiolecta and

Phaeodactylum Tricornutum); Crustaceans

(Artemia Franciscana and Tigriopus Fulvus); Fish

(Dicentrarchus Labrax); Chemical Characterization

1. INTRODUCTION

Produced formation water (PFW) is water naturally pre-

sent in sedimentary formations from which oil and gas

are mined. It is piped to the surface during the produc-

tion process and may be discharged into the sea when

the rejection is not possible. Before discharge, PFWs are

treated directly on platform to reduce oil and solid sus-

pended content [1]. In spite of this treatment, PFWs still

include oil and particles.

In Italy, like in other Countries, the legislation binds

to control the oil content in the PFW when they are dis-

charged into the sea [2]; for this reason, the PFW char-

acterization has been limited for several years to meas-

urement of “oil in water”, which means analysis of non

polar aliphatic hydrocarbons. However, PFW contains a

variety of compounds such as metals (i.e. barium, copper,

zinc, and iron), volatile aromatic compounds (benzene,

toluene, ethylbenzene, xylenes, called BTEX), semi-

volatile compounds (naphthalene, phenanthrene, diben-

zothiophene and their C1-C3 alkyl homologues), phenols

alkylated up to C7, organic acids (C1-C6 compounds) and

some additives of possible employment (i.e. diethylene

glycol, called DEG) [3].

For this reason, during the last years many authors

have characterized PFWs with respect to these com-

pounds (metals, aromatic and aliphatic hydrocarbons,

phenols and additives) and to the toxicity of PFWs.

The most data-gathering is related to PFWs collected

on platform after treatment process and untreated in

laboratory later on [4-8]. Few data are referred to

PFWs collected on oil platforms below treatment sys-

tem and filtered in laboratory subsequently [3,9].

There are scattered data about PFWs originated from

Italian offshore gas installations (Adriatic Sea): some

L. Manfra et al. / Natural Science 2 (2010) 33-40

chemical analyses were made on seawaters and mussels

near Adriatic platforms [10]; a methodological approach

was proposed to study the environmental impact of oil

and gas offshore platforms [11]; preliminary results were

published on metal content and toxicity of PFWs coming

from gas Adriatic platforms [12-15].

In these studies, the PFWs generally showed to be toxic

and their toxicity was higher for samples unfiltered in

laboratory. This effect was observed probably because of

particulate phase influence. The effects of particulate could

be to mechanic level (oral ingestion and digestion) and/or a

chemical process (adsorption) [7,12].

The aim of this paper was to investigate the toxicity of

PFWs originated from three natural gas platforms in the

Adriatic Sea (Italy). These PFWs were collected below

treatment system occurred on platforms and then filtered

in laboratory. Their toxicity was evaluated using the in-

tegrated response of many species. The eco-toxicological

battery included six species belonging to different tro-

phic levels: a bacterium (Vibrio fischeri) representative

of the debris chain, two algae species (Dunaliella tertio-

lecta and Phaeodactylum tricornutum) as primary pro-

ducers, two crustaceans (Artemia franciscana and Ti-

griopus fulvus) as primary consumers and a fish (Dicen-

trarchus labrax) as representative of the highest trophic

level (secondary consumer).

Besides, a chemical characterization of PFWs was re-

ported to go with eco-toxicological assessment. We in-

vestigated the metals, BTEX, PAHs and DEG. Metals

and PAHs were analyzed both in filtered and particulate

PFWs, because these compounds are present above all as

particles [7,16]. BTEX and DEG were recorded directly

in the whole sample of PFWs. This choice was necessary

because BTEX are partitioned between gas and liquid

phases, therefore the particulate matter does not influ-

ence their concentration; moreover they are volatile

compounds and the filtration procedure causes loss of

analytes. DEG was also analyzed in unfiltered sample

because it is highly soluble in water, not much volatile

and it does not tend toward absorption on particles [17].

Analytical methods by themselves were not able to

give information on what happens when organisms are

exposed to PFWs, which concentrations are toxic and

which is ecological impact of a PFW discharge. The use

of bioassays, together with the classic chemical analyses,

can contribute to the understanding of these aspects.

2. MATERIALS AND METHODS

2.1. Sampling and Sample Treatment of

Produced Formation Water (PFW)

PFW samples were collected from three different gas

platforms situated at about 20 km off the Adriatic coast

(Pescara and Rimini, Italy): one of these (PFW1) was

collected in October 2005 and the other two (PFW3 and

PFW2) in June 2006.

On offshore platforms PFW is stored in a tank which

empties when it is full load. All PFWs were sampled

from a tap located on the platform, which receives the

PFW after this has had a physical-chemical treatment

(depressurization, gravity separation techniques, activa-

ted carbon filtration). The physical-chemical parameters

of PFWs (salinity, pH, conductibility, ORP and oxygen

dissolved) were measured in laboratory by multi-pa-

rameter probe (YSI, mod. 556MPS) (Table 1).

For the bioassays, about ten litres of PFW were im-

mediately filtered (Millipore®, 0.45 µm) and refrigerated

in polystyrene vessels at 4°C until their execution. The

bioassays were carried out in 72 hours.

The PFWs were stored in different containers accord-

ing to type of chemical analyses. For the metals two li-

tres were filtered (Millipore®, 0.45 µm), acidified with

high purity nitric acid and refrigerated at 4°C until

analysis; the filters were stored at -20°C. For BTEX 10

mL of PFW were stored in SPME dark vials (Varian S. p.

A); a magnetic stirrer bar was inserted in each vial prior

to sealing the vial by magnetic steel closures equipped

with Teflon septa. The vials were refrigerated at 4°C and

the samples were acidified at pH=2 with HCl and satu-

rated with NaCl. For the PAHs analysis, one litre of

PFW was immediately filtered (Millipore®, 0.45 µm)

and, together with the filters, stored at 4°C. For the DEG

analysis one litre of sample was collected in dark glass

bottles, saturated with mercury chloride and refrigerated

at 4°C to avoid photochemical and bacterial activity.

2.2. Bioassays

The bioassays were carried out on filtered samples, ac-

cording to the methods reported in Table 2 and summa-

rized for each taxon as follows:

Bacteria: Controls and different concentrations for each

PFW sampled (dilution ratio 1:2) were tested according to

the Basic Protocol [18] and the method ISO [19] with

Table 1. Physical-chemical parameters of production formation water and information on platforms.

PFW Salinity

(PSU) pH Conductibility

(mS/cm2) ORP

Oxygen

dissolved

(%)

Volume flux of

PFW (mc/year)

Platform

Installation

(year)

Platform distance

from coast (Km)

Water

depth

(m)

PFW1 34 7 51 -10093 6000 1991 36 116

PFW2 37 7 56 -10596 3000 1972 15 18

PFW3 37 8 55 -7086 3000 1991 21 23

L. Manfra et al. / Natural Science 2 (2010) 33-40

bacteria coming from freeze-dried SDI. PFW salinity was

not adjusted prior to testing. The Software Microtox Om-

niTM v. 1.16 was utilized to calculate the EC50 and EC20

values (effect concentration of 50% and 20% respectively)

and the Dunnett test was used to calculate the NOEC

value (no observed effect concentration).

Algae: One control and some concentrations for

each PFW sampled were tested according to the ISO

method [20] with Phaeodactylum tricornutum strain

1090-1° and Dunaliella tertiolecta strain 13.86, ob-

tained from the Plant Physiology Institute of Gottingen

University (Germany). Algal growth medium was

prepared with artificial seawater [20]; for D. tertio-

lecta nutrients, according to the IRSA-CNR method

[21] and vitamins according to the ISO method [20]

were added. The algal inoculum had an initial density

of 10000 cells mL-1 ± 10% for P. tricornutum and 2000

cells mL-1± 10% for D. tertiolecta. Regression analysis

technique was performed for the determination of EC50

and EC20; the Dunnett test was used to calculate the

NOEC value.

Crustaceans: A control and some concentrations for

each PFW sampled were tested with nauplii of Artemia

franciscana , according to the APAT IRSA-CNR method

[22], and with nauplii of Tigriopus fulvus, according to

the ISO/FDIS method [23] as modified by Faraponova

et al. [24,25]. Reference cysts of A. franciscana were

obtained from the Quality Assurance Research Divi-

sion U. S. Environmental Protection Agency (Cincin-

nati OH 45268, USA) or from the Laboratory for Bio-

logical Research in Aquatic Pollution, University of

Ghent (Belgium). The eggs of A. franciscana were

hatched in synthetic seawater and the nauplii were

used within 48 hours of hatching [22]. Synchronized

nauplii (24-48h) of T. fulvus were collected from a

culture of two hundred females taken from a mass

laboratory culture originated from the Italian coast

(Calafuria, Livorno) and supplied with an algal mix-

ture (Tetroselmis suecica and Isochrysis galbana, ratio

1:2). Probit analysis was performed for the determina-

tion of EC50 and EC15, the Dunnett test was used to

calculate the NOEC value.

Fish: One control and some concentrations for each

PFW sampled were tested with juveniles of Dicen-

trarchus labrax (80 days old, length of 3.74±0.28 cm

and weight of 0.48±0.08 g), according to the EPA [26]

and OECD [27] methods. Organisms were supplied by

the hatchery production plant ASA (Rome), stabled in

synthetic seawater with salinity of 20±1 PSU for 15 days

and fed with granulated food until 24 hours before the

test. Probit analysis was performed for the determination

of EC50 and EC15, the Dunnett test was used to calculate

the NOEC value.

The results were compared to a toxicity scale reported in

Table 3. On the basis of this toxicity scale, the samples

were classified as follows: 1) toxic 10≤ EC50<100, 20≤

EC20<50, effect percentage ≥50; 2) weakly toxic EC50>100,

EC20>50, 20≤effect percentage<50; 3) no toxic EC50 no

calculable, EC20>100, effect percentage 20.

2.3. Analysis of Metals

Determination of iron (Fe), copper (Cu), zinc (Zn), lead

(Pb), chromium (Cr), manganese (Mn), nickel (Ni), bar-

ium (Ba), arsenic (As), cadmium (Cd) and mercury (Hg)

was carried on both filtered and particulate samples. The

filtered sample was directly analyzed. The metal disso-

lution of particulate fraction collected on the filters was

conducted using microwave-assisted digestion (Mile-

stone MLS Ethos TC) with 3 mL of HNO3 and 9 mL of

HCl. The metal concentrations were determined by a

graphite furnace atomic absorption with Zeeman back-

ground correction technique (SpectrAA-220Z, Varian)

and by coupled emission plasma ICP-OES (Liberty AX,

Varian). For Hg analysis a Direct Mercury Analyzer

(DMA-80, FKV) instrument was used (EPA Method

[28]). All samples were run in triplicate. The quantifica-

tion limits (LOQ) were: 0.0005 mg/l for Hg and Cd, 0.01

mg/L for the other metals.

2.4. Analysis of Organic Compounds

BTEX: The analyses were extracted and pre-concen-

trated by means Solid Phase Micro Extraction (SPME)

using a stable flex fiber of divinilbenzene-carboxen-

poly-dimethylsiloxane (film thickness: 55/30 µm) (Su-

pelco®) by head space sampling. The analytical deter-

minations of BTEX were carried out in unfiltered sam-

ples using a modified EPA method [29]. A gas chroma-

tography coupled with mass spectrometry (GC HP 5790

Agilent Technologies® and MS 5973 Network Agilent

Technologies®) were used. The method detection limits

were 1 µg/L for benzene and 0.1 µg/L for toluene, ethyl

benzene and xylenes.

PAHs: The analyses were investigated in filtered sam-

ples and on the particulate matter retained by the filter

(Millipore®, 0.45 µm). The analyses were extracted by

the filtered samples by means Solid Phase Extraction

technique. The treatment of filters was carried out by

ultrasonic extraction for 20 minutes with 10 mL of di-

chloromethane. Then, both the extraction phases were

evaporated at 1-2 mL with a gentle nitrogen flow. Af-

terward, 1 mL of toluene was added and the residual

dichloromethane was completely removed. All solvents

were capillary GC grade supplied by Sigma-Aldrich.

The analyses of PAHs were carried out in gas chroma-

tography coupled with mass spectrometry (GC HP

5790® and MS 5973 Network Agilent Technologies).

The LOQ was 1 µg/L for each analysis.

DEG: An extraction procedure of DEG was carried

out with 2 mL SPE cartridges packed with 200 mg of EN

V+stationary phase (International Sorbent Technology,

L. Manfra et al. / Natural Science 2 (2010) 33-40

Table 2. Experimental conditions of bioassays (*for PFW1 were tested the concentrations: 10-20-40-80%).

Vibrio

fischeri

Phaeodactylum

tricornutum

Dunaliella

tertiolecta

Artemia

franciscana Tigriopus fulvus Dicentrarchus

labrax

Organisms/

Life stage cells unialgal

culture

unialgal

culture nauplii 48h nauplii 48h juveniles

Strain/origin commercially

available culture culture

commercially

available culture hatchery

Type of test static static static static static static

Time exposure 5-10-15min. 72h 72h 96h 96h 96h

Intensity of lux Not required 7000 7000 3000-4000 500-1200 500-800

Photoperiod

(L:D) Not required 24:0 24:0 14:10 16:8 16:8

Dilution water/

control

synthetic

seawater synthetic seawatersynthetic seawatersynthetic seawatersynthetic sea-

water synthetic seawater

Salinity (PSU) 35 32 32 35 38 20

Temperature

(°C) 15±1 20 ± 2 20 ± 2 25 ± 2 18 ± 2 20  1

pH 8.0 – 8.2 8  0.5 8  0.5 6.5 – 8.5 8.0 ± 0.3 7.5  0.5

Vessel 5mL 100mL 100mL 50 mL

culture plates 12

wells 2000 mL

Volume/well 1mL 25mL 25mL 40mL 3mL 1800mL

N°organisms/well - 10000/mL 2000/mL 10 10 5

N°of concentra-

tions (Range)

(6-11-22-45-90%)

(6-12-25-50-100%)

*(6-12-25-50-100%)

(6-12-25-50-100%)

(5-10-20-40-80%)

(6-12-25-50-100%)

N°of replicates 3 3 3 3 3-4 3

Feeding during

the test absent absent absent D. tertiolecta absent absent

Endpoint/Effect bioluminescence

inhibition rate

growth inhibition

rate

growth inhibition

rate

immobilization

rate

mortality rate;

moult release rate mortality rate

Expression of

endpoint

EC50;EC20

NOEC

EC50;EC20

NOEC

EC50;EC20

NOEC

EC50;EC15

NOEC

EC50;EC15

NOEC

EC50;EC15

NOEC

Acceptability

(effect control) 10% >0.04/h >0.04/h 10%

10% (mortality)

20% (moult

release)

10%

Glamorgan, UK). The off-line solid-phase extraction/

pre-concentratio n technique was followed by a nano-

scale flow injection/direct-electron ionization (EI) mass

spectrometric analysis. A quadrupole mass spectrometer

(Palo Alto, CA) was coupled with a Direct-Electron

Ionization (EI) [30-32]. Using this approach, DEG was

detected within a concentration of 31 µg/L [33].

Table 3. Toxicity scale used in this paper to classify the toxic-

ity of Production Formation Water (PFW).

Effect

(%)

EC50

(%)

EC20 or

EC15 (%)

TOXICITY

ASSESSMENT

%<20 n.c. >100 no toxic

20≤%<50 >100 >50 weakly toxic

≥50 10≤%<100 20<%<50 toxic

3. RESULTS

3.1. Bioassays

The results of the eco-toxicological battery are reported

in Table 4. The three filtered PFWs resulted toxic ac-

cording to the overall assessment related to bioassays.

The species showed different sensitivity to PFW: the two

microalgae and Artemia franciscana showed higher val-

ues of EC50 and EC20 (EC15) than the other organisms,

indicating weak toxicity. In particular, Artemia did not

record toxicity for PFW1 (no efficient concentration was

calculable). The other crustacean T. fulvus showed toxic

effects for all PFWs (PFW2>PFW1≥PFW3) related to

both mortality and moult release. The sub-lethal effect

was already observed at PFW concentrations that were

not causing mortality of nauplii (20-80) %. The fish spe-

cies D. labrax showed a toxic response similar to the one

of T. fulvus, with a minimum value of EC50 equal to 15%

and maximum value of 47% as follows: PFW2>PFW1≥

L. Manfra et al. / Natural Science 2 (2010) 33-40

PFW3. The bacterium V. fischeri recorded lower toxicity

than T. fulvus and D. labrax but yet a toxic effect was

observed for all PFWs (PFW1>PFW3≥PFW2).

3.2. Analysis of Metals

In filtered sample, Ba, Mn and Zn showed detectable

concentrations. There were not significant differences

between PFW2 and PFW3 exclusive of Ba and Mn.

These two metals showed higher concentrations of one

order in PFW2 than PFW3. In particulate sample, all

metals were detectable except Pb and Hg. Ni, Cd and As

registered detectable concentrations only in PFW3. Ba,

Zn and Fe showed highest concentrations and some sig-

nificant differences among the PFWs analyzed. Ba con-

centration was higher of one order in PFW1 and PFW2

than PFW3; Zn was higher of two orders in PFW2 and

PFW3 than PFW1; Fe was higher of one order in PFW3

than PFW1 and PFW2.

3.3. Analysis of Organic Compounds

As reported in introduction section, BTEX and DEG

were analysed on unfiltered PFWs. The analyses of the

three platforms pointed out that the volatile organic

compounds (BTEX) were detected at very high concen-

trations by the following ranking: PFW1 (1281.8 μg/L)

>PFW3 (66.5 μg/L)>PFW2 (48.0 μg/L) (Table 6),

showing for PFW1 values almost twenty times higher

than ones of PFW2 and PFW3. The DEG showed con-

centrations ranging from 2400 to 13000 μg/L by the fol-

lowing ranking of the fields: PFW3>PFW2>PFW1 (Ta-

ble 6). PAHs were investigated both in filtered and par-

ticulate sample but they were lower than LOQ (1 μg/L)

in filtered PFWs. In particulate sample PAHs showed the

trend as follows: PFW1 (150.0 μg/L)>PFW3 (126.0

μg/L)>PFW2 (100.0 μg/L), with values about of the

same magnitude order. The congeners with two and

three rings recorded the following concentrations: 87

μg/L in PFW1 compared to 150 μg/L of the total PAHs

content; 54 μg/L in PFW2 compared to 100 μg/L of total

PAHs concentration, and 66 μg/L in PFW3 compared to

126 μg/L of total PAHs. The detected concentrations

were of the same order of magnitude for all three PFW

investigated.

4. DISCUSSIONS

The bioassays showed that the PFWs were toxic even if

filtered. EC50 values ranged between the minimum of

14.8 % and values higher than 100 %. Some of the sam-

ples did record no toxicity at the EC50 level observed

Table 4. Bioassay results related to three Italian Production Formation Waters and toxicity evaluation according to toxicity

scale (n.c. not calculable; n.d. not determined).

Species

(time of exposure, end point) % PFW1 PFW2 PFW3 PFW1 PFW2 PFW3

EC50 67 (59-75)> 90 > 90

EC20 20(18-23) 29(27-31)28(25-31)

Vibrio fischeri

(15 min. bioluminescence) NOEC - - -

toxic toxic toxic

EC50 > 80 > 100 > 100

EC20 > 80 52

(46-58)

(24-111)

Phaeodactylum tricornutum

(72h growth)

NOEC 40 25 25

weakly

toxic

weakly

toxic

weakly

toxic

EC50 > 80 n.d. n.d

EC20 > 80 n.d n.d

Dunaliella tertiolecta

(72h growth) NOEC 40 n.d n.d

weakly

toxic n. d n. d.

EC50 > 100 > 100 > 100

EC15 > 100 86

(55-259)

(42-462)

Artemia franciscana

(96h immobilization)

NOEC n.c. 50 25

no toxic weakly

toxic

weakly

toxic

EC50 29 15 44

EC15 19 8 29

Tigriopus fulvus

(96h mortality) NOEC 10 5 20

toxic toxic toxic

EC50 23 25 77

EC15 n.c. n.c. n.c.

Tigriopus fulvus

(96h moult release) NOEC 10 5 10

toxic toxic toxic

EC50 32

(27-39)

(n.c)

EC15 23

(15-28)

(n.c)

Dicentrarchus labrax

(96h mortality)

NOEC 13 6 6

toxic toxic toxic

L. Manfra et al. / Natural Science 2 (2010) 33-40

Table 5. Metal concentrations in filtered samples of two Produced Formation Waters, total suspended solids and metal concen-

trations in particulate samples of Produced Formation Water from three offshore gas platforms in the Adriatic Sea (Italy).

Parameters Unit PFW2 PFW3 PFW1 PFW2 PFW3

FILTERED PARTICULATE

Total suspended solid mg 177.42 367.05 398.10

Ba mg/L 1.63 0.13 309.65 237.75 13.50

Cr mg/L <0.01 <0.01 0.12 1.34 0.45

Cu mg/L <0.01 <0.01 0.05 0.55 0.42

Mn mg/L 0.34 0.04 0.84 1.05 0.77

Ni mg/L <0.01 <0.01 0.07 <0.01 0.35

Pb mg/L <0.01 <0.01 <0.01 <0.01 <0.01

Zn mg/L 0.18 0.37 0.14 61.92 59.77

Cd mg/L <0.0005 <0.0005 <0.0005 <0.0005 0.62

Fe mg/L <0.10 <0.10 242.40 775.70 1335.00

As mg/L <0.01 <0.01 0.01 <0.01 9.25

Hg mg/L <0.0005 <0.0005 <0.0005 <0.0005 <0.0005

Table 6. Organic compound concentrations in Produced Formation Water (PFW) samples from three offshore gas platforms in

the Adriatic Sea (Italy).

Analytes PFW1 (µg/L)PFW2 (µg/L) PFW3 (µg/L)

Benzene 256.0 10.4 20.4

Toluene 50.6 14.1 12.1

Ethyllbenzene 115.2 7.7 13.8

Xilenes (o,m,p-xylene) 860.0 14.8 20.2

BTEX

(unfiltered sample)

BTEX　 1281.8 47.0 66.5

DEG (unfiltered sample) Diethylene glycol 2400 9600 13000

Naphtalene 14 8 11

Acenaphtylene 21 15 17

Acenaphthene 19 15 15

Fluorene 16 4 6

Phenanthrene 13 8 10

Anthracene 4 4 7

Fluorantrene 12 10 12

Pyrene 10 7 10

Benzo(a)anthracene 8 4 7

Crysene 5 6 7

Benzo(b)fluorantene 6 4 4

Benzo(k)fluorantene 6 5 6

Benzo(a)pyrene 5 3 3

Dibenzo(a,h)anthracene 4 4 4

Benzo(g,h,i)perylene 4 3 4

Indenopyrene 3 < 1 3

PAHs 2　- 3 ring congeners 87 54 66

PAHs

(particulate sample)

PAHs　 150 100 126

butdid show evidence of a toxic response at the EC20

level. The EC50 data lied within or were higher than the

range (5.54-20.73%) previously reported for another

filtered PFW originated from an Italian gas platform and

assayed by bacteria and sea urchins [14]. Ours EC50 data

also were higher than values related to unfiltered PFWs

coming from the North Sea platforms [4-8]. This shows

that the filtered samples have generally lower toxicity

than the untreated samples.

The difference of sensitivity among the species has

been quite remarkable: T. fulvus and D. labrax showed

the highest toxicity (EC50<50%), followed by V. fischeri

(EC20<30%). Artemia and the two algae did not record

significant toxic effect (EC20>50%).

L. Manfra et al. / Natural Science 2 (2010) 33-40

In addition to the toxicity assessment, we analyzed

chemically PFW (metals, BTEX, PAHs and DEG). Ap-

preciable concentrations of Ba, Mn and Zn were re-

corded in filtered samples while also high quantities of

Fe were registered in particulate samples. Ba is probably

related to drilling fluid residuals of PFW [7], Zn may be

derived from corrosion or chipping of galvanized struc-

tures on the platform or in the oil/water separator system

[34] and Fe could have natural origin or derive from

corrosive events. The lower weight aromatic hydrocar-

bons (BTEX) were found by significant concentrations

in liquid phase, while the PAHs were recorded only on

particulate samples. DEG concentrations also were of

milligram order in liquid phase but very low compared

to the threshold of 3500 mg/L imposed by the PFW dis-

charge authorization decrees issued by the Italian Minis-

try of the Environment.

An integrated evaluation of the eco-toxicological and

chemical results showed that test-organisms were espe-

cially sensitive when exposed to PFWs containing Ba,

Mn, Zn and BTEX. T. fulvus and D. labrax showed the

highest toxicity in PFW2 containing high concentrations

of Ba, Mn and Zn. V. fischeri showed the highest toxic

effect in PFW1 that recorded the highest quantities of

BTEX. Nobody among the test-organisms indicated a

preference for PFW3 containing the highest value of

DEG. Moreover, DEG is not toxic alone but could de-

termine co-solvent effects with other chemical com-

pounds [35].

5. CONCLUSIONS

Our results indicate that a filtration treatment might di-

minish PFW toxicity. If a similar treatment was carried

out on the platform before the PFW discharge, the eco-

logical risk associated to the discharge would be proba-

bly reduced.

Besides, the results confirm the different sensitivity of

test-organisms belonging to different trophic levels. Be-

cause PFW chemical composition is so variable for type

and concentration of contaminants, test-organisms that

are tolerant to a type of PFW could be sensitive to others.

For this reason, we think that it is not correct to establish

a single species to investigate the PFWs but a battery of

species should always be applied in order to have inte-

grated responses.

6. ACKNOWLEDGEMENTS

The present work was funded by the Italian Ministry of

Environment, Land and Sea. We thank Lucio Lattanzi

for analysis of BTEX and PAHs, Achille Cappiello and

Giorgio Famiglini for DEG analysis, Manuela Dattolo,

Silvia Mariotti and Antonella Cozzolino for metal analy-

sis. The authors acknowledge B. Trabucco for construc-

tive comments. We thank the Aquaculture Plant Nuovo

Azzurro (Civitavecchia, Roma-Italy) for providing the

larvae of Dicentrarchus labrax.

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