anA

ianirn016inci

laden glycols are usually regenerated (stripped of water) ina stripping column (Twijnstra, 1997). Because the efciency of theregeneration processes occurring in the glycol-based dehydrationdevices is less than 100%, glycols could be introduced in the marine

NPD), phenols, organic acids and additives (e.g. glycols)(Brendehaugh et al., 1992; Neff, 2002). These compounds arepresent in variable amounts depending on the geological charac-teristics of the reservoir, the type of hydrocarbons (gas or oil), thedegree of exploitation of the reservoir, and the efciency of thetreatment adopted (Utvik, 1999; Wills, 2000; OSPAR, 2004). SincePW composition is complex and very variable, toxicity can bedifferent depending on its chemical characteristics (Higashi et al.,

* Corresponding author. Tel.: 39 06 61570496; fax: 39 06 61561906.

Contents lists available at

Marine Environm

lse

Marine Environmental Research 77 (2012) 141e149E-mail address: andrea.tornambe@isprambiente.it (A. Tornamb).1. Introduction

During off-shore extraction processes, natural gas is normallysaturated with water vapour and thereby water molecules couldcombine with hydrocarbons to form crystalline-structured solidhydrates (Carroll, 2009). Glycols (triethylenic glycol, diethyleneglycol and ethylene glycol) are the chemicals most often used indehydration of natural gas (Sorensen et al., 2000). They are a groupof organic compounds named aliphatic alcohols which are char-acterized by the presence of two hydroxy functional groups linkedto methyl subunits (AIHA, 1985). In a typical glycol-based dehy-dration device, water vapour is removed from the gas stream ina glycol-absorber and the dried gas then leaves the absorber forfurther processing or transport (Katz and Lee, 1990). The water-

environment through the discharge of production waters (PWs)from off-shore extraction plants (Cappiello et al., 2007).

PW originates from water naturally present in geologicalformations (formation water) mixed with the seawater injected inthe oil/gas eld (process water) to maintain reservoir pressure. It ispiped to the surface during the production process and may bedischarged into the sea when the rejection is not possible,becoming the major efuent discharged during the hydrocarbonsproduction phase (Patin, 1999). Before discharge, PWs are treateddirectly on platform to reduce oil and suspended solids content but,in spite of this treatment, PWs still include many inorganiccompounds (i.e. trace metals), volatile aromatic compounds(benzene, toluene, ethylbenzene, xylenes - BTEX), semi-volatilesubstances (i.e. naphthalene, phenanthrene, dibenzothiophene -Received 2 September 2011Received in revised form16 December 2011Accepted 16 December 2011

Keywords:Off-shore platformsDiethylene glycolProduced watersEcotoxicologyBioassayMarine/brackish organismsEffects-synergistic0141-1136/$ e see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.marenvres.2011.12.006prevent formation of gas hydrates. It may be released into the sea accidentally or in discharged producedwaters (PWs). PWs samples from off-shore gas platforms in the Adriatic Sea (Italy) have been used in thisstudy. The objectives of the study were: a) to evaluate the toxicity of DEG for marine organisms; b) toevaluate if a high DEG content in PWs may alter their toxicity; c) to verify whether the DEG thresholdconcentration established by the Italian legislation (3.5 g/l) for PWs discharged at sea is safe for marineenvironment. Ten different species (Vibrio scheri, Phaeodactylum tricornutum, Dunaliella tertiolecta,Brachionus plicatilis, Artemia franciscana, Tigropus fulvus, Mytilus galloprovincialis, Crassostrea gigas, Tapesphilippinarum and Dicentrarchus labrax) have been exposed to DEG; four of these species were alsoexposed to PWs in combination with DEG. The results showed that: a) DEG is not toxic at levels normallydetected in Adriatic PWs; b) DEG in combination with PW showed mainly additive or synergistic effects;c) short-term bioassays showed that the DEG limit of 3.5 g/l could be acceptable.

2011 Elsevier Ltd. All rights reserved.Article history: Diethylene glycol (DEG) is commonly used to dehydrate natural gas in off-shore extraction plants and toa r t i c l e i n f o a b s t r a c tShort communication

Toxicity evaluation of diethylene glycolwaters of off-shore gas platforms in themarine/estuarine species

Andrea Tornamb a,*, Loredana Manfra a, Livia MarFederica Savorelli b, Anna Maria Cicero a, Claudia Va ISPRA e Institute for Environmental Protection and Research, via di Casalotti, 300 e 0bARPA e Agenzia Regionale Prevenzione e Ambiente dellEmilia-Romagna, Sezione Prov

journal homepage: www.ell rights reserved.d its combined effects with produceddriatic Sea (Italy): Bioassays with

i a, Olga Faraponova a, Fulvio Onorati a,o Lamberti a, Erika Magaletti a

6 Rome, Italyale di Ferrara, via Bologna, 534 e 44124 Ferrara, Italy

SciVerse ScienceDirect

ental Research

vier .com/locate/marenvrev

results on DEG and on the mixture DEG PWs are reported in thispaper. Two sets of toxicity tests have been carried out. In the rstset, a battery of ten species was exposed to different DEG concen-trations. The test species included bacteria (Vibrio scheri), algae(Phaeodactylum tricornutum and Dunaliella tertiolecta) rotifers(Brachionus plicatilis), crustaceans (Artemia franciscana and Tigropusfulvus) molluscs (Mytilus galloprovincialis, Crassostrea gigas, Tapesphilippinarum) and sh (Dicentrarchus labrax). In the second set oftoxicity tests, one species for each trophic level (decomposers,primary producers, consumers and predators) was exposed to PWsin combination with DEG in order to assess possible synergisticeffects and to verify whether the current threshold value of DEG indischarged PWs (3.5 g/l) is a safe concentration for the marineenvironment.

2. Materials and methods

2.1. Sampling

Samples of PWs were collected from three off-shore gas plat-forms located at about 20 km from the Adriatic coast (one nearPescara and two near Rimini, Italy). One sample for each platformhas been taken: PW1was collected in October 2005, PW2 and PW3in June 2006. All PWs were sampled by high density polyethylenebottles from a tap located on the platform, downstream of thetreatment plant, and then immediately ltered (Millipore,

nmental Research 77 (2012) 141e1491992; Neff, 2002; Holdway, 2002). Discharge of PWs into the seamay cause impacts on the biota but usually adverse effects occuronly within the mixing zone around the production platforms(Burns et al., 1999; Cianelli et al., 2008). Chemical characteristics,potential effects and modelling of PW dispersion have beeninvestigated by several studies in areas characterized by the pres-ence of off-shore platforms discharging PW into the sea (e.g. NorthSea, Gulf of Mexico, Mediterranean Sea, coastal areas of Australiaand of Southern California) (Cianelli et al., 2011 and referencestherein). Irrespective of the variations in their chemical composi-tion, PWs have a relatively low toxicity (Holdway, 2002; Neff, 2002;OGP, 2005). Negligible or non-toxic effects have also been observedon marine organisms in the Adriatic Sea (Manfra et al., 2007;Cianelli et al., 2008). However, very few data are available on thepotential impact of chemicals on PW toxicity (Henderson et al.,1999 on 11 chemicals including biocides, corrosion inhibitors anddemulsiers; Beyer et al., 2001) and very limited data are related tothe toxicity of diethylene glycol (DEG) (Kent et al., 1999; Gorbi et al.,2009), that is in Italy the additive used for dehydration of naturalgas and the most used additive in off-shore gas platforms.

DEG is a relatively non volatile compound, due to its low vapourpressure, and is water-soluble. The octanol-water partitioningcoefcient is very lowand hence bioaccumulation is not expected tobe signicant, while hydrolysismay be an important fate process forDEG in water (Kent et al., 1999). A maximum allowable concentra-tion of DEG in PWs, equal to 3.5 g/l, has been established only in Italy(as required by Authorization Decrees of the Ministry of Environ-ment), on the basis of few experimental data available on marineaquatic toxicity on Cyprinodon variegatus, Skeletonema costatum,Mysidopsis bahia and Artemia salina (Kent et al., 1999), that suggesta relatively lowDEG toxicity. Previous studies (Cappiello et al., 2007;Cianelli et al., 2008) and 2001e2010 data on chemical character-ization of PWs in the Adriatic Sea (data from authorization requeststo the Ministry of the Environment for PW discharge at sea,unpublished) showed that DEG concentration in PWs is generallylower than the maximum allowable concentration and ranges from

chosen to take into consideration a) species belonging to differenttrophic levels (decomposers, primary producers, consumers andpredators); b) the observation of different endpoints, such asbacterial bioluminescence (V. scheri), algal growth (D. tertiolecta,P. tricornutum), immobilization (A. franciscana), mollusc embryodevelopment (M. galloprovincialis, C. gigas, T. philippinarum) andmortality (B. plicatilis, T. fulvus and D. labrax); c) the use of short-duration bioassays (

3. Results and discussion

Two sets of tests were carried out in order to explore DEGtoxicity alone and in combination with PWs. In the rst set, theresponses of the ten species exposed to increasing concentrationsof DEG dosed alone have been evaluated and are reported inTable 5. Appreciable toxic effects have been observed at DEGconcentrations higher than 9 g/l; in fact the effect concentrations(EC15/EC20/EC50) of the tested species were higher than this value,except for T. fulvus (EC15 2.9 g/l and EC50 5.9 g/l).

crustaceans Kent et al. (1999) reported LC50 values for M. bahiaranging from a 24 h LC50 of 54.9 g/l to a 96 h LC50 of 36.9 g/l and forA. salina (now A. franciscana) a 24 h LC50 higher than 10.0 g/l, thatwas conrmed by our 96 h LC50 result of 15.7 g/l, while T. fulvusshowed a higher sensitivity (96 h LC50 of 5.9 g/l). For marinemicroalgae Kent et al. (1999) reported EC50 values for Skeletonemacostatum (diatom) ranging from a 24 h EC50 of 8.9 g/l to a 96 h EC50of 40.8 g/l that is consistent with our 72 h EC50 result of 57.4 g/l forP. tricornutum (diatom), whileD. tertiolecta (green alga) showed lesssensitivity to DEG (72 h EC50 of 90.4 g/l).

Rp

333633

s 3

Table 3Concentrations of the mixtures of produced water (PW) and diethylene glycol (DEG) tested with four marine/brackish species in the second set of toxicity tests. Abbreviationsas in Table 2.

Species PW1 conc. (%) DEG NOECa (g/l)

PW2 EC15/20b (%) DEG NOECa (g/l)

PW2 EC15/20b (%) DEG EC15/20b (g/l)

PW2 EC15/20b (%) 3.5 (g/l) DEG

PW3 EC15/20b (%) DEG NOECa (g/l)

PW3 EC15/20b (%) DEG EC15/20b (g/l)

PW3 EC15/20b (%) 3.5 (g/l) DEG

V. scheri (7.9e11.9e17.8e26.7e40.0e60.0e90.0) 2.4

29.0 2.4 29.0 14.0 29.0 3.5 28.0 2.4 28.0 14.0 28.0 3.5

P. tricornutum (29.0e43.0e65.0e97.5) 5.0

51.7 5.0 51.7 19.5 51.7 3.5 67.8 5.0 67.8 19.5 67.8 3.5

A. franciscana (6.2e12.5e25.0e50.0e100.0) 6.2

85.7 6.2 85.7 9.4 85.7 3.5 77.2 6.2 77.2 9.4 77.2 3.5

D. labrax (10.4e15.6e23.4e35.1) 25.0

10.8 25.0 10.8 38.3 10.8 3.5 14.6 25.0 14.6 38.3 14.6 3.5

a No observed effect concentration (NOEC).b EC20 for V. scheri and P. tricornutum, EC15 for A. franciscana and D. labrax.

A. Tornamb et al. / Marine Environmental Research 77 (2012) 141e149144These results are consistent with those reported by Kent et al.(1999) in their review on DEG toxicity for freshwater and marineorganisms. For freshwater sh, Kent et al. (1999) reported 96 h LC50values for the rainbow trout (Oncorhynchus mykiss) from 52.8 g/l to62.9 g/l; for fathead minnows (Pimephales promelas) LC50 valuesranged from a 96 h LC50 of 75.2 g/l to a 48 h LC50 of 86.8 g/l; forDaphnia magna (freshwater crustacean) 24 h LC50 values rangedfrom higher than 10.0 g/l to 78.5 g/l; for freshwater algae (Sele-nastrum capricornutum) toxicity data ranged from 24 h EC50 6.4 g/lto 96 h EC50 19.9 g/l (endpoint population growth). For marine sh,Kent et al. (1999) reported LC50 values for C. variegatus ranging froma 24 h LC50 of 90.7 g/l to a 96 h LC50 of 62.1 g/l, while in our work the96 h EC50 for D. labrax was lower and equal to 40.3 g/l. For marine

Table 4Main procedural aspects of toxicity testing. Abbreviations as in Table 2.

Species Organisms Test type Testduration

Organisms pertest chamber

V. scheri Cell culture Static 50e300 106 cellsP. tricornutum Microalgal culture Static 72 h 104 cells/mlD. tertiolecta Microalgal culture Static 72 h 2$103 cells/mlB. plicatilis Nauplii Static 48 h 5A. franciscana Nauplii Static 96 h 10T. fulvus Nauplii Static 96 h 10M.galloprovincialis Early life stages Static 48 h 200e300 fertilized egg

C. gigas Early life stages Static 24 h 200e300 fertilized eggs 3T. philippinarum Early life stages Static 24 h 200e300 fertilized eggs 3D. labrax Juveniles Static 96 h 7 3

Species Endpoint Validity test criteria

V. scheri Bioluminescence inhibition Control bioluminescencP. tricornutum Growth rate inhibition Control growth rate >0D. tertiolecta Growth rate inhibition Control growth rate >0B. plicatilis Mortality Control mortality

marine/brackish

species.Abb

reviationsas

inTable2(From

Man

fraet

al.,20

10).

PW2

PW3

Toxicity

classication

d

EC50(%)

EC15/20(%)

NOEC

c(%)

EC50(%)

EC15/20(%)

NOEC

c(%)

PW1

PW2

PW3

>90

.029

.0a(27.0e

31.0)

90

.028

.0a(25.0e

31.0)

10

0.0

52.0a(46.0e

58.0)

25.0

>10

0.0

68.0a(24.0e

111.0)

25.0

Slightlytoxic

Slightlytoxic

Slightlytoxic

>10

0.0

86.0b(55.0e

259.0)

50.0

>10

0.0

77.0b(42.0e

462.0)

25.0

Non

toxic

Slightlytoxic

Slightlytoxic

15.5

(n.c.)

10.8b(n.c.)

6.3

47.1

(n.c.)

14.6b(n.c.)

6.3

Toxic

Toxic

Toxic

nmental Research 77 (2012) 141e149 1at levels generally detected in Adriatic PWs (from 0.5 mg/l to13 mg/l) (Cianelli et al., 2008; unpublished data of the Ministry ofEnvironment). This is also supported by sh biomarker results byGorbi et al. (2009), that report no signicant toxic effects up to5.0 g/l, with the only exception of a slight genotoxic damage(increased DNA fragmentation of blood cells), on D. labrax juvenilesexposed to increasing concentrations of DEG for 10 days.

Data on the chemical composition of the PWs used in the secondset of toxicity tests (Table 1) show that PW1 has the highest contentof metals (especially Ba and Fe) and of BTEX, and a slightly highercontent of polycyclic aromatic hydrocarbons (PAHs) compared toPW2 and PW3. In general, metals concentration for the three PWswas lower compared to that reported for PWs in the North Sea andin the Gulf of Mexico (Neff, 2002), but falls within the rangespreviously reported for Adriatic PWs (Mariani et al., 2004; Manfraet al., 2007; Fattorini et al., 2008; Gorbi et al., 2008). Withregards to hydrocarbons, in PW1 the BTEX content was higher thanthe PAHs content, as it is normally found in PWs from gas wells(Neff, 2002), while total hydrocarbons content in PW2 and PW3was lower than that in PW1, with PAHs concentrations greater thanBTEX concentrations. In all the three PWs, BTEX were found insignicant concentrations in the liquid phase, while the PAHs wererecorded only in the particulate matter (Manfra et al., 2010). Table 6reports the toxicity evaluation of PW1, PW2 and PW3 published by

Table 5Effect and no effect concentrations of DEG (g/l) for tenmarine/brackish species. Eachexperiment was repeated independently at least three times. Abbreviations as inTable 2.

Species DEGEC50 (g/l)

DEGEC15/20 (g/l)

DEGNOECc (g/l)

Toxicityclassicationd

V. scheri 40.7 3.1 14.1 1.7a 2.4 Non toxicP. tricornutum 57.4 5.6 19.5 3.5a 5.0 Non toxicD. tertiolecta 90.4 8.8 34.3 8.0a 25.0 Non toxicB. plicatilis 44.0 3.0 28.4 1.6b 25.0 Non toxicA. franciscana 15.7 0.8 9.4 1.0b 6.2 Non toxicT. fulvus 5.9 0.04 2.9 0.01b 0.5 Non toxicM. galloprovincialis 19.3 0.9 n.c. 12.6 Non toxicC. gigas 30.3 3.0 20.7b 12.6 Non toxicT. philippinarum 19.3 0.8 14.7b 7.9 Non toxicD. labrax 40.3 0.3 38.3 0.4b 25.0 Non toxic

n.c.: non-calculable.a EC20.b EC15.c No observed effect concentration (NOEC).d According to the GESAMP (2002) toxicity scale.

A. Tornamb et al. / Marine EnviroManfra et al. (2010). The EC50 values ranged between 15.5% andvalues higher than 100%; the EC15/EC20 ranged between 10.8% and68% while the lowest NOEC value was 6.3%. Applying the worst-case criterion, PW2 was the most toxic PW since it showed thelowest values of EC50, EC15 and NOEC (corresponding to the testwith D. labrax).

The second set of tests was aimed at obtaining theconcentration-response curves for the mixtures PWs DEG inorder to evaluate possible synergistic effects. When the observedeffects are higher than the predicted effect, the two components ofthe mixture are considered to be acting synergistically. Results arereported in Fig.1, Fig. 2 and Fig. 3 for tests with PW1, PW2 and PW3,respectively. In the test with PW1, an increasing concentration ofPW around the EC20 value was used, combined with a DEGconcentration corresponding to the NOEC value (Fig. 1). A clearsynergistic effect was found in D. labrax even with the addition ofthe lowest concentration of PW1, which resulted in 100% mortality(Fig. 1d). Tests with P. tricornutum also showed strong synergisticeffects, with an increased growth inhibition with increasingconcentrations of PW1 (from 16% to 80%; Fig. 1b). The observed andpredicted effect-response curves for bacteria (V. scheri) and Ta

ble

6Effect

andnoeffect

concentrationsof

produ

cedwaters(PW)(%)forfour

PW1

Specie-test

EC50(%)

EC15/20(%)

NOEC

c(%)

V.

sche

ri67

.0(59.0e

75.0)

20.0a(18.0e

23.0)

80

.0>80

.0a

40.0

A.franc

iscana

>10

0.0

>10

0.0b

100.0

D.lab

rax

32.0

(27.0e

39.0)

23.4b(15.0e

28.0)

12.6

n.c.:non

-calculable.

aEC

15.

bEC

20.

cNoob

served

effect

concentration(N

OEC

).dAccordingto

thetoxicity

scalereportedin

Man

fraet

al.(20

10).45

010

20

30

40

50

60

70

80

90

100

29 43 65 97,5

Gro

wth

ra

te

in

hib

itio

n %

PW1 (concentration %)

Predicted

Observed

b

0

10

20

30

40

50

60

70

80

90

100

6,2 12,5 25 50 100

Imm

ob

ilit

y %

PW1 (concentration %)

Predicted

Observed

0102030405060708090

100

10,4 15,6 23,4 35,1

Mo

rta

lity %

PW1 (concentration %)

Predicted

Observed

cd

0

10

20

30

40

50

60

70

80

90

100

7,9 11,9 17,8 26,7 40,0 60,0 90,0

Bio

lum

ine

sc

en

ce

in

hib

itio

n %

PW1 (concentration %)

Predicted

Observed

a

Fig. 1. Observed and predicted effects of PW1 with the addition of DEG at NOEC concentration on four marine/brackish species: a) concentration-response curves of Vibrio scherifor mixtures of PW1 plus 2.4 g/l DEG; b) concentration-response curves of Phaeodactylum tricornutum for mixtures of PW1 plus 5.0 g/l DEG; c) concentration-response curves ofArtemia franciscana for mixtures of PW1 plus 6.2 g/l DEG; d) concentration-response curves of Dicentrarchus labrax for mixtures of PW1 plus 25.0 g/l DEG.

0

10

20

30

40

50

60

70

80

90

100

3,5 5 20

Gro

wth

rate in

hib

itio

n %

DEG concentration (g/L)

Predicted

Observed

0

10

20

30

40

50

60

70

80

90

100

3,5 6,2 9,4

Im

mo

bility

%

DEG concentration (g/L)

Predicted

Observed

0

10

20

30

40

50

60

70

80

90

100

3,5 25 38,3

Mo

rta

lity

%

DEG concentration (g/L)

Predicted

Observed

b

dc

0

10

20

30

40

50

60

70

80

90

100

2,4 3,5 14

Bio

lu

min

es

ce

nc

e in

hib

itio

n %

DEG concentration (g/L)

Predicted

Observed

a

Fig. 2. Observed and predicted effects of mixtures of DEG at three concentrations (NOEC, 3.5 g/l, EC15/20) with the addition of PW2 at EC15/20 value on four marine/brackish species:a) concentration-response curves of Vibrio scheri for mixtures of DEG 29% PW2; b) concentration-response curves of Phaeodactylum tricornutum for mixtures of DEG 52% PW2;c) concentration-response curves of Artemia franciscana for mixtures of DEG 86% PW2; d) concentration-response curves of Dicentrarchus labrax for mixtures of DEG 11% PW2.

A. Tornamb et al. / Marine Environmental Research 77 (2012) 141e149146

Mo

rta

lity %

b

d

C, 3.entrd) c

nme0

10

20

30

40

50

60

70

80

90

100

3,5 6,2 9,4

Imm

ob

ilit

y %

DEG concentration (g/L)

Predicted

Observed

c

0

10

20

30

40

50

60

70

80

90

100

2,4 3,5 14

Bio

lum

ine

sc

en

ce

in

hib

itio

n %

DEG concentration (g/L)

Predicted

Observed

a

Fig. 3. Observed and predicted effects of mixtures of DEG at three concentrations (NOEconcentration-response curves of Vibrio scheri for mixtures of DEG 28% PW3; b) concconcentration-response curves of Artemia franciscana for mixtures of DEG 77% PW3;

A. Tornamb et al. / Marine Envirocrustaceans (A. franciscana) did not show statistically signicantdifferences (p > 0.05) (Fig. 1a and c). For PW2 and PW3, a concen-tration of PW corresponding to the EC20/EC15 was used, while DEGwas added in the concentrations corresponding to the NOEC, EC20/EC15 and 3.5 g/l (Figs. 2 and 3). The additions of DEG to PW2 did notshow marked effects (Fig. 2); the only signicant differencebetween predicted and observed effects, i.e. a moderate decrease intoxicity, was found in P. tricornutum (Fig. 2b). No signicantdifferences were also registered in PW3 DEG for V. scheri andD. labrax (Fig. 3a and d), while there were signicant synergisticeffects in A. franciscana and P. tricornutum at the highest concen-trations of DEG (9.4 and 20.0 g/l DEG, respectively) (Fig. 3c and b).

The only data available on the effects of co-exposure of organ-isms to DEG and PW are those reported by Gorbi et al. (2009), whohave exposed juveniles of D. labrax for ten days to 1% PW and 5%PW (same PW1 sample as the present work) to increasingconcentrations of DEG (1.0 g/l, 5.0 g/l and 10.0 g/l). Results showeda signicant increase in EROD activity in sh exposed to 5% PWwith the three DEG additions, while a signicant enhancement ofGlutatione S-transferases activity was observed only during co-exposures at 10.0 g/l of DEG with both PW concentrations. Theyalso reported that increased levels of aromatic metabolites (naph-thalene-type, pyrene-type, benzo[a]pirene-type) in the bile of shexposed to 1% and 5% PW concentrations were not affected by DEGadditions. Furthermore, a higher frequency of DNA strand breakshave been observed in organisms co-exposed to PW and DEG at allconcentrations tested.

The use of bioassays has been widely applied when monitoringthe impact of PWs discharged from off-shore platforms(Brendehaugh et al., 1992; Neff et al., 1992; Osenberg et al., 1992;Stagg et al., 1995; Stromgren et al., 1995; Frost et al., 1998;Henderson et al., 1999; Neff, 2002). In fact, given the variety ofchemicals that are present in PWs and their possible range of0

10

20

30

40

50

60

70

80

90

100

3,5 5 20

Gro

wth

ra

te

in

hib

itio

n %

DEG concentration (g/L)

Predicted

Observed

0

10

20

30

40

50

60

70

80

90

100

3,5 25 38,3DEG concentration (g/L)

Predicted

Observed

5 g/l, EC15/20) with addition of PW3 at EC15/20 value on four marine/brackish species: a)ation-response curves of Phaeodactylum tricornutum for mixtures of DEG 68% PW3; c)oncentration-response curves of Dicentrarchus labrax for mixtures of DEG 15% PW3.

ntal Research 77 (2012) 141e149 147concentration, the best way to evaluate potential environmentalimpacts is to assess whole PW toxicity for each off-shore platform,using a battery of marine organisms, preferably indigenous(Holdway, 2002). PWs toxicity for freshwater and marine organ-isms can widely differ and acute toxicity data from variousproduction areas vary from non-toxic (LC50 > 100%) to moderatelytoxic (LC50 < 1%) (Neff, 2002). However the environmental impactof the discharged PW is usually low, as a result of the rapid dilutionof the efuent into the sea (Holdway, 2002; Neff, 2002). Previousstudies on off-shore platforms in the Adriatic Sea also revealed lowPW toxicity and limited negative effects on the environment: PWsdischarge determines an increase in the concentration of metals insediments and mussels and moderate impacts on the benthicassemblages near the installations (Mariani et al., 2004; Manfraet al., 2007; Fattorini et al., 2008; Gorbi et al., 2008). Even thoughthere are numerous studies on PW toxicity and effects on biota,very few data are available on the effects of chemicals when addedto PWs (see Henderson et al., 1999; Beyer et al., 2001 and referencestherein) and only one study reports on the effects on marineorganisms of DEG combinedwith PW (Gorbi et al., 2009). The use ofadditives, such as DEG, is often necessary to improve the produc-tion of oil or gas of off-shore platforms. A limit concentration ofDEG for discharge of PWs is currently dened only in Italy (3.5 g/l,as required by Authorization Decrees of Ministry of Environment).From the results of the present work, it is reasonable to assume thatknowledge on the level of toxicity of single substances (i.e. DEG) isnot enough to derive concentration limits for discharge of PW, sincethere are possible synergistic effects that alter the response ofmarine organisms to such a complex matrix as PWs.

A possible explanation of the synergistic effects observed in thepresent study is to be found in the chemical and physical propertiesof DEG and of glycols in general. Water and glycols can act as co-solvents, greatly increasing the solubilization and transport of

bility of polycyclic aromatic substrates and may also alter the

the contrary, the toxicity of PW2 and PW3 could have been mainly

nmedue to the compounds already present in solution, so DEG additionscould have low impact on the toxicity of the PW sample.

In summary, the present work has provided the followingevidences: DEGwas conrmed toxic formarine/brackish organismsat concentrations not considered dangerous for the marine envi-ronment (GESAMP, 2002; UN, 2011) and normally not detected inAdriatic PWs (Cianelli et al., 2008). In fact, we observed that DEGalone has caused toxic effects at concentrations greater than 9 g/l,with the only exception of a EC15 of 2.9 g/l for the copepod T. fulvus.The presence of DEG in PWs may alter their toxicity since the DEGaddition over 5 g/l has produced, in some cases, synergistic effects.The safe threshold concentration of 3.5 g/l established in Italy couldbe considered acceptable for DEG in co-exposure with PWs,however chemical aspects on co-solvency of DEG in PWs should befurther investigated.

Acknowledgements

This research was funded by the Italian Ministry of the Envi-ronment within the Research Program Toxicity evaluation ofdiethylene glycol from produced waters of off-shore gas platformsand its potential effects on mediterranean marine species of ISPRA(former ICRAM).

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A. Tornamb et al. / Marine Environmental Research 77 (2012) 141e149 149

Toxicity evaluation of diethylene glycol and its combined effects with produced waters of off-shore gas platforms in the Ad ...1. Introduction2. Materials and methods2.1. Sampling2.2. Experimental design2.3. Toxicity tests2.4. Data analysis

3. Results and discussionAcknowledgementsReferences