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Influence of salinity and fish species on PAH uptake from dispersed

crude oil

Shahunthala D. Ramachandran , Michael J. Sweezey , Peter V. Hodson , Monica Boudreau , Simon C. Courtenay , Kenneth Lee ,

Thomas King , Jennifer A. Dixon Marine Pollution Bulletin 2006 ; 52:1182-1189

在不同鹽度下魚種攝取被分散原油 PAH之影響

Reporter : Bei-Chan Liu

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Introduction

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Oil spills

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The coastal areas

TemperatureSalinity

The solubility of toxic hydrocarbons from the crude oil.The effectiveness of chemical dispersants.The binding characteristics of residual oil fractions onto

suspended particles.

The accumulation of hydrocarbons by aquatic organisms could also be affected by their osmoregulatory adaptations.

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PAH(多環碳氫化合物 )

Rank among the most toxic component

of crude oil.

More soluble than alkanes that comprise an equal number of carbon atom.

Crude oil

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PAH Solubility

NaCl concentration 3.5% 20%

Solubility of toluene 70% 16%

The solubility of toluene in different salinity (McAuliffe 1987)

The low salinity coastal water or estuaries and would

have a greater adverse impact on aquatic organisms.

The mean reduction in solubility for 12 aromatic hydrocarbons (Sutton and Calder 1975)

Fresh water

Seawater 68±4.4%

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Salinity may modify the performance of chemical dispersants

Much of the work on dispersant effectiveness has tested marine conditions (32–34 salinity), with few freshwater tests.

Dispersants would not be used in shallow waters where dispersion would be limited.

Most dispersants are formulated to work within a narrow range of water salinities, close to that of seawater.

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Fish can accumulate soluble petroleum hydrocabons very rapidly. (Collier et al. 1995)

Gills are primary route of hydrocarbon uptake and excretion, usually by diffusion. (Thomas and Rice 1982)

The lighter PAHsVolatilize and

solubilize easier

The heavier and more toxic PAHs

Less soluble

If use dispersants ,the hydrophobic nature of the more toxic fractions enables them to partition directly from crude oil to lipid-rich tissues coming into contact with oil droplets.

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ObjectiveThis research was to measure changes in exposure of fish to PAH when MESA crude oil was dispersed at a range of salinities.

Exposure was estimated by measuring the induction of hepatic cytochrome P450 (CYP1A) activity, an indicator of PAH uptake.

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Materials and

methods

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Crude oil and dispersant

Crude oil :MESA sour crude Dispersant : Corexit 9500

MESA sour crude is insoluble in water and

non-volatile when dispersed.

Corexit 9500 is meant to be used on higher

viscosity oils and emulsions.

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Test fishes

Juvenile (8–10 weeks) rainbow trout: was chosen to enable comparisons

with freshwater data (0–15‰).

Mummichogs were chosen for exposure bioassays at 15‰ and 30‰ salinity.

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Preparation of WAFThe crude oil was weathered by

sparging with air for 130h.

A 1:9 mixture of oil and water

0 ‰ 15 ‰ 30 ‰

Mixture for 18h and settled for 1h

The WAF layer was separated from surface oil to use as exposure solution

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Preparation of CEWAF A 1:9 mixture of oil and water

15 ‰ 30 ‰0 ‰

Mixture for 18h of stirring

Corexit at a ratio of 1:20 of the oil was added with a further 1 h of stirring and then settled for 1 h.

The CEWAF emulsion layer was separated from surface oil to use as exposure solution.

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Exposure tests

A series of WAF concentrations

A series of CEWAF concentrations

five fish

After 48h

fish were anaesthetized with100 mg/L of MS-222.

fish were killed by severing the spinal cord.

Their livers wereremoved, weighed.

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A model CYP1A inducer, b-naphthoflavone (BNF,10 μg/L), served as a positive control.

0 ‰ 15 ‰ 30 ‰

livers

microcentrifuge tubes Centrifuges

The supernatant (S9 fraction) was removed

frozen in liquid nitrogen,and stored at -80 ℃.

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EROD assay

In liver

CYP1A (EROD) activity was expressed as pmol of resorufin produced per

min per mg protein in the S9 fraction.

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PAH analysisGas chromatography

300ml

20 ml dichloromethane

Dried by filtration through

sodium sulfate

concentratedto 1.0 mL

GC

PAH

TPH

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Spectrofluorometry

20ml

2 ml hexane

Shaken for 20 minand left for10 min The hexane layer

Spectrofluorometry

Total PAH

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Statistical analysis

Analyses of variance (ANOVA) were calculated from EROD activity values which had been log transformed to achieve normal distribution.

A one-way ANOVA with treatment as a factor was applied to detect differences among treatments (control, WAF and CEWAF).

Median effect concentrations (EC50) for the WAF and CEWAF exposures of each oil were calculated from induction curves using Graph Pad–Prism fitting a linear regression.

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Results

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EROD activity

potency decreased by 20- to 50-fold

0.01 0.1 1 10

0.01 0.1 1 10

EROD induction for BNF was similar

Mummichog EROD activity CEWAF

concentrations similar to trout EROD activity.

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Comparisons among EC50s

The ratio dropped by about 35-fold

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PAH concentrations in bioassay treatments0.1 v/v CEWAF

0ppt > 15ppt

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Total PAH

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Discussion

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Decreased exposure with increasing salinityThese experiments corroborate earlier work on increased exposure to PAH with chemical dispersion of crude oil (Ramachandran et al., 2004).

salinity EROD activity

dispersanteffectiveness

PAH solubility

binding capacity onto suspended particulate matter

osmoregulation in test fish

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Dispersant effect did not seem to change between salinities

of 0‰ and 15‰.

The dispersant was less effective at high salinities.

Interactions between PAH and particulates might also be affected by salinity.

Fish were not fed for 48 hprior to testing.

Dispersant effectiveness

Binding capacity onto suspended particulate matter

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Salinity effects on PAH uptake by fish is that salinity controls PAH solubility and bioavailability.

Two (naphthalenes) and three (phenanthrene)

ring compounds.

The low molecular weight (LMW)

The higher molecular weight (HMW)

Four (fluorene) and five (pyrene , chrysene) ringed co

mpounds.

Solubility : LMW ＞ HMW

PAH solubility

PAH molecule weight

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LMW

HMW

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Osmoregulation in test fish

Hypo-osmotic environment

Fish are subjected to diffusion of water from the surroundingmedium into the gill, as is the case with freshwater fish.

Hypo-osmotic environment iso-osmotic conditions

This process slows until iso-osmotic conditions.

In this study, responses of fish to PAH did not change between 0‰ and 15‰ salinity.

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15‰ 30‰

Reduced PAH uptake from CEWAF by mummichogs.

EROD activity in mummichog exposed to BNF

was reduced by one half

The reduction in PAH uptake at higher salinities might be due

to water and PAH efflux in response to osmotic gradients.

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Conclusion

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Oil spills

Low salinityFull salinity

PAH will be up to 60-fold

Use of dispersants 10 times 250 times

The increased solubility of PAH at lower salinities, especially the lower molecular weight two- and three-ringed homologs.

This solubility effect is enhanced by the apparent increased effectiveness of chemical dispersion at low salinities.

The potential risks to aquatic life of PAH toxicity following oil spills are enhanced in lower salinity waters such as estuaries and near coastalzones.

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