Method for generating parameterized ecotoxicity data of dispersed oil for use in environmental modelling

doi:10.1016/j.marpolbul.2011.07.015

Marine Pollution Bulletin

Volume 62, Issue 10, October 2011, Pages 2106-2113

https://doi.org/10.1016/j.marpolbul.2011.07.015 Get rights and content

Abstract

The aim of the work was to establish methodology for realistic laboratory-based test exposures of organisms to oil dispersions, specifically designed to generate parameterized toxicity data. Such data are needed to improve the value of numerical models used to predict fate and effects of oil spills and different oil spill responses. A method for continuous and predictable in-line production of oil dispersions with defined size distribution of different oil qualities was successfully established. The system enables simultaneous comparison between the effects of different concentrations of dispersion and their corresponding equilibrium water soluble fractions. Thus, net effects of the oil droplet fraction may be estimated. The method provides data for comparing the toxicity of oil dispersions generated both mechanically and with the use of chemical dispersions, incorporating the toxicity of both dissolved oil and droplets of oil.

Highlights

► Development of methodology to enable parameterization of toxicity data following exposure of test organisms to oil dispersions. ► Improving the value of numerical models used to predict fate and effects of oil spills. ► Establishment of continuous and predictable inline production of oil dispersions with defined oil droplet size distribution. ► Simultaneous comparison between the effects of dispersion and their corresponding equilibrium water soluble fractions. ► Supplying parameterized data and comparing toxicity of oil dispersions generated with or without chemical dispersants.

Introduction

Oil released into the sea will form surface oil slicks or be dispersed in small oil droplets with dissolved water soluble oil components in the water column. The relative proportion of the phases varies with time, the type of oil, the size and depth of the release, and physical parameters such as temperature, light conditions, wind and currents (Daling et al., 1990, National Research Council, 2005). In general, much attention has been focused on the oil itself due to its intrinsic physical properties, and the dissolved fraction because of its bioavailability. However, for filter-feeding organisms, oil droplets may make a significant contribution to toxicity due to uptake through the intestine.

In order to estimate possible adverse impact of petrogenic oil components on marine populations, exposure risk and exposure concentrations have to be calculated, and at present there is no alternative to numerical modelling for describing the fate and spreading of the oil. Although the droplet size distribution and total concentration of oil in water may be calculated, the toxicity is almost exclusively related to the dissolved fraction of oil (French McCay, 2002). However, releases of petrogenic products also cause the formation of oil-in-water dispersions which are an additional potential source of toxic effects. Limited knowledge exists on the quantitative effect of oil droplets and their potential contribution is either ignored or included as safety factors in environmental risk analyzes in order to cover for this uncertainty. In order to use data from exposure to oil dispersions in model simulations, the observed effect must be related to parameters that are predicted in time and space during simulations of oil spills. Included parameters may be the concentration of total and dissolved hydrocarbons, the corresponding chemical composition (reduced to component groups or single components) and the size distribution of the oil droplets.

Historically toxicity testing of oil in water has been focussed on the dissolved fraction of oil (e.g. CROSERF low energy stirring, e.g. Singer et al., 2000) or oil in water dispersions (e.g. CROSERF high energy stirring: Clark et al., 2001) where the standardized parameters have been oil loading (mg oil per litre of water) and mixing energy. In generating dispersions of oils with different viscosities and composition, variations in the oil load (mg/l) and mixing energy cause a great variation in the droplet size distribution and the ratio of dispersed: dissolved oil. Hence, those parameters need standardization. However, few attempts have been made to relate toxicity of oil in water dispersions to droplet size distributions and the distributions of oil components between oil and water.

Larvae of several species of fish prey on available micro algae (size range 2–20 μm) (Spectorova et al., 1974, Last, 1979, Stoecker and Govoni, 1984) as well as small zooplankton (Turner, 2004) during the early larval period, and may be suspected to ingest small oil droplets both directly and indirectly through contaminated food items. Oil droplets are also shown to attach to the gill surface of fish and thereby cause enhanced uptake of polyaromatic hydrocarbons (PAH) (Ramachandran et al., 2004).

The use of oil dispersants may in some cases effectively decrease the impact from oil spills on surface dwelling organisms such as marine birds and mammals, as well as shore living organisms. In the water column the use of dispersants will cause a temporary increase in the concentration of oil droplets as well as elevated concentrations of dissolved components, due to the increased contact area between oil and water. However, the water-soluble fraction does not increase in proportion to the concentration of oil, as demonstrated by Aurand and Coelho (1996) where a 10-fold increase in oil load caused an approximate doubling of the concentration of hydrocarbons in the water when generating WAF by the CROSERF method. Thus, when adding chemical dispersants to the oil, the dispersed: dissolved ratio will increase as the total concentration of oil increases. When evaluating the environmental effects in the water column when using chemical dispersants in combat of oil slicks, it is essential that the contribution of the oil droplet fraction to the overall toxicity is known.

A scientific committee under the US Ocean Studies Board some years ago reviewed the available literature on effects of oil and oil dispersions (National Research Council, 2005). The conclusions for the toxicological part of this work emphasized the need for parameterized data (page 275). Specific recommendations included identification of the relative contribution of the dissolved and dispersed oil phases to the overall toxicity, parameterized modes to predict photo-enhanced toxicity and evaluation of long term effects.

In the present paper, we describe methodology developed for providing parameterized data on oil dispersion toxicity, based on continuous generation of well defined and documented dilutions series of oil dispersion and water soluble fractions of oil in a flow-through system.

Section snippets

Design criteria

In laboratory scale experimental systems with dispersed oil, a loss of oil droplets from adhesion to equipment surfaces is expected due to a limited volume to surface ratio of the experimental set-ups. However, this effect may be reduced by system design and the choice of appropriate construction materials. The first challenge is to obtain and maintain a stable dispersion of oil droplets in the test vessels, minimizing surfacing of oil droplets during the test period. The solution to this

Generation of oil dispersions

The system for generating dispersions was tested at different temperatures with oils of different qualities. Examples of size distribution of oil droplets in the dispersion for two different weathered oils (+200 °C residue) are shown in Fig. 5. Troll crude oil (Fig. 5A) is an example of a naphthenic oil, whereas Skarv crude oil (Fig. 5B) is classified as a waxy oil. The dispersion from both oils showed a droplet size distribution at a flow at 200 ml/min with a distribution maximum based on volume

Method application studies

The system has been tested with first-feeding cod larvae (Gadus morhua L.) 9–17 days post hatching (Olsvik et al., 2010) and the calanoid copepod Calanus finmarchicus, Gunn. (Hansen et al., 2009). In both experiments the effects on gene expression were compared between a serious if dispersions and their corresponding water soluble fractions. The 4.5 l experimental vessels were stocked with 200–240 cod larvae 9 days post hatch, corresponding to approximately 50 mg wet weight per litre on day 17 post

Conclusions

The current test system has shown to produce predictable and controllable oil-in-water dispersions and corresponding WSFs. Due to the system of dilution by computer controlled oscillating magnetic valves the exposure regime can be easily controlled within a wide range with respect to time course and concentration range, and only limited by the exchange rate of water in the exposure vessels. The continuous generation of dispersions and WSFs enables quantification of the relative contribution to

Acknowledgements

This project was financed by the Research Council of Norway, Statoil ASA and The Norwegian Oil Industry Association (OLF).

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Marine Pollution Bulletin

Abstract

Highlights

Introduction

Section snippets

Design criteria

Generation of oil dispersions

Method application studies

Conclusions

Acknowledgements

References (17)

Characterization of crude oils for environmental purposes

Oil Chem. Pollut.

Statistical description of the bubble cloud resulting from the injection of air into a turbulent water jet

Int. J. Multiph. Flow

Transcriptional effects of dispersed oil and water-soluble fractions of oil on glutathione S-transferases in Atlantic cod (Gadus morhua) larvae

Chemosphere

Standardization of the preparation and quantification of water accommodated fractions of petroleum for toxicity testing

Marine Pollut. Bull.

Techniques for microbial control in the intensive rearing of marine larvae

Aquaculture

Artificial rearing of the Black Sea turbot larvae (Scophthalmus maeoticus)

Aquaculture

Cited by (82)

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Mind the gap – Relevant design for laboratory oil exposure of fish as informed by a numerical impact assessment model

Recommendations for the advancement of oil-in-water media and source oil characterization in aquatic toxicity test studies

Recommendations for advancing media preparation methods used to assess aquatic hazards of oils and spill response agents

Crude oil exposure of early life stages of Atlantic haddock suggests threshold levels for developmental toxicity as low as 0.1 μg total polyaromatic hydrocarbon (TPAH)/L

Co-exposure to UV radiation and crude oil increases acute embryotoxicity and sublethal malformations in the early life stages of Atlantic haddock (Melanogrammus aeglefinus)