Modeling mortality of eggs/larvae as a function of hydrocarbon concentration, exposure time and type of oil

Transcription

1 Modeling mortality of eggs/larvae as a function of hydrocarbon concentration, exposure time and type of oil An introduction Workshop on the effects of oil-spill on Pelagic Ecosystems, IMR Odd Willy Brude Jan 2008

2 Modeling mortality of eggs/larvae as a function of hydrocarbon concentration, exposure time and type of oil Mortality is a function of exposure Exposure is conditioned by: - Eggs/larvae to be present - Oil to be present (in the same area at the same time) in concentrations that gives lethal effects In order to model exposure one must know - Egg/larvae distribution at a given time (horizontal, vertical) - Oil dispersion and spread in water column In order to model/estimate effects one must know - Response to exposure (dose-response) Two choices of modelling approach - Separate models for egg/larvae distribution and oil drift - Integrated model (can calculate exposure dose over time ppb/hours) Slide 2

3 Egg/larvae distribution Cod eggs/larvae 1997 Data from IMR Det Norske Veritas AS. All rights reserved 25 February 2008 Slide 3

4 Egg/larvae distribution March/April May/June July/August Slide 4

5 Oil spill modeling Slide 5

6 Oil spill modeling Fate of oil Slide 6

7 Dispersion of oil into the water column Three separate processes: 1. amount of oil physically dispersed pr. time unit 2. physical characterization of dispersed oil (droplet size) 3. Release of components to water phase Amount of oil physically dispersed pr. time unit - Decreases with time and is dependent on type of oil, weathering and sea state (incl. temp), oil film thickness and area distribution. Droplet size distribution - Decide how much of the downmixed particles that stays in the water column - Is dependent on oil type, weathering and sea state Release of components to the water phase - Equilibrium is dependent of oil type (component composition), weathering (changes in composition), concentration and temperature - Kinetics is dependent of particle size and surface characteristics, and to a less degree concentration gradient Slide 7

8 Effects on eggs/larvae The effects of oil on fish eggs/larvae depends on - Concentration and composition of dissolved oil components - Duration of exposure There is a good scientific foundation for calculating effects of individual components in oil based on log Kow (Di Toro m.fl. 2000), The individual components are assumed to be toxic additive (French-McCay, 2002). In order to calculate toxicity, one has to know the exact composition of oil components in the water phase Crude oil are in general to a lesser degree water-soluble and moderate toxic to water column organisms The most heavy components (wax and tar compounds) are less soluble, while alkans and BTEX components are the most soluble In general the medium heavy oil are assumed to be most toxic. They are moderate soluble in water and moderate volatile (C8-C15) This implies that toxicity based on THC or total PAH has considerable uncertainty Slide 8

9 Water phase oil component composition 14 Statfjord crude, fresh 14 Troll crude, fresh ppm (mg / L seawater) Total WAF: 28.1 ppm VOCs (C 5 -C 10 ): 26.5 ppm ppm (mg / L seawater) Total WAF: 12.9 ppm VOCs (C 5 -C 10 ): 8.9 ppm C5-Sat C7-Sat C9-Sat C1-Ben C3-Ben TEOC PAH Polars C6-Sat C8-Sat Benzene C2-Ben C4-Ben Naph. Phenols 0 C5-Sat C7-Sat C9-Sat C1-Ben C3-Ben TEOC PAH Polars C6-Sat C8-Sat Benzene C2-Ben C4-Ben Naph. Phenols WAF (component composition) for Statfjord and Troll crude oil. Oil loading: 25 g/l, 13 C. (Hokstad et al. 1998) Slide 9

10 Water phase oil component composition/ loading rate ppm (mg / L seawater) Loading: 10g Troll crude/l seawater (OWR = 1:100) Total WAF: 11.7 ppm VOCs (C 5 -C 10 ): 10.1 ppm Toxicity (EC50): 0.98 ppm WAF (Microtox) ppm (mg / L seawater) Loading: 100mg Troll crude/l seawater (OWR = 1:10000) Total WAF: 1.29 ppm VOCs (C 5 -C 10 ): 0.77 ppm Toxicity (EC50): 0.30 ppm WAF (Microtox) 0 C5-Sat C7-Sat C9-Sat C1-Ben C3-Ben TEOC PAH Polars C6-Sat C8-Sat Benzene C2-Ben C4-Ben Naph. Phenols 0 C5-Sat C7-Sat C9-Sat C1-Ben C3-Ben TEOC PAH Polars C6-Sat C8-Sat Benzene C2-Ben C4-Ben Naph. Phenols WAF from fresh Troll crude oil. Effect of loading rate. (Hokstad et al., 1998). Slide 10

11 Lethal concentrations Typical values for dissolved components Slide 11

12 THC Råoljetester art: Metode Parameter Resultat, mg/l Fisk (diverse) OWD LL 50, 96 timer (6 tester) Laks OWD LL 50, 96 timer 258, 291 (to tester) Marint krepsdyr (Crangon crangon) OWD LL 50, 96 timer (19 studier) Marint krepsdyr (Mysidopsis bahia) WAF LL 50, 96 timer 618 Ferskvannskrepsdyr (Daphnia magna) WAF LL 50, 96 timer 36, 42 (to tester) Ferskvannskrepsdyr (Holmesimysis costata) WAF LL 50, 96 timer 39,5 Ferskvannskrepsdyr (Daphnia magna) WAF LL 50, 48 timer 36, 42 (to tester) Evertebrat OWD TLm, 96 timer Evertebrat OWD TLm, 48 timer 37,5; 63 Slide 12

13 Oil spill modeling Slide 13

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15 Mortality analysis Tapsandeler torskelarver 1990 dag nr 170 (ultimo juni) 8,0 7,0 6,0 Tapsandel (%) 5,0 4,0 3,0 2,0 1,0 0,0 Slide 15

16 Mortality analysis Gjennomsnittlige tapsandeler sildelarver Maksimale tapsandeler sildelarver 1,8 18,0 1,6 16,0 1,4 14,0 tapsandel årsklasse (%) 1,2 1,0 0,8 0,6 0,4 tapsandel årsklasse (%) 12,0 10,0 8,0 6,0 4,0 0,2 2,0 0, , Slide 16

17 Risk perception Petroleum activity Fisheries Probability: 10-3 Huge spill <10 % 10-4 Worst case period <10 % 10-5 Worst case exposure 1-5 % loss of larvae <10 % 10-6 Worst case loss of year class (<25 %) <10 % 10-7 Worst case reduction in spawning biomass (<35 %) ~ Yearly catch of spawning biomass (~35 %) Consequence: Serious env. damage Sustainable? Slide 17

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