Subscriber access provided by COLORADO COLLEGE
Article
Reproduction dynamics in copepods following exposure to chemically and mechanically dispersed crude oil Bjørn Henrik Hansen, Iurgi Salaberria, Anders Johny Olsen, Kari Ella Read, Ida Beathe Øverjordet, Karen Hammer, Dag Altin, and Trond Nordtug Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es504903k • Publication Date (Web): 06 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 23
Environmental Science & Technology
1 2
Reproduction dynamics in copepods following exposure to chemically and mechanically dispersed crude oil
3 4 5
Bjørn Henrik Hansen1*, Iurgi Salaberria1, Anders J. Olsen2, Kari Ella Read1, Ida Beathe Øverjordet1, Karen M. Hammer1, Dag Altin3 and Trond Nordtug1
6 7
1
SINTEF Materials and Chemistry, Environmental Technology, 7465 Trondheim, Norway
8
2
Norwegian University of Science and Technology, Department of Biology, 7491 Trondheim, Norway
9
3
Biotrix, 7022 Trondheim, Norway
10 11
*Corresponding author: Bjørn Henrik
[email protected], fax: +47 73595910
Hansen,
phone:
12 13
ACS Paragon Plus Environment
+47
98283892,
e-mail:
Environmental Science & Technology
14
ABSTRACT
15
Conflicting reports on the contribution of chemical dispersants on crude oil dispersion toxicity have
16
been published. This can partly be ascribed to the influence of dispersants on the physical properties
17
of the oil in different experimental conditions. In the present study the potential contribution of
18
dispersants to the reproductive effects of dispersed crude oil in the marine copepod Calanus
19
finmarchicus (Gunnerus) was isolated by keeping the oil concentrations and oil droplet size
20
distributions comparable between parallel chemically dispersed (CD, dispersant:oil ratio 1:25) and
21
mechanically dispersed oil (MD, no dispersant) exposures. Female copepods were exposed for 96 h
22
to CD or MD in oil concentration range of 0.2-5.3 mg L-1 (THC, C5-C36) after which they were subjected
23
to a 25-day recovery period where production of eggs and nauplii were compared between
24
treatments. The two highest concentrations, both in the upper range of dispersed oil concentrations
25
reported during spills, caused a lower initial production of eggs/nauplii for both MD and CD
26
exposures. However, copepods exposed to mechanically dispersed oil exhibited compensatory
27
reproduction during the last 10 days of the recovery period, reaching control level of cumulative egg
28
and nauplii production whereas females exposed to a mixture of oil and dispersant did not.
29 30
ACS Paragon Plus Environment
Page 2 of 23
Page 3 of 23
31
Environmental Science & Technology
TOC Abstract Art
32
ACS Paragon Plus Environment
Environmental Science & Technology
33
INTRODUCTION
34
Sea-borne crude oil is dispersed naturally by turbulence.1 As an oil spill response (OSR) action,
35
chemical dispersants can be applied to accelerate dispersion of oil into the water column and
36
subsequently enhance oil weathering through dissolution, spreading and biodegradation.1 These
37
dispersants may elicit direct toxic effects2, 3, and usage increases oil exposure to pelagic organisms.1
38
Hence, chemically dispersed oil (CD) may be more toxic than mechanically dispersed oil (MD).4-6
39
Traditionally water accommodated fractions (WAFs) of oil are used for toxicity testing of dispersions
40
in static or static-renewal exposure systems.7 To simulate environmentally relevant exposure
41
scenarios, WAFs are usually prepared by low energy stirring (LE-WAF), which leads to limited droplet
42
formation, high energy stirring (HE-WAF) and/or the addition of chemical dispersants (chemically
43
enhanced WAF (CE-WAF)). These WAF preparations are used to simulate differences in weather
44
(degree of wave action causing dispersion) and dispersant application. However, to determine the
45
contribution of chemical dispersant to the toxicity of oil dispersions, these conventional and widely
46
used methods are inadequate. The degree of oil droplet generation using such methods will be highly
47
affected by oil viscosity, oil dispersibility and dispersant efficiency, and oil dispersions (i.e. WAFs vs
48
CE-WAFs) will contain different oil concentrations and droplet size ranges. WAFs consist of a
49
particulate phase (dispersed fraction) and a water phase (dissolved fraction); the latter considered
50
being the most bioavailable and toxic fraction.8-11 Moreover, these two phases are not stable over
51
time in WAFs due to droplet surfacing velocity, being proportional to the diameter of the droplets
52
and the density of the oil, which will differ between the two treatments. This causes shifts in the
53
equilibrium between the two phases, thereby further impairing direct comparison between WAF and
54
CE-WAF. To determine the contribution of a chemical dispersant to the toxicity of oil dispersions, the
55
effects of mechanically and chemically dispersed oil differing only in the presence of dispersant
56
should be compared, while all other exposure parameters are maintained unaltered. Therefore a
57
standardized flow-through method for oil-in-water dispersion generation is to be preferred.12 It
ACS Paragon Plus Environment
Page 4 of 23
Page 5 of 23
Environmental Science & Technology
58
allows for in-line and continuous generation of comparable MD and CD in terms of oil concentration
59
and range of oil droplet size, thereby increasing the possibility to isolate a potential contribution of
60
chemical dispersant to toxicity.
61
Chemical validation of exposure solutions is essential to determine exposure concentrations, which
62
should be expressed in function of time to obtain the effect concentrations. However, oil droplet size
63
ranges of CE-WAF and WAF solutions are rarely reported in toxicity tests. Effect concentrations
64
derived from chemical analysis of exposure solutions containing oil droplets (e.g., HE-WAF/CE-WAF)
65
may underestimate the toxicity of the exposure solution and hamper reliable comparison with WAFs
66
that do not contain droplets, such as LE-WAF.
67
Predictions of the potential effects of chemical dispersant application as an OSR action requires sub-
68
lethal toxicity testing with adequate chemical validation to generate useful data for modeling.12, 13
69
Very few studies have investigated the resilience of an organism to recover from adverse
70
physiological effects following exposure to dispersed oil14 although this information is critical to
71
select the most environmentally beneficial OSR action.
72
The aim of the present study is to determine the contribution of a chemical dispersant to long-term
73
reproductive toxicity following a short exposure to dispersed oil in the marine copepod Calanus
74
finmarchicus. This calanoid is the dominating meso-zooplankton species of the Northeast Atlantic,
75
and constitutes a crucial ecological link between primary producers and fish.15 It resides in the upper
76
water masses during spring and summer16 where oil may be present after a surface oil spill.1
77
Comparable acute toxicity of mechanically and chemically dispersed oil was previously observed for
78
C. finmarchicus4 and its reproduction impaired by relatively high concentrations of mechanically
79
dispersed oil.14 Pregnant female copepods were therefore exposed for 96 h to three concentrations
80
(0.2, 1.0 and 5.3 mg oil L-1) of two comparable solutions of mechanically dispersed North Sea crude
81
oil or oil dispersed with the chemical dispersant Dasic NS. After exposure the copepods were allowed
ACS Paragon Plus Environment
Environmental Science & Technology
82
to recover in clean seawater for 25 days during which offspring (eggs and nauplii) were sampled daily
83
to assess for time-dependent effects on reproduction.
84 85
EXPERIMENTAL
86
Husbandry. Young fertilized females of the marine copepod C. finmarchicus were collected from the
87
continuous laboratory culture at NTNU/SINTEF Sealab17 and fed continuously 150 mg wet weight L-1
88
(224 µg carbon L-1) live Rhodomonas baltica algae. Water temperature (10°C ± 1°C) was controlled by
89
submerging all exposure chambers into a water bath.
90
Exposure. A naphthenic crude oil from the North Sea (Troll) was chosen for the study. The oil was
91
artificially weathered by heating to 200°C18, resulted in oil residues with evaporation loss
92
corresponding to approximately 0.5-1 day weathering on the sea surface, and the +200°C residue
93
was collected and used for the generation of oil dispersions. The weathered crude oil was dispersed
94
into filtered sea water (5 µm cartridge filter) through a series of nozzles, yielding a constant flow of
95
dispersion with a stable droplet concentration and size distribution (droplet diameter
