Coping with oil spills: oil exposure and anxiety among residents of Gulf Coast states after the Deepwater Horizon oil spill

Dear Editor,

We are grateful for the opportunity to improve our manuscript in light of the reviewer comments. We address each comment specifically below in blue text.

In addition, we have added information in the introduction about the ecological and community harms of the Deepwater Horizon drilling rig. The citations used throughout the paper have also been updated.

We realized that the variable indicating whether cleanup participation were paid or on a volunteer basis had an extraordinary amount of missing data. Therefore, we have deleted the one analysis based on that variable from this report.

Thank you for your consideration.
Zachary Goldman et al.

Editor’s Comments:

•    Although both reviewers consider this an important paper they make points that, if addressed, would strengthen it. One reviewer makes a number of points in relation to methodology and analysis that would make the paper easier to understand.
We have responded to the comments below.
•    The same reviewer asks for clarification about the relationship between this paper and ref 10. Such a clarification would be very helpful.
Our research group’s previous paper was about depression. This paper is about anxiety.
•    The other reviewer asks that more context is provided for the paper - e.g. with respect to similar large environmental incidents caused by oil spillages.
We have expanded our introduction.
•    This reviewer also would like to see the methodology set out more clearly - I suggest that placing the methodology in some broad psychological context or providing some theoretical background to the choice of approach or measures (e.g. mastery) might be one way of approaching those points.
We have responded to reviewer comments explaining that the choice of self-mastery scale was made by the agencies who developed and implemented this survey. We are limited in this analysis of public data to the variables measured. Our Tobit analysis is based on a common psychometric method for which we provide citation and present an illustration in Figure 1 to clarify.

Reviewer 1:

General statement about the manuscript
The research presented in this manuscript describes associations between oil exposure and anxiety after the Deepwater Horizon marine oil spill that occurred in April 2010 and evaluates the following:
1.    Effect modification by self-mastery
2.    Emotional support
3.    Clean-up participation
The authors indicate that the event was historic as it was the largest accidental marine oil spill to date. Their work tested the hypothesis that exposure to oil from the Deepwater Horizon event was associated with anxiety. As described by the authors the main conclusion from this research was oil contact can increase anxiety and this association can be mitigated by clean-up participation. The authors present a conclusion and discussion that support this.
We thank the reviewer for recognizing the consistency of our results and discussion.

Level of comprehensibility and the style of the paper
Following usual convention, the research was divided systematically into the following:  an introduction, methods, results, and discussion. The manuscript had gradual flow and readability with concepts introduced in a manner that followed a logical progression.
We appreciate the reviewer recognizing the clarity of our manuscript.

Level of importance
The authors present a manuscript with extremely important data, in part because this was such a large and protracted event, impacting public health, which was indicated as part the focus of the research. What makes this spill noteworthy or historic, was the catastrophic loss of human life, unique to this spill. Additionally, this event was a protracted spill that affected many people and their livelihoods. Much research has been done post Deepwater Horizon but as the authors indicate, little on the focus of their particular field of research.  Therefore, this manuscript predicts it will be likely the first to examine associations of anxiety in those that participated in clean-up activities compared to those that didn’t.
We thank the reviewer for recognizing the novelty and significance of this contribution.
This publication has high relevance for academics as well as members of governmental organisations, including oil spill response agencies. It could provide valuable information as to where to direct resources to support emotional health should another event occur.  Proactive techniques may be identified from this research.
We thank the reviewer for recognizing the potential translational value of this work.

Level of completeness
In reading this paper it appeared the introduction was very brief and addressing this brevity forms the basis of this review. This comment is given as there is some background knowledge that further sets the scene for the research and these additional factors if highlighted, could strengthen the introduction. While the paper reads extremely well, this reviewer feels deeper context for readers that are familiar with public health concepts but not oil spill responses could be provided by addressing three sections:
We appreciate the suggestions on how to better contextualize our work.
1.Additional commentary about the human cost of this spill, further to what is indicated in the manuscript:
•    It is acknowledged that there is background information in the introduction however, some more information on the event itself, such as further defining why this was such a historic event, in no small part because of the human cost to this event, life was lost.  Commentary on this aspect feels critical as the Deepwater Horizon was historic in part because of this uniqueness, because of loss of human life from the explosion on the rig that triggered the spill. Often in oil spill research there is discussion of wildlife, ecosystems, tourism, and livelihoods (as indicated in the manuscript) but this aspect may need reinforcing to describe why this was so historic and so unique.
We have added information describing how the Deepwater Horizon Oil Spill is unique, compared to other spills.
•    A brief statement citing other large spills that have also been termed historic, but for different reasons from the Deepwater Horizon, for example the Exon Valdez.
We have added information about other oil spills in the introduction. We have also added information about the financial impacts of the spill as well as examples of other disasters, such as the Hebei Spirit tanker disaster in Korea and the Exxon Valdez in Alaska.
2.Terminology
While some may argue this is an unnecessary addition this reviewer feels that this would assist readers, that may not understand oil spills or responses, providing context. These small points may strengthen the introduction while not distracting from the core of the research providing a birds-eye view or context including:
•    Dispersant is mentioned in the script as a method of remediation, there were other methods of remediation used in this spill response. A definition for the reader describing what dispersant is with a reference, would be useful as there are many different types and a long process of decision making before utilizing it.  A dispersant is also a contaminant, toxic and can contribute to the damage of the ecosystem and there are also human health implications.  As public health is a focus of this paper it may be worth mentioning.
We have added information about dispersants in the manuscript.
•    For readers that are unfamiliar with oil spill terminology, a simple statement converting barrels of oil to gallons would provide the reader with a clear understanding of the massive volume of oil discharged in this event and then provide a basis of understanding should they want to investigate other spills as a comparison of impact through volume spilled.
We have changed the units in the manuscript.
•    While a mention of the type of oil was mentioned a comment about different oils may be useful.  Why?  If it was a light fuel oil such as diesel, depending on weather conditions and other factors it theoretically evaporates easily and be dispersed by the energetic activity of the environment. Dispersed oil (while still toxic, highly volatile and damaging to the environment and animals) is less visible to residents, communities, and the general public, and may disperse before impacting coastlines in the area.  Heavy fuel oil or crude oil in an environment can have an impact on people as it is visually distressing, has a smothering effect on animals and the environment and widely reported in the media.
Although we appreciate the reviewer’s expertise on this issue, the survey we used did not distinguish between these categories and we have no way of knowing what kind of oil people encountered. Additionally, because the audience of this paper is largely comprised of phycologists who may see translational value to other community disasters, this level of detail may detract from the focus of the paper. In the interest of concision and because we are unsure of the type of oil, we respectfully prefer to leave the manuscript unchanged on this point.
3.Methods
•    Further discussion explaining why particular measurement tools were chosen over others would provide more insight. For example, self-mastery was mentioned as a key indicator tested, it would have been useful for me as a reader to know a little more about this beyond coping ability and further exploration or brief comment of why coping ability promotes resilience?
We are limited to the data collected by this large government survey in the past. The agencies implementing the study chose to measure self-mastery using this scale. We hypothesized self-mastery may be relevant to the mental health implications of an oil exposure, but this was speculative as noted in the manuscript.
•    Readers may experience some confusion about the terms “directly exposed to oil” and “direct contact” as both were presented. It is unclear if it refers to being exposed from the point of view of hands-on contact with oil through clean-up participation or activities as a volunteer or part of a professional oil spill response agency. Does “exposed” refer to residents seeing oil beached, or “exposed” to oil through loss of livelihood, employment or tourism. Clarification could remove any ambiguity for the reader. If there was “direct contact” was that as part of a professional oil spill response agency, part of an orchestrated clean-up effort as part of the Deepwater Horizon wider response or “exposed” individuals acting alone.  Knowing that could provide context around the anxiety that was experienced.
We appreciate the reviewer raising this ambiguity; we have changed the wording to “direct contact with oil” to be consistent with the wording of the survey questionnaire.

In summation
While the target audience for this manuscript may be involved in public health, other agencies will be very interested in this research. This is a very thought-provoking manuscript that provides useful but also important ideas and data. This subject is critical for integration into public health commentary in the future. Provision of further context including some terminology and explanation to the points noted in this review may assist future readers to gain full appreciation of the scale and complexity of the Deepwater Horizon event and the effect and anxiety it created within the community and individuals.
We appreciate the reviewer noting the importance of this manuscript.

Reviewer 2:

This is an important paper to show that reliefe activitis may have a beneficial effect on mental status of people affected by a disaster.
We thank the reviewer for noting the importance of this manuscript and providing constructive feedback below.

2. Methods
a It is not clear how the Tobit latent anxiety seviry is used for the study. Did the author re-calculate the level of anxiety among the participants? If so, please describe the modified anxiety levels in Table 2.  Or if the score was used for regression analyses, please describe it.
We provide a citation for Tobit regression in the manuscript for readers unfamiliar with this method. We have updated the wording of our methods text on page 6 to clarify that latent anxiety is a normally distributed latent variable. This is shown in Figure 1. We thank the reviewer for identifying this possible point of reader confusion.
b Please describe the definition of binge drinking.
We have clarified the definition of binge drinking as used in the survey.
c Please include the method of imputation used in Table 1 in the Method section.
We provide a citation for multiple imputation by chained equation on page 7. We have changed the text on page 7 to clarify our imputation model. We thank the reviewer for encourage us to clarify which variables were imputed.
d Please describe Wald test used in Table 3 and 4 in the Method section.
We have corrected this to say t-test.

3. Results
a Table1. What are the numbers in bracket means.
These are confidence intervals for the estimated population means or proportions. We have clarified this in the manuscript table legend.
b Please include average of anxiety score in each group so that the reader can see the trend.
Table 1 shows confounder/exposure and outcome/exposure relationships. It would be confusing to report confounder/outcomes relationships within this table. The requested exposure/outcome associations are presented in Table 3.
c Table 3 and 4 are not consistent with main manuscript. In manuscript the author use 'beta' as outcome, but the tables show 'difference in anxiety'. Also there is no explanation about what the difference in anxiety means e.g. what score was subtracted by what.   
We have clarified throughout the manuscript that the regression coefficient β corresponds to differences in anxiety according to levels of exposure (i.e., direct oil contact).
 
4. Discussion
a Although the author discusse the novelty of the article in 4.2, it is not clear how the article is different from the research of Reference 10.
The other paper by our research group was about depression, rather than anxiety.
b As the authors discussed, previous studies sometimes show negative impact of volunteering on mental health. Please add discission about the reason why this discrepancy occurs e.g. difference in disaster type, characteristics of the residents, etc.
We prefer to not speculate on topics beyond our expertise or the data in this study.

We thank the reviewer for these helpful comments.

Introduction: In April 2010, a fatal explosion on the Deepwater Horizon drilling rig in the Gulf of Mexico resulted in the largest marine oil spill in history. This research describes the association of oil exposure with anxiety after the Deepwater Horizon Oil Spill and evaluates effect modification by self-mastery, emotional support, and cleanup participation.

Methods: To assess the impacts of the Deepwater Horizon Oil Spill, the Centers for Disease Control and Prevention conducted the Gulf States Population Survey, a random-digit-dial telephone cross-sectional survey completed between December 2010 and December 2011 with 38,361 responses in four different Gulf Coast states­: Louisiana, Florida, Alabama, and Mississippi. Anxiety severity was measured using the Generalized Anxiety Disorder symptom inventory. We used Tobit regression to model underlying anxiety as a function of oil exposure and hypothesized effect modifiers, adjusting for socio-demographics.

Results: Latent anxiety was higher among those with direct contact with oil than among those who did not have direct contact with oil in confounder-adjusted models (β = 2.84, 95% CI: 0.78, 4.91). Among individuals with direct contact to oil, there was no significant interaction between participating in cleanup activities and emotional support for anxiety ( P = 0.20). However, among those with direct contact with oil, in confounder-adjusted models, participation in oil spill cleanup activities was associated with lower latent anxiety (β = -3.55, 95% CI: -6.15, -0.95).

Conclusion: Oil contact was associated with greater anxiety, but this association appeared to be mitigated by cleanup participation.