Gulf Longitudinal Follow-up (GuLF) Study

The Gulf Long-term Follow-up Study (GuLF STUDY, www.gulfstudy.nih.gov) was initiated in response to the April 2010 explosion of the Deepwater Horizon (DWH) drilling rig and resulting oil spill in the Gulf of Mexico, the largest marine oil spill in U.S. history. A total of 32,608 oil spill response and clean-up workers and non-workers completed an enrollment questionnaire (2011-2013). Over 11,000 individuals from the Gulf states completed a home visit that included collection of biospecimens and anthropometric measurements, including pulmonary function measures. In response to community concerns about reports of oil-related chemicals in the blood of some people years after the spill, we analyzed samples from 1,000 participants collected at home visit for volatile organic compounds including BTEX-h and styrene as well as metals. Levels of these chemicals, apart from styrene, a chemical unrelated to the oil spill, were not different from those in a nationally representative and local sample of NHANES participants once cigarette smoking was considered.

We explore the association between hypertension and both individual blood metal levels and the metal mixture. 957 participants who participated in the the biomonitoring subsample who had had blood measurement for at least one metal and baseline blood pressure measurements were included in the sample. We did not find overall cross-sectional associations between blood cadmium, lead, mercury, selenium levels and hypertension or blood pressure. We found some evidence suggesting that manganese might be positively associated with risk of hypertension. Associations varied somewhat by race and BMI (Xu, 2021).

Follow-up data were collected from 21,256 participants between 2013-2016. Mental health trajectories were assessed among those who had symptoms of depression, PTSD, or anxiety at enrollment and a random sample of the remainder in four mental health interviews over two years (n=2,969). Participants (n=3,403) living within 60 miles of New Orleans, LA or Mobile, AL completed a clinical exam (2014-2016) that included additional lung function tests, assessment of neurological function, and biological sample collection. A second follow-up interview was completed in May 2021 with a response rate of 61% among those who completed the first follow-up. Participants are being followed via linkage to cancer registries and the National Death Index. We currently have linked National Death Index data through 2019 (9 years of follow-up data since the spill) and plan to publish findings assessing oil spill cleanup work exposures related to all-cause and cause-specific mortality in early 2023.

Extensive efforts were made to characterize the exposures of study participants. We used questionnaires and monitoring measurements that had been taken during the spill to develop job exposure matrices for a wide range of possible exposures. This work involved recalibrating exposure measurements taken during cleanup, identifying numerous distinct exposure groups performing like-tasks defined by timing of work relative to the capping of the well, activities, and location, and developing new statistical approaches to deal with values below the LOD and other censoring. Ordinal exposure metrics (for THC, hierarchical job class, and exposure to burning and dispersants) have now been supplemented with quantitative measures of specific oil spill chemicals. The metrics have largely focused on inhalation exposures, but measures of potential dermal exposure are being finalized. A series of peer-reviewed papers describing these efforts were published this year as a monograph in the Annals of Work Exposures and Health were published (Stewart, 2022a; Stenzel 2022a; Stenzel 2022b; Groth 2022a; Huynh 2022a; Huynh 2022b; Huynh 2022c; Groth 2022b; Ramachandran 2022; Pratt 2022; Arnold 2022; Stenzel 2022c; Ng 2022; Stewart 2022b).

We continue to explore respiratory health effects. We recently evaluated modeled PM2.5 exposure estimates from burning and flaring of natural gas and oil during cleanup, finding that compared to workers not involved in or near the burning, those with higher cumulative PM2.5 exposure had substantially reduced FEV1, FVC and FEV1/FVC ratio (Chen et al., 2022). Similar dose-response trends were seen for average PM2.5 exposure and in analyses stratified by smoking and time from exposure to spirometry and when we restricted to workers without pre-spill lung disease. We also evaluated airborne crude oil chemicals in relation to symptoms-based asthma risk 1-3 years after the spill. We found that workers were at 60% higher risk of getting asthma than nonworkers. We also found that higher total hydrocarbons, a marker of crude oil exposure, was associated with increased risk in an exposure-dependent manner. Similarly, asthma risk also increased with increasing exposure to individual BTEX-H chemicals and the chemical mixture. With fewer cases, associations were less apparent for physician-diagnosed asthma alone (Lawrence, 2022).

We also continue to examine other chronic diseases in relation to oil spill cleanup exposures. In a study assessing oil spill cleanup-related total hydrocarbon exposure and hypertension, we used systolic and diastolic blood pressure measurements collected at the home visit (2011-2013) using a standardized protocol. Newly detected hypertension was defined as new onset antihypertensive medication use or elevated blood pressure detected at home exam. Among workers, those with higher cumulative total hydrocarbon exposure levels were more likely to have hypertension compared to those at the lowest level. Additionally, workers exposed to PM2.5 from burning were 1.26 times more likely to have newly diagnosed hypertension. Persons performing cleanup on water and response work also showed elevated likelihood of hypertension: Individuals were 1.34 and 1.51 times more likely, respectively, to have hypertension than compared to the lowest exposed job class (Kwok et al., 2022). We also recently reported associations between total hydrocarbon exposure and diabetes among 2,600 participants who completed a clinical exam and had no self-reported diabetes diagnosis prior to the spill. Incident diabetes mellitus was defined by self-reported physician diagnosis of DM, antidiabetic medication use, or a measured hemoglobin A1c value 6.5%. We observed an exposure-response relationship between maximum daily ordinal THC exposure level and incident diabetes, especially among overweight participants (Jardel, 2022). In a recently completed study, we assessed total hydrocarbons and volatile oil components BTEX-H in relation to myocardial infarction (MI) and CHD deaths. Among 22,809 workers without CHD before the cleanup, 542 had an incident CHD event. Results from this study led by University of North Carolina doctoral student Dazhe Chen have been submitted for publication.

Using area deprivation linked data, we continue to explore neighborhood impacts on GuLF participants. We assessed neighborhood disadvantage and immune-related illnesses. A paper evaluating frequency of pneumonia, colds, flu and other infectious conditions has been submitted for publication. Related work is exploring the influence of oil spill exposures. We are currently undertaking a large effort to link a wide range of geospatial environmental data to the GuLF Study to better understand the influence of other environmental and social exposures on the health of participants and whether these factors interact with any impacts from the spill.