Workers who had the highest exposure to hydrocarbons during the Deepwater Horizon oil spill disaster had a higher risk of having a hypertension diagnosis in the years following the event, a new study suggests.

Results showed that the highest exposure to total petroleum hydrocarbons during the cleanup operation was associated with a 31% higher risk of new hypertension 1 to 3 years later.

“What is remarkable is that we still found an increased risk of hypertension a couple of years after the cleanup had been completed. This suggests working in this environment even for a short period could have long-term health consequences,” lead author Richard Kwok, PhD, told theheart.org | Medscape Cardiology.

The study was published online in February 23 in JAMA Network Open.

For the study, Kwok, a scientist at the US National Institute of Environmental Health Sciences, and his colleagues estimated the levels of exposure to toxic hydrocarbons in 6846 adults who had worked on the oil spill cleanup after the Deepwater Horizon disaster in 2010, during which 200 million gallons of oil spilled into the Gulf of Mexico. They then investigated whether there was an association with the development of hypertension 1-3 years later.

“Clean-up efforts started almost immediately and lasted over a year,” Kwok noted. “In the first few months, oil flowed freely into the Gulf of Mexico which released high levels of volatile organic compounds into the air that the workers could have been exposed to. The exposures change over time because the oil becomes weathered and starts to decompose and harden. This is associated with a lower level of volatile organic compounds but can still cause damage,” he explained.  

Workers involved in the cleanup may have been there for just a few days or could have spent many months at the site and would have had different exposures depending on what types of jobs they were doing, Kwok reported.

“The highest levels of exposure to total hydrocarbons would have been to those involved in the early months of the oil spill response and cleanup when the oil was flowing freely, and those who were skimming oil off the water, burning oil, handling dispersants, or involved in the decontamination of the vessels. Others who were involved in the cleanup on land or support functions would have had lower exposures,” he said.

Each worker was interviewed and asked about their activities during the cleanup operation, the location of work, and period of work. Their level of exposure to total petroleum hydrocarbons (THCs) was estimated based on their self-reported activities, and when and where they worked.

Two measures of estimated cumulative THC were calculated: cumulative maximum daily exposure, which summed the maximum daily THC exposure level, and cumulative mean exposure, which summed the mean daily exposure levels. These THC values were categorized into quintiles based on the exposure distribution among workers.

Systolic and diastolic blood pressure measurements were collected for the workers during home exams from 2011-2013 using automated oscillometric monitors. Newly detected hypertension was defined as either antihypertensive medication use or elevated blood pressure since the spill.

Results showed a clear dose relationship between the level of THC exposure and the development of hypertension at follow-up.

Table. Cumulative Maximum THC Level (ppm-days)

Quintile	Prevalence Ratio for Hypertension (95% CI)
1	1 (ref)
2	1.05 (0.93 – 1.18)
3	1.29 (1.13 – 1.46)
4	1.25 (1.10 – 1.43)
5	1.31 (1.15 – 1.50)

 

Similar results were seen for the relationship between cumulative mean THC exposure levels and the development of hypertension.

Despite the limitations of accurately estimating THC exposure, Kwok believes the results are real. “We looked at many different covariates including smoking, education, gender, race, ethnicity, and body mass index, but even after controlling for all these we still saw an association between the amount of exposure to THC and risk of hypertension,” he noted.

But the risk of developing hypertension did appear to be greater in those individuals with other risk factors for hypertension such as high BMI or smokers. “There seems to be a combined effect,” Kwok said.

He pointed out that while previous studies have shown possible health effects related to THC exposure on an acute basis, in this study, the effect on blood pressure was still evident years after the exposure had ended.

Other occupational studies have looked at people in jobs that have had longer exposures to volatile organic compounds such as taxi drivers, but this is one of the first to look at the long-term effect of a more limited period of exposure, he added. 

“Our results suggest that the damage caused by THCs is not just an acute effect, but is still there several years later,” Kwok commented.  

He says he hoped this study will raise awareness of the health hazards to workers involved in future oil spills. “Our results suggest that we need better protective equipment and monitoring of workers and the local community with longer-term follow up for health outcomes.”

Another analysis showed no clear differences in hypertension risk between individuals who worked on the oil spill cleanup (workers) and others who had completed required safety training but did not participate in the clean-up operation (nonworkers). Kwok suggested this may have been a result of the “healthy worker effect,” which is based on the premise that individuals able to work are healthier than those unable to work.

This study was funded by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences.  The authors report no disclosures.

JAMA Network Open. Published online February 23. Full text

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