Primary sources of atmospheric sulfur dioxide are anthropogenic activities associated with the burning of fossil fuels and industrial processes that may have associations with various morbidities and mortalities. As such, several regional and global regulatory agencies have recommended ambient air limits to reduce environmental exposures. The objectives of this study were to evaluate ambient levels of sulfur dioxide surrounding an oil refinery on the island of CuraÇao. Levels which were then compared to literature values and recommended public health guidelines to determine potential public health risks. Concentrations of sulfur dioxide in Curacao were found to be among the highest globally with an increasing trend over time. While the epidemiological evidence does not conclusively suggest there is a health risk from these levels of exposure, SO2 concentrations greatly exceed regulatory and guidance levels and suggest that further emissions control is warranted. Future recommendations include a more rigorous epidemiological study in CuraÇao and expand the air monitoring efforts to include areas upwind of the refinery as well as additional petrochemical emissions.
Typical annual average concentrations of ambient sulfur dioxide, as of 2005, have ranged from 9 - 35 µg/m3 in North America, 8 - 36 µg/m3 in Europe, 40 - 70 µg/m3 in Latin America, 10 - 100 µg/m3 in Africa and 20 - 200 µg/m3 in Asia [
The Wider Caribbean Region (WCR) includes a number of developing countries for which agriculture, oil and gas exploration in conjunction with processing, provide valuable sources of income. As the WCR is one of the most tourism-dependent regions of the world, factors that affect environmental health and sustainability will have inevitable impacts to the economies and quality of life in many already-needy countries. Approximately 100 oil refineries are located within the WCR, with one of largest and oldest refineries, Isla Refineriá, being located in Willemstad, Curaçao [
Sulfur dioxide has been associated with various morbidities demonstrated by controlled exposure experiments conducted in the early 1950’s [
The short term effects from sulfur dioxide exposure at much lower and more plausible episodic concentrations between 0.20 and 1 ppm (524 - 2620 µg/m3) were also evaluated using controlled chamber experiments in normal, atopic and asthmatic volunteers [
The objective of this study was to conduct an exposure assessment for ambient levels of SO2 downwind of an oil refinery (Isla Refineriá) in Curaçao. This was accomplished by analyzing hourly, daily, and monthly SO2 measurements over a four year period (2010-2014) to determine if any temporal trends exist and to compare levels with public health guidelines in order to assess potential public health risks in Curaçao.
Approximately 40 miles off the coast of Venezuela lies the island of Curaçao in the southern Caribbean. Curaçao is located in the Southern Caribbean Dry Zone, which is characterized by a semi-arid to arid climate, with a distinguishable dry and rainy season, and sustained easterlies. The island is approximately 59 kilometers in length, 4 - 11 kilometers wide and a total land mass area of ~443 km2. The population of ~152,000 consists of greater than 50 nationalities with Dutch and Papiamento as the official languages. The majority of the population (>130,000) resides in Willemstad which is home to the Isla Refineriá.
Two air monitoring stations, Beth Chaim and Kas Chikitu, commissioned by the government of Curaçao have been collecting validated and continuous measurements of air quality parameters (SO2, PM10, TSP, H2S) since mid-2010. The Beth Chaim station is located at the western edge, downwind of the Schottegat industrial area of the refinery and only measures SO2 and TSP. Kas Chikitu is located approximately 2 - 3 km downwind in the Marchena/Wishi residential area and is primarily used to monitor the residential load of SO2, hydrogen sulfide (H2S) and PM10. Available hourly and daily measurements of SO2 were downloaded from June 1, 2010 through December 31, 2014 for analysis from the Kas Chikitu station. Twenty-four hour SO2 daily means were downloaded from the Beth Haim station (n = 1605) and the Kas Chikitu station (n = 1622). Monitoring stations operate in accordance with the ISO/IEC 17025 accreditation (certificate number L 426) of GGD Amsterdam using ultraviolet fluorescence (Thermo 43i-TLE and Thermo 450i Gas Analyzer) methodology to measure SO2. Daily meteorological data (i.e., temperature, precipitation, humidity, wind speed) in Curacao was downloaded from the Tutiempo Network from January 1, 2010 through December 31, 2014.
All SO2 data is expressed in µg/m3. All data analysis was performed using Statistica Version 6.1 (Stat Soft, Inc., Tulsa, OK). If data did not meet the assumptions of normality, nonparametric hypothesis tests were performed. If a potential explanatory variable was categorical (e.g., year), the nonparametric Kruskal-Wallis ANOVA was run using α = 0.05. If the Kruskal-Wallis ANOVA was found to be significant multiple comparisons revealed significant differences between categorical factors. Concentrations of SO2 were compared daily and annually and correlations were also evaluated against environmental factors (i.e., temperature, precipitation, humidity and wind speed).
Daily SO2 mean concentrations were downloaded from two local air stations in Curaçao, Beth Haim (n = 1605) and Kas Chikitu (n = 1622). The 24-hour daily mean concentrations ranged from 0.2 to 449 µg/m3 and 6.8 to 139 µg/m3 at the Beth Haim and Kas Chikitu stations, respectively (
Annual concentrations measured at the Beth Haim station increased 338% since 2010 and 36% since 2011. Similarly, annual concentrations increased at the Kas Chikitu station 36% since 2010 and 17% since 2011. Conversely, global trends for SO2 have illustrated decreases. For instance, a 50% decrease in annual
average SO2 concentrations was reported in the Yangtze Delta region of eastern China (2005-2010) and in Europe (2001-2010) [
The maximum annual mean concentrations for SO2 that are currently recommended by Curaçao and WHO are 80 µg/m3 and between 40 - 60 µg/m3, respectively. The SO2 annual mean concentrations in 2010, at both the Beth Haim (38.9 µg/m3) and Kas Chikitu (35.6 µg/m3) air stations, was the only year concentrations were less than the recommended guidelines, however, it is important to note the measurements were only for a 7 month period (July-December). The 24-hour guidelines issued by the European Commission and Curaçao both recommend 125 µg/m3 with three permissible excursions. Curaçao recommends the mean 24-hour maximum concentrations do not exceed 365 µg/m3 more than once per year. In addition, WHO recommends 24-hour maximum concentrations of 100 - 150 µg/m3. The number of days that exceed the 24-hour guidelines at both stations are also increasing over time. The 24-hour recommended SO2 guidelines were within compliance for the majority of 2010 (95%), 2011 (78%) and 2012 (84%) at the Beth Haim Station (
Many epidemiological studies have reported relative risk (RR) estimates, hazard ratios (HR) and odds ratios (OR) for associations between mortality and morbidity and SO2, yet results are somewhat inconclusive (Figures 5-7) [
Many of the studies reported relative risk estimates that were either close to or included unity or had large confidence intervals (
Several studies reported positive associations between SO2 and cardio related mortality and risk [
The relative risks reported for chronic obstructive pulmonary disease (COPD) and respiratory mortality or morbidity appear to be likewise inconclusive. Significant positive associations between SO2 and COPD were reported in Shiraz (674.9 µg/m3 annual mean; RR: 1.095, 95% CI: 1.07 - 1.11) and Tabriz, Iran (19 µg/m3 annual mean; RR: 1.0044, 95% CI: 1.0 - 1.011) [
A number of studies also reported odds ratios for various morbidities (
The hazard ratios reported for mortality and various respiratory morbidities also illustrated weak and inconsistent associations with SO2 and various endpoints (
In summary, the epidemiological studies presented a mix of weak positive associations (i.e., RR, HR, OR < 3.0) between health effects and SO2 and nonsignificant findings. Potential inconsistencies between studies and results could be due to confounding factors with copollutants and various study designs and methodology, making individual findings difficult to interpret and inconclusive as to the effect of observed levels of SO2 on health. In general, cardiovascular and respiratory effects and mortality were evaluated in locations with a wide range in annual mean concentrations ranging from 4 to 675 µg/m3.
Evidence regarding short-term exposures to SO2 were inadequate to infer an association with cardiovascular health [
Daily temperature, humidity, precipitation and wind speeds were analyzed for trends and correlations with SO2 concentrations. Briefly, the mean temperature (±standard deviation) from 2010 through 2014 was 27.9˚C (±1.2) and although Kruskal-Wallis multiple comparisons revealed annual differences (p < 0.000001) there were no observable trends (R2 = 0.0007). The mean humidity (77.7% ± 4.1%; R2 = 0.73) and precipitation (1.70 ± 6.9 mm; R2 = 0.75) from 2010 through 2014 both demonstrated moderately strong decreasing trends. Mean annual wind speeds (19.6 ± 4.7 km/h) demonstrated a strong increasing trend over time (R2 = 0.91). This is consistent with increasing global trends in wind speed [
There were no correlations found between SO2 and temperature at either the Beth Haim (r = 0.11) or the Kas Chikitu (r = 0.15) station. This is not surprising since the average year round temperature is ~28˚C with very little fluctuation.
Meteorological parameters can influence air pollution concentrations in ambient air, for instance, the frequencies and concentrations of pollution episodes can vary considerably over time and space depending on weather, which indicates the importance of climate change [
The objective of this investigation was to conduct an exposure assessment by analyzing levels of SO2 in ambient air surrounding Willemstad, Curaçao in order to determine if any temporal trends exist in the measured concentrations, to verify if measured levels exceed current public health guidelines and to identify potential health risks. In conclusion, concentrations of SO2 in Curaçao are among the highest reported globally and demonstrate an increasing trend over time. Levels of SO2 exceeded the annual and 24-hour guidelines recommended by Curaçao, the European Commission, and the World Health Organization.
Furthermore, both the 24-hour and annual mean concentrations of SO2 measured in Curaçao were within the ranges often associated with cardiovascular and respiratory effects and mortality as a result of short-term exposures. While the epidemiological evidence does not conclusively suggest there is a health risk from these levels of exposure, SO2 concentrations greatly exceed regulatory and guidance levels and suggest that further emissions control is warranted.
In a recent survey, 60% of 3230 children (ages 0 - 14) in Curaçao had asthma, which is more than four times the global average for children [
The authors wish to thank the Environmental Fund Netherlands Antilles (MINA Fund) and Mote Marine Laboratory for the financial support of this work. We are most grateful to George Keiffer (Curaçao Sea Aquarium), Gerard VanBuurt, Tone Moller (Avila Hotel) and the residents of Curaçao for the logistical support and for providing valuable insights and local knowledge to help us understand some of the societal issues and impacts from Isla Refineria on local communities.
Pulster, E.L., Johnson, G., Hollander, D., McCluskey, J. and Harbison, R. (2018) Exposure Assessment of Ambient Sulfur Dioxide Downwind of an Oil Refinery in Curaçao. Journal of Environmental Protection, 9, 194-210. https://doi.org/10.4236/jep.2018.93014