Assessment of Inhalable Particulate Matter Associated with a Refinery in Curaçao

Inhalation and atmospheric pollution studies have focused on particulate matter due to correlations and associations with various morbidities and mortalities. This research analyzed ambient concentrations of inhalable particulate matter (PM10) on the island of Curaçao in order to evaluate through comparative literature analysis and recommended public health guidelines the potential health risks. Available hourly, daily and monthly PM10 measurements were accessed from June 2010 through December 2014 from a local air monitoring station in Willemstad. Mean annual concentrations of PM10 (31 122 μg/m) in Curaçao are among the highest reported globally, demonstrating an increasing trend over time and exceed current public health guidelines recommended by local and international agencies. While the epidemiological evidence is inadequate to infer a causal association between health effects and long-term exposures of the measured PM10 concentrations, the results indicate that emissions controls are not adequate for compliance with international exposure standards.


Introduction
Air pollution may be considered an environmental health risk having been associated with a number of acute (e.g., respiratory and cardiovascular events, hospital and emergency room admissions) and chronic (e.g., chronic bronchitis, lung cancer, mortality) effects [1].In many cases it is difficult to determine direct causality with one particular constituent of air pollution (PM, sulfur dio-xide, carbon monoxide, VOCs, etc.) due to its complexity and multiple sources, the inability to assign area exposure values to individuals, as well as the unavoidable confounding inherent to large scale environmental epidemiology studies.While more than 98% of air pollution in urban settings are gases or vapor-phase compounds, more recent inhalation and atmospheric pollution studies have focused on particulate matter due to some correlations with mortality and adverse respiratory health effects [2] [3].It has been suggested that up to 8% of premature mortalities globally are related to both indoor and outdoor concentrations of particulate matter, though these findings are difficult to interpret given the uncertainties present in the respective study designs [4] [5] [6] [7].A number of studies have suggested associations between long-term exposure to PM and various health effects including accelerated cardiovascular and respiratory mortality, compromised lung function and relative increase of lung cancer risk [2] [8] [9] [10] [11].Inhalable particulate matter (PM 10 ), specifically, has been associated with increases in daily mortality and hospital admissions for respiratory distress (pneumonia, asthma and decreased lung function in children) [9] [12].Though the multi-factorial nature of these outcomes and the inability to disentangle confounding factors make it impossible to know if PM is the causative agent behind morbidities and mortalities the findings warrant investigating potential risks from exposure to this type of air pollution.
Many factors contribute to the chemical composition of PM, including combustion sources, climate, season, and type of urban and/or industrial pollution [3].Particulate matter can be emitted from both natural and anthropogenic sources with both primary (directly emitted) and secondary (atmospherically derived) components [13].Primary sources include wildfires, sea spray, organic matter and the combustion of both fossil fuels and biofuels.Secondary sources of PM include wood smoke, gaseous vegetative emissions and vehicular emissions and other condensates from atmospheric chemistry.The major components of PM consist of inert compounds, semivolatile organic compounds, metals, carbonaceous material mainly from combustion and vehicle exhaust, biological material, and minerals.The density, concentration, and composition of particulate matter can vary widely among geographic locations.
Refinery operations have been associated with atmospheric emissions of a wide variety of criteria air pollutants, including particulate matter.The type and quality of the crude oil, refinery process and refined products all influence the variability, composition and amount of emissions from one refinery to another.

One of the largest and oldest refineries in the Wider Caribbean Region is Isla
Refineriá, which opened in 1918 and is located within the densely populated capital of Willemstad, Curaçao on the shores of Schottegat Bay.Although, the refinery was considered obsolete in the mid-1980s, it is still in use today processing ~335,000 barrels per day yet it has not been able or required to comply with environmental standards and permit requirements [14].
The objectives of this study were to analyze hourly, daily, and monthly PM 10 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.

Site Selection
Curaçao is an island in the southern Caribbean, ~40 miles off the Venezuelan coast.It is currently considered a constituent country of the Kingdom of the Netherlands since its dissolution in 2010 from the Netherland Antilles.Curaçao is located in the Southern Caribbean Dry Zone approximately 12˚ north of the equator, which is characterized by a semi-arid to arid climate, with a distinguishable dry (March-September) and rainy season (October-February), and sustained easterlies.Curacao is typically warm and sunny with an average temperature of 27˚C and an average annual rainfall of approximately 570 mm.The island is approximately 59 kilometers in length, 4 -11 kilometers wide and a total land mass area of ~443 km 2 .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.

Data Analysis
All PM 10 data is expressed in μg/m 3 .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 cate-gorical factors.Concentrations of PM 10 were compared daily and annually and correlations were also evaluated against environmental factors (e.g.temperature, humidity and wind speed).observed with a strong increasing trend (R 2 = 0.94) over time.In general, the 2014 mean annual PM 10 concentrations were significantly (p > 0.00001) higher than the previous four years.

Global Comparisons of Ambient PM10 Concentrations
The annual average PM 10 concentrations have increased 74% since 2010.Excluding 2010, since measurements are only for a seven month period, the annual average increased 61% since 2011.In contrast, PM 10 concentrations in the US have shown a 34% decrease in the 24-hour average concentrations since 1999 and a 31% decrease in annual average ambient concentrations since 1990 (http://www.epa.gov/airtrends).The 2014 annual mean concentrations for PM 10 in Curaçao (121.5 μg/m 3 ) is among some of the highest concentrations reported globally, measuring approximately 13 times higher than those reported in Iceland (9 μg/m 3 ), yet were two times lower than levels recorded in Pakistan (282 μg/m 3 ).

Potential Risks of PM10 Inhalation
There are a number of epidemiologic studies reporting the associations of PM 10 with various health outcomes, including mortality, morbidity and increased emergency room visits and hospitalization, though these results are difficult to interpret due to the inability of these studies to adequately control for confounding and the potential for exposure misclassification (Figures 5-7) [11] [16]- [43].This study primarily focused on literature published after 2010 since there are several meta-analyses and reviews covering literature published prior to 2010.The relative risk reported for various mortality demonstrate positive associations with PM 10 , however the data is somewhat inconsistent (Figure 5).For instance, two studies reported positive associations for respiratory mortality,   where only one was statistically significant [19] [28].Liang et al. [28] reported positive associations, with respiratory mortality (RR: 1.347, 95% CI: 0.990 -1.833) during the winter months in Taiwan with a mean PM 10 concentration of 66.7 μg/m 3 .However this association was not significant since the RR included unity and had a wide confidence interval range suggesting greater uncertainty.
In contrast, a meta-analysis consisting of 26 studies in China with annual PM 10 concentrations ranging from 44 -156 μg/m 3 , reported positive associations between short-term PM 10 exposure and respiratory mortality (RR: 1.0057, 95% CI: 1.004 -1.0075), though the de minimis magnitude of effect makes this finding difficult to interpret [19].
Similarly, relative risks for cardio related mortality also demonstrated both significant and non-significant results with PM [28].All were significant with the exception of the study by Liang et al. [28] which found a positive yet non-significant association between PM 10 and all-cause mortality in Taiwan (RR: 1.059; 95% CI: 0.999 -1.122).In addition, positive associations between lung cancer mortality and long-term PM 10 exposures (RR: 1.05; 95% CI: 1.03 -1.07) were found in a meta-analysis of 19 studies conducted globally [11].However, none of these measures of association achieved a magnitude of effect that clearly demonstrates a direct impact of PM on mortality in exclusion of other factors.
The relative risks reported for various morbidity and hospitalizations is much less convincing of positive associations with PM 10 since many of the studies report near or include unity (Figure 6) [11]  2) [24].However, the confidence intervals are relatively wide suggesting increased uncertainty.Relative risks reported for incidences of lung cancer among two meta-analyses were also positive yet were not statistically significant since both included unity [11].
In summary, the epidemiological studies presented demonstrate some associations between health effects and PM 10 although results are mixed, often presented with large amounts of uncertainty, and effect sizes on the level of minutiae.Cardiovascular and respiratory effects and mortality were observed in locations with annual mean concentrations ranging from 7.7 -270 µg/m 3 .Potential inconsistencies between studies and results could be due to different PM 10 constituents between geographical regions as well as various study designs and me-Journal of Environmental Protection thodology, though there is an inherent inability of the cited studies to adequately control confounding and reliably assign area exposure estimates to individuals.
The USEPA concluded that the evidence provided in the literature and the biological plausibility was suggestive of a causal relationship between short-term exposures to PM 10-2.5 and cardiovascular effects, respiratory effects, mortality, yet there was inadequate evidence to suggest causative relationships with long-term exposures [18].

Environmental Factors and PM10 Concentrations
Daily temperature, humidity, precipitation and wind speeds were analyzed for trends and correlations with PM 10 concentrations (Figure 8).wind speed [44].There was a weak to moderately strong correlation between PM 10 concentrations and wind speed (Figure 9).There were no correlations found between PM 10 and temperature (r = 0.04) and only a weak, negative correlation with humidity (r = −0.22).

Conclusions
The objectives of this investigation were to analyze levels of PM 10 in ambient air surrounding Willemstad, Curaçao in order to determine if any temporal trends exist in the measured concentrations, verify if measured levels exceed current public health guidelines and to identify potential health risks.In conclusion, concentrations of PM 10 in Curaçao are among the highest reported globally and demonstrate an increasing trend over time.Levels of PM 10 exceeded the annual and 24-hour guidelines recommended by Curaçao, the European Commission, World Health Organization and the USEPA.Furthermore, both the 24-hour and annual mean concentrations of PM 10 measured in Curaçao were within the ranges speculated by the USEPA to impact cardiovascular and respiratory outcomes and mortality as a result of short-term exposures.In addition, increasing wind speeds were correlated with increasing PM 10 concentrations over time potentially impacting residents within the plume trajectory.However, as the epidemiological evidence is inadequate to infer causality between health effects and chronic, long-term exposures to PM 10 , the strongest conclusion that can be drawn from this analysis is that local emissions controls are inadequate to meet international PM 10 public health standards.Future research needs in Curaçao include expanding the air monitoring efforts to include areas upwind of the refinery as well as additional petrochemical emissions, including but not limited to sulfur dioxide, particulate matter (PM 10 and PM 2.5 ), benzene, as well as both the vapor and particulate phases of ambient PAHs.Additional environmental studies are encouraged to evaluate the extent of contamination in a variety of biota and matrices (i.e.water, sediment, and fish).
Since mid-2010, two air monitoring stations, Beth Chaim and Kas Chikitu, located in Willemstad, Curaçao have been collecting validated and continuous measurements of air quality parameters (SO 2 , PM 10 , TSP, H 2 S).The Beth Chaim station is located at the western edge, downwind of the Schottegat industrial area of the refinery and only measures SO 2 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 SO 2 , hydrogen sulfide (H 2 S) and PM 10 .Available hourly and daily measurements of PM 10 were downloaded from June 1, 2010 through December 31, 2014 for analysis from the Kas Chikitu station.Twenty-four hour PM 10 daily means (n = 1603) measured at the Kas Chikitu station were analyzed.Monitoring stations operate in accordance with the ISO/IEC 17025 accreditation (certificate number L 426) of GGD Amsterdam using tapered element oscillating balance (TEOM 50C) methodology to measure PM 10 .

Figure 2 .
Figure 2. Annual mean concentrations of PM 10 (μg/m 3 ) measured at the Kas Chikitu air monitoring station in Curaçao for the years 2010 through 2014.The current European Commission's annual (40 μg/m 3 ) recommendation is depicted with a dashed line.
that are currently recommended by Curaçao and the European Commission are 75 and 40 μg/m 3 , respectively.The annual mean concentrations for the years 2011 through 2014 exceeded the current PM 10 guidelines recommended by the European Commission (40 μg/m 3 ).Additionally, mean annual PM 10 concentrations for 2013 (95.9 μg/m 3 ) and 2014 (121.5 μg/m 3 ) both exceeded the island's guidelines for PM 10 (75 μg/m 3 ).Mean 24-hour maximum concentrations of PM 10 have also been recommended by NAAQS (150 μg/m 3 ), the European Commission (50 μg/m 3 ) and Curaçao (150 μg/m 3 ).The number of days that have exceeded the 24-hour daily maximum concentrations of PM 10 has demonstrated strong increasing trends in this study (Figure

Figure 3 .
Figure 3. Number of days per year PM 10 concentrations exceeded recommended guidelines.Strong increasing trends were observed for the number of days exceeding the European Commission's recommended guidelines (R 2 = 0.85) as well as recommendations by Curaçao and the NAAQS (R 2 = 0.87).The current 24-hour maximum concentrations recommended by the European Commission, NAAQS and Curaçao are 50 µg/m 3 , 150 µg/m 3 and 150 µg/m 3 , respectively.

Figure 4 .
Figure 4. Percentages of each year that were either in compliance or exceeded current maximum 24-hour guidelines for PM 10 concentrations.Strong decreasing trend was observed in annual compliance.

Figure 6 .
Figure 6.Relative risk estimates (95% CI) for PM 10 associated morbidity and hospital admissions from published literature.

Figure 7 .
Figure 7. Hazard ratios (95% CI) for PM 10 associated mortality and morbidity from published literature.