Correlation of Human Health Conditions with Air Quality in the Border Bi-National Region

Summary of the Study

This study was done as part of an effort to understand the relationship between human health and air pollution in the border bi-national region. The daily PM10 and PM2.5 mass concentrations and the daily 8-hr maximum O3 concentration in Las Cruces were used as air pollution metrics. Emergency room visits and hospital admissions for respiratory and cardiovascular symptoms were retrieved from Memorial Medical Center.

Doña Ana County in New Mexico regularly experiences high levels of particulate matter, associated mostly with mineral particles. Residents of Hispanic/Latino origin constitute the largest population group in the region. We investigate the associations of ambient particulate matter and ozone with hospital emergency room and admissions for respiratory and cardiovascular visits in adults.

We used trajectories regression analysis to determine the local and regional components of particle mass and ozone. We applied Poisson generalized models to analyze hospital emergency room visits and admissions adjusted for pollutant levels, humidity, temperature and temporal and seasonal effects.

We found that sources within 500 km of the study area accounted for most of particle mass and ozone concentrations. Sources in southeast Texas, Baja California and southwest US were the most important regional contributors. Statistically significant increases of cardiovascular disease (CVD) ER visits were estimated for PM10 (3.1% (95%CI: -0.5 – 6.8)), PM10-2.5 (2.8% (95%CI: -0.2 – 5.9) for all adults and O3 (15.1% (95%CI: 0.5 – 31.9) for adults above 65 years during the warm period (April-September). When high PM10 concentrations were excluded, strong effects for respiratory emergency room visits for both PM10 (3.2% (95%CI: 0.5 – 6.0) and PM2.5 (5.2% (95%CI: -0.5 – 11.3)) were computed.

Our analysis indicated effects of PM10, PM2.5 and O3 on emergency room visits during the April-September period in a region impacted by windblown dust and wildfires.

Discussion of the Study and Suggestions

Doña Ana County is located in south-central New Mexico and encompasses the city of Las Cruces. It borders the bi-national El Paso-Ciudad Juarez metropolitan area. Its population in 2010 was 209,234, mostly of Hispanic/Latino origin (65.9%; 46.7% for New Mexico and 16.7% for the US). High PM10 levels have regularly been measured throughout the county with a PM10 non-attainment area (i.e. in violation of the 24-hr national ambient air quality standard in the US) in Anthony, NM since 1991. Episodes of high PM10 and PM2.5 levels in the region were associated with high winds in spring and low winds in winter. PM10-2.5 particles of geological origin dominated PM10 mass and accounted for 25% of PM2.5. The PM2.5-to-PM10 ratio for low wind speed particulate matter pollution events for sites in New Mexico was 0.11 as compared to 0.22 for sites in El Paso, indicating the possible influence of emissions from unpaved roads. The southern part of Doña Ana County was also designated as a maintenance area (i.e. previously non-attainment area) for O3 in 2004 and existing daily levels are frequently above 70 ppbv. We previously determined that wildfires may contribute up to 13 ppbv on daily 8-hour maximum O3 concentrations. Effects have been previously identified for childhood respiratory hospitalizations for both low- and high-wind particulate pollution events in El Paso, TX.

In this study, we identified and quantified the local and regional contributions to PM10, PM2.5 and O3. Sources within 500 km south (SW and SE New Mexico) of the study area contributed the most to particle mass and O3 concentrations. Most of PM10 and PM2.5 was of geologic origin, with the PM10-2.5 fraction dominating (about 75%) the total PM10 mass. Road dust from unpaved and paved roads was one of the most important sources of PM10 and PM2.5 in the study area. There are two unique types of high particulate pollution in the region. The first one is described by low wind air stagnation from December to February, which was attributed to emissions from unpaved roads. The second is facilitated by strong winds resulting in the re-suspension of loose soil particles into the air. These dust storms occur in mid-April from source regions within 500 km of the study area. The regions with the highest contributions to PM10, PM2.5 and O3 were Baja California, southwest US (southern Arizona and California), southeast Texas and Pacific Northwest. The seasonal variability of the air mass residence times indicated that the contributions from southwest US and Baja California were more pronounced in winter and spring, while emissions from sources in southeast Texas were mostly present in the summer. Owing to differences in source emissions, particles in the southwestern US were mostly composed of carbonaceous aerosol and dust particles. In comparison, sulfate and nitrate were the primary components of particulate matter in Texas. The chemical composition of particles has been previously determined to modify cause-specific hospital admissions.

An initial assessment of the existing public health status indicators using the Hospital Inpatient Discharge Data (HIDD) and the Behavioral Risk Factor Surveillance System (BRFSS) for the study area showed that the asthma mortality rate in Doña Ana County (1.5 per 1,000,000) was 50% higher than the mortality rates in New Mexico and nationwide. Asthma hospitalization rates have increased by 0.2 per 10,000 per year from 1999 to 2010, with higher hospitalization rates being observed for females than for males (ages 18-44; 3.5-19.5 per 10,000 for females to 1.7-9.6 per 10,000 for males). For COPD, the mortality rate was 41.5 per 1,000,000 (45.6 in New Mexico and 41.1 in the US) and hospital admissions rates increasing by 0.3 per 10,000 per year. Heart failure was the leading cause of mortality in Doña Ana County for ages 65+, with a rate of 14.1 per 100,000. Heart-related hospital admissions decreased from 19.8 per 10,000 in 1999 to 16.6 per 10,000 in 2004 and remained unchanged since then.

We estimated the effects of ambient PM10, PM2.5, PM10-2.5 and O3 upon hospital ER visits and hospitalizations. There were twice as many ER visits for respiratory symptoms as compared to admissions for all adults; but the opposite was true for the elderly. For CVD morbidity, admissions were up by 1.5 times over ER visits for all adults and three times for elderly. Substantial differences of the effects of air pollution have been previously observed using hospital ER visits and admissions attributed to differences in air pollution mix, as well as demographic and socioeconomic characteristics, and the type and severity of the symptoms.

We found effects of the PM10, PM10-2.5 and O3 with respiratory and CVD hospital ER visits and admissions for adults 65+ years. When we removed days with extreme concentrations many associations reached statistical significance indicating a logarithmic shape of the association under investigation. The estimated effects were not statistically significant (some of which were marginal). This does not necessarily indicate the lack of an effect but rather the relatively small population size in the rural study area. Furthermore, access to health care and health insurance may also have an effect. In Doña Ana County, only 70% of residents have health insurance coverage and about 20% were unable to get health care due to cost. Positive but not statistically significant associations were previously observed. The percent increases of hospital admissions for asthma during high and low wind PM2.5 events for people of all ages in El Paso, Texas were .11% (95% CI: -4- 28) and 2% (95%CI: -4 - 21). Low income individuals covered by Medicaid (patients under the age of 65 with a minimum of 133% of the federal poverty level ($29,700 for a family of four)) were more susceptible to both high and low wind pollution events.

In a study in Spokane, Washington, in which the contribution of soil dust particles was considerable (Spokane, WA is currently characterized as a maintenance, previously non-attainment, area for PM10), the percent increases for respiratory ER visits for a 25 ?g/m3 increase of lag1 PM10 and PM10-2.5 were 1% (95%CI: -1-4) and 1% (95%CI: -2 - 4). That study found no association between respiratory hospital admissions and PM10, PM2.5 mass concentrations, but they estimated non-statistically significant risks for cardiac admissions (PM10: 0% (95% CI: -4 - 3); PM2.5 2% (95% CI:-1-5)). Comparable results but not consistent associations were also observed for respiratory admissions particles and O3 in Rome, Italy and Madrid, Spain.

We estimated significant effects between cardiovascular ER visits and PM10, PM10-2.5 and O3 during the warm period (April to September). This period included the high wind PM10 episodes and summertime O3 events. Higher effects of air pollution during the hotter period of the year have been identified earlier in similar settings. We observed a strong effect of summertime O3 concentrations on cardiovascular ER visits among the elderly. These associations were also recently observed in Reykjavik, Iceland, an urban setting with low PM10 levels, and were attributed to temporary increase of interleukin-1?, decrease of plasminogen activator inhibitor 1 and plasminogen and changes in heart rhythm. In addition, statistically significant effects of PM10 and PM2.5 were computed when days with extreme particles’ concentrations were excluded from the analysis.

Finally, we found indications of associations between respiratory ER visits or cardiovascular admissions with the contributions from southeast Texas for PM10, PM2.5 and O3. This region includes two coal-fired power plants (Carbón I and II with 1200 and 1400 megawatt capacities located approximately 32 km south of the U.S.-Mexico border near the town of Eagle Pass, Texas), oil refining, oil-fired power production, steel production, and other industrial operations. The Tampico region on the Gulf of Mexico has many oil refining and oil-fired power generation facilities. Previous studies found statistically significant associations of Ni and V, both tracers of diesel combustion, with cardiovascular diseases. Negative associations between the three pollutants and CVD admissions were computed for the other four regions (central Pacific Ocean, Pacific Northwest, southwest US and Baja California).

Overall, we investigated the effects of the particulate matter and O3 on respiratory and cardiovascular ER visits and hospital admissions in adults in a region influenced by mineral dust particles as well as wildfires. We generally found positive associations with air pollution and respiratory and CVD morbidities that were statistically significant when extreme values were excluded. Regional transport from southeast Texas also showed positive albeit non-statistical association with both morbidity indicators. Reduced health insurance coverage and access to healthcare facilities may obscure the effects of air pollution on health in smaller cities and rural communities and with large percentages of minorities. Future research may include examining the effect of air pollution on childhood ER and hospital admissions since children may spend more time outdoors. Furthermore, the effects of specific types of events such as dust storms and fire-related O3 may be examined.