The residents living on the Navajo Nation in the Four Corners region of NM have been monitoring air pollution from a nearby coal mine.
Residents frequently document a black dust covering their home and belongings. It’s common to collect this black dust along the sock line and shoes while walking around the property. The community members have collected 18 samples, two show high levels of particulate matter (PM 10) and nine show elevated levels of silica.
Particulate Matter 10 (PM 10): According to the US EPA, exposure to particle pollution can lead to a variety of health effects. Particle pollution – especially fine particles – contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including premature death in people with heart or lung disease, nonfatal heart attacks, irregular heartbeat, aggravated asthma, decreased lung function, and increased respiratory symptoms such as irritation of the airways, coughing or difficulty breathing.
Silicon: the silicon levels detected near the BHP coal mine are 30 times higher than ordinary urban locations and 10 times higher than a site impacted by an industrial facility. Crystalline silica has been classified as a human lung carcinogen. Additionally, breathing crystalline silica dust can cause silicosis, which in severe cases can be disabling, or even fatal. Further testing is required to determine the amount of silicon in the sample that it is in the form of crystalline silica.
The data collected by the Mesquite community bucket brigade was analyzed by Mark Chernaik, Ph.D. of Science for Citizens. We’ll let Dr. Chernaik provide a little more insight into the air samples that have been analyzed so far:
The two samples [Four Corners Location 1 Jan. 18th & 22nd] contain very high levels of PM10 (66 and 58 ug/m3 respectively) well above the WHO 24-hour standard of 50 ug/m3. The silicon levels are also very high – 7.8 and 5.1 ug/m3 respectively – comprising about 10% of the overall PM10 amounts, which is very unusual. Also unusual are the iron levels – 2.3 and 1.6 ug/m3 (see column E) – which are as high as some of the highest iron levels we measured in the Claymont Clean Air project (air sampling near a scrap metal facility).
With high PM10 levels that correlate with high silicon and iron levels (I am tempted to go back through the data and calculate correlation coefficients of Si vs. Fe vs. PM10), I think we are on reasonably solid ground concluding that coal dust (a source of both silicon and iron) is a predominant source of elevated PM10 at [Four Corners Location 1].
The new data continues the trend of elevated, unhealthy levels of PM10 and elevated levels of silicon. The PM10 level of 53.1 ug/m3 recorded at [Four Corners Location 1] on 4 December 2012 exceeds the WHO acute (24-hour) standard for this pollutant. The observation of light winds during the sampling on 29 November 2012 coupled with high PM10 and silicon levels suggest that these pollutants are not simply associated with windblown soils. Lower PM10 and silicon levels on 12 December 2012 may have been caused by rain observed on the day that sample was collected.
Iron levels were also quite high – averaging a little over 1 ug/m3 in the four samples. These iron levels are comparable (slightly higher) than what we have observed as long-term average iron levels near the scrap metal processing facility in Claymont, Delaware.
I am attaching a document that is useful for comparing the silicon levels we are seeing in the Four Corners project to silicon levels measured elsewhere in the U.S. Please see the discussion on pages 3-24 to 3-30 of the USEPA 1996 Effects of inhaled silica document.
Some key points:
In the Four Corners project, silicon levels are averaging 4 ug/m3 and PM10 levels are averaging just under 40 ug/m3. The silicon levels of 4 ug/m3 are on the high end, but not uncommon – and not healthy – but the ratio of silicon-to-PM10 of 10% is at the upper end of the range of levels found elsewhere throughout the U.S.
Regarding iron levels in the air samples: I looked over the data, and iron levels have averaged 0.7 ug/m3 overall, which is elevated above background levels (typically 0.1 ug/m3), but not quite as high as at Claymont, where iron levels in PM-10 averaged 1.0 ug/m3 – but then again, the Claymont monitoring sites are next to an iron scrap metal facility. Chronic exposure to iron ore dust in the air has been associated with a form of pneumoconiosis (black lung disease) called siderosis, but I don’t know at what levels – I’ll have to look that one up.
The long-term health-based standard for crystalline silica is 3 ug/m3, and we are finding silicon levels averaging 3.3. ug/m3 at the monitoring sites. However, considering that silicon has a molecular weight of 28 and silica has a molecular weight of 60, then if 100% of the silicon in the samples were in the form of crystalline silica, then the average crystalline silica levels would be 7.1 ug/m3 [ = (60/28) x 3.3 ug/m3]; If 50% of the silicon in the samples were in the form of crystalline silica, then the average crystalline silica levels would be 3.5 ug/m3 [ = 0.5 x (60/28) x 3.3 ug/m3]; and so on.
To put the silicon levels in some perspective: When DNREC did speciation of PM2.5 at Wilmington and Dover, it found silicon levels of 0.078 and 0.082 ug/m3, respectively (this is data from the study published in 2005 that we used to compare results from Claymont to). In the Phase III monitoring we did at Claymont, Delaware, in which air quality is impacted by a metal scrap processing facility, silicon levels averaged around 0.33 ug/m3. So, the silicon levels we are seeing near the BHP coal mine (averaging now 3.3 ug/m3) are 30 times higher than ordinary urban locations (Wilmington and Dover) and 10 times higher than a site impacted by an industrial facility.
Coal dust can sometimes have significant amounts of crystalline silica (SiO2), which is an inhalation hazard. The air samples had relatively large amounts of silicon (especially in the sample collected on the day the battery died). However, the XRF test procedure doesn’t tell us what form this silicon is in: whether the hazardous crystalline silica form (e.g. quartz) or the less hazardous amorphous silica form. Fortunately, there are tests for determining crystalline silica levels in air samples.
See, also: Bunell, J.E., et al (2010) “Navajo Coal Combustion and Respiratory Health Near Shiprock, New Mexico.” Journal of Environmental and Public Health. http://www.hindawi.com/journals/jeph/2010/260525/ [Which focuses on indoor air quality].