The Burlington Hill Truth 2013

Occupational & Environmental Epidemiology

Naturally Occurring Asbestos

Naturally occurring asbestos (NOA) is the name for a group of fibrous minerals that occur naturally in soil and ultramafic rock formations. Is NOA present in Washington State?

The United States Geological Survey (USGS) has currently identified NOA locations in the western part of the state. Although there are no current active asbestos mines in Washington State today, there are other active sites that mine other minerals which could contain asbestos. These areas are identified as either a mine, a potential mine, or naturally exposed rock formations.

How can naturally occurring Abestos affect my health?

Exposure to asbestos can cause some types of lung cancer as well as mesothelioma (cancer of the tissue covering the internal organs). Asbestos enters your body by breathing in asbestos fibers. Once asbestos fibers are caught in the lungs, they remain there permanently.

If naturally occurring asbestos is not disturbed and fibers are not released into the air, then it is not a health risk.
What are some ways in which I might disturb naturally occurring asbestos material?

Leaf blowing in areas where bare soil is known to contain NOA.
Hammering, chiseling and excavating, while in areas known to contain NOA.
Using machinery to plow or plant large tracts of land with NOA in the soil.
Drilling into asbestos rock formations with heavy equipment.
Grading, landscaping or excavating soil containing NOA.
Removing known NOA material and transporting the material to other locations.
What are some steps I can take to prevent exposure to naturally occurring asbestos?
Leave NOA in place and undisturbed.
Limit dust-generating activities by wetting the area with water prior to and during the activity.
Cover or cap NOA material with three to six inches of soil that contains less than 0.25 percent asbestos (Note: other materials may be also substituted in place of soil).
Maintain the area covered with plants to prevent erosion.

How can I determine if naturally occurring asbestos is in my area?

Find identified naturally occurring asbestos sites in Wahington state.
Consider contacting a licensed professional geologist in your area: Board for Licensing of Geologists 

What do I do if my construction, drilling, landscaping or other activity occurs in an area where naturally occurring asbestos or ultramafic rock formations are known to exist?

Activities that could disturb naturally occurring asbestos include the cutting of new roads, excavation, chipping or hammering on rocks containing asbestos, sifting dry materials and/or other activities that may cause the release of asbestos fibers into the air. It is important to determine whether naturally occurring asbestos is present before conducting such activities. If a site is found to contain asbestos, steps should   be taken to minimize exposure to the public and workers.

Health hazard mitigation and regulation for asbestos (naturally occurring and otherwise) is administered    by the Asbestos Hazard Management Program (AHMP) Division of Public Health.

Additional Information for the General Public

Agency for Toxic Substances and Disease Registry (ATSDR): Naturally Occurring Asbestos 
U.S. Environmental Protection Agency (EPA): Naturally Occurring Asbestos: Approaches for Reducing Exposure (PDF) 

Additional Information for Contractors

Washington State: Naturally Occurring Asbestos Sites  
Washington State Air Resources Board: Naturally Occurring Asbestos 

Residential Proximity to Naturally Occurring Asbestos and Mesothelioma Risk in California
Xue-lei Pan, Howard W. Day, Wei Wang, Laurel A. Beckett, and Marc B. Schenker

Department of Public Health Sciences, Department of Geology, and Department of Statistics, University of California at Davis, Davis, California

Rationale: Little is known about environmental exposure to low levels of naturally occurring asbestos (NOA) and malignant mesothelioma (MM) risk.

Objectives: To conduct a cancer registry-based case control study of residential proximity to NOA with MM in California. Methods: Incident MM cases (n 2,908) aged 35 yr or more, diagnosed between 1988 and 1997, were selected from the California Cancer Registry and frequency matched to control subjects with pancreatic cancer (n 2,908) by 5-yr age group and sex. Control subjects were selected by stratified random sampling from 28,123 incident pancreatic cancers in the same time period. We located 93.7% of subjects at the house or street level at initial diagnosis. Individual occupational exposure to asbestos was derived from the longest held occupation, available for 74% of MM cases and 63% ofpancreaticcancers.Occupationalexposuretoasbestoswasdetermined by a priori classification and confirmed by association with mesothelioma.

Main Results: The adjusted odds ratios and 95% confidence interval for low, medium, and high probabilities of occupational exposures to asbestos were 1.71 (1.32–2.21), 2.51 (1.91–3.30), and 14.94 (8.37–26.67),respectively.Logisticregressionanalysisfromasubset of 1,133 mesothelioma cases and 890 control subjects with pancreatic cancer showed that the odds of mesothelioma decreased approximately 6.3% for every 10 km farther from the nearest asbestos source,anoddsratioof0.937(95%confidenceinterval0.895–0.982), adjusted for age, sex, and occupational exposure to asbestos.

Conclusions: These data support the hypothesis that residential proximity to NOA is significantly associated with increased risk of MM in California.

Keywords: CancerRegistry case-controlstudy; GIS;malignant mesothelioma; naturally occurring asbestos; occupational exposure to asbestos
Epidemiologic studies have confirmed that occupational exposure to asbestos causes mesothelioma (1–7). However, almost all population-basedstudies havefound that manymesothelioma cases had no known occupational exposure to asbestos. Some of these cases could be due to domestic and neighborhood exposure to asbestos, or even environmental exposure to naturally occurring asbestos (NOA). An association with domestic or neighborhood exposure to asbestos or other mineral fibers and an increased risk of mesothelioma has been found in several locations including Australia (8), South Africa (9), Italy (10), and New Jersey (11). Studies among residents of two Anatolian villages in Turkey showed that the astounding high incidence of malignant mesothelioma results from environmental exposure to carcinogenic tremolite and erionite, a fibrous zeolite, which

(Received in original form December 22, 2004; accepted in final form June 19, 2005) Supported by the National Cancer Institute (Project Grant IR03CA81615-01).
Correspondence and requests for reprints should be addressed to Marc B. Schenker, M.D., M.P.H., Division of Environmental & Occupational Health, Department of Public Health Sciences, University of California, Davis, One Shields Avenue, TB168 Davis, CA 95616-8638. E-mail:
Am J Respir Crit Care MedVol 172. pp 1019–1025, 2005
Originally Published in Press as DOI: 10.1164/rccm.200412-1731OC on June 23, 2005
Internet address:
is present in the volcanic tuffs that are used as building stone (12). An association between environmental exposure to NOA and mesothelioma has been observed in Cyprus (13), Greece
(14), New Caledonia (15), Corsica (16), China (17), and Italy (18), but no research has studied the association of residential distance from environmental (nonoccupational) asbestos and mesothelioma risk (19).
It remains unknown whether environmental exposure to low levels of NOA also causes mesothelioma. Research has failed to find a threshold level below which there is no mesothelioma risk, and low-dose exposure to asbestos can cause mesothelioma (20). Most epidemiologic studies for mesothelioma have failed to find evidence of occupational, domestic, or neighborhood exposure to asbestos in a sizable proportion of mesothelioma cases (7). For example, 25% of mesothelioma cases in a Spanish case–control study had no significant occupational, domestic, or neighborhood exposure to asbestos (3). It is plausible that exposure to NOA may account for a portion of those mesothelioma cases. California has large amounts of serpentinite and other ultramafic rocks that are the predominant but not exclusive source of NOA and are distributed mostly in the Sierra Nevada, Coast Ranges, and Klamath Mountains in Northern and Central California (Figure 1). The most common type of asbestos is chrysotile, but other types including tremolite are also found in California. (21). There have been increasing concerns about whether an increased risk of mesothelioma is associated with environmental exposures to NOA in these areas. Some of these areas include new housing developments and potential exposure to a large number of people.
Statewide cancer reporting in California has been mandated by law since 1985, and beginning in January 1988, the California Cancer Registry (CCR) has covered the entire population in California through nine regional population-based cancer registries. The CCR is one of the largest comprehensive populationbased statewide cancer registries in the world, covering more than one tenth of the U.S. population. About 300 incident cases of malignant mesothelioma per year are reported in California. It is estimated that more than 98.9% of all mesothelioma cases diagnosed in California are reported to the California Cancer Registry (22). This study used a unique opportunity to evaluate the association between exposure to potential sources of indigenous environmental asbestos and incidence of mesothelioma. California has more serpentinite and ultramafic rocks than other states in the United States, and its distribution is patchy, with exposed areas separated from unexposed areas (23). Additionally, California’s large population provided us with an adequate sample size to study this rare cancer.

Case Ascertainment and Control Selection
Incident cases of malignant mesothelioma diagnosed from 1988 through 1997 in California were identified from the CCR. The International Classification of Diseases for Oncology, Second edition (ICD-O-2, 1990), was used by the CCR for the period covered by the study (22). The case series consisted of all reported patients ages 35 yr or older

Figure 1. Distribution of ultramafic rocks in California.
diagnosed with malignant mesothelioma (histology ICD-O-2 codes 9050–9053) from 1988 through 1997 in California. For each case, one control frequency-matched by 5-yr age group and sex was selected by stratified random sampling from patients diagnosed with incident malignant pancreatic cancer (primary site ICD-O-2 codes C250–259) reported to the CCR in the same period.

Assessment of Residential Proximity to NOA
No maps exist that illustrate the distribution of NOA in California. However, ultramafic rocks are the principal source of asbestos and may be used as a proxy for its natural occurrence. To locate known bodies of ultramafic rock, we used a digital version of the geologic map of California, at a scale of 1:750,000, created in 1970 by the California Department of Conservation, Division of Mines and Geology (24). Residential proximity to NOA was estimated as the distance to the edge of the nearest known body of ultramafic rock. Distances were measured using the spatial analyst feature in the GIS software ArcView 3.1 (ESRI, Redlands, CA) (25) using the digital geologic map of California and the latitude and longitude of an address at initial diagnosis from the CCR records. The latitude and longitude were obtained from the online Tele Atlas North America’s Eagle Geocoding Server (www. The server returned the geocoding results with the original address, standardized address, latitude, longitude, accuracy, and source of the match for every address. Because there are only two small asbestos sources in Southern California, the nearest distance was calculated excluding these two deposits (Figure 1).

Assessment of Occupational Exposure to Asbestos
Occupational exposure to asbestos is a dominant risk factor for mesothelioma, and it is unlikely that the potential weak association between residential proximity to sources of NOA and incidence of mesothelioma would be detectable if we did not control for occupational exposure. Ideally, actual exposure level and duration of each occupation should be considered, but it was impossible to obtain that information for each occupation or job title. In this study, occupational exposure to asbestos was estimated using only CCR records on the longest held occupation or industry. Because there is a significant positive dose–response relationship between the risk of asbestosis and duration and intensity of occupational exposure to asbestos, we ranked occupational exposure to asbestos for some occupations based on asbestosis proportionate mortality ratios (PMR) of these occupations. An occupation with higher asbestosis PMR is assumed to have a higher likelihood of occupational exposure to asbestos. We used data from the Work Lung Disease Surveillance Report by National Institute for Occupational Safety and Health (26), augmented with a study by Cocco and colleagues (27), to rank occupations according to their probability of occupational exposure to asbestos. Occupations with high, moderate, and low probabilities of occupational exposure to asbestos were defined as those that have asbestosis PMR 15, PMR 3–15, and PMR 3, respectively. In addition, shipyard workers were considered to have a high probability of occupational exposure (26), and all occupations with no recognizable sources of asbestos were assigned the lowest probability. When a subject had more than one occupation, the probability of exposure to asbestos assigned to an individual was the maximum probability in his or her record. Because asbestosis PMRs were available for a limited number of occupations in the National Institute for Occupational Safety and Health report, a job-exposure matrix for asbestos developed by Cocco and colleagues was also used to rank occupational exposure to asbestos (27). Occupations with high occupational asbestos exposure were shipyard worker, insulator, plumber, pipefitter, steamfitter, and boilermaker (26). Major occupations with moderate probability were mechanic, electrician, sheet metal worker, welder, sailor, navy serviceman, and construction labor (26, 27).

Statistical Analysis
Cases were compared with controls initially by univariate analyses. Chi-square tests were used to compare sex and known occupational exposure, and Wilcoxon rank-sum tests for age and nearest distance from asbestos deposits. Logistic regression was then used to confirm the association between mesothelioma and occupational exposure. Multivariate logistic regression models were used to assess the relationship between mesothelioma risk and asbestos exposure from naturally occurring deposits, adjusted for occupational exposure, age at initial diagnosis (continuous variable), and sex (examined both in pooled models and stratified by sex). The primary models grouped occupation by category of exposure, with unexposed groups as the reference. The influence of occupation was examined both as a confounder and as a potential interaction with residential proximity. Nearest distance in kilometers from naturally occurring deposits was initially examined as a continuous variable, with zero corresponding to residence within a natural asbestos zone. The primary model assumed that the log odds of mesothelioma decreased linearly with distance, so that a 1-km increase in distance was assumed to decrease risk in the odds by a constant percentage, regardless of the location. Results were reported in units of 10-km change for easier interpretation of small coefficients. The assumption of linearity was examined graphically, using plots of locally reweighted smoothed (lowess) log odds versus distance and fractional polynomials (28). Secondary analyses examined alternative relationships to distance, including square root, natural logarithm, and reciprocal transformations of nearest distance; and grouping distance into categories of 50 km, 100 km, and 150 km or more. Model fit was checked by Pearson and Deviance goodness-of-fit statistics and Hosmer and Lemeshow diagnostics (28). All analyses were performed in STATA release 6 (29).

A total of 2,966 incident cases diagnosed with malignant mesothelioma were reported to the California Cancer Registry in the period between 1988 and 1997. There were 17 duplicate records deleted and 41 cases younger than 34 years were removed. The study included 2,908 malignant mesothelioma cases (2,354 men and 554 women). We selected 2,908 control subjects frequency matched by 5-yr age group and sex by stratified random sampling from the 28,123 incident cases of malignant pancreatic cancer reported to the CCR in the same period.
Among 5,816 subjects, mesothelioma cases and control subjects with pancreatic cancer in our study were balanced in vital status (93% versus 97%), percentages of data abstracts from inpatient oroutpatient records (96% versus92%), race/ethnicity, and marital status by sex (Table 1). The percentage of histologic diagnosis of mesothelioma cases was significantly higher than for control subjects with pancreatic cancer (82% versus 56%). Data on the longest-held occupation and industry were available for 74% of mesothelioma cases and 63% of control subjects with pancreatic cancer, respectively. All cases and control subjects were located based on their residential addresses at initial diagnosis. Among these, 93% of geocodes were completed at a house or street level (the most precise), 6% at a geographic centroid of a five-digit zip code, and only 0.3% at a geographic centroid of a city or county (the least precise). Geographic coding rates were comparable in cases and control subjects (Table 1).
Logistic regression analyses were restricted to the subset of 1,133 mesothelioma cases and 890 control subjects with pancreatic cancer who had complete data on residence, age, sex, and occupation. Univariate analyses in this data set showed nearly identical age distributions and proportion of males. The cases had substantially higher frequency of occupational exposures to asbestos (Table 2).
Age-adjusted logistic regression analysis for occupational exposure to asbestos showed that occupations with a high probability of occupational exposure to asbestos in men such as boilermaker, insulator, plumber, pipefitter, steamfitter, sheet metal worker, electrician, and painter were strongly associated with mesothelioma risk, whereas few female cases and control subjects had occupations with a high probability of occupational asbestos exposure. This supported the hypothesis that the difference of mesothelioma incidences between men and women mainly resulted from different occupational exposures to asbestos. Industries with high probability of occupational exposure to asbestos in men such as shipyard and Navy were significantly associated with the elevated mesothelioma risk (Table 2).
In the primary analysis of the association of NOA and mesothelioma, a multivariate logistic regression model was fitted, assuming a constant percent change in the odds of mesothelioma with a 10-km increase in nearest distance, adjusted for the effects of age, sex, and occupational exposure (Table 3). The estimated effect was a 6.3% decrease (computed from the odds ratio as [(1 0.937) 100%] in the odds of a mesothelioma case for every 10 km farther away from a NOA source (95% CI, 1.8– 10.5%; p 0.006). Occupational exposure, as expected, was the strongest predictor of an increased odds of mesothelioma, with a significant dose–response relationship. Age and sex as major risk factors of mesothelioma and matching factors in this study were included in the final multivariate model to adjust for the impact of imbalance in age and sex from exclusion of cases and controls with unknown occupational exposure and more than 100-km nearest distances.
An analysis excluding the cases with a moderate or high probability of occupational asbestos exposure gave very similar

CasesControl SubjectsCasesControl Subjects
Clinical Characteristicsn 2,354 (%)n 2,354 (%)n 554 (%)n 554 (%)
Age, yr
Probability of occupational exposure to asbestos69.70 10.6769.75 10.7368.56 12.4468.77 12.52
None794 (34)1068 (45)303 (55)282 (51)
Low367 (16)259 (11)19 (3)8 (1)
Medium355 (15)170 (7)15 (3)3 (1)
High287 (12)27 (1)6 (1)1 (0)
Retired282 (12)406 (17)109 (20)109 (20)
Unknown269 (11)424 (19)102 (18)151 (27)
Nearest distance (km)* Median55.2115.5112.3131.4
Range (P5, P95) Sources of abstract2.0, 316.92.1, 311.42.3, 318.72.6, 315.4
Inpatient/outpatient2,250 (96)2,162 (92)526 (95)514 (93)
Private physician36 (2)6 (0)6 (1)0 (0)
Laboratory8 (0)85 (4)3 (1)19 (3)
Nursing home2 (0)4 (0)3 (1)2 (0)
Autopsy only25 (1)35 (1)8 (1)2 (0)
Death certificate only Diagnostic methods33 (1)62 (3)8 (1)17 (3)
Histology1,922 (82)1,307 (56)466 (84)320 (58)
Cytology265 (11)374 (16)65 (12)87 (16)
Radiography58 (2)318 (14)5 (1)75 (14)
Clinical57 (2)109 (5)7 (1)22 (4)
Visualization5 (0)110 (5)0 (0)22 (4)
Types of address matching47 (2)136 (6)11 (2)28 (5)
House or street level (the best)2,170 (92)2,233 (94)525 (95)523 (94)
Centroid of a 5-digit zipcode177 (8)113 (5)26 (5)29 (5)
Centroid of a county (the worst)7 (0)8 (0)3 (0)2 (0)
Vital status (dead)2,195 (93)2,291 (97)472 (85)536 (97)
* Two-sample Wilcoxom rank-sum test for the nearest distance: p 0.0141 for men; p 0.0724 for women.
CasesControl SubjectsCasesControl Subjects
Exposure to Asbestosn 1,803*n 1,524*OR†95% CI†n 343*n 294*OR†95% CI†
Farming Occupation33550.50.3–0.8170.10.0–0.9
Plumber, pipefitter,26211.42.7–48.310
Sheet metal worker3364.82.0–11.500
Probability of occupational exposure to asbestos46391.00.6–1.510
Definition of abbreviations: CI: confidence interval; OR: odds ratio.
* Excludes records with “unknown” or “retired” in the longest held industry and occupation data items.

† Adjusted for age at initial diagnosis (continuous).
results. Among all subjects the odds ratio for mesothelioma for a 10-kmincrease innearest distancewas 0.943 (95%CI, 0.896–0.922). The observed odds ratios for men and women were 0.939 (95% CI, 0.887–0.994) and 0.961 (95% CI, 0.861–1.073), respectively.
Figure 2 illustrates the shift in the log odds of mesothelioma versus pancreatic cancer as the distance from NOA sources increases among men and women. People who lived closer to an asbestos source had a greater chance of having mesothelioma, and the chance decreased steadily as the distance increased. In stratified analyses of men and women, we saw comparable findings, although the results in women were based on small samples and were not statistically significant (results not shown). Fractional polynomial analysis suggested that the nearest distance was reasonably included in the multivariate logistic regression model as a linear continuous independent variable for residential proximity to sources of NOA, which is the assumption for including the distance as a continuous variable in the logistic regression model. Logistic regression diagnostics supported the use of this model, with no evidence for model failure or interactions (results not shown).

We obtained similar results when we repeated the analysis using only subjects with a nearest distance of 50 km or less. When we repeated the analysis using either subjects with 150 km or less or all subjects, using the log-transformed nearest distance rather than the nearest distance in the multivariate logistic regression models, wealso found that there wasan inverse relationship between the log-transformed nearest distance and risk of mesothelioma (data not shown).

Pleural mesotheliomas accounted for 91% of the total cases. When only pleural mesothelioma cases were used, proximity to NOA was significantly and positively associated with case status for both men and women. On the contrary, when only peritoneal mesothelioma cases were used, proximity to NOA was not significantly associated with case status and did not show a trend with distance.

Results of this cancer registry–based case control study for mesothelioma in California demonstrated that residential proximity to geologic sources of NOA in California was independently and positively associated with case status. The odds of being a mesothelioma case are 6.3% lower than the odds of being a control subject for every 10 km farther from the nearest asbestos source. These findings were adjusted for occupational exposure to asbestos, age at initial diagnosis, and sex. The association was observed in both men and women, although the association was statistically significant in men only.

Our study confirmed that some occupations such as shipyard worker, boilermaker, insulator, plumber, pipefitter, and steamfitter, and industries such as shipping, construction, and Navy had higher occupational exposure to asbestos and were strongly associated with an increased risk of malignant mesothelioma, consistent with results from previous studies of mesothelioma (1–6, 30). Although it is likely that occupational exposure misclassification exists, our study did see the expected dose–response relationship between occupational exposure to asbestos and mesothelioma. The method defined by asbestosis PMR for occupations based on the longest held occupation and industry available in CCR dataappeared reasonable to classifyoccupational exposure to asbestos.
A major strength of this study was the very large number of incident mesothelioma cases used to assess the potentially weak association between exposure to NOA and mesothelioma inci-
VariablesCasesControl SubjectsOR95% CIzp |z|
All subjectsn 1,133n 890
Distance (every 10 km)
Probability of occupational exposure to asbestos0.9370.895–0.9822.720.006
Menn 962n 746
Distance (every 10 km)
Probability of occupational exposure to asbestos0.9350.888–0.9852.550.011
Womenn 171n 144
Distance (every 10 km)
Probability of occupational exposure to asbestos0.9520.853–1.0620.880.381
Analysis is based on cases and controls with data of occupational exposure, age, sex, and nearest distance range from 0 to 100 km). p |z| p value for z-test.
Definition of abbreviations: 95% CI 95% confidence interval of odds ratio; OR adjusted odds ratio from multivariate logistic regression analysis e^b; z z-
score for test of b 0.
dence. The large size of this study provided us with a unique opportunity to detect relatively low-dose exposures to NOA in the presence of significant occupational exposure to asbestos. Another strength of this study was that GIS approaches were used to characterize potential individual exposure to NOA in a

Figure 2. (A)Lowess-smoothedpredictedlogoddsof mesotheliomaversus nearest distance from naturally occurring asbestos deposits—men (adjusting for age, sex, and occupational exposure) and (B) lowess-smoothed predicted log odds of mesothelioma versus nearest distance from naturally occurring asbestos deposits—women (adjusting for age, sex, and occupational exposure).
very efficient way. Geocoding of residential addresses provided more accurate assessment of potential environmental exposure to NOA at the individual level than methods using less precise geographic classification.
Selection bias should be limited in our study because the data on mesothelioma and pancreatic cancer were both obtained by the CCR in a comparable way. The data included all registered cases, and the control patients were selected using stratified random sampling from patients with malignant pancreatic cancer in the same time period.
A limitation of the registry based study was lack of accurate andcompletelifetimeoccupationalhistoriesonindividualcasesand controls. Incomplete occupational data and lack of duration and intensity of occupational exposure to asbestos in the past made it difficult for us to evaluate occupational exposure to asbestos using common occupational exposure assessments such as jobexposure matrices and expert assessment for exposures. Although the CCR was supposed to record the patient’s longestheld occupation and industry, it often listed only current or most recent occupation. Occupational exposure is the predominant cause of asbestos-induced mesothelioma. We should be cautious to explain our results because our assessment for occupational exposure to asbestos was based on incomplete occupational history on individual cases and control subjects.
Another limitation of the study was the lack of a reliable and acceptable job-exposure matrix for asbestos to characterize the potential of individual occupational exposure to asbestos based on occupation or job titles. Therefore we had to derive occupational exposure to asbestos based on incomplete information on occupations and industries. Misclassification for occupational exposure was unavoidable in this study. Although the National Institute for Occupational Safety and Health has reported asbestosis PMR for selected occupations and industries to reflect strength of occupational exposure to asbestos, it included only limited occupations and industries with higher occupational exposure to asbestos and more asbestosis cases (26). The job-exposure matrix for asbestos developed by Cocco and Dosemeci in 1998 lacked validation of occupational exposure to asbestos (27), and too many occupations were defined as exposed in a study of mesothelioma in Australia (31).

The study was also limited by the lack of complete lifetime residential history on individual cases and controls. When we calculated the distance to the nearest NOA from subject residential address at initial diagnosis, we had to assume that subject’s residential address at initial diagnosis was the same as the longest residential address in his or her life. Exposure misclassification in our study could either decrease or increase the observed dose– response relationship. Incomplete residential data and lack of residential duration in one’s lifetime made it difficult to accurately assess environmental exposure to naturally occurring and other asbestos sources. Reliable assessment of exposure to NOA using GIS approaches ideally depends on accurate and complete residential histories. A field study is needed to examine the relationship between actual asbestos exposure potential and the distance to the nearest asbestos sources. In additionally, consideration should be given to the impact of age of potential exposure, deposit size, residence duration, nature of human disturbance activity, meteorologic conditions, and other geologic/demographic attributes on the actual or potential exposure to NOA.

Our study is based on ultramafic rock-specific GIS map, but notasbestos-specific GISmap fordistribution ofasbestos sources in California. A new digital map with more accurate and specific information about asbestos sources in California needs to be developed for further studies. It is essential for public health efforts to assess more accurately potential exposure to NOA. Some efforts should be increased to characterize the location of asbestos deposits using imaging spectroscopy to map ultramafic rocks, serpentinites, and tremolite-actinolite–bearing rocks in California (32).
Frequency matching was used to minimize confounding from age andsex. We were unableto control forpotential confounding from domestic or residential exposure to asbestos because these data were not available for this study. Selection bias was limited because the data included all eligible cases from the populationbased CCR and the control subjects were selected by stratified random sampling from the same population-based cancer registry. The data were collected in a similar manner for cases and control subjects; therefore, information bias from the data collection was limited, although some information bias cannot be avoided. For example, data on the longest occupation and industry were available for 74% of mesothelioma cases and 63% of pancreatic cancer cases in the CCR records. Because patients diagnosed with mesothelioma may be more likely to have been asked about occupational history and asbestos exposure, this may have led to overestimating occupational exposure to asbestos in this study.
We have found that residential proximity to NOA shows an independent and dose–response association with mesothelioma risk. The findings are biologically plausible in view of the known strong association of occupational asbestos exposure and mesothelioma, and the observation of an association of NOA and mesothelioma in other areas of the world (33). A prospective case–control study based on asbestos-specific GIS map in California should be done with incident mesothelioma cases. This would facilitate obtaining accurate and complete lifetime residential and occupational histories. Further research also is needed to develop a model to evaluate relationship between actual environmental exposure to NOA and major influencing factors, and to develop public health strategies to reduce exposure to asbestos from environmental sources.

Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

1.Howel D, Gibbs A. Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region. Occup Environ Med 1999;56:51–58.
2.Goldberg M, Banaei A, Goldberg S, Auvert B, Luce D, Gueguen A. Past occupational exposure to asbestos among men in France. Scand J Work Environ Health 2000;26:52–61.
3.Agudo A, Gonzalez CA, Bleda MJ. Occupation and risk of malignant pleural mesothelioma: a case-control study in Spain. Am J Ind Med 2000;37:159–168.
4.Kishimoto T, Ozaki S, Kato K, Nishi H, Genba K. Malignant pleural mesothelioma in parts of Japan in relationship to asbestos exposure. Ind Health 2004;42:435–439.
5.Zellos L, Christiani DC. Epidemiology, biologic behavior, and natural history of mesothelioma. Thorac Surg Clin 2004;14:469–477.
6.Godleski JJ. Role of asbestos in etiology of malignant pleural mesothelioma. Thorac Surg Clin 2004;14:479–487.
7.Iwatsubo Y, Pairon J. Pleural mesothelioma: dose-response relation at low levels of asbestos exposure in a French population-based casecontrol study. Am J Epidemiol 1998;148:133–142.
8.Hansen J, de Klerk NH, Musk AW, Hobbs MS. Environmental exposure to crocidolite and mesothelioma: exposure-response relationships. Am J Respir Crit Care Med 1998;157:69–75.
9.Abratt RP, Vorobiof DA, White N. Asbestos and mesothelioma in South Africa. Lung Cancer 2004;45:S3–S6.
10.Magnani C, Dalmasso P, Biggeri A, Ivaldi C, Mirabelli D, Terracini B. Increased risk of malignant mesothelioma of the pleura after residential or domestic exposure to asbestos: a case-control study in Casale Monferrato, Italy. Environ Health Perspect 2001;109:915–919.
11.Berry M. Mesothelioma incidence and community asbestos exposure. Environ Res 1997;75:34–40.
12.Salih E, Ahmet UD. Malignant pleural mesothelioma in Turkey, 2000– 2002 [review]. Lung Cancer 2004;45:S17–S20.
13.McConnochie K, Simonato L, Mavrides P, Christofides P, Mitha R, Griffiths
DM, Wagner JC. Mesothelioma in Cyprus. IARC Sci Publ 1989;90: 411–419.
15. Luce D, Bugel I, Goldberg P, Goldberg M, Salomon C, Billon-Galland MA, Nicolau J, Quenel P, Fevotte J, Brochard P. Environmental exposure to tremolite and respiratory cancer in New Caledonia: a case-control study. Am J Epidemiol 2000;151:259–265.
16. Rey F, Viallat JR, Boutin C, Steinbauer J, Alessandroni P, Jutisz P, Di Giambattista D, Billon-Galland MA, Hereng P, Dumortier P, et al. Environmental mesotheliomas in northeast Corsica. Rev Mal Respir 1993;10:339–345.
17. Luo S, Liu X, Mu S. Asbestos related diseases from environmental exposureto crocidoliteinDa-yao, China:I:review ofexposure andepidemiological data. Occup Environ Med 2003;60:35–42.
18. Bernardini P, Schettino B, Sperduto B, Giannandrea F, Burragato F, Castellino N. Three cases of pleural mesothelioma and environmental pollution with tremolite outcrops in Lucania. G Ital Med Lav Ergon 2003;25:408–411.
19. Orenstein MR, Schenker MB. Environmental asbestos exposure and mesothelioma. Curr Opin Pulm Med 2000;6:371–377.
20. Hillerdal G. Mesothelioma: cases associated with non-occupational and low dose exposure. Occup Environ Med 1999;56:505–513.
21. Rice SJ. Asbestos. Calif Div Mines Bull 1957;176:49–58.
22. PerkinsC,CohenR,YoungJL, SchlagR,WrightWE.CancerinCalifornia: details site and histology, 1990–1994. Sacramento, CA: California Department of Health Services, Cancer Surveillance Section; 1997.
23. Churchill RK, Hill RL. A general location guide for ultramafic rocks in California—areas more likely to contain naturally occurring asbestos: California Division of Mines and Geology Open-File Report, 2000–19; 2000.
24. Jennings CW. Geologic data map no. 2: Sacramento, CA. California Department of Conservation, Division of Mines and Geology, geologic map of California (1:750:000); 1977.
25. Ormsby T, Alvi J. Extending ArcView GIS: teach yourself to use ArcView GIS extensions. New York: ESRI Inc.; 1999.
26. National Institute for Occupational Safety and Health. Work-related lung disease surveillance report, 1999. Cincinnati, OH: CDC, National Institute for Occupational Safety and Health (DHHS [NIOSH] publication no. 2000-105).
27. Cocco PL, Dosemeci M. Peritoneal cancer and occupational exposure to asbestos: results from the application of a job-exposure matrix. Am J Ind Med 1999;35:9–14.
28. Hosmer DW, Lemeshow S. Applied logistic regression, 2nd ed. New York: Wiley-Interscience; 2000.
29. StataCorp. Stata statistical software: release 6. College Station, TX: Stata Corporation; 1999.
30. Teschke K, Morgan MS, Checkoway H. Mesothelioma surveillance to locate sources of exposure to asbestos. Can J Public Health 1997;88:
31. Yeung P, Rogers A, Johnson A. Distribution of mesothelioma cases in different occupational groups and industries in Australia. Appl Occup Environ Hyg 1999;14:59–67.
32. Swayze GA, Higgins CT, Clinkenbeard JP, Kodaly RF, Clark RN, Meeker GP, Sutley SJ. Preliminary report on using imaging spectroscopy to map ultramafic rocks, serpentinites, and tremolite-actinolite-bearing rocks in California. California Geological Survey Geologic Hazards Investigation 2004-01.
33. Hillerdal G. Mesothelioma: cases associated with non-occupational and low dose exposures. Occup Environ Med 1999;56:505–513
Landslides Potentially Containing Asbestos 
July 9, 2009

Landslides can be destructive, destroying houses, infrastructure, and kill or injure people. However, we don’t usually think about landslides being bad for your health.

Washington State has a complex geology. Much of the western Cascades is made up of accreted terrains , composed of both oceanic and continental rocks. Parts of these terrains contain asbestos (which occurs naturally, despite a relatively large number of people believing it artificial). Asbestos is a fairly blanket term for a wide variety of minerals, some harmless, some very dangerous. The most well known example of the dangers of asbestos can be seen in Libby, Montana, where vermiculite mining with occurrences of fibrous tremolite asbestos caused widespread health problems and death for many of the residences and workers.

In Washington State, asbestos outcrops across the state. Most of the outcrops are small, uneconomical to mine or develop and probably pose little danger with limited exposure. However, some larger deposits occur in Snohomish, Skagit, Whatcom, Kittitas, and Klickitat Counties. These deposits can cause weakness within rocks and are sometimes associated with weak, friable material, places where we would expect landslides to occur. The prime landslide that contains asbestos in Washington State is the Swift Creek Landslide in Whatcom County. The landslide material is composed mostly of serpentinite, a friable, weak rock in terms of stability with high amounts of chrysotile. Its origin was probably an uplifted oceanic plate that was probably composed of ultramafic material, such as dunite that was then metamorphosed and transformed into serpentinite. The landslide has produced a significant amount of material which has been transported downhill into the valley below, depositing chrysotile laden sediments. These sediments, especially during flood events, deposit in places where people can come into long-term exposure, which can result in long-term health problems. 

Swift Creek might be the most well known landslide to contain asbestos in Washington State, but since asbestos occurs throughout Washington State, many other landslides have the potential to contain asbestos. This map represents deep-seated landslides that have the potential to contain asbestos within them.

Washington State Asbestos-DSLS Map

This map was created by overlaying identified asbestos occurrences found in Bulletin No. 37, Inventory of Washington Minerals (Valentine and Huntting, 1960) with the 100k geologic units (with slight modification on unit selection). The units that were identified with asbestos occurrences were then intersected with deep-seated landslides from DGER Washington’s Statewide Landslide Database (the database is located within the menu). These deep-seated landslides are of all ages, from relict to active. Points were then selected at the centroid of the polygons to create a point file of landslides that potentially contain asbestos materials. It isn’t a perfect method by any means, but it at least gives us an idea that more of these landslides probably exists throughout Washington State. I am in the process of intersecting the landslide layer with ultramafic units known to contain serpentinite, which will help expand and potentially more accurately capture landslides potentially containing asbestos.

Valentine, Grant M.; Huntting, Marshall T., reviser, 1960, Inventory of Washington minerals; Part I–Nonmetallic minerals; 2nd edition: Washington Division of Mines and Geology Bulletin 37, Part I, 2nd ed., 2 v. 
Posted in General Landslides | Tagged Asbestos, Chrysotile, deep seated, Kittitas, Klickitat, Landslide, Landslides, Map, Mass Wasting, Serpentinite, Skagit, Snohomish, Swfit Creek, Washington State, Whatcom |