Investigating the influence of urban land use on asbestos concentration and identifying the most vulnerable areas in Shiraz, Iran

Our plain-English summary of Investigating the influence of urban land use on asbestos concentration and identifying the most vulnerable areas in Shiraz, Iran, by S. Norzaee, S. Darvishali, M. Farzadkia, et al (Scientific Reports, 2025).

The study

• Authors: S. Norzaee, S. Darvishali, M. Farzadkia, A.J. Jafari, M. Gholami, A. Shahsavani, M. Kermani
• Journal: Scientific Reports
• Published: 2025;15(1):27591
• Read it: PubMed · Publisher · Free full text

Abstract

This study investigated asbestos fiber concentrations and associated health risks in Shiraz over a period of one year and examined their relationship with various land use factors. Samples were analyzed using phase-contrast microscopy (PCM), and health effects were assessed using the EPA's IRIS method. We examined the relationship between asbestos fiber concentrations and road network density, population, number of bus stations, and green space. The results showed that 10% of the sampling sites in Shiraz had low asbestos fiber concentrations, 20% had medium concentrations, 60% had high concentrations, and 10% had very high concentrations. The mean ELCR for asbestos inhalation was 1.44 × 10-4, indicating a cancer risk for 1.44 out of every 10,000 people. The highest ELCR values were found in the west, near the Shiraz Ring expressway, and in the southeast, near high-traffic areas. Additionally, no positive correlation was found between asbestos concentrations and population, bus stations, or green space, but there was a significant positive correlation with road network density. Motor vehicle traffic is the primary source of asbestos pollution, posing a significant health risk. Traffic control measures and replacing asbestos in brake pads with alternative materials are necessary to reduce pollution in Shiraz.

© 2025. The Author(s).

In plain English

This study measured airborne asbestos fibers in the outdoor air of Shiraz, Iran. It used 18 rooftop sampling stations and collected 72 eight-hour samples across four seasons between May 2019 and February 2020. Fibers were counted by phase-contrast microscopy, and the study did not identify which asbestos fiber types were in its samples. The mean concentration was 1.25 fibers per liter. Seasonal means ranged from 0.92 in summer to 1.55 in winter. The highest readings, 2.56 to 2.64 fibers per liter, were at Stations 7 and 14 in autumn. Ten percent of sites exceeded the 2 fibers per liter limit the authors cited. Fiber levels correlated positively with road network density (coefficients 0.610 to 0.820) but showed no significant relationship with weather. In a regression model, population density and bus stops were also positively associated, while green space was not statistically significant. The estimated mean excess lifetime cancer risk is reported inconsistently: 2.89 per 10,000 people in the results, and 1.44 per 10,000 in the abstract and conclusions. The authors concluded that road networks and traffic played a key role and recommended phasing out asbestos-containing brake materials.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Ambient air monitoring study over one year, with spatial (GIS) analysis, correlation and regression analysis against land use, and an EPA-model cancer risk assessment
• Who was studied: Outdoor air at 18 sampling stations in Shiraz, Iran (industrial, traffic and residential areas), sampled once per season from May 2019 to February 2020, giving 72 samples. Risk estimates used the city's adult population from 2016 census data.
• Exposure: Airborne fibers counted by phase-contrast microscopy (NIOSH 7400 method), defined as longer than 5 micrometers with an aspect ratio of at least 3:1. The study did not identify the asbestos fiber types in its samples. The introduction mentions white asbestos only as background, in noting Iran's 2007 ban. Land-use factors studied were road network density, population, bus stations and green space.
• Main results:
  • The mean asbestos concentration across all stations was 1.25 fibers per liter. The reported range of 0.92 to 1.55 fibers per liter matches the seasonal means.
  • The highest concentrations were at Stations 7 and 14 in autumn (2.56 to 2.64 fibers per liter). The lowest was at Station 2 in summer (0.03 fibers per liter).
  • Sites by concentration level: 10% low (below 0.5 fibers per liter), 20% moderate (0.5 to 1), 60% high (1 to 2) and 10% very high (above 2). The 10% above 2 fibers per liter exceeded the threshold the authors cited.
  • Winter had the highest seasonal mean (1.55 fibers per liter) and summer the lowest (0.92 fibers per liter). Spring was 1.01 and autumn 1.44 (Table 2).
  • There was no significant relationship between fiber levels and wind speed, humidity or temperature (n = 72).
  • Fiber concentration correlated significantly with road network density: Spearman coefficients of 0.610, 0.792 and 0.820 within 300, 500 and 700 m of the stations (p less than 0.01). In Table 4, the correlations for bus stations, population and green space were not marked significant.
  • In the multiple linear regression model (adjusted R squared 0.773), road density had the strongest positive association (beta 0.679, p less than 0.001). Population density (beta 0.441, p 0.015) and bus stops (beta 0.361, p 0.026) were also positive and statistically significant. Green space was not significant (p 0.301).
  • The results section gives excess lifetime cancer risk from 8.3 in 100,000 to 5.22 in 10,000, with a mean of 2.89 in 10,000. This is near or above the upper end of the EPA acceptable range the authors cite.
  • Under more realistic exposure assumptions, the sensitivity analysis lowered the risk estimates by over 70% in some cases. Table 6 shows a maximum of 1.52 and a minimum of 0.24 in 10,000 under scenario b, compared with 5.22 and 0.82 in 10,000 under continuous lifetime exposure.
  • The highest estimated cancer risk was in the areas of Stations 14 and 7. Once population was taken into account, the areas of Stations 14 and 8 had the highest population-level risk.
• The authors' conclusion: The authors concluded that there was a positive and significant relationship between asbestos levels and road networks, and that road networks, seasonal changes and traffic played a key role. They recommended stronger regulation and phased removal of asbestos-containing brake materials, plus regular monitoring in the high-risk areas they identified.
• Limitations the authors state:
  • Cancer risk estimates change a lot depending on the exposure assumptions used.
  • The small green-space effect may reflect limited differences in green space across the city and needs further study with a larger dataset.
  • Differences in station characteristics and measurement strategies may affect comparisons with other studies.
  • The study did not directly test whether traffic-reduction measures would lower exposure.

Topics

Medical terms in this study, explained in our Lexicon: Brake Lining.

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• Monitoring of airborne asbestos fibers in an urban ambient air of Shahryar City, Iran: levels, spatial distribution, seasonal variations, and health risk assessment — F. Taghizadeh, A.J. Jafari, et al. (2019)
• Spatio-seasonal variation, distribution, levels, and risk assessment of airborne asbestos concentration in the most industrial city of Iran: effect of meteorological factors — M. Kermani, A. Jonidi Jafari, et al. (2021)
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• Identifying predictors of personal exposure to air temperature in peri-urban India — C. Milà, A. Curto, et al. (2020)
• The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method — A.M. Johnston, A.D. Jones, et al. (1982)

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