Arsenic in air, cancer risks and background levels
Humans are exposed to inorganic arsenic in drinking water, soil and the air, and to organic arsenic compounds, especially in fish and shellfish. Arsenic occurs in the air bound to particles, mainly in the fine particle fraction, and consists almost exclusively of the more toxic form of inorganic arsenic (As III and As V).
Arsenic enters the air mainly due to smelters (of non-ferrous metals) and in the combustion of coal containing high arsenic levels (WHO, 2000). The reasons for regulating the concentrations of arsenic in ambient air are the effects that emissions to air can have on human health and the environment. Research on arsenic and lung cancer began in Sweden, where workers at Boliden Rönnskärsverket smelting plant were found to have a five times higher risk of dying from lung cancer.
Arsenic in ambient air is now a known carcinogenic (IARC Group I), after extensive research (IARC, 2012), and it has not been possible to establish a threshold for adverse effects on human health (WHO, 2000). If there does not seem to be a threshold value (i.e., a value below which no effect has been found with sufficient evidence), a so-called level of protection must instead be calculated with the accepted number of extra cancer cases in the event of lifelong exposure. Target levels can then be set, such as one extra cancer case per 100,000 or one million inhabitants in the event of lifelong exposure. The WHO has estimated that the lifetime excess risk of lung cancer is one per million at an airborne arsenic content of 0.7 (0.66) ng/m³ based on a traditional linear extrapolation from occupational studies (including Boliden Rönnskär) to low-dose exposure (WHO, 2000).
The US EPA uses the same approach as the WHO, but they only use domestic studies (their guidelines) and get a slightly higher risk estimate. This means that they set a lifetime excess risk of cancer of one per million at an airborne arsenic content of 0.2 ng/m³ (US EPA). In 2000, an EU expert group discussed if there might be an impact threshold (EC, 2000). In the presentation of results they concluding that there was no convincing evidence for an impact threshold, with other words there are no safe levels of Arsenic in air (EC, 2001). Following the publication of the EU position paper, further studies have shown lung cancer at arsenic exposures without any apparent threshold level (Swedish Environmental Protection Agency, 2008). The European body ECHA (2013) has compiled calculations, the latest of which is from DECOS 2012. The Dutch Expert Committee on Occupational Safety (DECOS) used the same methodology as the WHO but instead used the study that found the method to be of the highest quality and found that the lifetime risk of lung cancer is 1 per million at an air content of arsenic at 0.9 ng/m3 (ECHA, 2013).
To summarize, arsenic in the air is carcinogenic and the risk increases with dose and there does not seem to be evidence for threshold of effect according to the WHO (2000). Different expert bodies have calculated acceptable cancer risks, based on different samples of studies. The excess lifetime risk level is one per million inhabitants at a concentration of 0.2–0.9 ng/m³, while the the WHO assessment being 0.7ng/ m³. Unlike other countries, the EU does not have a defined acceptable risk, it is therefore a philosophical/political question about how many extra cancer cases to allow in society. Economically, lung cancer cases tend to be one of the most expensive outcomes, partly through medical costs, loss of work ability and partly through the suffering you are exposed to before you die.
Figure 1, Arsenic in PM10, Umweltbundesamt II 4.2 mit Daten der Messnetze der Länder und des Bundes.
Background concentrations in Europe have decreased over the past 20 years and are now mostly below 1 ng/m³ (EEA, 2023) (Figure 2). The statistics are in whole numbers and do not determine how much less than 1 ng/m³. As can be seen in Figure 1, with Germany as an example due to its large industrial sector, levels are well below 1 ng/m³ in most area with levels reaching 1.5 ng/m³ in industrial areas. Thus, the feasibility of reaching a health-based limit value seems good with little effort in most of the EU.
Figure 2, Annual averages of arsenic in air 2018 (EEA, 2023)
DECOS (2012) Arsenic and inorganic arsenic compounds. Health-based calculated occupational cancer risk values. 2012; publication no. 2012/32.
EC (2000). Ambient Air Pollution by As, Cd and Ni compounds (Position Paper-Final). European Commission. Available at http://ec.europa.eu/environment/air/pdf/pp_as_cd_ni.pdf
EC (2001) Scientific Questions to the CSTEE on Arsenic https://ec.europa.eu/health/scientific_committees/environmental_risks/op...
ECHA (2013) Final report for Arsenic Report number ECHA/2011/01 – SR-11
EEA (2023) Annual mean arsenic concentrations in 2018 https://www.eea.europa.eu/data-and-maps/figures/annual-mean-arsenic-conc... downloaded 2023-07-1
International Agency for Research on Cancer: IARC (2012) vol. 100C: A review of human carcinogens
US Environmental Protection Agency (EPA). Arsenic. https://cfpub.epa.gov/ncea/iris/iris_documents/documents/subst/0278_summ...
WHO (2000) Air quality guidelines for Europe; second edition No. 91.