New Zealand is often seen as a ‘clean and green’ country with levels of pollution much lower than those in the rest of the world, but recent research by Auckland Council has revealed that levels of air pollution in Queen Street (Auckland’s main street) are in fact rising. According to the research, Queen Street levels of black carbon, which are ultra-fine carbon particles emitted to the air and formed through the incomplete combustion of fossil fuels, biofuels and biomass, are more than three times higher than in Canadian cities and two times higher than concentrations in major cities in Europe and the U.S.(1).

Like other forms of fine airborne particulate matter (PM10 particles), black carbon can enter deep into the lungs, and travel into the bloodstream to become deposited into tissues such as the brain or heart. Both short- and long-term exposure is linked with serious health effects. Epidemiological studies have shown an increase in morbidity and mortality rates from chronic obstructive pulmonary disease after exposure to elevated levels of air pollution, and associations between lung cancer and cardiovascular diseases are well established(2, 3). Exposure to traffic related particulate matter is also increasingly associated with an increased risk of birth defects, and Alzheimer’s disease and other dementias in later life(4, 5).

Black carbon also contributes to a warming effect on our climate(6, 7), and to the melting of snow and glaciers(8). Genotoxic and other damaging effects on plants, are also evident as a result of particulate matter pollutants(9).

The biggest source of high levels of black carbon in the council Queen St study was identified as diesel emissions from older buses, trucks, ferries and ships. While replacing diesel buses with electric buses, introducing modern electric trams and pedestrianising Queen Street in the future would reduce black carbon, the currently very high levels of exposure to pedestrians and others working in or visiting the area or similar inner city locations in other cities, are of concern. Similarly high black carbon levels in other New Zealand cities, towns and locations, have been shown to be unacceptably high(10-11).

In Asian cities it is a common sight to see locals wearing a mask to protect their lungs against the damaging effects of vehicle, smoke or factory pollution and so-called toxic smog. Good quality masks provide some form of a physical barrier to filter out some of these harmful airborne particles, but wearing them can be cumbersome.

It is appropriate also, to consider the potential support that certain medicinal plants can provide to lung health, when there is exposure to a high level of airborne pollution. In cities such as Beijing, Delhi and Mexico City, high levels of air pollution have increased demand for herbal products that enhance lung function, and may help protect against some of the numerous damaging health effects that particulate matter and other airborne pollutants can have.

As written about in February 2016 after my visit to Singapore, there are many herbs traditionally used for lung conditions and upper respiratory tract infections, which seem to work at least partially through gently encouraging the natural expectoration process of the millions of cilia cells lining our bronchial trees. The role of these is to remove excess mucus and potentially harmful substances such as particulate matter or unwanted allergens, so enhancing their ability to fulfill this protective function, can be useful. Mucilaginous (polysaccharide hydrocolloid rich) and expectorant herbs such as marshmallow (Althaea officinalis), mullein (Verbascum thapsus) and the NZ native hoheria (Hoheria populnea), seem to work in this manner. Other traditional lung herbs such as elecampane (Inula helenium), white horehound (Marrubium vulgare) and horseradish (Armoracia rusticana), can also be helpful.

In Britain the root of elecampane was traditionally prepared into a candy as a protection against ‘bad air’, and research now suggests this volatile oil and sesquiterpene lactone rich plant may help protect against some of the more serious potential outcomes of exposure to high levels of airborne pollutants.

Increasing data is emerging on potential cancer protective effects of elecampane, and separate research teams have found it to inhibit the growth of a range of different types of human cancer cell lines in vitro, yet not damage normal cells(12, 13). Potential antitumour activity for elecampane extracts against certain forms of brain cancer, has also been reported(14).

Horseradish is a popular European plant whose root has been used not only to make a hot sauce, but also as a traditionally used warming expectorant and lung tonic. It contains phytochemicals which are well absorbed orally and have established chemo-preventive effects. Anti-mutagenic properties and protective effects against DNA damage shown by horseradish(15) are also of interest, as DNA damage prevention is an important mechanism involved in cancer prevention by dietary compounds.

To summarise, efforts should continue to reduce the sources of black carbon and other forms of airborne pollution. However, chemo-preventive or protective effects shown by various herbal extracts against cellular damage and carcinogenicity may be helpful when exposure to air pollution is unavoidable. Inhalation or ingestion of these in appropriate concentrations at or soon after the time of exposure, may impart short term resistance against the many damaging effects of airborne pollutants, and should be further explored.

Refs:
1. ‘Toxic Air Threat’. New Zealand Herald, Nov 7 2018. http://www.nzherald.co.nz
World Health Organisation, Health risks of particulate matter from long-range transboundary
air pollution, 2006. http://www.euro.who.int/__data/assets/pdf_file/0006/78657/E88189.pdf
2. Segersson D et al, Int J Environ Res Public Health. 2017 Jul; 14(7): 742. Published online 2017 Jul 7.
3. Kilian J, Kitazawa M, Biomed J. 2018 Jun;41(3):141-162. doi: 10.1016/j.bj.2018.06.001. Epub 2018 Jul 17.
4. Wang L et al, J Public Health (Oxf). 2018 Aug 18. doi: 10.1093/pubmed/fdy137. [Epub ahead of print]
5. Bond TC, Sun H. Environ Sci Technol. 2005 Aug 15;39(16):5921-6.
6. Ramanathan V et al, Nature. 2007 Aug 2;448(7153):575-8.
7. Painter TH et al, Proc Natl Acad Sci U S A. 2013 Sep 17;110(38):15216-21
Rai PK, Ecotoxicol Environ Saf. 2016 Jul;129:120-36
8. Davy PK, & Trompetter WJ (2018a). Black carbon in New Zealand. GNS Science, Lower Hutt.
9. Davy, PK, & Trompetter, WJ (2018b). Heavy metals, black carbon and natural sources of particulate matter in New Zealand. GNS Science, Lower Hutt.
12. Dorn DC et al, Phytotherapy Res, Aug 16 (epub ahead of print), 2006.
13. Spiridonov NA et al, Phytotherapy Res 19(5): 428-432, 2005.
14. Koc K et al, J Cancer Res Ther. 2018 Apr-Jun;14(3):658-661
15. Gafrikova M et al, Molecules. 2014 Mar 14;19( 3):3160-72.