In my last post I mentioned that some researchers have been looking into how we can get rid of polycyclic aromatic hydrocarbons (PAHs) that contaminate water or soil or air. Based on a review by Gan et al. (2009), we have four main avenues for this: solvent extraction; bioremediation; chemical, photo-, and electro- degradation; and thermal treatment. The first option is quicker than the others, but only removes the PAHs, rather than degrading them, so we would still need a second step to fully get rid of them. Thermal treatment is effective since it completes the combustion process, but is more expensive. Chemical, photo-, and electro-degradation do remove PAHs, but there are concerns that the new substances created may be just as or more toxic than what we started with.
Earthworms can both degrade and sequester PAHs- this can help with bioremediation of soils. Photo courtesy of pfly- license link
What about bioremediation? As I mentioned in a previous post, there are some species that degrade PAHs and can be helpful in cleaning up contamination. One of the challenges here is that this is a long-term process-we have to wait for results. It is also easier to accomplish for contaminated liquids than for soils (Haritash & Kaushik 2009) because PAHs tend to cling to soil particles. Yap et al. (2010) found that adding vegetable oil to contaminated soil helped dissolve PAHs so that microbes could access them for degradation, but large quantities of oil were needed for highly contaminated soils, and that could create new issues. I did find some studies which suggested there may be more options than we originally thought for bioremediation. A 2007 study by Khan et al. found that fiber made from cattails were effective at absorbing PAHs from contaminated water- in locations where cattails have become invasive, this could be a way to utilize ‘weeds.’ And we should remember our soil engineers, earthworms, when thinking about soil bioremediation. In addition to creating aerated soil where microbes can work more quickly, it turns out that earthworms are largely resistant to pollutants and even help degrade PAHs with enzymes (Sinha et al. 2008).
Why should we work to remove PAHs from contaminated air, soil, and water? PAH-contamination of soils has been shown to alter the bacterial community, which can impact ecosystem function (Zhou et al. 2009). We also track these particles inside on our shoes, and, once inside, they are protected from degradation and can persist for a long time, especially in carpets (Lewis et al. 1999)- crawling children are then exposed to carcinogens and mutagens. As I mentioned in a previous post, PAHs are also associated with liver lesions, lung cancers, and other diseases. There is also evidence that prenatal exposure to PAHs increases the incidence of anxiety, depression, and attention problems in children (Perera et al. 2012).
So we have some options for removing PAHs once they are present, but it probably makes more sense to prevent their occurrence in the first place– what can each of us do on either front? My next post will take a look at that.
Works cited:
Gan, S, Lau, EV and HK Ng. 2009. Remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Journal of Hazardous Materials 172: 532-549.
Haritash, AK and CP Kaushik. 2009. Biodegradation aspects of polycyclic aromatic hydrocarbons (PAHs): a review. Journal of Hazardous Materials 169: 1-15.
Khan, E, Khaodhir, S and P Rotwiron. 2007. Polycyclic aromatic hydrocarbon removal from water by natural fiber sorption. Water Environment Research 79: 901-911.
Lewis, RG, Fortune, CR, Willis, RD, Camann, DE and JT Antley. 1999. Distribution of pesticides and polycyclic aromatic hydrocarbons in house dust as a function of particle size. Environmental Health Perspectives 107: 721-726.
Perera, FP, Tang, D, Wang, S, Vishnevetsky, J, Zhang, B, Diaz, D, Camann, D and V Rauh. 2012. Prenatal polycyclic aromatic hydrocarbon (PAH) exposure and child behavior at age 6-7. Environmental Health Perspectives 120: 921-926.
Sinha, RK, Bharambe, G and D Ryan. 2008. Converting wasteland into wonderland by earthworms- a low-cost nature’s technology for soil remediation: a case study of vermiremediation of PAHs contaminated soil. Environmentalist 28: 466-475.
Yap, CL, Gan, S and HK Ng. 2010. Application of vegetable oils in the treatment of polycyclic aromatic hydrocarbons-contaminated soils. Journal of Hazardous Materials 177: 28-41.
Zhou, HW, Wong, AHY, Yu, RMK, Park, YD, Wong, YS and NFY Tam. Polycyclic aromatic hydrocarbon-induced structural shift of bacterial communities in mangrove sediment. Microbial Ecology 58: 153-160.