Petroleum hydrocarbon soil pollution resulting from the production and use of fossil fuels like oil and gas is a little-known but widespread environmental concern. Crude oil and petroleum products such as diesel can release into the soil through transport, storage or spills.
How and why do petroleum hydrocarbons enter soil?
Petroleum products reach the soil through industrial accidents (such as equipment failure) or oil spills that occur at drilling sites. This can lead to the release of drilling fluids, crude petroleum, and refined petroleum products used for the equipment into soils. Other 'fossil-fuelled' links to soil pollution are hydraulic fracking, a widely and increasingly used method to extract oil and gas. Disposal of excavated material from the drilling of natural gas borehole near the gas well site can lead to point source pollution of soil, as well as accidental wastewater surface spill on the soil. The use of mineral oils for lubricating machinery and chainsaws during logging can also cause soil contamination, leading to up to 7 million liters of oil being released into forest soils in Poland (Iwan et al., 2015).
Studies from across Europe have determined that mineral oil is amongst the most common soil contaminants, accounting for 33.7% of soil pollution at contaminated sites. In Nigeria, oil spills are commonplace, with around 4,919 oil spills occurring in the last six years (Agency Report, 2021). The main reasons for crude oil spills in Nigeria that the lucrative oil industry has cited are vandalism and crude oil theft.
Left: Screenshot from Nigerian Oil Spill Monitoring, Right: Oil spill in Mauritius (Source: American Geosciences).
There is even a monitoring site that reports around 75% of oil spills are due to sabotage and theft. However, concerns have been raised that international oil companies including Shell and Chevron are most responsible for oil spills and provide the data for these monitoring sites. Although aware of dilapidated equipment, these companies might avoid responsibility by moving offshore and selling their production facilities to gullible, profit-motivated local companies that are often not equipped to deal with equipment failure or accidents (Mongabay, 2021).
How do petroleum compounds contaminate soil?
Petroleum contains components such as PAHs (polyaromatic hydrocarbons) which are toxic to soil micro and meso organisms as well as humans, as they are carcinogenic. Petroleum spills can affect water movement in soils by leading them to become hydrophobic. Petroleum hydrocarbons undergo weathering, which could involve physiochemical, physical, chemical, or biological influences. Figure 1 shows the fate of oil following a terrestrial oil spill event, including changes to the plant and soil community. Volatilization occurs when lighter fractions of the oil volatilize into the atmosphere as the oil spreads across the landscape.
Following a pollution event, some petroleum hydrocarbon fractions can be highly toxic to soil biota and to humans if it enters the food chain. As hydrocarbons lock away nutrients and water or cause direct toxicity to soil microorganisms, reduction in diversity and evenness of a microbial community can occur as only hydrocarbon tolerant/degrading species persist (Truskewycz et al., 2019).
Figure 1. (A) Plant death, (B) anaerobic zones, (C) altered soil structure, (D) volatilization, (E) hydrocarbon percolation, (F) aerobic zones, (G) initial decrease in microbial populations and diversity, (H) hydrocarbon contaminated groundwater. Source: Truskewycz et al. (2019).
Along with remediating contaminated soils and placing adequate safeguards to prevent petroleum leakages into soils, the urgent transition to a low-carbon economy through reduced reliance on fossil fuels can hopefully help to tackle this issue to conserve soils and improve human health.
References
Agency Report. (2021, July 6). Nigeria records 4,919 oil spills in 6 years, 4.5trn barrels stolen in 4 years — Minister. Premium Times Nigeria. https://www.premiumtimesng.com/news/headlines/471901-nigeria-records-4919-oil-spills-in-6-years-4-5trn-barrels-stolen-in-4-years-minister.html
FAO and UNEP. (2021). Global assessment of soil pollution: Report. https://doi.org/10.4060/cb4894en
Klamerus-Iwan, A., Błońska, E., Lasota, J., Kalandyk, A., & Waligórski, P. (2015). Influence of Oil Contamination on Physical and Biological Properties of Forest Soil After Chainsaw Use. Water, Air, & Soil Pollution, 226(11), 389. https://doi.org/10.1007/s11270-015-2649-2
Niger Delta communities in ‘great danger’ as month-old oil spill continues. (2021, December 8). Mongabay Environmental News. https://news.mongabay.com/2021/12/niger-delta-communities-in-great-danger-as-month-old-oil-spill-continues/#:%7E:text=by%20Mongabay%20on%206%20December,be%20relocated%20for%20their%20safety
Truskewycz, A., Gundry, T. D., Khudur, L. S., Kolobaric, A., Taha, M., Aburto-Medina, A., Ball, A. S., & Shahsavari, E. (2019). Petroleum Hydrocarbon Contamination in Terrestrial Ecosystems—Fate and Microbial Responses. Molecules, 24(18), 3400. https://doi.org/10.3390/molecules24183400
Wollin, K.-M., Damm, G., Foth, H., Freyberger, A., Gebel, T., Mangerich, A., Gundert-Remy, U., Partosch, F., Röhl, C., Schupp, T., & Hengstler, J. G. (2020). Critical evaluation of human health risks due to hydraulic fracturing in natural gas and petroleum production. Archives of Toxicology, 94(4), 967–1016. https://doi.org/10.1007/s00204-020-02758-7