Introduction
The use of petroleum hydrocarbons for energy and raw materials in
various applications is increasing significantly, leading extensive
release of hydrocarbon contaminants to affect air, soil, surface water
and groundwater. Phytoremediation has been an appealing technology to
clean contaminated soil and water as it does not require extensive
capital investment and can enhance soil properties. However, studies
rarely explored the efficacy of phytoremediation in one of the world’s
most polluted desert soils, caused by the deliberate destruction of
oilfield installations during the First Gulf War in 1990-1991
(Hirschmann 2005;
Omar
et al. 2009).
In addition to possible previous land degradation and climate change
impacts (Berdugo, et al 2020), the soil was contaminated by oil spillage
from 798 sabotaged oil-wells. Moreover, formation water (over 10% salt
content) and over 6 billion gallons of seawater (4% salt content) used
to extinguish the burning oil wells flowed from the damaged wells and
accumulated in the natural depressions of the landscape. The areas were
termed ‘oil lakes’ (CIC, 2003). The damage resulted in contaminating
over 40 million m3 of soil with oil and salt residues,
resulting various types of oil contaminations including wet ‘oil lakes’
dry ‘oil lakes’, and oil-contaminated soil piles. Although the crude oil
was mostly pumped out (Al-Daher et al., 1998), nonetheless the petroleum
penetrated down 30 cm or deeper across large swathes of soil. The Kuwait
Environmental Public Authority (KEPA: Beatona, Kuwait Official
Environmental Portal, 2013) reported that oil lakes changed the soil
texture, killed wildlife, and in some cases seeped into the soil layers
reaching the only freshwater aquifer in northern Kuwait. This severely
contaminated desert ecosystems continue to this day, and in the worst
affected areas, it is thought that the pollution would likely persist
for decades (Hirschmann 2005).
Over the years, the crude oil further broke down to smaller molecules
such as polycyclic
aromatic
hydrocarbons (PAHs). Most PAHs are hydrophobic, display high stability,
and can persist for decades in the environment
(Wagrowski
& Hites 1997; Hirschmann 2005). The amplified possibility of
biomagnification due to their lipophilic nature increases the chance of
persistence and trophic-level transfer in impacted ecosystems.
Plant species have different responses to, and tolerance of, oil
contamination. Hence, that plant communities are usually changed by the
impacts of such contamination with petroleum hydrocarbon-tolerant
species becoming dominant once the initial high-toxic impacts subside to
allow re-colonisation. An earlier study
(Al-Ateeqi
2010) identified two native plant species growing in oil-polluted soils
in Kuwait: Haloxylon salicornicum (Amaranthaceae) andCyperus conglomeratus (Cyperaceae). These species, along with a
third plant considered as a possible phytoremediator species,Rhanterium epapposum (Asteraceae), are widespread in Kuwait
(Halwagy
& Halwagy 1974; Al-Shehabi & Murphy 2017). The three species are also
present in other oil-producing regions of several North African and
Middle Eastern countries
(www.gbif.org/species/3758958;
www.gbif.org/species/2714301;
www.gbif.org/species/3110118).
Suitable phytoremediation management procedures require a good
understanding of native plant species response to hydrocarbon
contamination. Abdullah et al. (2020) assessed the ecosystem resiliency
to total petroleum hydrocarbon (TPH) contamination in Kuwait using
remote sensing and GIS. This study found that autogenic recovery of
native desert plants occurred within a few years as 34% of the TPH
contaminated areas were re-colonised with native desert plants. The
contamination levels of TPH also changed over time and the variations
could be significantly correlated with the soil type, vegetation type,
geological substrates, geomorphological features, and annual
precipitation. The study shed light on the succession process of
vegetation survival and growth over TPH contaminated soils, but did not
report the response of specific native desert communities to different
TPH contamination at different concentration levels.
The primary goal of the present paper is to test whether indigenous
species commonly found in oil-impacted habitats such as H.
salicornicum species could establish and grow successfully in desert
soils contaminated with petroleum hydrocarbons. In our research, we
assessed the hypothesis that some native plant communities in Kuwait are
able to tolerate conditions in weathered oil-polluted soils containing
oil by products (polycyclic aromatic hydrocarbons: PAHs), and that some
of their component species may have potential as phytoremediator. The
outcome of this study provides a useful low-cost, and ecologically
friendly option by delineating a better understanding of utilizing
native plant species to assist with clean-up operations in arid regions.
These results are of especial importance to the United Nations general
assembly declaration in 2019 of its 2021-2030 UN Decade of ecosystem
restoration (Willemen et al., 2020).