The effect of hazardous pollutants from coal combustion activity: Phytotoxicity assessment of aqueous soil extracts
Graphical abstract
Introduction
Coal is the most abundant fossil fuel, supplying some 30–40% of commercial global energy. Its use is likely to increase throughout the world, regardless of the environmental costs (Singh et al., 2015). Namely, the coal combustion results in ash and gas emissions into the atmosphere (Saikia et al., 2015), where they are washed out by rainfall, and transferred into the soil and surface waters. Coal ash is a solid by-product composed of toxic residues (Mardon and Hower, 2004), mainly potentially toxic trace elements (PTEs, like Cd, Ni, As, etc.) and persistent organic pollutants (e.g. PAHs, polycyclic aromatic hydrocarbons), capable of migration into floral and aquatic matrices, causing them adverse effects (Manzo et al., 2008, Saikia et al., 2016, Awoyemi and Dzantor, 2017). The PPP (Istrian Peninsula, Croatia, Fig. 1) was powered with superhigh-organic-sulphur (SHOS) Raša coal during the period 1970–2000. That coal has been renowned in world terms for its exceptionally high content of sulphur, up to 14% (Medunić et al., 2016a, Medunić et al., 2017). Given that the locality is inside the coastal karst environment (Fig. 1), well known for its vulnerability, it is important to evaluate its environmental quality in the context of previous as well as recent exposure to coal and/or ash airborne particles (Frančišković-Bilinski et al., 2017, Marović et al., 2004). Generally, multidisciplinary studies of the fate of PTEs, and PAHs in the environment are necessary due to their longlasting cycles there and consequences for human health. The previous studies (Medunić et al., 2016b) determined that soil surrounding the PPP had been polluted primarily by the SHOS Raša coal combustion decades ago. The downwind soil locations are polluted with S (up to 4%), PAHs (up to 13,500 ng/g), and Cd (up to 4.70 mg/kg). Also, cytotoxic effects on fish cells of the most polluted soil and ash water extracts were statistically significant.
Historical deposition of coal combustion residues contaminates soils and ultimately groundwater in many areas and may have impacts for decades afterwards (Bogan et al., 1999, Harkness et al., 2016). In this study, we aimed to assess phytotoxic potential of aqueous extracts of soil collected from the vicinity of the PPP using Lemna test (growth inhibition test), a reliable toxicity bioassay procedure (ISO, 20079, 2004) for evaluation of different test matrices (Becker et al., 2002). Being of a small size, and having the rapid growth over a wide range of pH and vegetative propagation, duckweed L. minor proves to be an ideal test system. It has been published that various pollutants, PAHs and heavy metals included, disturb the balance in the cell redox cycle that consequently leads to an increased production of reactive oxygen species (ROS) and modulation of antioxidative system (Babu et al., 2005). Thus, oxidative stress parameters – lipid peroxidation (MDA content), the levels of proteins and glutathione as well as activities of antioxidative enzymes (catalase and ascorbate peroxidase) were also determined.
Section snippets
Study area description
The PPP's location is on the southeastern coast of the Istrian Peninsula, at the very end of the Plomin Bay (Fig. 1).
It covers an area of about 54 ha, and is owned by the Croatian Power Corporation (HEP). For the reception and transport of coal, a concession has been granted for additional 3 ha of a sea area. The area mostly belongs to the Kršan municipality, while the coastal edge of the Plomin Bay belongs to the city of Labin. The harbor area includes the Plomin Luka and Plomin settlements
Results and discussion
In this study, toxicological and chemical characterization was used to evaluate the effects of micropollutants present in aqueous extracts of soil from the vicinity of the PPP. The effects of the previous (SHOS Raša coal) and current (imported) coal and coal combustion residues on the soil in the proximity of the PPP was evaluated using Lemna biotest.
Conclusion
This study shows the adverse legacy of the decades-old coal combustion activity. Obtained results demonstrate that even aqueous extracts from soil polluted by the SHOS Raša coal produce significant phytotoxic effects as evidenced by inhibition of growth, decrease of chlorophylls, glutathione and antioxidative enzymes activities as well as increase of lipid peroxidation level in L. minor. The observed phytotoxicity of aqueous soil extracts is clearly correlated to a relatively high mobility of
Conflicts of interest
None.
Acknowledgement
The authors thank Tonči Urošević who carried out a part of the laboratory work for his Master's degree. Dr. Nenad Tomašić (PMF) is thanked for the help with field work.
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