Effect of alkyl polyglucoside and nitrilotriacetic acid combined application on lead/pyrene bioavailability and dehydrogenase activity in co-contaminated soils
Graphical abstract
Introduction
Co-contaminations of organic and inorganic pollutants are frequently found in the environment (Nadal et al., 2011). As a group of priority control pollutant, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment (Liao et al., 2015). Some studies have demonstrated that PAHs and heavy metals (HMs) are frequently found together as contaminants in soil. Among heavy metals, lead (Pb) is a poison element, which is known to be a persistent environmental problem and frequently coexist with PAHs (Cachada et al., 2012). Phytoremediation, due to its environmentally sound and lower cost, are widely studied for remove PAHs or HMs from soil (Sun et al., 2013, Ehsan et al., 2014). However, PAHs and HMs in soil usually exhibit poor availability, which limits the application of phytoremediation (An et al., 2011, Cheng et al., 2008). The enhanced phytoremediation by chemical method is a promising technology for the removal of PAHs and HMs. Surfactants which are a group of chemicals can assist in increasing the water solubility of organic pollutants. They have been proven to be very effective in promoting phytoremediation for PAHs. For example, studies indicated that the presence of some nonionic surfactants (polyoxyethylene sorbitan monooleate; polyoxyethylene and dodecanol) at relatively low concentrations resulted in significant positive effects on phytoremediation for pyrene-contaminated soil (Gao et al., 2007). Liao et al. (2015) also found that surfactants (Triton X-100, rhamnolipid and saponin) could enhance the removal of pollutants from contaminated soil during phytoremediation. Chelating agents are compounds that can make heavy metals desorbed from soil. Their characteristic of increasing the plant-available fraction and uptake amounts, and transport metals to aboveground parts made them have been widely used in phytoremediation to enhance remediation efficiency (Lee and Sung, 2014). For example, Kanwal et al. (2014) investigated that ethylenediaminetetraacetic acid (EDTA) improves the capability of plants to uptake heavy metals (Pb) from polluted soil.
Alkyl polyglucoside (APG), a nonionic surfactant produced from renewable resources such as fatty alcohols and glucose, was studied to remove PAHs from soil (Liu et al., 2013). As a biodegradable chelating agent, nitrilotriacetic acid (NTA) was found that it can desorb HMs (such as Pb) from soil with no environmental effects (Freitas and Nascimento, 2009). As a consequence, using APG and NTA together may be a promising way to enhance phytoremediation for PAHs and HMs co-contaminated soil without secondary pollution. Besides, the combination of APG and NTA may have synergistic effect on phytoremediation for PAHs or HMs. However, few researches have been concentrated on this combined application.
Bioavailability of PAHs and HMs in soil is the key factor in determining efficiency of phytoremediation (Megharaj et al., 2011, Ayanka et al., 2015). Chelating agents can increase the plant-available fraction and uptake amounts, and transport HMs by desorbing HMs from soil (Shen et al., 2002, Lee and Sung, 2014). Surfactants have been proven to be very effective in promoting the mobilization of organic compounds of relatively low water solubility (Sun et al., 2013). So, to measure the possibility of this approach for enhancing phytoremediation, it is of great importance to evaluate bioaccessiblity of PAHs and HMs in soil by application of APG and NTA. In addition, when the mixed compounds of APG and NTA are applied their respective effect on bioavailability of PAHs or HMs will be influenced each other. Exchangeable fraction of metal extracted by MgCl2 and bioaccessible PAH extracted by butanol, the most easily available for plant uptake, was used to discuss the bioavailability of metal and PAH in soil (Kim et al., 2010, Wei et al., 2014). However, there is no report showed that whether and how APG and NTA affect each other on the effects of increasing bioavailability of PAHs and Pb.
Soil enzymes, derived primarily from soil microorganisms, plant roots, plant and animal residues, can be the indicator to measure the effectiveness of soil to support biochemical process involving the decomposition of PAHs (Zhou et al., 2011). Enzymes involved in the degradation of PAHs are oxygenase, dehydrogenase and lignolytic enzymes (Haritash and Kaushik, 2009). Dehydrogenase, an intracellular enzyme, is the catalyst for important metabolic process which includes the decomposition for organic inputs and detoxification of xenobiotics (Zhang et al., 2014). So, this study uses the dehydrogenase activity (DHA) as a model to reveal the effects of application of APG and NTA on soil enzymes.
In a short, the aim of this study was to discuss the possibility of the combined application of NTA and APG by investigating the effects of alone application of APG or NTA and combined application of APG and NTA on pyrene and Pb bioaccessiblity, as well as on DHA.
Section snippets
Chemicals
Pyrene (purity: 98%) was purchased from Aladdin Reagent. APG used in the test was C12/14-APG (APG1214) obtained from the China Research Institute of Daily Chemical Industry (Shanxi, China). The other chemicals, analytical grade or better, were bought from Sinopharm.
Soil preparation
The soil (air-dried, 2 mm sieved) in this study was collected from the top of the soil profile of a field without previous exposure to pyrene and Pb contamination in Shanghai University, China. Its properties are as follows: pH 8.3;
Bioaccessiblity of Pb and pyrene in soil
Exchangeable metals in the soil are considered to be easily available for plant uptake. Comparison of the amount of exchangeable Pb in soil between groups (Fig. 1) indicated that NTA was significantly effective in increasing bioavailable Pb in soil. This phenomenon can be explained that NTA can combined Pb from soil matrix to form soluble Pb-NTA complexes (Freitas and Nascimento, 2009). Besides, slight enhancement on bioavailable Pb in soil was also found in the treatments of alone APG
Conclusions
APG and NTA respectively played dominant role on increase bioaccessible pyrene and exchangeable Pb. And synergy on bioaccessibility of pyrene and Pb were achieved with the combined application of APG and NTA. It was found that the combination of NTA and APG had great effect on improving the dehydrogenase activity. The relationship among APG/NTA, bioaccessibility of pyrene/Pb and the DHA correlation were conducted. Addition of APG and NTA can affect DHA directly by themselves and indirectly by
Notes
The authors declare no competing financial interest.
Acknowledgments
The work was funded by the National Natural Science Foundation of China (No. 41373097), Program for Innovative Research Team in University (No. IRT13078).
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2021, Journal of Environmental ManagementCitation Excerpt :Alkyl polyglucoside (APG) mixed with nitritotriacetic acid (NTA) had the highest performance in improving the bioaccessibility of pyrene. The activity of DHO was higher when combining the application of NTA and APG, indirectly affected by changing in the solubility of pyrene (Chen et al., 2016a,b). NTA and APG at 1 and 2 g kg−1 of soil, respectively, had no significant negative impact on Scirpus triqueter yield and their combined application had a positive effect on pyrene degradation (Chen et al., 2016a,b).