Abstract
Microbes are susceptible to contaminant effects, and high concentrations of chemical in soil can impact on microbial growth, density, viability and development. As a result of relative sensitivity of microbes to contaminants, toxicity data are important in determining critical loads or safe levels for contaminants in soil. Therefore the aim of this study was to assess the impact of phenanthrene and the 3-ring nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) on soil microbial respiration. Soil samples were amended with phenanthrene and its 3-ring nitrogen-containing analogues and respiration rates (using substrate induced respiration), CO2 production inhibition and/or stress and total culturable microbial numbers were measured over a 90 days soil-contact time. The study showed that inhibition of phenanthrene amended soils occurred in the first 60 days, while the nitrogen-containing analogues impacted on respiration with increased concentration and contact time. Time dependent inhibitions were more than 25 % portraying N-PAHs toxic and inhibitory effects on microbial synthesis of the added carbon substrate. Further, statistical analysis of data revealed statistically significant differences in the respiration rates over time (p < 0.05). This suggests that soil microorganisms may be more sensitive to N-PAHs in soil than the homocyclic PAH analogues. This current study provides baseline toxicity data to the understanding of the environmental impact of N-PAHs, and assists science-based decision makers for improved management of N-PAH contaminated sites.
Highlights
Soil is a complex microhabitat, supporting diverse microbial populations, which play an important role in breakdown and transformation of organic matter in fertile soils with many species contributing to different aspects of soil fertility (OECD 2000)
Removal of phenanthrene and 3‐ring N‐PAHs from soil over time The removal of phenanthrene and similar 3-ring nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) was measured in the soil over 90 days (Fig. 1)
Not showing a consistent trend, the results showed that increasing N-PAHs (B[h]Q and 1,7-Phen) contamination resulted in reductions in the colony forming units (CFUs) (Table 5)
Summary
Soil is a complex microhabitat, supporting diverse microbial populations, which play an important role in breakdown and transformation of organic matter in fertile soils with many species contributing to different aspects of soil fertility (OECD 2000). Microbial uptake and conversion of chemicals is continuously taking place throughout the biosphere and it is widely known that indigenous microflora which utilizes organic contaminants in soil as carbon/energy sources are ubiquitous in the environment (Leung et al.2007) Any interference with these biochemical processes may potentially affect nutrient cycling and impact the health and fertility of soil (OECD 2000). Phenanthrene and its nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) consist of three aromatic rings containing carbon with one or two atoms of nitrogen These chemicals are semi-volatile, persistent, toxic, ubiquitously distributed (Švábenský et al 2009; EC 2011; Anyanwu et al 2013), and are widely produced by industrial activities (petroleum derived, combustion sources and biological sources) (Švábenský et al 2009; Hazardous Substance Data Bank 2010; EC 2011; Anyanwu and Semple 2015a). The available published data are limited, there are considerable evidence indicating their toxicity to humans and ecological receptors (Bleeker et al 2002; Hazardous Substance Data Bank 2010; EC 2011; Brar et al 2010; IARC 2012; Anyanwu et al 2013; Anyanwu and Semple 2015a, b, c)
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