Impact of Black Carbon in the Extraction and Mineralization of Phenanthrene in Soil

Abstract

During the past century, increased biomass burning and fossil fuel consumption have drastically increased the input of black carbon (BC) into the environment, and that has been shown to influence the behavior of organic contaminants in soil. A study was conducted to investigate the effects of BC on the relationship between aqueous hydroxypropyl-beta-cyclodextrin (HPCD) extraction and microbial mineralization (bioaccessibility) of 14C-phenanthrene (10 mg kg(-1)) in four soils amended with 0, 0.1, 0.5, 1, 2.5, and 5% (% dry wt soil) activated charcoal, a type of BC. Mineralisation was monitored over 20 d incubation, within respirometric assays, using an inoculum containing a phenanthrene-degrading pseudomonad and compared to HPCD extraction (24 h) using 50 mM aqueous solution; analyses were conducted after 1, 25, 50, and 100 d soil-phenanthrene contact time. Statistical analyses revealed that for each soil the addition of BC led to significant (P < 0.001) reductions in both HPCD extractability and microbial mineralization. Linear correlations for BC concentrations of 0% (r2 = 0.95; slope = 0.89) and 0.1% (r2 = 0.67; slope = 0.95) revealed a highly significant (P < 0.01) relationship between HPCD extractability and total mineralization (20 d), indicating a direct prediction of phenanthrene bioaccessibility by HPCD. However, in soils amended with 0.5, 1, 2.5, and 5% BC exhibited r2 values ranging 0.51-0.13 and slopes of 2.19-12.73. This study has shown that BC strongly sorbs phenanthrene causing reductions in extractability and, to a lesser extent, bioaccessibility to degrading microorganisms.

Influence of biochar and compost on soil properties and tree growth in a tropical urban environment

“…It is beyond the scope our work to identify the optimum proportions and application rates of these additions. It is possible that insufficient application may result in below optimal plant performance while excessive application may result in toxicity (Craul 1999;Rhodes et al 2008). Both short-and long-term studies spanning a range of species will therefore be necessary to facilitate a fuller understanding of these relationships.…”

Impact of Biochar on Organic Contaminants in Soil: A Tool for Mitigating Risk?

“…Black carbon (BC) is the collective term for thermally altered products ranging from partly charred to highly condensed forms of organic carbon, which includes chars, charcoals, biochars, soots and graphite [13]. BC is recalcitrant and has been shown to influence mobility, extractability and/or bioavailability of HOCs in soil [11,14,15]. Further, biochar has been shown to aid in stabilising and restoring SOM in soils [16].…”

“…Therefore, successful management techniques have involved the introduction of recalcitrant SOM into the soil that can enhance the "locking up" of pollutants while providing suitable habitats and substrates for microbial degradation of bioavailable contaminants [59][60][61][62][63][64]. This can be achieved by the addition of biochar to soils [14,65,66].…”

“…Despite being highly recalcitrant, biochar has the potential to be degraded by microorganisms co-metabolically [108]. This was demonstrated by labelling biochar feedstock with 14 C before pyrolysis and exposing the biochar to microorganisms in the presence of glucose. Following the removal of the glucose, biochar decomposition decreased strongly [109].…”

“…It is believed that the increased sorption of organic contaminants will decrease the bioavailable/bioaccessible fraction of contaminant for uptake and biodegradation [128,131,132]. Rhodes et al [14] first assessed the extractability of spiked PAHs using HPCD in black carbon (BC)-amended soils. Results showed that amount of extracted 14 C-phenanthrene decreased with an increase in black carbon concentration and contact time ( Figure 3) with <1% extracted in soils amended with >2% BC.…”