Evaluating the effects of bioremediation on genotoxicity of polycyclic aromatic hydrocarbon-contaminated soil using genetically engineered, higher eukaryotic cell lines

Abstract

Bioremediation is one of the commonly applied remediation strategies at sites contaminated with polycyclic aromatic hydrocarbons (PAHs). However, remediation goals are typically based on removal of the target contaminants rather than on broader measures related to health risks. We investigated changes in the toxicity and genotoxicity of PAH-contaminated soil from a former manufactured-gas plant site before and after two simulated bioremediation processes: a sequencing batch bioreactor system and a continuous-flow column system. Toxicity and genotoxicity of the residues from solvent extracts of the soil were determined by the chicken DT40 B-lymphocyte isogenic cell line and its DNA-repair-deficient mutants. Although both bioremediation processes significantly removed PAHs from the contaminated soil (bioreactor 69% removal, column 84% removal), bioreactor treatment resulted in an increase in toxicity and genotoxicity over the course of a treatment cycle, whereas long-term column treatment resulted in a decrease in toxicity and genotoxicity. However, when screening with a battery of DT40 mutants for genotoxicity profiling, we found that column treatment induced DNA damage types that were not observed in untreated soil. Toxicity and genotoxicity bioassays can supplement chemical analysis-based risk assessment for contaminated soil when evaluating the efficacy of bioremediation.

Figure 1

Total PAH concentration of soil before and after bioremediation. (a) Soils from five consecutive sampling times during 7-d cycle in the bioreactor treatment. (b) Soils from both the control column and biostimulated column at four sampling points along each column after 2.5-year column treatment. Values are mean ± SD of triplicates. BFS: untreated bioreactor feed soil; BTS: bioreactor treated soil; CPS: untreated column packing soil; CTR: control-column treated soil; BIO: biostimulated-column treated soil.

Figure 2

LD of soil before and after bioremediation for parental DT40 cell line and its Rad54^−/− mutant. (a) Soils from five consecutive sampling times during 7-d cycle in the bioreactor treatment. (b) Soils from both control column and biostimulated column at four sampling points along each column after 2.5-year column treatment. Values are mean ± SD of three separate experiments. Abbreviations are as defined in Figure 1.

Figure 3

Inverse correlations between LD₅₀ and concentrations of tPAH for parental DT40 cell line (a) and its Rad54^−/− mutant (b), and between LD₅₀ and concentrations of total residue for parental DT40 cell line (c) and its Rad54^−/− mutant (d). Each data point represents the mean for each soil sample (total 15 samples) including untreated column packing soil, all sampling points along each column, untreated bioreactor feed soil, and all sampling events for bioreactor-treated soil during the 7-d. Asterisks indicate the correlation is statistically significant (p< 0.05).

Figure 4

LD₅₀ (a) and relative LD₅₀ (b) of soil before and after 2.5 year column treatment in the test with a battery of DT40 cell lines. Values are mean ± SD of three separate experiments. Different letters are assigned to conditions for which there was a significant difference (p<0.05). Asterisks indicate values significantly less than 1 (p< 0.05). CPS: untreated column packing soil; CTR-A: control-column treated soil at Port A; BIO-A: biostimulated-column treated soil at Port A.