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Comparing the solid phase and saline extract Microtox assays for two polycyclic aromatic hydrocarbon-contaminated
Carolyn M Acheson1, Qin Zhou, Yonggui Shan
1U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Cincinnati, Ohio 45268, USA. acheson.carolyn@epa.gov
Environmental Toxicology and Chemistry
|February 26, 2004
Summary
The solid phase Microtox assay is a more sensitive and reliable method for evaluating toxicity in polycyclic aromatic hydrocarbon (PAH)-contaminated soils compared to saline extract methods. This bioassay offers a fuller understanding of soil remediation treatment performance.
Area of Science:
- Environmental Science
- Ecotoxicology
- Soil Science
Background:
- Remedial treatment performance is often assessed solely by chemical concentrations.
- Incorporating toxicity bioassays provides a more comprehensive evaluation of treatment efficacy.
- The Microtox assay, particularly the solid phase method, is valuable for assessing soil and sediment toxicity.
Purpose of the Study:
- To compare the performance of solid phase and saline extract Microtox assays.
- To evaluate the utility of the solid phase Microtox assay for soils contaminated with polycyclic aromatic hydrocarbons (PAHs).
- To optimize solid phase Microtox assay procedures, including sample holding times and replication.
Main Methods:
- Two experiments were conducted using two PAH-contaminated soils.
- Experiment 1: Refined solid phase assay procedures, assessing sample holding times (up to 2 weeks), replication (8 replicates initially, 3 recommended), and reference toxicant controls (phenol).
- Experiment 2: Compared solid phase and saline extract Microtox assays with varying mixing times (5 min to 16 h).
Main Results:
- Solid phase Microtox assay procedures were refined; samples showed stable toxicity for up to two weeks.
- Three replicates per sample provided >95% statistical power for the solid phase assay.
- Phenol served as a reliable reference toxicant (mean EC50 = 21.76 mg/L).
- The solid phase Microtox assay was significantly more sensitive than the saline extract assay, yielding EC50 values 7 to 50 times lower.
- Saline extract assay results were variable for mixing times under 2 hours.
Conclusions:
- The solid phase Microtox assay is a robust and sensitive tool for assessing the toxicity of PAH-contaminated soils.
- It offers a more reliable and sensitive measure of toxicity compared to saline extract methods.
- This assay enhances the evaluation of soil remediation treatment performance.