Antibody-based Biosensor for Rapid Sediment Screening of PAHs

A new technology developed at the Virginia Institute of Marine Science uses antibodies to detect polycyclic aromatic hydrocarbons (PAHs) in sediment porewater. This approach has the potential to complement existing sediment analytical methods such as passive sampling and offer promise as a low-cost evaluation of potential sediment contamination.

PAHs are persistent environmental pollutants often originating from the incomplete combustion of organic matter that can accumulate as complex mixtures in sediments. Generally the freely dissolved concentration of chemicals in sediment porewater (C_free) is considered a better predictor of bioavailability and toxicity to aquatic organisms compared to total sediment concentrations that include sorbed fractions. Passive sampling methods have emerged as the most accurate and sensitive methods to measure C_free and are used as a primary line of evidence to support site-specific sediment management practices.¹ A recently developed immunoassay-based “biosensor” method is a promising portable approach to quantify PAHs in aqueous media,² can be performed with a small volume of mechanically extracted porewater ultimately making it a viable tool for initial measurement of PAH C_free in sediments prior to  passive sampler deployment.

A portable antibody-based PAH biosensor allows for rapid screening of the bioavailable concentration, which when combined with passive sampling, is an effective tool for active sediment management.

Evaluation of Biosensor Performance in Petroleum-Impacted Sediment.

Total PAHs (ΣPAHs) C_free using the biosensor method and SP3^TM passive samplers were used for a variety of sediment types containing PAHs to evaluate the potential for the biosensor to serve as a screening tool to flag sediments unlikely to be toxic to aquatic life.³ Porewater was obtained via centrifugation and analyzed using the antibody-based biosensor method that has a high affinity for parent and alkylated PAHs with 3 to 5 rings.² SP3^TM passive samplers were deployed in jars with collected sediment. After tumbling, weighing and solvent-extraction, samplers were analyzed via standard methods (EPA 8270) and C_free calculated.¹ C_free of PAHs were also predicted using USEPA Equilibrium Partitioning (EqP) modelling.

Results

The results from the four sediments from this study indicated that the biosensor produced comparable results to the C_free ΣPAH measured by the SP3^TM passive sampler and predicted by the EqP as shown in Figure 1. Overall, the relative agreement between the biosensor and SP3^TM passive samplers is notable despite the fact that they use completely different methods to quantify and detect C_free. Agreement between the 1-carbon and 2-carbon EqP model was observed for 3 out of the 4 test sediments, with values for C_free ΣPAHs for the Creosote test sediment EqP model values displaying a high bias, highlighting the importance of obtaining accurate C_free measurements.

C_free PAH measurements or predictions within sediments is undertaken in order to predict the potential adverse impact on biota and/or resolve the contribution of PAHs relative to other sediment characteristics with sediment toxicity. The Toxic Unit (TU) approach from C_free passive samplers results or EqP predications is a means to evaluate the potential toxicity to aquatic life. ΣTU values less than one are considered to indicate sediments in which PAH-derived toxicity are not expected, whereas ΣTU values above one suggests that the absence of potential toxicity cannot be assumed without additional evaluation.¹ Mean PAH ΣTU from SP3^TM passive samplers were below one for low petroleum and urban sediment and above one for high petroleum and creosote sediment samples, which agreed with both the EqP 1-carbon and 2-carbon models. The biosensor values for C_free ΣPAH for high petroleum and creosote sediment were higher than the previously noted 10 μg/L biosensor threshold where onset of mortality was observed in toxicity tests,⁴ whereas the values for the low petroleum and urban reference sediment were well below the threshold. Therefore, all approaches for potential PAH toxicity in sediment agree with one another.

The equilibrium partitioning model, SP3^TM passive sampler and the biosensor were in agreement for the prediction of PAH toxicity in all sediment test samples.

Implications and Conclusions

The measured C_free PAH results for the different test sediments suggested that the biosensor is a promising tool for the evaluation of the availability and potential toxicity of PAHs to aquatic life at sediment sites. Real-time data can be acquired rapidly at the site which can aid in the prioritization of sediment location for additional evaluations such as additional C_free measurements by SP3^TM passive samplers, toxicological testing or other ecological evaluations. Further evaluation, standardization and commercialization of the technology would provide another resource for remedial investigations by sediment assessment practitioners.

More Information on Sediment Pore Water Measurement Technology

Visit https://www.siremlab.com/sediment-pore-water-sampler/ or contact Brent Pautler at bpautler@siremlab.com.

References

1. USEPA. 2017. Laboratory, Field and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual. EPA/6006R-16/357.
2. Li, X., Kaattari, S.L., Vogelbein, M.A., Vadas, G.G., Unger, M.A. 2016. A highly sensitive monoclonal antibody-based biosensor for quantifying 3-5 ring polycyclic aromatic hydrocarbons (PAHs) in aqueous environmental samples. Sensing and Biosensing Research. 7: 115-120.
3. Conder, J., Jalalizadeh, M., Luo, H., Bess, A., Sande, S., Healey, M., Unger, M.A. Evaluation of a Rapid Biosensor Tool for Measuring PAH Availability in Petroleum-Impacted Sediment. In Preparation.
4. Hartzell, S.E., Unger, M.A., Vadas, G.G., Yonkos, L. 2018. Evaluating porewater PAH-related toxicity at a contaminated sediment site using a spiked field-sediment approach. Environ. Chem. And Toxicol. 37:893-902.