George G. Vadas

Near real‐time, on‐site, quantitative analysis of PAHs in the aqueous environment using an antibody‐based biosensor

Rapid, on-site, quantitative assessments of dissolved polycyclic aromatic hydrocarbons (PAHs) were demonstrated for two field applications. The platform, a KinExA Inline Sensor (Sapidyne Instruments), employed the monoclonal anti-PAH antibody, 7B2.3, which has specificity for 3- to 5-ring PAHs. A spatial study was conducted near a dredging site where contaminated sediments were being removed, and a temporal study was performed during a rainfall event. Most importantly, the generation of near real-time data guided management decisions in the field and determined proper sampling protocols for conventional analyses. The method was able to determine PAH concentrations as low as 0.3 µg/L, within 10 min of sample acquisition, and to assess 80+ samples (not including standards and blanks) in less than 3 d. These results were compared with a laboratory-based gas chromatography-mass spectrometry method in which a wide array of PAHs, including alkylated homologs, were examined. This system shows great promise as a field instrument for the rapid monitoring of PAH pollution.

Predicting survival of grass shrimp (Palaemonetes pugio) during ethylnaphthalene, dimethylnaphthalene, and phenanthrene exposures differing in concentration and duration

Both exposure duration and concentration determine the lethal consequences of polycyclic aromatic hydrocarbons (PAHs) released during oil spills. Many factors, such as weathering, tidal transport, and addition of surfactants, can change the composition of individual dissolved compounds and the duration over which an individual is exposed. Conventional toxicity testing methods produce effect metrics, such as the median lethal concentration (LC50), that are not applicable to predicting mortality at all toxicant exposure durations that are likely to occur during a spill. In the present study, survival time models were developed that explicitly include toxicant exposure duration and concentration to predict time-to-death for grass shrimp (Palaemonetes pugio) exposed to three PAHs (1-ethylnaphthalene, 2,6-dimethylnaphthalene, and phenanthrene) commonly found in the water-soluble fraction derived from oil. Conventional 48-h LC50s also were calculated for the compounds (ethylnaphthalene, 295 microg/L; dimethylnaphthalene, 500 microg/L; and phenanthrene, 360 microg/L). In contrast to LC50s, survival models and associated response surfaces can be used to predict the proportions of shrimp that will die at various times throughout the exposure period.

Predicting survival of grass shrimp (Palaemonetes pugio) exposed to naphthalene, fluorene, and dibenzothiophene†

The composition and persistence of dissolved polycyclic aromatic hydrocarbons (PAHs) released to the water column during oil spills are altered by weathering, tidal transport, and addition of dispersants. Conventional toxicity effect metrics, such as the median lethal concentration (LC50), are inaccurate predictors of mortality from all toxicant exposure duration/concentration combinations likely to occur during spills. In contrast, survival models can predict the proportions of animals dying as a consequence of exposures differing in duration and intensity. Extending previous work with ethylnaphthalene, dimethylnaphthalene, and phenanthrene, survival time models were developed that include exposure duration and concentration to predict time to death for grass shrimp (Palaemonetes pugio). Two additional PAHs (naphthalene and fluorene) and a heterocyclic aromatic hydrocarbon (dibenzothiophene) were evaluated for the present study. Preliminary explorations of these models confirmed that quantitative structure- activity regression models were possible for predicting survival model parameters from compound characteristics. Conventional 48-h LC50s also were calculated for the compounds and combined with published LC50s to predict relative PAH toxicity to P. pugio based on octanol-water partitioning.

Evaluating porewater polycyclic aromatic hydrocarbon–related toxicity at a contaminated sediment site using a spiked field‐sediment approach

Although the complexity of contaminant mixtures in sediments can confound the identification of causative agents of adverse biological response, understanding the contaminant(s) of primary concern at impacted sites is critical to sound environmental management and remediation. In the present study, a stock mixture of 18 polycyclic aromatic hydrocarbon (PAH) compounds was prepared to reflect the variety and relative proportions of PAHs measured in surface sediment samples collected from discrete areas of a historically contaminated industrial estuary. This site-specific PAH stock mixture was spiked into nontoxic in-system and out-of-system field-collected reference sediments in dilution series spanning the range of previously measured total PAH concentrations from the region. Spiked sediments were evaluated in 10-d Leptocheirus plumulosus tests to determine whether toxicity in laboratory-created PAH concentrations was similar to the toxicity found in field-collected samples with equivalent PAH concentrations. The results show that toxicity of contaminated sediments was not explained by PAH exposure, while indicating that toxicity in spiked in-system (fine grain, high total organic carbon [TOC]) and out-of-system (course grain, low TOC) sediments was better explained by porewater PAH concentrations, measured using an antibody-based biosensor that quantified 3- to 5-ring PAHs, than total sediment PAH concentrations. The study demonstrates the application of site-specific spiking experiments to evaluate sediment toxicity at sites with complex mixtures of multiple contaminant classes and the utility of the PAH biosensor for rapid sediment-independent porewater PAH analysis. Environ Toxicol Chem 2018;37:893-902.

EVALUATING POREWATER PAH-RELATED TOXICITY AT A CONTAMINATED SEDIMENT SITE USING A SPIKED FIELD-SEDIMENT APPROACH

Although the complexity of contaminant mixtures in sediments can confound the identification of causative agents of adverse biological response, understanding the contaminant(s) of primary concern at impacted sites is critical to sound environmental management and remediation. In the present study, a stock mixture of 18 polycyclic aromatic hydrocarbon (PAH) compounds was prepared to reflect the variety and relative proportions of PAHs measured in surface sediment samples collected from discrete areas of a historically contaminated industrial estuary. This site-specific PAH stock mixture was spiked into nontoxic in-system and out-of-system field-collected reference sediments in dilution series spanning the range of previously measured total PAH concentrations from the region. Spiked sediments were evaluated in 10-d Leptocheirus plumulosus tests to determine whether toxicity in laboratory-created PAH concentrations was similar to the toxicity found in field-collected samples with equivalent PAH concentrations. The results show that toxicity of contaminated sediments was not explained by PAH exposure, while indicating that toxicity in spiked in-system (fine grain, high total organic carbon [TOC]) and out-of-system (course grain, low TOC) sediments was better explained by porewater PAH concentrations, measured using an antibody-based biosensor that quantified 3- to 5-ring PAHs, than total sediment PAH concentrations. The study demonstrates the application of site-specific spiking experiments to evaluate sediment toxicity at sites with complex mixtures of multiple contaminant classes and the utility of the PAH biosensor for rapid sediment-independent porewater PAH analysis. Environ Toxicol Chem 2018;37:893-902.