Crayfish test: Polyaromatic hydrocarbons assessed

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  • Published: May 15, 2014
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Crayfish test: Polyaromatic hydrocarbons assessed

Predicting PAHs passively

Signal crayfish - Pacifastacus leniusculus - http://en.wikipedia.org/wiki/Pacifastacus_leniusculus

A predictive model for the determination of average polycyclic aromatic hydrocarbon (PAH) concentrations in the freely dissolved phase and those present in resident aquatic organisms, such as crayfish, is being developed by US researchers.

Crayfish are an important part of the seafood economy but are highly susceptible to contamination by toxic chemicals from industrial waste water, oil spills and other sources of environmental concern. The accumulation of PAHs in their tissues, for instance, can pose a significant long-term health threat to anyone eating exposed seafood. As such, health officials are charged with identifying and mitigating uncontrolled releases of such chemicals. Unfortunately, there is a downside to the collection and testing of samples, primarily in that it is not always timely but it is time-consuming as well as expensive and secondarily such sample collection can disrupt already at-risk ecosystems still further.

Semipermeable surrogates

Now, Norman Forsberg, Brian Smith, Greg Sower, and Kim Anderson of the Environmental and Molecular Toxicology Department, at Oregon State University, in Corvallis, have devised an approach to extracting data from passive samplers and utilising the tools of cheminformatics, such as two-factor partial least squares calibration, to predict PAH accumulation in a given population of crayfish. The model could predict almost three-quarters (more than 72 percent) of the variation in concentrations of PAHs but was also successful within three times the measured values. "Importantly, PLS calibration provided a means to estimate PAH concentrations in tissues when concentrations were below detection in the freely dissolved phase," the team explains. "Having a predictive approach to estimate concentrations of hazardous chemicals in aquatic organism tissues would be useful to risk assessors in instances when tissue data are limited," the team says. It might thus be able to provide timely health warnings following an incident, such as a spill or waste water discharge.

The team points out that earlier predictive models have tended to focus on bioaccumulation factors (BAFs) and so can give estimates of the impact of an incident that are inaccurate by orders of magnitude in terms of the levels of contamination actually present in the tissues of the aquatic organisms. Moreover, if levels of a contaminant are below detection limits in the aqueous phrase BAFs become notoriously unreliable. A clearer understanding of partitioning of a contaminant between the aquatic environment and the tissues of living sea creatures leads to a much more effective measure and predictive tool that exploits semi-permeable membrane devices (SPMDs) as surrogates of diffusion into living tissue.

Passive sample

Forsberg and colleagues thus sampled different classes of PAHs in the freely dissolved phase using SPMDs and to corroborate their findings collected co-located resident crayfish from several locations within the Portland Harbor area. They opted for crayfish because these creatures have a less efficient metabolic system for breaking down and so detoxifying PAHs and the chemical excretion rate is much lower than that of aquatic vertebrates. Moreover, these creatures have a relatively small range. Of course, once the model was developed and the SPMD surrogates calibrated against the actual data from the living creatures, there should no longer be any need to collect more creatures to test the waters.

"Human health and ecological risk assessments are often challenged by a limited amount of site-specific data for contaminant concentrations in resident aquatic biota. Combining passive sampling with PLS calibration appears to provide a means to fill this knowledge gap," the team concludes.

"We are looking at further validating and testing the model with another paired study," Anderson told SpectroscopyNOW." We are expanding to other resident organisms such as clams."

Related Links

Environ Sci Tech, 2014, online: "Predicting polycyclic aromatic hydrocarbon concentrations in resident aquatic organisms using passive samplers and partial least squares calibration"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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