Last Month's Most Accessed Feature: Turtle takeaway: Pollution monitor at the Great Barrier Reef

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  • Published: Oct 3, 2017
  • Categories: Base Peak
thumbnail image: Last Month's Most Accessed Feature: Turtle takeaway: Pollution monitor at the Great Barrier Reef

Marine biomonitors

A non-specific mass spectrometric screening method has been used to detect pollutants in green sea turtles from the coastal region of the Great Barrier Reef by comparing with free-ranging turtles using a case control protocol.

Image: NPA / Ryan Fura

Marine species around the world are at risk from man-made chemicals entering the waters and some of them have been afforded the dubious distinction of acting as indicators of marine health. Shellfish are prime examples as they accumulate metals and can be used to estimate the degree of pollution of the surrounding waters. Off the east coast of Australia at the Great Barrier Reef, this honour falls to the humble green sea turtle.

It has been recognised that the turtle is a good candidate for monitoring marine pollution because it is near the bottom of the food chain, so will not accumulate chemicals by eating other creatures. In addition, it has a long lifetime and tends to stay in a particular location which is near to land, so will have first hand experience of pollutants that enter the sea. These prime factors led scientists in Australia to acknowledge that green sea turtles would be excellent species for both environmental monitoring and biomonitoring.

Amy Heffernan and a team of researchers from The University of Queensland, Brisbane, the University of Melbourne, the Department of Environment and Heritage Protection, Townsville, the World Wildlife Fund for Nature-Australia, Brisbane, and the University of Almeria, Spain, decided to study turtles to see if they could act as monitoring agents. Mirroring techniques used in the clinical sciences, they compared the pollutant load of turtles collected from a remote, pristine location with those from two areas known to be affected by urban, industrial and agricultural activities.

Testing turtle blood

Green sea turtles were sampled from the Howick Group of Islands in the remote north and from Cleveland Bay which is an urban and industrial region. The second polluted area was Upstart Bay which is impacted by agriculture and mining and receives water from the Burdekin river which is one of the most polluted on the continent. A mass green sea turtle extinction event occurred in this bay in 2012, with a neurotoxic agent one of the prime suspects. All of the turtles were estimated to have lived in their respective areas for 10-20 years.

Blood was taken from turtles from each location and subjected to a non-specific extraction procedure that was optimised for polar pesticides and members of the group known as pharmaceuticals and personal care products (PPCPs), 26 compounds in total. The extracts were analysed using a liquid chromatograph linked to a high-resolution mass spectrometer operating under electrospray ionisation in positive and negative modes.

The research team went to great lengths to eliminate interfering compounds by also analysing field and procedural blanks. In this way, DEET and several parabens were identified as contaminants from sample processing, the likely source of them all being from direct contact with individual(s) who had been using a treatment such as sunscreen (parabens) and an insecticide (DEET).

The data were processed manually due to the dearth of adequate databases of environmental and emerging contaminants and their metabolites. However, this was not a trivial task with 5000 tandem mass spectra per injection generating about 860,000 spectra in total. The first step involved reducing the number of spectral features by comparing the spectra from the pristine and polluted regions using a combination of retention time, significance (p-value), effect size (log fold-change), monoisotopic mass and ion products. Then each feature was prioritised using a colour coding scheme.

In this way, the spectral features for Upstart Bay were reduced from 4761 to 56 in positive-ion mode and 4940 to 9 in negative-ion mode. Those from Cleveland Bay were similarly reduced from 4761 and 4630 to 24 and 37, respectively. Although this approach is time consuming, it is far less likely to miss metabolic and transformation products than library search techniques.

Pollutant cocktail

A number of suspect compounds were detected in the green sea turtles at both locations. In Upstart Bay turtles, benzenetriol sulphate is a biomarker of exposure that is probably a metabolite of benzene produced in the liver by the action of hydroxyl radicals. Lipid peroxidation products of fatty acids that were found were designated biomarkers of effect.

A further compound that was tentatively identified was possibly a fragrance (traseolide or galaxolide). 3-Indolepropanoic acid, which has neuroprotective properties against lipid peroxidation and oxidative stress, and vanillylmandelic acid, a metabolite of the stress hormones epinephrine and norepinephrine, were also detected. Ecklonialactone A, an oxylipin from brown algae that was found in the blood, is related to the turtle diet.

At the other location, Cleveland Bay, a number of common industrial chemicals such as isoquinoline and sulphonic acids were found in the turtle blood, as well as a metabolite of the pesticide ethiofencarb. The presence of docosanamide and oleamide could be a result of pollution or they might be endogenous compounds. A polybrominated compound was also detected but not identified.

The findings correlated with recently reported levels of metals, particularly cobalt, and clinical markers such as bilirubin and alkaline phosphatase, providing more evidence of oxidative stress and lipid peroxidation.

The results appear to confirm the success of this approach to pollution monitoring that uses case control by comparing affected turtles with those from a pristine environment as well as data filtering to ease the data processing. They show how the pollutants affect turtles which, in turn, could be used as biomonitors of pollution as they live in one location for many years. A principal components analysis was also able to group the turtles correctly from each location.

The non-target approach "has the potential to enhance hazard identification in biota and environmental samples" the team concluded, especially since library searching is limited due to the poor representation of environmental compounds, metabolites and transformation products.

Related Links

Science of the Total Environment 2017, 599-600, 1251-1262: "Non-targeted, high resolution mass spectrometry strategy for simultaneous monitoring of xenobiotics and endogenous compounds in green sea turtles on the Great Barrier Reef"

Article by Steve Down

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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