Analysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometryby Arthur Zastepa, Frances R. Pick, Jules M. Blais, Ammar Saleem

Analytica Chimica Acta

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Year
2015
DOI
10.1016/j.aca.2015.02.056
Subject
Environmental Chemistry / Analytical Chemistry / Spectroscopy / Biochemistry

Text

Analytica Chimica Acta xxx (2015) xxx–xxx

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ACA 233771 No. of Pages 9

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Analytica Chimica ActaAnalysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometry

Arthur Zastepa *, Frances R. Pick, Jules M. Blais, Ammar Saleem

Centre for Advanced Research in Environmental Genomics, University of Ottawa, 30 Marie Curie Private, K1N 6N5 Ottawa, Ontario, Canada

H I G H L I G H T S G R A P H I C A L A B S T R A C T  First analytical method for intracellular microcystins (MCs) in sediment.  Includes a suite of variants (LR, 7dmLR, RR, YR, WR, LA, LF, LY, LW) and nodularin.  Reports the first measurements of

MCs in sediment pore waters.  MCs detected in >100 year old lake sediments suggesting long-term preservation.  Sediment-pore water distribution (Kd) differed between variants suggesting differences in environmental fate.

A R T I C L E I N F O

Article history:

Received 7 December 2014

Received in revised form 18 February 2015

Accepted 21 February 2015

Available online xxx

Keywords:

Microcystin variants

Lake sediment

Sediment pore water

Intracellular cyanotoxins

Accelerated solvent extraction

High performance liquid chromatographytandem mass spectrometry

A B S T R A C T

The fate and persistence of microcystin cyanotoxins in aquatic ecosystems remains poorly understood in part due to the lack of analytical methods for microcystins in sediments. Existing methods have been limited to the extraction of a few extracellular microcystins of similar chemistry. We developed a single analytical method, consisting of accelerated solvent extraction, hydrophilic–lipophilic balance solid phase extraction, and reversed phase high performance liquid chromatography-tandem mass spectrometry, suitable for the extraction and quantitation of both intracellular and extracellular cyanotoxins in sediments as well as pore waters. Recoveries of nine microcystins, representing the chemical diversity of microcystins, and nodularin (a marine analogue) ranged between 75 and 98% with one, microcystin-RR (MC-RR), at 50%. Chromatographic separation of these analytes was achieved within 7.5 min and the method detection limits were between 1.1 and 2.5 ng g1 dry weight (dw). The robustness of the method was demonstrated on sediment cores collected from seven Canadian lakes of diverse geography and trophic states. Individual microcystin variants reached a maximum concentration of 829 ng g1 dw on sediment particles and 132 ng mL1 in pore waters and could be detected in sediments as deep as 41 cm (>100 years in age). MC-LR, -RR, and -LA were more often detected while MC-YR, -LY, -LF, and -LW were less common. The analytical method enabled us to estimate sediment-pore water distribution coefficients (Kd), MC-RR had the highest affinity for sediment particles (log Kd = 1.3) while MC-LA had the lowest affinity (log Kd = 0.4), partitioning mainly into pore waters. Our findings confirm that sediments serve as a reservoir for microcystins but suggest that some variants may diffuse into overlying water thereby constituting a new route of exposure * Corresponding author. Tel.: +1 613 818 1620.

E-mail address: arthur.zastepa@gmail.com (A. Zastepa). http://dx.doi.org/10.1016/j.aca.2015.02.056 0003-2670/ã 2015 Elsevier B.V. All rights reserved. journa l home page : www.e l sev ier .com/ loca te /acaPlease cite this article in press as: A. Zastepa, et al., Analysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometry, Anal. Chim. Acta (2015), http://dx. doi.org/10.1016/j.aca.2015.02.056 of ro 2 A. Zastepa et al. / Analytica Chimica Acta xxx (2015) xxx–xxx

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ACA 233771 No. of Pages 9chromatography followed by RP-HPLC-UV). 2.2. Sediment sampling and preparation

Table 1 lists seven lakes from which sediment cores were collected in duplicate using a modified gravity corer [22]. Cores

In order to develop an extraction method for intracellular microcystins, sediments were spiked with a well-characterized culture of Microcystis sp. and the recovery of each intracellular microcystin from sediments was compared to that from the culture alone. Semi-dry sediment was spiked with Microcystis sp. CPCCfollowing the dissipation persistence of different mic 1. Introduction

Microcystins are a diverse class of cyclic heptapeptides produced by cyanobacteria in freshwaters [1]. They are the most prevalent cyanotoxins and can reach toxic concentrations in surface waters, which can affect human and wildlife health [1].

During algal blooms, microcystins are typically found within living cells and on suspended particles, but dissolved microcystins can arise as blooms dissipate [2,3]. Microcystins can subsequently deposit into surficial sediments by adsorption to particulates [4–6] and within intact cyanobacterial cells [7–10] that settle to the lake bottom. Intracellular microcystins have also been found in benthic cyanobacteria growing on the surface sediments of shallow lakes [11–13] as well as in viable cyanobacterial colonies from deep sediments [14]. These reports highlight the need for an extraction method capable of rupturing the cells within sediments to recover intracellular toxins in addition to extracellular microcystins adsorbed to particles or dissolved within sediment pore waters.

Some progress has been made in the extraction and quantitation of extracellular microcystins from sediments. However, only four variants of similar chemistry have been tested thus far [15–18] and laboratory and field studies suggest differences in the adsorption properties of different microcystins [3,19,20]. Furthermore, no method has yet demonstrated the recovery of microcystins from intact cyanobacterial cells in sediments despite increasing evidence of the significance of this microcystin pool [7–14].