ELECTRONIC SUPPLEMENTARY MATERIAL

SEDIMENTS, SEC 1 • SEDIMENT QUALITY AND IMPACT ASSESSMENT • RESEARCH ARTICLE

Investigating speciation and toxicity of heavy metals in anoxic marine sediments – a case study from a mariculture bay in Southern China

Bing Xia 1, 3 • Pengran Guo 2 • Yongqian Lei 2 • Tao Zhang 1 • Rongliang Qiu 1 • Klaus- Holger Knorr 3, 4

Received: 30 January 2015 / Accepted: 9 September 2015 © Springer-Verlag Berlin Heidelberg 2015

Responsible editor: Marc Babut

1School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China

2Guangdong Provincial Public Lab of Analysis and Testing Technology, China National Analytical Center (Guangzhou), Guangzhou 510070, China

3Department of Hydrology, University of Bayreuth, Bayreuth, Germany

4Present address: Institute for Landscape Ecology, Hydrology Group, University of Münster, 48149 Münster, Germany

Corresponding authors:  Klaus-Holger Knorr [email protected]

 Pengran Guo [email protected]

1 The purpose of XRD analysis

Sequential extraction procedures for speciation of metals, e.g. the Tessier method (Tessier et al. 1979), the BCR method (Ure et al. 1993), and the Forstner method (Ngiam and Lim 2001), were developed for natural sediments or artificial materials (Dodd et al. 2000) to extract defined heavy metal fractions such as acid soluble, reducible, oxidisable (including organic bound and sulfide bound), and residual fractions. However in mariculture bays of China, especially in mariculture bays of Guangdong province, intensive mariculture can cause exceptionally high eutrophication, favoring reducing and anoxic conditions, thereby also increasing sulfide contents in surface sediments (Cao et al. 2007; Wu et al. 1994). Sequential extraction procedures for natural sediment are not fully suitable for mariculture area sediments because the procedure of these methods (such as the extraction of organic matter bound fraction) uses oxidizing extractants which have a strong impact on sedimentary sulfides; therefore these methods cannot be used to evaluate the sulfidic fraction separately. On the other hand, low contents of sulfides in other sediment samples less affected by mariculture also limit the applicability of the AVS-SEM approach (Chapman et al. 1998; Fang et al. 2005). Thus, we propose to use a revised protocol to assess the heavy metals speciation in mariculture area sediments with a broad range of geochemical conditions (Guo et al. 2009; Wang et al. 2011). The results of sequential extraction procedures are subject to uncertainties for many reasons, such as dissolution of nontarget mineral phases and concurrent release of metals of interest, or redistribution between species during the extraction procedure. This remains a common limitation in sequential extraction procedures, nevertheless they are still widely employed due to their simplicity and the possibility to perform such investigation in less equipped laboratories (Dodd et al. 2000). To provide support for the selectivity of our proposed approach, X-ray diffraction analysis (XRD) was used to investigate the efficiency and selectivity of the extraction steps on sediment minerals. More details on the method development have been published elsewhere (Wang et al. 2011).

Materials and Methods After freeze-drying of bulk sediments and the extracted residuals, sample powders were

2 X-rayed as thin films. The range of the diffraction angle was 5°～90°, at a scanning rate of 0.048°/step and a step time of 576 s. Diffraction data were analyzed by Jade 5.0 software (PDF 2004 cards).

Results from XRD analysis As depicted in the figures below, the mineralogy of the investigated sediments is diverse and comprises several phases that should be adequately reflected in the different fractions of our sequential extraction: calcite (d=4.70658 、 2.98539Å), kaolinite

(d=7.10972、3.55149、3.23309、1.53905 Å), montmorillonite (d=9.99548、4.45181 Å), iron oxide minerals (d=2.81105 、 2.59912 、 1.94572 Å), illite

(d=9.99548、4.9722、4.45181、3.33670、3.23309、1.99102 Å), chlorite (d=7.10872、4.97722、3.55149 Å), quartz (d=3.33670、4.23980、2.45048、2.27895、2.12309、1.81561 Å), etc. After extraction by step1-step4, reflecting the non-residual fractions, the diffraction peak intensities of minerals such as calcite, montmorillonite, iron oxide minerals disappeared or were reduced significantly. This indicated that the extraction of non-residual metals could effectively dissolve these minerals. After a single extraction representing the AVS-SEM extraction (equivalent to the single step4 of the sequential extraction) the changes of the diffraction peaks were quite similar to changes observed after extracting the non-residual fraction. This indicates, not surprisingly, that the AVS extraction provides a bulk extract of the non-residual fractions, but does not provide information about the lability of the predominant fraction. However, XRD is not suitable to directly support our statement that the residual fraction was attacked by the AVS-SEM, due to the high contents of Si and Al (indicator elements of this fraction). Therefore, changes in Si or Al are obscured by too high background. We only can use XRD as an indirect support, stating that although we extracted e.g. less Ni, similar non-residual phases were extracted. Therefore we attribute the excess Ni from AVS-SEM to the residual fraction.

3 Fig. S1 X-ray diffraction patterns and predominant mineral phases for a sediment sample prior to extraction

4 Fig. S2 Changes in mineralogy of the sediment sample after extraction of non-residual fractions (step 1 ～ step 4) by the proposed sequential extraction scheme

5 Fig. S3 Changes in mineralogy after extraction of AVS from sediment samples, equivalent to step 4 in the proposed sequential extraction scheme

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