The origin of speciation: Trace metal kinetics over natural water/sediment interfaces and the consequences for bioaccumulation

doi:10.1016/j.envpol.2008.09.037

Environmental Pollution

Volume 157, Issue 2, February 2009, Pages 519-527

https://doi.org/10.1016/j.envpol.2008.09.037 Get rights and content

Abstract

The speciation of heavy metals was measured over a variety of natural and undisturbed water/sediment interfaces. Simultaneously, two benthic species (oligochaete Limnodrilus spp. and the midge Chironomus riparius) were exposed to these sediments. Under occurring redox conditions, free ion activities of trace metals Cd, Cu, Ni, Pb, and Zn were measured with a chelating exchange technique, while geochemical conditions (i.e., redox) remained in tact. Free ion activities were compared with total dissolved concentrations in pore waters and surface waters in order to relate speciation to bioaccumulation. Limnodrilus spp. and C. riparius have accumulation patterns that could be linked to time-dependent exposure concentrations, expressed as chemical speciation, in the surface water and the sediment's pore water. Concentrations of free metal ions in the overlying surface water, rather than in sediment pore water, proved to be the best predictor for uptake. For the first time, measurements are obtained from sediments without disturbing physical–chemical conditions and thus bioavailability, a major restriction of other studies so far.

Introduction

The assessment of ecological risks of heavy metals in the aquatic environment is historically linked to generic quality standards, based on total contents in sediment. It is not widely known however that the quality standards for sediments are basically derived from aquatic tests, converting LC5-values via equilibrium partitioning to solid phase. The European Water Framework Directive (WFD) now aims at assessing risks of pollutants in the water phase by allowing chemical or bioavailability to be taken into account.

The general concept of (bio)availability of metals becomes clear when body concentrations of field-collected organisms are compared to those from laboratory exposure tests using disturbed and oxygenated sediments or waters. Concentrations of organic and inorganic compounds differ significantly, both in the close environment as in the organism itself (Vink et al., 2005, Simpson and Batley, 2007). This phenomenon is explained by chemical speciation, which originates from the lability of metal species. The most labile form is the freely dissolved ion, M²⁺, followed by dissolved inorganic metal–ion pairs (e.g., M–OH⁺, M–Cl⁺, M–CO₃) and organic forms (M–DOM).

This concept of lability, however, has in recent years been more often theorized than actually shown by empirical data. This is mainly due to the fact that only few techniques have become available that actually measure free ion activities, let alone that these techniques are able to measure free ions repeatedly during exposure of organisms. The concept of the free ion activity model (FIAM), which is incorporated in biotic ligand models (BLM), assumes that the free aqueous metal ion concentration, rather than the total dissolved or sediment concentration, largely determines the toxicological or biological effect which is observed in organisms that are exposed to water or sediment containing heavy metals. Although there appear to be exceptions, many studies have demonstrated that a large variety of benthic taxa accumulate their metals from the water phase, sometimes even exclusively (e.g., Munger and Hare, 1997, Warren et al., 1998, Hare et al., 2001, Buchwalter and Luoma, 2005, Ciutat et al., 2005). Therefore, this study aims to test the hypothesis whether uptake can be predicted from speciation in the water phase.

In a critical review, Campbell (1995) concluded that studies that are suitable for testing the FIAM concept in the presence of natural dissolved organic matter (DOM) are extremely scarce. There are numerous studies that report on the effects of DOM on metal bioavailability, but virtually all of these are qualitative in nature (speciation is under defined). Campbell (1995) concluded that “future progress would be greatly aided by the development of methods capable of measuring the free ion concentration of metals in the presence of DOM”. Although some excellent quantitative studies have been carried out in recent years (e.g., Davison and Zhang, 1994, Campbell, 1995, Buchwalter and Luoma, 2005, Ciutat et al., 2005, Kola and Wilkinson, 2005, Luoma and Rainbow, 2005, DeSchamphelaere and Janssen, 2006, Veltman et al., in press), the results are not always in agreement.

Recently, a technique was introduced that largely overcomes the difficulties described above. This technique was introduced as Sediment Or Fauna Incubation Experiment, SOFIE in short (Vink, 2002). With this technique it is possible to quantify free metal ions, in pore water, at low-oxygen and reduced conditions, repeatedly, and in a non-destructive manner to the sample. Bioassays are conducted simultaneously in the same setting. Sediment samples are obtained in an undisturbed manner, including the overlying surface water.

This paper deals with the gradients and speciation of metal species, among which free ion activities, over natural water/sediment interfaces. The WFD-hypothesis is tested whether bioaccumulation can be predicted from the aqueous phase, taken into account the site-specific speciation. Six distinctly different river systems were sampled. The effect of metal uptake by sediment-dwelling organisms on metal speciation, and vice versa, is discussed.

Section snippets

Materials

This study was performed with a novel experimental technique (EU-patent nos. 1018200/02077121.8, October 2001, J. Vink, Rijkswaterstaat), which was introduced as Sediment Or Fauna Incubation Experiment, or SOFIE^® (Vink, 2002). In short, this “cell” consists of a core, 190 mm radius, 200 mm height, which is used as a sampling device to obtain undisturbed sediment, including the overlying surface water. After sampling, this water/sediment system becomes part of the cell. Pore water probes,

Results and discussion

Table 1 shows the solid phase characteristics of the six sites. The undisturbed (steady state) concentrations in pore water and overlying surface water are shown in Fig. 2.

Typically, steep redox gradients occur over the water/sediment interface, more or less pronounced for the various sites. Redox-sensitive compounds follow these gradients: denitrification precedes sulfate reduction, and anaerobic conditions were reached in most cases within 20 mm from the water/sediment interface. The

Acknowledgements

Parts of this work was funded by the European Commission's AquaTerra program, contract GOCE-CT-2003-505428. The following persons are gratefully thanked for their contribution: Hobbe Pijpker (Pijpker Laboratory Techniques), Kees Miermans (RIVM), Sylvia Dhondt (EPZ), Martina Vijver (CML), Jan Hendriks (RUN), Serge Rotteveel, Ria Kamps (Rijkswaterstaat).

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The origin of speciation: Trace metal kinetics over natural water/sediment interfaces and the consequences for bioaccumulation

Abstract

Introduction

Section snippets

Materials

Results and discussion

Acknowledgements

Aquat. Toxicol.

Ecotox. Environ. Saf.

Ecotox. Environ. Saf.

Aquat. Toxicol.

Comp. Biochem. Physiol. C

Environ. Poll.

Metal speciation. Effects on aquatic toxicity

Environ. Sci. Technol.

Differences in dissolved cadmium and zinc uptake among stream insects: mechanistic explanations

Environ. Sci. Technol.

Interactions between trace metals and aquatic organisms: a critique of the free-ion activity model

Assessing sediment contamination in estuaries

Environ. Toxicol. Chem.

In-situ speciation measurements of trace components in natural waters using thin-film gels

Nature

Copper toxicity to Paratya australiensis III: influence of dissolved organic matter

Environ. Toxicol. Chem.

A biotic ligand model predicting acute toxicity for Daphnia magna; the effects of calcium, magnesium, sodium, potassium, and pH

Environ. Sci. Technol.

Bioavailability models for predicting copper toxicity to freshwater green microalgae as a function of water chemistry

Environ. Sci. Technol.

Antimony and arsenic species in sediment pore water tested with the sediment or fauna incubation experiment

Environ. Sci. Technol.