Elsevier

Environmental Pollution

Volume 252, Part A, September 2019, Pages 616-626
Environmental Pollution

Mitigative effects of natural and model dissolved organic matter with different functionalities on the toxicity of methylmercury in embryonic zebrafish

https://doi.org/10.1016/j.envpol.2019.05.155Get rights and content

Highlights

  • Role of DOM composition in mitigating MeHg toxicity in zebrafish was examined.

  • DOMs with different DOC concentrations or functionalities mitigate MeHg toxicity to a different extent.

  • Aromatic thiols are the most effective mitigators in the toxicity of MeHg.

  • Humic-like DOMs mitigate MeHg toxicity more effectively than protein-like DOMs.

Abstract

Dissolved organic matter (DOM) occurs ubiquitously in aquatic environments and plays an intrinsic role in altering the chemical speciation and toxicity of methylmercury (MeHg). However, interactions between MeHg and natural DOM remain poorly understood, especially at the functional group level. We report here the mitigative effects of three natural organic matter (NOM) and five model-DOM under different concentrations (0, 1, 3, 10, 30 and 100 mg-C/L) on the toxicity of MeHg in embryonic zebrafish (<4 h post-fertilization, hpf). NOM are those from the Mississippi River, Yukon River, and Suwannee River, while model-DOM include those containing thiosalicylic acid, L-glutathione, dextran, alginic acid, and humic acid. We selected a MeHg concentration (100 n-mol/L) that reduces the survival rate of embryos at 24 hpf by 18% and increases malformations at 72 and 96 hpf. In the presence of DOM, however, the malformation rates induced by MeHg can be mitigated to a different extent depending on DOM concentrations, specific functional groups, and/or specific components. Model DOM with aromatic thiols was the most effective at mitigating the effects of MeHg, followed by L-glutathione, carbohydrates, and humic acid. NOM also mitigated the toxicity of MeHg dependent on their composition and/or effective DOM components as characterized by fluorescence excitation-emission matrix techniques. Specifically, humic-like DOM components are more effective in reducing the MeHg toxicity in the embryonic zebrafish compared to protein-like components. Further studies are needed to elucidate the interactions between DOM and MeHg and the mitigative mechanisms at the molecular level.

Introduction

Metals such as mercury (Hg) released into the environment from natural processes and anthropogenic activities pose potential threats to aquatic ecosystems (Mason et al., 1994; Risch et al., 2012). The global inventory of Hg emissions to the air from anthropogenic sources reached 2.5 ± 0.5 kiloton/y in 2018 (Outridge et al., 2018). After deposition into aquatic ecosystems, Hg can be converted into methylmercury (MeHg) through biological and environmental processes (Klapstein and O'Driscoll, 2018; Mora-Zamorano et al., 2016; Risch et al., 2012). Methylmercury is regarded as the most toxic and bioaccumulative form of Hg in aquatic environments and is of great environmental concern (Batchelar et al., 2013; Burgess and Meyer, 2008; Mergler et al., 2016).

MeHg makes up about 13–15% of the total water-borne Hg found in many freshwater systems in North America, and the concentrations ranged from 0.01 to 3.12 ng/L (Dennis et al., 2005). Fish are primarily exposed to MeHg through diet (Zhang et al., 2010). An exception to this is embryonic fish that are not feeding, and thus are mainly exposed to MeHg through water or from maternal sources. Embryonic and larval fish are more sensitive to MeHg than adult life stages. MeHg is readily taken up by aquatic organisms because of its ability to pass through cell membranes, and is subsequently transferred to higher trophic levels (Lee and Fisher, 2017; Samson and Shenker, 2000). Due to the strong affinity for sulfur, the ingested Hg can interact with proteins and enzymes, causing organ dysfunction and malformation at elevated concentrations (Cuello et al., 2012). Many studies have reported that embryonic exposure to MeHg causes a variety of teratogenic effects. Exposure of zebrafish embryos at concentrations between 80 and 120 nmol/L of MeHg leads to deformed axis, impaired development of fin fold (Samson and Shenker, 2000). In addition, cyclopia, tail flexures, and cardiac malformations in medaka and mummichog are induced by 260 nmol/L MeHg (Dial, 1978; Weis and Weis, 1977).

Previous studies have shown that the chemical speciation, bioavailability, and toxicity of MeHg can be affected by natural organic matter (NOM) in aquatic environments (Hill et al., 2009; Lawrence and Mason, 2001; Schartup et al., 2015). Dissolved organic matter (DOM) is a heterogeneous mixture of different compound-classes and molecular size-fractions, and can vary in composition, and reactivity (Aiken et al., 2011; Benner and Amon, 2015; Weishaar et al., 2003; Xu and Guo, 2017). Environmentally relevant concentration of DOM varies from <0.5 to up to 60 mg-C/L (e.g., Hansell and Carlson, 1998; Spencer et al., 2012; Stolpe et al., 2013). DOM has been shown to influence the solubility and chemical speciation of metals and the surface properties and toxicity of engineered nanoparticles (Baalousha et al., 2018; Guo et al., 2001; Kteeba et al., 2017; Philippe and Schaumann, 2014). DOM can influence the specific abundance and speciation of Hg in aquatic ecosystems along with changes in water chemistry and solar irradiation (Jeremiason et al., 2015; Klapstein and O'Driscoll, 2018). The interactions between MeHg and NOM have been investigated, and the Hg-DOM formation constants range from 1021 to 1040 at environmentally relevant concentrations for Hg and DOM (Dong et al., 2010; Miller et al., 2012). MeHg in biota has also been positively correlated to the amount of autochthonous DOM and reduced humic-like matter (Lescord et al., 2018).

A few studies have reported the formation of MeHg-GSH in cells either non-enzymatically or by enzymatic action (via glutathione S-transferase), which is excreted into the extracellular space in cultured human and mouse cells (Toyama et al., 2007). Lee and Fisher (2017) reported that DOM with thiol-containing compounds reduce the MeHg uptake by phytoplankton, and Ndu et al. found that humic acids reduce the bioavailability in the Escherichia coli (Ndu et al., 2012). However, the specific roles of DOM quantity and functional groups in regulating or mitigating the toxicity of MeHg in fish remain poorly understood, and the effect of natural DOM with different functionalities on the toxicity of MeHg in embryonic zebrafish has rarely been explored.

The main objective of this study was to elucidate the mitigative effect of natural and model DOM on the toxicity of MeHg in embryonic zebrafish under different dissolved organic carbon (DOC) concentrations and different functionalities, including thiolate aromatic, thiol peptide, carbohydrates (oligosaccharide and polysaccharide), humic acids, and different natural DOM components characterized by fluorescence excitation emission matrices (EEMs)-PARAFAC coupling techniques. Our results on the role of different DOM functional groups and different NOM components in regulating the mortality and teratogenic effects in embryonic zebrafish should provide a deeper understanding of the interactions of DOM with MeHg and their influence on environmental impact.

Section snippets

Chemicals

Methylmercury (MeHg) chloride (CH3ClHg, CAS# 115-09-3, Sigma-Aldrich) was used as the source of MeHg in this study. The stock solution of MeHg (3 mmol-Hg/L in ethanol) was prepared and stored at −20 °C. Five model DOM samples with different functionalities and three different NOM samples isolated from various rivers were used in the experiments to elucidate the role of DOM quantity and quality in mitigating MeHg toxicity. Model DOM included 1) thiosalicylic acid (TA, containing aromatic thiol),

Characterization of bulk DOM

Contents of total organic carbon (TOC %) in initial powder DOM samples and zeta potential and optical properties are listed in Table 1. The optical properties include CDOM (in terms of a254 (m−1)), fluorescence indices, and major fluorescent DOM components derived from EEMs-PARAFAC analysis. TOC content was the highest in thiosalicylic acid compared with other DOM samples, consistent with their difference in formula. For the NOM samples, the TOC content in the SNOM was up to 53.7%, considerably

Discussion

In aquatic environments, DOM can form complexes with MeHg (Schartup et al., 2015). The interactions of MeHg with different organic functional groups within the bulk DOM pool may alter the chemical speciation of Hg and the toxicity of MeHg to aquatic organisms (Hintelmann et al., 1997; Toyama et al., 2011). Our results show that DOM with thiols, especially aromatic thiols, can effectively mitigate the effect of MeHg in zebrafish eleutheroembryos. This is at least partly due to the fact that

Conclusions

The mitigative effects of three NOM samples and five model DOM samples on the toxicity of MeHg in embryonic zebrafish were examined to elucidate the role of different organic functionalities and DOM components. Overall, the results indicated that each DOM under a certain DOC concentration can effectively mitigate the deformation of zebrafish eleutheroembryos induced by MeHg. Among all model DOM, the thiol aromatic group was the most effective organic compound. In terms of fluorescent DOM

Acknowledgements

We gratefully acknowledge Hui Lin for his assistance in the DOM analysis, Rebekah Klinger and Gayle Metch for their technical assistance in zebrafish husbandry and incubation experiments, and Pat Anderson for the measurements of mercury concentration. We thank the associate editor and two anonymous reviewers for their constructive comments and valuable suggestions, which greatly improved the manuscript. This work was supported in part by the University of Wisconsin-Milwaukee Research Growth

References (67)

  • C.S. Lee et al.

    Bioaccumulation of methylmercury in a marine diatom and the influence of dissolved organic matter

    Mar. Chem.

    (2017)
  • R. Mason et al.

    The biogeochemical cycling of elemental mercury: anthropogenic influences

    Geochem. Cosmochim. Acta

    (1994)
  • P.K. Pullela et al.

    Fluorescence-based detection of thiols in vitro and in vivo using dithiol probes

    Anal. Biochem.

    (2006)
  • M.R. Risch et al.

    Spatial patterns and temporal trends in mercury concentrations, precipitation depths, and mercury wet deposition in the North American Great Lakes region, 2002-2008

    Environ. Pollut.

    (2012)
  • J.C. Samson et al.

    The teratogenic effects of methylmercury on early development of the zebrafish , Danio rerio

    Aquat. Toxicol.

    (2000)
  • S. Singh et al.

    Chromophoric dissolved organic matter (CDOM) variability in Barataria Basin using excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC)

    Sci. Total Environ.

    (2010)
  • C.A. Stedmon et al.

    Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy

    Mar. Chem.

    (2003)
  • B. Stolpe et al.

    Abundance, size distributions and trace-element binding of organic and iron-rich nanocolloids in Alaskan rivers, as revealed by field-flow fractionation and ICP-MS

    Geochem. Cosmochim. Acta

    (2013)
  • T. Toyama et al.

    Cytoprotective role of Nrf2/Keap1 system in methylmercury toxicity

    Biochem. Biophys. Res. Commun.

    (2007)
  • H. Xu et al.

    Molecular size-dependent abundance and composition of dissolved organic matter in river, lake and sea waters

    Water Res.

    (2017)
  • H. Xu et al.

    Intriguing changes in molecular size and composition of dissolved organic matter induced by microbial degradation and self-assembly

    Water Res.

    (2018)
  • Z. Zhou et al.

    Characterization of bulk and chromophoric dissolved organic matter in the Laurentian Great Lakes during summer 2013

    J. Great Lakes Res.

    (2016)
  • A. Zsolnay et al.

    Differentiating with fluorescence spectroscopy the sources of dissolved organic matter in soils subjected to drying

    Chemosphere

    (1999)
  • G.R. Aiken et al.

    Influence of dissolved organic matter on the environmental fate of metals, nanoparticles, and colloids

    Environ. Sci. Technol.

    (2011)
  • M.-A. Akimenko et al.

    Differential induction of four msx homeobox genes during fin development and regeneration in zebrafish

    Development

    (1995)
  • H. Alkaissi et al.

    Genome-wide association study to identify genes related to renal mercury concentrations in mice

    Environ. Health Perspect.

    (2016)
  • A. Amirbahman et al.

    Association of methylmercury with dissolved humic acids

    Environ. Sci. Technol.

    (2002)
  • M. Baalousha et al.

    Natural organic matter composition determines the molecular nature of silver nanomaterial-NOM corona

    Environ. Sci. Nano.

    (2018)
  • K.L. Batchelar et al.

    Evidence of impaired health in yellow perch (Perca flavescens) from a biological mercury hotspot in northeastern north America

    Environ. Toxicol. Chem.

    (2013)
  • R. Benner et al.

    The size-reactivity continuum of major bioelements in the ocean

    Ann. Rev. Mar. Sci.

    (2015)
  • N.M. Burgess et al.

    Methylmercury exposure associated with reduced productivity in common loons

    Ecotoxicology

    (2008)
  • M.J. Carvan et al.

    Mercury-induced epigenetic transgenerational inheritance of abnormal neurobehavior is correlated with sperm epimutations in zebrafish

    PLoS One

    (2017)
  • H. Chen et al.

    Identification of mercury and dissolved organic matter complexes using ultrahigh resolution mass spectrometry

    Environ. Sci. Technol. Lett.

    (2017)
  • Cited by (14)

    • The concentration of dissolved organic matter impacts the neurobehavior in female zebrafish exposed to cyclophosphamide

      2024, Comparative Biochemistry and Physiology Part - C: Toxicology and Pharmacology
    • New insights into the role of marine plastic-gels in microplastic transfer from water to the atmosphere via bubble bursting

      2022, Water Research
      Citation Excerpt :

      The organic carbon concentrations of 1 and 10 ppm of alginic acid sodium salts were 0.18 ± 0.04 and 2.17 ± 0.06 mg-C/L, respectively. The addition of alginic acid sodium salts in this experiments is within the organic carbon range expected in the natural environment (Cao et al., 2018; Li et al., 2019a; Shiu et al., 2017). The range of pH value in the all experiments was 5.72-5.96.

    • Dissolved organic matter (DOM) was detected in MSWI plant: An investigation of DOM and potential toxic elements variation in the bottom ash and fly ash

      2022, Science of the Total Environment
      Citation Excerpt :

      At some landfills, especially poorly managed ones, organic matters are degraded, and leachate containing organic matters and synthetic chemicals in the form of DOM are generated (Baghanam et al., 2020; Ma et al., 2021). Moreover, previous studies found that the toxicity and mobility of PTEs are closely related to their interactions with DOM (Abdelrady et al., 2020; D. Li et al., 2019). DOM can interact with PTEs through multiple mechanisms (e.g., adsorption, redox reactions, complexation) (Deonarine et al., 2021).

    View all citing articles on Scopus

    This paper has been recommended for acceptance by Dr. Sarah Harmon.

    View full text