Register      Login
Environmental Chemistry Environmental Chemistry Society
Environmental problems - Chemical approaches
RESEARCH ARTICLE (Open Access)

Metal speciation from stream to open ocean: modelling v. measurement

Edward Tipping A C , Stephen Lofts A and Anthony Stockdale B
+ Author Affiliations
- Author Affiliations

A Centre for Ecology and Hydrology, Lancaster Environment Centre, Lancaster, LA1 4AP, UK.

B School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

C Corresponding author. Email: et@ceh.ac.uk

Environmental Chemistry 13(3) 464-477 https://doi.org/10.1071/EN15111
Submitted: 30 May 2015  Accepted: 16 July 2015   Published: 6 October 2015

Journal Compilation © CSIRO Publishing 2016 Open Access CC BY-NC-ND

Environmental context. The chemical speciation of metals strongly influences their transport, fate and bioavailability in natural waters. Analytical measurement and modelling both play important roles in understanding speciation, while modelling is also needed for prediction. Here, we analyse a large set of data for fresh waters, estuarine and coastal waters, and open ocean water, to examine how well measurements and modelling predictions agree.

Abstract. We compiled a data set of ~2000 published metal speciation measurements made on samples of fresh waters, estuarine and coastal waters, and open ocean waters. For each sample, we applied the chemical speciation model WHAM7 to calculate the equilibrium free metal ion concentrations, [M] (mol L–1), amounts of metal bound by dissolved organic matter (DOM), ν (mol g–1), and their ratio ν/[M] (L g–1), which is a kind of ‘local’ partition coefficient. Comparison of the measured and predicted speciation variables for the whole data set showed that agreements are best for fresh waters, followed by estuarine and coastal waters, then open-ocean waters. Predicted values of ν/[M], averaged over all results for each metal, closely follow the trend in average measured values, confirming that metal reactivity, and consequent complexation by DOM, in natural waters accord with the expectations of the speciation model. Comparison of model predictions with measurements by different analytical techniques suggests that competitive ligand–stripping voltammetry methods overestimate metal complexation by DOM, and therefore underestimate [M]. When measurements by other methods are compared with predictions, for all metals, reasonable agreement with little bias is obtained at values of ν > 10–6 mol g–1 DOM, but at lower values of ν, the model predictions of [M] are mostly higher than the measured values, and the predictions of ν and ν/[M] are mostly lower. Research is needed to establish whether this reflects analytical error or the failure of the model to represent natural high-affinity ligands.


References

[1]  T. M. Florence, G. E. Batley, P. Benes, Chemical speciation in natural waters. Crit. Rev. Anal. Chem. 1980, 9, 219.
Chemical speciation in natural waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL3MXht1Kru7o%3D&md5=5452e43dc17f2c18ce4fc25b92aa3503CAS |

[2]  P. G. C. Campbell, Interactions between trace elements and aquatic organisms: a critique of the free-ion activity model, in Metal Speciation and Bioavailability in Aquatic Systems (Eds A. Tessier and D.R. Turner) 1995, pp. 45–102 (Wiley: Chichester, UK).

[3]  J. E. Groenenberg, S. Lofts, The use of assemblage models to describe trace element partitioning, speciation, and fate: a review. Environ. Toxicol. Chem. 2014, 33, 2181.
The use of assemblage models to describe trace element partitioning, speciation, and fate: a review.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhsFKntrjP&md5=bb6ec4022067a322f9aeaa68b4a7ab10CAS | 24862928PubMed |

[4]  P. G. C. Campbell, P. M. Stokes, Acidification and toxicity of metals to aquatic biota. Can. J. Fish. Aquat. Sci. 1985, 42, 2034.
Acidification and toxicity of metals to aquatic biota.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL28Xotlelsw%3D%3D&md5=1f26c9c0ccd7d9e9a5f2431062a299cfCAS |

[5]  M. Gledhill, E. P. Achterberg, K. Li, K. N. Mohamed, M. J. A. Rijkenberg, Influence of ocean acidification on the complexation of iron and copper by organic ligands in estuarine waters. Mar. Chem. 2015,
Influence of ocean acidification on the complexation of iron and copper by organic ligands in estuarine waters.Crossref | GoogleScholarGoogle Scholar |

[6]  F. J. Millero, R. Woosley, B. Ditrolio, J. Waters, Effect of ocean acidification on the speciation of metals in seawater. Oceanogr. 2009, 22, 72.
Effect of ocean acidification on the speciation of metals in seawater.Crossref | GoogleScholarGoogle Scholar |

[7]  M. Pesavento, G. Alberti, R. Biesuz, Analytical methods for determination of free metal ion concentration, labile species fraction and metal complexation capacity of environmental waters: a review. Anal. Chim. Acta 2009, 631, 129.
Analytical methods for determination of free metal ion concentration, labile species fraction and metal complexation capacity of environmental waters: a review.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhsFWis73L&md5=558d25cba093deffd9e9232673c8391cCAS | 19084618PubMed |

[8]  J. Buffle, G. Horvai, In Situ Monitoring of Aquatic Systems: Chemical Analysis and Speciation 2000 (Wiley: New York).

[9]  E. Tipping, Cation Binding by Humic Substances 2002 (Cambridge University Press: Cambridge, UK).

[10]  E. Tipping, WHAM – a chemical equilibrium model and computer code for waters, sediments and soils incorporating a discrete-site electrostatic model of ion-binding by humic substances. Comput. Geosci. 1994, 20, 973.
WHAM – a chemical equilibrium model and computer code for waters, sediments and soils incorporating a discrete-site electrostatic model of ion-binding by humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXhtlyhtrY%3D&md5=7ded37c9af50999f549148d9595f8de2CAS |

[11]  C. J. Milne, D. G. Kinniburgh, W. H. Van Riemsdijk, E. Tipping, Generic NICA–Donnan model parameters for metal-ion binding by humic substances. Environ. Sci. Technol. 2003, 37, 958.
Generic NICA–Donnan model parameters for metal-ion binding by humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXosVWgsQ%3D%3D&md5=2eda2310a7221ae42b73f399e3b9e8b5CAS | 12666927PubMed |

[12]  J. W. Guthrie, N. M. Hassan, M. S. A. Salam, I. I. Fasfous, C. A. Murimboh, J. Murimboh, C. L. Chakrabarti, D. C. Grégoire, Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal ion and labile complexes and a computer speciation model, WHAM V and VI. Anal. Chim. Acta 2005, 528, 205.
Complexation of Ni, Cu, Zn, and Cd by DOC in some metal-impacted freshwater lakes: a comparison of approaches using electrochemical determination of free-metal ion and labile complexes and a computer speciation model, WHAM V and VI.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXkslyhsg%3D%3D&md5=4f6eabd66f3094be1b10367828dc9a03CAS |

[13]  E. R. Unsworth, K. W. Warnken, H. Zhang, W. Davison, F. Black, J. Buffle, J. Cao, R. Cleven, J. Galceran, P. Gunkel, E. Kalis, D. Kistler, H. P. van Leeuwen, M. Martin, S. Noël, Y. Nur, N. Odzak, J. Puy, W. van Riemsdijk, L. Sigg, E. J. M. Temminghoff, M.-L. Tercier-Waeber, S. Topperwien, R. M. Town, L. Weng, H. B. Xue, Model predictions of metal speciation in freshwaters compared to measurements by in situ techniques. Environ. Sci. Technol. 2006, 40, 1942.
Model predictions of metal speciation in freshwaters compared to measurements by in situ techniques.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XhtlSku7o%3D&md5=317db11fd744633a6ba8cae2f0cd8eaeCAS | 16570619PubMed |

[14]  S. Lofts, E. Tipping, Assessing WHAM/Model VII against field measurements of free metal ion concentrations: model performance and the role of uncertainty in parameters and inputs. Environ. Chem. 2011, 8, 501.
Assessing WHAM/Model VII against field measurements of free metal ion concentrations: model performance and the role of uncertainty in parameters and inputs.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtlykt73J&md5=6d5203022a7c53649a5ef04da5785dcbCAS |

[15]  A. Stockdale, E. Tipping, S. Lofts, Dissolved trace metal speciation in estuarine and coastal waters: comparison of WHAM/Model VII predictions with analytical results. Environ. Toxicol. Chem. 2015, 34, 53.
Dissolved trace metal speciation in estuarine and coastal waters: comparison of WHAM/Model VII predictions with analytical results.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXitFaqtLfF&md5=57eef4367bc789fdb5ce2e81a0779c9fCAS | 25387688PubMed |

[16]  A. Stockdale, E. Tipping, J. Hamilton-Taylor, S. Lofts, Trace metals in the open oceans: speciation modelling based on humic-type ligands. Environ. Chem. 2011, 8, 304.
Trace metals in the open oceans: speciation modelling based on humic-type ligands.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXptVWrsbc%3D&md5=79d2c4570666578baa92db699bb728f0CAS |

[17]  E. Tipping, V. I. Humic Ion Binding Model, An improved description of the interactions of protons and metal ions with humic substances. Aquat. Geochem. 1998, 4, 3.
An improved description of the interactions of protons and metal ions with humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXntlSjuro%3D&md5=cf0c6c40511e5000b173c62e5266b947CAS |

[18]  E. Tipping, S. Lofts, J. E. Sonke, Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances. Environ. Chem. 2011, 8, 225.
Humic Ion-Binding Model VII: a revised parameterisation of cation-binding by humic substances.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXptVWrsL0%3D&md5=bda1097b974d554ee7c343f673c6e24bCAS |

[19]  C. T. Driscoll, A procedure for the fractionation of aqueous aluminium in dilute acid waters. Int. J. Environ. Anal. Chem. 1984, 16, 267.
A procedure for the fractionation of aqueous aluminium in dilute acid waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL2cXhvFOms78%3D&md5=425c8c68872e4b822a813f80c2a2ac1fCAS |

[20]  C. A. Backes, E. Tipping, An evaluation of the use of cation-exchange resin for the determination of organically complexed Al in natural acid waters. Int. J. Environ. Anal. Chem. 1987, 30, 135.
An evaluation of the use of cation-exchange resin for the determination of organically complexed Al in natural acid waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL2sXls1WhsLo%3D&md5=7278d545f50bf3a0af175d3b0e1cd380CAS |

[21]  G. Scarano, E. Bramanti, A. Zirino, Determination of copper complexation in seawater by a ligand competition technique with voltammetric measurement of the labile metal fraction. Anal. Chim. Acta 1992, 264, 153.
Determination of copper complexation in seawater by a ligand competition technique with voltammetric measurement of the labile metal fraction.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK38XltFyjtLw%3D&md5=2f117431becd1f65730bbc31b7c6a402CAS |

[22]  F. L. L. Muller, Interactions of copper, lead and cadmium with the dissolved, colloidal and particulate components of estuarine and coastal waters. Mar. Chem. 1996, 52, 245.
Interactions of copper, lead and cadmium with the dissolved, colloidal and particulate components of estuarine and coastal waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XjsFOntb8%3D&md5=f7484f59854ce2d0b41003cc5cad5b78CAS |

[23]  D. Tang, K. W. Warnken, P. H. Santschi, Organic complexation of copper in surface waters of Galveston Bay. Limnol. Oceanogr. 2001, 46, 321.
Organic complexation of copper in surface waters of Galveston Bay.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXjtVWgsLY%3D&md5=8e46e927edc5ba79861b98b3fa7a1eabCAS |

[24]  C. M. G. van den Berg, Evidence for organic complexation of iron in seawater. Mar. Chem. 1995, 50, 139.
Evidence for organic complexation of iron in seawater.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXotVaqu78%3D&md5=4101779cf873e2d3a2cbed4c5060f882CAS |

[25]  E. J. J. Kalis, L. Weng, F. Dousma, E. J. M. Temminghoff, W. H. Van Riemsdijk, Measuring free metal ion concentrations in situ in natural waters using the Donnan membrane technique. Environ. Sci. Technol. 2006, 40, 955.
Measuring free metal ion concentrations in situ in natural waters using the Donnan membrane technique.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtlars7rK&md5=05ff63516e243bb72f201b3e7303e1d9CAS |

[26]  K. H. Coale, K. W. Bruland, Copper complexation in the north-east Pacific. Limnol. Oceanogr. 1988, 33, 1084.
Copper complexation in the north-east Pacific.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1MXksVCluw%3D%3D&md5=7f7e91fb3bde3102334e068a20b07c56CAS |

[27]  C. Fortin, P. G. C. Campbell, An ion-exchange technique for free-metal ion measurements (Cd2+, Zn2+): applications to complex aqueous media. Int. J. Environ. Anal. Chem. 1998, 72, 173.
An ion-exchange technique for free-metal ion measurements (Cd2+, Zn2+): applications to complex aqueous media.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXis12gtLY%3D&md5=558cde496f597fdaaa6a6089bda8f0b1CAS |

[28]  C. Fortin, Y. Couillard, B. Vigneault, P. G. C. Campbell, Determination of free Cd, Cu and Zn concentrations in lake waters by in situ diffusion followed by column equilibration ion-exchange. Aquat. Geochem. 2010, 16, 151.
Determination of free Cd, Cu and Zn concentrations in lake waters by in situ diffusion followed by column equilibration ion-exchange.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhsFyjt7rN&md5=caf11fd6e783b47736715c86f6abf3e0CAS |

[29]  A. Zirino, D. A. Van der Weele, S. L. Belli, R. DeMarco, D. J. Mackey, Direct measurement of CuIIaq in seawater at pH 8 with the jalpaite ion-selective electrode. Mar. Chem. 1998, 61, 173.
Direct measurement of CuIIaq in seawater at pH 8 with the jalpaite ion-selective electrode.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXktVymsbY%3D&md5=f4943244e1870a69b224fdad712476e4CAS |

[30]  S. Bayen, K. J. Wilkinson, J. Buffle, The permeation liquid membrane as a sensor for free nickel in aqueous samples. Analyst 2007, 132, 262.
The permeation liquid membrane as a sensor for free nickel in aqueous samples.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXitVOksrk%3D&md5=d3264d33ab396acc4b2dbb2ff8640f3fCAS | 17325760PubMed |

[31]  N. Parthasarathy, M. Pelletier, J. Buffle, Hollow fiber-based supported liquid membrane: a novel analytical system for trace metal analysis. Anal. Chim. Acta 1997, 350, 183.
Hollow fiber-based supported liquid membrane: a novel analytical system for trace metal analysis.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXlsVWgt70%3D&md5=169593e37fcf08a45d0b1800c9bb30c1CAS |

[32]  W. Stumm, J. J. Morgan, Aquatic Chemistry, 3rd edn 1996 (Wiley: New York).

[33]  F. J. Millero, D. R. Schreiber, Use of the ion-pairing model to estimate activity coefficients of the ionic components of natural waters. Am. J. Sci. 1982, 282, 1508.
Use of the ion-pairing model to estimate activity coefficients of the ionic components of natural waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL3sXksVejsL4%3D&md5=e7b3be7c14a9ef6699082c3a085ffd5dCAS |

[34]  R. H. Byrne, L. R. Kump, K. J. Cantrell, The influence of temperature and pH on trace metal speciation in seawater. Mar. Chem. 1988, 25, 163.
The influence of temperature and pH on trace metal speciation in seawater.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1MXhtlWqtg%3D%3D&md5=60df343f250dfb55f0754f635a47f964CAS |

[35]  A. De Robertis, C. De Stefano, S. Sammartano, Equilibrium studies in natural fluids: a chemical speciation model for the major constituents of sea water. Chem. Spec. Bioavail. 1994, 6, 65.
| 1:CAS:528:DyaK2MXitVGjsr0%3D&md5=8d1272eb824ba8becb64e386d1ac5a78CAS |

[36]  S. E. Bryan, E. Tipping, J. Hamilton-Taylor, Comparison of measured and modelled copper binding by natural organic matter in freshwaters. Comp. Biochem. Physiol. C – Toxicol. Pharmacol. 2002, 133, 37.
Comparison of measured and modelled copper binding by natural organic matter in freshwaters.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD38nmsFGhtA%3D%3D&md5=2dd391377220c31e2717c75fd746375cCAS | 12356515PubMed |

[37]  E. Tipping, C. Woof, M. A. Hurley, Humic substances in acid surface waters – modeling aluminium binding, contribution to ionic charge-balance, and control of pH. Water Res. 1991, 25, 425.
Humic substances in acid surface waters – modeling aluminium binding, contribution to ionic charge-balance, and control of pH.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3MXitlClsr4%3D&md5=a65a05259716c28016b79eba2658bd29CAS |

[38]  S. Lofts, E. Tipping, J. Hamilton-Taylor, The chemical speciation of FeIII in freshwaters. Aquat. Geochem. 2008, 14, 337.
The chemical speciation of FeIII in freshwaters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXht12gtLzN&md5=0c5f0efcdcd768cd55fdcd8bfc9f6428CAS |

[39]  E. Tipping, C. Rey-Castro, S. E. Bryan, J. Hamilton-Taylor, AlIII and FeIII binding by humic substances in freshwaters, and implications for trace metal speciation. Geochim. Cosmochim. Acta 2002, 66, 3211.
AlIII and FeIII binding by humic substances in freshwaters, and implications for trace metal speciation.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38XmslKktbk%3D&md5=c0d4c88b8a3edd2164fe3daa206e62b7CAS |

[40]  M. Sillanpää, Environmental fate of EDTA and DTPA, in Reviews of Environmental Contamination and Toxicology (Ed. G. W. Ware) 1997, Vol. 152, pp. 85–111 (Springer: New York).

[41]  S. Baken, F. Degryse, L. Verheyen, R. Merckx, E. Smolders, Metal complexation properties of freshwater dissolved organic matter are explained by its aromaticity and by anthropogenic ligands. Environ. Sci. Technol. 2011, 45, 2584.
Metal complexation properties of freshwater dissolved organic matter are explained by its aromaticity and by anthropogenic ligands.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXjtFKqtbo%3D&md5=1a4ba87011f61693f0b98519fda2c0b6CAS | 21405071PubMed |

[42]  I. A. M. Ahmed, J. Hamilton-Taylor, M. Bieroza, H. Zhang, W. Davison, Improving and testing geochemical speciation predictions of metal ions in natural waters. Water Res. 2014, 67, 276.
Improving and testing geochemical speciation predictions of metal ions in natural waters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2cXhs1WqsLfO&md5=c9ad572487aedf514c6a3cd08f42a5d4CAS |

[43]  M. L. Wells, Marine colloids and trace metals, in Biogeochemistry of Marine Dissolved Organic Matter (Eds D. A. Hansell, C. A. Carlson) 2002, pp. 367–404 (Academic Press: London).

[44]  F. M. M. Morel, N. M. Price, The biogeochemical cycles of trace metals in the oceans. Science 2003, 300, 944.
The biogeochemical cycles of trace metals in the oceans.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXjsVyjsLk%3D&md5=c9e39d3fdfa28c650219e4b0f457a654CAS |

[45]  E. Tipping, Modelling the interactions of HgII and methylmercury with humic substances using WHAM/Model VI. Appl. Geochem. 2007, 22, 1624.
Modelling the interactions of HgII and methylmercury with humic substances using WHAM/Model VI.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXpt1yls7w%3D&md5=404de1eb1931c9b177c74f82425e165bCAS |

[46]  R. S. Eriksen, D. J. Mackey, R. van Dam, B. Nowak, Copper speciation and toxicity in Macquarie Harbour, Tasmania: an investigation using a copper ion-selective electrode. Mar. Chem. 2001, 74, 99.
Copper speciation and toxicity in Macquarie Harbour, Tasmania: an investigation using a copper ion-selective electrode.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXhvFWls7k%3D&md5=a5d05cc35c9b6981ee203af6517c8b82CAS |

[47]  H. P. van Leeuwen, R. M. Town, Kinetic limitations in measuring stabilities of metal complexes by competitive ligand exchange adsorptive stripping voltammetry (CLEAdSV). Environ. Sci. Technol. 2005, 39, 7217.
Kinetic limitations in measuring stabilities of metal complexes by competitive ligand exchange adsorptive stripping voltammetry (CLEAdSV).Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXns1aisLk%3D&md5=32716e96ac260ec7bd97e55bc9ce7c1cCAS | 16201651PubMed |

[48]  I. A. M. Ahmed, J. Hamilton–Taylor, S. Lofts, J. C. L. Meeussen, C. Lin, H. Zhang, W. Davison, Testing copper-speciation predictions in freshwaters over a wide range of metal–organic matter ratios. Environ. Sci. Technol. 2013, 47, 1487.
Testing copper-speciation predictions in freshwaters over a wide range of metal–organic matter ratios.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhslGhsw%3D%3D&md5=581330935373ead076e7eb0b0097e6b5CAS |

[49]  A. Stockdale, E. Tipping, S. Lofts, S. J. Ormerod, W. H. Clements, R. Blust, Toxicity of proton–metal mixtures in the field: linking stream macroinvertebrate species diversity to chemical speciation and bioavailability. Aquat. Toxicol. 2010, 100, 112.
Toxicity of proton–metal mixtures in the field: linking stream macroinvertebrate species diversity to chemical speciation and bioavailability.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXhtFGjurbM&md5=6a9579e1eca139935498e8aeee3d20feCAS | 20701986PubMed |

[50]  E. Tipping, C. D. Vincent, A. J. Lawlor, S. Lofts, Metal accumulation by stream bryophytes, related to chemical speciation. Environ. Pollut. 2008, 156, 936.
Metal accumulation by stream bryophytes, related to chemical speciation.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhsVSgtb3J&md5=50f02427f9ba4cb31d1e8d280e4874f1CAS | 18541353PubMed |

[51]  E. Tipping, S. Lofts, Metal mixture toxicity to aquatic biota in laboratory experiments: application of the WHAM-FTOX model. Aquat. Toxicol. 2013, 142–143, 114.
Metal mixture toxicity to aquatic biota in laboratory experiments: application of the WHAM-FTOX model.Crossref | GoogleScholarGoogle Scholar | 23994673PubMed |

[52]  E. Tipping, S. Lofts, Testing WHAM-FTOX with laboratory toxicity data for mixtures of metals (Cu, Zn, Cd, Ag, Pb). Environ. Toxicol. Chem. 2015, 34, 788.
Testing WHAM-FTOX with laboratory toxicity data for mixtures of metals (Cu, Zn, Cd, Ag, Pb).Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC2MXltFSksLs%3D&md5=a2856b734cc1fe90ff8cc8c60e923612CAS | 25318827PubMed |

[53]  L. Sigg, F. Black, J. Buffle, J. Cao, R. Cleven, W. Davison, J. Galceran, P. Gunkel, E. Kalis, D. Kistler, M. Martin, S. Noel, Y. Nur, N. Odzak, J. Puy, W. Van Riemsdijk, E. Temminghoff, M. L. Tercier-Weber, S. Toepperwien, R. M. Town, E. Unsworth, K. W. Warnken, L. P. Weng, H. B. Xue, H. Zhang, Comparison of analytical techniques for dynamic trace metal speciation in natural freshwaters. Environ. Sci. Technol. 2006, 40, 1934.
Comparison of analytical techniques for dynamic trace metal speciation in natural freshwaters.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xht1yhsLk%3D&md5=d5016d472512f001bdd15dec070ccd7aCAS | 16570618PubMed |

[54]  J. Feldmann, P. Salaün, E. Lombi, Critical review perspective: elemental speciation analysis methods in environmental chemistry – moving towards methodological integration. Environ. Chem. 2009, 6, 275.
Critical review perspective: elemental speciation analysis methods in environmental chemistry – moving towards methodological integration.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhsVSlurfK&md5=3fede31ae41e217f2c5bc5bb8cb355ddCAS |

[55]  A. M. Mota, J. P. Pinheiro, M. L. S. Goncalves, Electrochemical methods for speciation of trace elements in marine waters. Dynamic aspects. J. Phys. Chem. A 2012, 116, 6433.
Electrochemical methods for speciation of trace elements in marine waters. Dynamic aspects.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38Xmt1ektb0%3D&md5=38f02b3dfdbc2401db343e8312b8bdf4CAS | 22540875PubMed |