Submitted in part candidature for an Msc in Environmental Techniques in Earth System Science'

1
The speciation of solute and sediment-bound
metals in the mining affected Tisa drainage
basin, Eastern Europe.
Graham Bird (gbb97_at_aber.ac.uk) Institute of
Geography and Earth Sciences, University of Wales
Aberystwyth, Aberystwyth, Ceredigion, SY23 3DB
Sampling and Analytical methodologies Surface
waters and channel sediments were sampled at 34
sites along the study reach. Samples 1-17 were
collected by Macklin et al. (in press) during
2000, samples 18-34 were collected by the author
during July 2001. Water samples were filtered
through 0.45mm membranes, acidified with HNO3 and
analysed for Al, As, Cd, Cu, Hg, Ni, Pb and Zn
using ICP-MS. Field measurements of EC and pH
were made (Eh was also measured on the Tisa and
Cris rivers) at the time of sampling. Given the
limitations of Pt electrodes used in Eh meters,
values of Eh were calibrated using the Fe2/Fe3
redox pair An Eh/pH stability diagram was
constructed for As species. Channel sediments
were collected using a stainless steel trowel,
air-dried and sieved to lt63mm. A four-stage SEP
adapted from Tessier et al. (1979) was used to
identify partitioning analogous to 1)
bioavailable 2) Fe/Mn oxide 3) organic
matter/sulphides and 4) residual phases.
Reference materials and blind duplicates were
also included. All supernatants were analysed
for As, Cd, Cu, Ni, Pb and Zn using ICP-MS.
Introduction The speciation of metals in the
environment is of primary importance to their
toxicity and mobility, perhaps more so than total
concentrations. The need to determine the
speciation of metals in mining affected fluvial
catchments is particularly important where human
interaction with the riverine environment is
widespread. Solute speciation is governed by the
Eh and pH of the aqueous environment. In
sediments, metals will be partitioned amongst
various organic and inorganic phases of the
sediment with differing adsorption strengths.
The nature solute speciation and sediment-metal
partitioning will affect the environmental
significance of metals in the environment.
Figure 1 A map showing the sample sites used by
this study.
The study area Thirty-four samples were were
taken along a 828 km trans-boundary study reach
comprising the rivers Lapus, Somes, Tisa and
Cris. The rivers Lapus and Somes flow through
Maramures County in northwest Romania, a region
that is extensively mined for base and precious
metals. The Baiut mine is situated at the top of
the study reach, the River Lapus is also fed by
the Rivers Cavnic and Sasar, which drain actively
mined land. The River Tisa is dammed between
sites 22 and 23.

• Study aims
• To investigate patterns in metal distribution and
  metal speciation within the study reach through
  the use of Eh/pH diagrams and a sequential
  extraction procedure (SEP).
• To assess the environmental significance of
  metals of metalliferous pollution within the
  reach and evaluate the importance of
  trans-boundary metal movement.
• The application of a heavy metal pollution index
  (HPI) to metal concentrations in surface waters.

Plate 1 Filtering a surface water sample
Plate 2 Collecting channel sediment
Solute metal concentrations Metal concentrations
in the Lapus and Somes rivers peak downstream of
the Baiut mine at sites 1 and 2 and are above EU
Maximum Admissible Concentrations (EU MAC).
Concentrations reduce downstream of the mine as
water pH increases (r2 0.8) but peak again
downstream of the River Sasar confluence. In the
rivers Tisa and Cris concentrations of all
metals, except Hg, are below EU MAC and Guide
limits and generally below global averages.
Table 1 Descriptive statistics of solute metal
concentrations Figure 2 indicates
downstream patterns of Cd and Hg along the study
profile. Cd patterns are typical of Al, As, Cu,
Ni, Pb and Zn patterns in the study
reach.
Solute metal speciation in the rivers Tisa and
Cris The rivers Tisa and Cris have a
geochemically stable surface water environment
(pH range 7.4 8.4, Eh range 0.18V 0.21V).
This has resulted in a spatially stable pattern
of speciation for As, Cd, Cu, Hg, Ni, Pb and Zn
as can be seen in Figure 4 in relation to As.
Calibrated and uncalibrated Eh/pH relationships
generally exhibit similar stability predictions.
Potential problems related to toxicity
and mobility of metals are mitigated by the low
concentrations present in the rivers Tisa and
Cris. Hg provides a relevant example of the
implications of different species predictions
made by calibrated and uncalibrated Eh
relationships (Figure 5). Predictions made using
the uncalibrated relationship suggest that Hg
will be present as Hg2 ions with SO42- anions
compared to the HgO compound predicted using
calibrated Eh. Free Hg ions will be more
susceptible to conversion to highly toxic
organo-mercurials.
Sediment-bound metal partitioning Percentage
recoveries of summed metal concentrations in each
phase versus phase four (Aqua-Regia soluble)
repeats suggest a good experimental and
analytical performance. Mean recovery was 93
percent, with the negative discrepancy a likely
result of slight dilution effects during the use
of the SEP. Partitioning patterns were spatially
stable particularly along the River Tisa as
indicated by Cd in Figure 6, the figure also
indicates the importance of organic
matter/sulphides near to the Baiut mine
(six-metal mean partitioning of
96). Table 2 shows the dominant phase
to which each metal was partitioned in along the
Romanian and Hungarian sections of the study
reach. To remove the skewing effect site 1 was
omitted from mean calculations. Cd and Zn are
strongly associated with the bioavailable, the
similar partitioning patterns of these two metals
is unsurprising given their close geochemical
association. Table 2 Dominant partitioning of
metals Figure 7 indicates that at sites
where sediment-metal concentrations of As, Cd and
Zn exceed New Dutch List action values the
environmental significance of Cd and Zn is
generally much greater due to dominant
partitioning in the bioavailable
fraction.
Figure 4 Stability of As species predicted using
Eh and pH.
Al As Cd Cu Hg Ni
Pb Zn Lapus/Somes Mean 152 11.7
13.3 172 0.8 48.9
36.7 2169 Range 390-884
1.3-124 0.0-143 1.6-2118 nd-1.5
6.7-448 4.6-389 12.9-17611 Tisa/Cris Mean
9.4 2.4 0.1
1.9 4.8 1.2 0.8
5.4 Range 2.1-75 1.5-3.9
nd-0.6 0.5-3.5 0.4-26.6 0.6-1.9
nd-2.8 nd-52
Calibrated Eh Uncalibrated Eh
Cris
Tisa
Tisa
Lapus
Somes
Figure 5 Partitioning of Cd within channel
sediments.
Figure 5 Stability of Hg species predicted using
Eh and pH
No data point concentration is non-detectable
Rivers Lapus and Somes Rivers Tisa and
Cris As Residual (65.8)
Residual (79.1) Cd Bioavailable
(72.1) Bioavailable (73.9) Cu
Fe/Mn oxides (31.1) Residual
(40.3) Ni Residual (42.1)
Residual (54) Pb Fe/Mn oxides
(77.9) Fe/Mn oxides
(65.4) Zn Bioavailable (51.1)
Fe/Mn oxides (37.7)
Calibrated Eh Uncalibrated Eh
Figure 2 Cd and Hg concentrations in surface
waters.
Heavy Metal Pollution Index (HPI) The index was
developed by Mohan et al. (1996) for the
assessment of groundwater pollution. The HPI is
a arithmetic mean quality method based upon a
composite of measured concentrations for a number
of metals versus water quality guidelines (EC
80/778/EEC). Figure 3 highlights HPI values
calculated at each site, values exceeding 100
indicate water is unfit for human consumption.
Removal of Hg from the HPI reduces all
coefficients for the rivers Tisa and Cris to
lt10.

• Conclusions
• Water and sediment geochemistry on the River
  Lapus are influenced by the Baiut mine, however
  with increasing distance downstream the influence
  of local point sources and background
  geochemistry increase.
• The HPI can be seen to be a highly useful
  quantitative approach to assessing water quality
  and suggests water especially in the River Tisa
  should not be used for human consumption.
• The influence of speciation upon toxicity and
  mobility of solute metals in the River Tisa is
  mitigated by low concentrations and alkaline pH.
  Hg is more problematic due to potential for
  conversion to organo-mercurials.
• Partitioning of sediment-bound metals is
  spatially stable, especially in the River Tisa.
  The Baiut mine exerts an influence in the upper
  Lapus with metals bound to the sulphide phase.
• Cd and Zn are environmentally significant due
  to association with the bioavailable phase,
  especially a pollution hot-spots in the Lapus and
  Somes. As is environmentally insignificant due
  to its dominant association with the residual
  phase.

As
Cd
Zn
Bioavailable Fe/Mn oxides
Organic/sulphides Residual

• References
• Mohan S. V., Nithila P., and Reddy S. J. (1996)
  Estimation of heavy metals in drinking water
  and development of heavy metal pollution index.
  Journal of Environmental Science and Health (A31)
  pp283-289
• Tessier A., Campbell P. G. C. and Bisson M.
  (1979) Sequential extraction procedure for the
  speciation of trace metals. Analytical
  Chemistry (51) pp844-851.

Lapus
Tisa
Somes
Cris
Figure 3 Calculated HPI values for individual
sample sites.
Figure 7 Partitioning of As, Cd and Zn at
pollution hot-spots.
Submitted in part candidature for an Msc in
Environmental Techniques in Earth System
Science. 1st October 2001