Chemical modeling of groundwater in the Banat Plain, southwestern
Romania, with elevated As content and co-occurring species by
combining diagrams and unsupervised multivariate statistical
approaches
Sinziana Butaciu
a
, Marin Senila
b
, Costel Sarbu
a
, Michaela Ponta
a
, Claudiu Tanaselia
b
,
Oana Cadar
b
, Marius Roman
b
, Emil Radu
c
, Mihaela Sima
d
, Tiberiu Frentiu
a, *
a
Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, Arany Janos 11, 400028, Cluj-Napoca, Romania
b
National Institute for Research and Development of Optoelectronics Bucharest, Research Institute for Analytical Instrumentation, Donath 67, 400293, Cluj-
Napoca, Romania
c
National Institute of Hydrology and Water Management, Bucuresti-Ploiesti 97, 013686, Bucharest, Romania
d
Romanian Academy, Institute of Geography, Dimitrie Racovita 12, 023993, Bucharest, Romania
highlights
Groundwater naturally enriched with inorganic arsenic species.
Classification of groundwater sources using Fuzzy Hierarchical Cross-Clustering.
PO
4
3
eAsO
4
3
ion exchange and water-rocks interactions as sources of As.
Na
þ
eF
epH cluster as marker for As naturally enriched groundwater.
Co-occurrence of As species and F
under the influence of HCO
3
and alkaline pH.
article info
Article history:
Received 15 July 2016
Received in revised form
21 December 2016
Accepted 26 December 2016
Available online 29 December 2016
Handling Editor: X. Cao
Keywords:
Groundwater
Arsenic speciation
Cluster analysis
Principal component analysis
Fuzzy hierarchical cross-clustering
abstract
The study proposes a combined model based on diagrams (Gibbs, Piper, Stuyfzand Hydrogeochemical
Classification System) and unsupervised statistical approaches (Cluster Analysis, Principal Component
Analysis, Fuzzy Principal Component Analysis, Fuzzy Hierarchical Cross-Clustering) to describe natural
enrichment of inorganic arsenic and co-occurring species in groundwater in the Banat Plain, south-
western Romania. Speciation of inorganic As (arsenite, arsenate), ion concentrations (Na
þ
,K
þ
, Ca
2þ
,
Mg
2þ
, HCO
3
, Cl
,F
, SO
4
2
, PO
4
3
, NO
3
), pH, redox potential, conductivity and total dissolved substances
were performed. Classical diagrams provided the hydrochemical characterization, while statistical ap-
proaches were helpful to establish (i) the mechanism of naturally occurring of As and F
species and the
anthropogenic one for NO
3
, SO
4
2
, PO
4
3
and K
þ
and (ii) classification of groundwater based on content of
arsenic species. The HCO
3
type of local groundwater and alkaline pH (8.31e8.49) were found to be
responsible for the enrichment of arsenic species and occurrence of F
but by different paths. The PO
4
3-
eAsO
4
3-
ion exchange, water-rock interaction (silicates hydrolysis and desorption from clay) were asso-
ciated to arsenate enrichment in the oxidizing aquifer. Fuzzy Hierarchical Cross-Clustering was the
strongest tool for the rapid simultaneous classification of groundwaters as a function of arsenic content
and hydrogeochemical characteristics. The approach indicated the Na
þ
eF
-
epH cluster as marker for
groundwater with naturally elevated As and highlighted which parameters need to be monitored. A
chemical conceptual model illustrating the natural and anthropogenic paths and enrichment of As and
co-occurring species in the local groundwater supported by mineralogical analysis of rocks was
established.
© 2016 Elsevier Ltd. All rights reserved.
* Corresponding author.
E-mail address: ftibi@chem.ubbcluj.ro (T. Frentiu).
Contents lists available at ScienceDirect
Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere
http://dx.doi.org/10.1016/j.chemosphere.2016.12.130
0045-6535/© 2016 Elsevier Ltd. All rights reserved.
Chemosphere 172 (2017) 127e137