Tracing the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain, India: a source identification perspective

In Environmental Geochemistry and Health
Volume (Issue): 32
Peer-reviewed Article

Arsenic contamination in groundwater is
of increasing concern because of its high toxicity and
widespread occurrence. This study is an effort to trace
the factors responsible for arsenic enrichment in
groundwater of the middle Gangetic Plain of India
through major ion chemistry, arsenic speciation,
sediment grain-size analyses, and multivariate statistical
techniques. The study focuses on the distinction
between the contributions of natural weathering and
anthropogenic inputs of arsenic with its spatial distribution
and seasonal variations in the plain of the state
Bihar of India. Thirty-six groundwater and one
sediment core samples were collected in the premonsoon
and post-monsoon seasons. Various graphical
plots and statistical analysis were carried out using
chemical data to enable hydrochemical evaluation of
the aquifer system based on the ionic constituents,
water types, hydrochemical facies, and factors controlling
groundwater quality. Results suggest that the
groundwater is characterized by slightly alkaline pH
with moderate to strong reducing nature. The general
trend of various ions was found to be
Ca2?[Na?[Mg2?[K?[NH4
?; and HCO3
-[
Cl-[SO4
2-[NO3
-[PO4
3-[F- in both seasons.
Spatial and temporal variations showed a slightly
higher arsenic concentration in the pre-monsoon
period (118 lg/L) than in the post-monsoon period
(114 lg/L). Results of correlation analyses indicate
that arsenic contamination is strongly associated with
high concentrations of Fe, PO4
3-, and NH4
? but
relatively low Mn concentrations. Further, the enrichment
of arsenic is more prevalent in the proximity of
the Ganges River, indicating that fluvial input is the
main source of arsenic. Grain size analyses of
sediment core samples revealed clay (fine-grained)
strata between 4.5 and 7.5 m deep that govern the
vertical distribution of arsenic. The weathering of
carbonate and silicate minerals along with surfacegroundwater
interactions, ion exchange, and anthropogenic
activities seem to be the processes governing
groundwater contamination, including with arsenic.
Although the percentage of wells exceeding the
permissible limit (50 lg/L) was less (47%) than that
reported in Bangladesh and West Bengal, the percentage
contribution of toxic As(III) to total arsenic
concentration is quite high (66%). This study is vital
considering that groundwater is the exclusive source of
drinking water in the region and not only makes
situation alarming but also calls for immediate
attention.

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