Arsenic-contaminated groundwater used for drinking in China is a health threat that was first recognized in the 1960s. However, because of the sheer size of the country, millions of groundwater wells remain to be tested in order to determine the magnitude of the problem. We developed a statistical risk model that classifies safe and unsafe areas with respect to geogenic arsenic contamination in China, using the threshold of 10 micrograms per liter, the World Health Organization guideline and current Chinese standard for drinking water. We estimate that 19.6 million people are at risk of being affected by the consumption of arsenic-contaminated groundwater. Although the results must be confirmed with additional field measurements, our risk model identifies numerous arsenic-affected areas and highlights the potential magnitude of this health threat in China.
Measurements of trace metal species in situ in a softwater
river, a hardwater lake, and a hardwater stream were
compared to the equilibrium distribution of species calculated
using two models, WHAM 6, incorporating humic ion
binding model VI and visual MINTEQ incorporating NICA−Donnan. Diffusive gradients in thin films (DGT) and
voltammetry at a gel integrated microelectrode (GIME)
were used to estimate dynamic species that are both labile
and mobile. The Donnan membrane technique (DMT)
and hollow fiber permeation liquid membrane (HFPLM)
were used to measure free ion activities. Predictions of
dominant metal species using the two models agreed
reasonably well, even when colloidal oxide components
were considered. Concentrations derived using GIME were
generally lower than those from DGT, consistent with
calculations of the lability criteria that take into account
the smaller time window available for the flux to GIME. Model
predictions of free ion activities generally did not agree
with measurements, highlighting the need for further work
and difficulties in obtaining appropriate input data.
Several techniques for speciation analysis of Cu, Zn, Cd,
Pb, and Ni are used in freshwater systems and compared
with respect to their performance and to the metal
species detected. The analytical techniques comprise the
following: (i) diffusion gradients in thin-film gels (DGT);
(ii) gel integrated microelectrodes combined to voltammetric
in situ profiling system (GIME−VIP); (iii) stripping
chronopotentiometry (SCP); (iv) flow-through and hollow
fiber permeation liquid membranes (FTPLM and HFPLM); (v)
Donnan membrane technique (DMT); (vi) competitive ligand-exchange/stripping voltammetry (CLE−SV). All methods
could be used both under hardwater and under softwater
conditions, although in some cases problems with
detection limits were encountered at the low total
concentrations. The detected Cu, Cd, and Pb concentrations
decreased in the order DGT ≥ GIME−VIP ≥ FTPLM ≥
HFPLM ≈ DMT (>CLE−SV for Cd), detected Zn decreased
as DGT ≥ GIME−VIP and Ni as DGT > DMT, in agreement
with the known dynamic features of these techniques.
Techniques involving in situ measurements (GIME−VIP)
or in situ exposure (DGT, DMT, and HFPLM) appear to be
appropriate in avoiding artifacts which may occur
during sampling and sample handling.
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