5 research outputs found
CaracterĂsticas hidroquĂmicas da água da sub-bacia hidrográfica do Rio Poxim–Sergipe / Hydrochemical characteristics of water in the Poxim – Sergipe river hydrographic sub-basin
Nesse estudo foram investigados, usando o digrama de Gibbs e as razões iĂ´nicas, os mecanismos que controlam a hidrogeoquĂmica da água da sub-bacia hidrográfica do rio Poxim, situada no estado de Sergipe, Nordeste do Brasil. Amostras de água de superfĂcie foram coletadas no perĂodo seco de 2005 e chuvoso de 2006 em 15 estações distribuĂdas ao longo da sub-bacia, e nos perĂodos seco e chuvoso de 2013 e 2014, apenas nas estações 5, 8, 12 e 15. As amostras foram analisadas para determinação dos seguintes parâmetros: temperatura, pH, sĂłlidos totais dissolvidos, sĂłdio, potássio, cálcio, magnĂ©sio, cloreto, sulfato e bicarbonato. A abundância iĂ´nica ocorreu na seguinte ordem Na+ > Ca2+ > Mg2+ e HCO3- > Cl- > SO42-. O diagrama de Gibbs indicou a precipitação atmosfĂ©rica e as interações água – rocha, como principais fatores que controlam a hidrogeoquĂmica dos constituintes dissolvidos na água. AtravĂ©s das razões iĂ´nicas foi possĂvel inferir que o sĂłdio e cloreto foram originários da dissolução da halita e do sal marinho carreado atravĂ©s da deposição atmosfĂ©rica, enquanto o cálcio e magnĂ©sio foram resultantes da dissolução dos carbonatos (calcita, dolomita).
Effects of Fe(III) and quality of humic substances on As(V) distribution in freshwater : use of ultrafiltration and Kohonen neural network.
Humic substances (HS) are ubiquitous organic compounds able to affect mobility and availability of
arsenic (As) in aquatic systems. Although it is known that associations between HS and As occur mainly
via iron (Fe)-cationic bridges, the behaviour and distribution of this metalloid in HS- and Fe-rich environments
is still not fully understood. In this paper, the quality of HS from different rivers in Brazil and
Germany and its influence on the behaviour of As(V) under different Fe(III) concentrations were investigated.
HS were extracted from four different rivers (Cascatinha, Holtemme, Selke and Warme Bode),
characterised and fractionated into different molecular weight sizes (10, 5 and 1 kDa). Complexation
tests were performed using an ultrafiltration system and 1 kDa membranes. All data was analysed using
the Kohonen neural network (SOM e Self organising maps). All samples, except Selke, exhibited similar
results of free As (<1 kDa). The results suggested that associations between HS, Fe and As were
dependent on nitrogen (N)earomatic carbon (C), amount of sulphur (S) and the molecular size of the HS.
Although all HS appeared to be similar after looking at most variables analysed, the SOM could
discriminate them into three different groups. Characterisation of the HS indicated that they had
terrestrial material (from C3 plants) as precursor material. Most of the As and Fe was distributed in the
fractions of higher (>10 kDa) and lower (<1 kDa) size. HS quality is an important factor to take into
account when studying the behaviour of As in HS-rich environments
Distribution and bioavailability of arsenic in natural waters of a mining area studied by ultrafiltration and diffusive gradients in thin films.
The distribution of metals and metalloids among particulate, dissolved, colloidal, free, and labile forms in
natural waters is of great environmental concern since it determines their transportation behaviour and
bioavailability. Organic matter can have an important role for this distribution process, since it is an
important complexing agent and ubiquitous in the aquatic environment. We studied the distribution,
mobility and bioavailability of Al, As and Fe in natural waters of a mining area (Quadril atero Ferr?fero,
Brazil) and the influence of organic matter in these processes. Water samples were taken from 12 points
during the dry and rainy seasons, filtrated at 0.45 mm and ultrafiltrated (<1 kDa) to separate the particulate,
colloidal and free fractions. Diffusive gradients in thin films (DGT) were deployed at 5 sampling
points to study the labile part of the elements. Total and dissolved organic carbon and the physicochemical
parameters were measured along with the sampling. The results of ultrafiltration (UF) and DGT
were compared. The relationship among the variables was studied through multivariate analysis
(Kohonen neural network), which showed that the seasonality did not impact most of the samples. Fe
and Al occurred mainly in the particulate fraction whereas As appeared more in the free fraction. Most of
the dissolved Fe and Al were inert (colloidal form) while As was more labile and bioavailable. The results showed that sampling points with a higher quantity of complexed Fe (colloidal fraction) showed less
labile As, which may indicate formation of ternary complexes among organic matter, As and Fe