Increasing concentrations of arsenic and vanadium in (southern) Swedish streams

Abstract

The aim of this study was to investigate temporal trends and controlling factors of As and V in running waters throughout Sweden. For this purpose, data on stream water chemistry from 62 streams of varying catchment size and characteristics, included in the Swedish environmental monitoring programmes were evaluated. The geochemical software Visual MINTEQ was used to model the speciation and trend analyses were performed on total concentrations of As and V as well as modelled fractions (dissolved species as well as arsenate and vanadate adsorbed to ferrihydrite). The trend analyses showed increasing total concentrations of As and V in southern Sweden. Concentrations of As and V correlated significantly to Fe concentrations in 59 and 60 of the 62 streams respectively, indicating that Fe is an important determining factor for As and V concentrations in Swedish streams. This was confirmed by the geochemical modelling that indicated that the adsorbed fraction is the dominant form of As and V and that the concentrations of As and V in Swedish streams are thus highly determined by concentrations of colloidal or particulate Fe. It is therefore suggested that the increasing trends of As and V are to a large extent due to increasing concentrations of colloidal Fe, which is stabilised by increasing concentrations of DOC. Further the geochemical modelling indicates that the dissolved fraction of As and V generally is small, with the exception of a few streams with high pH and/or phosphate concentrations.

Speciation and hydrological transport of metals in non-acidic river systems of the Lake Baikal basin: Field data and model predictions

“…With the current data-supported predictions, we show that sorption to ferrihydrite is an important process in river systems at even higher pH values, with over 70 % of Pb adsorbed onto ferrihydrite at pH [ 8. For V, our results show the same (over 70 %) amount of sorption to ferrihydrite at pH [ 8; similar values were previously only identified in acidic to neutral pH river systems (Wällstedt et al 2010). The dissolved fractions of Pb and V are under-predicted in the model to a similar extent as dissolved Fe (Table S4).…”

“…However, both the model results and measurements agree on the high suspended concentrations of Al and Fe, suggesting that both precipitates are important for Zn sorption at the investigated pH range. This contrasts with the reported results for lower pH ranges, where ferrihydrite alone controlled Zn sorption (Jung et al 2005;Wällstedt et al 2010).…”

“…Both Fe and Pb modelling have been shown by others to produce robust predictions that agree well with measurements in several types of river systems, including acidic (e.g. Tonkin et al 2002;Wällstedt et al 2010;Nystrand et al 2012) and non-acidic conditions (e.g. Tonkin et al 2002;SanchesEspana et al 2006;Balistrieri et al 2007;Hayzoun et al 2015).…”

“…Comparisons between speciation predictions and observations have been made for different metals in various types of natural systems (Butler et al 2009;Gustafsson et al 2009;Wällstedt et al 2010;Nystrand et al 2012). However, most of these studies have focused on the behaviour of limited number of metals, in acidic waters.…”

“…Sorption was estimated using the diffuse layer model (DLM) using the default database in Visual MINTEQ based on Dzombak and Morel (1990) and Karamalidis and Dzombak (2010) for ferrihydrite and gibbsite, respectively. The only exception was vanadate adsorption to ferrihydrite, for which the adsorption constants were changed based on Wällstedt et al (2010). For more detailed description of the modelling parameters, procedure and assumptions, please see supplementary information (S3).…”