Acidification trends in Sweden

A Swedish hydrochemical monitoring program, which was started during the International Hydrological Decade (1965–1975), has been evaluated with respect to trends and regional differences in acidic deposition and stream water quality. Despite the more than twofold decrease in S emissions in Sweden since the early 1970's, there was only a marginal decrease in sulphate level in precipitation, indicating that long-range transport dominates precipitation chemistry. Trend analyses of stream water data gave practically no evidence that surface water quality had been changing since the late 1960's, i.e., no time lagged or accumulating effects of acidic deposition during past decades could be demonstrated. The difference between the wet deposition of S in southern and northern parts of Sweden was found to be smaller than previously reported. In the northern catchment areas, the input of S was considerably larger than the output. The statistical uncertainty of the trend estimates raises questions about the effectivity of present hydrochemical monitoring programs in detecting environmental changes.     

Influence of pH and organic substance on the adsorption of As(V) on geologic materials

The adsorption of As(V) on alumina, hematite, kaolin and quartz has been measured as a function of pH (2 to 10), and As concentrations (10^?4 to 10 ^?8 M; in the alumina and kaolin systems only). The effects of sulfate (0 to 80 mg L^?1) and fulvic acid (0 to 25 mg L^?1) were studied. The charge of the solid surface and the As speciation in solution (determined by pH) were the most important chemical parameters affecting the sorption behavior. At pH below PZC of the solid, there was a qualitative correlation between the adsorption and the anion exchange capacity of the solid. For hematite at low pH (below 5) there was a reduction of the adsorption possibly related to the formation of positively charged species. The presence of sulfate or fulvic acid reduced the adsorption.     

Effects of acidification and natural organic materials on the mobility of arsenic in the environment

Effects of acidification on adsorption and potential mobility of various As forms have been studied in batch-type distribution experiments. The adsorption of As on alumina decreased in the order As(V) > MMAA = DMAA > As(III) at pH below 6 and As(V) > As(III) > MMAA = DMAA at pH above 6. The adsorption reached a maximum around pH 5 for As(V), pH 7 for As(III) and pH 4 for MMAA and DMAA. The presence of a fulvic acid at concentration levels of 10 mg L^?1 or higher generally reduced the As adsorption in the pH range 5 to 7. In light of both laboratory and field observations environmental acidification would increase the leaching of As from soils or sediments to surface and groundwaters under reducing conditions, but could also reduce the mobility due to enhanced adsorption under oxidizing conditions.