Effects of humic substances and pH on the speciation and adsorption of cadmium, mercury and arsenic
1991 (English)Doctoral thesis, comprehensive summary (Other academic)
The emission of acidifying substances to air causes not only immediate, easily observable effects on the environment, but also slowly emerging indirect effects. Among the latter, special attention has been given to changes in mobility and bioavailability of trace elements in the environment. The present study focused on cadmium, mercury and arsenic, because these elements are highly toxic and represent potential hazards to human health. In particular the combined effects of pH and fulvic acids (FA) on the behavior of these elements in soiVwater systems were investigated. To provide mechanistic explanations, laboratory experiments under controlled conditions were emphasized. A complementary field and population study of the speciation and human uptake of arsenic from well water was also performed.
Speciation studies showed that Cd-FA complexes and, in particular, Hg-FA complexes can play important roles in humic waters. At an FA concentration as high as 10 mg/1. Hg-FA complexes would, in fact, be the predominant species at pH 5.5-6.5. The large differences between previously reported formation constants could be attributed to differences in the analytical technique used to evaluate the underlying experiments. Ultrafiltration is suggested to be the best method for studying metal-FA interactions in natural systems.
The adsorption studies represented an attempt to make conventional laboratory experiments more realistic: the determination of distribution coefficients was carried out at naturally occurring concentrations of trace elements and in the presence of naturally occurring organic matter. Theresults of the experiments showed- that the well-known increase in the mobility of cadmium in acidified environments is counteracted by fulvic acids. Similar results were obtained for mercury, although the possibility of reduction of Hg(II) to Hg(I) or Hg(O) must also be taken into account.Leaching of arsenic is usually not associated with soil acidification, but a dramatic effect in this regard has been shown in connection with a pH reduction to 4 (or lower) in the studies of adsorption of As(V) on alumina, hematite and kaolin. In addition, a low pH should favor both thefonnation of the more mobile As(III) species and the release of arsenic from iron hydroxide phases. If humic matter is present, the mobility of arsenic could be further increased.
Increased exposure to toxic elements has repeatedly --been mentioned as one of the possible consequences of the on-going acidification of the environment. The combined field and population study in the municipality of Smedjebacken showed that arsenic is one of the elements that must be considered in this context. Even with an arsenic concentration as low as 15 Jlg/1, drinking water can account for the major fraction of the exposure to toxic inorganic arsenic forms.
Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 1991. , 54 p.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 65
Social Sciences Interdisciplinary
IdentifiersURN: urn:nbn:se:liu:diva-35359Local ID: 26405ISBN: 91-7870-783-8OAI: oai:DiVA.org:liu-35359DiVA: diva2:256207
1991-05-29, Sal Elysion, Hus-T, Universitetsområdet Valla, Linköping, 10:00 (Swedish)
Papers, included in the Ph.D. thesis, are not registered and included in the posts from 1999 and backwards.2009-10-102009-10-102012-07-11Bibliographically approved