Leaching of microelement contaminants in a long-term field study

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Abstract

A field experiment with microelement loads was set up on loamy-textured, calcareous chernozem soil formed on loess. The ploughed layer contained about 5% CaCO3 and 3% humus. The soil was well supplied with Ca, Mg, Mn and Cu, moderately supplied with N and K, and weakly supplied with P and Zn. The water table is at the depth of 15 m, the water-balance of the area is negative, and the site is drought-sensitive. Salts of the 13 examined microelements were applied at 4 levels in the spring of 1991.Treatments were arranged in split-plot design, in a total of 104 plots with two replications. Loading rates were 0, 90, 270 and 810 kg/ha per elements in the form of AlCl3, NaAsO2, BaCl2, CdSO4, K2CrO4, CuSO4, HgCl2, (NH4)6Mo7O24, NiSO4, Pb(NO3)2, Na2SeO3, SrSO4, and ZnSO4. Soil profiles of the control and the 810 kg/ha treatment were sampled in the 3rd, 6th and 10th year of the trial. The mixed samples, consisting of 5 cores/plot, were taken every 30 cm to the depth of 60 (1993), 90 (1996) and 290 (2000) cm. NH4-acetate + EDTA-soluble element content was determined. The scheme for vertical movement of soluble elements in soil profile as a function of time is shown in Fig. 1. The main conclusions of the study can be drawn as follows: 1. On contaminated soil with 810 kg/ha loading rates, As, Hg, Ni, Cu, Pb, Ba and Sr displayed no significant vertical movement. The movement of these elements is blocked in the soil-plant system: their accumulation in the above-ground plant parts usually remains below 5-10 mg/kg D.M., with the exception of Ba and Sr which showed a somewhat higher accumulation. On this soil the above elements do not seem to be dangerous contaminants either to soil, groundwater or plants. Extreme As and Hg loads, however, resulted in phytotoxicity in some plants. 2. Moderate extent of leaching occurs in the case of Zn and Cd, when they are enriched significantly. Their accumulation was moderate in the above-ground plant parts. Zn is not a dangerous pollutant either for soil, plants or groundwater at this site. Cd, however, is a very dangerous element from the human toxicological point of view and more extreme Cd loads also proved to be toxic for soil life, crops yield and quality. 3. Cr, Se, and Mo (in the form of chromate, selenate and molybdenate anions) exhibited great mobility in the soil and partly in the soil-plant system. Cr was hardly detectable in the above-ground floral parts. Its rapid leaching, however, can jeopardize groundwater quality. Se showed hyperaccumulation in all plant organs with high toxicity for all kind of crops. Mo also showed two or three orders of magnitude greater accumulation in plant parts, resulting in products unfit for animal or human consumption. Under our experimental conditions Cr(VI), Se, Mo can be classified as dangerous contaminants, since the anion forms remained stabile for a long time in this well-aerated calcareous environment.

Original languageEnglish
Pages (from-to)287-296
Number of pages10
JournalCentral European Geology
Volume57
Issue number3
DOIs
Publication statusPublished - Sep 1 2014

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Keywords

  • leaching
  • long-term experiment
  • microelements
  • soil pollution

ASJC Scopus subject areas

  • Geology

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