Behaviour of 137Cs in forest humus detected across the territory of the Czech Republic.

The activity concentration of 137Cs in samples of coniferous forest humus collected across the territory of the Czech Republic in 1995 and 2005 was analysed, and it was found significantly correlated with the surface deposition caused by the Chernobyl accident. The effective (12.8 y) and environmental (22.3 y) half-lives of radiocaesium in humus were calculated and compared with those in spruce bark. The impact of important forest stand factors, that is, precipitation, content of organic matter, age of trees and pH, on the behaviour of 137Cs in humus was studied. It was observed that humus samples with a higher proportion of organic matter, higher pH(H2O) and pH(CaCl2) contained higher amounts of 137Cs. Conversely, with the age of trees, the activity concentration of 137Cs in humus is decreasing. Higher precipitation and humus acidity decrease the reduction rate of the 137Cs in humus. These stand factors increase bioavailability of 137Cs in humus. The transfer and retention of available 137Cs in biomass of organisms living in humus for a long time can satisfactorily explain the longer residence time of 137Cs in humus affected by the studied factors.

A quarter century of biomonitoring atmospheric pollution in the Czech Republic.

The Czech Republic (CZ) had extremely high emissions and atmospheric deposition of pollutants in the second half of the 1980s. Since the beginning of the 1990s, moss, spruce bark and forest floor humus have been used as bioindicators of air quality. In the first half of the 1990s, seven larger areas were found to be affected by high atmospheric deposition loads. Six of these "hot spots" were caused by industrial pollution sources, mainly situated in coal basins in the NW and NE part of the country, and one large area in the SE was affected by increased deposition loads of eroded soil particles. After restructuring of industry in CZ, these hot spots were substantially reduced or even disappeared between 1995 and 2000. Since 2000, only two larger areas with slightly increased levels of industrial pollutant deposition and a larger area affected by soil dust have repeatedly been identified by biomonitoring. The distribution of lead isotope ratios in moss showed the main deposition zones around important emission sources. Very high SO2 emissions led to extreme acidity of spruce bark extracts (pH of about 2.3) at the end of the 1980s. The rate of increasing bark pH was strikingly similar to the rate of recovery of acid wet deposition measured at forest stations in CZ. By about 2005, when the median pH value in bark increased to about 3.2, the re-colonisation of trees by several epiphyte lichen species was observed throughout CZ. An increase in the accumulation of Chernobyl-derived 137Cs in bark was detected at about ten sites affected by precipitation during the time when radioactive plumes crossed CZ (1986). Accumulated deposition loads in forest floor humus corresponded to the position of the moss and bark hot spots.

Long-term retention of (137)Cs in three forest soil types with different soil properties.

Current (137)Cs activity concentrations were studied at three localities in individual soil horizons of Stagnosol, Arenic Podzol and Haplic Cambisol soil units in soil blocks with dimensions of 20 × 20 × 40 cm situated below pine canopies (n = 3) and spruce canopies (n = 3), and below small canopy gaps, at least 15 × 15 m in area (n = 3 + 3), which have probably endured since 1986. The main zone of (137)Cs accumulation in all the localities was found to be in the organic horizons (H and F). No significant transport and accumulation of (137)Cs into illuvial soil horizons (Bm, Bs or Bhs, Bv and Bv/IIC) was found. The estimated current total (137)Cs activity concentrations in the soil blocks 40 cm in depth were only slightly higher below the coniferous canopy than they were below nearby canopy gaps. The inventory of (137)Cs in the soils was found to be in accordance with the estimated (137)Cs inputs from the Chernobyl fallout and from global fallout. The low amounts of (137)Cs found accumulated in the aboveground biomass (mosses, grasses, needles) did not substantially bias the studied radiocaesium balance in the soils. The vertical migration rate of (137)Cs in soils (cm/year) had a tendency to be higher below canopies than below canopy gaps and below pine canopies than below spruce canopies. We expected the current (137)Cs activity concentrations in the individual soil horizons to be related to the studied soil parameters: pH (H2O), pH (CaCl2), content of organic matter and mineral portion and portion of humic and fulvic acid contents (Q4/6). However, this was not confirmed. Similarly, we observed a weak tendency toward higher (137)Cs activity in soils below the canopy than in soils below canopy gaps. The available gaps used in our study may have been too small, and they may have been affected by an accumulation of litter and humus containing (137)Cs from the surrounding plots situated below neighbouring canopies.

Long-term behaviour of 137Cs in spruce bark in coniferous forests in the Czech Republic.

Activity concentrations of (137)Cs were detected in more than 400 outer spruce bark samples collected at sites variably affected by Chernobyl fallout across the Czech Republic in 1995 and 2010. The temporal changes in the (137)Cs activities were found. The mean effective half-life (TEF) for (137)Cs in spruce bark was 9.6 years, and the mean environmental half-life (TE) was 14 years. The effective half-lives were significantly higher in areas with higher long-term annual precipitation sums. Coefficient a in linear regression y = ax + b of half-lives on precipitation sums was 0.015 y mm(-1) for TEF and 0.036 y mm(-1) for TE. The aggregated transfer factor of (137)Cs from soil to bark was determined and the pre-Chernobyl bark contamination related to year 2010 was estimated.

The performance of moss, grass, and 1- and 2-year old spruce needles as bioindicators of contamination: a comparative study at the scale of the Czech Republic.

Moss (Pleurozium schreberi), grass (Avenella flexuosa), and 1- and 2-year old spruce (Picea abies) needles were collected over the territory of the Czech Republic at an average sample density of 1 site per 290km(2). The samples were analysed for 39 elements (Ag, Al, As, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Hg, K, La, Li, Mg, Mn, Mo, Na, Nd, Ni, Pb, Pr, Rb, S, Sb, Se, Sn, Sr, Th, Tl, U, V, Y and Zn) using ICP-MS and ICP-AES techniques (the major nutrients Ca, K, Mg and Na were not analysed in moss). Moss showed by far the highest element concentrations for most elements. Exceptions were Ba (spruce), Mn (spruce), Mo (grass), Ni (spruce), Rb (grass) and S (grass). Regional distribution maps and spatial trend analysis were used to study the suitability of the four materials as bioindicators of anthropogenic contamination. The highly industrialised areas in the north-west and the far east of the country and several more local contamination sources were indicated in the distribution maps of one or several sample materials. At the scale of the whole country moss was the best indicator of known contamination sources. However, on a more local scale, it appeared that spruce needles were especially well suited for detection of urban contamination.

Linking chemical elements in forest floor humus (Oh-horizon) in the Czech Republic to contamination sources.

While terrestrial moss and other plants are frequently used for environmental mapping and monitoring projects, data on the regional geochemistry of humus are scarce. Humus, however, has a much larger life span than any plant material. It can be seen as the "environmental memory" of an area for at least the last 60-100 years. Here concentrations of 39 elements determined by ICP-MS and ICP AES, pH and ash content are presented for 259 samples of forest floor humus collected at an average sample density of 1 site/300 km2 in the Czech Republic. The scale of anomalies linked to known contamination sources (e.g., lignite mining and burning, metallurgical industry, coal fired power plants, metal smelters) is documented and discussed versus natural processes influencing humus quality. Most maps indicate a local impact from individual contamination sources: often more detailed sampling than used here would be needed to differentiate between likely sources.

Mercury distribution around the Spolana chlor-alkali plant (central Bohemia, Czech Republic) after a catastrophic flood, as revealed by bioindicators.

The current mercury concentrations in moss Hypnum cupressiforme, in forest floor humus and in oak and pine bark were determined in a 10-km radius around a chlor-alkali plant affected by a flood in 2002. Similar distribution patterns of Hg had accumulated in four bio-indicators, irrespective of different Hg concentrations in the analysed biological matrices. No accumulation of extremely Hg-contaminated materials was found in the flooded parts. The bio-indicators, used alone or in combination, can be recommended for effective and reliable determination of Hg contamination levels around Hg sources.

Determination of 36 elements in plant reference materials with different Si contents by inductively coupled plasma mass spectrometry: comparison of microwave digestions assisted by three types of digestion mixtures.

Closed-vessel microwave digestion of nine standard reference plant materials (NIST, BCR, IAEA) and a laboratory standard of plant material with different Si contents assisted by HNO3 + H2O2 (procedure A), HNO3 + H2O2 + HF + H3BO3 (procedure B) and HNO3 + H2O2 + HBF4 (procedure C) were used to determine the recovery of 36 elements by ICP-MS: Ag, Al, As, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, In, La, Li, Mn, Mo, Nd, Ni, Pb, Pr, Rb, Sb, Se, Sn, Sr, Th, Tl, U, V, W, Y, Zn. Additions of HF + H3BO3 and HBF4 in procedures B and C exceeded by 10% (B1, C1) and 100% (B2, C2) the equivalent concentrations of Si in the samples determined by ICP-OES. Most recoveries of certified elements (e.g., Al*, Cu, Mo*, Rb*, Sb*, Th) decreased significantly (*p < or = 0.05) with increasing Si content in plant reference materials digested by procedure A, while the recoveries from procedures B and C decreased insignificantly only for Mo and Sb. Digestions B and C gave significantly higher recoveries of Al, Sb, W and REEs, which were tighter to the reference values of these elements. A similar effect was found for Cu, Fe, Li, Ni, Sn, Th, Tl, V, Zn, Ba, Rb and Sr recoveries in samples with Si contents exceeding 2000 microg g(-1). If the Si content in plant samples is less than 10 mg g(-1), digestion of 0.5 g of plant samples through 0.05 mL of HF and 0.5 mL of 4% H3BO3 or 0.1 mL of HBF4 is recommended to get satisfactory results for most of the elements. For materials with Si content exceeding 10 mg g(-1) the weight of the sample for digestion should be reduced to 0.25 g. However, the operation of potential interferences should be taken into account and eliminated through correction equations and adequate dilution of the samples.