Experimentally induced effects of heavy metal on microbial activity and community structure of forest mor layers

This study compared the toxic effects of adding chromium (Cr), zinc (Zn), lead (Pb), molybdenum (Mo), nickel (Ni), and cadmium (Cd) at three dose levels to mor layer samples in laboratory experiments. Microbial activity in the form of soil respiration was monitored for 64 days. At the end of the experimental period, the composition of the soil microbial community structure was analysed by phospholipid fatty acid (PLFA) analysis. The metals added induced changes in the microbial community structure and affected respiration negatively, indicating toxicity. The microbial community structure (principal component analysis of the PLFA pattern) for all metals was significantly related to microbial activity (cumulative respiration), indicating intimate links between microbial community structure and activity. The most striking result in this study was that the shift in the microbial community because of metal stress was similar for all metals. Thus, the PLFA i16:0 increased most in relative abundance in metal-polluted soils, followed by other PLFAs indicative of Gram-positive bacteria (10Me16:0, 10Me17:0, 10Me18:0, a17:0 and br18:0). The PLFA 16:1 omega 5 was consistently negatively affected by metal stress, as were the PLFAs 18:1, 18:1 omega 7 and 19:1a. However, a significant separation between Cr- and Cd-polluted soils was observed in the response of the PLFA cy19:0, which decreased in abundance with Cr stress, and increased with Cd stress. Furthermore, the PLFA 18:2w6, indicating fungi, only increased with Cr and Zn stress. The effective doses of the metals, ranked with regard to background metal concentrations, decreased in the order: Zn > Cr > Pb > Mo > Ni > Cd. We concluded that interpretation of results of microbial activity from experiments of metal toxicity should include microbial structural patterns and background metal concentrations

Consequences in daily life after stroke : A systematic literature review

Syfte: Att beskriva konsekvenser som uppstår i vardagen för personer med stroke. Metod: En litteraturstudie valdes som design för att sammanställa publicerade kvantitativa och kvalitativa forskningsstudier. Dessa studier söktes i databaserna Cinahl, Amed och Medline med sökorden stroke, consequence, coping, adapting, everyday life och daily life. Sökorden kombinerades sedan på olika vis för att få fram de mest relevanta artiklarna, d v s de som svarade på syftet och frågeställningarna. Resultat: Av artiklarna framkom att olika konsekvenser uppstod i samband med aktivitet och delaktighet, i olika omgivningar och i samband med personliga faktorer. Strategier som personer med stroke använde sig av var att undvika vissa situationer, utföra saker på ett annat sätt eller omvärdera betydelser av situationer. Inifrån- och utifrånperspektivet nämner att aktivitetsbegränsningar uppstår i samband med den nya livssituationen. Utifrånperspektivet nämner att personer med stroke var beroende i ADL aktiviteter på grund av sina funktionsnedsättningar och tog därför hjälp av andra. Inifrånperspektivet belyser att personer med stroke engagerade sig i nya aktiviteter och fick planera dessa i förväg. Utifrånperspektivet nämner att för personer som var beroende av elrullstol uppstod problem i samband med olika barriärer i miljön. Båda perspektiven belyser hur personer med stroke blev mindre delaktiga i sociala sammanhang efter insjuknandet och vikten av att uppnå ett bra självförtroende för att kunna hantera funktionsnedsättningar bättre. Slutsats: Det framkom att personer med stroke oavsett funktionsnedsättning har kommit på många strategier för att hantera vardagen. Socialt stöd var en avgörande faktor för att uppnå en livssituation som var tillfredställande, trots detta blev många personer med stroke mindre delaktiga i samhället. Betydelsen av socialt stöd och att kunna utföra aktiviteter självständigt efter insjuknandet av stroke är något som arbetsterapeuter borde fokusera på i utformningen av behandlingar för personer med stroke

Critical Limits for Hg(II) in soils, derived from chronic toxicity data

Published chronic toxicity data for Hg(II) added to soils were assembled and evaluated to produce a data set comprising 52 chronic endpoints, five each for plants and invertebrates and 42 for microbes. With endpoints expressed in terms of added soil Hg(II) contents, Critical Limits were derived from the 5th percentiles of species sensitivity distributions, values of 0.13 μg (g soil)-1 and 3.3 μg (g soil organic matter)-1 being obtained. The latter value exceeds the currently-recommended Critical Limit, used to determine Hg(II) Critical Loads in Europe, of 0.5 μg (g soil organic matter)-1. We also applied the WHAM/Model VI chemical speciation model to estimate concentrations of Hg2+ in soil solution, and derived an approximate Critical Limit Function (CLF) that includes pH; log [Hg2+]crit = - 2.15 pH – 17.10. Because they take soil properties into account, the soil organic matter-based limit and the CLF provide the best assessment of toxic threat for different soils. For differing representative soils, each predicts a range of up to 100-fold in the dry weight-based content of mercury that corresponds to the Critical Limit

Impact of soil properties on critical concentrations of cadmium, lead, copper, zinc and mercury in soil and soil solution in view of ecotoxicological effects

Concern about the input of metals to terrestrial ecosystems is related to (i) the ecotoxicological impact on soil organisms and plants (Bringmark et al. 1998; Palmborg et al. 1998) and also on aquatic organisms resulting from runoff to surface water and (ii) the uptake via food chains into animal tissues and products, which may result in health effects on animals and humans (Clark 1989). Effects on soil organisms, including microorganisms/macrofungi and soil fauna, such as nematodes and earthworms, are reduced species diversity, abundance, and biomass and changes in microbe-mediated processes (Bengtsson and Tranvik 1989; Giller et al. 1998; Vig et al. 2003). Effects on vascular plants include reduced development and growth of roots and shoots, elevated concentrations of starch and total sugar, decreased nutrient contents in foliar tissues, and decreased enzymatic activity (Prasad 1995; Das et al. 1997). A review of these phytotoxic effects is given by Balsberg-Påhlsson (1989). Effects on aquatic organisms, including algae, Crustacea, and fish, include effects on gill function (Sola et al. 1995), nervous systems (Baatrup 1991), and growth and reproduction rates (Mance 1987). Environmental quality standards or critical limits, often also denoted as Predicted No Effect Concentrations, or PNECs, for metals in soils and surface waters related to those effects serve as a guide in the environmental risk assessment process for those substances

Partitioning of Hg between solid and dissolved organic matter in the humus layer of boreal forests

The mobility of mercury (Hg) deposited on soils controls the concentration and toxicity of Hg within soils and in nearby streams and lakes, but has rarely been quantified under field conditions. We studied the in situ partitioning of Hg in the organic top layer (mor) of podsols at two boreal forest sites differing in Hg deposition and climatic regime (S. and N. Sweden, with pollution declining to the north). Soil solution leaching from the mor layer was repeatedly sampled using zero-tension lysimeters over 2 years, partly in parallel with tension lysimeters. Concentrations of Hg and dissolved organic carbon (DOC) were higher while pH was lower at the southern site (means +/- SD: Hg=44 +/- 15 ng L-1, DOC=63.0 +/- 31.3 mg L-1, pH=4.05 +/- 0.53) than at the northern site (Hg=22 +/- 6 ng L-1, DOC=41.8 +/- 12.1 mg L-1, pH=4.28 +/- 0.43). There was a positive correlation over time between dissolved Hg and DOC at both sites, even though the DOC concentration peaked during autumn at both sites, while the Hg concentration remained more constant. This correlation is consistent with the expected strong association of Hg with organic matter and supports the use of Hg/C ratios in assessments of Hg mobility. In the solid phase of the overlying O-f layer, both Hg concentrations and Hg/C ratios were higher at the southern site (means +/- SD: 0.34 +/- 0.06 mu g g(-1) dw and 0.76 +/- 0.14 mu g g(-1) C, respectively) than at the northern site (0.31 +/- 0.05 mu g g(-1) dw and 0.70 +/- 0.12 mu g g(-1) C, respectively). However, concentrations in the solid phase differed less than might be expected from the difference in current atmospheric input, suggesting that the fraction of natural Hg is still substantial. At both sites, Hg/C ratios in the upper half of the mor layer were only about two thirds of those in the lower half, suggesting that the recent decrease in anthropogenic Hg deposition onto the soil is offset by a natural downward enrichment of Hg due to soil decomposition or other processes. Most interestingly, comparison with soil leachate showed that the average Hg/C ratios in the dissolved phase of the mor layers at both sites did not differ from the average Hg/C ratios in the overlying solid organic matter. These results indicate a simple mobilisation with negligible fractionation, despite differences in Hg deposition patterns, soil chemistry and climatic regimes. Such a straight-forward linkage between Hg and organic matter greatly facilitates the parameterisation of watershed models for assessing the biogeochemical fate, toxic effect and critical level of atmospheric Hg input to forest soils

Critical levels of atmospheric pollution: criteria and concepts for operational modelling of mercury in forest and lake ecosystems

Mercury (Hg) is regarded as a major environmental concern in many regions, traditionally because of high concentrations in freshwater fish, and now also because of potential toxic effects on soil microflora. The predominant source of Hg in most watersheds is atmospheric deposition, which has increased 2- to > 20-fold over the past centuries. A promising approach for supporting current European efforts to limit transboundary air pollution is the development of emission-exposure-effect relationships, with the aim of determining the critical level of atmospheric pollution (CLAP, cf. critical load) causing harm or concern in sensitive elements of the environment. This requires a quantification of slow ecosystem dynamics from short-term collections of data. Aiming at an operational tool for assessing the past and future metal contamination of terrestrial and aquatic ecosystems, we present a simple and flexible modelling concept, including ways of minimizing requirements for computation and data collection, focusing on the exposure of biota in forest soils and lakes to Hg. Issues related to the complexity of Hg biogeochemistry are addressed by (1) a model design that allows independent validation of each model unit with readily available data, (2) a process- and scale-independent model formulation based on concentration ratios and transfer factors without requiring loads and mass balance, and (3) an equilibration concept that accounts for relevant dynamics in ecosystems without long-term data collection or advanced calculations. Based on data accumulated in Sweden over the past decades, we present a model to determine the CLAP-Hg from standardized values of region- or site-specific synoptic concentrations in four key matrices of boreal watersheds: precipitation (atmospheric source), large lacustrine fish (aquatic receptor and vector), organic soil layers (terrestrial receptor proxy and temporary reservoir), as well as new and old lake sediments (archives of response dynamics). Key dynamics in watersheds are accounted for by quantifying current states of equilibration in both soils and lakes based on comparison of contamination factors in sediment cores. Future steady-state concentrations in soils and fish in single watersheds or entire regions are then determined by corresponding projection of survey data. A regional-scale application to southern Sweden suggests that the response of environmental Hg levels to changes in atmospheric Hg pollution is delayed by centuries and initially not proportionalamong receptors (atmosphere much greater than soils not equal sediments > fish; clearwater lakes much greater than humic lakes). This has implications for the interpretation of common survey data as well as for the implementation of pollution control strategies. Near Hg emission sources, the pollution of organic soils and clearwater lakes deserves attention. Critical receptors, however, even in remote areas, are humic waters, in which biotic Hg levels are naturally high, most likely to increase further,and at high long-term risk of exceeding the current levels of concern: less than or equal to 0.5 mg (kg fw)(-1) in freshwater fish, and 0.5 mg (kg dw)(-1) in soil organic matter. If environmental Hg concentrations are to be reduced and kept below these critical limits, virtually no man-made atmospheric Hg emissions can be permitted