Sequential supercritical fluid extraction (SSFE) for estimating the availability of high molecular weight polycyclic aromatic hydrocarbons in historically polluted soils

Sequential supercritical fluid (CO2) extraction (SSFE) was applied to eight historically contaminated soils from diverse sources with the aim to elucidate the sorption-desorption behavior of high molecular weight polycyclic aromatic hydrocarbons (PAHs). The method involved five extraction phases applying successively harsher conditions by increasing fluid temperature and density mobilizing target compounds from different soil particle sites. Two groups of soils were identified based on readily desorbing (available) PAH fractions obtained under mildest extraction conditions (e.g., readily desorbing fractions of fluoranthene and pyrene significantly varied between the soils ranging from <10 to >90%). Moreover, extraction behavior strongly correlated with molecular weight revealing decreasing available PAH fractions with increasing weight. Physicochemical soil parameters such as particle size distribution and organic dry mass were found to have no distinct effect on the sorption-desorption behavior of PAHs in the different soils. However, PAH profiles significantly correlated with readily available pollutant fractions; soils with relatively less mobile PAHs had higher proportions of five- and six-ring PAHs and vice versa. Eventually, biodegradability corresponded well with PAH recoveries under the two mildest extraction phases. However, a quantitative relationship was only established for soils with biodegradable PAHs. Out of eight soils, five showed no biodegradation including the four soils with the lowest fraction of readily desorbing PAHs. Only one soil (which was found to be highly toxic to Vibrio fischeri) did not match the overall pattern showing no PAH biodegradability but large fractions of highly mobile PAHs, concluding that mass transfer limitations may only be one of many factors governing biodegradability of PAHs.     

Pyrene degradation in forest humus microcosms with or without pine and its mycorrhizal fungus

The mineralization potential of forest humus and the self-cleaning potential of a boreal coniferous forest environment for polycyclic aromatic hydrocarbon (PAH) compounds was studied using a model ecosystem of acid forest humus (pH = 3.6) and pyrene as the model compound. The matrix was natural humus or humus mixed with oil-polluted soil in the presence and absence of Scots pine (Pinus sylvestris L.) and its mycorrhizal fungus (Paxillus involutus). The rates of pyrene mineralization in the microcosms with humus implants (without pine) were initially insignificant but increased from Day 64 onward to 47 microg kg(-1) d(-1) and further to 144 microg kg(-1) d(-1) after Day 105. In the pine-planted humus microcosms the rate of mineralization also increased, reaching 28 microg kg(-1) d(-1) after Day 105. The 14CO2 emission was already considerable in nonplanted microcosms containing oily soil at Day 21 and the pyrene mineralization continued throughout the study. The pyrene was converted to CO2 at rates of 0.07 and 0.6 microg kg(-1) d(-1) in the oily-soil implanted microcosms with and without pine, respectively. When the probable assimilation of 14CO2 by the pine and ground vegetation was taken into account the most efficient microcosm mineralized 20% of the 91.2 mg kg(-1) pyrene in 180 d. The presence of pine and its mycorrhizal fungus had no statistically significant effect on mineralization yields. The rates of pyrene mineralization observed in this study for forest humus exceeded the total annual deposition rate of PAHs in southern Finland. This indicates that accumulation in forest soil is not to be expected.     

Antimony uptake by <Emphasis Type="Italic">Zea mays</Emphasis> (L.) and <Emphasis Type="Italic">Helianthus annuus</Emphasis> (L.) from nutrient solution

We investigated the extent of Sb uptake by maize (Zea mays) and sunflower (Helianthus annuus) from nutrient solutions containing concentrations from 3 to 24 mg/L of potassium antimonate, with the aim of determining the potential of Sb to enter the food chain. The maximum shoot Sb concentrations in Z. mays and H. annuus were 41 mg/kg and 77 mg/kg dry weight, respectively. There was no significant difference in Sb uptake between species. The average bioaccumulation coefficients (the plant/solution concentration quotients) were 1.02 and 1.93 for Z. mays and H. annuus, respectively. Phosphate addition did not affect plant growth or Sb uptake. Antimony uptake by both Z. mays and H. annuus is unlikely to pose a health risk to animals and humans.     

Pharmazeutisch aktive Substanzen in kleinen Fließgewässern

Background

Current hydrological research is increasingly focusing on pharmaceutically active compounds (PhACs). Concerning the issue of quality of drinking water, this problem has also become the focus of public interest. However, in spire of the fact that the fate of chemicals in surface waters has been assessed in great detail, the influence of groundwater-exchange is yet only little known.

Goal

This study gives emphasis to the question of how transport and degradation of PhACs interact with the exchange of surface water with groundwater. Special interest is given to alternating groundwater regimes.

Methods

Based on a small stream system in the north of Berlin, Germany, a one-dimensional compartment-model was established using differential mass-balance. The stream which, at its mouth, discharges 0.3 m³ s^?1 is already well investigated and thus provides a good empirical data basis. The processes taken into account by the model were ‘exchange of surface-water with groundwater’, ‘decomposition’ as well as ‘transport’ of PhACs. Calculations were performed using the commonly used analgesic Diclofenac as an example and defining 81 scenarios by different groundwater regimes. Hasse Diagramm Technique was used to compare the scenarios.

Results

All scenarios show a big influence of groundwater-exchange to the fate and concentration of PhACs in surface waters. In the case of the modelled stream system, dilution by groundwater was more responsible for a decrease in concentration than degradation was. Furthermore, on the background of a standard scenario, the loss due to groundwater by 5.4 percent was in the same magnitude as the loss due to decomposition (9.7 percent). A crucial difference between punctual versus linear afflux of groundwater has not been observed.

Discussion

The alteration of discharge resulted in a big influence of the case differentiation between ‘constant velocity’ and ‘constant cross-section’. Furthermore, the model was based on the assumption that groundwater was unloaded with PhACs or diluted very well in comparison to the stream. In contrast, regarding measurements in the catchment, groundwater could even be a diffuse source of the contamination of the stream.

Conclusions

The fate of PhACs in our model is crucially driven by interactions with groundwater. Therefore, assessing the risk emanating from substances like Diclofenac, it is very important to regard their accessibility to decomposition as well as the morphology of the stream-system and its interactions with the groundwater.

Perspectives

In this model, the process of transport from the surface to groundwater back to the surface was dealt with insufficiently; in order to be able to observe fully developed interaction in a further step of modelling, a groundwater-transportmodel should be coupled completely with a surface-water-model.     

Specialization and interaction strength in a tropical plant-frugivore network differ among forest strata

The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant-frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic frugivores) and forest dependence (50 forest species, 38 visitors). Overall, complementary specialization was similar to that in other plant-frugivore networks. However, the plant-frugivore interactions in the canopy stratum were less specialized than in the mid- and understory, whereas primary and secondary forest did not differ. Plant specialization on frugivores decreased with plant height, and obligate and partial frugivores were less specialized than opportunistic frugivores. The overall impact of a frugivore increased with the number of visits and the specialization on specific plants. Moreover, interaction strength of frugivores differed among forest strata. Obligate frugivores foraged in the canopy where fruit resources were abundant, whereas partial and opportunistic frugivores were more common on mid- and understory plants, respectively. We conclude that the vertical stratification of the frugivore community into obligate and opportunistic feeding guilds structures this plant-frugivore network. The canopy stratum comprises stronger links and generalized associations, whereas the lower strata are composed of weaker links and more specialized interactions. Our results suggest that seed-dispersal relationships of plants in lower forest strata are more prone to disruption than those of canopy trees.