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.     

Whole-mount in situ TUNEL method revealed ectopic pattern of apoptosis in cadmium treated naupliar larvae of barnacle (Balanus amphitrite Darwin)

The effect of cadmium on stage II naupliar larvae of barnacle (Balanus amphitrite Darwin) was investigated. Barnacle larvae were exposed to 0-15 microM CdCl(2) for 24 h. Apoptotic cells were stained by the terminal deoxyribonucleotidyl transferase mediated dUTP nick end labelling (TUNEL) method. Incidence of apoptosis, as measured by numbers of animals with ectopic pattern of apoptosis as well as numbers of apoptotic cells per animal, was assessed using confocal microscopy. An increase in incidence of apoptosis was observed in the experimental animals with an increase in cadmium concentration. Mortality increased, and motility decreased, when barnacle larvae were exposed to an increasing concentration of cadmium. The relationship between the occurrence of apoptosis and swimming behaviour was investigated in larvae exposed to 10 microM CdCl(2). Significant increases in apoptosis were detected in the non-motile and dead nauplii. This study suggested that whole-mount in situ TUNEL method may be used to study increased occurrence of apoptotic cells in crustacean larvae.     

Testing model feasibility and sufficiency through laboratory simulation: A case study

Complex computer simulations of ecological models often fail to have much impact on later stages of applied research and management. We believe that this reflects a methodological gap. We present a case study where we try to bridge this gap. A recently published general model for insect outbreak has not yet been tested adequately in the field because of the complexity, size, and time involved in real-world insect pest outbreaks. However, a modified version of the model can be used to predict complex dynamics for a laboratory managed population of vinegar flies (Drosophila melanogaster).A comparison of the dynamics of the laboratory system with the simulation predictions allowed us to conclude that the model is “feasible”, i.e. under certain circumstances the model can predict the dynamics of some real system. These results were obtained despite considerable environmental and biological variability, indicating the robustness of the model. The factors chosen for the model appear to be “sufficient” to describe the real system's essential dynamics. Testing for feasibility and sufficiency should, in our opinion, always precede the much more expensive stages of field testing.     

Spatial variability in characteristics and trace metal levels in sediments from watercourses

Assessing sediment quality requires sampling designs which address variability. Often however, only one sample or composited sample is collected at a sample site. Existing studies on sediment variability or sampling strategies primarily concern lake or marine sediments. Two rivers and one canal were sampled to assess sediment variability. Further, it was determined if sediment contamination in running water could be predicted by using visual criteria and/or knowledge of the presence of depositional and erosion areas. Metal concentrations and sediment characteristics were measured in different visually distinct areas of the river. At all sample sites the coefficient of variance was relatively high for most sediment characteristics (1.4‐ > 100%) and metal levels (15.3–63.6%). In one river the majority of sediment characteristics variation was between two sediment types and detected by visually distinct differences. Significant differences in cadmium and zinc concentrations were also detected. Contrary to what was expected, cadmium, and zinc levels were highest in the coarse fraction. No differences were found in the second river. In the canal a greater concentration of fine grained sediments and metals were found in the deep areas. It was not possible to predict sediment areas with the highest levels of metal contamination using visual criteria or knowledge of the erosion and sedimentation pattern of the river.     

Mortality of pollen beetle (Meligethes spp.) larvae due to predators and parasitoids in rape fields and the effect of conservation strips

In 1996–1999, different mortality factors of pollen beetle larvae were investigated in twenty six rape fields in the northern part of Switzerland which had either a wild flower strip or an extensively managed meadow adjacent to the long side of the field. At 3 and 30 m into the crop from the conservation strip, total mortality, mortality from predators, parasitoids and unspecified factors were measured. Total pollen beetle larval mortality was 66–96%. Mortality caused by predators was 16–27% and there was no significant difference between mortality at 3 m and that 30 m from the extensively managed meadows. However, in fields with wild flower strips adjacent to them, the percentage mortality from predators was significantly greater at 30 m than at 3 m. The range of parasitism of pollen beetle larvae was 0–54% and was on average greater at 3 m than at 30 m. In fields with wild flower strips, the percentage parasitism with Tersilochus heterocerus was significantly higher than in fields with extensively managed meadows. However, mortality from all parasitoids was only 1–2% and there was no significant difference between 3 and 30 m. The effect of parasitoids on pollen beetle mortality was masked by the high unspecified mortality and the mortality from predators. The unspecified mortality was 46–72% and was significantly greater in 1998 and 1999 than in 1996 and 1997. These differences are probably because of meteorological factors (wet in 1999 and dry in 1998). The possible influences of the two types of conservation strips on pollen beetle larval density were investigated. The results show that in fields with adjacent wild flower strips, the pollen beetle larvae were more evenly distributed (but not significantly so) than in fields with extensively managed meadows where larval density decreases faster from the edge into the rape field.