Agent-based analysis and support for incident management

This paper presents an agent-based approach for error detection in incident management organizations. The approach consists of several parts. First, a formal approach for the specification and hierarchical verification of both traces and properties. Incomplete traces are enriched by enrichment rules. Furthermore, a classification mechanism is presented for the different properties in incident management that is based on psychological literature. Classification of errors provides insight in the functioning of the agents involved with respect to their roles. This insight enables the provision of dedicated training sessions and allows software support to give appropriate warning messages during incident management.     

Modeling polychlorinated biphenyl sorption isotherms for soot and coal

Sorption isotherms (pg-ng/L) were measured for 11 polychlorinated biphenyls (PCBs) of varying molecular planarity from aqueous solution to two carbonaceous geosorbents, anthracite coal and traffic soot. All isotherms were reasonably log-log-linear, but smooth for traffic soot and staircase-shaped for coal, to which sorption was stronger and more nonlinear. The isotherms were modeled using seven sorption models, including Freundlich, (dual) Langmuir, and Polanyi-Dubinin-Manes (PDM). PDM provided the best combination of reliability and mechanistically-interpretable parameters. The PDM normalizing factor Z appeared to correlate negatively with sorbate molecular volume, dependent on the degree of molecular planarity. The modeling results supported the hypothesis that maximum adsorption capacities (Q_max) correlate positively with the sorbent’s specific surface area. Q_max did not decrease with increasing sorbate molecular size, and adsorption affinities clearly differed between the sorbents. Sorption was consistently stronger but not less linear for planar than for nonplanar PCBs, suggesting surface rather than pore sorption.     

Effects of black carbon on bioturbation-induced benthic fluxes of polychlorinated biphenyls

It is unknown whether carbonaceous geosorbents, such as black carbon (BC) affect bioturbation by benthic invertebrates, thereby possibly affecting sediment-water exchange of sediment-bound contaminants. Here, we assess the effects of oil soot on polychlorinated biphenyl (PCB) mass transfer from sediment to overlying water, for sediments with and without tubificid oligochaeta as bioturbators. PCB levels were so low that toxicity to the oligochaeta played no role, whereas soot levels and binding affinity of PCBs to soot were so low that pore water PCB concentrations were not significantly affected by binding of PCBs to soot. This setup left direct effects of BC on bioturbation activity as the only explanation for any observed effects on mass transfer. Mass transfer coefficients (K_L) for benthic boundary layer transport were measured by a novel flux method using Empore™ disks as a sink for PCBs in the overlying water. For the PCBs studied (logK_ow 5.2-8.2), K_L values ranged from 0.2 to 2 cm × d⁻¹ in systems without tubificids. Systems with tubificids showed K_L values that were a factor of 10-25 higher. However, in the presence of oil soot, tubificids did not cause an increase in mass transfer coefficients. This suggests that at BC levels as encountered under field conditions, the mechanism for reduction of sediment-water transfer of contaminants may be twofold: (a) reduced mass transfer due to strong binding of the contaminants to BC, and (b) reduced mass transfer of contaminants due to a decrease in bioturbation activity.     

Absorption of polycyclic aromatic hydrocarbons to cellulose

Polycyclic aromatic hydrocarbons (PAHs) are widespread toxic chemicals. The environmental fate of these chemicals is in part controlled by sorption to (organic matter in) sediments and soils. One of the most abundant organic matter compounds on earth is cellulose. Remarkably, sorption of PAHs to cellulose has hardly been studied; only two reports on the binding of some low-molecular-weight PAHs exist in the literature. In this study, sorption of PAHs to cellulose was investigated in more detail, by measuring isotherms for a series of 13 PAHs, covering a wide hydrophobicity range. The results indicated that sorption of PAHs to cellulose is a linear partition process for all PAHs investigated (phenanthrene-indeno[1,2,3-cd]pyrene). The affinity of PAHs for cellulose appeared to be about 400 times lower than for octanol and even up to 300000 times lower than for black carbon or coal. Linked to the estimated yearly production of cellulose and black carbon, these results suggest that cellulose is probably not a major environmental sorption domain for PAHs.     

Black carbon: the reverse of its dark side

The emission of black carbon is known to cause major environmental problems. Black carbon particles contribute to global warming, carry carcinogenic compounds and cause serious health risks. Here, we show another side of the coin. We review evidence that black carbon may strongly reduce the risk posed by organic contaminants in sediments and soils. Extremely efficient sorption to black carbon pulls highly toxic polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, polybrominated diphenylethers and pesticides into sediments and soils. This increased sorption is general, but strongest for planar (most toxic) compounds at environmentally relevant, low aqueous concentrations. Black carbon generally comprises about 9% of total organic carbon in aquatic sediments (median value of 300 sediments), and then may reduce uptake in organisms by up to two orders of magnitude. This implies that current environmental risk assessment systems for these contaminants may be unnecessarily safe.     

Metal-induced tolerance in the freshwater microbenthic diatom Gomphonema parvulum

The benthic diatom Gomphonema parvulum Kützing is a common species in both clean and metal contaminated rivers. Our aim was to investigate whether metal-induced tolerance could explain the persistance of this taxon under metal polluted conditions. G. parvulum strains were isolated from a Zn- and Cd-contaminated stream and from a relatively clean ("reference") stream. The strains were cultured in synthetic medium as mono-specific biofilms to maintain their specific benthic growth features. Moreover, the strain from the metal polluted stream was cultured in plain and Zn- and Cd-enriched synthetic medium. Short-term (5 h) toxicity experiments with Zn were performed with the strains using pulse amplitude modulated (PAM) fluorometry. Zn lowered significantly the minimal chlorophyll fluorescence (F0) and the photon yield (phi(p)) of the exposed strains after 5 h exposure. The actual Zn concentrations that caused a 50% reduction (EC50's) of the phi(p) of the strain from the metal polluted stream were significantly higher than those of the isolate from the unpolluted stream. The absence of tolerance to Cu of the "polluted" strain indicated that Zn tolerance resulted from specific induction by chronic exposure to Zn in the field. Observations on field biofilms confirmed a higher tolerance of the G. parvulum population from the polluted stream than of the G. parvulum population from the reference stream. A genetic nature of this metal adaptation was supported by the persistance of the Zn tolerance of the polluted strain 2 years after isolation.     

High frequency monitoring reveals phytoplankton dynamics

Phytoplankton is an important water quality indicator because of its high species differentiation, growth rates and responsiveness to environmental actuators. The new European Water Framework Directive calls for assessment of the duration, intensity and succession of phytoplankton blooms to determine the ecological status of various types of waters. For common phytoplankton growth rates basic signal processing theory yields a minimum monitoring frequency of once per day, which is much more than applied in standard practice. To assess the nature of this discrepancy we followed the behaviour of about 40 groups of organisms/particles found in the Oude Rijn river by a two-week daily cytometric analysis. Particle counts of the 20 most abundant groups are shown. Their variation rate and magnitude confirm that daily sampling is needed to follow such ecosystems in detail. It is shown that limiting the monitoring to the "coarse line" does not allow a correspondingly decreased sampling frequency. Automated systems may fill the gaps between the microscopical examinations by gathering highly frequent information. The information depth of bulk measurements is poor however, and not used as such. The data shown here demonstrate that modern scanning flow cytometry (SFC) offers an information depth close to the taxonomic level. In the past decade, acquisition and operation costs of these systems have come down considerably, whereas operation is hands free, even in situ and submerged, and data analysis has become more efficient. SFC is used most efficiently complementary to microscopical analyses for mutual validation. In these cases it presents a realistic solution to generate the essential high frequency observations required to assess ecosystem variability.     

Species-specific responses to metals in organically enriched river water, with emphasis on effects of humic acids

Invertebrate communities in polluted rivers are often exposed to a wide variety of compounds. Due to complex interactions, 'pollution tolerant' species are not necessarily the most tolerant species to toxicants tested under standard laboratory conditions. It was hypothesized that the distribution of species in polluted rivers is not only dependent on the tolerance of species to toxicants, but also on species-specific capacities to modify or compensate for negative effects of toxicants. To test this hypothesis, species-specific responses to metals in organically enriched river water were studied under controlled conditions. The zebra mussel Dreissena polymorpha and the midge Chironomus riparius were exposed to metal-polluted water from the River Dommel. Additionally, the (interactive) effects of metals and humic acids (HA) on both species were evaluated. In spite of a lower tolerance of Chironomus riparius to metals in laboratory studies, the midge was the most tolerant of the two test species to metal-polluted site water. The results indicated that the sensitivities of the two test species determined in laboratory tests were inversely related to their sensitivities to polluted river water. In accordance with these results, midge larvae were protected from copper (Cu) toxicity by HA, while metal toxicity was not reduced (Cu) or even amplified (cadmium) by HA for the zebra mussel. Thus, the presence of (naturally occurring) HA in site water may partly account for discrepancies between responses of species to bioassays and toxicity tests. It is suggested that these differences in responses to metals in site water are strongly influenced by species-specific preferences for organic compounds (like HA). It is concluded that the response to organic compounds present in site water largely determines whether a species is classified as 'pollution tolerant' or 'pollution sensitive'.