Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.     

1,2,4-trichlorobenzene marine risk assessment with special emphasis on the Osparcom region North Sea

A risk assessment on 1,2,4-trichlorobenzene was carried out specifically for the marine environment according to the methodology laid down in the EU Risk Assessment Regulation 1488/94 and the Guidance Documents of the EU Existing Substances Regulation 793/93. The study consists of the collection and evaluation of data on effects and environmental concentrations from analytical monitoring programs in large rivers and estuaries in the North Sea area. The risk is indicated by comparing the predicted environmental concentration (PEC) with the predicted no-effect concentrations (PNEC) for the marine aquatic environment. A PNECwater) value of 0.3 microg/l and a PNECsed value of 38 microg/kgdw were derived from the results of toxicological studies in organisms representing three trophic levels, i.e. aquatic plants, invertebrates and fish. Based on monitoring data two situations are distinguished: a typical case and a worst case with a PECwater of <0.047 and 0.1 microg/l, respectively, and a PECsed of 40 and 90 microg/kgdw, respectively. The calculated PEC/PNEC ratios were 0.16 and 0.3 for water and 1 and 2.4 for sediment, respectively. It was concluded that no risks are expected for aquatic organisms. Based on the combination of worst-case assumptions risks to benthic organisms could not be fully excluded, but since all open uses of 1,2,4-trichlorobenzene will be ended following the EU risk assessment outcome of 2001 any potential risk is expected to be reduced accordingly. 1,2,4-trichlorobenzene is not considered toxic according to the EU criteria and the available data on persistence of 1,2,4-trichlorobenzene indicate a half-life in water of a few days and a significant biodegradation potential. The bioaccumulation potential is low to moderate with most BCF ratios for fish ranging from 600 to 1400 and one highest of 2020. Based on an extensive evaluation of persistence, biodegradation and bioaccumulation data it is concluded that 1,2,4-trichlorobenzene is not a PBT, since it does not fulfill any of the EU criteria. Biomagnification in the food chain is not expected due to the relatively high elimination rate constants.     

Mutualistic stability in the arbuscular mycorrhizal symbiosis: exploring hypotheses of evolutionary cooperation

The 450-million-year-old symbiosis between the majority of land plants and arbuscular mycorrhizal fungi (AMF) is one of the most ancient, abundant, and ecologically important mutualisms on Earth. Yet, the evolutionary stability of mycorrhizal associations is still poorly understood, as it follows none of the constraints thought to stabilize cooperation in other well-known mutualisms. The capacity of both host and symbiont to simultaneously interact with several partners introduces a unique dilemma; detecting and punishing those exploiting the mutualism becomes increasingly difficult if these individuals can continue to access resources from alternative sources. Here, we explore four hypotheses to explain evolutionary cooperation in the arbuscular mycorrhizal symbiosis: (1) pseudo-vertical transmission and spatial structuring of plant and fungal populations leading to local adaptation of partners; (2) luxury resource exchange in which plants trade surplus carbon for excess fungal nutrients; (3) partner choice allowing partners to associate with better cooperators; and (4) host and symbiont sanctions which actively reward good partners and punish less cooperative ones. We propose that mycorrhizal cooperation is promoted by an exchange of surplus resources between partners and enforced through sanctions by one or both partners. These mechanisms may allow plant and fungal genotypes to discriminate against individuals employing exploitative strategies, promoting patterns of partner choice. Together these selection pressures provide a framework for understanding the stabilization of mycorrhizal cooperation over evolutionary time.     

Sorption of organic compounds to activated carbons. Evaluation of isotherm models

Sorption to ‘hard carbon’ (black carbon, coal, kerogen) in soils and sediments is of major importance for risk assessment of organic pollutants. We argue that activated carbon (AC) may be considered a model sorbent for hard carbon. Here, we evaluate six sorption models on a literature dataset for sorption of 12 compounds onto 12 ACs and one charcoal, at different temperatures (79 isotherms in total). A statistical analysis, accounting for differences in the number of fitting parameters, demonstrates that the dual Langmuir equation is in general superior and/or preferable to the single and triple Langmuir equation, the Freundlich equation, a Polanyi–Dubinin–Manes equation, and the Toth equation. Consequently, the analysis suggests the presence of two types of adsorption sites: a high-energy (HE) type of site and a low-energy (LE) type of site. Maximum adsorption capacities for the HE domain decreased with temperature while those for the LE domain increased. Average Gibbs free energies for adsorption from the hypothetical pure liquid state at 298 K were fairly constant at −15 ± 4 and −5 ± 4 kJ mol⁻¹ for the HE and LE domain, respectively.     

Dioxin and dioxin-like PCB exposure of non-breastfed Dutch infants

The exposure of humans to PCDD/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans) and dioxin-like PCBs (dl-PCBs, i.e. polychlorinated non-ortho and mono-ortho biphenyls) occurs predominantly via the intake of food. Young children have a relatively high intake of these substances, due to their high food consumption per kilogram body weight. As the exposure of non-breastfed infants to these compounds has not been assessed before in The Netherlands, we studied the dietary intake of 17 PCDD/Fs and 11 dioxin-like PCBs in 188 Dutch non-breastfed infants between 4 and 13 months. The food intake of the infants was assessed by a 2-d food record. From these data PCDD/F and dioxin-like PCB intake was calculated using PCDD/F and dioxin-like PCB concentrations of food products sampled in 1998/1999 in The Netherlands. The long-term PCDD/F and dioxin-like PCB exposure of the infants was calculated using the statistical exposure model (STEM). For infants of 5 months the chronic exposure to PCDD/F and dioxin-like PCB was 1.1pg WHO-TEQ (toxic equivalents) per kilogram body weight (bw) per day (95th percentile: 1.7pg WHO-TEQ/kg bwxd), which mainly originated from infant formula and vegetables and increased to 2.3pg WHO-TEQ/kg bwxd (95th percentile 3.7pg WHO-TEQ/kg bwxd) for infants just over 1 year old eating the same food as their parents. The percentage of formula-fed infants with an exposure exceeding the TDI of 2pg WHO-TEQ/kg bwxd was 5% at 5 months, 49% at 9 months and 64% at 12 months.     

Degradation of toxaphene in aged and freshly contaminated soil

Degradation of toxaphene in soil from both newly contaminated (from Sweden) and aged spills (from Nicaragua) were studied. The newly contaminated soil contained approximately 11 mg kg(-1) toxaphene while the aged Nicaraguan soil contained approximately 100 mg kg(-1). Degradation was studied in anaerobic bioreactors, some of which were supplied with lactic acid and others with Triton X-114. In this study we found that the lower isomers Parlar 11, 12 were degraded while the concentration of isomer Parlar 15 increased. This supported an earlier evaluation which indicated that less chlorinated isomers are formed from more heavily isomers. Lactic acid when added to the soil, interfere with the degradation of toxaphene. Lactic acid was added; several isomers appeared to degrade rather slowly in newly contaminated Swedish soil. The Swedish soil, without any external carbon source, showed the slowest degradation rate of all the compounds studied. When Triton X-114 at 0.4 mM was added, the degradation rate of the compounds increased. This study illustrates that biodegradation of toxaphene is a complex process and several parameters have to be taken into consideration. Degradation of persistent pollutants in the environment using biotechnology is dependent on bioavailability, carbon sources and formation of metabolites.     

Risk assessment of metals and organic pollutants for herbivorous and carnivorous small mammal food chains in a polluted floodplain (Biesbosch, The Netherlands)

A risk assessment was made for a carnivorous and a herbivorous food chain in a heavily polluted natural estuary (Biesbosch), by determining the most critical pollutants and the food chain most at risk. Exposure of food chains to metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) was assessed by analyzing dietary concentrations, internal concentrations, and biomarkers of exposure. Common shrew (Sorex araneus) and bank vole (Clethrionomys glareolus) were selected as representative small mammal species for the carnivorous and herbivorous food chain, respectively, and earthworms (Lumbricus rubellus) and snails (Cepaea nemoralis) as representative prey species for the carnivorous food chain. Metals contributed most to the total risk for small mammals and earthworms. PCBs, but not PAHs, contributed to the overall risk for S. araneus at regularly flooded locations. The carnivorous food chain appeared most at risk given the higher exposure levels and bioaccumulating potency found for contaminants in S. araneus.     

Column experiments to assess the effects of electron donors on the efficiency of in situ precipitation of Zn,Cd, Co and Ni in contaminated groundwater applying the biological sulfate removal technology

BACKGROUND, AIMS AND SCOPE: In a previous study, we explored the use of acetate, lactate, molasses, Hydrogen Release Compound (HRC, which is based on a biodegradable poly-lactate ester), methanol and ethanol as carbon source and electron donor to promote bacterial sulfate reduction in batch experiments, this with regards to applying an in situ metal precipitation (ISMP) process as a remediation tool to treat heavy metal contaminated groundwater at the site of a nonferrous metal work company. Based on the results of these batch tests, column experiments were conducted with lactate, molasses and HRCI as the next step in our preliminary study for a go-no go decision for dimensioning an on site application of the ISMP process that applies the activity of the endogenous population of sulfate-reducing bacteria (SRB). Special attention was given to the sustainability of the metal precipitation process under circumstances of changing chemical oxygen demand (COD) to [SO4(2-)] ratios or disrupted substrate supply. METHODS: To optimize the ISMP process, an insight is needed in the composition and activity of the indigenous SRB community, as well as information on the way its composition and activity are affected by process conditions such as the added type of C-source/ electron donor, or the presence of other prokaryotes (e.g. fermenting bacteria, methane producing Archaea, acetogens). Therefore, the biological sulfate reduction process in the column experiments was evaluated by combining classical analytical methods [measuring heavy metal concentration, SO4(2-)-concentration, pH, dissolved organic carbon (DOC)] with molecular methods [denaturing gradient gel electrophoresis (DGGE) fingerprinting and phylogenetic sequence analysis] based on either the 16S rRNA-gene or the dsr (dissimilatory sulfite reductase) gene, the latter being a specific biomarker for SRB. RESULTS AND DISCUSSION: All carbon sources tested promoted SRB activity, which resulted within 8 weeks in a drastic reduction of the sulfate and heavy metal contents in the column effluents. However, unexpected temporal decreases in the efficiency of the ISMP process, accompanied by the release of precipitated metals, were observed for most conditions tested. The most dramatic observation of the failing ISMP process was observed within 12 weeks for the molasses amended column. Subsequent lowering the COD/ SO4(2-) ratio from 1.9 to 0.4 did not alter the outcome of sulfate reduction and metal precipitation efficiency in this set-up. Remarkably, after 6 months of inactivity, bacterial sulfate reduction was recovered in the molasses set up when the original COD/ SO4(2-) ratio of 1.9 was applied again. Intentional disruption of the lactate and HRC supplies resulted in an immediate stagnation of the ISMP processes and in a rapid release of precipitated metals into the column effluents. However, the ISMP process could be restored after substrate amendment. 16S rDNA-based DGGE analysis revealed that the SRB population, in accordance with the results of the previously performed batch experiments, consisted exclusively of members of the genus Desulfosporosinus. The community of Archaea was characterized by sequencing amplicons of archaeal and methanogen-specific PCR reactions. This approach only revealed the presence of non-thermophilic Crenarchaeota, a novel group of organisms which is only distantly related to methane producing Euryarchaeota. DGGE on the dsrB genes was successfully used to link the results of the ISMP process to the community composition of the sulfate reducing bacteria. CONCLUSIONS: In the case of an intentional disruption of substrate supply, the ISMP process failed most likely because the growth and activity of the indigenous SRB community stopped due to a lack of a carbon and electron donor. On the other hand, the cause of the sudden temporal shortcomings of the ISMP process in the presence of different substrates was not immediately clear. It was first thought to be the result of competition between methanogenic prokaryotes (MP) and sulfate reducers, since the formation of small amounts of CH4 (0.01-0.03 ppm ml(-1) was detected. However, the results of molecular analyzes indicate that methanogens do not constitute a major fraction of the microbial communities that were enriched in the column experiments. Therefore, we postulate that the SRB population becomes inhibited by the formed metal sulfides. RECOMMENDATION AND PERSPECTIVE: Our results indicate that the ISMP process is highly dependent on SRB-stimulation by substrate amendments and suggest that this remedial approach might not be viable for long-term application unless substrate amendments are continued and environmental conditions are strictly controlled. This will include the removal of affected aquifer material from the metal precipitation zone at the end of the remediation process, or removal of metal precipitates when the microbial activity decreases. Additional tests are necessary to investigate what will happen when clear groundwater passes through the reactive zone while no more C-sources are amended and all indigenous carbon is consumed. Also, the effects of dramatic increases in sulfate- or HM-concentrations on the SRB-community and the concomitant ISMP process need to be studied in more detail.     

Air quality measurements for the aerosol research and inhalation epidemiology study

Measurements of pollutant gases, airborne particulate matter mass and composition, and meteorology have been made at a core site near downtown Atlanta, GA, since August 1998 in support of the Aerosol Research and Inhalation Epidemiology Study (ARIES). This site is one of eight in the Southeastern Aerosol Research and Characterization network. The measurement objective is to provide a long-term, multivariate dataset suitable for investigating statistical associations of respiratory and cardiovascular disease with airborne particulate matter composition, meteorology, and copollutant gases through epidemiologic modeling. Measurements are expected to continue through 2010. Ancillary multiyear measurements at additional sites in the Atlanta metropolitan area and in short-term exposure assessments have been used to estimate the exposure/measurement error associated with using data from a central site to approximate human exposures for the entire area. To date, 13-, 25-, and 53-month air quality datasets have been used in epidemiologic analyses.