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Chlorination is the most widely used technique for disinfection of drinking water. A consequence of chlorination is the formation of Disinfection By-Products (DBPs). The formation of DBPs in drinking water results from the reaction of chlorine with naturally occurring organic materials, principally humic and fulvic acids. This paper focuses on the effect of humic substances on the formation of twenty-four compounds belonging to different categories of DBPs. This investigation was conducted in two water treatment plants in Greece, Menidi and Galatsi, from July 1999 to April 2000. Humic substances were determined by the diethylaminoethyl (DEAE) method with subsequent UV measurement. The techniques used for the determination of DBPs were liquid-liquid extraction, gas chromatography and mass spectrometry. The concentrations of DBPs were generally low. Total trihalomethanes (TTHMs) ranged from 5.1 to 24.6 microg L(-1), and total haloacetic acids (HAAs) concentration ranged from 8.6 to 28.4 microg L(-1), while haloaketones (HKs) and chloral hydrate (CH) occurred below 1 microg L(-1). The content of humic substances was found to influence the formation of DBPs and especially TTHMs, trichloroacetic acid (TCA), dibromoacetic acid (DBA), CH, 1,1-dichloropropanone (1.1-DCP) and 1,1,1-trichloropropanone (1,1,1-TCP). Seasonal variation of TTHMs and HAAs generally followed that of humic substances content with peaks occurring in autumn and spring. The trends of 1,1-DCP, 1,1,1-TCP and CH formation seemed to be in contrast to TTHMs and HAAs. Trends of formation of individual compounds varied in some cases, probably due to influence of parameters other than humic substances content. Statistical analysis of the results showed that the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DBA are strongly affected from humic substances content (at 0.01 confidence level). The opposite is true for dichloroacetic acid (DCA) concentration. Humic substances also vary to a statistically significant degree during different months, as well as the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DCA. The variance of DBA was not statistically significant. Regarding the effect of sampling station, humic substances content showed no statistically significant difference between the two raw water sources studied.

1. Chemosensory communication between flowers and pollinators is a fundamental component of terrestrial biodiversity, given the importance of olfaction to foraging animals. In this respect, exploring chemically mediated interspecific interactions in natural assemblies may provide novel insights into the ecofunctional significance of volatile organic compounds (VOCs) for plant-insect co-evolution. However, multispecies datasets of associations between plant semiochemicals and arthropods are still very rare and tend to lack community context. Here, we present the first insect-floral VOC meta-network using plant-pollinator visitation data and the plants' floral scent blends, collected in a Mediterranean scrubland. 2. We assembled the insect-VOC meta-network by substituting each plant species in the plant-pollinator network with the blend of VOCs it emits. Furthermore, we identified the modules of the network that is the most densely connected insectVOC groups. After describing the role of the species in the network, we focused on the bees of the community, and by building phylogenetically informed GLS models, we found the species traits predicting the degree of chemical specialization. 3. Modularity analysis of the meta-network revealed tight associations between several classes of VOCs and pollinator groups. Linkage patterns suggest positive associations between (a) Megachilidae bees and sesquiterpenes, (b) Apidae and Andrenidae bees and benzenoids/phenylpropanoids, and (c) wasps, C6 green-leaf volatiles and specific terpenoids. Benzenoids were found to be the least influential and most specialized chemical class in the community, whereas sesquiterpenes represented the most influential one. Furthermore, the degree of chemical generalization of the bees in the meta-network was significantly associated with their ecological generalization, body mass and phenology, whereas their contribution to the network's structure was related to their level of sociality. 4. Synthesis. Our findings help to disclose the ecofunctional significance of the floral volatile landscape and contribute novel testable hypotheses on the behavioural trends and chemical niches of pollinators in a natural community. The insect-volatilome meta-network is thus shown to be advantageous for detecting and visualizing patterns of chemically mediated interspecific interactions. Given the ubiquity of chemosensory biocommunication, our approach can be applied for investigating various types of ecological interactions in community contexts.

Application of chlorination for the disinfection of drinking water results in the formation of a wide range of organic compounds, called disinfection by-products (DBPs), which occur due to the reaction of chlorine with natural organic materials. The occurrence of DBPs was studied in samples from four drinking-water treatment plants (WTPs) and from the distribution network of Athens, Greece. Twenty-four compounds, which belong to different categories of DBPs, were monitored, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HAKs), chloral hydrate (CH) and chloropicrin (CP). Sampling was performed monthly for a period of two years, from three different points at each WTP and from eight points atthe distribution network. Samples were analyzed by GC-ECD methods, which included pretreatment with liquid-liquid extraction for volatile DBPs and acidic methanol esterification for HAAs. The results of the analyses have shown the presence of disinfection by-products belonging to all categories studied in all water samples collected after prechlorination. The major categories of DBPs detected were THMs and HAAs, while the other volatile DBPs occurred at lower concentrations. The concentrations of DBPs did not in any case exceed the maximum contaminant levels (MCL) set by USEPA and WHO. However, monitoring these compounds needs to be continued, because their levels could increase due to changes in the quality of water entering the water treatment plants. Reduction of the concentrations of DBPs could be achieved by optimization of the chlorination conditions, taking into account the effect of time. Moreover, research on alternative disinfection methods (e.g. ozone, chlorine dioxide, chloramines) and their by-products should be conducted to evaluate their applicability in the case of the drinking water of Greece.

The presence of organotin (OT) compounds was investigated in coastal areas (10 stations), wastewater treatment systems (six stations), rivers (19 stations) and lakes (12 stations) throughout Greece, in three sampling campaigns organized between October 1998 and September 1999. A screening method for the determination of toluene extractable organotins (TEOTs) by Electrothermal Atomic Absorption Spectrometry (ETAAS) was used during the first two sampling campaigns. TEOTs (sum of tributyltin, TBT, dibutyltin, DBT and triphenyltin, TPhT) were detected in most seawater and wastewater samples at concentrations up to 19.4 and 89.9 ng l−1, respectively, while they were detected occasionally in surface water. During the third sampling campaign, OT compounds were extracted in selected stations using direct derivatization with NaBEt4 in acidic medium and analysed by Gas Chromatography–Mass Spectrometry (GC–MS). In seawater, the levels of TBT, DBT and monobutyltin (MBT) were varied between < 2 and 70, 159 and 19 ng l−1, respectively and tend to decrease with increasing distance from the coastline. TPhT was not detected in any of the samples. Significant concentrations of OT species were detected in influent wastewater, up to 384, 76.2 and 67.8 ng l−1 for TBT, DBT and MBT, respectively. OTs were mainly associated with the suspended solids and were totally removed during wastewater treatment.

The formation of chlorination by-products (CBPs) was investigated through bench-scale chlorination experiments with river water. The compounds selected for analysis belonged to the groups of trihalomethanes, haloacetic acids, haloketones and haloacetonitriles. Trihalomethanes and haloacetic acids were the major species formed during chlorination, while haloketones and haloacetonitriles occurred at lower levels. The factors affecting the formation of these compounds were examined by two sets of experiments; the first with varying pH and reaction time, and the second with varying chlorine dose and temperature. Different effects of these factors were observed for different categories of CBPs, and in many cases, these effects were compound-specific, as confirmed by statistical analysis. Optimization of chlorination conditions in water treatment plants is a critical issue that should take into account the influence of chlorination parameters on the formation of individual CBPs.

The inhibition effect of arsenite, As(III), arsenate, As(V), inorganic mercury, Hg(II) and methylmercury, MeHg, on the respiration rate of activated heterotrophic sludge microorganisms was evaluated. As(III) and MeHg were much more toxic to activated sludge than As(V) and Hg(II) respectively. The effect of various experimental parameters on the toxicity, such as sludge age, concentration of suspended solids and exposure time, was investigated. An increase of sludge age or the concentration of suspended solids reduces the observed inhibition. Longer exposure seems to dramatically increase the inhibition of As(III), MeHg and Hg(II) during the first hours of exposure, while the later inhibition increases at a slower rate. On the contrary, in the presence of As(V), 24 hours after exposure, the respiration rate was similar to that of the control biomass.

This work evaluated the most commonly used methods for determining maximum heterotrophic specific growth rates ($\\mu _{m}$) in batch reactors. Parallel batch experiments were conducted under various initial substrate-to-biomass ($S_{0}/X_{0}$) ratios and values of the solids retention time ($\\theta _{c}$). The maximum specific growth rate,$\\mu _{m}$, was determined simultaneously according to measurements of oxygen consumption (i.e., oxygen uptake rate, OUR) and volatile suspended solids (VSS) increase. The$S_{0}/X_{0}$) ratio was found to significantly influence$\\mu _{m}$values. Under high$S_{0}/X_{0}$ratios (= 20), fast-growing bacteria seemed to gain a competitive advantage resulting in higher$\\mu _{m}$values than those obtained under low$S_{0}/X_{0}$ratios (= 1.5). The OUR-based estimate of$\\mu _{m}$($\\mu _{m({\\rm OUR})}$), under certain circumstances, is differentiated from$\\mu _{m}$that is based on exponential bacterial growth ($\\mu _{m({\\rm VSS})}$), and seems to be more a measure of substrate oxidation than a measure of bacterial growth. At high$S_{0}/X_{0}$ratio and low$\\theta _{c}$,$\\mu _{m({\\rm OUR})}$was significantly higher than the$\\mu _{m({\\rm VSS})}$, indicating that considerable uncoupling between anabolism and catabolism was occuring under these conditions. Batch experiments conducted at high$S_{0}/X_{0}$ratios seemed to be a more sensitive method for determining$\\mu _{m}$values in the presence of an inhibitor than tests conducted at low$S_{0}/X_{0}$ratios.

A simple method for the extraction of organotin compounds from water samples was developed in which both the instrumental parameters and the extraction/derivatization step were optimized. Organotin compounds (butyl-, phenyl- and octyl-) in tap water samples were ethylated with the addition of 2.5 ml of 0.4% w/v NaBEt sub(4) at pH 5.00 and subsequently extracted two times, for 10 min, with 3 and 2 ml of hexane. The combined extracts were analyzed with on-column capillary GC-QFAAS. The recoveries were quantitative for di- and tri- alkyltin compounds, whereas between 67 and 86% of the monoalkyltin compounds were recovered. The detection limits obtained ranged from 110 pg for monobutyltin to 500 pg for triphenyltin, as sensitivities were found to be compound dependent. The preparation of ethylated standards was also optimized. It was found that two subsequent extractions, with 1.0 and 0.5 ml of hexane were necessary for the quantitative recovery of the ethylated organotin compounds.

The mechanism of orthokinetic flocculation is assessed in relation to the geometric properties of laminar flow in an idealized capillary model of a granular filter. The velocity gradient (G), which controls the ultimate floe size, is shown to have a significant effect on the removal efficiency of the filter.