Characteristics of organic precursors and their relationship with disinfection by-products

The molecular weight distribution and chemical composition of precursors and their relationship with disinfection by-products (DBPs) were investigated. Most of the organic matter responsible for the major DBP precursors in the Pan-Hsin water are small compounds with a molecular weight less than 1 kDa. The hydrophobic acids display the greatest ability to produce DBP. Therefore, effective removal of small molecules or hydrophobic acidic organics prior to disinfection process will significantly reduce the DBP concentration in the finished water. Although the coagulation process is effective in removing large organic precursors and the removal efficiencies of CHCl3 formation potential and organic carbon increase proportionally to the molecular weight of the precursors, the conventional treatment methods have limited efficiency in eliminating small precursors, which have high DBP formation potential.     

From food to pest: Conversion factors determine switches between ecosystem services and disservices

Ecosystem research focuses on goods and services, thereby ascribing beneficial values to the ecosystems. Depending on the context, however, outputs from ecosystems can be both positive and negative. We examined how provisioning services of wild animals and plants can switch between being services and disservices. We studied agricultural communities in Laos to illustrate when and why these switches take place. Government restrictions on land use combined with economic and cultural changes have created perceptions of rodents and plants as problem species in some communities. In other communities that are maintaining shifting cultivation practices, the very same taxa were perceived as beneficial. We propose conversion factors that in a given context can determine where an individual taxon is located along a spectrum from ecosystem service to disservice, when, and for whom. We argue that the omission of disservices in ecosystem service accounts may lead governments to direct investments at inappropriate targets.

     

Daily trend of dissolved gaseous mercury concentration in coastal seawater of the Mediterranean basin.

A daily trend of DGM concentration in shallow coastal seawater has been measured in an area of the Mediterranean basin. Values up to 47 pg/l were determined for a photosynthetically active radiation (PAR) intensity of 350 W/m2. The lowest value (18 pg/l) has been observed before sunrise. A linear relationship between the PAR intensity and DGM production has been highlighted in an experiment on seawater samples exposed for 10 min to solar radiation. The processes involved in DGM production and losses are discussed.     

Chlorophyll a fluorescence, antioxidant enzymes and lipid peroxidation in tomato in response to ozone and benomyl.

Ozone is a widely distributed phytotoxic air pollutant and is known to reduce the yield of several important agricultural crops in Spain. However, benomyl has been found to lessen the adverse impact of ozone on plants. We studied the effects of ozone and benomyl on chlorophyll a fluorescence, antioxidant enzymes, and lipid peroxidation in tomato (Lycopersicon esculentum Mill. cv. Tiny Tim) grown in open-top chambers in the field. Our results indicate that benomyl prevented the peroxidation of membrane lipids and increased protection of PSII from ozone. There was also a significant reduction in the activity of the antioxidant enzyme superoxide dismutase in ozone-exposed plants that had not been treated with benomyl. Comparing plants treated with benomyl to untreated plants we found that, on exposure to ozone, a greater fraction of light absorption energy was cycled through the photosynthetic system in benomyl-treated plants, as shown by the higher PSII-mediated electron flow and the higher fraction of open PSII reaction centers. The values analyzed in the fluorescence parameters and lipid peroxidation were similar for plants without benomyl grown in a charcoal-filtered environment and benomyl-treated plants exposed to ozone.     

Analysis of the relationship between ambient levels of O3, NO2 and NO as a function of NOx in the UK

Monitoring data from the UK Automatic Urban and Rural Network are used to investigate the relationships between ambient levels of ozone (O₃), nitric oxide (NO) and nitrogen dioxide (NO₂) as a function of NO_x, for levels ranging from those typical of UK rural sites to those observed at polluted urban kerbside sites. Particular emphasis is placed on establishing how the level of ‘oxidant’, OX (taken to be the sum of O₃ and NO₂) varies with the level of NO_x, and therefore to gain some insight into the atmospheric sources of OX, particularly at polluted urban locations. The analyses indicate that the level of OX at a given location is made up of NO_x-independent and NO_x-dependent contributions. The former is effectively a regional contribution which equates to the regional background O₃ level, whereas the latter is effectively a local contribution which correlates with the level of primary pollution. The local oxidant source has probable contributions from (i) direct NO₂ emissions, (ii) the thermal reaction of NO with O₂ at high NO_x, and (iii) common-source emission of species which promote NO to NO₂ conversion. The final category may include nitrous acid (HONO), which appears to be emitted directly in vehicle exhaust, and is potentially photolysed to generate HO_x radicals on a short timescale throughout the year at southern UK latitudes. The analyses also show that the local oxidant source has significant site-to-site variations, and possible reasons for these variations are discussed. Relationships between OX and NO_x, based on annual mean data, and fitted functions describing the relative contributions to OX made by NO₂ and O₃, are used to define expressions which describe the likely variation of annual mean NO₂ as a function of NO_x at 14 urban and suburban sites, and which can take account of possible changes in the regional background of O₃.     

Phytoplankton and water quality characterization: experiences from the Swedish large lakes Mälaren, Hjälmaren, Vättern and Vänern

Phytoplankton and environmental variables have been monitored in the large Swedish lakes M?laren, Hj?lmaren, V?ttern and V?nern since the 1960s. Measures to reduce phosphorus input and industrial waste products were taken during the 1970s. The phosphorus loading was then reduced by 90-95% resulting in a halving of the phosphorus concentrations in the most affected basins. The phytoplankton community reacted rapidly with decreased biomasses of cyanobacteria in summer as well as decreased biomasses of spring diatoms and cryptophycean flagellates. Other reactions were a contracted period of water-bloom, an increased taxon richness, an increased evenness in the biomass over the growth season, and a change in the species size structure within the phytoplankton community. Furthermore, the species richness in the large lakes is compared in relation to lake characteristics. A presentation of the occurrence of toxic cyanobacteria in the lakes is also given. Maximum-minimum values of 13-0.1 micrograms microcystin L-1 are established in connection with water-blooms in Hj?lmaren and M?laren. The use of phytoplankton as a monitoring variable to detect water-quality changes is outlined and assessment criteria are presented.     

Sediment evidence of early eutrophication and heavy metal pollution of Lake Mälaren, central Sweden

Lake M?laren is the water supply and recreation area for more than 1 million people in central Sweden and subject to considerable environmental concern. To establish background data for assessments of contemporary levels of trophy and heavy metal pollution, sediment cores from the lake were analyzed. Diatom-inferred lake-water phosphorus concentrations suggest that pre-20th century nutrient levels in S?dra Bj?rkfj?rden, a basin in the eastern part of M?laren, were higher (c. 10-20 micrograms TP L-1) than previously assumed (c. 6 micrograms TP L-1). Stable lead isotope and lead concentration analyses from 3 basins (S. Bj?rkfj?rden, Gisselfj?rden and Ask?fj?rden) show that the lake was polluted in the 19th century and earlier from extensive metal production and processing in the catchment, particularly in the Bergslagen region. The lake has experienced a substantial improvement of the lead pollution situation in the 20th century following closure of the mining and metal industry. The lead pollution from the old mining industry was large compared to late-20th century pollution from car emissions, burning of fossil fuels and modern industries.     

Resistant sorption of in situ chlorobenzenes and a polychlorinated biphenyl in river Rhine suspended matter

The desorption kinetics of in situ chlorobenzenes (dichlorobenzenes, pentachlorobenzene and hexachlorobenzene) and 2,4,4^′-trichlorobiphenyl (PCB-28) were measured with a gas-purge technique for river Rhine suspended matter sampled in Lobith, The Netherlands. This suspended matter is the main source of sediment accumulation in lake Ketelmeer. In lake Ketelmeer sediment earlier observations showed that slow and very slow fractions dominate the desorption profile.

For the river Rhine suspended matter, only for PCB-28 a fast desorbing fraction of around 1.6% could be detected. The observed rate constants were on the average 0.2 h⁻¹ for fast desorption, 0.004 h⁻¹ for slow desorption, and 0.00022 h⁻¹ for very slow desorption. These values are in agreement with previous findings for the sediment from lake Ketelmeer and with available literature data on fast, slow, and very slow desorption kinetics.

The results from this study show the similarity of desorption profiles between river Rhine suspended matter, and the top layer sediment from lake Ketelmeer. This indicates that slow and very slow fractions are already present in material forming the top layer of lake Ketelmeer, and were not formed after deposition of this material in the lake. The absence of detectable fast fractions for most compounds could be caused by the absence of recent pollution of the suspended matter. But, the observations may also be explained by a rapid disappearance of compounds from the fast fraction due to a combination of a high affinity of very slow sites for these compounds, and their relatively high volatility.     

Application of the Microtox test and pollution indices to the study of water toxicity in the Albufera Natural Park (Valencia, Spain)

The toxic effects of waters collected from irrigation channels in a Mediterranean wetland (Albufera Natural Park, Valencia, Spain) were tested with the Microtox assay and compared with six pollution indices (PIs) defined from analytical parameters. Chemical oxygen demand (COD), biological oxygen demand (BOD), nutrients, heavy metals and pesticides were measured. The bioassay result (concentrations of the water sample (% V/V) that reduced light emission to 10%, 20% and 50%, EC10, EC20 and EC50, respectively (ECs)) was compared with the PIs. This comparison has demonstrated a general agreement between ECs and PIs, except in the case of irrigation channels affected by herbicides used in rice farming (molinate and thiobencarb). No pronounced inhibition was detected in the bioluminescence in relation to the eutrophic parameters in the irrigation waters for EC50 values, indicating that this parameter does not suffice to detect eutrophic waters. Data derived from irrigation water pollution and bioassay were assembled by multivariate statistical techniques (principal component analysis). These components were associated with various contamination sources.