Evaluation of the historical records of lead pollution in the annual growth rings and bark pockets of a 250-year-old Quercus crispula in Nikko,Japan

The annual growth rings and bark pockets of a 250-year-old Japanese oak (Quercus crispula), collected from the Nikko National Park, Japan in 2000 AD, were analysed by ICP mass spectrometry. The annual rings, sampled in 5-year increments, recorded Pb concentrations from 0.01 to 0.1 mg kg(-1) and there was no significant change in concentration with time. In contrast, bark pocket samples dating from 1875 to the present showed a progressive increase in Pb concentration with time, from approximately 0.1 to 10 mg kg(-1). Shoots of epiphytic moss growing on the tree trunk contained 17 mg kg(-1) Pb. The bark pockets recorded historical increases in airborne Pb pollution accompanying the industrialisation of Japan, which was initiated by the opening of Japan's borders from 1854. This increase was not reflected by the annual rings. The 206Pb/207Pb isotope ratio of the bark pockets decreased from approximately 1.18 to 1.16 from 1964 to the present, indicating changes in the sources of Pb pollution. The 206Pb/207Pb isotope ratio of the moss shoots was similar to the current bark (1.16). The data showed bark pockets to be more effective than annual rings for recording historical change in airborne lead pollution.     

Comparison of anaerobic dechlorinating enrichment cultures maintained on tetrachloroethene,trichloroethene, cis-dichloroethene and vinyl chloride

An anaerobic mixed microbial culture was enriched from soil and groundwater taken from a site contaminated with trichloroethene (TCE). This enrichment culture was divided into four subcultures amended separately with either perchloroethene (PCE), TCE, cis-dichloroethene (cDCE) or vinyl chloride (VC). In each of the four subcultures, the chlorinated ethenes were rapidly, consistently, and completely converted to ethene at rates of 30-50 micromol/l of culture per day, or an average 160 micro-electron equivalents/l of culture per day. These cultures were capable of sustained and rapid dechlorination of VC, and could not dechlorinate 1,2-dichloroethane, differentiating them from Dehalococcoides ethenogenes, the only known isolate capable of complete dechlorination of PCE to ethene. Chloroform (CF) and 1,1,1-trichloroethane, frequent groundwater co-contaminants with TCE and PCE, inhibited chlorinated ethene dechlorination. Most strongly inhibited was the final conversion of VC to ethene, with complete inhibition occurring at an aqueous CF concentration of 2.5 microM. Differences in rates and community composition developed between the different subcultures, including the loss of the VC enrichment culture's ability to dechlorinate PCE. Denaturing gradient gel electrophoresis of amplified bacterial 16S rRNA gene fragments identified three different DNA sequences in the enrichment cultures, all phylogenetically related to D. ethenogenes. Based on the PCR-DGGE results and substrate utilization patterns, it is apparent that significant mechanistic differences exist between each step of dechlorination from TCE to ethene, especially for the last important dechlorination step from VC to ethene.     

The impact of agricultural runoff on stream benthos in Hong Kong,China

We investigated three small streams in the New Territories of Hong Kong, China. In each stream, we compared the benthic macroinvertebrate fauna of one site immediately upstream of an area of agricultural land (market gardening) with a second site immediately downstream. Each pair of sites was < 300 m apart. Samples were taken at the end of the dry season (March 2000) and again (April 2000) just after heavy rainfall had caused runoff from the fields. The total number of taxa at the downstream sites was the same as that in the upstream sites in March. In April, the total taxon richness was lower at the downstream localities although this difference was statistically significant in only one stream. The acute toxic effect of runoff became clearer when focusing on the group of sensitive benthic fauna. The grouping was done by ranking the relatively physiological tolerance to organotoxins following the relevant literature (Bull. Environ. Contam. Toxicol. 67 (2001) 360). All streams showed a significant downstream decrease in the number of sensitive taxa in April, while in two of three streams the number of relatively tolerant taxa increased. Ordination (by n-MDS) confirmed this pattern. It revealed a marked temporal trend in all streams resulting from a decrease of sensitive taxa downstream that was not apparent at the upstream sites. The size of the observed effects varied among streams, and may have reflected differences in the composition of the agricultural runoff.     

The validity of the Gammarus:Asellus ratio as an index of organic pollution: abiotic and biotic influences.

In freshwaters. Gammarus spp. are more sensitive to organic pollution than Asellus spp. and the relative abundance of the two taxa has been proposed as a pollution index. We tested the validity of this by examining the relationship between the Gammarus: Asellus (G : A) ratio and (1) a suite of physico-chemical variables. (2) established biotic (average score per taxon, ASPT) and richness (species richness (S) and Ephemeroptera, Plecoptera and Trichoptera families richness (EPT family richness)) indices generated from the macroinvertebrate community. In addition, we investigated a suspected biotic interaction, predation, between Gammarus and Asellus. Both univariate and multivariate analyses showed that the G: A ratio was sometimes responsive to changes in parameters linked to organic pollution, such as BOD5 and nitrate levels. However, the G : A ratio also appeared responsive to variables not directly linked to organic pollution, such as conductivity and distance from source. There were significant positive correlations among the G : A ratio and the ASPT, S and EPT, indicating that changes in the relative abundances of Gammarus and Asellus were reflected in changes in the pollution sensitivity and richness of the wider macroinvertebrate community. A laboratory experiment revealed significant predation of Asellus aquaticus juveniles by Gammarus duebeni celticus adults, but no reciprocal predation. We propose that the G: A ratio may be useful as a crude measure of organic pollution that could supplement more complex indices in a multimetric approach to pollution monitoring or be used for monitoring individual sites, where a simple technique is required for monitoring purposes over a period of time. Also, we urge recognition of the possible role of biotic interactions among taxa used in the generation of pollution indices.     

Examination of three theories for mechanisms of cation-induced bioflocculation

Research from different studies has been used to support three different theories pertaining to the role of cations in bioflocculation. These theories are the alginate theory. Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, and divalent cation bridging (DCB) theory. The objectives of this research were to examine the role of cations in bioflocculation to determine which theory, if any, best describes cation induced bioflocculation. Experiments were performed using laboratory scale activated sludge systems with bactopeptone as a feed. The feed was supplemented with either calcium, magnesium, or sodium at increasing concentrations. Floc properties were analyzed in each reactor during steady state periods. The addition of calcium or magnesium to the feed individually resulted in improvements in SVI, CST, SRF, cake solids and floc strength and each of these divalent cations produced similar results. The addition of sodium to the feed resulted in a deterioration in floc properties relative to a control reactor. Analysis of these results suggest that the DCB theory best explains the role of cations. The discrepancies between different studies were examined and are thought to be a result of different experimental procedures in different studies and in particular the use of short-term batch tests versus continuous flow reactor studies. In addition, the implications of DCB theory suggests that activated sludge systems should attempt to lower the ratio of monovalent to divalent cations to improve floc properties and treatment performance.     

Book reviews

Selling the Welfare State: The Privatisation of Public Housing. Ray Forrest and Alan Murie. London: Routledge, 1988. 279pp. £35.00.

Affordable Housing and the Homeless. Jurgen Friedrichs (ed). Walter de Gruyter: Berlin and New York.

The Homeless in Contemporary Society. Richard D. Bingham, Roy E. Green and Sammis B. White. £29.95 cloth, £12.95 paper.     

Evaluation of alternative sludge settleability indices

Proposed modifications of the standard sludge volume index (SVI) to eliminate its unpredictable variation with suspended solids (SS) concentration include stirring, conduct of the test at constant SS concentration, and dilution. We have tested these modifications by making correlations between the respective indices and the content of filamentous organisms in activated sludge expressed in terms of total extended filament length. The results indicate that diluted SVI is the best index of sludge settleability among those tested. Correlation of diluted SVI with specific functional relationships between settling velocity and SS concentration would enable the application of this parameter to prediction of thickening capacity in secondary clarifiers.     

Evolution of operator decision making

Advances in control system technology have altered the types of decision making activities performed by control operators. The changes in decision making necessitate changes in configuration of the operator-process interface to support the new tasks. Alarms and displays that were adequate for operation a few years ago may prove totally inappropriate today as the role of the operator has shifted. This paper describes the changes in decision making in terms of accepted models of operator performance and discusses the impact on alarm/display requirements.     

Quantifying health improvements from water quantity enhancement: an engineering perspective applied to rainwater harvesting in West Africa

Knowledge of potential benefits resulting from technological interventions informs decision making and planning of water, sanitation, and hygiene programs. The public health field has built a body of literature showing health benefits from improvements in water quality. However, the connection between improvements in water quantity and health is not well documented. Understanding the connection between technological interventions and water use provides insight into this problem. We present a model predicting reductions in diarrhea disease burden when the water demands from hygiene and sanitation improvements are met by domestic rainwater harvesting (DRWH). The model is applied in a case study of 37 West African cities. For all cities, with a total population of over 10 million, we estimate that DRWH with 400 L storage capacity could result in a 9% reduction in disability-affected life years (DALYs). If DRWH is combined with point of use (POU) treatment, this potential impact is nearly doubled, to a 16% reduction in DALYs. Seasonal variability of diarrheal incidence may have a small to moderate effect on the effectiveness of DRWH, depending on the storage volume used. Similar predictions could be made for other interventions that improve water quantity in other locations where disease burden from diarrhea is known.     

Using bald eagles to indicate the health of the Great Lakes' environment

The bald eagle (Haliaeetus leucocephalus) is one of the most studied birds of North America, and a great amount of natural life‐history information, including the response of various stressors on the eagles' ability to reproduce, are well known. In Michigan, the eagle has been chosen to track the trends of bioaccumulative compounds of concern across watersheds in the state. The state has been divided into major watersheds, and 20% of these are surveyed each year. A control area in northern Minnesota, Voyageurs National Park, is also sampled annually. We report here on the methods used, the preliminary results of the 1999 field season, and how differences in mercury concentrations varied over a 10‐year period. Mercury in feathers of nestling eagles declined over time only in Lakes Michigan and Huron, but have not decreased among other subpopulations in Michigan. Concentrations of polychlorinated biphenyls (PCBs) and 4,4′‐DDE in blood plasma from nestling eagles have declined over time for most subpopulations; however, they remain greater for breeding areas associated with the Great Lakes' food web. Sea eagles of the genus Haliaeetus are a good sentinel species to track trends in bioaccumulative compounds in aquatic systems.