Desorption of arsenic from drinking water distribution system solids

Previous work has shown that arsenic can accumulate in drinking water distribution system (DWDS) solids (Lytle et~al., 2004) when arsenic is present in the water. The release of arsenic back into the water through particulate transport and/or chemical release (e.g. desorption, dissolution) could result in elevated arsenic levels at the consumers' tap. The primary objective of this work was to examine the impact of pH and orthophosphate on the chemical release (i.e. desorption) of arsenic from nine DWDS solids collected from utilities located in the Midwest. Arsenic release comparisons were based on the examination of arsenic and other water quality parameters in leach water after contact with the solids over the course of 168~hours. Results showed that arsenic was released from solids and suggested that arsenic release was a result of desorption rather than dissolution. Arsenic release generally increased with increasing initial arsenic concentration in the solid and increasing pH levels (in the test range of 7 to 9). Finally, orthophosphate (3 and 5 mg PO₄/L) increased arsenic release at all pH values examined. Based on the study results, utilities with measurable levels of arsenic present in their water should be aware that some water quality changes can cause arsenic release in the DWDS potentially resulting in elevated levels at the consumer's tap.     

Bioavailability and plant accumulation of heavy metals and phosphorus in agricultural soils amended by long-term application of sewage sludge

Amendment of agricultural soils with municipal sewage sludges provides a valuable source of plant nutrients and organic matter. Nevertheless, addition of heavy metals and risks of eutrophication continue to be of concern. Metal behaviour in soils and plant uptake are dependent on the nature of the metal, sludge/soil physico-chemical properties and plant species. A pot experiment was carried out to evaluate plant production and heavy metal uptake, soil heavy metal pools and bioavailability, and soil P pools and possible leaching losses, in agricultural soils amended with sewage sludge for at least 10 years (F20) compared to non-amended soils (control). Sewage sludge application increased soil pH, N, Olsen-extractable-P, DOC and exchangeable Ca, Mg and K concentrations. Total and EDTA-extractable soil concentrations of Cu and Zn were also significantly greater in F20, and soil metal (Cu, Mn and Zn) and P fractionation altered. Compared to the control, in F20 relative amounts of acid-extractable (Mn, Zn), reducible (Mn, Zn) and oxidisable (Cu, Zn) metal fractions were greater, and a dominance of inorganic P forms was observed. Analyses of F20 soil solutions highlighted risks of PO4 and Cu leaching. However, despite the observed increases in metal bioavailability sewage sludge applications did not lead to an increase in plant shoot concentrations (in wild plants or crop species). On the contrary, depending on the plant species, Mn and Zn tissue concentrations were within the deficiency level for most plants.     

Oxidation of trichloroethene over metal oxide catalysts: kinetic studies and correlation with adsorption properties

The performance of bulk chromium oxide is compared with that of a Mn commercial catalyst for the deep oxidation of trichloroethene (1000-2500ppmv, 55h(-1) space velocity) in air, in dry and wet (20000ppm of H(2)O) conditions, in terms of activity, selectivity and stability. Chromium oxide was found to be more active (on a catalyst weight basis), however its activity decreases continuously with time on stream. The presence of water increases its stability, the Mn catalyst showing the opposite behaviour. The effect of water on the Cr catalyst can be explained according to the Deacon equilibrium, as the presence of water tends to decrease the Cl(2) concentration, assumed to be responsible of the catalyst deactivation. Regarding to the selectivity, the Mn catalyst yields C(2)Cl(4), CCl(4) and CHCl(3) as organochlorinated by-products, whereas chromium oxide produces only trace amounts of CCl(4). Simple power-law kinetics expressions (first-order for Mn and zero-order for Cr) provide fairly good fits for the evolution of the conversion with the temperature. Furthermore, the kinetic behaviour of chromium oxide can be represented with a Langmuir-Hinshelwood model taking into account the chlorine inhibitory effect.     

The influence of radical architecture on cadmium bioaccumulation in the black mangrove, Avicennia germinans L

Two groups of Avicennia germinans plants with differences in the radical architecture were exposed under hydroponic conditions to 95ppm of cadmium (Cd) for a period of 24h. Later, Cd concentration in roots, stems and leaves was determined by graphite furnace atomic absorption spectrophotometry. Our results showed that, for both groups of plants, the roots accumulated higher concentration of Cd as compared to stems and leaves, though, the plants of group B displayed enhanced radical architecture, better growth performance, and lower Cd concentration as compared to plants of group A. In contrast, low values of leaves/roots Cd transportation index, and bioaccumulation factor were found in plants of group B. These results suggest that the higher radical architecture developed in plants of group B might better adjust the uptake of Cd as a result of an integrated network of multiple response processes for instances, production of organic acids, antioxidative replay, cell-wall lignification and/or suberization. Further studies will be focused in understanding the role of the radical system in mangrove plants with the rhizosphere activation and root adsorption to soil Cd under natural conditions.     

Algal-bacterial interactions in metal contaminated floodplain sediments

The aim of the present study was to investigate algal-bacterial interactions in a gradient of metal contaminated natural sediments. By means of multivariate techniques, we related the genetic structure (denaturing gradient gel electrophoresis, DGGE) and the physiological structure (community-level physiological profiling, CLPP) of the bacterial communities to the species composition of the algal communities and to the abiotic environmental variables, including metal contamination. The results revealed that genetic and physiological structure of the bacterial communities correlated with the species composition of the algal community, but hardly to the level of metal pollution. This must be interpreted as an indication for a strong and species-specific linkage of algal and bacterial species in floodplain sediments. Metals were, however, not proven to affect either the algal or the bacterial communities of the Dutch river floodplains.     

Zinc and cadmium accumulation and tolerance in populations of Sedum alfredii

To investigate the variation of Zn and Cd accumulation and tolerance of Sedum alfredii (a newly reported Zn/Cd hyperaccumulator), field surveys and hydroponic experiments were conducted among three populations of this species: two originating from old Pb/Zn mines in Zhejiang (ZJ) and Hunan (HN) Provinces and one from a "clean" site in Guangdong (GD) Province, China. Under field conditions, up to 12,524 and 12,253 mg kg(-1) Zn, and 1400 and 97 mg kg(-1) Cd in shoots of ZJ and HN plants were recorded respectively. Under hydroponic conditions, ZJ and HN plants accumulated significantly higher Zn and Cd in their leaves and stems, and possessed significantly higher Zn and Cd tolerance than GD plants. Among the two contaminated populations, ZJ plants showed higher Cd tolerance and accumulation (in leaves) than HN plants. The present results indicate that significant differences in Zn and Cd accumulation and tolerance exist in populations of S. alfredii.     

Copper, zinc and cadmium in marine cage fish farm sediments: an extensive survey

The diet of cage-farmed Atlantic salmon contains a range of trace metals, some of which have toxic properties, e.g. zinc, copper and cadmium. A survey of metal concentrations (ICP-MS analysis) in surface sediments of ca. 70 stations was carried out in both May and December 2000 around a Scottish fish farm. Additionally, at 13 stations on 2 orthogonal transects centered on the farm, sediments were analysed at 1cm intervals to 8 cm depth. Maximum concentrations in surface sediments were 921, 805 and 3.5 microg g(-1) for Zn, Cu and Cd, respectively, and were found at stations near the fish farm. The calculated losses from the farm (feed input minus fish output) were 87.0%, 4.3% and 14.0% of the background-corrected inventories for Zn, Cu and Cd, respectively, indicating that for Cu and Cd at least, the feed is not the only source.     

Evaluation of ogawa passive sampling devices as an alternative measurement method for the nitrogen dioxide annual standard in El Paso, Texas

Nitrogen Dioxide (NO₂) is a common urban air pollutant that results from the combustion of fossil fuels. It causes serious human health effects, is a precursor to the formation of ground level ozone, another serious air pollutant, and is one of the six criteria air pollutants established by the United States (U.S.) Clean Air Act (CAA). Ogawa Passive Sampling Devices (PSDs) for NO₂ were collocated and operated at six NO₂ Federal Reference Method (FRM) monitor locations in the El Paso, Texas area for the 2004 calendar year. Passive samples were taken at 2-week, 3-week, and 4-week intervals and compared against the continuously operating FRM monitors. Results showed that the collective NO₂ annual arithmetic mean for all passive monitors was identical to the NO₂ mean for all FRM monitors. Of the individual locations, three passive annual NO₂ means were identical to their corresponding FRM means, and three passive annual NO₂ means differed from their corresponding FRM means by only one part per billion (ppb). Linear correlation analysis between all readings of the individual NO₂ PSDs and FRM values showed an average absolute difference of 1.2 ppb with an r ² of 0.95. Paired comparison between high and low concentration annual NO₂ sites, seasonal considerations, and interlab quality control comparisons all showed excellent results. The ease of deployment, reliability, and the cost-savings that can be realized with NO₂ PSDs could make them an attractive alternative to FRM monitors for screening purposes, and even possibly an equivalent method for annual NO₂ monitoring. More tests of the Ogawa NO₂ PSD are recommended for different ecosystem and climate regimes.     

Size-related aspects of arm damage, tissue mechanics, and autotomy in the starfish Asterias rubens

 Arm damage is a widely reported but superficially investigated aspect of the biology of the starfish Asterias rubens L. In the present study, the incidence of arm damage was surveyed in populations of A.  rubens at two sites in the Firth of Clyde, Scotland, and three sites in Gullmarsfjorden, Sweden. The mean (±SD) incidence across all sites of individuals with basal arm damage (resulting from detachment at the basal autotomy plane) was 19.69 ± 8.86%, the incidence of those with distal arm damage (resulting from amputation at more distal levels) was 7.74 ± 10.01%. The mean incidence of arms with basal damage was 5.28 ± 4.12%, of those with distal damage 1.83 ± 2.45%. There was a significant negative correlation between size and the incidence of basal damage at all but one site, but no significant correlation between size and distal damage at any site. Mechanical tests on specimens of the aboral body wall from the basal region of the arm (which included the autotomy plane) and from a more distal region revealed that with increasing body size there was a significant increase in yield stress, ultimate stress and Young's modulus (stiffness) but no significant change in yield strain and ultimate strain. There was no significant difference between the relationships for basal and distal specimens. It is hypothesised that in larger individuals increased mechanical toughness replaces autotomy as an effective antipredator strategy. Using two methods to induce autotomy, a significant positive correlation between size and the delay between the onset of stimulation and arm detachment was found; this may represent a size-related decline in the efficiency of the autotomy mechanism through the relaxation of selection pressure. Since size is an unreliable indicator of age in A.  rubens, the trends identified herein can be interpreted only tentatively as age-associated phenomena. Received: 4 September 1999 / Accepted: 17 February 2000     

Spatial and temporal patterns of predation on seeds of the surfgrass Phyllospadix torreyi

Spatial and temporal patterns of predation on seeds of the seagrass Phyllospadix torreyi S. Watson were quantified at four sites near Santa Barbara, California, USA. Over a period of four flowering seasons during 1995 to 1998, monthly patterns of seed fall and intensity of seed predation were similar among sites, but were temporally quite variable. Abundance of dispersed seeds varied greatly both among seasons and years. Within any one year, seeds were present in the environment every month, but they peaked in abundance during the fall months following the annual flowering period. Seeds were more abundant during the earlier years of the study. The intensity of predation steadily increased throughout the study period, from a low of ≤10% seeds consumed during 1995 to ∼50% consumption by 1997, and it was not correlated with abundance of seeds in the environment. Pre-dispersal seed loss also was estimated in two flowering seasons by counting the numbers of seeds consumed prior to release from the plant, and was relatively low (<15%). No differences were detected among the four study sites in patterns of pre-dispersal loss. Field surveys were done at two sites to identify potential seed predators. Three of the most abundant species identified in these surveys were tested in the laboratory to determine size-specific patterns of feeding activity and to assess which early life stages of P. torreyi (fruits within spadices, dehisced fruits, seedlings) were most vulnerable to predation. All three of the early life stages were consumed. The crabs Pugettiaproducta (Randall) and Pachygrapsus crassipes Randall were much more voracious predators than the isopod Idotea resecata Stimpson. Received: 8 June 1999 / Accepted: 2 February 2000