Regiospecific dechlorination of spiked tetra- and trichlorodibenzo-p-dioxins by anaerobic bacteria from PCDD/F-contaminated Spittelwasser sediments

Samples were taken from sediment of the River Spittelwasser (district Bitterfeld, Germany), which is highly polluted with PCDD/Fs and other chloroorganic compounds. The sediment cores were separated into 10-20 cm thick layers, spiked with 50 microM of 1,2,3,4-tetrachlorodibenzo-p-dioxin and incubated for 8 months under anaerobic conditions in the presence of cosubstrates. Reductive dechlorination of the tetrachlorinated congener and formation of tri- and dichlorinated products were observed in all biologically active incubations. Analysis of subcultures spiked with 1,2,3- and 1,2,4-trichlorodibenzo-p-dioxin, respectively, revealed two different dechlorination pathways within the sediment cores. Pathway M was characterized by the simultaneous dechlorination of peri- and lateralchlorine atoms, whereas sequence SP was restricted to the dechlorination at positions flanked by chlorine atoms on both sides.     

Bioaccumulation of toxic metals (Cr, Cd, Pb and Cu) by seeds of Euryale ferox Salisb. (Makhana) W

The level of toxic metals Cr, Cd, Pb and Cu was determined in seeds, water and sediments collected from nine closed waterbodies of Darbhanga, north Bihar, used for cultivation of the edible aquatic macrophyte Euryaleferox Salisb. during harvesting season of the crop for two successive years (1996 and 1997). Seeds bioconcentrated appreciable amount of these toxic metals in the order Pb > Cr > Cu > Cd. The increased load of metal pollution due to domestic and municipal discharges threatened the habitats of the plant. The toxic metal contents in seeds were found positively correlated with the ambient concentration of metals in water and sediments. The importance of these findings has been discussed for national water resource economy of the country and human health perspectives.     

Estimating the human health risks from polychlorinated dioxins and furans in stack gas emissions from combustion units: implications of USEPA's dioxin reassessment

Shortly after promulgation of the Hazardous Waste Combustor MACT rule established regulatory limits for polychlorinated dioxins and furans (dioxins/furans) in incinerator stack gas, the US Environmental Protection Agency (USEPA) announced that facilities could still be required to demonstrate that stack emissions do not present an unacceptable risk to human health and the environment. Guidance for conducting this risk assessment activity, which was to be required under RCRA omnibus authority, was developed by the agency and released in 1998. The guidance represented an increase in complexity over previous documents developed by the agency and contains multiple chemical, fate and transport, and toxicological parameters which are to be used as default deterministic parameters in a complex series of algorithms which ultimately lead to numerical estimates of risk. As these changes were occurring, USEPA was also moving towards completion of its reassessment of dioxin. That series of documents has been the subject of considerable controversy and has, in several of its various drafts, proposed a number of changes, including modification of the existing toxic equivalency factor (TEF) approach and of the cancer potency factor of 2,3,7,8-tetachlorodibenzo-p-dioxin. At this time it is unclear what the impact of these changes will be on facilities progressing through the permitting process, because it is not intuitively obvious how changes in the risk assessment input parameters will impact the magnitude of the dioxinlfuran risk. In this paper, the receptor usually associated with the highest potential risk from dioxins/furans in a combustion risk assessment, the Subsistence Farmer, will be subjected to a sensitivity analysis to determine which of the multiple default input parameters will have the greatest influence on the potential cancer risk.     

Inter-cellular spike coincidences in visual detection tasks

Synchronized spike activity is discussed as a possible representational code for object integration and as a neuronal basis of attention, perception and awareness. As a byproduct of experiments in which monkeys were trained to detect simple figures composed of single Gabor patches in a noisy background of similar elements, we found in special cases increased spike synchrony above chance level specifically related to figure detection. The long latency of this effect is difficult to interpret. It may be a sign of the cognitive state of an animal when it perceives the figure.     

A chronology of nitrogen deposition in the UK between 1900 and 2000

Measurements of the concentrations of nitrogen compounds in air and precipitation in the UK have been made since the mid-19th century, but no networks operating to common protocols and having traceable analytical procedures were established until the 1950s. From 1986 onwards, a high-quality network of sampling stations for precipitation chemistry was established across the UK. In the following decade, monitoring networks provided measurement of NO₂, NH₃, HNO₃ and a satisfactory understanding of the dry deposition process for these gases allowed dry deposition to be quantified. Maps of N deposition for oxidized and reduced compounds at a spatial scale of 5 km × 5 km are available from 1986 to 2000. Between 1950 and 1985, the more limited measurements, beginning with those of the European Air Chemistry Network (EACN) provide a reasonable basis to estimate wet deposition of NO^? ₃?N and NH⁺ ₄?N. For the first half of the century, estimates of deposition were scaled with emissions assuming a constant relationship between emission and deposition for each of the components of the wet and dry deposition budget at the country scale. Emissions of oxidized N, which dominated total nitrogen emissions throughout the century, increased from 312 kt N annually in 1900 to a peak of 787 kt for the decade 1980–1990 and then declined to 460 kt in 2000. Emissions of reduced N, largely from coal combustion were about 168 kt N in 1900, increasing to a peak of 263 kt N in 2000 and by now dominated by agricultural sources. Reduced N dominated the deposition budget at the country scale, increasing from 163 kt N in 1900 to 211 kt N in 2000, while deposition of oxidized N was 66 kt N in 1900 and 191 kt N in 2000. Over the century, 68 Mt (Tg) of fixed N was emitted within the UK, 78% as NO _x , while 29 Mt of nitrogen was deposited (43% of emissions), equivalent to 1.2 t N ha^?1, on average, with 60% in the reduced form. Deposition to semi-natural ecosystems is approximately 15 Tg N, equivalent to between 1 and 5 t N ha^?1, over the century and appears to be accumulating in soil. The N deposition over the century is similar in magnitude to the total soil N inventory in surface horizons.     

The influence of atmospheric n deposition on nitrous oxide and nitric oxide fluxes and soil ammonium and nitrate concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO^? ₃ and NH⁺ ₄ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH⁺ ₄ and NO^? ₃ concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH⁺ ₄and NO^? ₃ in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH⁺ ₄, but the relationship between NH⁺ ₄ and N deposition (ln NH⁺ ₄ = 0.62 ln N_deposition+0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Phosphorus leaching at cold temperatures as affected by wastewater application and soil phosphorus levels

Land application of wastewater in the northern-tier United States during winter months has been suggested as a means to reduce cost of building storage lagoons. A study was initiated in 1996 to assess land application of potato-processing wastewater on a 120-ha field at Park Rapids, MN. One objective of this study was to evaluate the effects of soil P levels and temperature on P leaching in soil columns. In this paper, we report the P sorption, desorption, and leaching characteristics of a high-P (>200 mg kg(-1)) and a low-P (<25 mg kg(-1)) surface soil from the wastewater irrigation site. The leaching experiment was done with wastewater at 4 +/- 2 or 10 +/- 2 degrees C. The high-P soil resulted in an equilibrium P concentration of 8.0 mg L(-1) compared with 0.14 mg L(-1) for the low-P soil. When low-P wastewater was applied to the high-P soil, the soil acted as a P source, and the total phosphorus (TP) concentration in the leachate was 3.5 times higher than the input TP concentration (C0). When high-P wastewater was applied to the high-P soil, the soil acted as a P sink retarding the TP concentration in the leachate by 80%. Phosphorus desorption was higher at 10 degrees C compared with 4 degrees C. The results showed that depending on P levels of the soil and the wastewater, reduction or increase in leachate P will occur below the surface soil. However, further mobility of this P under field conditions will depend on the volume and rate of percolating water as well as the sorption-desorption characteristics of the subsoil.