De novo formation characteristics of dioxins in the dry zone of an iron ore sintering bed

The objectives of this work are to understand the details of the mechanism of dioxin formation in the part of a sintering bed termed the dry zone, and to obtain ideas on how to prevent their formation. Sinter mixtures of various composition types were heated in a packed bed reactor, and dioxins in the outlet gas and in the sinter mixture residue were measured. The dioxin formation potential of a simple sinter mixture composed of iron ore, coke and limestone was markedly lower than that of fly ash from a municipal solid waste incinerator (MSWI). In consideration of this result, a series of experiments were conducted using a sinter mixture impregnated with CuCl2. Experimental results showed that dioxin formation was temperature-dependent in the range of 300-550 degrees C, with the maximum observed at around 300 degrees C, which was quite similar to that of fly ash from the MSWI. The homologue distribution of PCDD/Fs in gas and solid reflected the possible difference in carbonaceous materials in coke and activated coke. Gaseous hydrogen chloride acted as a chlorinating reagent for dioxin formation.     

Investigation of hydrogeologic processes in a dipping layer structure: 1. The flow barrier effect

Numerical simulations of a field experiment were performed in order to study the processes contributing to lateral diversion of water flow in the unsaturated zone. The experimental site is a glacial delta with dipping layers of alternating finer and coarser sand. Model soil physical parameters for each of the stratigraphic layers were estimated from soil grain size distributions. Anisotropy of the hydraulic conductivity within the layers was critical in order to reproduce the flow pattern observed in the experiment. Capillary and hydraulic barriers were of minor importance for the observed lateral diversion.     

A modelling assessment of the atmospheric fate of volatile methyl siloxanes and their reaction products

Volatile methyl siloxanes break down in the atmosphere by reacting with OH radicals to form OH-substituted silanols. As the silanols become increasingly OH substituted they are increasingly likely to be removed from the atmosphere by wet and dry deposition. A simple equilibrium partitioning model was constructed to explore the relative rates of removal by different mechanisms (reaction vs. deposition) for siloxanes and their resultant silanols. A mass balance is calculated for the parent siloxane molecule and for each silanol, characterised by the number of OH substitutions. The model includes the effect of incomplete equilibrium between the vapour, adsorbed and dissolved phases of silanols in the atmosphere using a non-equilibrium factor (epsilon) expressing relative departure from equilibrium. Model results show: (1) maximum vapour-phase concentrations for non-substituted siloxanes and single-OH-substituted silanols; (2) maximum dissolved-phase and adsorbed-phase concentrations for two-OH-substituted silanols; (3) >99% of the original material will be removed in wet deposition and <1% in dry deposition as silanols. For increasing OH-substitutions, the decreasing concentration of precursor molecules (as a consequence of combined removal processes) means that concentrations are negligible, in all phases, beyond three or four substitutions. Predictions were relatively insensitive to assumed departures from phase equilibrium. Predictions of silanol hydrolysis in liquid water droplets suggest that the mix of diol chain lengths in precipitation may not be in thermodynamic equilibrium and will depend on atmospheric residence time and pH.     

A multi-variate statistical model integrating passive sampler and meteorology data to predict the frequency distributions of hourly ambient ozone (O3) concentrations

A multi-variate, non-linear statistical model is described to simulate passive O3 sampler data to mimic the hourly frequency distributions of continuous measurements using climatologic O3 indicators and passive sampler measurements. The main meteorological parameters identified by the model were, air temperature, relative humidity, solar radiation and wind speed, although other parameters were also considered. Together, air temperature, relative humidity and passive sampler data by themselves could explain 62.5-67.5% (R(2)) of the corresponding variability of the continuously measured O3 data. The final correlation coefficients (r) between the predicted hourly O3 concentrations from the passive sampler data and the true, continuous measurements were 0.819-0.854, with an accuracy of 92-94% for the predictive capability. With the addition of soil moisture data, the model can lead to the first order approximation of atmospheric O3 flux and plant stomatal uptake. Additionally, if such data are coupled to multi-point plant response measurements, meaningful cause-effect relationships can be derived in the future.     

The toxicity and toxic potential of fly ash from municipal incinerators assessed by means of a fish early life stage test

The toxicity and toxic potential of fly ash were assessed, using rainbow trout yolk sac fry. In contrast to fly ash itself, extracts of fly ash were extremely toxic, producing typical toxicopathological features of TCDD-intoxication. By comparison with earlier experiments using pure 2,3,7,8-TCDD, the toxic potential of fly ash was roughly estimated to be 75–125 ng.g^?1 toxic aequivalents TCDD. Obviously, this toxic potential is attributable for a minor part to 2,3,7,8-TCDD and for the greater part to the other chlorinated dioxin congeners and the dibenzofurans, present in fly ash.     

Tissue retention and metabolism of 2,3,4,3′,4′-pentachlorobiphenyl in mink and mouse

2,3,4,3′,4′-Pentachlorobiphenyl was retained as the unmetabolized parent compound in liver and fat from mouse and mink. In contrast, in mouse plasma - 4-hydroxy-2,3,5,3′,4′-pentachlorobiphenyl - was present in concentrations 15 times higher than that of the parent chlorobiphenyl. In mink plasma the parent compound and the 4-hydroxylated metabolite were present in similar concentrations. Faeces was the major excretion pathway in both animals. Both the mouse and the mink excreted mainly the parent compound accompanied by trace amounts of hydroxylated metabolites but the mink also excreted significant amounts of hydrophilic metabolites, that gave hydroxylated products after acidic hydrolysis. Five hydroxylated metabolites, 4-hydroxy-2,3,5,3′,4′-pentachlorobiphenyl, 4-hydroxy-3,5,2′,3′,4′-pentachlorobiphenyl, 2-hydroxy-3,4,2′,3′,4′-pentachlorobiphenyl, 5-hydroxy-3,4,2′,3′,4′-pentachlorobiphenyl and 5-hydroxy-2,3,4,3′,4′-pentachlorobiphenyl, were identified in excreta of mink and mouse.     

Qualitative and quantitative effects of ozone and/or sulfur dioxide on field-grown potato plants

Solanum tuberosum L. cv Norchip plants were grown in open-top chambers in the summer of 1986. Plants were treated with charcoal-filtered air, nonfiltered air, or nonfiltered air supplemented with 33, 66, or 99% of the ambient ozone (O3) concentrations from 1000 to 2000 h eastern daylight time daily. In addition, plants received charcoal-filtered air plus 0, 0.15 (393 microg m(-3)), 0.34 (891 microg m(-3)), or 0.61 (1598 microg m(-3)) ppm sulfur dioxide (SO2) from 0900 to 1200 h once every 14 d for a total of four treatments. Ozone induced a linear reduction in number and weight of Grade One (> 6.35-cm diameter) potato tubers and in total weight of tubers. Ozone also induced linear reductions in the percentage of dry matter of tubers and linear decreases in glucose and fructose content of Grade One tubers. Sulfur dioxide induced a stimulation and then decline of the number, percentage of dry matter, and sucrose content of Grade One tubers. The SO2 response best fit a quadratic curve. No O3 x SO2 interactions were detected for any of the yield or quality functions measured.     

An assessment of the impact of ambient ozone on field-grown crops in New Jersey using the EDU method: part 1-white potato (Solanum tuberosum)

Six potato cultivars were grown to maturity in field plots in New Brunswick, New Jersey, according to standard commercial practices over a 5-year period. One-half of the plots were given a periodic soil drench of an antioxidant (EDU) which has the capacity to protect foliage against ozone toxicity. Based upon visible foliar injury and total tuber yield, the cultivars Norland and Norchip proved significantly more sensitive to ambient ozone pollution than Green Mountain, Irish Cobbler, Belrus or Superior. When foliar injury was less than 20%, no impact on tuber yield was detected. However, when 75% of the foliage exhibited O(3) toxicity symptoms, tuber yield was reduced 25% and 31%, respectively, in 'Norland' and 'Norchip'. A review of results from studies in the US and Canada utilizing different assessment methodologies provides evidence that ambient ozone causes significant tuber yield reduction in sensitive white potato genotypes when foliar injury exceeds 20 to 40%.     

Effects of ozone and soil water deficit on roots and shoots of field-grown soybeans

Water-stressed and well-watered soybean (Glycine max cvs. Williams and Corsoy) plants were exposed to increasing seasonal doses of ozone (O(3)) using open-top field chambers and ambient air plots. Chamber O(3) treatments included charcoal filtered (CF) air, non-filtered (NF) air, NF + 0.03, NF + 0.06 and NF + 0.09 microl litre(-1) O(3). Soil water potentials measured at 25 and 45 cm averaged -0.40 MPa and -0.05 MPa, respectively, for the plots in the water-stressed and well-watered series. Total root length/core, root length densities, and biomasses (dry weights) were determined. With Williams, a very popular cultivar in recent years, total root length for all O(3) treatments averaged 58% more under water-stress conditions than in well-watered plots, but the range was from 136% to 11% more for NF air and NF + 0.09 microl litre(-1) O(3), respectively. Increasing the O(3) exposure dose did not affect root lengths or weights in the well-watered series. With Corsoy, water stress did not significantly increase root development. In both soil moisture regimes, with both cultivars, there was a linear decrease in seed yield and top dry weight as the O(3) exposure dose increased.     

The role of soil and active ingredient properties in degradation of pesticides: A preliminary assessment

Pesticide disappearance from soils was observed in laboratory studies in which leaching and runoff were impeded, and volatilisation and degradation evaluated. Advection by volatilisation was negligible for the less volatile chemicals, and significant for the more volatile (Trifluralin and Heptachlor). Basic statistics applied to degradation DT50 data of 14 active ingredients in four different soils showed that the properties of pesticides play a major role in determining their degradability.