Increase In SO Research Articles

Investigating regional differences in short-term effects of air pollution on daily mortality in the APHEA project: a sensitivity analysis for controlling long-term trends and seasonality.

Short-term effects of air pollution on daily mortality in eight western and five central-eastern European countries have been reported previously, as part of the APHEA project. One intriguing finding was that the effects were lower in central-eastern European cities. The analysis used sinusoidal terms for seasonal control and polynomial terms for meteorologic variables, but this is a more rigid approach than the currently accepted method, which uses generalized additive models (GAM). We therefore reanalyzed the original data to examine the sensitivity of the results to the statistical model. The data were identical to those used in the earlier analyses. The outcome was the daily total number of deaths, and the pollutants analyzed were black smoke (BS) and sulfur dioxide (SO(2)). The analyses were restricted to days with pollutant concentration < 200 microg/m(3) and < 150 microg/m(3) alternately. We used Poisson regression in a GAM model, and combined individual city regression coefficients using fixed and random-effect models. An increase in BS by 50 microg/m(3) was associated with a 2.2% and 3.1% increase in mortality when analysis was restricted to days < 200 microg/m(3) and < 150 microg/m(3), respectively. The corresponding figures were 5.0% and 5.6% for a similar increase in SO(2). These estimates are larger than the ones published previously: by 69% for BS and 55% for SO(2). The increase occurred only in central-eastern European cities. The ratio of western to central-eastern cities for estimates was reduced to 1.3 for BS (previously 4.8) and 2.6 for SO(2) (previously 4.4). We conclude that part of the heterogeneity in the estimates of air pollution effects between western and central-eastern cities reported in previous publications was caused by the statistical approach used and the inclusion of days with pollutant levels above 150 microg/m(3). However, these results must be investigated further.

Electrowinning of copper from sulfate electrolyte in presence of sulfurous acid

The electrowinning of copper from acidic sulfate solution in the presence of sulfurous acid using a graphite anode was investigated. The effects of operating variables including sulfur dioxide concentration, copper concentration, sulfuric acid concentration, current density and temperature on the cell voltage, anode potential, power consumption, current efficiency, deposit quality, surface morphology, crystallographic orientations and polarisation characteristics were studied. Other anode materials such as Pb/Sb, Pb/Ag, Ti and Ti–IrO 2 were also used to examine their effects on electrocatalytic activity for oxidation of SO 2 and deposit quality. A rectangular stainless steel cathode of length 8 cm, width 5 cm and thickness 2 mm was used for copper electrowinning. Increases in SO 2 concentration, copper concentration, sulfuric acid concentration and temperature lower the power consumption. These variables have no effect on the current efficiency of copper deposition. The presence of SO 2 in the copper electrolyte affects both the cathodic and anodic polarisation curves. In addition, it causes shifting of preferred orientations from (220) (111) (200) (311) to (111) (200) (220) (311). Changes in crystallographic orientation are also seen in the surface morphology of deposited copper. It is found that minimum power consumption together with maximum current efficiency and improved surface morphology can be achieved using a graphite anode.

Geochemical modeling of iron, sulfur, oxygen and carbon in a coastal plain aquifer

Fe(III) reduction in the Magothy aquifer of Long Island, NY, results in high dissolved-iron concentrations that degrade water quality. Geochemical modeling was used to constrain iron-related geochemical processes and redox zonation along a flow path. The observed increase in dissolved inorganic carbon is consistent with the oxidation of sedimentary organic matter coupled to the reduction of O 2 and SO 4 2− in the aerobic zone, and to the reduction of SO 4 2− in the anaerobic zone; estimated rates of CO 2 production through reduction of Fe(III) were relatively minor by comparison. The rates of CO 2 production calculated from dissolved inorganic carbon mass transfer (2.55×10 −4 to 48.6×10 −4 mmol l −1 yr −1) generally were comparable to the calculated rates of CO 2 production by the combined reduction of O 2, Fe(III) and SO 4 2− (1.31×10 −4 to 15×10 −4 mmol l −1 yr −1). The overall increase in SO 4 2− concentrations along the flow path, together with the results of mass-balance calculations, and variations in δ 34S values along the flow path indicate that SO 4 2− loss through microbial reduction is exceeded by SO 4 2− gain through diffusion from sediments and through the oxidation of FeS 2. Geochemical and microbial data on cores indicate that Fe(III) oxyhydroxide coatings on sediment grains in local, organic carbon- and SO 4 2−-rich zones have been depleted by microbial reduction and resulted in localized SO 4 2−-reducing zones in which the formation of iron disulfides decreases dissolved iron concentrations. These localized zones of SO 4 2− reduction, which are important for assessing zones of low dissolved iron for water-supply development, could be overlooked by aquifer studies that rely only on groundwater data from well-water samples for geochemical modeling.

Outdoor air pollution, low birth weight, and prematurity.

This study tested the hypothesis, suggested by several recent reports, that air pollution may increase the risk of adverse birth outcomes. This study analyzed all singleton live births registered by the Czech national birth register in 1991 in 67 districts where at least one pollutant was monitored in 1990-1991 (n = 108,173). Maternal exposures to sulfur dioxide (SO(2)), total suspended particles (TSP), and nitrous oxides (NO(x)) in each trimester of pregnancy were estimated as the arithmetic means of all daily measurements taken by all monitors in the district of birth of each infant. Odds ratios of low birth weight (< 2,500 g), prematurity (< 37 weeks of gestation), and intrauterine growth retardation (IUGR; < 10th percentile of birth weight for gestational age and sex) were estimated by robust logistic regression. The median (and 25th and 75th percentile) trimester exposures were 32 (18, 56) microg/m(3) for SO(2); 72 (55, 87) microg/m(3) for TSP; and 38 (23, 59) microg/m(3) for NO(x). Low birth weight (prevalence 5.2%) and prematurity (prevalence 4.8%) were associated with SO(2) and somewhat less strongly with TSP. IUGR was not associated with any pollutant. The effects on low birth weight and prematurity were marginally stronger for exposures in the first trimester, and were not attenuated at all by adjustment for socioeconomic factors or the month of birth. Adjusted odds ratios of low birth weight were 1.20 [95% confidence interval (CI), 1.11-1.30] and 1.15 (CI, 1.07-1.24) for a 50 microg/m(3) increase in SO(2) and TSP, respectively, in the first trimester; adjusted odds ratios of prematurity were 1.27 (CI, 1.16-1.39) and 1.18 (CI, 1.05-1.31) for a 50 microg/m(3) increase in SO(2) and TSP, respectively, in the first trimester. Low gestational age accounted for the association between SO(2) and low birth weight. These findings provide further support for the hypothesis that air pollution can affect the outcome of pregnancy.

Physiological responses of the lichen Xanthoparmelia mexicana to oxidative stress of SO 2

The objective of present article is to investigate the role and significance of free radicals in the mechanism of injury in the lichen Xanthoparmelia mexicana to SO 2 pollution. At 0.5 ppm SO 2 exposure phaeophytinization of chlorophyll (PQa value) dropped by 10%. Chlorophyll a, b and protein content decreased with the increase of SO 2. The activity of SOD enhanced significantly at 0.5 ppm exposure, but that of POD changed significantly only at 1.5 ppm exposure. GSH dramatically increased with SO 2 concentration. Its relative content elevated 30 and 120% at 0.5 and 1.5 ppm exposures. At all exposures, the content of MDA remained nearly unchanged. The activity of M1PDH was correlated with SO 2 stress intensity. Activity of G6PDH enhanced 130% at 0.5 ppm exposure compared with the control. Similarly, activity of trehalase enhanced 190% at 0.5 ppm exposure. Glucose content declined significantly with SO 2 concentration increased from 0.28 mg g −1 DW of the control to 0.14 mg g −1 DW at 0.5 ppm exposures. These results suggested that the chain injury reaction of oxidative stress could be mechanistically related to the efflux of energy and substrate between the two lichen symbionts, such as the metabolism of mannitol, trehalose and glucose.

Studies on the ion-beam modifications in ethylene diamine sulphate

The growth features, defect sub-structure and the influence of ion implantation on the (001) and (100) surfaces of ethylene diamine sulphate (EDS) single crystals have been studied. The surface micromorphology and defect substructure measurements of surface electrical conductivity and microhardness in both as-grown and He+ ion-implanted surfaces of EDS have also been studied. Optical and scanning electron microscopic investigations on the (001) surface of EDS revealed octogonal mother-liquor inclusions and spiral and hopper growth features. Chemical etching of the (100) surface revealed an increase in dislocation density on ion implantation, the etch pit morphology remaining the same. Studies on planar plastic anisotropy in both (001) and (100) surfaces indicated the crystallographic nature of the single crystal. Enhancement of surface electrical conductivity on ion implantation has been attributed to the formation, migration and increase in SO −4 ion concentration relative to the as-grown EDS surfaces.

Field tracer test for denitrification in a pyrite-bearing schist aquifer

A small-scale artificial tracer test performed on a schist aquifer in Brittany has helped clarify mechanisms and kinetics of in situ autotrophic denitrification. NO 3 was injected as a pulse simultaneously with a conservative tracer -Br −. During the test, which lasted 210 h, 73% of the injected Br − was recovered, as against only 47% of the NO 3. The 26% difference in the recovery of the two injected species is interpreted as being the result of denitrification, in part due to the direct oxidation of pyrite present in the solid aquifer according to the reaction: 5FeS 2+14NO 3 −+4H +→7N 2+10SO 4 2−+5Fe 2++2H 2O, and in part due to subsequent iron oxidation according to the reaction: NO 3 −+5Fe 2++6H +→1/2N 2+5Fe 3++3H 2O. Despite the potential increase in SO 4 and Fe resulting from denitrification through pyrite oxidation, the concentrations of these elements in the groundwater remain moderate due to the precipitation of minerals such as jarosite and/or natroalunite. Tracer transfer takes place in a heterogeneous medium which, according to the breakthrough curves, can be simplified to a dual-porosity aquifer comprising a high-permeability (fractures or large fissures) medium of low porosity from which only minor denitrification of circulating NO 3-bearing water was observed and a low-permeability (small fissures) medium of high porosity which induces a higher denitrification rate in the circulating NO 3-bearing water. The kinetics of the denitrification reaction are high compared with results obtained for other environments and can be described by a first-order model with a half life of 7.9 days for the low-porosity medium and only 2.1 days for the high-porosity medium.

Approche expérimentale par crue artificielle de la participation du réseau hydrographique àl’exportation de phosphore par un petit bassin versant rural

Resume Une crue artificielle est realisee sur un troncon de ruisseau du bassin versant du Mercube (Haute-Savoie, France) afin de rendre compte du role du reseau hydrographique dans la transmission et l’emission de particules et de phosphore. Seul le phosphore d’origine diffuse est concerne. Cette experimentation se deroule en injectant de l’eau naturellement marquee par une teneur elevee en sulfates et chargee de suspensions. Elle met en evidence (1) les zones de stockage et de relargage des matieres en suspension dans le reseau hydrographique, (2) l’importance de l’effet piston sur le renouvellement des eaux en crue et (3) la capture du phosphore soluble au cours du transfert. L’augmentation du debit liee a l’onde de pression met en mouvement les sediments deposes au fond du lit. De ce fait, le phosphore est emis a l’exutoire d’abord lieaux particules remises en suspension, puis associea l’eau injectee. La contribution du reseau hydrographique a l’emission de phosphore n’est pas negligeable. Le meme phenomene se retrouve dans une crue reelle d’intensitecomparable.

Air quality impacts as a result of changes in energy use in China’s Jiangsu Province

Potential changes in air quality associated with increases in SO 2 emissions resulting from industrial growth for Jiangsu Province and the Shanghai Municipality in China are evaluated for the years 1990 (current) and 2010 (future) with a “no further control” scenario. Two long-range transport models are used to estimate airborne concentrations and deposition of SO 2 and sulfate, based on available data on emissions originating from area and major point sources. Modeling results demonstrate how human health and ecological impacts are related to the projected scenario of industrial growth, in terms of the critical level (or concentration) and critical loads. The current approach provides an effective and valuable tool for preliminary assessment of potential impacts of these changes on human health and critical ecosystems in the region for use in integrated energy and environmental risk assessments.

Influence of SO3 on the Phase Relationship in the System CaO–SiO2–Al2O3–Fe2O3

The influence of the additive SO3 on the phase relationships in the quaternary system CaO‐SiO2‐Al2O3‐Fe2O3 was investigated by observing the change of volume ratio of 3CaOSiO2 (C3S) to 2CaOSiO2 (C2S) + CaO (C) in the sintered material with the increase of SO3 content. The primary phase volume of C3S in the quaternary phase diagram shrank with the increase of SO3 and disappeared when the SO3 content exceeded 2.6 wt% in the sintered material. Changes in the peritectic reaction relationship between CaO (C), 2CaOSiO2 (C2S), 3CaOSiO2 (C3S), 3CaOAl2O3 (C3A), 4CaOAl2O3Fe2O3 (C4AF), and liquid were also observed and discussed.

Experimental evidence for in-cloud production of aerosol sulphate

The modification of physical and chemical properties of aerosols passing through clouds has received considerable attention over recent years. Some of these transformations are related to in-cloud chemical reactions, particularly the oxidation of sulphur dioxide (SO 2) to sulphate (SO 4 2−. The Great Dun Fell experiment provided an opportunity to investigate the connection between the chemistry within cloud droplets and the processing of an aerosol population. We have noted significant increases in SO 4 2− in the aerosol population downstream of the cloud compared to the aerosol entering the cloud. These increases are connected to both S(IV) oxidation in the liquid phase and to the entrainment of new air into the cloud, supplying reactants such as H 2O 2 to the system. The addition of SO 4 2− mass to the aerosol is also associated with changes in the NH 4 + aerosol concentrations, possibly as a result of neutralisation of the acidified cloud droplets by NH 3. The study was performed taking into account dynamical mixing of air masses as well as possible sampling artefacts.

Study of modified calcium hydroxides for enhancing SO 2 removal during sorbent injection in pulverized coal boilers

Several modified calcium hydroxides were prepared by lime hydration using NaCl, KCl, calcium lignosulfonate, ethanol-water solutions and combinations of them, to obtain sorbents with enhanced capacity to remove SO 2. The sorbents were characterized in a drop tube reactor in similar conditions to those existing during sorbent injection in pulverized coal boilers. The greatest increases in SO 2 retention were obtained with calcium lignosulfonate as additive or using ethanol-water solutions in the CaO hydration process. The alkali promoters (NaCl and KCl) acted mainly on the product layer diffusivity. Calcium lignosulfonate modified the pore size distribution of the calcined hydrate and decreased the mean particle size of the modified calcium hydroxide by up to five times. The use of ethanol-water solutions during the hydration process decreased the mean particle size of the modified hydrate and improved the porous structure of the calcined hydrate, mainly by increasing the porosity. To combine the favourable effects of these additives, several sorbents were prepared by combinations of them. The best sulfur retentions were obtained with sorbents modified by a combination of calcium lignosulfonate and hydration with ethanol-water solutions. The effect of the combination of additives on the sorbent properties was not the same as that of their action separately, and their effect on sulfur retention was not cumulative.

Decreased Performance of Melasoma lapponica (Coleoptera: Chrysomelidae) Fumigated by Sulphur Dioxide: Direct Toxicity Versus Host Plant Quality

We separated direct and indirect effects of sulphur dioxide on performance of the leaf beetle Melasoma lapponica L. Ramets of naturally growing bushes of Salix borealis (Fries) Nasar., enclosed in plastic chambers, were infested by 1st instars and fumigated with either ambient air or 1 of 4 SO 2 concentrations (100, 200, 500, and 1,000 μg/m 3 ) for 15 d. Simultaneously, larvae that were fed leaves from these chambers were reared outside chambers. Survival of insects grown outside chambers increased or stayed the same with an increase of SO 2 concentration applied to their host individuals, indicating that action of SO 2 from food was neutral or beneficial for insects. Therefore the decrease in survival of insects grown in chambers with an increase of SO 2 concentration was attributed to the direct toxicity of sulphur dioxide. Changes in beetle weight were not significant in both experiments.

The influence of air staging in the reduction of SO 2 by limestone in a fluidized bed combustor

To meet the legislation on limiting NO x and SO x emission from large combustion plants, SO 2 emissions may need to be reduced by about 60–70%. The authors' technique for achieving significant reduction in SO 2 emissions from combustion systems burning large coals utilizes limestone for in situ reduction of SO 2 in fluidized bed combustors. A recent technique for reducing NO x emissions combines staged combustion with ammonia injection. However, concern has arisen about the effect of low primary air:coal ratio (PACR), and hence low bed oxygen levels, on the rate of reaction between calcined limestone and SO 2. This paper reports on the significance of air-staging on the reduction of SO 2 emissions by limestone in a fluidized bed combustor. The experimental rig consisted of a stainless steel combustor 2 m high and 0.3 m 2 in section. Fluidizing air was supplied through a multihole distributor and secondary air was introduced into the freeboard via an injector whose height could be adjusted. The experiments were carried out at overall fluidizing velocities between 1 and 2 m s −1, bed temperatures of 830–880°C, 5–40% excess air levels and bed particle size of 313 + 690 μm. Various levels of air-staging (10–50%) were investigated (equivalent to PACRs of between 0.84 and 1.4, respectively). An uncooled sampling probe located at the cyclone exit was used to determine SO 2. The results showed that SO 2 emissions could be reduced by over 50% using limestone under unstaged combustion conditions. There was little effect of staged combustion on SO x emissions without limestone. When limestone was used, the effectiveness of sulfur capture decreased (by almost 50%) as the level of air-staging was increased. The bed temperature had the most significant effect on sulfur retention by limestone (10% at 880°C to almost 60% at 830°C). A decrease in overall fluidizing velocity resulted in an increase in SO x reduction. The present work has provided significant data on the parameters that influence SO x retention by limestone during staged combustion.

Effect of Ferric Oxide on the High-Temperature Removal of Hydrogen Sulfide over ZnO-Fe2O3 Mixed Metal Oxide Sorbent

The effect of ferric oxide on the removal of hydrogen sulfide over ZnO-Fe{sub 2}O{sub 3} mixed metal oxide sorbents and on the oxidative regeneration of sulfided sorbents was investigated. When ferric oxide was added to the zinc oxide, the reduction of ZnO was retarded by interaction of ZnO with ZnFe{sub 2}O{sub 4}. This interaction was confirmed by larger binding energies of Zn 2P{sub 3/2} and Zn 2P{sub 1/2}, identified by ESCA, of the ZnO-ZnFe{sub 2}O{sub 4} sorbent than those of ZnO. Zinc ferrite with a spinel structure yielded not only high H{sub 2}S removal capacity but also much SO{sub 2} generation. A linear increase of SO{sub 2} generation was confirmed up to 50 wt % Fe{sub 2}O{sub 3}. Resulting from the thermal decomposition of H{sub 2}S over metal sulfides, H{sub 2} generation increased with respect to Fe{sub 2}O{sub 3} according to a quadratic equation. Channeling, caused by sintering during sulfidation, made the flow path of the reactant change and thus pure ZnO sorbent and the sorbent containing 3 wt % Fe{sub 2}O did not sulfurate completely. Addition of Fe{sub 2}O{sub 3} prevented surface structural change like sintering of ZnO during sulfidation.

Modelling seasonal and long-term dynamics of anions in an acid forest soil, Solling, Germany

A deterministic model was applied to simulate soil water chemistry data, collected during an 18-year period in an acid forest soil in Solling, Germany. In this paper, the hydrochemistry of Cl, NO 3 and SO 4 is discussed. Seasonal and long-term variations of Cl concentrations in soil solution were successfully simulated as a result of atmospheric deposition and hydrological processes. The marked increase of SO 4 concentrations at 90 cm depth during the 1970s could be simulated satisfactorily using adsorption equilibrium. Here we assumed that high SO 4 deposition loads in the 1970s entered a soil which had reached a state of near saturation with respect to adsorbed SO 4 in the preceding decades. In the 1980s, measured and simulated SO 4 concentrations at 90 cm depth decreased, due to reduced SO 4 deposition. Modelled resupply of SO 4 to solution by desorption was less than observed, particulary in periods with high water fluxes. In wet periods, when observed N releases from the litter layer were high, simulated N concentrations in litter percolates were lower than observed values. Elevated N concentrations at 90 cm depth occurred when the N-input into the mineral soil exceeded approximately 4 kmol ha −1 yr −1.

Growth responses of N and S deficient white clover and burr medic to SO 2, NO and NO 2

White clover and burr medic plants were exposed to SO 2, NO and NO 2 under conditions of probable nitrogen and sulphur deficiency in open top chambers for 4 h day −1, 7 days week −1 for 149 days to determine if the growth changes in nitrogen and sulphur deficient plants resulting from long term exposure to SO 2 could be ameliorated by NO and NO 2. Burr medic was very sensitive to SO 2, as 80 ppb SO 2 decreased shoot weight by about 70%, and stem length by 30%. The halving of shoot weight of white clover by exposure to 29 ppb NO and NO 2 for 4 h day −1 for 149 days suggests a very high sensitivity to NO and NO 2. Although the unexposed plants were deficient or marginal in sulphur nutrition, exposure to SO 2 did not result in a corresponding improvement in plant growth. This is despite exposure to SO 2 causing a substantial increase in leaf sulphur concentrations, and an improvement in nutrition to adequate or high levels. A linear decrease in shoot weight with increase in SO 2 concentration suggests that the toxic effects of SO 2 overwhelmed any potential beneficial effects. The toxic effects of SO 2 on vegetative growth were found to be additively increased by the additional presence of NO and NO 2. Although they were probably nitrogen-deficient, when the white clover plants were fumigated with NO and NO 2, shoot weight was halved but the rate of sulphur accumulation by leaves was doubled. Nitrogen deficiency may induce partial closure of stomata, but, ironically, the uptake of NO 2 may partially relieve the nitrogen deficiency increasing stomatal conductance, causing enhanced uptake of SO 2 and growth inhibition.

Humex (Humic lake acidification experiment): Chemistry, hydrology, and meteorology

The Humex project is an on-going whole-catchment manipulation project that studies the relationship between humic substances (HS) in soil and water and the acidification processes. The project is based on a dystrophic lake, which is artificially divided into experimental and control halves. This report describes the lake and its catchment and the technical installations used for the artificial acidification of the 1.8 ha terrestrial experimental area and the corresponding 0.9 ha lake. Chemical data from the experimental lake half and the control half are presented, covering a period of 24 months before and 30 months after start of treatment with H 2SO 4 and NH 4NO 3. The results show that dividing the lake into two basins resulted in only small changes in the inorganic water chemistry. The concentration of HS, however, changed due to the difference in the ratio between lake volume and catchment area. The acidification treatment resulted in a 10% increase in ionic strength, mostly due to an increase in SO 4, accompanied by Ca, Mg and Na. There was also a significant increase in the concentrations of NO 3, NH 4, and organic N. The increase in SO 4 and organic N can not be explained only by the amount of chemicals added directly to the lake.

The role of humic substances in the acidification response of soil and water—Results of the Humic Lake Acidification Experiment (HUMEX)

Major results of the Humic Lake Acidification Experiment (HUMEX) are summarized, based on 2 y of pretreatment and 2.5 y of posttreatment data. The major objectives of the HUMEX project are to quantify the role of acid deposition on the properties of humic substances (HS) and the role of humic substances (HS) in the acidification processes that occur in soil and water. The project involves artificial acidification of one half of a divided dystrophic lake and the corresponding catchment. A combination of sulphuric acid and ammonium nitrate has been applied via sprinkler systems, mounted on trees, during precipitation events since 1990. The treatment has resulted in small changes in water quality, including an increase in SO 4, NO 3, and H + concentrations in the lake water and in the soil water of some of the upper soil horizons, and small changes in the nature of the HS. The results of biological studies show increased toxicity in fish, increase in the phytoplankton primary production, and disappearance of some of the dominating species of zooplankton. Epiphytic growth increased in the treated basin, whereas a group of macrophytes was reduced. Present knowledge of the relationships between chemical changes and biological response is not sufficient to explain the observed changes in biota.

Microbial growth and sulphur immobilization following the incorporation of plant residues into soil

The interaction between microbial growth and S immobilization was investigated in an arable soil amended with oil-seed rape (young leaves) and barley straw (1% w/w). Initially, the rape decomposed more rapidly (40 vs 10% by day 5) and produced a larger microbial biomass (990 μg C g −1 soil) than the straw (710 μgCg −1 soil). The biomass in both of the amended soils then decreased to amounts 30–50% higher than those in the unamended soil by day 35 and was maintained at these levels throughout the 195 day incubation. Most of the rape-S (>80%) and straw-S (>60%) added to the soil was released as SO 4 2−-S or converted to biomass-S in 5 days. By this time, the amount of S assimilated by the biomass in the rape-amended soil was three times that found using straw. Biomass-S in both soils then decreased but remained twice as high in the rape-amended soil over the period of 15–195 days. The biomass in the straw amended soil had a similar C:S (85–120:1) to that of the unamended soil but was narrower (40–50:1) in the rape-amended soil. By day 5, SO 4-S in both of the amended soils had increased significantly. The increase in SO 4 2−-S in the rape-amended soil was maintained over the 195 day incubation, suggesting that this S was available for plant uptake. However, by day 15, a net immobilization of soil S by the biomass (25% of soil inorganic S) was found using straw. This immobilized S was retained by the biomass throughout the 195 day incubation and was, therefore, unavailable for plant growth. This suggests that the incorporation of plant residues such as straw which contain low amounts of S may decrease the plant availability of soil S.