Environmental risk appraisement of disinfection by-products (DBPs) in plant model system: Allium cepa

The organic toxicants formed in chlorinated water cause potential harm to human beings, and it is extensively concentrated all over the world. Various disinfection by-products (DBPs) occur in chlorinated water are genotoxic and carcinogenic. The toxicity is major concern for chlorinated DBPs which has been present more in potable water. The purpose of the work was to evaluate genotoxic properties of DBPs in Allium cepa as a plant model system. The chromosomal aberration and DNA laddering assays were performed to examine the genotoxic effect of trichloroacetic acid (TCAA), trichloromethane (TCM), and tribromomethane (TBM) in a plant system with distinct concentrations, using ethyl methanesulfonate (EMS) as positive control and tap water as negative control. In Allium cepa root growth inhibition test, the inhibition was concentration dependent, and EC₅₀ values for trichloroacetic acid (TCAA), trichloromethane (TCM), and tribromomethane (TBM) were 100 mg/L, 160 mg/L, and 120 mg/L respectively. In the chromosome aberration assay, root tip cells were investigated after 120 h exposure. The bridge formation, sticky chromosomes, vagrant chromosomes, fragmented chromosome, c-anaphase, and multipolarity chromosomal aberrations were seen in anaphase–telophase cells. It was noticed that with enhanced concentrations of DBPs, the total chromosomal aberrations were more frequent. The DNA damage was analyzed in roots of Allium cepa exposed with DBPs (TCAA, TCM, TBM) by DNA laddering. The biochemical assays such as lipid peroxidation, H₂O₂ content, ascorbate peroxidase, guaiacol peroxidase, and catalase were concentration dependent. The DNA interaction studies were performed to examine binding mode of TCAA, TCM, and TBM with DNAs. The DNA interaction was evaluated by spectrophotometric and spectrofluorometric studies which revealed that TCAA, TCM, and TBM might interact with Calf thymus DNA (CT- DNA) by non-traditional intercalation manner.

     

Formation of strong airway irritants in a model mixture of (+)-α-pinene/ozone

The airway irritation of (+)-α-pinene, ozone, mixtures thereof, and formaldehyde was evaluated by a mouse bioassay, in which sensory irritation, bronchoconstriction, and pulmonary irritation were measured. The effects are distinguished by analysis of the respiratory parameters. Significant sensory irritation (assessed from reduction of mean respiratory rate) was observed by dynamic exposure of the mice, over a period of 30 min, to a ca. 22 s old reaction mixture of ozone and (+)-α-pinene from a Teflon flow tube. The starting concentrations were 6 ppm and 80 ppm, respectively, which were diluted and let into the exposure chamber. About 10% ozone remained unreacted (0.4 ppm), <0.2 ppm formaldehyde, <0.4 ppm pinonaldehyde, <2 ppm formic acid, and <1 ppm acetic acid were formed. These concentrations, as well as that of the unreacted (+)-α-pinene (51 ppm), were below established no effect levels. The mean reduction of the respiratory rate (30%) was significantly different (p≪0.001) from clean air, as well as from exposure of (+)-α-pinene, ozone, and formaldehyde themselves at the concentrations measured. Addition of the effects of the measured residual reactants and products cannot explain the observed sensory irritation effect. This suggests that one or more strong airway irritants have been formed. Therefore, oxidation reactions of common naturally occurring unsaturated compounds (e.g., terpenes) may be relevant for indoor air quality.     

Development and characterization of cell line from the gill tissue of Catla catla (Hamilton, 1822) for toxicological studies

Catla gill cell line (ICG) was established from gill tissue of Indian major carp (Catla catla), a freshwater fish cultivated in India. The cell line was maintained in Leibovitz’s L-15 supplemented with 10% fetal bovine serum. These cells have been sub-cultured more than 55 passages over a period of 2 years. The ICG cell line consists predominantly of epithelial-like cells. The cells were able to grow at a wide range of temperatures from 24 °C to 32 °C with an optimum temperature of 28 °C. The growth rate of gill cells increased as the fetal bovine serum (FBS) proportion increased from 2% to 20% at 28 °C with optimum growth at the concentrations of 10% or 15% FBS. Amplification of mitochondrial gene 12s rRNA using primers specific to C. catla confirmed the origin of this cell line from C. catla. The cells were successfully cryopreserved and revived at passage numbers 25, 35, 45 and 55. The cytotoxicity of three metal salts (ZnCl₂, CuSO₄ and CdCl₂) was assessed in ICG cell line using multiple endpoints such as MTT, Neutral Red assay, Alamar Blue assay and Coomassie Blue protein assay. Acute toxicity assay on fish were conducted by exposing C. catla for 96 h to three metal salts under static conditions. Statistical analysis revealed good correlation with r² = 0.908–0.985 for all combinations between endpoints employed. Linear correlations between each in vitro EC₅₀ and the in vivo LC₅₀ data were highly significant.     

Mutagenicity and genotoxicity assessment of industrial wastewaters

The genotoxicity of industrial wastewaters from Jajmau (Kanpur), was carried out by Ames Salmonella/microsome test, DNA repair-defective mutants, and Allium cepa anaphase–telophase test. Test samples showed maximum response with TA98 strain with and without metabolic activation. Amberlite resins concentrated wastewater samples were found to be more mutagenic as compared to those of liquid–liquid extracts (hexane and dichloromethane extracts). The damage in the DNA repair defective mutants in the presence of Amberlite resins concentrated water samples were found to be higher to that of liquid–liquid-extracted water samples at the dose level of 20 μl/ml culture. Among all the mutants, polA exhibited maximum decline with test samples. Mitotic index (MI) of root tip meristematic cells of A. cepa treated with 5, 10, 25, 50, and 100 % (v/v) wastewaters were significantly lower than the control. Complementary to the lower levels of MI, the wastewaters showed higher chromosomal aberration levels in all cases investigated.     

An insight into the influence of low dose irradiation pretreatment on the microbial decolouration and degradation of Reactive Red-120 dye

The influence of low dose irradiation pretreatment on the microbial decolouration and degradation of Reactive Red-120 (RR-120) dye was investigated in detail by using Pseudomonas sp. SUK1. About 27%, 56% and 66% decolouration of 150 ppm RR-120 dye solution was observed by applying 0, 0.5 and 1 kGy doses, respectively, in the first step followed by microbial treatment for 24 h under static condition. Similarly, about 70%, 88% and 90% TOC removal was observed by applying 0, 0.5 and 1 kGy doses, respectively, in the first step followed by the microbial treatment for 96 h under static condition. The radiation induced fragmented products of RR-120 at doses of 0.5 and 1 kGy were investigated by FTIR and electrospray ionization-MS analysis. The induction of the enzymes viz. laccase, tyrosinase, azoreductase and NADH-2,6-dichlorophenol indophenol reductase was studied in the decolourised solution obtained after irradiating 150 ppm RR-120 dye solution with 0 and 1 kGy doses followed by the microbial treatment for 96 h under static condition. The enzymatic degradation products were studied by FTIR, HPLC and GC–MS. The toxicity study of the treated dye solution on plants revealed the degradation of RR-120 into non-toxic products by combined radiation-microbial treatment. This study explores a reliable and promising way to use industrially viable dose (?1 kGy) and microbial strain viz. Pseudomonas sp. SUK1 for permissible safe disposal of dye solutions from textile industries.     

Ozone response to precursor controls: comparison of data analysis methods with the predictions of photochemical air quality simulation models

Comparisons were made between the predictions of six photochemical air quality simulation models (PAQSMs) and three indicators of ozone response to emission reductions: the ratios of O₃/NO_z and O₃/NO_y and the extent of reaction. The values of the two indicator ratios and the extent of reaction were computed from the model-predicted mixing ratios of ozone and oxidized nitrogen species and were compared to the changes in peak 1 and 8 h ozone mixing ratios predicted by the PAQSMs. The ozone changes were determined from the ozone levels predicted for base-case emission levels and for reduced emissions of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x). For all simulations, the model-predicted responses of peak 1 and 8 h ozone mixing ratios to VOC or NO_x emission reductions were correlated with the base-case extent of reaction and ratios of O₃/NO_z and O₃/NO_y. Peak ozone values increased following NO_x control in 95% (median over all simulations) of the high-ozone (>80 ppbv hourly mixing ratio in the base-case) grid cells having mean afternoon O₃/NO_z ratios less than 5 : 1, O₃/NO_y less than 4 : 1, or extent less than 0.6. Peak ozone levels decreased in response to NO_x reductions in 95% (median over all simulations) of the grid cells having peak hourly ozone mixing ratios greater than 80 ppbv and where mean afternoon O₃/NO_z exceeded 10 : 1, O₃/NO_y was greater than 8 : 1, or extent exceeded 0.8. Ozone responses varied in grid cells where O₃/NO_z was between 5 : 1 and 10 : 1, O₃/NO_y was between 4 : 1 and 8 : 1, or extent was between 0.6 and 0.8. The responses in such grid cells were affected by ozone responses in upwind grid cells and by the changes in ozone levels along the upwind boundaries of the modeling domains.     

Organochlorine pesticide residues in maternal blood,cord blood,placenta, and breastmilk and their relation to birth size

There is a growing concern that persistent organic pollutants like organochlorine pesticides (OCPs) can impair fetal growth and affect birth size. However, currently available epidemiological evidence is inconclusive. In this case-control study, we examined the association between exposure to hexachlorocyclohexane (HCH) and its isomers (α-HCH, β-HCH and γ-HCH), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) and birth size. We recruited 60 infant-mother pairs, comprising of 30 term, small for gestational age babies with their mothers (Case group), and another 30 term, appropriate for gestational age babies with their mothers (Control group). This study was conducted in a tertiary hospital in Delhi, India, between March, 2009 and February 2010. Organochlorine pesticides were estimated in maternal blood, cord blood, placenta and breastmilk samples, using gas–liquid chromatography. Transplacental and transmammary transfer of OCPs was assessed by correlating the maternal blood OCP levels with those in cord blood and breastmilk by simple linear regression. The birthweight, crown heel length, head circumference, mid-arm circumference and ponderal index of the neonates was correlated with OCP levels in the maternal blood, cord blood, placenta and breastmilk. The OCP estimates were compared between samples of the case and control group. There was a significant (P < 0.001) transplacental transfer of all OCPs, however the transmammary transfer was insignificant for most OCPs except α-HCH. The OCP levels in the case group were higher than the control group; these were significantly more for t-HCH in cord blood and breastmilk; β-HCH in maternal blood, cord blood and breastmilk; DDE in placenta and DDT in breastmilk. There was a significant negative correlation between birthweight and t-HCH levels in maternal blood (P = 0.022), cord blood (P < 0.001), placenta (P = 0.008) and breastmilk (P = 0.005); β-HCH in cord blood (P < 0.001) and placenta (P = 0.020); γ-HCH in placenta (P = 0.045); and DDT (P = 0.009). Length at birth had a significant negative correlation with t-HCH in cord blood (P = 0.014) and breastmilk (P < 0.001); β-HCH in cord blood (P = 0.016) and breastmilk (P = 0.012); DDE in placenta (P = 0.016); and DDT in breastmilk (P = 0.006). Similarly, OCP levels were also found to be negatively correlated with head circumference, ponderal index and chest circumference in neonates. We conclude that prenatal exposure to some OCPs could impair the anthropometric development of the fetus, reducing the birthweight, length, head circumference, chest circumference and ponderal index.     

Emissions of PCDD/Fs,PCBs, and PAHs from legacy on-road heavy-duty diesel engines

Exhaust emissions of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxin/furan (PCDD/F) congeners, tetra–octa PCDD/F homologues, 12 WHO 2005 polychlorinated biphenyl (PCB) congeners, mono–nona chlorinated biphenyl homologues, and 19 polycyclic aromatic hydrocarbons (PAHs) from three legacy diesel engines were investigated. The three engines tested were a 1985 model year GM 6.2 J-series engine, a 1987 model year Detroit Diesel Corporation 6V92 engine, and a 1993 model year Cummins L10 engine. Results were compared to United States’ mobile source inventory for on-road diesel engines, as well as historic and modern diesel engine emission values. The test fuel contained chlorine at 9.8 ppm which is 1.5 orders of magnitude above what is found in current diesel fuel and 3900 ppm sulfur to simulate fuels that would have been available when these engines were produced. Results indicate PCDD/F emissions of 13.1, 7.1, and 13.6 pg International Toxic Equivalency (I-TEQ) L⁻¹ fuel consumed for the three engines respectively, where non-detects are equal to zero. This compares with a United States’ mobile source on-road diesel engine inventory value of 946 pg I-TEQ L⁻¹ fuel consumed and 1.28 pg I-TEQ L⁻¹ fuel consumed for modern engines equipped with a catalyzed diesel particle filter and urea selective catalytic reduction. PCB emissions are 2 orders of magnitude greater than modern diesel engines. PAH results are representative of engines from this era based on historical values and are 3–4 orders of magnitude greater than modern diesel engines.     

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate,n-butyl acrylate,methyl methacrylate and ethyl methacrylate

The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO₃ radicals with a series of acrylate esters: ethyl acrylate (k₁), n-butyl acrylate (k₂), methyl methacrylate (k₃) and ethyl methacrylate (k₄) at 298 ± 1 K and 760 Torr. The obtained rate constants are k₁ = (1.8 ± 0.25) × 10^?16 cm³ molecule^?1 s^?1, k₂ = (2.1 ± 0.33) × 10^?16 cm³ molecule^?1 s^?1, k₃ = (3.6 ± 1.2) × 10^?15 cm³ molecule^?1 s^?1, k₄ = (4.9 ± 1.7) × 10^?15 cm³ molecule^?1 s^?1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO₃ radicals. In addition, the atmospheric lifetimes of the compound against NO₃ attack are estimated and the results show that NO₃ reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.     

The effects of evaporating essential oils on indoor air quality

Essential oils, predominantly comprised of a group of aromatic chemicals, have attracted increasing attention as they are introduced into indoor environments through various forms of consumer products via different venues. Our study aimed to characterize the profiles and concentrations of emitted volatile organic compounds (VOCs) when evaporating essential oils indoors. Three popular essential oils in the market, lavender, eucalyptus, and tea tree, based on a nation-wide questionnaire survey, were tested. Specific aromatic compounds of interest were sampled during evaporating the essential oils, and analyzed by GC-MS. Indoor carbon monoxide (CO), carbon dioxide (CO₂), total volatile organic compounds (TVOCs), and particulate matters (PM₁₀) were measured by real-time, continuous monitors, and duplicate samples for airborne fungi and bacteria were collected in different periods of the evaporation. Indoor CO (average concentration 1.48 vs. 0.47 ppm at test vs. background), CO₂ (543.21 vs. 435.47 ppm), and TVOCs (0.74 vs. 0.48 ppm) levels have increased significantly after evaporating essential oils, but not the PM₁₀ (2.45 vs. 2.42 ppm). The anti-microbial activity on airborne microbes, an effect claimed by the use of many essential oils, could only be found at the first 30–60 min after the evaporation began as the highest levels of volatile components in these essential oils appeared to emit into the air, especially in the case of tea tree oil. High emissions of linalool (0.092–0.787 mg m⁻³), eucalyptol (0.007–0.856 mg m⁻³), d-limonene (0.004–0.153 mg m⁻³), ρ-cymene (0.019–0.141 mg m⁻³), and terpinene-4-ol-1 (0.029–0.978 mg m⁻³), all from the family of terpenes, were observed, and warranted for further examination for their health implications, especially for their potential contribution to the increasing indoor levels of secondary pollutants such as formaldehyde and secondary organic aerosols (SOAs) in the presence of ozone.     

Effect of DTPA on Cd solubility in soil – Accumulation and subsequent toxicity to lettuce

In a controlled environment experiment, using Cd spiked soil, lettuce plants were grown under a range of DTPA levels and were subsequently harvested to determine levels of phytoaccumulation. Cadmium phytoaccumulation significantly increased with increasing soil Cd level (P < 0.05) but unexpectedly decreased with increasing DTPA levels, despite the fact that solubility of Cd was increased in the soil. Cadmium translocation (from root to shoot) increased after DTPA application. Lettuce growth was inhibited by both Cd and DTPA (at and above 10 and 500 mg kg^?1 respectively), as a result of higher Cd mobility and subsequent toxicity which was caused by DTPA higher dosages. Metal solubility in the soil (ranged between 2.8 and 26.5 mg kg^?1) was found to be significantly higher (P < 0.01) as compared to control with increasing DTPA levels even after 3 months of DTPA application. Cadmium tissue concentration in all DTPA treatments was less than in the corresponding control treatment, indicating a negative effect of DTPA application on Cd uptake. In conclusion, lettuce was an unsuitable plant species for Cd accumulation, at least when associated with a DTPA chelator.     

Distribution and relationships of As,Cd, Pb and Hg in freshwater fish from five French fishing areas

The concentrations of arsenic, cadmium, mercury and lead in 149 muscle samples of eight freshwater fish species (European eel, bream, common carp, European catfish, roach, perch, pike and pikeperch) from five different French fishing areas from contaminated and control sites were measured by inductively coupled plasma mass spectrometry after microwave digestion under pressure. No significant correlation was found between the condition factor (CF), based on the length–mass relationship, and As, Cd and Pb levels in all the samples analysed, but a positive correlation was detected between CF and Hg levels (P < 0.0001, R = 0.49). Positive correlations with body length were only found for Hg in roach (P < 0.05, R = 0.32) and Pb in bream (P < 0.05, R = 0.48) and correlations with both body weight and length were also found for Hg in pike (P < 0.05, R = 0.90 and 0.86) and Cd in European eel (P < 0.01, R = ?0.35 and ?0.37). The average content and the standard deviation in fish muscle samples was 0.007 ± 0.012, 0.102 ± 0.077, 0.142 ± 0.097 and 0.035 ± 0.053 mg kg^?1 of wet mass for Cd, As, Hg and Pb, respectively. Significant differences were established between groups of predatory fish and non-predatory fish for Hg and Pb, and between control and contaminated sites in the whole selection and also within feeding guilds, i.e. the values of Hg in the benthophagic fish were significantly different between these sites. Finally, these results were also compared for each species with previous French and European studies.     

In vitro biotransformation of PBDEs by root crude enzyme extracts: Potential role of nitrate reductase (NaR) and glutathione S-transferase (GST) in their debromination

In order to investigate the enzyme transformation of PBDEs and to track the key enzymes involved in PBDE degradation in plants, in vivo exposure of plants of ryegrass, pumpkin and maize and in vitro exposure of their root crude enzyme extracts to PBDEs were conducted. Degradation of PBDEs in the root crude enzyme solutions fit well with the first order kinetics (R² = 0.52–0.97, P < 0.05), and higher PBDEs degraded faster than the lower ones. PBDEs could be transformed to lower brominated PBDEs and hydroxylated-PBDEs by the root crude enzyme extracts with debromination as the main pathway which contributed over 90% of PBDE depletion. In vitro and in vivo exposure to PBDEs produced similar responses in root enzyme activities of which the nitroreductase (NaR) and glutathione-transferase (GST) activities decreased significantly, while the peroxidase, catalase and cytochrome P-450 activities had no significant changes. Furthermore, higher enzyme concentrations of NaR and GST led to higher PBDE debromination rates, and the time-dependent activities of NaR and GST in the root crude enzyme extracts were similar to the trends of PBDE depletion. All these results suggest that NaR and GST were the key enzymes responsible for PBDE degradation. This conclusion was further confirmed by the in vitro debromination of PBDEs with the commercial pure NaR and GST.     

Ultrafine particles near a major roadway in Raleigh,North Carolina: Downwind attenuation and correlation with traffic-related pollutants

Ultrafine particles (UFPs, diameter < 100 nm) and co-emitted pollutants from traffic are a potential health threat to nearby populations. During summertime in Raleigh, North Carolina, UFPs were simultaneously measured upwind and downwind of a major roadway using a spatial matrix of five portable industrial hygiene samplers (measuring total counts of 20–1000 nm particles). While the upper sampling range of the portable samplers extends past the defined “ultrafine” upper limit (100 nm), the 20–1000 nm number counts had high correlation (Pearson R = 0.7–0.9) with UFPs (10–70 nm) measured by a co-located research-grade analyzer and thus appear to be driven by the ultrafine range. Highest UFP concentrations were observed during weekday morning work commutes, with levels at 20 m downwind from the road nearly fivefold higher than at an upwind station. A strong downwind spatial gradient was observed, linearly approximated over the first 100 m as an 8% drop in UFP counts per 10 m distance. This result agreed well with UFP spatial gradients estimated from past studies (ranging 5–12% drop per 10 m). Linear regression of other vehicle-related air pollutants measured in near real-time (10-min averages) against UFPs yielded moderate to high correlation with benzene (R² = 0.76), toluene (R² = 0.49), carbon monoxide (R² = 0.74), nitric oxide (R² = 0.80), and black carbon (R² = 0.65). Overall, these results support the notion that near-road levels of UFPs are heavily influenced by traffic emissions and correlate with other vehicle-produced pollutants, including certain air toxics.     

Fate of caffeine in mesocosms wetland planted with Scirpus validus

Uptake, accumulation and translocation of caffeine by Scirpus validus grown in hydroponic condition were investigated. The plants were cultivated in Hoagland’s nutrient solution spiked with caffeine at concentrations of 0.5–2.0 mg L^?1. The effect of photodegradation on caffeine elimination was determined in dark controls and proved to be negligible. Removal of caffeine in mesocosms without plants showed however that biodegradation could account for about 15–19% of the caffeine lost from solutions after 3 and 7 d. Plant uptake played a significant role in caffeine elimination. Caffeine was detected in both roots and shoots of S. validus. Root concentrations of caffeine were 0.1–6.1 μg g^?1, while the concentrations for shoots were 6.4–13.7 μg g^?1. A significant (p < 0.05) positive correlation between the concentration in the root and the initial concentrations in the nutrient solution was observed. The bioaccumulation factors (BAFs) of caffeine for roots ranged from 0.2 to 3.1, while BAFs for shoots ranged from 3.2 to 16.9. Translocation from roots to shoots was the major pathway of shoot accumulation. The fraction of caffeine in the roots as a percentage of the total caffeine mass in solution was limited to 0.2–4.4% throughout the whole experiment, while shoot uptake percentage ranged from 12% to 25% for caffeine at the initial concentration of 2.0 mg L^?1 to 50–62% for caffeine at the initial concentration of 0.5 mg L^?1. However, a marked decrease in the concentration of caffeine in the shoots between d-14 and d-21 suggests that caffeine may have been catabolized in the plant tissues subsequent to plant uptake and translocation.     

Ecotoxicity of xanthene dyes and a non-chlorinated bisphenol in soil

Soil eco-toxicity testing was conducted in support of Canada’s Chemical Management Plan (CMP) to fill data gaps for organic chemicals known to primarily partition to soil, and of which the persistence and inherent toxicity are uncertain. Two compounds representative of specific classes of chemicals: non-chlorinated bisphenols containing an –OH group (4,4′-methylenebis(2,6-di-tert-butylphenol (Binox)) and xanthene dyes (2′,4′,5′,7′-tetrabromo-4,5,6,7-tetrachloro-3′,6′-dihydroxy-, disodium salt (Phloxine B), 2′,4′,5’,7′-tetrabromofluorescein (TBF), 4′,5′-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF)) were evaluated. The effect of these substances on plant growth (Elymus lanceolatus and Trifolium pratense) and soil invertebrate survival and reproduction (Folsomia candida and Eisenia andrei) were assessed using a field-collected sandy soil. Binox was persistent throughout testing (up to 63 d) with an average recovery of 77 ± 2.9% at test end. Binox was not toxic to plants (IC50s > 1076 mg kg^?1) or E. andrei (IC50s > 2651 mg kg^?1); however, a significant reduction in F. candida adult survival and reproduction (IC50 = 89 (44–149) mg kg^?1) was evident. Phloxine B was also persistent throughout testing, with an average recovery of 82 ± 3.0% at test end. Phloxine B was significantly more toxic than Binox, with significant reductions in plant root growth (IC50s ? 11 mg kg^?1) and invertebrate reproduction (IC50s ? 22 mg kg^?1). DBF toxicity was not significantly different from that of Phloxine B for plant root growth (IC50s ? 30 mg kg^?1), but was significantly less toxic for shoot growth (IC50s ? 1758 mg kg^?1), and invertebrate adult survival (IC50s ? 2291 mg kg^?1) and reproduction (IC50s ? 451 mg kg^?1). A comparison between all four xanthene dyes was completed using F. candida, with the degree of toxicity in the order of Phloxine B ? TBF ～ DBF > TCF. The results from these studies will contribute to data gaps for poorly understood chemicals (and chemical groupings) under review for environmental risk assessments, and will aid in the validation of model predictions used to characterize the fate and effects of these substances in soil environments.     

Gas-phase chemistry of benzyl alcohol: Reaction rate constants and products with OH radical and ozone

A bimolecular rate constant, k_{OH+Benzyl alcohol}, of (28 ± 7) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with benzyl alcohol, at (297 ± 3) K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, k_{O3+Benzyl alcohol}, of approximately 6 × 10^?19 cm³ molecule^?1 s^?1 was determined by monitoring the decrease in benzyl alcohol concentration over time in an excess of ozone (O₃). To more clearly define part of benzyl alcohol's indoor environment degradation mechanism, the products of the benzyl alcohol + OH were also investigated. The derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to positively identify benzaldehyde, glyoxal and 4-oxopentanal as benzyl alcohol/OH reaction products. The elucidation of other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible benzyl alcohol/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms.     

Nitrous oxide emissions from mineral and organic soils of a Norway spruce stand in South–West Germany

Due to the high temporal and spatial variability of N₂O fluxes, estimates of N₂O emission from temperate forest ecosystems are still highly uncertain, particularly at larger scales. Although highest N₂O emissions with up to 7.0 kg N ha⁻¹ yr⁻¹ were mainly reported for soils affected by stagnant water, most of the reported gas flux measurements were performed at forest sites with well-aerated soils yielding mostly to low mean annual emission rates less than 1.0 kg N ha⁻¹ yr⁻¹. This study compares N₂O fluxes from upland (Cambisols) and temporally water-logged (Gleysols, Histosols) soils of the Central Black Forest (South-West Germany) over a period of 2 yr. Mean annual N₂O fluxes from investigated soils ranged between 0.2 and 3.9 kg N ha⁻¹ yr⁻¹. The fluxes showed a large variability between the different soil types. Emissions could be clearly ranked in the following order: Cambisols (0.26–0.75 kg N ha⁻¹ yr⁻¹)<Gleysols (1.37–2.68 kg N ha⁻¹ yr⁻¹)<Histosol (3.66–3.95 kg N ha⁻¹ yr⁻¹). Although the Cambisols cover two-thirds of the investigated area, only about half of the overall N₂O is emitted from this soil type. Therefore, regional or national N₂O fluxes from temperate forest soils are underestimated if soils characterised by intermediate aeration conditions are disregarded.     

Dechlorination of hexachlorobenzene using lead–iron bimetallic particles

Synthesized lead–iron (Pb/Fe) bimetallic particles were applied to dechlorinate hexachlorobenzene (HCB) under various conditions (e.g. bimetal amount, initial pH value, reaction temperature, and reaction duration). The results showed that adding Pb onto Fe benefited the dechlorination of HCB and the bimetal with 1.4% Pb content performed best. The degradation rate decreased regularly as the initial pH value of the aqueous increased from 1.9 to 11.1 except for pH 7.0 where the fastest dechlorination rate emerged. The dechlorination could be enhanced by increasing the amount of Pb/Fe or the reaction temperature. The dechlorination ratio of HCB within 15 min increased from 24.3% to 81.3% when Pb/Fe amount increased from 0.1 g to 0.8 g. The dechlorination followed pseudo-first-order kinetics, and the dechlorination rate constants were 0.0027, 0.0064, 0.0157, and 0.0321 min^?1 at 25, 50, 70, and 85 °C, respectively, and the activation energy (E_a) of the dechlorination by Pb/Fe was 37.86 kJ mol^?1.     

Trace gas variations at Cape Point,South Africa,during May 1997 following a regional biomass burning episode

During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO₂, CO, CH₄ and O₃ amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl₄ and CH₃CCl₃) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm⁻² and from 2.3 to 1.3 mW cm⁻², respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH₄ relative to CO₂ mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH₄ the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH₄) have been obtained for the C₂–C₃ hydrocarbons (e.g. ethene at 229.3 ppt ppb⁻¹), whilst the C₄–C₇ hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb⁻¹).