A 250 ha agricultural catchment has been characterized with respect to its hydrogeology and groundwater contamination by pesticides from October 1999 to August 2004. Five years after the ending of atrazine (At) application, used since the sixties, At and deethylatrazine (DEA) are still systematically quantified at the outlet of the watershed with concentrations from 0.07 to 0.43 microg l(-1) for At, and between 0.14 and 1.16 microg l(-1) for DEA. Isoproturon and chlortoluron are detected in only one (0.3 microg l(-1)) and two (0.7 and 2.0 microg l(-1)) of the 124 semi-monthly samples, respectively. DEA concentrations can be very different between two samples with a 15-day time step. The annual mean exported fluxes of cumulated At and DEA are stable, which indicates a long time transfer in the unsaturated or saturated zone with a progressive leaching of the stock of At and DEA probably accumulated in the soil and the vadose zone. These fluxes, between 0.90% and 2.82% of the annual mean dose of At applied before 1999, similar to those calculated in several studies at the bottom of the root zone, could be explained by low adsorption and degradation properties of At and DEA in the unsaturated and saturated zone. 相似文献
The exposure to benzene, toluene, xylenes and total hydrocarbons among 25 individuals exposed to exhaust from a snowmobile equipped with a two-stroke engine has been evaluated. Sampling was performed by pumped and diffusive sampling in parallel. There was a relatively bad agreement between the two air-sampling methods. The bad agreement can in part be explained by back diffusion of the substances from the samplers, a high face velocity, and deposition of droplets of unburned gasoline onto or in the vicinity of the samplers.
The levels of benzene ranged from not detectable (0.01 mg m−3) to 2.5 mg m−3. For toluene, xylenes and total hydrocarbons the exposure was 0.10–12.0, 0.05–13.0 and 0.90–273 mg m−3 respectively. The result from two measurements on individuals travelling on an open sleigh at the rear of the vehicle indicated higher levels of benzene, 0.7–0.8 mg m−3. Children are often riding as a passenger on a sledge and may thus have a higher exposure than their parents. This study indicates that spare time driving a snowmobile may cause a considerable exposure to benzene. Using a four-stroke engine equipped with a catalyst could reduce the exposure. To reduce the exposure for the passenger on a sleigh an extension of the exhaust pipe may be effective. 相似文献
Background, Aims and Scope Polycyclic Aromatic Hydrocarbons (PAHs) are known for their adverse and cumulative effects at low concentration. In particular,
the PAHs accumulate in sewage sludge during wastewater treatment, and may thereafter contaminate agricultural soils by spreading
sludge on land. Therefore, sludge treatment processes constitute the unique opportunity of PAH removal before their release
in the environment. In this study, the ability of aerobic microorganisms to degrade light and heavy PAHs was investigated
in continuous bioreactors treating trace-level PAH-contaminated sludge.
Methods Several aerobic reactors were operated under continuous and perfectly mixed conditions to simulate actual aerobic sludge
digesters. Three sterile control reactors were performed at 35°C, 45°C or 55°C to assess PAH abiotic losses under mesophilic
and thermophilic conditions. Three biological reactors were also operated at 35°C, 45°C or 55°C. Furthermore, 250 mM methanol
were added in an additional mesophilic reactor (35°C). All reactors were fed with long-term PAH-contaminated sewage sludge,
and PAH removal was assessed by inlet/outlet mass balance. In this study, PAH compounds ranged from 2 to 5-unsubstituted aromatic
rings, i.e. respectively from Fluorene to Indeno(123cd)pyrene.
Results and Discussion Significant abiotic losses were observed for the lightest PAHs (fluorene, phenanthrene and anthracene), while biodegradation
occurred for all PAHs. More than 80% of the lightest PAHs were removed. Biodegradation rates inversely correlated with the
increasing molecular weight, and seemed limited by the low bioavailability of the heaviest PAHs (only 50% of removal). The
enhancement of PAH bioavailability by increasing the process temperature or adding methanol was tested. A temperature increase
from 35°C to 45°C and then to 55°C significantly enhanced the biodegradation of the heaviest PAHs from 50% to 80%. However,
high abiotic losses were observed for all PAHs at 55°C, which was attributed to volatilization. Optimal conditions were found
at 45°C considering the low abiotic losses and the high PAH biodegradation rates. Similar performances were achieved by addition
of methanol in the sludge. It was concluded that increasing temperatures or addition of methanol favored PAH diffusion from
solids to an aqueous compartment, and enhanced their bioavailability to PAH-degrading microorganisms.
Conclusion In this study, the use of long-term acclimated aerobic ecosystems showed the high potential of aerobic microorganisms to
degrade a wide range of PAHs at trace levels. However, PAH biodegradation was likely controlled by their low bioavailability.
Two aerobic processes have been finally proposed to achieve efficient decontamination of sewage sludge, at 45°C or in the
presence of methanol. The PAH concentrations in reactor outlet were lower than the French requirements, and allow the treated
sludge to be spread on agricultural land.
Recommendations and Outlook The two proposed aerobic processes used physical or chemical diffusing agents. The global ecological impact of using the
latter agents for treating trace level contamination must be considered. Since methanol was completely removed during the
process, no additional harm is expected after treatment. However, an increase of temperature to 45°C could drastically increase
the energy demand in full-scale plants, and therefore the ecological impact of the process. Moreover, since bioavailability
controls PAH biodegradation, efficiency of the processes could also be influenced by the hydraulic parameters, such as mixing
and aeration rates. Further experimentations in a pilot scale are therefore recommended, as well as a final assessment of
the global environmental benefit of using such aerobic processes in the bioremediation of trace level compounds.
- Abbreviations (PAHs): Ant – anthracene; B(a)A – benzo(a)anthracene ; B(b)F – benzo(b)fluoranthene; B(k)F – benzo(k)fluoranthene;
B(ghi)P – benzo(g,h,i)perylene; B(a)P – benzo(a)pyrene; Chrys – chrysene; DB – dibenzo(a,h)anthracene; Fluor – fluoranthene;
Fluo - fluorene; Ind – indeno(1,2,3-c,d)pyrene; Phe - phenanthrene; Pyr – pyrene
- * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on 'Chemistry and Environment', 29 August
to 1 September 2004, Bordeaux, France. 相似文献
Groundwater remediation technologies, such as pump-and-treat (PTS) and funnel-and-gate systems (FGS), aim at reducing locally appearing contaminations. Therefore, these methodologies are basically evaluated with respect to their capability to yield local improvements of an environmental situation, commonly neglecting that their application is also associated with secondary impacts. Life cycle assessment (LCA) represents a widely accepted method of assessing the environmental aspects and potential impacts related to a product, process or service. This study presents the set-up of a LCA framework in order to compare the secondary impacts caused by two conceptually different technologies at the site of a former manufactured gas plant in the city of Karlsruhe, Germany. As a FGS is already operating at this site, a hypothetical PTS of the same functionality is adopted. During the LCA, the remediation systems are evaluated by focusing on the main technical elements and their significance with respect to resource depletion and potential adverse effects on ecological quality, as well as on human health. Seven impact categories are distinguished to address a broad spectrum of possible environmental loads. A main point of discussion is the reliability of technical assumptions and performance predictions for the future. It is obvious that a high uncertainty exists when estimating impact specific indicator values over operation times of decades. An uncertainty analysis is conducted to include the imprecision of the underlying emission and consumption data and a scenario analysis is utilised to contrast various possible technological variants. Though the results of the study are highly site-specific, a generalised relative evaluation of potential impacts and their main sources is the principle objective rather than a discussion of the calculated absolute impacts. A crucial finding that can be applied to any other site is the central role of steel, which particularly derogates the valuation of FGS due to the associated emissions that are harmful to human health. In view of that, environmental credits can be achieved by selecting a mineral-based wall instead of sheet piles for the funnel construction and by minimising the steel consumption for the gate construction. Granular activated carbon (GAC) is exclusively considered as the treatment material, both in-situ and on-site. Here it is identified as an additional main determinant of the relative assessment of the technologies since it is continuously consumed. 相似文献