Toxicity of tire debris leachates

Data on the indicators of environmental impact of tire debris, originated from the tire abrasion on roads, are extremely scarce, while it is well known that tires may produce deleterious effects. Tire debris contains significant quantities of zinc (Zn) which may be released by tire rubber. We have used tire particles (TD) produced in laboratory from new rubber. Two sets of experiments were set up to obtain eluates. One set used 50 and 100 g/L TD to produce eluates at pH 3-7. The Zn quantity was measured with a Inductively Coupled Plasma-Atomic Emission Spectrometry. The eluates at 1%,10%,50%,100% concentrations in culture media were tested on Raphidocelis subcapitata, Daphnia magna and Xenopus laevis embryos (FETAX test). The other set of experiments was performed putting 250 mg/L TD in a column with glass beads to control particle dispersion during the elution process. We demonstrate that factors such as pH, size and particles aggregation deeply influence the elution process, that the amount of Zn leached from particles is related to their aggregation rather than their quantity. These results, even though do not reflect the real environmental toxicity of the leachates, can be successfully used for comparative purposes allowing an initial assessment of the potential effect of tire derived particles.     

Tire debris organic extract affects Xenopus development

Tire debris (TD) and its organic components were identified as a main source of PM10 atmospheric and water pollution. Because few data are available on the embryotoxic effects of TD organic components, the lethal and teratogenic potential of tire debris organic extract (TDOE) was evaluated using the frog embryo teratogenesis assay-Xenopus (FETAX), coupled with a histopathological screening of the survived larvae. From stage 8 to stage 47, Xenopus laevis embryos were exposed to TDOE at concentrations of 50, 80, 100, 120 and 140 mg/L. The results showed 50 mg/L TDOE to be the non-observable effect concentration (NOEC). TDOE mortality at 80 mg/L was significantly higher than the control, but did not increase further with higher concentrations. A good concentration-response was observed for percentages of malformed larva and from 80 mg/L on these percentages were significantly higher than the control. Therefore, probit analysis gave a 144.6 mg/L TC50. At 120 and 140 mg/L, many larvae were plurimalformed. The most frequent alterations observed were abnormal gut coiling, microphthalmia, monolateral anophthalmia, and narrowing eyes. The histological screening mainly revealed ocular malformations such as double retina, retina nervous cell layer coiling, and altered lens. Moreover severe vacuolisation and necrosis were scored in liver and axial musculature. These results strongly support the assumption that TDOE is a powerful teratogen for X. laevis.     

RANS-based simulation of transverse turbulent mixing in a 2D geometry

Although transverse mixing is a significant process in river engineering when dealing with the discharge of pollutants from point sources or the mixing of tributary inflows, no theoretical basis exists for the prediction of its rate, which is indeed based upon the results of experimental works carried on in laboratory channels or in streams and rivers. The paper presents the preliminary results of a numerical study undertaken to simulate the transverse mixing of a steady-state point source of a tracer in a two-dimensional rectangular geometry, which is expected to reproduce a shallow flow. This geometry is that of Lau and Krishnappan (J Hydraul Div 13(HY10):1173–1189, 1977), who collected turbulent mixing data for a shallow flow. In the numerical study an approach based on the Reynolds Averaged Navier–Stokes (RANS) equations was applied, where the closure problem was solved by using turbulent viscosity concept. Particularly, the classical two-equations k–? model was used. Two methods were applied to the model results to evaluate the turbulent transverse mixing coefficient. The effect on transverse mixing of a grid located upstream the tracer source was also studied. Numerical results were generally higher than the experimental data. This overestimation could be explained considering the hypothesis of isotropic turbulence underlying the k–? model, which can lead to large turbulent viscosities and rate of mixing. However, RANS-based results may still be considered acceptable also providing the large uncertainties associated with literature predictive equations.     

Dragutin T. Mihailović, Igor Balaž and Darko Kapor: Time and methods in environmental interfaces modelling: personal insights

Environmental Fluid Mechanics -     

Experimental study of a positive surge. Part 1: basic flow patterns and wave attenuation

A positive surge results from a sudden change in flow that increases the depth. It is the unsteady flow analogy of the stationary hydraulic jump and a geophysical application is the tidal bore. Positive surges are commonly studied using the method of characteristics and the Saint-Venant equations. The article presents the results from new experimental investigations conducted in a large rectangular channel. Detailed unsteady velocity measurements were performed with a high temporal resolution using acoustic Doppler velocimetry and non-intrusive free-surface measurement devices. Several experiments were conducted with the same initial discharge (Q = 0.060 m³/s) and six different gate openings after closure resulting in both non-breaking undular and breaking bores. The analysis of undular surges revealed wave amplitude attenuation with increasing distance of surge propagation were in agreement with Ippen and Kulin theory. Also, undular wave period and wave length data were relatively close to the values predicted by the wave dispersion theory for gravity waves in intermediate water depths.     

Contact Tank Design Impact on Process Performance

In this study three-dimensional numerical models were refined to predict reactive processes in disinfection contact tanks (CTs). The methodology departs from the traditional performance assessment of contact tanks via hydraulic efficiency indicators, as it simulates directly transport and decay of the disinfectant, inactivation of pathogens and accumulation of by-products. The method is applied to study the effects of inlet and compartment design on contact tank performance, with special emphasis on turbulent mixing and minimisation of internal recirculation and short-circuiting. In contrast to the conventional approach of maximising the length-to-width ratio, the proposed design changes are aimed at addressing and mitigating adverse hydrodynamic structures, which have historically led to poor hydraulic efficiency in many existing contact tanks. The results suggest that water treatment facilities can benefit from in-depth analyses of the flow and kinetic processes through computational fluid dynamics, resulting in up to 38 % more efficient pathogen inactivation and 14 % less disinfection by-product formation.     

Industrial point source CO<Subscript>2</Subscript> emission strength estimation with aircraft measurements and dispersion modelling

CO₂ remains the greenhouse gas that contributes most to anthropogenic global warming, and the evaluation of its emissions is of major interest to both research and regulatory purposes. Emission inventories generally provide quite reliable estimates of CO₂ emissions. However, because of intrinsic uncertainties associated with these estimates, it is of great importance to validate emission inventories against independent estimates. This paper describes an integrated approach combining aircraft measurements and a puff dispersion modelling framework by considering a CO₂ industrial point source, located in Biganos, France. CO₂ density measurements were obtained by applying the mass balance method, while CO₂ emission estimates were derived by implementing the CALMET/CALPUFF model chain. For the latter, three meteorological initializations were used: (i) WRF-modelled outputs initialized by ECMWF reanalyses; (ii) WRF-modelled outputs initialized by CFSR reanalyses and (iii) local in situ observations. Governmental inventorial data were used as reference for all applications. The strengths and weaknesses of the different approaches and how they affect emission estimation uncertainty were investigated. The mass balance based on aircraft measurements was quite succesful in capturing the point source emission strength (at worst with a 16% bias), while the accuracy of the dispersion modelling, markedly when using ECMWF initialization through the WRF model, was only slightly lower (estimation with an 18% bias). The analysis will help in highlighting some methodological best practices that can be used as guidelines for future experiments.     

In vivo microspectroscopy monitoring of chromium effects on the photosynthetic and photoreceptive apparatus of Eudorina unicocca and Chlorella kessleri

In microorganisms and plants, chromium (Cr) is not essential for any metabolic process, and can ultimately prove highly deleterious. Due to its widespread industrial use, chromium has become a serious pollutant in diverse environmental settings. The presence of Cr leads to the selection of specific algal populations able to tolerate high levels of Cr compounds. The varying Cr-resistance mechanisms displayed by microorganisms include biosorption, diminished accumulation, precipitation, reduction of Cr(6+) to Cr(3+), and chromate efflux. In this paper we describe the effects of Cr(6+) (the most toxic species) on the photosynthetic and photoreceptive apparatus of two fresh water microalgae, Eudorina unicocca and Chlorella kessleri. We measured the effect of this heavy metal by means of in vivo absorption microspectroscopy of both the thylakoid compartments and the eyespot. The decomposition of the overall absorption spectra in pigment constituents indicates that Cr(6+) effects are very different in the two algae. In E. unicocca the metal induced a complete pheophinitization of the chlorophylls and a modification of the carotenoids present in the eyespot after only 120 h of exposition at a concentration equal or greater than 40 microM, which is the limit for total Cr discharge established by US EPA regulations. In C. kessleri, chromium concentrations a hundred times higher than this limit had no effect on the photosynthetic machinery. The different tolerance level of the two algae is suggested to be due to the different properties of the mucilaginous envelope and cell wall covering, respectively, the colonies of Eudorina and the single cells of Chlorella, which binds chromium cations to a different extent.     

Verification of Wind-Driven Volatilization Models

Mass-transfer processes of paramount importance, such as reaeration and volatilization, occur at the air–water interface. Particularly, volatilization is intensively studied because it can be a relevant removal process for toxic contaminants from flowing and standing surface waters. The paper provides a comparison among predictive equations available from literature for standing waters for the case of MTBE contamination. Most of the considered equations tend to overestimate the volatilization rate, while three equations offer a good fit with the observed data. Finally, these equations are applied to a larger amount of field data.