Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator.

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.     

Hyperaccumulator Thlaspi caerulescens (Ganges ecotype) response to increasing levels of dissolved cadmium and zinc

Hyperaccumulation of metals by plants involves at least three processes: efficient absorption by roots, efficient root-to-shoot translocation and hypertolerance through internal detoxification. In this study, Thlaspi caerulescens was separately exposed to Cd and Zn at 0, 50, 100 and 200 μ M for 7 d to monitor plant responses in hydroponics. Significant dose-dependent accumulation was observed for both metals, mainly in roots (up to 3.2 and 9.2 mg g ^?1 for Cd and Zn, respectively). However, Cd was more phytotoxic in terms of plant growth and photosynthesis. This higher toxicity was also evidenced by MetPLATE bioassay. Root exudation was significantly correlated to Cd and Zn translocation (r>0.85) proving its involvement in facilitating metal uptake. As for antioxidative responses, plants reacted to Cd and Zn by broadly exhibiting an elevation of glutathione reductase activity before declining at 200 μ M due to higher phytotoxicity. By contrast, superoxide dismutase activity was unlikely to be affected by both metals. Root-to-shoot apoplastic flow was traced using a fluorescent dye (trisodium-8-hydroxy-1,3,6-pyrenetrisulfonic acid; PTS), whose concentration in leaves increased to a certain extent with Cd and Zn accumulation, indicating that heavy metals have a comparable effect to drought or salinity in promoting the passive diffusion of water and solutes. Nevertheless, Cd at 200 μ M hindered the diffusion of PTS and consequently affected the apoplastic transport in plants.     

Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.