Long-term effects of soil heterogeneity on cadmium behaviour in soil

A deterministic model for long-term behaviour of contaminants in the rootzone is developed that includes sorption, leaching, and plant uptake. The model is applied to cadmium accumulation in a sandy soil and uptake of cadmium by barley. Sensitivity analysis showed that the sensitivity of the leaching rate to changes in soil chemical and soil physical parameters decreases as a function of time, and becomes zero when steady state is reached. In contrast, accumulation of cadmium in soil and the plant uptake rate of barley are increasingly sensitive to soil chemical and soil physical parameters as time preceeds. To analyse cadmium behaviour in a field that is heterogeneous with respect to soil physical properties, the interstitial flow velocity was assumed to be a random, lognormally distributed variate. Using Monte Carlo simulation, the average plant uptake rate appeared to be much higher in the stochastic analysis than in the deterministic approach. Steady state is reached after a very long period of time. For a lognormally distributed proton activity, causing heterogeneity with respect to the sorption capacity of the soil, the model predicted similar deviations from the deterministic approach. It is concluded that reference values for groundwater and crop quality are exceeded earlier in a heterogeneous field than in a homogenous soil profile. Moreover, when average values suggest an acceptable situation, variability of the leaching rate and the plant uptake rate can still cause exceedance of reference values in part of the field. Therefore, it is reasoned that environmental quality standards should take soil heterogeneity into account.     

Degradation of ethinyl estradiol by nitrifying activated sludge

Degradation of ethinyl estradiol (EE2) by nitrifying activated sludge was studied with micro-organisms grown in a reactor with feedback of sludge fed with only a mineral salts medium containing ammonium as the sole energy source. Ammonium was oxidised by this sludge at a rate of 50 mg NH4+ g(-1) DW h(-1). This activated sludge was also capable of degrading EE2 at a maximum rate of 1 microg g(-1) DW h(-1). Using sludge with an insignificant nitrifying capacity of 1 mg NH4+ g(-1) DW h(-1), no degradation of EE2 was detected. Oxidation of EE2 by nitrifying sludge resulted in the formation of hydrophilic compounds, which were not further identified. Most probably degradation by nitrifying sludge results in a loss of estrogenic activity, as hydroxylated derivatives of EE2 are known to have a substantially lower pharmacological activity than EE2.     

The Aerosol Research and Inhalation Epidemiology Study (ARIES): PM2.5 mass and aerosol component concentrations and sampler intercomparisons

The Aerosol Research and Inhalation Epidemiology Study (ARIES) was designed to provide high-quality measurements of PM2.5, its components, and co-varying pollutants for an air pollution epidemiology study in Atlanta, GA. Air pollution epidemiology studies have typically relied on available data on particle mass often collected using filter-based methods. Filter-based PM2.5 sampling is susceptible to both positive and negative errors in the measurement of aerosol mass and particle-phase component concentrations in the undisturbed atmosphere. These biases are introduced by collection of gas-phase aerosol components on the filter media or by volatilization of particle phase components from collected particles. As part of the ARIES, we collected daily 24-hr PM2.5 mass and speciation samples and continuous PM2.5 data at a mixed residential-light industrial site in Atlanta. These data facilitate analysis of the effects of a wide variety of factors on sampler performance. We assess the relative importance of PM2.5 components and consider associations and potential mechanistic linkages of PM2.5 mass concentrations with several PM2.5 components. For the 12 months of validated data collected to date (August 1, 1998-July 31, 1999), the monthly average Federal Reference Method (FRM) PM2.5 mass always exceeded the proposed annual average standard (12-month average = 20.3 +/- 9.5 micrograms/m3). The particulate SO4(2-) fraction (as (NH4)2SO4) was largest in the summer and exceeded 50% of the FRM mass. The contribution of (NH4)2SO4 to FRM PM2.5 mass dropped to less than 30% in winter. Particulate NO3- collected on a denuded nylon filter averaged 1.1 +/- 0.9 micrograms/m3. Particle-phase organic compounds (as organic carbon x 1.4) measured on a denuded quartz filter sampler averaged 6.4 +/- 3.1 micrograms/m3 (32% of FRM PM2.5 mass) with less seasonal variability than SO4(2-).     

Aerosol light-scattering in The Netherlands

The relation between the (midday) aerosol light-scattering and the concentrations of nitrate and sulfate has been assessed at a site near the coast of the North Sea in The Netherlands. Midday was selected for the measurements because this is the time at which the aerosol is most effective in the scattering of solar radiation. Automated thermodenuders were used for the hourly measurement of the concentration of nitrate and sulfate with a lower detection limit of 0.1 μ m⁻³. The site is operational since October 1993. The first-year average dry aerosol light-scattering (measured with an integrating nephelometer at a wavelength of 525 nm) was 0.71 × 10⁻⁴ m^1̄. In arctic marine air the aerosol light-scattering was a factor of 10 lower than the average value, in polluted continental air it was up to a factor of 10 higher. The ratio of the total aerosol light-scattering to the concentration of sulfate was 20 m² g⁻¹. The contribution of nitrate to the aerosol light-scattering was higher than that of sulfate in the winter and of about equal magnitude in the summer period. In November and December of 1993, the humidity dependence of the aerosol light-scattering was investigated. Two types of (continental) aerosol were found with respect to the humidity behavior. One type showed a significant increase in light-scattering at the deliquescence points of ammonium nitrate and ammonium sulfate, with that of ammonium nitrate the most pronounced. The second type of continental aerosol did not show deliquescence, but followed the typical humidity dependence of aerosol in a supersaturated droplet state. In this latter aerosol type, nitrate dominated over sulfate. It was concluded from the study that the aerosol light-scattering in The Netherlands, in particular its humidity dependence, is governed by (ammonium) nitrate.     

Chemo-denitrification of nitrate-polluted water

Nitrate-nitrogen reduction was studied in the presence of ferrous iron and a copper catalyst. In a batch system, it was found that the reduction was very fast at pH 8.1 and slow at pH 7.5. A temporary accumulation of nitrate and hydroxylamine was noted. It was found that the reduction of nitrite-nitrogen in the presence of ferrous iron partly continued to ammonium. Decreasing the amount of reagents led to a slower reduction rate but a lower accumulation of nitrite and hydroxylamine. A continuous system was described whereby more than 50% of the initial nitrate could be removed.     

Relation between the molecular structure and the adsorption of arylcarbamate, phenylurea and anilide pesticides in soil and model organic adsorbents

The adsorption data of the pesticides have been correlated with several molecular parameters. The most significant relation was obtained with a multilinear combination of the hydrophobicity constant π and the Hildebrand's constant δ which is influenced by the molecular interactions properties of the aromatic ring of the solutes.     

Performance assessment of a zeolite treatment wall for removing Sr-90 from groundwater

Laboratory and modeling studies were conducted to assess the potential performance of a permeable reactive barrier constructed of a natural zeolite material at the West Valley Demonstration Project in western New York State. The results of laboratory column tests indicated that the barrier material would be effective at removing strontium from groundwater under natural gradient conditions. Two one-dimensional contaminant transport models were developed to interpret the data. A single-solute retardation factor model provided good agreement with the column test data, but time-consuming extraction and analysis of the zeolite material was required to parameterize the model. A preliminary six-solute model was also developed based on the assumption of competitive cation exchange as the primary removal mechanism. Both models yielded similar predictions of the long-term performance of the barrier, but the cation exchange model predicted higher effluent concentrations during the first 1000 pore volumes of operation. The cation exchange framework has several advantages, including the ability to calibrate the model using only data from column effluent samples, and the ability to account for site-specific differences in the groundwater cation composition. However, additional laboratory work is needed to develop a suitably robust model.