A new concept: the use of neutrally-buoyant microemulsions for DNAPL remediation

Even in the absence of mobilization of dense nonaqueous phase liquid (DNAPL), the microemulsion that forms when the surfactant solubilizes a dense contaminant such as trichloroethylene will be more dense than water and tends to migrate downward. This paper addresses the issue of migration with a new concept: surfactant enhanced aquifer remediation at neutral buoyancy. Laboratory results of surfactant remediation in two-dimensional model aquifers show that downward migration of microemulsion containing solubilized dense contaminants can be reduced to an acceptable level, even in the absence of capillary barriers in the aquifer. One model experiment was designed to exhibit a small degree of vertical migration and full capture of the microemulsion at the extraction well. The second experiment was designed to demonstrate the effect of large buoyancy forces that lead to excessive downward migration of the microemulsion. Density measurements of aqueous solutions containing sodium dihexyl sulfosuccinate surfactant, isopropanol, trichloroethylene, and sodium chloride are presented. A companion paper presents the results of the flow and transport calculations needed for this approach to surfactant flooding.     

Buffer zone widths for honeybees from ground and aerial spraying of insecticides

The relative field hazards of insecticides to honeybees have been estimated by considering intrinsic toxicity levels and field application rates. This approach is extended here to a consideration of buffer zones downwind of sprayed areas by estimating the distance at which bees would encounter an LD(50) dose from spray drift. 'LD(50) distances' are determined for both ground and aerial spraying of ground crops in Britain using published data on spray deposition under various weather conditions. For ground spraying at low wind speeds (< or =3 m s(-1)), this zone of risk is up to 5 m for the great majority of compounds. Aerial spraying in unstable atmospheric conditions appears to produce drift deposits of about the same order of magnitude as from ground spraying at wind speeds of about 4 m s(-1), with maximum LD(50) distances of < or =40 m for chlorpyrifos, fenitrothion and triazophos. For aerial spraying in stable atmospheric conditions these distances would be much greater. Pieris brassicae larvae are contrasted with honeybees in their relative sensitivities to insecticides and consequent LD(50) distances.     

90-day oral toxicity of ziram: a thyrostatic and hepatotoxic study

Ziram, a dithiocarbamate fungicide, is extensively used in crop protection. Daily oral doses of ziram (5 and 25 mg kg(-1) day(-1)) for 30, 60 and 90 days produced significant mortality in male rats. The fungicide also caused a significant increase in the thyroid:body weight ratio, histological changes, and a reduced activity of thyroid (125)I uptake and protein bound (125)I. However, the animals did not show any change in the clinical enzyme profile of the liver, serum and brain. It is believed that ETU, the degradation product of ziram and a known antithyroid compound, is the causative agent for the high mortality, as well as for the pronounced thyrostatic and hepatotoxic effects found in the experimental animals.     

Pollen germination is impeded by tap water

Pollen germination in vitro is totally inhibited in tobacco (Nicotiana tabacum) and other species if tap water is used to prepare the germination medium. This effect is already fully present if tap water accounts for only 25% of the medium. Furthermore, the pollen grains deteriorate rapidly and the culture medium turns yellowish-brown. The water toxicity is not caused by one or several compounds regularly monitored by the water authorities but can be removed by ion exchange purification. Although the factor(s) responsible for the inhibition were not identified, the study clearly shows the presence of such a contaminant in three different Orange County (Southern California) water wells. The fact that a fundamental botanical process like pollen germination is inhibited by a factor in drinking water not included in water quality control causes some general health concern. In addition, crop yield might be largely reduced if overhead spray irrigation with this water is utilized. The experiments also suggest that pollen germination in vitro could serve as a sensitive and simple bioassay for water quality.     

Effects of elevated CO2, nitrogen supply and tropospheric ozone on spring wheat-II. Nutrients (N, P, K, S, Ca, Mg, Fe, Mn, Zn)

CO(2) enrichment is expected to alter leaf demand for nitrogen and phosphorus in plant species with C(3) carbon dioxide fixation pathway, thus possibly causing nutrient imbalances in the tissues and disturbance of distribution and redistribution patterns within the plants. To test the influence of CO(2) enrichment and elevated tropospheric ozone in combination with different nitrogen supply, spring wheat (Tritium aestivum L. cv. Minaret) was exposed to three levels of CO(2) (361, 523, and 639 microl litre(-1), 24 h mean from sowing to final harvest), two levels of ozone (28.4 and 51.3 nl litre(-1)) and two levels of nitrogen supply (150 and 270 kg ha(-1)) in a full-factorial design in open-top field chambers. Additional fertilization experiments (120, 210, and 330 kg N ha(-1)) were carried out at low and high CO(2) levels. Macronutrients (N, P, K, S, Ca, Mg) and three micronutrients (Mn, Fe, Zn) were analysed in samples obtained at three different developmental stages: beginning of shoot elongation, anthesis, and ripening. At each harvest, plant samples were separated into different organs (green and senescent leaves, stem sections, ears, grains). According to analyses of tissue concentrations at the beginning of shoot elongation, the plants were sufficiently equipped with nutrients. Elevated ozone levels neither affected tissue concentrations nor shoot uptake of the nutrients. CO(2) and nitrogen treatments affected nutrient uptake, distribution and redistribution in a complex manner. CO(2) enrichment increased nitrogen-use efficiency and caused a lower demand for nitrogen in green tissues which was reflected in a decrease of critical nitrogen concentrations, lower leaf nitrogen concentrations and lower nitrogen pools in the leaves. Since grain nitrogen uptake during grain filling depended completely on redistribution from vegetative pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO(2) enrichment in a similar manner to nitrogen. Phosphorus concentrations in green tissues, on the other hand, were not, or only slightly, affected by elevated CO(2). In stems, 'dilution' of all nutrients except manganese was observed, caused by the huge accumulation of water soluble carbohydrates, mainly fructans, in these tissues under CO(2) enrichment. Whole shoot uptake was either remarkably increased (K, Mn, P, Mg), nearly unaffected (N, S, Fe, Zn) or decreased (Ca) under CO(2) enrichment. Thus, nutrient cycling in plant-soil systems is expected to be altered under CO(2) enrichment.     

Assessment of trace metal distribution and contamination in surface soils of Hong Kong

An intensive investigation was conducted to study the distribution of trace metals in surface soils of Hong Kong and to assess the soil environmental quality. From results of cluster analysis, and comparisons among soil types and areas, it is clearly shown that increases in trace metal concentrations in the soils were generally extensive and obvious in urban and orchard soils, less so in vegetable soils, whilst rural and forest soils were subjected to the least impact of anthropogenic sources of trace metals. However, some of the forest soils also contained elevated levels of As, Cu, and Pb. Urban soils in Hong Kong were heavily polluted by Pb from gasoline combustion. Agricultural soils, both orchard and vegetable soils, usually accumulated As, Cd, Cu, and Zn originating from applications of pesticides, animal manures, and fertilizers. In general, trace metal pollution in soils of the industrial areas and Pb pollution in the soils of the commercial and residential areas were obvious.     

Effects of degree of water saturation on dispersivity and immobile water in sandy soil columns

Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the water in the pore volume as mobile. However, about 10% of the pore water, independent of the degree of saturation, was found to be immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two water regions, indicating that the immobile water is essentially isolated from the flowing water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-water velocities when these soils are desaturated.     

Natural phillipsite as a matrix for a slow-release formulation of oxamyl

The performance of phillipsite as a matrix for slow-release formulation of oxamyl [N,N-dimethyl-2-methylcarbamoyl-oxymino-2-(methylthio)acetamide] was tested. The adsorption kinetics followed a first-order law, and the adsorption isotherm fitted well in a two-surface Langmuir model, suggesting a double mechanism of interaction between oxamyl and the sorbent. The sorption mechanism, studied by FTIR, provided two fractions of oxamyl. The first one is sorbed on the mineral surface, linked by H-bonding, and the second one is constituted by a multilayer of oxamyl molecules linked by a water bridge between them. The release kinetics of oxamyl from a substratum zeolite-oxamyl also follows a first-order law, with two stages that correspond to both fractions of oxamyl previously detected.