Efficiency of solar water disinfection photocatalized by titanium dioxide of varying particle size.

Titanium dioxide photocatalysed water disinfection is induced by the interaction of light with TiO(2), which generates highly reactive free hydroxyl radicals (OH(*)). These free radicals create lethal damage that leads to bacterial death. Normally, decreasing TiO(2) particle size increases the area of light interaction. This may possibly increase the concentration of OH(*) generated and hence increases disinfection efficiency. Moreover, decreasing the particle size increases the force of attraction between the particles and cells, which could create aggregates that may contribute to the local OH(*) concentration. In the present investigation cells of Escherichia coli were used as the test microorganism, TiO(2) as the photocatalyst and sunlight as the light source. Four different surface areas of TiO(2) particles corresponding to 10, 50, 80-100 and > or =300 m(2) g(-1) were tested at a concentration of 1 g l(-1). Disinfection efficiency increased with increasing the surface area producing a maximum between 80-100 m(2) g(-1) followed by a reduction at > or =300 m(2) g(-1). The reduction in the efficiency at this relatively high surface area was attributed to the increase in the local concentration of OH(*). This increase may be high enough to initiate radical-radical interaction that would compete with bacterial cells and reduce the chance of bacterial cell-radical interaction taking place. Moreover, the phenomenon of TiO(2) aggregation with bacterial cells plays an important role, and the extent of aggregation increases with decreasing particle size. Such aggregation could augment the concentration of OH(*) within the cell vicinity. This suggests that surface area is a key factor in determining the efficiency of disinfection, and that concentration is a vital factor.

Mercury pollution from irrigation with treated sewage water (TSW).

The lack of potable water in arid countries leads to the use of treated sewage water (TSW) for crop growth. Mercury accumulation (up to 500 ng/g) in agricultural soil originating from daily irrigation with TSW was found at two sites fed separately from a hospital sewage plant and an industrial plant. A control site irrigated with potable water ([Hg] <0.01 ng/ml) had much reduced levels in soil (<12 ng/g). Cold-vapour analysis of TSW revealed that Hg concentrations fluctuated widely, and were between 10-100 times higher than those of potable water. The TSW data originated from a total of 46 samples (1 L each), from both plants, collected over a 6-month period. The Hg levels varied from 0.1 to 1.0 ng/ml, which suggested that the possible source of the accumulation could be found in continuous irrigation with comparatively higher Hg levels. Remedial measures could be approached from the perspective of curbing this inconsistency to produce more consistent Hg concentrations below 0.5 ng/ml. It was found that the electrical conductivity of TSW is a useful indicator to rapidly monitor fluctuations in treatment. A novel development in the study was the potential capacity of the plastic TSW discharge-pipes to behave as crude 'chromatographic' columns for possible Hg adsorption. If this property of the pipes is developed further it could have a considerable mitigating effect on the Hg levels. Possible recommendations for remediation to limit the Hg levels and promote sustainable development are discussed.

Optimization of a high-performance liquid chromatography method to quantify bilirubin and separate it from its photoproducts: effect of column length, Ph, mobile phase composition, and flow rate.

A rapid reversed-phase (RP) high-performance liquid chromatography method for the isolation of bilirubin from its photoproducts (e.g., biliverdin) is reported. The method is based on isocratic elution using methanol:water as the mobile phase. A 24 full-factorial experimental design approach was adopted. For the optimization, the best separation was obtained using a flow rate of 1.50 mL/min, a mobile phase of 99:1 methanol:water (v/v) at pH 3.60, and a 150 x 4.6 mm id RP (C18) column containing 5-microm particles. These conditions produced the fastest total retention time of 3.38 +/- 0.055 min, and other chromatographic parameters were acceptable. Under the optimum conditions, a linear calibration curve for bilirubin was obtained over the 1.0-40.0 microg/L concentration range studied. The limit of quantification was 0.79 g/L and the limit of detection was 0.24 microg/L. Bilirubin in solution was monitored by ultraviolet detection at 450 nm.

Chemical and photolytical transformation of biomedically significant compounds in the presence of deuterated solvents.

The effect of the nature of solvent on the properties of biomedically important compounds is of particular importance. The conversion of certain biomedical compounds with deuterated solvents is an area of research that has not been accorded adequate recognition in the literature. We explored this area in the interest of shedding some light on the possible effects of solvent on the nature of the solute. The transformation of specific medically important compounds such as bilirubin, thymine, uracil, dehydrocholesterol (7-DHC) and vitamin D(3) was observed in the presence of deuterated solvents such as heavy water and deuterated chloroform. The products of the relevant reactions were confirmed spectrophotometrically. An additional feature to our investigation involved the photolysis of the aforementioned compounds by solar irradiation. The pure samples were dissolved in solutions of the deuterated solvents, corresponding to concentrations of typically 10(-2) mM, and exposed to sunlight for about 15-30 min. The deuterated solvents caused chemical transformation in all chemical compounds tested, and produced intense characteristic absorbance maxima between 200 and 700 nm. Sunlight exposure was also effective in either augmenting the effects of deuterated solvent as in bilirubin and 7-DHC or reducing it as with thymine or having no effect as with uracil or completely changing it as in vitamin D(3). It has been shown that the use of deuterated solvents produces unique chemical and photochemical conversions of bilirubin, 7-DHC, thymine, uracil and vitamin D(3). This was attributed to the fact that deuterated compounds display a somewhat different chemistry to their ordinary counterparts and that possibly thermodynamic considerations could be responsible for the novel transformations.

Risk assessment of chromium and arsenic in date palm leaves used as livestock feed.

Appreciable levels of total chromium (Cr) and arsenic (As) were found (by emission spectroscopy) in date palm leaves, which form a significant ingredient in livestock feed. The levels in the fruit were considered safe for human consumption. Our work involved evaluation of the distribution of these elements in the leaves during the developmental stages of the fruiting season. Thirty-six leaf specimens of the Fard cultivar were collected 9, 15 and 20 weeks, respectively, after pollination and subjected to a standard digestion procedure. Sample masses of typically 1 g (dry weight) were prepared in 25 ml dilute acid solution and investigated for trace levels of Cr and As by ICP-AES. Eleven soil samples collected at random during the growth stages were subjected to a similar digestion procedure and analysis. According to the literature, the permissible mean levels of Cr and As in plants are 200 and 80 ng/g (dry weight), respectively. We used these values as our guideline to assess the "risk" levels in our samples of interest. In the case of Cr, about 45% of the specimens possessed levels between 250 and 700 ng/g, while a significant number produced levels between 1000 and 5000 ng/g. With regard to As, about 70% of the samples were above the documented permissible mean value. As a result of the unusually high Cr concentrations in some cases, the feasibility of Cr "accumulation" in the leaves was examined. Insects and other organisms subsist on the leaves and an added concern was the accumulation of these elements in the food chain. The study formed an interesting contribution to environmental research, and the impact of our assessment on the environment is discussed.

A comparative study on gamma irradiation of unconjugated bilirubin in aqueous and non-aqueous solutions.

Dilute aqueous and non-aqueous solutions of bilirubin were exposed to gamma radiation to examine the effects of ionizing radiation on the concentrations of a specimen of this nature. The ionising radiation emanated from a (137)Cs source, and was applied to 5.2 x 10(-2) mmol L(-1) solutions of the unconjugated specimen in 0.05 mol L(-1) aqueous NaOH and chloroform. Depletion of bilirubin after exposure was common to both solvents. Complete degradation was accomplished with doses in excess of 100 Gy. In the case of NaOH, it was found that the presence of molecular oxygen contributed more efficiently to the degradation process, than irradiation in air. When the experimental conditions were changed to nitrogen, the degradation process was suppressed. The sole by-product of merit originating from the NaOH work was the short-wavelength isomer of biliverdin, at 330 nm. In the case of chloroform, the exclusive product of interest was characterised as the long-wavelength isomer of biliverdin that absorbs in the broad region commencing from about 620 nm. The non-aqueous study was conducted in the presence and absence of molecular oxygen, with no significant changes in the results. Optimum production of the isomers in question occurred at a gamma dose of about 80 Gy. The general species of interest were monitored spectrophotometrically, and the results were treated mathematically to facilitate evaluation of the data. Our work represents the development of a facile gamma-ray method for the exclusive production of specific isomers of biliverdin, which are useful components in biosynthetic research.

Monitoring of cadmium in "on" and "off" date palms.

The study demonstrated that the mature dates we investigated were considered safe for human consumption. However, our findings revealed that much of the early fruit and leaves, which appeared at the advent of the fruiting season, possessed elevated levels of cadmium (Cd) that could accumulate in the food chain and thus impact adversely on the environment. In addition, animal feed for livestock contains date leaves, which should be restricted to the mature ones. The monitoring of cadmium in date palms is of considerable interest to environmental science and the thrust of this work, therefore, involved measurement, by ICP, of Cd in dates and corresponding leaf specimens, and evaluation of its distribution during the developmental stages of the fruiting season. Thirty-six date samples and 36 leaf specimens of the Fard cultivar were collected from "on" and "off" date palms during the Kimri, Bisir and Rutab stages of the fruiting season and subjected to suitable digestion procedures. Sample masses of typically 1 g (dry weight) were prepared in 25 ml dilute acid solution and investigated for trace levels of Cd by ICP-AES. Special attention was paid to contamination and the validation of our methodology. The Cd "threshold" in our study was 50 ng/g, in keeping with the levels of tolerance appearing in the literature. For the dates we found elevated levels of Cd [> 50 ng/g] in most of the samples, for both categories of "on" and "off" trees, during the Kimri stage. In the case of the leaves, the "on" samples revealed significant values up to 125 ng/g in Bisir, in some cases, but the trend for the "off" trees remained the same with the highest levels [> 100 ng/g] recorded during Kimri. Safe levels were attained during Rutab for all specimens. The possibility of a connection between Cd toxicity and the alternate-bearing phenomenon is discussed and this could be the subject of future interest.

252Cf: the potential for activation analysis of selected medium-weight and heavy elements in the limited neutron flux of a partially depleted 50 microg source.

A 50 microg 252Cf source, depleted by about 2 orders of magnitude from its original neutron output, was used to examine the sensitivity of neutron activation analysis for a selection of 20 pure materials and compounds containing elements with atomic numbers greater than 40. Generally speaking, the sensitivity is seriously restricted by the neutron flux of the source, but in certain specific cases the nuclear properties of the elements concerned, such as thermal absorption cross-section, isotopic abundance and half-life of the radioactive product were considered for the production of a practicable gamma-ray yield. A description of the irradiation assembly and the conditions of activation are presented. Detection limits varied between 30 microg g(-1) to 8.2 mg g(-1) based on the most suitable gamma-ray of the radionuclide of interest. For purposes of determining trace and minor concentrations of selected elements, a source of this nature could be acquired at a nominal cost especially in developing countries that do not have access to a nuclear reactor.

Recycling of petroleum-contaminated sand.

The environmental impact of using petroleum-contaminated sand (PCS) as a substitute in asphalt paving mixtures was examined. An appreciable component of PCS is oily sludge, which is found as the dregs in oil storage tanks and is also produced as a result of oil spills on clean sand. The current method for the disposal of oily sludge is land farming. However, this method has not been successful as an oil content of < 1% w/w is required, and difficulty was encountered in reaching this target. The reuse of the sludge in asphalt paving mixtures was therefore considered as an alternative. Standard tests and environmental studies were conducted to establish the integrity of the materials containing the recycled sludge. These included physical and chemical characterization of the sludge itself, and an assessment of the mechanical properties of materials containing 0%, 5%, 22% and 50% oily sludge. The blended mixtures were subjected to special tests, such as Marshall testing and the determination of stability and flow properties. The experimental results indicated that mixtures containing up to 22% oily sludge could meet the necessary criteria for a specific asphalt concrete wearing course or bituminous base course. To maximize the assay from the recycled material, the environmental assessment was restricted to the 50% oily sludge mixture. Leachates associated with this particular mixture were assayed for total organic residue and certain hazardous metal contaminants. The results revealed that the organics were negligible, and the concentrations of the metals were not significant. Thus, no adverse environmental impact should be anticipated from the use of the recycled product. Our research showed that the disposal of oily sludge in asphalt paving mixtures could possibly yield considerable savings per tonne of asphalt concrete, and concurrently minimize any direct impact on the environment.

Recycling of paint-contaminated grit.

The impact on the environment of using paint-contaminated grit (PCG) as a partial or full replacement for sand in Portland cement mortar and asphalt concrete mixtures was investigated. The grit waste material originated from abrasive blasting of offshore steel structures. There is a major environmental concern regarding the safe disposal of the spent blasting abrasives that contain paint chips or paint particles and other debris removed from the surface of the steel structures. This work investigated the potential reuse of PCG in Portland cement concrete (PCC) and hot mix asphalt concrete. Several studies were conducted to establish the integrity of the materials containing the recycled grit. These included the chemical and physical characterization of natural sand and PCG, the assay of leaches associated with the grit material for hazardous metal contaminants, such as Cr, Cd and Pb, and the assessment of the mechanical properties of the PCG-substituted mortars by applying special tests (such as Marshall stability and determination of the flow properties) to the PCG-substituted asphalt concrete mixtures. The overall results demonstrated that the potential reuse of PCG in PCC and asphalt concrete mixtures would not pose any environmental threat and could produce several benefits, such as reduced disposal costs, protection of water sources from improper disposal practices and reduced costs in the production of natural aggregates and asphalt cement.