Kafui Nyavor

Trace Elements In Water, Fish and Sediment from Tuskegee Lake, Southeastern Usa

The concentrations of trace elements in water, sediment and fish samples from Tuskegee Lake located in Southeastern United States were investigated in this study. The Lake is utilized both as a source for municipal drinking water, and for recreational fishing. The water quality characteristics over two sampling periods, the speciation of metals in the Lake sediments, the risk to water column contamination and levels of heavy metals in largemouth bass (Micropterus salmoides) samples from the Lake were evaluated. The Lake water quality characteristics were mostly below the recommended drinking water standards by the United StatesEnvironmental Protection Agency (US EPA) and the European Union (EU) except for aluminum, iron, manganese and thallium. In addition, the average values of Cr, As, Mn, Zn and Cl- in the water samples analyzed were higher than the respective reference values for fresh water. To study the speciation of metals in the Lake sediments, ten elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn) in four grain sizes (< 710 μm – 250 μm, < 250 μm – 75 μm, < 75 μm – 53μm, and < 53 μm) were subjected to sequential extractions. Irrespective of grain size, the elements analyzed were distributed in both the non-residual and residual phases except Ni that was found only in the residual fraction. The potential risk to Lake water contamination was highest downstream (Sites 1 and 2) based on the calculated global contamination factors. From the calculated individual contamination factors, Mn and Pb followed by Zn, Cu, Cr, Co and V posed the highest risk to water contamination. Based on this study, the human health risks for heavy metals in fish caught from Tuskegee Lake are low for now, and irrespective of the source of fish, concentrations of metals in muscle tissues were all below the recommended Food and Agriculture Organization (FAO) maximum limits for Pb (0.5 mg Kg-1), Cd (0.5 mg Kg-1), Cu (30 mg Kg-1), and Zn (30 mg Kg-1) in fish.

Chemical quality of bottled waters from three cities in eastern Alabama

Twenty-five brands of bottled waters consisting of both purified and spring types collected randomly from three Alabama cities, USA were assessed for their suitability for human consumption. Water quality constituents analyzed include pH, conductivity, alkalinity, chloride, nitrate + nitrite, sulfate, phosphate, total carbon (TC), inorganic carbon (IC), total organic carbon (TOC), and 27 elements on the inductively coupled plasma-optical emission spectrometer (ICP-OES). The results obtained were compared with US EPA drinking water standards and the European union (EU) drinking water directive. Ni was non-detectable in all the samples and Cu, Pb, Sb, Zn, Mn, Al, Cr, Mg, P, Ca, sulfate, chloride and nitrates + nitrites were all below their respective USEPA drinking water standards or EU maximum admissible concentrations (MAC). The conductivity, pH, As, Cd, Hg, Zn, Se and Tl values in some samples exceeded the EU and USEPA standards for drinking water. No sample had pH > 8.5, but seven bottled water brands analyzed were acidic (pH < 6.5). Most of the sampled brands had TOC concentrations exceeding 3 mg/l. The concentrations of most water quality constituents analyzed, in most cases, were higher in the spring water brands compared to the purified or distilled brands of bottled water. A one-way parametric analysis of variance (ANOVA) conducted on pH, conductivity, IC, TOC, Ca, Na, K, Mg, Se, sulfate, chloride and nitrate + nitrite values for 10 brands of bottled water to ascertain the homogeneity of variances within and between the brands, suggested significant differences in variances across the brands at a 95% confidence level except for selenium, sodium and calcium.

Levels of 26 elements in infant formula from USA, UK, and Nigeria by microwave digestion and ICP-OES

Abstract The presence of toxic elements in powdered and liquid infant milk may create significant health problems for infants. Babies (0–6 months old) may be more at risk because their only food may be infant formula. In this study, infant formula samples sold in major supermarket chains in Nigeria, the UK and USA were analyzed for their metal contents and estimated daily intakes of these elements were determined. Seventeen brands (three samples per brand) of infant formula samples were analyzed for various essential (Ca, Co, Cu, Cr, Fe, Mg, Mn, Mo, Na, and Zn) and non-essential (Ag, Al, As, Ba, Be, Cd, Hg, Ni, Pb, Sb, Sn, Sr, Ti, Tl, U, and V) elements. Known weights and aliquots of the dry, powdered and liquid infant milk, respectively, were digested on the Ethos Plus microwave labstation. Digests were then analyzed with Perkin-Elmer DV 3300 inductively coupled plasma–optical emission spectrometer (ICP–OES). The observed values of SRM 8435 (Whole Milk Powder) analyzed using the same procedure were in agreement with the NIST certified values. The mean concentrations of the elements in milk-based and soy-based formulas, estimated mean daily intakes through infant formulas, and analysis of variances (ANOVA) across infant formula brands are presented. The results suggest that soy-based powder infant formulas generally had higher element levels than milk-based powder formulations, irrespective of source. The European Union (EU) drinking water maximum admissible concentrations for aluminium and barium and the US EPA standard for thallium were violated in some infant formula brands. Cadmium, lead, nickel and chromium were below their respective limits in drinking water and, also, the estimated daily intakes of Pb and Cd from infant formula were below the FAO/WHO Joint Expert Committee on Food Additives recommended provisional tolerable weekly intakes (PTWI) of 25 and 70 μg/kg body weight, respectively. Some brands had low nutritional contents when compared with the recommended dietary allowances (RDA) and dietary reference intakes (DRI) for use in North America. Only brands 7–9 and 12 (UK), and brands 13, 16 and 17 (USA) met the DRI for zinc. The daily intakes of iron (5.03 mg/day) from brand 2 (UK) and magnesium (23.9 mg/day) from brand 10 (UK) were below their respective recommended intake values. However, all the brands met the calcium DRI value of 210 mg/day.

The leaching of chromium from cement-based waste form via a predominantly biological mechanism

Abstract An evaluation of the leaching of chromium from 100% cement waste forms was carried out in this study using a refined biofilm formation method. Approximately 50% of the total chromium was leached from the experimental sample (exposed to bacterial broth of pH∼2.00) within the first 24 h of evaluation. No chromium was detected in the effluent of the control sample (exposed to sterile medium chemically acidified to give pH comparable to that of bacterial broth) within the same period. An increase in the duration of the first stage of the process from 24 h to 3 days did not result in the release of chromium from the control. Comparative evaluation for the leaching of calcium gave results that contrasted sharply with those obtained for chromium. Similar levels of calcium were leached from both control and experimental samples within the first 24 h of evaluation. Evaluations carried out at elevated levels of chromium in the waste form did not result in any change in trend for both calcium and chromium. A predominant biological mechanism involving active mobilization of chromium from the matrix is suggested for the difference in leaching of chromium from control and experimental waste forms.

Microbial stability evaluation of cement-based waste forms at different waste to cement ratio.

An evaluation of the effect of differences in chromium nitrate to cement ratio on the microbial stability of a chromium nitrate/cement waste form, as reflected in the leaching of chromium, calcium, magnesium and aluminum; was carried out in this study. An increase in the proportion of chromium in the waste form from 4.8 to 8.7% had no noticeable effect on microbial stability, with the total chromium leached essentially unchanged. Further increases in the proportion of chromium in the waste form from 8.7 to 10.7%, and from 10.7 to 15.9% resulted in a substantial decrease in microbial stability, with 3-fold and 1.3-fold increase in the total chromium leached, respectively, observed. For calcium, increases in the chromium proportion were accompanied with increases in the total calcium leached even though the increases were not in direct proportion to the increases in chromium proportion. For magnesium and aluminum, increases in the proportion of chromium within the range 4.8-10.7% were accompanied with increases in the total respective metals leached, with minor variation for each metal. On the whole, the maximum percentage chromium leached from the different waste forms was substantially lower than those of the other metals.

Kinetic analysis of data obtained from studies on microbial degradation of cement waste forms, using shrinking core models.

Model equations based on analytical solutions of two shrinking core models (acid dissolution or shrinking unreacted core (SUC) model, and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement waste forms. Two current approaches of waste form microbial stability evaluation (Nuclear Regulatory Commission (NRC) method and refined biofilm formation) were used to generate the data. Good linear correlations with R(2)>0.95 were obtained for the leaching data from both the NRC and biofilm approaches, using the model equation based on the bulk diffusion concept. Analyses using the model equation based on the acid dissolution model generally gave poor correlations except when data obtained from biofilm formation method was normalized.

A refinement of the biofilm formation method for waste forms stability evaluation.

A refinement of the biofilm formation method for waste form stability evaluation was carried out in this study. Refinement of the biofilm formation method became necessary because of the reduced contrast in degradation between control and experimental samples. The reduction in contrast was occasioned by the long duration of exposure (12 days) of the control samples to sterile medium of low pH in the first stage. Results of evaluation carried out reveal that the duration of the first stage of the biofilm formation method can be reduced to 24 h, with substantial increase in the contrast between degradations experienced by control and experimental samples. Reduction of the first stage can be done without compromising the efficiency of the inoculation process, which the longer duration of the first stage was originally intended to ensure. A doubt as to actual formation of biofilms on experimental samples, resulting from the use of non-sterile tubings and glass wares in the second stage, was also addressed in this study. Results reveal that substantial attachment of microbes occur on the surfaces of experimental samples in the first stage, thus any supply of microbes via the tubings and glass wares in the second stage is only additional and inconsequential.

Development of a biofilm formation method for waste forms stability evaluation.

The development of an accurate assessment protocol is critical for the prediction of long-term performance of waste disposal systems under field conditions. In this study, the development of a biofilm formation method for the evaluation of waste forms stability to microbially induced degradation (MID) is reported. The development process involved significant modifications to the existing Nuclear Regulatory Commission (NRC) approach. In the biofilm formation method, the control media and fermenter broths are designed to be of similar pH to avoid overestimation of the microbes capability to degrade the waste forms. In the NRC approach, the pH values are different. The existing one-stage process of the NRC approach is also replaced with a two-stage process in the biofilm formation method. This is to ensure full evaluation of the microbes involvement in waste forms degradation. The first stage of the two-stage process is for biofilm formation and the second is for biofilm evaluation. The use of a two-stage process eliminates the possibility of substrate limitation, resulting in values of degradation indices that are about two times higher than those obtained using the single-stage NRC approach. Two waste forms (100% Tuskegee cement and 21% cobalt chloride/79% cement) were used in the development of the biofilm formation method. Both waste forms showed evidence of biofilm formation. The formation of biofilm on the cobalt-containing waste form indicates a lack of anti-microbial capability of cobalt.

Enhanced biodegradation of methylhydrazine and hydrazine contaminated NASA wastewater in fixed-film bioreactor.

The aerobic biodegradation of National Aeronautics and Space Administration (NASA) wastewater that contains mixtures of highly concentrated methylhydrazine/hydrazine, citric acid and their reaction product was studied on a laboratory-scale fixed film trickle-bed reactor. The degrading organisms, Achromobacter sp., Rhodococcus B30 and Rhodococcus J10, were immobilized on coarse sand grains used as support-media in the columns. Under continuous flow operation, Rhodococcus sp. degraded the methylhydrazine content of the wastewater from a concentration of 10 to 2.5 mg/mL within 12 days and the hydrazine from ∼0.8 to 0.1 mg/mL in 7 days. The Achromobacter sp. was equally efficient in degrading the organics present in the wastewater, reducing the concentration of the methylhydrazine from 10 to ∼5 mg/mL within 12 days and that of the hydrazine from ∼0.8 to 0.2 mg/mL in 7 days. The pseudo first-order rate constants of 0.137 day-1 and 0.232 day-1 were obtained for the removal of methylhydrazine and hydrazine, respectively, in wastewater in the reactor column. In the batch cultures, rate constants for the degradation were 0.046 and 0.079 day-1 for methylhydrazine and hydrazine respectively. These results demonstrate that the continuous flow bioreactor afford greater degradation efficiencies than those obtained when the wastewater was incubated with the microbes in growth-limited batch experiments. They also show that wastewater containing hydrazine is more amenable to microbial degradation than one that is predominant in methylhydrazine, in spite of the longer lag period observed for hydrazine containing wastewater. The influence of substrate concentration and recycle rate on the degradation efficiency is reported. The major advantages of the trickle-bed reactor over the batch system include very high substrate volumetric rate of turnover, higher rates of degradation and tolerance of the 100% concentrated NASA wastewater. The results of the present laboratory scale study will be of great importance in the design and operation of an industrial immobilized biofilm reactor for the treatment of methylhydrazine and hydrazine contaminated NASA wastewater.

Evaluation of microbial stability of simulated solid and liquid waste forms using a refined biofilm formation method.

A refined biofilm formation method was used to evaluate the stability of a simulated liquid waste form containing a simulated liquid waste (salts) and cement in three different proportions, and a simulated solid waste form containing a simulated solid waste (resin) and cement in three different proportions. The experimental samples of all the simulated liquid waste forms showed evidence of microbial growth on them after 3 days of evaluation as indicated by substantial increase in sulfate production, and exhibited considerable instability to microbial degradation as indicated by substantial leaching of calcium. The experimental samples of all the simulated solid waste forms showed evidence of inhibition of growth of Thiobacillus thiooxidans for about 18 days, after which the growth of the microbe became evident in two out of three. Within the growth inhibition period, the differences between experimental and control samples were minor. After the growth of T. thiooxidans became evident, comparatively higher degradations were observed for the experimental samples of the resin containing solid waste forms.