Metal cation adsorption is the predominant chemical mechanism governing the attenuation of toxic metal movement in soils. Clay minerals are the primary adsorbent surfaces in soils due to their ubiquitous nature and large reactive surface area. This study examined the relative affinity of the metals cadmium, nickel and zinc for the clay minerals kaolinite and montmorillonite. The influence which different mineral adsorbents and different complexing ligands in solution have on the adsorption of metal ions was assessed using the Hard-Soft Acid-Base Principle as a theoretical framework for predicting the maximum extent of adsorption and rate of adsorption. The HSAB principle is that hard bases prefer to complex hard acids and soft bases prefer to complex soft acids. The hypothesis that initiated these investigations was that the hard-soft character of mineral surfaces is due to their surface functional groups and can be measured using metal cation adsorption selectivity experiments where pH and complex ion formation are controlled. When complex ion formation in aqueous solution was minimized (i.e. in Ca(ClO₄)₂), adsorption decreased in the order of decreasing softness, CD > Zn > Ni for both clay minerals. Montmorillonite behaved as a slightly harder Lewis base than kaolinite, sorbing the harder Ni and Zn ions to a greater extent than Cd, although both minerals behaved as soft Lewis bases. In the presence of chloride and sulfate ligands, adsorption sequences changed and reflected results from typical soil solution studies. In some cases the adsorption sequences can be explained using the HSAB principle together with computer speciation data and this approach merits further consideration and research. Adsorption over time and calculated adsorption rate constants were generally consistent with equilibrium selectivity data. Adsorption rates decreased in the order Cd > Zn > Ni in Ca(ClO₄)₂ for both clay minerals. The adsorption curves reflect a two-step adsorption process involving a rapid exchange-type reaction followed by a much slower adsorption involving diffusion into the crystal or alteration of the surface through the formation of a new solid phase involving the adsorbed ions.

No description available.

The partitioning among plant uptake, leaching from and storage in soil of micronutrient metals following heavy applications of poultry manure was studied in three greenhouse experiments. Following these experiments, the study examined the effect of manure application on content and composition of soil organic matter and also the distribution of metals in the organic fractions. Poultry manure was surface-applied to Grigg and Monroe silt loam soil columns at rates of 0, 20 and 40 t/ha in each of the first two experiments, whereas the third tested the residual effect of the manure applications. Treatments were replicated four times and completely randomized. The soil columns were planted to corn (Zea mays L.) and leached daily with demineralized water at an average rate of 1.0 cm/day for 30-40 days. Following leaching and harvest of the corn, the soil columns were sampled in two sections for chemical analysis. Metals in the soils, leachates and corn tissue were determined by atomic absorption spectrophotometry. Manure application significantly (P < 0.01) influenced corn yield in Experiments I and II. The 20 t/ha rate increased yield more than the 40 t/ha treatment. Yield increases over the check treatment in Experiment I were about 400% and 300% from the 20 and 40 t/ha treatments respectively. In Experiment II, yield response was significantly curvilinear (P < 0.01), with the 20t rate giving the highest yield. The possibility of NH₃ toxicity and excess soluble salt injury resulting from the 40 t/ha rate was suggested. In Experiment III yield increases over the check treatment were about 300% and 500% from the 20 and 40 t/ha previous rates respectively. The study found no evidence for significant uptake or leaching of the toxic heavy metals (Cd, Cr, or Pb), such as is usually encountered with sewage sludge application. In Experiments I and II, total uptake of Mn, Fe, Zn, and Cu increased with the application of 20 t/ha and then decreased with the 40 t rate. In Experiment III, previous manure applications led to increases in uptake of these metals. The concentration of these metals in corn tissue decreased with the application of 20 t/ha and then increased with the 40 t rate in Experiment I. However, In both Experiments II and III the tissue metal concentration decreased with manure application. These effects were attributed largely to changes in yield. However, in no case did changes in concentration of metals exceed suggested tolerance limits. These results suggested that relatively high rates of poultry manure may be applied to the soil without appreciable danger of developing conditions of micronutrient metal toxicities. High manure rates led to increased leaching losses of K and Na. However, leaching losses of Mn, Fe, Zn, and Cu decreased with the application of 20 t/ha and then increased with the 40 t rate. Assuming independent contributions of metals from various potential sources, ratios of uptake and leaching losses to the input sources were examined. Both uptake and leaching losses of metals were small in magnitude in comparison with initial soil total levels and manure input. Despite the varied patterns of uptake and leaching losses of metals in response to the manure application, their storage in soil increased with rates of application. There was no consistent pattern in the distribution of metals in the top and lower halves of the soil columns after Experiments I and II. Examination of the distribution of organic fractions and associated metals following the greenhouse experiments indicated that soil organic matter content increased with manure application. The humic acid fraction made up 69 to 75% and the fulvic fraction 25 to 31% of the soil extractable organic matter. Despite such a high proportion of organic matter in the humic fraction, the data indicate that a greater proportion of metals in the organic fraction was associated with the fulvic fraction. / Land and Food Systems, Faculty of / Graduate

No description available.

The present study was carried out to determine the levels of heavy metals, Arsenic (As), Chromium (Cr), Cadmium (Cd) and Lead (Pb) in samples of water, sediments, and specimens from sheep known to graze and drink from Wonderfontein stream around the Khutsong area in the North West Province of South Africa. Determination of heavy metal levels was carried out using Atomic Absorption Spectrophotometer. Abundance of metals in water samples followed the trend As>Pb>Cd>Cr, while that in sediments followed the trend: Pb>As>Cr>Cd. Faecal levels were highest for Cr, followed by Cd, As then Pb, while serum levels were highest for As, Cd Cr and then Pb. The metal concentration in liver, kidney and muscle showed the following trends respectively: As>Cd>Cr>Pb ; As>Pb>Cd>Pb and As>Cd >Cr> Pb. The liver, kidney and muscle samples had higher concentration of As compared to other heavy metals. Generally, most samples showed a higher concentration in As. The mean concentrations of heavy metals in ppm were compared with European Commission Regulation, World Health Organisation, Korean Soil Environmental Conservation Act and the Australian New Zealand Food Standards maximum acceptable levels. The metal levels generally tended to be higher than the permissible levels and thus, public health risks. A survey conducted also revealed that the community in Khutsong does not have the knowledge on environmental contamination due to mining effluents and the effects thereof. The varying levels of water and sheep specimen contamination with As, Cd, Cr and Pb revealed in this study imply public health risks. Further biomonitoring, public and animal health studies are therefore indicated in this area. / Thesis (Msc in Agric Animal Health) North-West University, Mafikeng Campus, 2012

1,2-Dichloroethane (1,2-DCA), a short chain chlorinated aliphatic compound, is one of the most hazardous toxic pollutant of soil and groundwater, with an annual production in excess of 5.44 × 109 kg. The major concern over soil contamination with 1,2-DCA stems largely from health risks. Owing to their toxicity, persistence and potential for bioaccumulation, there is a growing interest in technologies for their removal. Many sites are, however, co-contaminated with a complex mixture of 1,2-DCA and heavy metal contaminants. Co-contaminated environments are considered difficult to remediate because of the mixed nature of the contaminants and the fact that the two components often must be treated differently. Therefore, the objective of this study was to evaluate the aerobic biodegradation of 1,2-DCA by autochthonous microorganisms in soil co-contaminated with 1,2-DCA and heavy metals, namely; arsenic (As3+), cadmium (Cd2+), mercury (Hg2+) and lead (Pb2+), via a direct and quantitative measurement of the inhibitory effects of heavy metals in a microcosm setting. Effects of various metal concentrations and their combinations were evaluated based on the following: (i) degradation rate constants; (ii) estimated minimal inhibitory concentrations (MICs) of metals; (iii) concentrations of heavy metals that caused biodegradation half-life doublings (HLDs); and (iv) heavy metal concentrations that caused a significant effect on biodegradation (> 10% increase in t½ of 1,2-DCA). The effects of biostimulation, bioaugmentation and the addition of treatment additives on the biodegradation process were evaluated. The presence of heavy metals was observed to have a negative impact on the biodegradation of 1,2-DCA in both clay and loam soil samples, with the toxic effect being more pronounced in loam soil for all heavy metal concentrations except for Hg2+, after 15 days. Heavy metal concentrations of 75 mg/kg As3+, 840 mg/kg Hg2+, and 420 mg/kg Pb2+, resulted in 34.24%, 40.64%, and 45.94% increases in the t½ of 1,2-DCA, respectively, in loam soil compared to clay soil. Moreover, the combination of four heavy metals in loam soil resulted in 6.26% less degradation of 1,2-DCA compared to clay soil, after 15 days. Generally, more than 127.5 mg/kg Cd2+, 840 mg/kg Hg2+ and 420 mg/kg of Pb2+ was able to cause a > 10% increase in the t½ of 1,2-DCA in clay soil, while less than 75 mg/kg was required for As3+. An increased reduction in 1,2-DCA degradation was observed with increasing concentration of the heavy metals. In clay soil, a dose-dependant relationship between k1 and metal ion concentrations in which k1 decreased with higher initial metal concentrations was observed for all the heavy metals tested except Hg2+. Ammonium nitrate-extractable fractions of bioavailable As3+ and Cd2+ concentrations varied greatly, with approximately < 2.73% and < 0.62% of the total metal added to the system being bioavailable, respectively. Although bioavailable heavy metal fractions were lower than the total metal concentration added to the system, indigenous microorganisms were sensitive to the heavy metals. Biostimulation, bioaugmentation and amendment with treatment additives were all effective in enhancing the biodegradation of 1,2-DCA in the co-contaminated soil. In particular, biostimulation with fertilizer, dual-bioaugmentation and amendment with CaCO3 were most efficient in enhancing 1,2-DCA degradation resulting in 41.93%, 59.95% and 51.32% increases in the degradation rate constant of 1,2-DCA in the As3+ co-contaminated soil, respectively, after 20 days. Among all the treatments, dualbioaugmentation produced the highest 1,2-DCA degrading population of up to 453.33 × 107 cfu/ml in the Cd2+ co-contaminated soil. On comparison of the As3+ and Cd2+ co-contaminated soil undergoing either biostimulation or dual-bioaugmentation, similarity in the denaturing gradient gel electrophoresis (DGGE) banding patterns was observed. However, the banding patterns for the different bioremediation options demonstrated a difference in bacterial diversity between the fertilized and dual-bioaugmented samples. DGGE profiles also indicate that while numerous bands were common in the fertilized co-contaminated soils, there were also changes in the presence and intensity of bands due to treatment and temporal effects. Dehydrogenase and urease activities provided a more accurate assessment of the negative impact of heavy metals on the indigenous soil microorganisms, resulting in up to 87.26% and 69.58% decreases in activities, respectively. In both the biostimulated and bioaugmented soil microcosms, dehydrogenase activity appeared biphasic with an initial decrease followed by an increase in the treated soils over time. Results from this study provide relevant information on some alterations that could be introduced to overcome a critical bottle-neck of the application of bioremediation technology. In conclusion, the bioremediation strategies adopted in this study may be used as a rational methodology for remediation of sites co-contaminated with 1,2-DCA and heavy metals, subject to a thorough understanding of the microbial ecology and physico-chemical parameters of the site. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2009.

by Lau Wai Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1981. / Bibliography: leaves 189-205.

Mining industry has been identified as the main sustenance of the South African economy, however the negative impacts of the industry on the ecological systems cannot be over emphasized due to the released waste which is mostly heavy metals into the environment. The study evaluated six heavy metal (A1, Cu, Fe, Ni, Pb and Cr) contents in a tailings dam from a specific mine site. Two sets of samples for the investigation were measured, that is, one in year 2012 and the other in year 2013. In the year 2012, the sample set was only taken at a distance profile of 500 meters from the foot of the dam, whereas the sample set taken in the year 2013 was for the 500 and 1500 meter distance profiles from the foot of the dam. The year 2012 and 2013 sample sets for the 500m distance profile were sampled very similarly to each other. A kilogram of each sample was taken as per grid format. The samples at varied depths were taken at 0-cm depth for the top layer, 20cm depth for the second layer, and 30cm depth for the third layer. The samples for the surface varied distance were taken at 1 m, 2m, 3m, and 4m away from each 500m and 1500 sampling points. The 2012 samples were analysed using characterization methods namely ICP MS and The 2013 samples were analysed using the ICP OES. The comparison of the field results for the six heavy metals studied (A1, Fe, Pb, Cu, Ni and Cr) was performed using statistical analytical methods, namely ANOVA. The statistical analysis results for heavy metals (A1, Fe, Pb, Cu, Ni and Cr) from sample and 2013 revealed that the group means are not significantly different from each other which means that there is no significant difference in (A1, Fe, Pb, Cu, Ni and Cr) concentrations with respect to both depth and distance. The observations from both 2012 and 2013 indicate the results of the samples are in agreement. In addition, the comparative average concentrations of the three results obtained reach the same conclusion that the tailing dam probably does not introduce considerable or significant amounts of these metals (A1, Fe, Pb, Cu, Ni and Cr) into the surrounding soils. / Chemical Engineering / M. Tech. (Chemical Engineering)

A study was conducted to test for the presence of heavy metals (Cu, Mn, and Zn) in surface sediments of the Puerco River channel in the aftermath of a toxic spill in 1979 near Church Rock, New Mexico. Analysis of samples from five sites downstream from the spill showed that these substances were not present in unusually large amounts, though an increasing gradient of metal concentration with distance downstream was revealed. Statistical analysis revealed the Cu, Mn, and Zn were associated with clay and silt, soil organic matter, organic carbon, and carbonates, all of which existed as extraneous, uncontrolled variables. Adjusted metal concentrations, obtained with covariate analyses, confirmed the increasing gradient downstream. Clay and silt also increased downstream. Some toxic substances may have leached into the riverbed; possible mechanisms for this process are also discussed and further study to substantiate or disprove this hypothesis is recommended.

Mining industry has been identified as the main sustenance of the South African economy, however the negative impacts of the industry on the ecological systems cannot be over emphasized due to the released waste which is mostly heavy metals into the environment. The study evaluated six heavy metal (A1, Cu, Fe, Ni, Pb and Cr) contents in a tailings dam from a specific mine site. Two sets of samples for the investigation were measured, that is, one in year 2012 and the other in year 2013. In the year 2012, the sample set was only taken at a distance profile of 500 meters from the foot of the dam, whereas the sample set taken in the year 2013 was for the 500 and 1500 meter distance profiles from the foot of the dam. The year 2012 and 2013 sample sets for the 500m distance profile were sampled very similarly to each other. A kilogram of each sample was taken as per grid format. The samples at varied depths were taken at 0-cm depth for the top layer, 20cm depth for the second layer, and 30cm depth for the third layer. The samples for the surface varied distance were taken at 1 m, 2m, 3m, and 4m away from each 500m and 1500 sampling points. The 2012 samples were analysed using characterization methods namely ICP MS and The 2013 samples were analysed using the ICP OES. The comparison of the field results for the six heavy metals studied (A1, Fe, Pb, Cu, Ni and Cr) was performed using statistical analytical methods, namely ANOVA. The statistical analysis results for heavy metals (A1, Fe, Pb, Cu, Ni and Cr) from sample and 2013 revealed that the group means are not significantly different from each other which means that there is no significant difference in (A1, Fe, Pb, Cu, Ni and Cr) concentrations with respect to both depth and distance. The observations from both 2012 and 2013 indicate the results of the samples are in agreement. In addition, the comparative average concentrations of the three results obtained reach the same conclusion that the tailing dam probably does not introduce considerable or significant amounts of these metals (A1, Fe, Pb, Cu, Ni and Cr) into the surrounding soils. / Chemical Engineering / M. Tech. (Chemical Engineering)