Dissertations / Theses on the topic 'Cadmium – Environmental aspects'

Phytoextraction is an innovative method that can be implemented to remove lead (Pb), cadmium (Cd), and zinc (Zn) from contaminated soil. A two-year field and growth chamber study was conducted to determine the effectiveness of several soil amendments in the phytoextraction or stabilization of Pb, Cd and Zn. Field plots were established at the Memorial Drive Dump site (Muncie, IN). Amendments included composted municipal solid waste (MSW) (25 Mg/ha), dried sewage sludge (SS) (25 Mg/ha), citric acid (2 mmol/kg soil), ethylenediaminetetraacetic acid (EDTA) (2 mmol/kg soil), and a control. A mixed grass crop was capable of survival and growth in the contaminated soil; in contrast, Helianthus annuus (sunflower) and Ambrosia artemisiifolia (ragweed) failed to become established. Soil Pb and Zn occurred primarily in the carbonate, organic-bound and residual forms (23.1%, 31.8%, and 44.4%, Pb, respectively and 11.4%, 26.5%, and 60.2% Zn, respectively). Soil Cd occurred primarily in the soluble, carbonate, and residual forms (21.8%, 21.3%, and 27.4%, respectively). In a growth chamber leaching study, soil Pb was most rapidly leached from the 0.1 M EDTA treatment (51.7 mg Pb over 200 pore volumes); the 0.001M resulted in the lowest leaching. Soil Pb was most rapidly leached using 0.1 M HEDTA (52.1 mg Pb over 200 pore volumes). The 0.001 M HEDTA rate resulted in lowest Pb leaching. Addition of an NPK solution resulted in minimal Pb leached. The MSW and dried sludge treatments resulted in the greatest dry matter production on the plots. Dry matter production was significantly (p >0.05) higher in the MSW (1.09 MT/ha) and SS (95 MT/ha) treatments. Addition of EDTA, citric acid and MSW significantly (p < 0.05) increased the amount of Cd uptake into plant tissue. The study also demonstrated the ability of vegetation to establish and grow on toxic soil and to uptake Pb, Cd, and Zn.
Department of Natural Resources and Environmental Management

Cadmium in the ocean has a nutrient-like cycling pattern: with biological uptake at the surface, subsequent sinking in particulate form and then regeneration as dissolved species in deeper waters. Many measurements have been made over time of the ratio of the concentrations of dissolved Cd to those of PO₄ (Cd/PO₄) in the world ocean and this has become one of the best relationships documented between a trace metal and a nutrient. Combined with the measurements of the Cd/Ca ratio in foraminifera, the Cd/PO₄ ratio has been used to reconstruct the oceanographic circulation patterns that existed during past glacial periods and hence provides information on past climate changes. In the present study Cd/PO₄ ratios of the Southern Indian Ocean in surface and deep waters were investigated. The slopes of the relationships between Cd and PO₄ concentrations in waters of this region are high compared to the global correlations, and lie between those reported for other parts of the Southern Ocean and the Pacific Ocean. In surface waters of the Southern Indian Ocean, Cd/PO₄ ratios decrease from regions exhibiting high nutrient-low chlorophyll (HNLC) characteristic in the south to oligotrophic waters further north. It is also found that particulate Cd plays an important role in regulating the high Cd/PO₄ ratios reported in waters south of the Polar Front. Very low Cd/PO₄ ratios were measured in waters associated with the Subtropical Front southeast of New Zealand compared to other Southern Ocean and global oceanic waters. Seasonal variations in the Cd/PO₄ ratios measured for these waters strongly suggest they are associated with a significant biological uptake of dissolved Cd particularly during the phytoplankton growth season in summer. Dissolved Fe concentrations in the Southern Indian Ocean and seasonal variations of Fe in waters off the Otago Coast (southeast of New Zealand) suggest that Fe may stimulate phytoplankton growth and this might result in lower Cd/PO₄ ratios in surface waters through enhanced Cd uptake relative to PO₄ by the phytoplankton. However there is no distinct relationship between dissolved Fe concentrations and the dissolved Cd/PO₄ ratios measured in these surface waters. This finding is in disagreement with the recent 2006 hypothesis put forward by J.T. Cullen, which proposed that waters exhibiting low dissolved Cd/PO₄ ratios were associated with the HNLC regions. From a consideration of the potential Zn concentrations calculated from Si concentration measurements reported for these waters, it would appear that Zn may play a more important role than Fe in regulating Cd/PO₄ ratios in these waters. Measurements of dissolved and total Cd concentrations relative to those of PO₄ were also undertaken in the Otago Harbour and immediate surrounding coastal waters. These exhibited higher Cd concentrations and higher Cd/PO₄ ratios than open ocean waters further off the Otago Coast. The particulate Cd concentrations showed a negative correlation with Cd concentrations measured in cockle species (Austrovenus stuchburyi) collected in the harbour, suggesting that particulate Cd is not the source of Cd measured in the tissue of this species. The concentrations of Cd and other trace metals were also measured in samples of green mussel (Perna canaliculus), ribbed mussel (Aulacomya atra maoriana) and oyster (Saccostrea cucullata) collected from Otago Harbour and possible correlations explored between these concentrations and other parameters such as the shellfish condition indices and environmental gradients in the harbour. In summary, measurements of dissolved and particulate Cd concentrations in the water column can provide unique information on a number of processes occurring in the global marine environment.

Evaluation of heavy metal accumulation in soils and plants is of environmental importance due to their health effects on humans and other biota. Phytoremediation is an emerging technology that can stabilize or remove heavy metals in soil utilizing metal tolerant plant species (metallophytes). The objectives of this study were to: (1) assess a Superfund site, and a lead-acid battery dump for concentrations of soil lead (Pb) and cadmium (Cd); (2) assess the various chemical fractions of Pb and Cd at both sites; (3) identify native herbaceous vegetation surviving in the contaminated soils; and (4) evaluate plant uptake of Pb and Cd. Soil Pb and Cd concentrations at the Superfund site averaged 55,480 and 8.5 mg/kg, respectively. Soil Pb at the Superfund site occurred primarily in the carbonate, sulfide/residual, and organic chemical fractions (41.6, 28.6, and 26.7, respectively). Soil Pb and Cd concentrations at the dump site averaged 29,400 and 3.9 mg/kg, respectively. Soil Pb occurred mostly in the organic and carbonate fractions as 48.5 and 42.5% respectively. Plant uptake of Pb at both sites ranged from non-detectable (Agrostemma githago, Plantago rugeli, Alliaria officinalis shoots), to 1800 mg/kg (Agrostemma githago root). Cd uptake was maximal in Taraxacum officinale at 15.4 mg/kg (Superfund site). In the majority of plants studied, root Pb and Cd content was higher than for shoots (>_65%). Tissue and soil fractions yielded r2 of 0.61 and 0.57 for the soluble and carbonate-Pb fractions, respectively. The plants with the greatest tissue concentrations of Pb and Cd were predominantly herbaceous species, some of which produce sufficient biomass to be practical for phytoremediation technologies.
Department of Natural Resources and Environmental Management

Effects of episodic exposures have gained attention as the regulatory focus of the Clean Water Act has shifted away from continuous-flow effluents. Standardized laboratory toxicity tests require that exposure be held constant. However, this approach may not accurately predict organism responses in the field following episodic exposures such as those associated with rain-driven runoff events or accidental pollutant discharge. Using a modified version of the 7-day short-term chronic test recommended by the US Environmental Protection Agency, Ceriodaphnia dubia were exposed to copper or cadmium for durations ranging from 1 minute to 24 hours. In addition, adult reproductive recovery and effects on second generation individuals was assessed following select copper exposures. Finally, cadmium exposures were compared in reconstituted hard water (RHW) and municipal treated wastewater effluent (TWE). Following exposure, organisms were transferred to clean RHW or TWE and maintained for the remainder of the test. No- and lowest observed effect concentrations (NO- and LOECs) increased logarithmically with respect to logarithmic decreases in duration regardless of metal, endpoint or water type. Effective concentrations of cadmium however, were usually higher than those of copper, especially in TWE. LOECs for C. dubia survival following 24-hour and 5-minute exposures to copper were 116 and 417 µg/L, respectively. LOECs for fecundity were 58 and 374 µg/L, respectively. Neonate production of first generation adult C. dubia appeared to recover from pulsed copper exposure upon examination of individual broods. Cumulative mean neonate production however, showed almost no signs of recovery at exposure durations ≥3 hours. Pulse exposure to copper also resulted in diminished fecundity of unexposed second generation individuals. Such effects were pronounced following parental exposure for 24 hours but lacking after parental exposures ≤3 hours. LOECs for C. dubia survival following 24-hour and 5-minute exposures to cadmium in RHW were 44 and 9000 µg/L, respectively. LOECs for fecundity were 16 and 5000 µg/L, respectively. In TWE, LOECs for C. dubia survival were 83 and >10,000 µg/L, respectively. LOECs for fecundity in TWE were 48 and 7000 µg/L, respectively. Runoff pollution is site and event specific, however, data presented herein may be useful as a predictive tool under various conditions.

Heavy metal bioaccumulation in aquatic organisms may occur through direct or indirect uptake routes. Research indicates that the significance of uptake route varies with contaminant and organism exposed. The relative importance of different metal sources in aquatic systems was investigated by exposing freshwater snails to dietary or dissolved sources of cadmium. Snails were exposed to control, contaminated food only, contaminated water only, and contaminated food and water treatments. During the 15-day exposure, samples were taken to determine Cd concentration in snail soft tissue, snail shell, algal food, and overlying water. Analyses of snail soft tissue and shells indicate that exposure route significantly affects Cd concentrations in the tissues. In both cases, dissolved Cd is the primary contributor to metal body burden.

The technological development and application of waste-to-resource strategy is significantly critical and crucial in both environmental and manufacturing industries, via which we do not only provide practical treatments to toxic waste materials but also translate them into usable products. It has been considered as a preferred method which should be applied in future wastewater treatment strategies. In this study, we investigated the process of incorporating cadmium oxide and nickel oxide into ceramic-based materials with the phases of CdAl4O7, and CdFe2O4. Such products are of less harmful effect to the natural environment and can also be of beneficial use with their good mechanical properties identified by nano-indentation. We proved the possibility and provided an opportunity to convert the waste from wastewater treatment process to a new material resource. XRD is preferred for characterizing solid mixtures to determine the relative abundances of crystalline phases during the reaction process. As a result, we can obtain the relative abundance information on the growth of the crystalline products, such as CdAl4O7, and CdFe2O4 according to the change of fabrication temperatures. In that case, the starting reaction temperature and the optimized temperature (at which the completed reaction could be achieved) could be revealed. In Cd-Al system, the starting temperature for CdAl4O7 formation is 900 °C, and the optimized formation temperature is around 1020 °C. On the other hand, for Cd-Fe system, such temperatures are of 700 °C and 850 °C correspondingly. In our research, it is shown that the ceramic-process is an effective strategy to stabilize the waste hazardous metals (cadmium and nickel) by materials such as aluminate, ferrite, and kaolin commonly used in ceramic industry. Through this method, the difficult-to-treat wasted metals would become reusable and applied in building and infrastructure projects. Products containing CdAl4O7, CdFe2O4 and NiAl2O4 have shown higher resistance to acidic leaching, comparing to CdO and NiO used as the starting materials to simulate the waste metal forms discharged from the industrial stream. Furthermore, similar measurements by alkaline attack on the sintered products (NiAl2O4 containing samples) were also studied. Besides the investigation to leaching behavior, the mechanical properties are also measured by nano-indentation in our work. The incorporation of metal waste into the fabrication of ceramic products is valuable due to the preferred stabilization mechanisms of crystal structures and the large volume of ceramic products needed by the construction industry. Furthermore, because the product safety and functionality should not be compromised, a fundamental understanding of the surface properties of metal containing phases should be further established, rather than relying solely on data from regulatory tests on bulk samples. Therefore, the results of this study demonstrate the superior mechanical properties of nickel spinel containing products, comparing to the cristobalite silica matrix, under severe acid attack.
published_or_final_version
Civil Engineering
Master
Master of Philosophy

Despite improved liner design, there are still reported incidences of landfill leachate, rich in heavy metals, percolating through to groundwater and threatening ecosystems. This thesis introduces the concept of segregating municipal solid wastes (MSW) according to their major heavy metals and their metal's adsorption compatibility. Each segregated portion can be disposed in a different landfill compartment to minimize leaching of these heavy metals with the greatest bioactive impact. The validity of the concept was evaluated by batch and column retention mobility studies using copper (Cu) alone or with either lead (Pb) or cadmium (Cd) in solutions bearing various pHs. This was supported by selective sequential extraction (SSE) to determine the affinity to specific liner fractions. The following summarizes the procedure used.
Beforehand, a soil column test using sand with 5 and 10% bentonite was conducted to develop an equation predicting liner permeability, k , under simulated field conditions. The column permeability test revealed that a liner with 5% bentonite resulted in a k value which respected the North American criteria of 10-5 m/s.
In the batch experiments, solutions with Cu alone or with Cd or Pb, adjusted to pH of 3.7, 5.5 or 7.5, were applied to sand liners with 0%, 5% or 10% bentonite, having CEC's of 2.0, 6.4, and 10.8 (cmol(+) kg-1 ), respectively. Bentonite, pH and Pb significantly affected Cu adsorption. Cu was adsorbed by the liners at pH <6.5 whereas Cu precipitated at pH >6.5. Cu retention was higher in the presence of Cd than in that of Pb, at all combinations of CEC and pH. Competition between metals was greater in liners with lower CEC and therefore fewer adsorption sites. Limiting Pb in a landfill compartment can improve Cu adsorption at pH's below the precipitating threshold.
In the SSE procedure, the liner samples were centrifuged, decanted from their solutions and each adsorption fraction analyzed for Cu content. Results indicated that the carbonate fraction adsorbed more Cu, and that Pb significantly increased the mobility of Cu due to competition for exchangeable sites.
In the final soil column test using a sand liner with 5% bentonite, the leachate had an initial pH of 3.7. The leaching test confirmed the compatibility of Cu with Cd. The leaching of Cu was greater in the presence of Pb. Total metals in leachate was greater for the Cu-Cd solutions than for the Cu-Pb, because of Cd's relatively high mobility. The sequential extraction results showed again that the carbonate fraction dominated metal adsorption. Total heavy metal leaching followed the order of Cu/Cd > Cu/Pb > Cu alone.
Thus, disposing MSW in landfill compartments based on their heavy metal compatibility can minimize migration of heavy metals.

Lethal toxicity values (96 h LC50; mg Cd/L) for the test species were similar: Lepomis cyanellus, 11.52; Notropis lutrensis, 6.62; Pimephales promelus, 3.58. However the effects of cadmium concentration and exposure time on temperature tolerance varied between species. Neither cadmium concentration nor exposure time had a significant effect on the CTM of green sunfish. Both cadmium concentration and exposure time had a significant effect on the CTMs of red shiners and fathead minnows. By day 10 mean CTMs were 2.3 t- 4.5 C (red shiners) and 4.2 to 5.7 C (fathead minnows) lower than control CTM. These results suggest a potential problem in cadmium contaminated systems for high environmental temperatures to stress or kill fish.

The aim of this study was to investigate the cadmium (Cd) exposure level from traditional food in Fort Resolution, Northwest Territories. Cd concentration in the liver and kidney of caribou and moose exceeded the action level (1 $ mu$g/g) established by Agriculture Canada, but the frequencies of consumption of these foods were relatively low. Cd intakes from traditional food ranged from 0.01 to 1713 $ mu$g/day/person. Average Cd intakes from traditional food were estimated to be 10% and 6% of the Provisional Tolerable Weekly Intake (PTWI), 7 $ mu$g/kg body weight/person, for women and men, respectively. The major contributors to the total Cd intake on a population basis were moose liver for women, and flesh of moose and caribou for men. The average Cd inhaled from cigarette smoking was 21.1 $ pm$ 9.1 $ mu$g/day/person. Total Cd intakes from traditional food and smoking were estimated to be 24% and 20% of the PTWI for women and men, respectively. The total Cd intakes of smokers and nonsmokers were significantly different (p $<$ 0.001). The total Cd intake via market and traditional food, and cigarette smoking was 246.4 $ mu$g/week which was lower than the PTWI, 500 $ mu$g/week. Another objective of this study was to investigate an effect of food preparation on Cd speciation in food. (Abstract shortened by UMI.)

Thesis (MSc)--University of Stellenbosch, 2006.
ENGLISH ABSTRACT: The development of potential genetically based resistance to cadmium (Cd) after long-term exposure to this metal at a sublethal concentration, was investigated in earthworm specimens belonging to the genus Eisenia. Adult (clitellate) earthworms from a long-term laboratory Cdexposed population (> 78 generations) and from other populations having no previous history of metal exposure were exposed to increasing concentrations (0; 2.5; 5; 10 and 20 mg/l) of Cd in the form of CdSO4. Different biomarkers and molecular markers were used to determine whether the specimens from the long-term Cd-exposed population had acclimatized or adapted to the metal contaminated environment. Acclimation was investigated at different physiological and biochemical levels using the following three biomarkers: the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay (MTT assay) measuring mitochondrial activity and cell viability; the single cell gel electrophoresis assay (comet assay) measuring DNA strand breaks and the biosynthesis of metallothioneins (MTs) that have the function of lowering metal toxicity. Earthworms from the long-term exposed substrate as well as specimens from populations not exposed to Cd were used. Adaptation was investigated by looking at both allozyme polymorphism at seven enzyme encoding loci and DNA polymorphism using chosen neutral and selectable genetic markers. The markers used were cytochrome c oxydase subunit I (COI) and metallothionein-2 (mt-2) respectively. This was done amongst the same pool of populations. Additionally, the DNA polymorphism study also aimed at genetically identifying the species utilized in this study thereby determining whether these earthworms belong to the species Eisenia fetida or Eisenia andrei. MTs biosynthesis did not generate the expected data mainly due to the fact that a suitable antibody could not be obtained (discussed in Chapter 5 section 5.3.3.). Similarly, the assessment of DNA polymorphism at the chosen selectable genetic marker mt-2 did provide information relevant to understanding the potential development of resistance to Cd in the long-term metal contaminated group. COI sequences generated in this study were compared to E. fetida and E. andrei COI sequences available on Genbank. Consequently, specimens used in this study were identified as possibly belonging to the species E. andrei. Allozyme polymorphism revealed no fixed genetic differences between the long-term Cd exposed laboratory culture and the rest of the populations. All the populations departed from Hardy-Weinberg equilibrium (χ2 > 5.9; p < 0.05), and showed a low mean heterozygosity per locus (Ho ≤ 0.21), probably due to inbreeding. Cell viability and proliferation as tested by the MTT assay revealed that coelomocytes, isolated from the long-term Cd-exposed group showed the highest viability (98.42%) compared to those from other groups (+/- 80%). Kruskal-Wallis ANOVA (H2, 225=109.7165 p < 0.001) revealed that the long-term Cd-exposed laboratory culture showed a better response to acute exposure to Cd, thus demonstrating that these worms have developed some kind of tolerance to Cd. Similarly, the comet assay showed that in the long-term Cd-exposed specimens, less DNA breaks occurred after Cd exposure than in the unexposed groups. Of all the comet parameters assessed in this study (comet tail length, tail moment and tail DNA percentage), tail DNA percentage seemed to be more sensitive although all three parameters indicated that long-term Cd-exposed specimens were more resistant than unexposed specimens as shown by the number of single strand DNA breaks induced by exposure to higher concentrations of Cd (p < 0.001). The comet and the MTT assays indicated that the earthworms with a previous history of Cd exposure have developed increased fitness towards higher doses of Cd, compared to previously unexposed groups. These findings mainly proved that several mechanisms could come into play at the physiological and biochemical level to allow the Cd exposed population to acclimatize to its chemically stressful environment. Clear genetic support for the differences found between the tested populations was not obtained, but needs to be investigated further using Cd selectable markers such as the mt-2 gene, in order to come to a more conclusive deduction.
AFRIKAANSE OPSOMMING: Die moontlike ontwikkeling van geneties gebaseerde weerstand teen kadmium (Cd) by erdwurms van die genus Eisenia, na langtermyn blootstelling aan die metaal by 'n subletale konsentrasie, is ondersoek. Volwasse (klitellate) erdwurms van 'n langtermyn laboratorium Cdblootgestelde bevolking (< 78 generasies) asook van ander bevolkings met geen voorgeskiedenis van metaal blootstelling nie, is blootgestel aan 'n reeks van Cd konsentrasies (0; 2.5; 5; 10; en 20 mg/l) in die vorm van CdSO4. Verskillende biomerkers en molekulêre merkers is gebruik om vas te stel of die erdwurms geakklimeer of aangepas het by die metaal in die gekontamineerde omgewing. Akklimasie is op verskillende fisiologiese en biochemiese vlakke getoets deur die volgende drie biomerkers te gebruik: Die 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromied toets (MTT toets), wat mitochondriale aktiwiteit en sel lewensvatbaarheid meet; die enkel sel elektroforese toets (Komeettoets) wat DNS string breuke meet; die biosintese van metallotioniene (MT's) wat metaalvergiftiging verlaag. Erdwurms van die langtermyn blootstellingsubstraat asook eksemplare van bevolkings wat nie aan kadmium blootgestel was nie, is gebruik. Aanpassing is ondersoek deur gebruik te maak van allosiem polimorfisme, waar 7 ensiem koderende lokusse gebruik is asook van DNS polimorfisme deur neutrale genetiese merkers te selekteer. Die merkers wat gebruik is, was sitochroom c oksidase, subeenheid I (COI) en metallotionien-2 (mt-2) respektiwelik. Hierdie toetse is met dieselfde groepe bevolkings uitgevoer. 'n Bykomende van die studie aspek waar ook van DNS polimorfisme gebruik gemaak is, was daarop gemik om die spesie wat vir die huidige studie gebruik is, geneties te identifiseer en om vas te stel of die erdwurms aan die spesie Eisenia fetida of Eisenia andrei behoort. Die MT biosintese het nie die verwagte data gegenereer nie, hoofsaaklik weens die feit dat geskikte teenligaampies nie beskikbaar was nie (bespreek in Hoofstuk 5 afdeling 5.3.3). Soortgelyk, het die waardebepaling van DNS polimorfisme by die geselekteerde genetiese merker mt-2 nie genoegsame informasie verskaf om die potensiaal van die ontwikkeling van weerstand teen Cd in die langtermyn blootgestelde groep te verstaan nie. COI geenvolgordes van E. fetida en E. andrei wat op Genbank beskikbaar was, is gebruik om met die resultate van die huidige studie te vergelyk. Die spesie wat tydens die huidige studie gebruik is, is op hierdie wyse geïdentifiseer as E. andrei. Allosiem polimorfisme het geen vaste genetiese verskille tussen die langtermyn blootgestelde laboratoriumkulture en die ander bevolkings getoon nie. Al die bevolkings het verskil van die Hardy-Weinberg ewewigstoestand (χ2 > 5.9; p < 0.05) en het 'n lae heterosigositeit per lokus getoon (Ho ≤ 0.21), moontlik as gevolg van inteling. Sellewensvatbaarheid en proliferasie soos getoets met die MTT toets, het getoon dat selomosiete, geïsoleer vanuit die langtermyn Cd blootgestelde groep, die hoogste lewensvatbaarheid (98.42%) gehad het in vergelyking met die ander groepe (+/- 80%). Kruksal-Wallis ANOVA (H2, 225=109.7165 p < 0.001) het getoon dat die langtermyn Cd blootgestelde laboratoriumkultuur 'n beter respons vir akute blootstelling aan Cd gehad het. Hierdeur is gedemonstreer dat hierdie wurms 'n soort toleransie teenoor kadmium ontwikkel het. Soortgelyk het die komeettoets aangetoon dat daar in die langtermyn blootgestelde eksemplare minder DNS breuke voorgekom het na verdere blootstelling aan Cd as in die ander groepe. Van al die komeet parameters wat tydens die studie gemeet is (komeet stertlengte, Olive stert moment en stert DNS persentasie), het die stert DNS persentasie geblyk om die mees sensitiefste te wees, alhoewel al drie parameters aangetoon het dat die langtermyn Cd blootgestelde eksemplare meer weerstandbiedend was teen induksie van DNS enkelstring breuke weens Cd blootstelling (p < 0.001), as die wat nie voorheen blootgestel was nie. Die komeet en MTT toetse het aangetoon dat erdwurms met 'n voorgeskiedenis van Cd blootstelling 'n toenemende fiksheid teen hoër dososse van Cd ontwikkel het as die wat nie voorheen aan kadmium blootgestel was nie. My bevindings kon hoofsaaklik toon dat verskeie meganismes op die fisiologiese en biochemiese vlak 'n rol sou kon speel om Cd blootgestelde bevolkings by 'n chemies stresvolle omgewing te laat akklimeer. Duidelike ondersteuning vir die verskille tussen die getoetsde bevolkings deur van Cd geselekteerde merkers soos die mt-2 geen gebruik te maak om 'n meer finale afleiding te kan maak is nie verkry nie en behoort verder ondersoek te word.

The University of North Texas Stream Research Facility (UNTSRF) was designed to examine contaminant impacts on effluent-dominated stream ecosystems. Stream mesocosms, fed municipal effluent from the City of Denton, TX, Pecan Creek Water Reclamation Plant (PCWRP), were treated with 0, 15 or 140 µg/L cadmium for a 10-day study in August 2000. Laboratory toxicity test and stream macroinvertebrate responses indicated that cadmium bioavailability was reduced by constituents of effluent-dominated streams. The Biotic Ligand Model (BLM) for Cd was used to predict a 48 hour Cd EC50 for Ceriodaphnia dubia of 280 µg/L in these effluent-dominated streams. This value is higher that an EC50 of 38.3 µg/L Cd and a 7-day reproduction effect level of 3.3 µg/L Cd generated for C. dubia in reconstituted laboratory hard water. These results support use of a cadmium BLM for establishing site-specific acute water quality criteria in effluent-dominated streams. Although not affected by 15 µg/L treatments, organisms accumulated Cd in 15 µg/L treated streams. Hence, over longer exposure periods, Cd accumulation may increase and a no effect level may be lower than the observed 10-day no effect level of 15 µg/L. A toxicity identification evaluation procedure was utilized with in vitro and in vivo bioassays to identify estrogenic compounds in PCWRP effluent, previously identified to seasonally induce vitellogenin (VTG) in male fathead minnows. Steroids, nonylphenol ethoxylate metabolites, and other unidentified compounds were identified as causative effluent estrogens. These findings suggest that in vivo VTG bioassays should be used to confirm in vitro Yeast Estrogen Screening assay activity when effluents are fractionated or screened for estrogenicity. A subsequent 90-day cadmium study was initiated to assess long-term effluent and cadmium effects on fish endocrine function. Juvenile fathead minnows were placed in UNTSRF pool sections of replicate streams treated with 0, 5, 20 or 80 µg/L Cd. Male VTG was induced at each treatment level, indicating that PCWRP effluent was estrogenic during fall 2001. 20 and 80 µg/L Cd treatments reduced male circulating estradiol levels and critical swimming performance. Future studies are needed to assess impacts of environmental estrogen exposure on fish calcium metabolism and vertebral integrity.

Microphytobenthos (MPB), a mixed community of microscopic, photosynthetic organisms, algae and cyanobacteria, inhabiting the top few millimetres of bottom sediment, is a key component of intertidal mudflats. It accounts for a significant proportion of estuarine primary production, forms the base of the food chain and influences sediment distribution and resuspension (through production of extracellular polymeric substances (EPS)). Diatoms dominate the microphytobenthos community in the mid-latitudes of the Northern Hemisphere. Estuarine sediments, are a sink for metal contaminants derived from fluvial, marine and atmospheric sources. Whilst metal releases to estuaries have declined in recent years due to increased regulation and declining industrial activity, metals previously discharged and which are now locked up in saltmarsh sediments remain a concern. For example, there are indications that saltmarshes are already being eroded, due to climate change related sea level rise, in some locations. This erosion may result in the redistribution of historically contaminated sediment to locations, such as the mudflats, where it is more available to biota, such as the MPB. In addition to causing redistribution, climate change effects, such as increasing temperatures and storminess, may also alter the bioavailability of metals to MPB. Increased concentrations of metals within the MPB could potentially increase their transfer to higher organisms through the food chain with potential impacts for biota. Whilst planktonic algae have been well studied with respect to metal uptake from the water column, there has been little research involving MPB and uptake of metals from sediment. The extent to which contaminant uptake by microphytobenthic algae occurs and under what conditions is therefore poorly understood. The research presented uses laboratory, mesocosm and field studies, to gain an understanding of processes governing metal bioavailability and mechanisms for uptake from sediment to the diatoms of the MPB under the complex and variable conditions of intertidal mudflats. A laboratory study using a single diatom species Cylindrotheca closterium found that uptake of cadmium (Cd) varied with sediment properties revealing the importance of sediment particle size and organic matter content in metal bioavailability to diatoms. Additionally, this study showed that the presence of diatoms altered Cd partitioning between sediment, overlying and pore water. Specifically there was an increase in Cd in the overlying and pore water when diatoms were present, indicating that diatoms mobilise metals from the sediment to the water column potentially increasing metal bioavailability to other biota. A study was conducted using an intertidal mesocosm to increase the realism of the study system and examine uptake to a natural MPB community. Diatoms were found to have higher concentrations of all the metals analysed (except tin) than other types of algae (filamentous and sheet macroalgae), confirming their importance as a study organism with respect to metal uptake and potential mobilisation through the food chain. Sediment disturbance was shown to increase metal uptake (iron, aluminium, vanadium and lead) from the sediment to algae. This is of concern due to predicted increases in storminess which are likely to increase sediment disturbance, with the likelihood that uptake of metals to diatoms will increase in the future. However, there were also indications of an antagonistic effect of temperature on disturbance, whilst disturbance increased bioavailability and uptake, increasing temperatures reduced uptake of some metals. This highlights the importance of considering the effects of multiple stressors in complex systems. Field studies showed that concentrations of some metals were related to their position on the mudflat whilst others were related to sampling date, indicating that there may be seasonal controls, such as to the presence of greater diatom biomass in spring and autumn, on metal uptake from the sediment. The research conducted has increased understanding of metal uptake to microphytobenthic diatoms from sediment and the influence they have in transferring metals from sediment to water, however the research also raises a number of new questions. For example, there appeared to be a link between sediment organic matter content and bioavailability of metals to diatoms, although the relative contribution of the diatoms, other algae, cyanobacteria and EPS to the sediment organic matter warrants further investigation. Furthermore, it has shown that the use of laboratory and mesocosm studies for this type of research can produce similar outcomes to those observed in the field but under more controlled and easily manipulated conditions, although field studies will continue to be vital in improving understanding of metals availability and transfer.

Extraction, production, utilization and disposal of material resources have been undertaken continuously for much of human histories. Unavoidably, all of these activities have disturbed our environment, and subsequently have been harmful to humans and ecosystems in this and future generations. Due to time lag associated with both environment impact and the effects of measures taken to reduce this impact, existing approaches (i.e. monitoring and reacting) do not give sufficiently rapid feedback for effective environmental management. With regard to the complexity and concern related to environment-health chain effects, there is currently no environmental tool or approach that can provide comprehensive information and indicators covering all major environment and health themes, to enable decision makers to make informed judgements about regional policies and plans, relating to the sustainable use and disposal of material resources. Consequently, there is a need for developing a new approach by taking account of a multidisciplinary concept used in this thesis. Substance Flow Analysis (SFA) has been mainly applied in order to provide input information for Health Risk Assessment (HRA). The SFA approach provides the quantity of the substance that is transported (flows) and stored in the system (stock), and of which sub-system, flow, and process is the greatest concern. The HRA approach provides estimates of human health risk associated with site, activity and facility. An environmental fate and transport model is another key knowledge area incorporated into the HRA process. An integrating method of SFA, environmental fate and transport, and HRA is developed and illustrated by a case study of cadmium in Australia. This thesis shows that this new integration of existing stand-alone methods can provide holistic information and useful indicators covering all significant economic activities, environment, flows, and health risk assessment for selected substances. This enables better decision making on the use and disposal of substances at a range of levels in the economy, from corporations to regions and nations.

Long-term low-level ingestion of cadmium (Cd) causes human health problems, and in Australia, vegetables supply ~40% of the Cd in the typical diet. Plants take up Cd from the soil; however, the uptake is poorly predicted by simple soil tests, such as the total concentration of Cd (Cdt). Therefore, a greater understanding of Cd behaviour in soils is needed to improve the prediction of Cd uptake by plants and open a new path to minimise the risks for human health. The objectives of the research in this thesis were to: identify key soil properties affecting Cd behaviour, identify/develop selective methods to measure them, and to formulate a conceptual model of Cd partitioning. These objectives were based on the hypothesis that empirical modelling informed by a better understanding of Cd chemistry would accurately describe Cd partitioning in soil. To test the hypothesis, the key properties were measured on soils from the peri-urban fringe of Greater Sydney (n = 41) and a series of models of increasing complexity were fitted to the data. A model with three explanatory variables— log10 Cdt, pH and log10 ECEC (effective cation exchange capacity)—explained 94.6% of variation in log10 CdCa (the concentration of Cd in solution in a suspension of soil in 10 mM CaCl2), which strongly supported the hypothesis. The study also indicated that the explanatory variables, Cdt, pH and ECEC, may describe Cd behaviour in many soils, and that for these general models, partition coefficients, such as log10 (Cdt/CdCa), are unsuitable dependent variables. The preceding model used Cdt as an explanatory variable, notwithstanding that labile Cd (CdE) was mechanistically preferable. However, CdE can only be measured using isotopic techniques: a requirement that has constrained the evaluation of CdE as an index of Cd behaviour and bioavailability. Therefore, a simple proxy measure of CdE was investigated. The literature indicated that solutions of chloride salts might selectively extract CdE, and Cd extracted into 1 M NH4Cl (CdNH4Cl) was compared with CdE measured by stable isotope dilution ICPMS. For 23 soils from the partitioning study, 1 M NH4Cl failed to completely extract CdE, unless the pH was less than 5. The cause(s) of this effect will be investigated with the aim of developing a universally applicable measure of CdE that does not require isotopic measurements. All models of Cd uptake by plants rely on soil properties measured on homogenised samples, although the distribution and bioavailability of Cd vary spatially in the field. Were such variability to increase at the micro-scale, its effects could erode the accuracy with which models could predict Cd behaviour and uptake. Consequently, I tested whether the distribution of Cd could be mapped by using synchrotron micro-x-ray fluorescence spectroscopy (micro- XRFS): the most sensitive method of observation. The soils examined contained 0.3–6.4 mg Cd/kg, i.e. were typical agricultural soils, and one was spiked to ~100 mg Cd/kg. Micro-XRFS mapped the Cd in the spiked soil, and in one particle in the other soils. For typical agricultural soils, the sensitivity realised in this study would have been sufficient to characterise the average Cd binding site, but fell at least 10-fold below that needed to map the Cd distribution in them. The research satisfied the objectives, advanced knowledge of Cd behaviour in soils, and provided new research leads. These leads include the possibility of developing general models of Cd partitioning in soils, derivatives of which may predict Cd uptake by plants. The accuracy of these models may be strengthened by the use of CdE as an explanatory variable, but may be weakened by the effects of in situ variation in the distribution of Cd. The benefits to human health of agricultural practices that decrease dietary Cd justify continuation of research to develop models that accurately predict Cd uptake by plants.
Doctor of Philosophy (PhD)

Anthropogenic activities generate waste products that pollute the environment with bacteria and heavy metals. This research assessed pollution of the Kahwa River, Bukavu Town, DRC with cadmium and lead (HMs) and bacterial enteropathogens. A survey of businesses, households and healthcare facilities showed general use of the river to remove effluent and waste. Indicator organisms were cultured at over 200 cfu/100 ml showing faecal contamination of the river water. Antibiotic resistance was shown by enteropathogenic Vibrio cholerae and Salmonella typhi to ampicillin and cotrimoxazole with some sensitivity shown to ciprofloxacin. River water contained HMs at around 40 times the World Health Organisation limit for drinking water. The bacteria, particularly from river sediment, tolerated HMs up to a concentration of 1.5 mg/ml. The presence in the Kahwa River of antibiotic-resistant pathogens showing tolerance to HMs has serious public health implications
Environmental Management
M.Sc. (Environmental management)