This study investigated the short-term inhibitory effects of 8 chlorinated compounds on aquatic microorganism heterotrophic activity. A technique involving the measurement of substrate uptake rates using radio-actively labeled glucose was employed. All compounds studied have been identified as foreign pollutants in aquatic environments and include the highly toxic ones DDT, dieldrin and a PCB (Aroclor 1254). The aquatic microorganisms were predominatly bacteria. On a short-term basis, the PCB and tetrachlorophenol were the most toxic pollutants, decreasing the maximum glucose uptake rate (Vmax) by 50 percent at 250 ppb concentrations. The remaining pollutants had little effect under 2500 ppb. In addition, tetrachlorophenol was the only compound to significantly increase glucose turnover time (Tt). Results from other experiments were: the toxicity of tetrachlorophenol varied according to the (environmental) water temperature; tetrachlorophenol affected the uptake of glucose more than that of two amino acids, alanine and glutamic acid; with respect to di-, tri-, and tetrachlorophenol, neither the chlorine percentage per pollutant molecule, nor the number of pollutant molecules per mole of water, varied linearly with the pollutant's ability to inhibit glucose uptake; the combined toxicities of various pollutants reduced uptake to only 9 percent below the average of their separate effects; and none of the 4 pollutants tested for long-term effects (DDT, PCB, dieldrin and tetrachorophenol) inhibited uptake after 4 days. It was concluded that the two tests (Type I and Type II as described in Section 2) were quick and reliable techniques for assessing the short and long-term effects of a concentration of a pollutant on heterotrophic activity. It was also determined that other pollutants should be tested for their long-term effects under a variety of conditions (for example, their effects on different substrates and on the sediment microbial community). / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M. Sc. (Zoology)) -- University of Limpopo, 2019 / Many South African rivers, including the Ga-Selati River have been deteriorating for the past few decades, due to an increase in mining, industrial, agricultural and domestic activities. Around mid-January 2014, the Ga-Selati River was contaminated by mine spills from a nearby phosphate mine, which polluted the river and killed many fish species. This river is a primary source of water for many activities (e.g. mining, industrial, agricultural and domestic activities), and as a result, large numbers of reservoirs, farm dams, and inter-basin transfer schemes have been constructed to increase the reliability of water supply along this river. Contamination of surface waters by agricultural pesticides and fertilizers, as well as by industrial metals, is a cause of increasing public concern. The Ga-Selati River is a major tributary for the Olifants River, among other tributaries (Steelpoort River and Blyde River) and it plays a significant role in the Kruger National Park and other private game reserves in the catchment. This River is also known to supply water of very low quality into the main stem of the Olifants River. The Olifants River System has been described as degraded and is contaminated with metal and chemicals, and is considered to be one of the most threatened river systems in South Africa. The aim of the study was to investigate the ecological state of the Ga-Selati River and the impact of water and sediment quality on the aquatic invertebrate communities, and to propose measures to prevent further degradation of the river ecosystem by human disturbance. The main objectives were to: (i) establish the current physico-chemical composition of the river water and sediment along the entire length of the Ga-Selati River, (ii) to determine if poor water quality at the lower end of the river is due to pollution inputs in the lower reaches, or the result of cumulative pollution inputs along the entire length of the river, (iii) Assess the impact of water and sediment quality on the aquatic macro-invertebrate assemblages in the river. The concentrations of pH, and DO were high at all sites. If there was any sort of pollution in the river, especially downstream by the mining sites, we expected these two variables to be lower. The water variables such as EC, TDS and salinity showed a gradual increase from upstream to downstream. There were also elevated levels of certain metals, such as Mg, Na, Ti, B, Sr, K and Ca showing a pollution gradient. The v high concentrations of metals in water samples indicate that the Ga-Selati River is heavily impacted downstream by anthropogenic activities such as illegal dumping/littering at site 6 and mining activities at site 7 to site 9. Some of the metal concentration (Na, Mg, K and Ca) in the river were found to be extremely high compared to other rivers in the region. Metal concentrations in sediment samples were very high compared to water samples River. The nutrient concentrations at the Ga-Selati River were high but did not show a pollution gradient. The macro-invertebrate assemblages in the Ga-Selati River were rich in Ephemeroptera, Diptera and Trichoptera. Site 1 and site 2 accounted for most of the sensitive families, reflecting good water quality at these two sites, while site 9, a downstream site recorded the highest number of tolerant families.. The variations in the macro-invertebrate distribution were shown by the differences in the water quality at the various sites by the CCA plot. The effects of main pollution factors such as, EC, TDS, turbidity and nutrients were correlated with the distribution of tolerant taxa. / National Research Foundation (NRF) and Vlir

Sewage pollution of surface waters is a pressing issue of global concern, even in regions with extensive wastewater and sewage treatment infrastructure. Contaminants, like harmful bacteria that can cause gastrointestinal disease and hinder economic growth and development, enter natural waters through a variety of point and non-point source discharges that range from treated to untreated. With increasing urbanization, aging infrastructure, and changing precipitation patterns due to climate change, it is increasingly important to understand and predict the persistence and transport of sewage-derived bacterial pollution in surface waters. To effectively monitor and predict these contaminants, it is critical to understand sewage-derived bacteria’s extra-enteric ecology, or the ecological dynamics they experience after transitioning from a primary habitat (like the human gastrointestinal system) to a secondary habitat (like natural waters). Dynamics of fecal bacteria are assumed to be driven by loss, as commonly observed for the fecal indicator bacteria (FIB), Enterococcus sp., with sunlight exposure as the dominant driver (i.e., greatest impact on population dynamics). However, particle association of FIB may alter their persistence and transport in natural waters, though this aspect of extra-enteric ecology is rarely included in predictive models. Models predicting persistence and transport of fecal bacteria and pathogens could be improved by incorporating information on the impacts of particle association on dominant loss rates of FIB and the population dynamics of various indicated pathogenic groups. Further, it is important to understand the variation in and drivers of surface water optical properties, like water transparency, due to the likely importance of light penetration to fecal bacteria environmental persistence. This dissertation aims to address the critical knowledge gaps of how particle association influences the extra-enteric ecology of various sewage-derived bacteria and how optical properties relevant to the light-dependent mortality of FIB vary spatially and temporally in an urban-influenced water body. To do so, I employ a combination of empirical, modeling, and observational techniques. The Hudson River Estuary (HRE) is an ideal field site for this research because of its consistent problems with sewage pollution, especially following precipitation events, despite significant improvements following the Clean Water Act in 1972. Managing human health risks associated with sewage pollution is especially important for this water body that runs through the NY/NJ metropolitan area with its 19 million stakeholders. Further, previous research quantifying FIB dynamics has predominantly been conducted in clear, low turbidity water columns. Experiments constraining the dynamics of FIB in water with low clarity, like in the HRE, would fill this important knowledge gap in the field of sewage pollution monitoring and modeling. Chapter 1 assesses the impact of particle association on dominant growth rates and persistence of the brackish fecal indicator bacteria, Enterococcus sp. (also called enterococci). In this chapter, I conducted a series of natural water microcosm laboratory experiments to quantify dominant growth rates of enterococci. I then used these growth rates to parameterize a 1-dimensional advection-diffusion-decay model to simulate enterococci persistence in waters ranging from clear, quiescent lakes to turbid, turbulent waters. This combined empirical and mathematical modeling approach led to four major conclusions related to the persistence and transport of enterococci in natural waters: 1) particle association increases dominant growth rates (light-induced and dark, temperature-dependent growth) and induces sinking of enterococci, 2) particle association increases simulated enterococci persistence, 3) simulated enterococci persist longer in more turbid and/or more turbulent waters, and 4) discharge timing later in a diel cycle increases simulated Enterococcus sp. persistence. Results from this chapter demonstrate the importance of distinguishing free-living and particle-associated Enterococcus sp. in models of their persistence and transport and provide empirical data for independently constraining their population dynamics. Further, the simulated persistence indicates that sewage-derived fecal bacteria discharged into water bodies like the HRE will last longer than discharges in clear, calm waters (e.g. Lake Tahoe) and even clear, turbulent waters (e.g. coastal ocean in California). This information is broadly applicable to water quality management and indicates how variability in turbidity or turbulence within a water body could alter sewage discharge persistence and exposure risk for the public. Model sensitivity testing confirmed the consistent impact of particle association on enterococci persistence and reaffirms the need for FIB models to include particle association. An adapted version of Chapter 1 was published in Water Research (Myers and Juhl 2020). Because particle association increases enterococci persistence and growth rates, it is important to determine if particle association similarly affects co-occurring pathogenic bacteria and if particle association prevalence is similar. Chapter 2 is a valuable complement to Chapter 1 and addresses key knowledge gaps related to ambient pathogen abundance, particle association, and correlation with FIB in surface waters, in addition to the effect of particle association on dominant pathogen growth rates. In this chapter, I report multi-year observations of abundance and particle association proportions in the HRE for four bacterial genera: the fecal indicator Enterococcus sp., two enteric pathogens (Salmonella sp. and Shigella sp.) and a naturally-occurring, marine pathogen (Vibrio sp.). I found that mean particle association ranged from 34% to 49% and that overall abundances were significantly positively correlated across all genera. The second major goal of this chapter was to determine if particle association impacted dominant growth rates of pathogens similarly to the effect observed for enterococci (Chapter 1). In experiments similar to those in Chapter 1, I quantified the fraction-specific (free-living, particle-associated, and total) temperature and light-dependent growth of the three pathogenic genera. Overall, particle association consistently increased temperature- and light-dependent growth rates across genera, similarly to Chapter 1, though particle association did not benefit Vibrio sp. as much as the enteric genera. I found that Salmonella sp. had similar temperature- and light-dependent growth rates to enterococci. By contrast, Shigella sp. growth rates were greater than those of enterococci. As expected due to its different origin, Vibrio sp. also had dissimilar growth rates to enterococci. Interestingly, Shigella sp. behaved more similarly to Vibrio sp., with increasing dark period growth with temperature, which is opposite of the trend observed for the other two enteric organisms (Salmonella sp. and enterococci). The disparities and similarities of dominant growth rates between enterococci and 2 co-occurring fecal pathogens, together with the finding that abundances were positively correlated across all genera, suggests that enterococci are good indicators of recent sewage pollution, but have limitations in their use for assessing extended water column persistence of some co-occurring pathogenic bacteria. Information in this chapter is important for our understanding of FIB use to monitor sewage pollution persistence and for water quality management to minimize human exposure risk, especially in water bodies where environmental persistence is likely longer, like in turbid and turbulent waters (as shown in Chapter 1). Persistence simulations in Chapter 1 demonstrated that water transparency (modeled as diffuse attenuation of light, 3), was critical for determining the persistence of enterococci. It is then important to understand how water transparency varies throughout a water body to eventually predict how sewage bacteria persistence timescales vary. Chapter 3 examines the spatial and temporal variability of water transparency and its primary drivers (suspended particulate matter (SPM), chlorophyll, and colored dissolved organic matter (CDOM)) throughout the terrestrially- and marine-influenced HRE using observational and laboratory techniques. Data in this chapter indicate that water transparency in the HRE is predominantly controlled by SPM (measured as turbidity) and, to a lesser degree, chlorophyll. Despite some dramatic changes in inputs affecting the primary drivers (e.g. decreased sewage pollution - NYCDEP 2012, decreased chlorophyll concentrations - Caraco et al. 1997; Smith et al. 1998, and increased dissolved organic carbon transport - Findlay 2005) in the HRE, the dominance of turbidity in determining water transparency found in this study was consistent with work in the 1980s (Stross and Sokol 1989). Together, the findings by Stross and Sokol 1989 and in this chapter suggest that future work on understanding water transparency variability and its impact on sewage bacteria persistence in the HRE should focus on quantifying the variability in SPM. In contrast to other estuarine systems, CDOM absorption in this chapter minimally impacted water transparency (measured here via KdPAR). This chapter also documents spatial and temporal variability of water transparency and its primary drivers in the HRE. Turbidity and chlorophyll fluorescence varied seasonally, generally consistent with trends in other estuarine systems. Turbidity, chlorophyll, and CDOM absorption were all elevated after increased river flow from Tropical Storm Isaias. All three primary drivers of water transparency were also commonly higher for nearshore and tributary sites, as opposed to mid-channel sites, possibly due to increased shallow bed resuspension and terrestrial runoff. In the upper, freshwater portions of the estuary, CDOM absorption was highest, indicating a greater relative importance of CDOM on water transparency in this region. Data in this chapter also demonstrated that Wastewater Treatment Plant (WTP) outfalls commonly had elevated optical brighteners and (Sl(275-295), a CDOM slope ratio that indicates excess smaller CDOM molecules at a treated discharge, and a contrasting influence on CDOM absorption. This information could then allow CDOM absorption and optical brightener fluorescence to be used as indicators of treated or untreated discharges that could be measured on a faster timescale than current bacteria monitoring via culture-based techniques. Appended to this dissertation are results from experiments examining bacterial community composition for free-living and total populations in the HRE, which provide additional context for the research presented in this dissertation. The free-living and and total bacteria communities were not found to be significantly different, which indicates that there are not distinct communities in free-living and particle-associated fractions. Together with results from Chapters 1 and 2, this indicates that particle association may increase growth rates for bacteria that become particle-associated, instead of particles supporting the development of a unique and more resistant bacteria community. Four of the five fecal core families (bacteria commonly found in human fecal samples) were also identified in samples for these experiments, though relative abundance of these groups for free-living and total fractions were largely uncorrelated with each other over time. This finding demonstrates a notable influence of sewage inputs on the bacterial community in the HRE. Finally, these observations demonstrate that bacteria community composition varied seasonally, as noted by the significant influence of temperature and salinity on bacterial community composition. A wide variety of genera were strongly associated with colder (<12°C) water temperatures and samples from colder water generally exhibited higher alpha diversity. The findings from this dissertation have significantly contributed to our understanding of the extra-enteric ecology of the fecal indicator bacteria Enterococcus sp. and multiple co-occurring potential pathogens. This dissertation demonstrates that particle association must be considered in models of sewage-derived bacteria persistence. This dissertation also deepens our current understanding of water transparency drivers and their spatial and temporal heterogeneity in the turbid and turbulent system of the HRE. The results from this dissertation are useful for improving predictions of sewage pollution persistence and, by extension, minimizing human exposure risk to potentially harmful bacteria. These findings are broadly applicable beyond the HRE, to water bodies of varying turbidity and turbulence conditions.

No description available.

Two adsorption/microcoulometric methods have been investigated for total organic halogen (TOX) in water. TOX, a proposed water-quality parameter, is a rapid, surrogate method to detect halides microcoulometrically and does not require compound identification before water quality can be judged. An XAD resin is used to concentrate organic halides that are eluted by a two-step, two-solvent procedure, followed by analysis using :chromatography or pyrolysis to convert organic halides to halide. In the granular activated carbon (GAC) method, the entire GAC-organic halide sample is pyrolyzed. TOX measurements of model compounds are comparable by both methods, but GAC was found to be superior to XAD for adsorption of chlorinated humics in drinking water and chlorinated lake water.

Thesis (M.Sc. (Aquaculture)) -- University of Limpopo, 2020 / The aim of the study was to assess the extent to which biological indicators and biomarkers can be used to monitor the pollution status of the Sand and Blood Rivers. Physico-chemical parameters were assessed as a primary approach in assessing pollution status of the Sand and Blood Rivers. Temperature, pH, dissolved oxygen (DO), biological oxygen demand (BOD), turbidity, total dissolved solids (TDS), total nitrogen, phosphorus and ammonia were assessed during the rainy and dry seasons. Physico-chemical parameters showed spatial and temporal variation. The hierarchical average linkage cluster analysis grouped the reference sites (S1 and B1) into one group and sites after points of discharge (B2, S2, S3, S4 and S5) into another group. This grouping was due to the pollution status of each site, with the reference sites less polluted than the sites downstream of the wastewater treatment plant effluent points of discharge. The canadian council of ministers of the environment water quality index (CCME WQI) categorized reference sites as good, whilst sites after points of discharge were categorized as poor. This shows that the Sand and Blood Rivers are degrading. Heavy metal contamination in water, sediment and grass from the Sand and Blood Rivers was evaluated during the rainy season and dry season. All assessed heavy metals (Cadmium, Chromium, Copper, Iron, Lead, Manganese, Nickel, and Zinc) were below the detection limit in water, with an exception for Iron and Manganese. All metals assessed were also below the probable effect levels (PEL) according to the CCME. Geo-accumulation Index showed that the Sand and Blood Rivers were not contaminated with heavy metals. The enrichment factor (EF) further showed that only site B2 was enriched with manganese from anthropogenic activities. Heavy metal assessment in Cyperus exaltatus showed that this grass is a poor candidate for phytoremediation. Macroinvertebrates were used as biological indicators to assess pollution status of the Sand and Blood Rivers. Macroinvertebrates were sampled according to South African scoring system (SASS) and identified using aquatic invertebrates of South African rivers field guide. The SASS and average score per taxon (ASPT) categorized all sampling sites as critically modified. The family-level biotic index (FBI) also showed that the Sand and vi Blood Rivers are enriched with organic pollution. The reference sites recorded high macroinvertebrates diversity, compared to the sites after points of discharge. All indices used showed spatial and temporal variation in the water quality of the Sand and Blood Rivers. The relationship between macroinvertebrates and physico-chemical parameters were explored with the use of canonical correspondence analysis (CCA). The CCA triplots showed that the reference sites were associated with pollution sensitive taxa, whilst pollution tolerant taxa were associated with sites after points of discharge. Moreover, sites after points of discharge strongly correlated with phosphorus, nitrogen, ammonia, BOD and TDS. Clarias gariepinus gills and liver histology were used as biomarkers in assessing pollution status in the Sand and Blood Rivers. Gills and liver samples were qualitatively and semi-quantitatively assessed. Fish from the reference sites had less gill lesions than fish from sites downstream. Alterations such as hyperplasia of interlamellar, fusion of secondary lamellae, epithelial lifting and hyperplasia of secondary lamellae were observed in fish collected from downstream. Fish from downstream also showed more liver alterations than fish from the reference sites. Alterations such as melano-macrophage centers (MMC), macrovesicular steatosis, sinusoid congested with kupffer cells, nuclei pleomorphism and vacuolation were identified in liver of fish from sites S4 and S5. This was further confirmed by the high gill and liver indices of fish from downstream. Acetylcholinesterase enzyme (AChE) enzyme in brain and lactate dehydrogenase (LDH) in liver of Clarias gariepinus were used as biomarkers in assessing pollution status of the Sand and Blood Rivers. Both AChE and LDH enzymes were lower on fish from downstream compared to fish from the reference sites. This shows that AChE and LDH enzymes on fish from downstream were inhibited. This was attributed to the use of pesticides on farms surrounding the Sand and Blood Rivers and also the discharge of poorly treated sewage effluent from the Polokwane and Seshego wastewater treatment plants (WWTP’s). The Sand and Blood Rivers are surrounded by farms that utilize pesticides in their practice. This study showed that biological indicators and biomarkers can be used to assess pollution status of the Sand and Blood Rivers. However, biological vii indicators and biomarkers should be used in concurrence with physico-chemical parameters. / Department of Agriculture Forestry and Fisheries, Water Research Commission (WRC) and Aquaculture Research Unit.

Thesis (M.Sc. (Zoology)) -- University of Limpopo, 2020 / Water pollution has been one of the major concerns all over the world for at least the past two decades. In South Africa, the Olifants River System is one of the most polluted river systems. Anthropogenic activities being carried out within the Olifants River Catchment area pose threats to the aquatic ecosystem. The Upper and Middle catchments are being characterised by intensive mining, industries, agricultural practices and inadequate sewage treatments. Thus, the aim of this study was to investigate the influence of mining activities on the water quality and health status of the Steelpoort River, a tributary of the Olifants River System. This was achieved through assessing the quality of water by analysing physico-chemical parameters, macro nutrients and metals at four selected sites, determining the response of macro invertebrate assemblages to water quality using the South African Scoring System (SASS) version 5 and determining the diversity of fish using the Fish Response Assessment Index (FRAI). Sampling of water, sediment, macro-invertebrates and fish was done seasonally (August 2017 – May 2018) at four selected sites. Site 1 and site 2 were located upstream while site 3 and site 4 were located midstream and downstream respectively. Water and sediment samples were analysed by WATERLAB (PTY) LTD by means of Inductively Coupled Plasma Optical Spectrometry (ICP-OES). Macro-invertebrates were sampled following the SASS protocol. Macro-invertebrates were identified, counted and recorded then released back to the river. Fish were sampled following the FRAI index protocol. The results obtained indicated that the system variables; pH, water temperature, dissolved oxygen and total dissolved solids fell within the target water quality range (TWQR) for aquatic ecosystems. However, some concentrations of macro-nutrients recorded were above the TWQR. These include ammonium at site 3 and nitrogen at sites 2, 3 and 4 which indicated that there was a variation in the influx of macro-nutrients into the river at different river sections. The higher concentrations of ammonium and nitrogen may adversely affect the functioning and survival of biological communities. The metal results indicated that most metals (As, B, Ba, Cd, Cu, Pb, Ni and Cr) fell within the recommended water and sediment quality guidelines (DWAF 1996c; CCME 2012). Chromium concentrations recorded in sediment were above the sediment quality guideline at all the selected sites (CCME 2012). Iron and Zn were also above the guideline values at all selected sites. In terms of physico-chemical parameters and metal concentrations indicated that the water quality of the Steelpoort River was fairly good. The macro-invertebrates were also analysed; their abundance, distribution and family richness indicated that there was a deterioration of water quality from upstream to downstream which may be an indication of increase in influx of pollutants and modifications in the stream such as flow, cover and microhabitat. The highest macro invertebrate abundance and richness was at site 1 while the lowest was at sites 3 and 4. Site 3 was highly modified while site 1 was the least modified site. The Ephemeroptera, Plecoptera and Trichoptera index (EPT) and Ephemeroptera, Plecoptera and Trichoptera/Chironomidae ratio (EPT/C ratio) analysis also confirmed that the water quality of the Steelpoort River is deteriorating from upstream to downstream. Site 1 had the highest value of EPT while site 2 had the highest value of EPT/C. Site 3 had the lowest value for both EPT and EPT/C ratio. The higher EPT and EPT/C ratio indicate the presence of highly sensitive taxa. The Canonical Correspondence Analysis (CCA) indicated a strong correlation between metals (Pb, Cr, Mg, As and Se) and macro-invertebrates (Pleidae, Ecnomidae, Athericidae, Synlestidae, Lestidae and Pyralidae). The SASS 5 results also indicated deterioration of water quality from upstream to downstream with the highest values of SASS score and Average Score Per Taxon (ASPT) being recorded at site 1 followed by site 2 while the lowest SASS score and ASPT were at site 3 followed by site 4. The use of fish as biological indicator also supported the same pattern of water quality deterioration and influx of pollutants which was previously indicated as increasing from upstream to downstream of the Steelpoort River. Site 1 had the highest fish abundance, while site 4 had the lowest fish abundance. However, the fish species richness was highest at site 4 while the lowest species richness was at site 1. The Shannon Weiner Diversity Index also supported that site 4 had the highest fish species richness while site 1 had the lowest species richness. The FRAI results indicated that different sites were in different Ecological Categories (EC). The ECs showed a trend from higher EC category upstream to lower EC category downstream. Site 1 had an EC of C followed by site 2 with an EC of C/D, site 4 with EC of D and then site 3 with the lowest EC of D/E. This might serve as an indication of decrease in habitat availability, increase of pollutants input and increase in stream modification. The CCA showed a weak correlation system variables and fish species. However, a strong correlation was observed between most metals and most fish species with the exception of Mesobola brevianalis Boulenger, 1908, Chiloglanis pretoriae Van Der Horst, 1931, Labeobarbus marequensis Smith, 1841 and Enteromius neefi (Greenwood, 1962). In conclusion, the water in the Steelpoort River is still in relatively good condition. However, increasing mining, industrial and agricultural practices in the catchment area results in increase of pollutants input into the river system. All the four selected sites were contaminated to some degree, with site 3 being the most affected site and site 1 being the least affected site. For this reason, it is important to continuously monitor the health status of the Steelpoort River and to educate the nearby communities who rely on this river for water supply about the quality of the water from the Steelpoort River. / DSI-NRF SARCHI (Ecosystem Health)

M.S.

Estimates of the concentration of cadmium constituting a threat to aquatic ecosystems were derived from laboratory tests conducted at two levels of the biological hierarchy. A population level estimate was derived from single species toxicity tests and a community level estimate was derived from laboratory tests on microbial communities. Estimates were compared to each other and to an ecosystem level estimate derived from reports of ecological health and ambient cadmium levels in rivers, lakes, and streams. Estimates of permissible levels for short term exposures differed by an order of magnitude. Single species toxicity tests indicated that a level of 46.1 ug Cd/L would affect only 5% of taxa. The corresponding estimate from the community level test was 459.4 ug Cd/L. Similar estimates of permissible levels for chronic exposures were not significantly different (1.02 and 0.20 ug Cd/L, single species arid community level tests, respectively). Both of the laboratory derived estimates of permissible levels for chronic exposure fell within a rational range; the minimum level defined by median cadmium levels reported in healthy aquatic systems (0.05 ug Cd/L), and the maximum level defined by median cadmium levels reported in damaged aquatic systems (9.2 ug Cd/L). However, the community level estimate was obtained more efficiently, permitting an estimate of effects on diversity from a single test. Single species level tests, community level tests, and field studies each contributed unique information to hazard evaluation. Using information from all levels will strengthen predictions. / Master of Science

Master of Science