M.Sc. / The disinfection of drinking water is an important step in the water treatment process. However, toxic (unwanted) disinfection by-products (DBPs) are often produced during the disinfection of drinking water. One such group of DBPs are the nitrosamines such as N-Nitrosodimethylamine (NDMA). Nitrosamines, particularly NDMA, are highly carcinogenic, mutagenic and teratogenic. The US Environmental Protection Agency (USEPA) placed these compounds into the group B2, which indicates compounds of probable human carcinogens. The USEPA integrated risk information system (IRIS) database lists an estimated 10-6 lifetime cancer risk level for NDMA in drinking water of 0.7 ng/L. The formation of NDMA during drinking water disinfection, particularly chloramination, has been linked to the formation of NDMA through a reaction between monochloramine and organic nitrogen precursors via unsymmetrical dialkylhydrazine intermediates, such as unsymmetrical dimethylhydrazine (UDMH). UDMH is oxidized by dissolved oxygen to form NDMA. Therefore, it is also crucial to remove NDMA precursors (UDMH and dimethylamine (DMA)), before disinfection is carried out. Also, the chlorination of secondary wastewater can result in the formation of NDMA. In this research project, determination of nitrosamines, especially NDMA was done at four different water treatment plants in South Africa. Water samples collected from Midvaal, Sedibeng, Magalies (Vaalkop and Klipdrift) and Rand Water treatment plants were qualitatively analysed for the presence of NDMA. Also, the determination of possible NDMA precursors such as dimethylamine and UDMH was investigated in water samples collected from Sedibeng water treatment plant. The water samples were collected before and after each drinking water treatment process (coagulation, sedimentation, filtration, chlorination and chloramination or ozonation). Solid phase microextraction (SPME) was employed in the extraction of the water samples. Polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to be the most efficient fibre for the SPME extraction procedure. The water samples vi were then qualitatively analysed using gas chromatography-mass spectrometry (GC-MS). Very small amounts of NDMA were detected in water samples collected from Sedibeng water treatment plant. There was no detectable presence of NDMA or other nitrosamines in water samples collected from the other treatment plants. Water-insoluble cyclodextrin (CD) polyurethanes were then used to ascertain how much of the NDMA they would remove. The CD polymers showed capacity to remove NDMA and dimethylamine (which is a known NDMA precursor) in the water samples with 80% removal efficiency for NDMA (when comparing peak area before and after treatment with CD polymers) and approximately 98% removal rate for DMA.

Since Actinomycetes have been isolated from finished public drinking water, it is believed that the organisms are unaffected by the chlorination and flocculation of water treatment plants and pass as spores through the filters into the general distribution system. For this reason it was deemed imperative to study the toxic effects of these organisms.

This thesis studies antibiotic sensitivity of bacteria isolated from city water distribution systems.

Excess fluoride in groundwater used for drinking can pose serious health hazards, especially in poor, rural areas of the developing world lacking water treatment. The World Health Organization recommends a maximum fluoride contaminant level of 1.5 mg/L in drinking water [1]. Over 200 million people in low- and middle-income countries currently drink groundwater over that limit [2]. Current field detection of fluoride typically uses HACH kits, with several groups developing smartphone based alternatives [3]. These methods are based on colorimetry. The HACH kit is limiting because appropriate training is required, results are sensitive to competing ion contamination and chlorine, the glassware must be clean, and repetition is needed to ensure reliability [4]. The use of a smartphone for in-field detection of fluoride is promising and takes a strong step towards quick, easy, reliable, and portable fluoride detection. Our research takes the concept of a portable device one step further by using a fundamentally different, and simpler, mode of detection. We have demonstrated the use of optical fibers as an alternative, non-colourimetric fluoride detection method. The tip of a single mode optical fiber is coated with a thin film of Al and is immersed in an aqueous fluoride solution. The reaction between fluoride and the Al coating changes internal reflection proportional to fluoride concentration which is measured by a photodetector as an output voltage. We made great steps in optimizing the methods, materials, and code required for this sensor. Additionally, we built a device to allow approximate standardization of Al thickness as a function of the distance from the target and time of sputtering. We established the best practical thickness of Al coating, improved repeatability between sputter deposition events, and implemented an optical switch into the experimental set-up. / Graduate / 2021-07-28

The effects of different levels of fluoride in drinking water on different parameters of femurs and incisors of female rats were studied. Rats and their offspring, before and after weaning, were used for the study. Mother rats received 0, 1 and 5 ppm fluoride in drinking water. After weaning, the offspring were given the following treatments: 0-0, 0-1, 0-5, 1-0, 1-1, 1-5, 5-0, 5-1 and 5-5; the first number indicating fluoride level of mother's water during mating, pregnancy and lactation and the second number indicating the fluoride level of water given to the offspring. Femurs and top and bottom incisors were collected from mother rats, 21 day old pups and 300g. body weight pups. Femurs were analysed for ash, calcium, phosphorus and fluoride content and breaking strength. Only fluoride analyses were done on incisors. Fluoride ion electrodes (Orion models 94-09 and 96-09) were used for fluoride analysis. Mother rats that received 1 and 5 ppm of fluoride showed on increase in fluoride content of teeth. There was no increase in the fluoride content of weanling rat teeth suggesting that there was no maternal transfer of fluoride to the offspring. A significant increase in fluoride content of femur and teeth of all the groups of 300g. offspring, that received 1 and 5 ppm of fluoride, was observed as compared to the control group (0-0). No significant differences in other femur parameters of 300 g. offspring were observed. Significant differences in fluoride content of femurs and incisors of 300g. rat offspring were found due to pre and post-weaning fluoride treatments. Combined pre and post-weaning fluoride administration resulted in higher fluoride content of femurs and incisors. At the levels used in this study, pre-weaning fluoride administration alone does not appear to affect the fluoride content of bone and teeth of the rat offspring, but fluoride, when given ofter weaning does contribute to the increased fluoride content of bone and teeth.

In order to identify hexavalent chromium (Cr6) sources, behavior, and treatability, this thesis has profiled Cr6 in seven full-scale drinking water treatment plants and six distribution systems. Bench-scale jar tests assessed the treatment efficacy of coagulation and developed strategies to remove ultra-low level (0.01- 1.0 ~tg/L) Cr6. All water sources measured in this project contained dissolved Cr6 greater than or equal to the California Public Health Goal (0.02 ~g/L Cr6). The investigated coagulation plants did not remove Cr6; in fact, four of the seven treatment plants inadvertently added Cr6 to the treated waters. Thirteen types of drinking water treatment chemicals were evaluated as a potential non-water source of chromium. Amongst these, only iron-based coagulants contained trace levels of chromium sufficient to account for the observed increases at the full-scale plants. Other discussed non-water sources include leaching of chromium-bearing infrastructure or oxidation of Cr3. One of the treatment systems showed chlorine oxidized Cr3 to Cr6 and raised the finished concentration, in less than seven hours. One suggested improvement strategy was to use ferrous iron to reduce and remove Cr6 during coagulation. Bench-scale tests showed ferrous iron and a cationic polymer improved removal of both Cr6 and Total Cr. Chlorine interfered with that reduction. The full-scale test of this reduction-coupled coagulation treatment successfully decreased the finished Cr6 concentration when 40% ferrous iron was used and the point of chlorination was moved downstream from the coagulation process.

Given rising concern over elevated lead in drinking water in the aftermath of the Flint Water Crisis, forthcoming revisions to the U.S. EPA Lead and Copper Rule (LCR), and federal funding designated for replacing lead service lines, lead-tin solder corrosion control will become increasingly important. Lead-tin solder is often a dominant source of lead in drinking water for homes built before 1986 and has been the source of several recent high-profile water lead contamination events. This dissertation advances fundamental understanding of lead-tin solder corrosion by demonstrating that 1) elevated nitrate in water can trigger severe solder corrosion associated with very high LCR action level exceedances, 2) spallation of metallic solder to water is a source of lead contamination, 3) zinc orthophosphate offers superior corrosion control to mitigate nitrate attack, and 4) free chlorine can inhibit solder corrosion by electrochemical reversal. These principles were also applied to an exemplary related problem of lead contamination of food stored in tin cans. The conventional understanding is that lead-tin solder corrosion is worsened by low pH, low alkalinity, and elevated chloride relative to sulfate, but a utility that recently switched to a source water previously classified as non-corrosive suffered severe contamination from lead solder. The incident was characterized by the detachment of large chunks of metallic, lead-bearing solder particles from copper pipe joints that sometimes clogged aerators of consumers' faucets. It also caused a 90th percentile lead level of 131 ppb, which was much higher than reported for the 2001-2004 Washington D.C. lead crisis (79 ppb) or the 2014- 2016 Flint, MI water lead crisis (29 ppb). An exhaustive investigation of possible causes eventually revealed a strong correlation (r2=0.79) between seasonal fluctuations in surface water nitrate levels and the 90th percentile lead. The association of high lead with nitrate was unambiguously proven in bench-scale experiments using both copper coupons with new 50:50 lead-tin solder and harvested pipes with aged solder (extracted from a home with ongoing lead release issues) that replicated the characteristic spallation of solder particles (up to 7-mm in length) to water. Lead levels were occasionally >1,000 ppb in homes and >100,000 ppb in the bench experiments with harvested pipe after exposure to high nitrate above 8 mg/L. This finding is especially concerning given that nitrate is not currently identified as a factor affecting solder corrosion in EPA corrosion control guidance and source water contamination by nitrate is increasingly problematic. It was critically important to identify the mechanism by which nitrate caused solder spallation. Analysis of lead-tin solder surfaces in the bench-scale tests and harvested pipes indicated that nitrate preferentially attacked tin in the solder alloy. Nitrate severely detinned solder alloys > 40% tin by weight, causing cracking and detachment of metallic chunks of lead-tin solder from copper surfaces in a matter of weeks. Pure lead and alloys with less than 30% tin corroded more uniformly in the presence of nitrate and were not subject to spallation. Nitrate is reduced to a combination of ammonia and other nitrogenous compounds via reduction reactions that drove lead-tin solder corrosion at the anode. Nitrate also caused 1.3 times more metal weight loss by corrosion than could be explained by Faraday's law even in short-term 32-hour experiments, consistent with a previously identified "chunk effect" and anomalously high tin anode weight loss in nitrate solutions. This severe solder spallation mechanism has never been reported previously in drinking water environments and seems to be unique to nitrate for high tin-content alloys. This discovery also raises concerns about the possibility of pipe joint failures using lead-free tin-based solders that became more commonplace after the federal ban on lead solder in 1986. Common corrosion control strategies, including the use of phosphate corrosion inhibitors, failed to adequately reduce 90th percentile lead levels at the utility affected by runoff water with high nitrate after 6 months of application. Studies using new lead-tin solder and harvested pipes with aged solder demonstrated that zinc orthophosphate outperformed orthophosphate in controlling corrosion in high nitrate water and reduced lead release by 82-90% compared to phosphate alone or no inhibitor. The benefits of zinc orthophosphate improved with time and the dose of zinc delivered to the pipes. When zinc orthophosphate was applied at the water treatment plant, the 90th percentile lead levels in the affected community fell below the action level within 6 months. Analysis of the pipe scale demonstrated that zinc orthophosphate works by coating the interface usually subject to intense galvanic corrosion between copper and solder. Disinfectants may also play a role in controlling lead contamination from solder. Two water utilities in the Pacific Northwest experienced lead action level exceedances for decades due to solder corrosion while using the same source water with chloramine disinfectant. After one utility switched to a similar water source using free chlorine disinfectant, lead release dropped to low levels within months. This was consistent with laboratory experiments conducted at the second utility more than three decades ago that indicated much lower lead release using free chlorine versus chloramine using the water utility's source water. There was previously no explanation for the benefits from free chlorine, but it was recently demonstrated that chlorine can cause electrochemical reversal of a copper-lead pipe galvanic cell, which dramatically reduced lead release to water. It was hypothesized that a similar reaction could occur for lead-tin solder as well. This was confirmed when lead-tin solder and copper connections exposed to 4 mg/L free chlorine in circulating rigs experienced electrochemical reversal in some waters over a period of weeks. The electrochemical reversal was accompanied by dramatic decreases in lead release, concomitant with the formation of insoluble lead (IV) oxide scale. In some situations where traditional corrosion inhibitors are not effective, it is possible that electrochemical reversal due to free chlorine may control lead solder corrosion, either unintentionally or purposefully. This new understanding of nitrate's ability to exacerbate lead contamination from lead-tin alloys in drinking water was then extended to concerns about lead contamination of food stored in tin-plated cans. Fruits and their juices can contain nitrate, and if lead is present in the tin plating, the resulting corrosion is predicted to cause significant contamination. Twenty-one brands of canned pears from across the U.S. were assessed for lead content, and one brand was found to contain 2-3 times higher lead in the fruit (average=14 ppb, max=38 ppb) and syrup (average=7 ppb, max=15 ppb) than other brands. The brand of cans with higher lead in the fruit also had higher levels of lead in the can materials: surface lead levels in the interior tin-plate was 0.1% by mass on average (max=0.60%) and 7.5% by mass on average (max=29%) in the interior seam, which is up to 146 times the 0.2% value advised in FDA guidelines for lead in food-contact surfaces. Follow-up testing with three brands of canned pears confirmed lead levels in the syrup were also associated with higher levels of ammonia in the juice—ammonia is a reaction product of nitrate corrosion of tin in the can. To confirm that the can material was the source of the lead contamination, the pear cans were emptied and then refilled with a variety of synthetic solutions containing up to 50 mg/L NO3-N. The higher nitrate levels always formed ammonia and were associated with higher lead release in some cases. The use of lead-tin alloys (either lead-bearing tin-plate or solder) in unlined canned goods with solutions known to contain nitrates can create unnecessary lead exposure for consumers. This dissertation provides novel insights into lead-tin solder corrosion with profound implications for water lead contamination, the integrity of potable water infrastructure, and corrosion control strategies in potable water. Rising concerns about nitrate contamination of source waters underscore the importance of understanding these effects on lead and public health. As illustrated by the application of these principles to lead contamination of tin-lined fruit cans, the results may also enhance understanding of corrosion of tin-based materials in electronics, museum artifacts, electrochemical water treatment, and in the automotive and aerospace industries. / Doctor of Philosophy / Given rising concern over elevated lead in drinking water in the aftermath of the Flint Water Crisis, forthcoming revisions to the U.S. EPA Lead and Copper Rule (LCR), and federal funding designated for replacing lead service lines, the issue of lead-tin solder corrosion control will become increasingly important. Lead-tin solder is often a dominant source of lead in drinking water for homes built before 1986 and has been the source of several recent high-profile water lead contamination events. This dissertation advances the fundamental understanding of lead-tin solder corrosion by demonstrating that 1) high source water nitrate levels can trigger severe solder corrosion associated with elevated lead release in drinking water, 2) detachment (i.e., spallation) of metallic solder to water is a source of lead contamination, 3) zinc orthophosphate offers superior corrosion control to mitigate nitrate attack, and 4) free chlorine disinfectant can inhibit solder corrosion by electrochemical reversal. These principles were also applied to an exemplary related problem of lead contamination of food stored in tin cans. It is understood that lead-tin solder corrosion can be affected by water chemistry, but a utility that recently switched to a new source water previously classified as non-corrosive was surprised to discover severe water lead contamination from solder. The contamination was characterized by the detachment of large chunks of lead-bearing solder particles from copper pipe joints that sometimes clogged aerators of consumers' faucets. It also caused a 90th percentile lead level of 131 ppb, a level much higher than reported for the 2001-2004 Washington D.C. lead crisis (79 ppb) or the 2014-2016 Flint, MI water lead crisis (29 ppb). The presence of such large chunks of lead-bearing solder is contrary to the belief that water lead contamination occurs by the dissolution of lead rust from solder. An exhaustive investigation of possible causes eventually revealed that lead release in this community was strongly related to seasonal fluctuations in surface water nitrate levels. The association of high lead with nitrate was unambiguously proven in experiments using both copper coupons with new 50:50 lead-tin solder and harvested pipes with aged solder that had been extracted from a home with ongoing lead release issues, which replicated the characteristic spallation of solder particles (up to 7-mm in length) to water. Lead levels were occasionally >1,000 ppb in homes and >100,000 ppb in the bench experiments with harvested pipe after exposure to high nitrate above 8 mg/L. These levels of water lead contamination are amongst the highest ever recorded. This discovery is especially concerning given that nitrate is not currently identified as a factor affecting solder corrosion in EPA corrosion control guidance and source water contamination by nitrate is increasingly problematic. It was critically important to better understand the mechanism by which nitrate caused solder spallation. Analysis of lead-tin solder surfaces in the bench-scale tests and harvested pipes indicated that nitrate preferentially attacked tin in the solder alloy. Nitrate is reduced to a combination of ammonia and other nitrogenous compounds while contributing to lead-tin solder corrosion at the anode. Nitrate severely degraded solder alloys with >40% tin by weight, causing cracking and detachment of metallic chunks of lead-tin solder from copper surfaces in a matter of weeks. Pure lead and alloys with less than 30% tin corroded more uniformly in the presence of nitrate and were not subject to spallation. Nitrate corrosion also caused 1.3 times more water contamination than predicted by conventional chemical reactions that do not consider spallation, even in short-term 32-hour experiments. This severe solder spallation mechanism has never been reported previously in drinking water environments and at present seems to be unique to nitrate for solder alloys with high tin content. This discovery also raises concerns about the possibility of pipe joint failures, and associated pipe bursting and water damage, when using lead-free tin-based solders that became more commonplace after the federal ban on lead solder in 1986. Common corrosion control strategies, including the use phosphate corrosion inhibitors, failed to adequately reduce 90th percentile lead levels at the utility affected by runoff water with high nitrate after 6 months of application. Studies using new lead-tin solder and harvested pipes with aged solder demonstrated that zinc orthophosphate outperformed orthophosphate in controlling corrosion in high nitrate water, reducing lead release by 82-90% compared to phosphate alone or no inhibitor. The benefits of zinc orthophosphate improved with time and the dose of zinc delivered to the pipes. When zinc orthophosphate was applied at the water treatment plant, the 90th percentile lead levels in the affected community fell below the action level within 6 months. Analysis of the pipe scale demonstrated that zinc orthophosphate works by coating the interface usually subject to the most intense galvanic corrosion between copper and solder. Disinfectants used to kill bacteria in drinking water may also play a role in controlling lead contamination from solder. Two water utilities in the Pacific Northwest experienced lead action level exceedances for decades due to solder corrosion while using the same source water with chloramine disinfectant. After one utility switched to a similar water source using free chlorine disinfectant, lead release dropped to low levels within months. This was consistent with results from a laboratory study conducted more than three decades ago at the second utility that indicated much lower lead release using free chlorine versus chloramine using this water utility's source water. There was previously no explanation for the benefits from free chlorine, but it was recently demonstrated that chlorine can control lead pipe corrosion by reversing normal electrochemical reactions which dramatically reduced lead release to water. It was hypothesized that chlorine could have a similar effect for lead-tin solder as well. That hypothesis was confirmed when lead-tin solder and copper connections exposed to 4 mg/L free chlorine in circulating rigs experienced electrochemical reversal in a synthesized version of this water within weeks. The electrochemical reversal was accompanied by dramatic decreases in lead release, along with the formation of protective lead (IV) oxide pipe scale. These unexpected benefits of free chlorine may help explain why some water utilities with water normally considered corrosive have not been experiencing lead solder corrosion problems or lead action level exceedances. This new understanding of nitrate's ability to exacerbate lead contamination from lead-tin alloys in drinking water was then applied to concerns about lead contamination of food stored in tin-plated cans. Fruits and their juices can contain nitrate, and if lead is present in the tin plating, the resulting corrosion is predicted to cause significant contamination. Twenty-one brands of canned pears from across the U.S. were assessed for lead content, and one brand was found to contain 2-3 times higher lead in the fruit (average=14 ppb, max=38 ppb) and syrup (average=7 ppb, max=15 ppb) than other brands. The brand of cans with higher lead in the fruit also had higher levels of lead in the can materials: surface lead levels in the interior tin-plate was 0.1% by mass on average (max= 0.60%) and 7.5% by mass on average (max=29%) in the interior seam, which is up to 146 times the 0.2% value advised in FDA guidelines for lead in surfaces that contact food. Follow-up testing with three brands of canned pears confirmed lead levels in the syrup were also associated with higher levels of ammonia (a reaction product formed by nitrate corrosion of tin in the can) in the juice. To confirm that the can material and high levels of nitrate in the original food contributed to the lead contamination, the pear cans were emptied and then refilled with a variety of synthetic solutions containing up to 50 mg/L nitrate. The higher levels of nitrate always formed ammonia and were associated with higher lead release in some cases. The use of tin alloys (either lead-bearing tin-plate or solder) to package acidic food containing nitrate can create unnecessary lead exposure for consumers. This dissertation provides novel insights into lead-tin solder corrosion with profound implications for water lead contamination, the integrity of potable water infrastructure, and corrosion control strategies in potable water. Rising concerns about nitrate contamination of source waters underscore the importance of better understanding these effects on lead and public health. As illustrated by the application of these principles to lead contamination of tin-lined fruit cans, these results may also enhance understanding of corrosion of tin-based materials in electronics, museum artifacts, electrochemical water treatment, and in the automotive and aerospace industries.

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