2019 Projects

This project evaluated treatment alternatives for water resources contaminated with algal toxins. An established advanced oxidation process (UV/H2O2) was compared with an emerging one (UV/Cl2) in terms of (a) effectiveness for detoxifying the three most common variants of algal hepatotoxin microcystin (LR, RR and YR), and (b) potential to increase the formation of regulated disinfection byproducts [four trihalomethanes (THMs) and nine haloacetic acids (HAAs)] and an unregulated nitrogenous byproduct (NDMA) due to the interaction of the process with algal organic matter and nitrate in the water. The toxicity of the products was assessed with a protein phosphatase inhibition assay (PP2A). Products were also analyzed with HPLC/MS/MS. Disinfection byproducts were assessed using the corresponding EPA methods (551.1, 552.3 and 521) with any modifications described in the report. The results shown that both methods are effective against the three microcystins; however, microcystin LR is also highly susceptible to reaction with chlorine and UV/Cl2 offers an additional advantage of direct chlorine reaction. The PP2A assay was not able to conclusively determine whether the transformation products retain any residual hepatotoxicity; however, HPLC/MS/MS analysis indicated that ADDA group of the molecule that is considered to be responsible for microcystin toxicity is a susceptible reaction site in both advanced oxidation and direct chlorination, and the resulting products are likely non-toxin. More work needs to be done to determine it with certainty, which may include conducting PP2A assays in pure water samples to avoid matrix interference with the analysis, or performing ADDA-specific assays (e.g. ELISA). Addition of nitrate or algal DOM to the sample matrix did not significantly affect the formation of THMs and HAAs, with the exception of chloroform. However, the effect on chloroform, while statistically significant, is unlikely to affect the regulatory compliance for utilities. On the other hand, NDMA formation was considerably increased by both nitrate and algal DOM. NDMA remained below 10 ng/L which is set as advisory level in some states in all samples. The amounts of nitrate and algal DOM used in the experiments were on the high end of environmentally relevant range. However, formation of nitrogenous DBPs warrants additional investigation.

Lead in drinking water continues to put children at risk of irreversible neurological impairment. Understanding drinking water system characteristics that influence blood lead levels is needed to prevent ongoing exposures. The objective is to assess the relationship between children’s blood lead levels and drinking water system characteristics using Bayesian networks. Methods include 40,742 individual blood lead records from 2003-2017 for children in Wake County, North Carolina, were matched with the characteristics of 178 community water systems. Bayesian networks were machine-learned to evaluate the drinking water variables associated with blood lead levels ≥2 µg/dL and ≥5 µg/dL. The model was used to predict geographic areas and water utilities with elevated lead risk. The results are that drinking water characteristics were not significantly associated with children’s blood lead levels ≥5 µg/dL but were important predictors of blood lead levels ≥2 µg/dL. Whether 10% of water samples exceeded 2 ppb of lead in the most recent year prior to the blood test was the most important water system predictor and increased the risk of blood lead levels ≥2 µg/dL by 42%. The model achieved an area under the receiver operating characteristic curve of 0.792 (±0.8%) during ten-fold cross validation, indicating good predictive performance. Conclusively, water system characteristics are predictive of blood lead levels ≥2 µg/dL and may be used to identify areas that are at higher risk of water lead exposure. The significance is that current drinking water regulatory thresholds for lead are insufficient to detect the levels in drinking water associated with children’s blood lead levels.

In this project, we evaluated the photodegradation kinetics of wastewater derived emerging contaminants in treatment wetlands. We used dissolved organic matter (DOM) characterization tools and simulated irradiation experiments to investigate the relationship between photochemical behavior and wetland processing of wastewater effluents. Samples were collected from a treatment wetland site and a wastewater treatment plant (WWTP) in North Carolina. Cimetidine (CME), amoxicillin (AMX), 17𝞪-ethinyl estradiol (EE2), and atenolol (ATL) were selected as target contaminants to evaluate photoreactivity of sampled waters. Target compounds were individually dissolved in the collected samples and their decay during irradiation was measured using HPLC methods. The direct photolysis photodegradation rates and quantum yields were calculated for AMX, EE2, and ATL, as these pharmaceuticals have been shown to undergo both direct and indirect photodegradation in sunlit waters. Photochemically produced reactive intermediates, such as excited triplet states of dissolved organic matter ( 3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH) were found to be substantially sensitized by both treatment wetland samples and WWTP effluents. •OH acted as the main photoreactant responsible for the phototransformation of AMX, ATL, and EE2. Photodegradation of CME was entirely due to singlet oxygen formation from irradiated DOM. Phototransformation rates and quantum yield coefficients were calculated to estimate the photochemical fate of the pharmaceuticals in sampled waters. Overall, photodegradation was fastest for CME, followed by EE2, and then AMX and ATL. It was observed that photoreactivity was higher in lagoon treated wastewaters than compared to vegetated wetland cells and secondary wastewater effluents. Some samples were observed to have an enhanced •OH formation yield which led to significantly higher phototransformation rates. This was suggested to be due to the activity of photo-Fenton reactions and DOM dependent hydroxylators. Optical indices for DOM characteristics were computed from ultraviolet–visible (UV-Vis) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy. ATL and EE2 photoreactivity was observed to be negatively correlated to humic and fulvic DOM components. The absorbance ratio (E2:E3) was found to be positively correlated only to CME phototransformation rates. Results from this study suggest that plant-derived organic matter from vegetated wetland cells can decrease photoreactivity of treatment wetland waters.

The primary purpose of this study was to assess salinization impact (spatial and temporal) on mercury (Hg) cycling in coastal plain wetlands of North Carolina. We hypothesized that salinization of coastal freshwater wetlands increases methylmercury (MeHg) levels, as the sulfate-reducing bacteria (SRB), dominant groups that promote methylation of an inorganic form of mercury Hg (II) is stimulated by elevated levels of sulfate (SO₄²-) derived from saltwater. To achieve our goal, we collected water, sediment, and biota (note that biota was not included in the proposal) samples every month, between April and September 2019. We measured total Hg, MeHg, sulfate (SO₄²-), and dissolved organic carbon (DOC) levels along with the necessary field measurements (e.g., salinity, temperature, and dissolved oxygen). Total mercury (THg) levels for surface water samples ranged widely among the sites, and the highest levels were observed in Freshwater Wetland (at Point Peter site), where the DOC levels were the highest as well. Also, we observed increasing aqueous filtered MeHg concentrations (3.13 and 3.72 ng/L) in May and July in Freshwater Wetland, when the sulfate levels were at the peak (i.e., 4.85 and 4.79 mg/L, respectively). So far, our results for water samples suggest that the salinization of freshwater wetlands elevates MeHg levels in surface water. However, our analyses for sediment and biota samples are still ongoing (will be finalized in summer 2020) and will give us a better understanding of salinization impact on mercury cycling in coastal plain wetlands.

The two goals of this project were (1) to understand the spatial distribution of green infrastructure (GI) in schoolyards and associated benefits across school districts and communities that these school districts serve in North Carolina, (2) to understand how the placing GI in schoolyards, which we refer to as green schoolyards, improve children’s access to nature and its benefits through a case study in the City of Raleigh. This proposal addresses Focus Area 3: Community Development and Stormwater/Watershed Management through engaging children and teachers in public schools to better understand the existing capacity of GI on school grounds and potential benefits to children and communities. Specifically, we addressed three research questions: R1) Do schools enhance or mitigate inequities in children’s exposure to GI? R2) Does greening schoolyards improve students’ perceptions of the benefits of schoolyards? and R3) What factors predict children’s play in nature-rich areas as compared to traditional outdoor places in schoolyards. For R1, we focused on tree canopy and total greenness across four largest school districts in North Carolina, and for R2 and R3, we focused on nature-based elements in individual schoolyards, the use of schoolyards by students and teachers and the perception of students. The results of this project highlight that (1) public elementary schoolyards provide equitable exposure to tree canopy cover and total greenness, and public school systems are a promising partner to expand GI and urban greening equitably; (2) students’ positive view of schoolyards are more influenced by nature based activities and teacher-led activities than greening schoolyards alone; (3) teachers can play a considerable role in unlocking the benefits that exist in green schoolyards by promoting children playing in nature-rich areas. Our findings can serve as a decision support for better GI planning, design for stormwater management and other co-benefits in partnership with schools.