Date of Award
Doctor of Philosophy
Michael L. Thompson
Overpopulation is one of the major causes of many environmental problems we experience today. With increasing population, the demand for quality food and clean water is becoming difficult to realize. Although with advancement in technology, we are still able to cope with the demand, but eventually we will exhaust the supply for quality food and clean water as well as the different methods of achieving them.
Quality food and clean water are necessities to live. To help in delivering these needs, federal regulations and policies were developed and implemented to protect the public from environmental contaminants that might be hazardous to human health. Contaminants such as organic compounds are ubiquitous in the environment because they are component of most goods that the public use on a daily basis. When these organic compounds are released into the environment they could undergo different processes such volatilization, microbial degradation, photodegradation, movement by run-off, adsorbed and held strongly in the soil, or move with the soil-water. When a hazardous organic compound is strongly held in the soil, it is possible that it will be taken-up by crops for human consumption or as feedstock. Organic compounds that are mobile in the water may also be taken-up by aquatic species, will bioaccumulate, or leach to the groundwater contaminating the source of the drinking water.
A group of compounds found to disrupt the endocrine systems that brought a great concern to the scientific community was observed three decades ago. These compounds are collectively referred to as endocrine disrupting chemicals (EDC) and sometimes endocrine active compounds (EAC). Since then, various research studies have been conducted to potentially cover all aspects of EDCs. To establish the presence, and the spatial and temporal distribution of EDCs, monitoring studies of surface and even groundwater were often conducted. The effect of EDCs to wildlife, such as the feminization of frogs and fishes, and the potential health problems to humans were also intense research areas that involves EDCs.
To determine the overall environmental risk of EDCs, the fate and transport of these compounds need to be evaluated as well. The fate and transport studies will explore the movement of these compounds in soil, water, and air. Also, how the physical and chemical properties of these compounds changes as they interact with other chemicals, microorganisms, and other components of the soil-water systems, such as the native dissolved organic matter (soil) and the exogenous dissolved organic matter (biosolids-derived). EDCs maybe released from residential, industrial, and agricultural sources. In wastewater treatment plant, the EDCs and other contaminants may not be completely removed during the treatment process and ends up in the biosolids and effluents. To recycle the carbon and the plant nutrients such as nitrogen and phosphorus, the biosolids are applied in agricultural fields and the effluents are used as irrigation water in relatively dry regions.
The fate and transport study of EDCs is not well-explored. Since there are a lot of chemicals that are manufactured and released daily, and a lot of variability in the systems condition (ex. temperature, moisture, and pH) that impact the fate and transport of the EDCs, generating more data will definitely help in establishing more reliable results. Adsorption and column transport experiments are some of the processes used to predict the fate and transport of EDCs.
In this study, three endocrine disrupting chemicals (EDCs), bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4-NP), were chosen because of their varying physico-chemical properties. Among the three compounds, BPA is the least hydrophobic and 4-NP is the most hydrophobic. We are hoping that these compounds can be used as model compounds to study the potential environmental risk of other organic pollutants with similar physico-chemical properties that are released in soil-water system. The impact on the transport of EDCs were also investigated in systems where the native dissolved organic matter and exogenous biosolids-derived dissolved organic matter (BDOM) were present.
The concentrations of BPA, EE2, and 4-NP were monitored for six months at two wastewater treatment plants in Iowa and at their corresponding upstream and downstream discharge locations. The monitoring was conducted to assess if the three EDCs of interest were actually present in the wastewater effluent and water system. Results showed that BPA, EE2, and 4-NP were detectable in the water samples, although the frequency of detection was variable throughout the six months. The result also showed that the concentrations detected were below the method detection limit (MDL), and suggested that the analytical method adopted for the monitoring studies of environmental concentrations of organic contaminants were an important consideration in conducting this type of analysis.
Soil materials are complicated matrices by themselves and in combination with water and biosolids-derived dissolved organic matter, the system becomes even more complex. Also, studying the interactions and fates of the three EDCs simultaneously in soil-water-BDOM systems is challenging, and therefore simplified systems, i.e., working with individual EDCs and interaction with individual system component (BDOM-carbon to soil, EDCs to soil adsorption-desorption, EDC to BDOM adsorption) was employed in this study.
The two soils used are Hanlon and Zook soil samples. The two soil samples have contrasting properties. Of the two soils, the Zook soil sample has higher total organic carbon, total organic nitrogen, and higher clay content. The biosolids-derived dissolved organic matter that was extracted from the anaerobically digested biosolids from the Ames Wastewater Pollution Control Facility was characterized and was dominated by N-acetylated carbohydrates and aromatic components. Adsorption of BDOM to the two soils revealed the predicted maximum adsorption capacity and intensity was 188 mg C kg-1 soil and 0.015 L kg-1 soil, respectively for Hanlon soil sample and 640 mg C kg-1 soil and 0.015 L kg-1 soil, respectively for the Zook soil sample. Although the Zook soil sample had a higher maximum adsorption capacity, the intensity of adsorption for both soils was low and of the same magnitude, which suggests that the BDOM-carbon is likely to be mobile in saturated conditions. Some components of the BDOM-carbon were adsorbed to the soil samples, and fractionation of the BDOM-carbon revealed that hydrophobic acid (HoA), hydrophobic neutral (HoN), and hydrophilic base (HiB) structural fractions dominated the adsorption. Some adsorption mechanisms proposed were cation bridging, hydrophobic partitioning, and electrostatic attraction.
The parameters determined to predict the behavior of the EDCs adsorbed to the two soil samples were described by the Freundlich-Langmuir model. This model allowed us to calculate the n parameter or the index of heterogeneity of sorption energy. The difference between the n values limits our ability to compare sorption capacities of the two soils. For example, for EE2, the n values calculated were 0.73 and 1.93 for the Hanlon and Zook soils samples, respectively.
Among the three EDCs, the 4-NP had the highest adsorption maximum capacity (Qmax) and adsorption affinity constant (KLF) predicted based on the combined Langmuir-Freundlich model for both soil samples. Between the two soil samples, the Zook soil sample had a maximum adsorption capacity about 50 times higher and an adsorption affinity about ten times higher than the Hanlon soil samples. The EE2 had a higher adsorption affinity than the BPA, but the BPA had a higher maximum adsorption capacity than EE2. The BPA exhibited about the same magnitude of adsorption capacity and adsorption affinity for both soil samples. 4-NP, the most hydrophobic EDC, had the highest adsorption capacity and affinity, while the least hydrophobic BPA had the lowest adsorption affinity.
The extent of binding between the EDC and the BDOM is important because it predicts the EDC-BDOM complex formation. The formation of a complex between the EDC and BDOM helps in understanding the role of the BDOM in transport, e.g., enhancing or deterring the movement of EDCs in the soil-water system. The results showed that BPA is strongly associated with the BDOM fraction, while EE2 and 4-NP did not form a strong association with the BDOM. Considering the other adsorption results from the concurrent study, we hypothesized that the BDOM will carry with it the BPA as it moves in the soil water, while the EE2 and 4-NP will most likely interact with the soil materials.
To test the hypothesis of the influence of BDOM on the transport of BPA, a packed soil column experiment was conducted using the Hanlon and Zook soil samples. There were two concentration levels of BDOM used: 10 mg C L-1 and 40 mg C L-1. The BDOM was mixed with the BPA first before passing it through the soil column. The results showed that, contrary to the hypothesis that the BDOM would enhance the transport of BPA, the presence of exogenous BDOM enhanced the retention of the BPA in both soil samples.
The data generated from this research project will be a valuable source of information for future studies of organic pollutants with similar physico-chemical properties. The result could also serve as a basis to improve the federal and state policy and regulatory frameworks pertaining to the direct discharge of organic chemicals from residential and industrial areas, land application of biosolids, and the re-use of effluent as irrigation water.
The monitoring study showed detection of the three EDCs but the frequency of detection varied at each month of sampling. The result of monitoring could be used as a baseline data when in the future, the focus of monitoring study is on the different seasons of sampling (temporal variability). Estrogens and BPA were detected at polluting levels in groundwater (Focazio et al., 2008; Adeel et al., 2017). One process to reclaim the groundwater is soil aquifer treatment (Mansell et al., 2003). The results generated from this study could be used to improve the efficiency of the treatment process because the removal mechanisms is most likely influenced by hydrophobic or hydrophilic characteristic of the carbon structural fraction of the adsorbent used (Mansell et al., 2003). Also, we can improve the technology in wastewater treatment processes to eliminate most of the EDCs before they are released. Part of the waste treatment process is the use of soil as component of the bedding material that adsorbs the organic contaminants. The adsorption intensity, adsorption capacity, and retardation parameter values could therefore be a used to improve the adsorptive capability of the bedding materials used.
Rivas, Fritzie, "The role of biosolids-derived dissolved organic matter on the interaction of selected endocrine-disrupting chemicals with two alluvial soils" (2018). Graduate Theses and Dissertations. 16450.