The Relative Importance of Physicochemical Properties of Organic Contaminants in Aquatic Ecosystems
Doctor of Philosophy (PhD)
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Measured physical/chemical properties of chemicals can be impacted by varying environmental conditions, subsequently influencing chemical environmental fate and exposure. For example, salinity has been reported to influence the water solubility of organic chemicals entering marine ecosystems. However, there is limited data available on salinity impacts on chemical sorption as well as bioavailability and exposure estimates used in the chemicals regulatory assessment. The salinity impact were demonstrated on the estimates of environmental fate of model compounds with different polarities including pesticides, and polycyclic aromatic sulfur heterocycles (PASHs). The n-octanol/water partition coefficient (KOW) was measured in both distilled-deionized water as well as artificial seawater (3.2%). A linear correlation curve estimated salinity may increase the log KOW value 2.6% per one log unit increase in distilled water (R2 = 0.968). The water solubility, bioconcentration factor, organic carbon soil/sediment sorption coefficient, and acute toxicity in fish were estimated for chemicals using the measured log KOW values by EPI SuiteTM. The water solubility of pesticides was measured in both distilled-deionized water as well as artificial seawater (3.2%). Salinity appears to generally decrease the water solubility and increase partitioning potential. Environmental fate estimates indicate elevated chemical sorption to sediment, bioavailability, and toxicity in artificial seawater suggesting that salinity should be accounted when conducting exposure estimates for marine organisms. In addition, the relative impact of volatilization and hydroxyl radical degradation on estimates of PASH overall dissipation after entry into aquatic ecosystems as a function of depth (0.1, 1 and 2 m) were investigated using the EPA Exposure Analysis Modeling System (EXAMS). The hydroxyl radical rate constant (K.OH) and Henry’s law constant (H) of PASHs were determined in distilled water. Simulated dissipation of PASHs using EXAMS suggest that volatilization is a dominant fate pathway for the higher molecular weight and less polar C2-DBT and C4-DBT at all depths and DBT and C1-DBT at 0.1 m. However, model scenarios suggest hydroxyl radical degradation may significantly contribute to the degradation of more polar DBT and C1-DBT at 1 m and 2 m depths.
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Saranjampour, Parichehr, "The Relative Importance of Physicochemical Properties of Organic Contaminants in Aquatic Ecosystems" (2017). LSU Doctoral Dissertations. 4468.