Characterization of Organic Compounds as Complex Mixtures in the Environment: Method Development and Applications

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Hundreds-of-thousands of organic chemicals have been produced and introduced to global market. The large number of man-made chemicals potentially released to the environment together with their transformation products makes it difficult to characterize the environmental risks from the complex organic mixture. This is because most constituents of the mixture are unidentified or lesser-known to environmental chemist and risk assessors. Among the lesser-known chemicals in the environment, some can possibly pose high risk to the ecosystem and human population. There is a need to identify the high-risk ones and characterize their sources, environmental fate and impact. The long-term objective of my research program is to identify lesser-known organic contaminants with high potential risk in the environment and to characterize their sources, environmental fate and impact. To achieve the objective, I will use high-resolution mass spectrometry based techniques for non-targeted chemical analysis and computer model simulations on environmental fate and risk of organic chemicals. Different methods will be developed to link information gained from the instrument with chemical properties and environmental hazards. As one short-term objective, a convolutional neutral network based machine-learning model will be developed with information gained from non-targeted analysis as input (GC and LC retention indices, accurate mass, mass defect, abundances of isotopes, fragment losses). Output of the model includes environmental persistence, bioaccumulation potential and toxicity. The convolutional neutral network will be trained with empirical and in silico predicted data. Another method to be developed is to project all possible structures of chemical peaks detected in non-targeted analysis onto chemical space that can disclose environmental hazards of detected chemicals. Using the approaches, detected chemicals can be ranked and selected based on their environmental hazards. In addition, lesser-known chemicals of environmental concerns will also be identified based on their systematic variation with temporal, spatial and other trends in environmental factors. The different approaches developed for retrieval important chemicals from non-targeted analysis will be applied to atmospheric and aquatic samples in source regions. Chemicals with high potential risk revealed by the developed methods will become candidates for further assessment on their sources, environmental fate and impact. Revolving around the objective of identifying chemicals of potential environmental concerns with newly developed methods, the proposed research program will facilitate the characterization of the influence of chemical stressors as complex mixtures on the ecosystems and provide an early warning before chemicals reaching thresholds that would irreversibly deteriorate ecosystem and influence human health. This research will also provide scientific support for chemical management.