Comparison between traditional and experimental aquatic toxicology



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Complex mixtures of anthropogenic chemicals including pharmaceuticals, pesticides, and industrial chemicals, are entering the aquatic environment via surface runoff, leaching, and effluent discharge. The increasing chemical load has raised concerns in regard to the protection of aquatic ecosystem health. This dissertation focuses on two different approaches to evaluate aquatic toxicity due to chemicals. The first approach focuses on adverse outcome pathways (AOP) to understand the interactions between contaminants and molecular initiating events and the translation of molecular level insults to apical level endpoints such as behavior and growth which are relevant to an ecological risk assessor. The impacts of two chemical classes (azole and strobilurin) of fungicides on aquatic vertebrate (zebrafish, Danio rerio) were studied using the AOP approach. Several molecular, cellular, and apical endpoints were assessed in embryo-larval zebrafish exposed to azole and strobilurin fungicides. The azole fungicides were shown to induce lipid peroxidation and apoptosis whereas strobilurin fungicides decreased mitochondrial bioenergetics, induced oxidative stress, and was associated with decreased swimming behavior and growth. These kinds of studies are vital to understand the impact of individual or classes of contaminants on aquatic organisms and they also generate data to help a risk assessor make informed decisions to protect aquatic health. Although prior knowledge of exposure is beneficial, in the natural environment, aquatic organisms may be exposed to complex chemical mixtures with an unknown composition and toxicity. The recent advances in analytical instrumentation (e.g. high-resolution mass spectrometry) could help us to understand the composition of complex chemical mixtures using a non-targeted analysis workflow. This dissertation explored a new approach to understand and predict impacts of complex mixtures on aquatic health. This approach integrates information from the non-targeted analysis into a quantitative structural activity relationship model to predict molecular level toxicity signatures, called NTA-QSAR workflow. The applicability of NTA-QSAR workflow was validated by toxicity testing of an effluent dominated stream (Lubbock Canyon Lake System) using early life stages of zebrafish. The NTA-QSAR workflow predicted that water samples from the Lubbock Canyon Lake System may act on receptors from the gonadotropin releasing hormone receptor pathway, the serotonin receptor signaling pathway, and the adrenergic receptor signaling pathway in aquatic vertebrates. The impact on the gonadotropin releasing hormone receptor pathway and the serotonin receptor signaling pathway were confirmed by exposing early life stages of zebrafish to ambient water samples. This research will aid in chemical fingerprint guided effect analysis of complex chemical mixtures which could ultimately help risk assessors in the protection of environmental and human health.



Aquatic toxicology, Emerging contaminants, Complex chemical mixtures, Non-targeted analysis, Quantitative structural activity relationships, Zebrafish