Jessica Mendoza

Jessica developed an interest in ecotoxicology during her undergraduate studies at the University of Waterloo, where she was first introduced to aquatic contaminant research through Dr. Mark Servos’ BIOL 488 course. This early exposure shaped her interest in how anthropogenic stressors influence freshwater ecosystems and wildlife.

She completed her MSc under the supervision of Dr. Mark Servos (University of Waterloo) and Dr. Mark McMaster (Environment and Climate Change Canada), focusing on the use of white sucker (Catostomus commersonii) as a sentinel species to assess contaminant exposure in lake-connected tributary systems influenced by a pulp and paper mill in Terrace Bay, Ontario, discharging into Jackfish Bay on Lake Superior.

A key challenge in this system was distinguishing truly exposed fish from individuals originating in connected but unimpacted populations, which could confound interpretation of exposure and recovery signals. To address this, her research applied stable isotope analysis (δ¹³C and δ¹⁵N) in both fish and macroinvertebrates to evaluate spatial and temporal variation in food web structure and potential effluent-derived signals. While isotope signatures in white sucker were strongly influenced by movement and habitat use and did not consistently track changes in mill operation, macroinvertebrate isotope signatures more clearly reflected shifts associated with mill activity, highlighting their value as more stable indicators of environmental change.

Complementary biomarker analysis using mixed function oxygenase (MFO) activity (EROD) showed clear induction in fish exposed to effluent-impacted sites, with stronger responses observed when the mill was operating compared to periods of shutdown. These results confirmed ongoing exposure of fish to biologically active compounds in effluent and demonstrated that physiological responses could vary rapidly with changes in discharge conditions, particularly during fall sampling periods.

Overall, her research showed that while white sucker were effective sentinel species for monitoring exposure, their mobility limited the reliability of stable isotopes as standalone tracers. Instead, combining physiological biomarkers with stable isotope analysis in lower trophic organisms provided a more robust framework for assessing effluent impacts and recovery in large lake-connected systems such as Lake Superior.