Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Heidi Swanson

Advisor Role

Supervisor

Abstract

Fish consumption is the primary pathway for human exposure to methylmercury (MeHg), a global contaminant of concern known to cause adverse health effects. Fort Albany First Nation, a remote Indigenous community in northern Ontario that relies on fish for both subsistence and cultural practices, has expressed concern regarding the safety of local fish consumption. Community members and leaders have communicated several priorities for scientific research that are the foundation of this thesis. Specifically, consumers of wild-caught fish have asked how traditional cooking methods may affect mercury concentrations in fish, and how mercury concentrations in little-studied organs, such as liver and stomachs, compares to concentrations in the more conventionally-studied muscle tissues.

To address these concerns, four fish species commonly harvested in the region (Walleye, Northern Pike, Longnose Sucker, and Lake Whitefish) were collected from the Albany River by harvesters. Muscle and select organs (liver, stomach, and guts) were sampled. Fish muscle samples were prepared in three ways (i.e., treatments): raw, pan-fried, and smoked. Samples representing each preparation type (treatment) were divided in half. One half was analyzed for total mercury (THg) following freeze-drying. The other half underwent an in vitro gastrointestinal digestion model procedure to quantify bioaccessibility of mercury. Concentrations of mercury and percent bioaccessible mercury were compared among species and preparation types. Liver, stomach, and guts samples were freeze-dried and analyzed for THg concentrations, and compared to muscle tissue samples.

Total mercury concentrations (dry weight) were highest in Walleye (average = 1.79 mg/kg; n = 50), followed by Northern Pike (average = 1.52 mg/kg; n = 53), Longnose Sucker (average = 0.80 mg/kg; n = 62), and Lake Whitefish (average = 0.53 mg/kg; n = 50). Percent bioaccessible mercury differed significantly among species (two-way ANOVA; F = 6.81, df = 3,135, p = 0.0003) and treatments (F = 766.78, df = 2,135, p < 0.0001), with a significant interaction between the two factors (F = 4.41, df = 6,135, p < 0.0004). Within each species, bioaccessible mercury was significantly lower in both cooked treatments compared to raw samples (p < 0.0001). No significant difference between the pan-fried and smoked cooking methods was observed for benthic species (Longnose Sucker and Lake Whitefish), whereas there were significant differences between cooking methods for the predatory species (Walleye and Northern Pike). Within each species, THg concentrations varied significantly among tissue types. In general, concentrations were highest in muscle, although for Lake Whitefish, mercury levels were higher in liver than in muscle. These findings provide community-specific data that may help refine existing fish consumption advisories by bridging the gap between theoretical risk based on raw tissue mercury concentrations and practical exposure under local cooking and consumption practices.

Convocation Year

2026

Convocation Season

Spring

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