Alexandria Keeble-Toll

Keeble-Toll, A. C. Monohan, D. Brown, and G. Pearson. Mercury in Fish of the American and Bear River Watershed Reservoirs: Tissue Analysis and Strategies for Minimizing Exposure at Lake Clementine and Rollins Reservoir, California. California State University, Chico. Summer 2016.


The primary pathway of human exposure to mercury is the consumption of contaminated fish. Identification of patterns of fish tissue mercury levels are a key mechanism for understanding risk drivers and human exposure potential. Site-specific fish tissue data aid the Office of Environmental Health Hazard Assessment (OEHHA) in the development of consumption advisories. This research consists of Year 1 of a three year project to collect fish data from six reservoirs downstream of historic hydraulic mines in the Cosumnes, American, Bear, Yuba watershed region. Angler survey data informed sampling to ensure that commonly caught and consumed species were harvested from Lake Clementine and Rollins Reservoir and was used to evaluate posted fish consumption advice as a mechanism for protecting human health. A total of 72 samples from four species groups were collected in 2015. Geometric mean THg (ppm, wet weight) were highest for black bass at both Lake Clementine (n = 8, THg = 0.40) and Rollins Reservoir (n = 26, THg = 0.54), with a significant positive relationship between fish total length and THg at both water bodies (Lake Clementine: rho = 0.85, p<0.05; Rollins Reservoir: rho = 0.85, p<0.01). Sunfish data for both reservoirs were lower in THg than black bass (Rollins Reservoir: n = 24, THg= 0.16; Lake Clementine: n = 29; THg = 0.12), with a significant positive relationship between fish total length and THg at Lake Clementine (rho = 0.83, p<0.01) but not Rollins Reservoir. These data allow OEHHA to develop site-specific fish consumption advice at both locations and can be used as baseline data to determine if future actions to address inorganic mercury (Hg) sources at legacy gold mines results in reduced human exposure risk at downstream water bodies.

Student Bio

Alex completed her undergraduate studies in 2002 (B.A., Sociology, magna cum laude, UCLA) and received her first graduate degree in 2006 (M.A., Sociology, CSU, Sacramento). Alex completed her second graduate degree in 2016 (M.Sc., Environmental Science, with distinction, CSU, Chico). She has been designing and executing multidisciplinary research projects on mining impacts in Nevada County for over ten years using approaches that include Environmental Inequality Formation (EIF) modeling to examine legacy mine impacts, Q-Methodology to explore subjective views in mine permit processes, participant observation and field surveys to understand angler catch and consumption patterns, and biological data collection and analysis to support public health advisories for mercury contaminated fish.