Uptake rates of food-chain and waterborne mercury by fish: field measurements, a mechanistic model, and an assessment of uncertainties

Abstract

John R. Post, Rena Vandenbos, and Donald J. McQueen Abstract: We develop a model of mercury uptake by age-0 yellow perch, Perca flavescens, through consumption and respiration, based on a published species- and age-specific bioenergetics model and published mercury kinetics models. We use the model in conjunction with field estimates of growth, diet, temperature experience, and mercury concentration to examine the seasonal patterns in methyl mercury uptake through respiration and through the food chain, and loss rates through depuration. Seasonal variation in environmental temperature, body size, diet, and prey availability create seasonal variation in the rate of methyl mercury uptake and in the proportion of uptake from aqueous and food sources. Methyl mercury uptake was primarily from aqueous sources during the spring and fall and was dominated by food sources in the summer. Key uncertainties in our understanding of the processes of mercury uptake by fish include (i) quantitative relationships between water chemistry and respiratory uptake, (ii) quantitative estimates of intestinal tract methylation, ( iii) empirical measures of the allometry of mercury depuration, and (iv) the degree of seasonal variability in mercury speciation and methylation-demethylation processes. These uncertainties hinder our ability to more fully understand and quantify the sources and pathways of uptake of mercury by fish.