Prediction of contaminant accumulation by free‐living organisms: Applications of a sigmoidal model

Abstract

Abstract-The accumulation of contaminants by free-living organisms has traditionally been determined with permutations of the deterministic model: Ct = Ce(1 -e -kt). However, studies utilizing a variety of species and exposure scenarios now suggest that significant deviations may occur from this classic form. In many cases noted to date, these deviations have involved a sigmoidal pattern of accumulation.While there may be no one single causal mechanism responsible for the expression of such a pattern in all cases studied, the application of a flexibly shaped Richards sigmoidal model can improve goodness of fit to the data relative to the classic model form. Several examples are presented for use of the Richards model: accumulation of 137Cs by free-living American coots (Fulica americana) and yellow-bellied turtles (Pseudemys scripta), and Hg accumulation by mosquitofish (Gambusia affinis).

Bioaccumulation of cesium‐137 in yellow bullhead catfish (Ameiurus natalis) inhabiting an abandoned nuclear reactor reservoir

“…Equilibrium muscle 137 Cs concentration, as well as time to equilibrium, were explicitly estimated using a reparameterized Richards function [30,31]. Estimates of asymptotic body mass and time to attainment of asymptote were similarly derived to further explore the relationship between body mass and 137 Cs bioaccumulation.…”

“…The Richards function [32] is a parent function of fixed‐shape growth curves (e.g., classic or monomolecular, von Bertalanffy, Gompertz, logistic) that is capable of assuming an infinite number of sigmoid shapes. A reparameterized Richards function [30,33] can be used as a three‐or four‐parameter uptake, or growth, model depending on the incorporation of a parameter to estimate initial contaminant concentration, or birth weight. Estimates are then derived for asymptotic concentration or mass ( C ??…”

“…In initial model runs, m was allowed to vary (the “complete model”). The procedure was then repeated with the constraint m = 0 (“reduced model”), and the difference in residual sums of squares evaluated by the F test [30,35,36]. When F is not significant in this test, allowing m to vary does not improve the predictive power of the model, and constraining m = 0 reduces the error in estimating the other parameters.…”

Methods for and approaches to evaluating susceptibility of ecological systems to hazardous chemicals.

“…For example, susceptibility of (52) fish and birds to mercury is reduced by the (18) presence of selenium (34). This apparently operates at the absorption or uptake level (53) (35), but the effects on populations and (18) communities are clear. Energy relationships of different (37) trophic levels affect bioaccumulation, and (54) thus long-term effects of hazardous chemicals (36).…”

“…Species diversity can be interpreted only with an understanding of what species diversity should be in a relatively pristine system. (35 predict additional differences in c susceptibility to hazardous ch These will be discussed below. ) the list is not exhaustive, it is mea an overview of the kinds of fac affect susceptibility (Table 1).…”