Egg Selenium Concentrations as Predictors of Avian Toxicity

Abstract

a ecological planning and toxicology, inc., 5010 SW Hout St., Corvallis, OR 97333-9540 ABSTRACT Aquatic birds are exposed to selenium through their diet by ingesting aquatic invertebrates that have accumulated selenium from water and the food chain. However, dietary composition is highly variable among species, over time, and across sites, making it difficult to provide accurate estimations of dietary exposure for particular species at specific locations. Selenium accumulates in the egg, resulting in embryo malformation, embryonic death, and decreased survival of juveniles. If the relationship between egg concentration and these reproductive parameters can be defined with sufficient certainty, then risk assessments can be performed through analysis of egg selenium concentrations. Other researchers have proposed egg toxicity thresholds that lead to conclusions of widespread selenium toxicoses in waterbirds. However, we believe these values are overly conservative and that it is unlikely that selenium is posing a significant risk to wild birds in areas where the current water quality criterion is being met. Through the use of simple statistical models (logit, probit, and Weibull functions) we are able to express mortality and teratogenicity relationships for mallards (Anas platyrhynchos) in such a manner that the risk manager can be presented with information about the probability of reduced duckling survival if mean egg selenium (MES) concentrations are known. Data analysis indicates that the two endpoints (mortality * Corresponding author: Dr. Anne Fairbrother, ecological planning and toxicology, inc., 5010 SW Hout St., Corvallis, OR 97333-9540;Fairbrother, et al.and teratogenesis) cannot be distinguished statistically. Commonly used effects thresholds (the EC 10 and EC 20 ) correspond to 16 and 21 mg/kg dw MES using the most sensitive endpoint, chick mortality. Both of these values are higher than the 6 mg/kg dw level proposed by Skorupa (1998) who based his estimate on field-observational data potentially confounded by other environmental stress factors. The mortality and teratogenicity endpoints presented here relate selenium exposure to risk to individuals within a population and do not provide information about the probability of selenium causing changes in population growth rates, either at the local or regional levels.

Elemental selenium particles at nano-size (Nano-Se) are more toxic to Medaka (Oryzias latipes) as a consequence of hyper-accumulation of selenium: A comparison with sodium selenite

“…Since the margin between salutary and toxic effects of selenium is very narrow, safety margin and potential toxic effects are important questions to be addressed when consider the role of selenium in dietary supplements. In recent years, the selenium criteria for aquatic life and the proposed toxicity thresholds have become a controversial topic (Chapman, 1999;DeForest et al, 1999;Fairbrother et al, 1999). Some researchers have suggested a dietary selenium toxicity threshold value of 3-4 g Se/g (Maier and Knight, 1994), which is comparable to the selenium concentration in fish food used in our experiment (1.57 ± 0.03 g Se/g dw).…”

The American Dipper as a Bioindicator of Selenium Contamination in a Coal Mine-Affected Stream in West-Central Alberta, Canada

“…It was only slightly lower than 8 μg g −1 , another oft-cited mean egg toxicity threshold (Ohlendorf and Santolo, 1994;Seiler et al, 2003). However, it was lower than mean egg selenium thresholds (12.5, 13, 16, and 12-15 μg g −1 ) based on experimental studies with captive mallards (Fairbrother et al, 1999;Adams et al, 2003;Ohlendorf, 2003;Brix et al, 2005).…”

Analysis of Field and Laboratory Data to Derive Selenium Toxicity Thresholds for Birds

“…Egg inviability is slightly less sensitive than chick mortality [15], whereas teratogenesis tends to be less sensitive than chick mortality by a factor of 1.5-to 3-fold [10,12]. A fourth endpoint, clutch inviability, is toxicologically equivalent to egg inviability but is evaluated on a henwise (i.e., clutchwise) basis rather than on an individual-egg basis.…”

“…Previously, Fairbrother et al [13] reported an estimated EC10 of 26 mg/kg dry weight for teratogenesis and of 16 mg/kg dry weight using both probit and logit models for duckling survival. One data point reported by Heinz et al [35] was not included in the analysis (as discussed by Fairbrother et al [12]), because the mean egg selenium concentration (15.9 mg/kg dry wt) associated with duckling mortality (i.e., 76%, corrected for control mortality) was higher, by a factor of seven-or eightfold, than would be expected as compared to all other data in the dataset. 1 and 2).…”