Falling participation rates is one of the most significant challenges facing survey research today. To curb this negative trend, scholars have searched for factors that can increase and decrease citizens’ willingness to participate in surveys. In this article, we investigate the timing effects of survey invitation e-mails on participation rates in a university-based online panel with members of the Swedish public. Through two large-scale experimental studies, we examine whether the day of week ( N = 11,294) and time of day ( N = 47,279) for sending out survey invitations impact participation rates. We also ask respondents when they prefer to answer surveys. We find that the timing of survey invitations affects participation rates, however, the effects are small, short-lived, and even out within a week. We also find that the effects of timing vary by employment status and age. The results have implications for scholars and practitioners who utilize online panels for web surveys. When quick answers are important, there may be some limited gains of tailoring the timing of the survey invitation to different individuals. In surveys with more extended field periods, however, such efforts seem less warranted.

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Uptake and biliary excretion of metals were studied in rainbow trout, Oncorhynchus mykiss, exposed through spiked sediment to a mixture of seven heavy metals. Metal concentrations and toxicity of bile and blood plasma were used as indicators of exposure. Among the seven metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) only three (Cu, Hg, and Pb) were concentrated in the bile (bile-plasma ratio >1). Bile-plasma ratios in the rainbow trout were similar to those found in rats for Cu and Hg. Daphnia magna bioassays were used to determine toxicity of bile and blood plasma in the same trout. Toxicity of bile and blood plasma increased after treatment with acid. An analysis of variance (ANOVA) showed that toxicity of bile and blood plasma to D. magna in metal-exposed trout was significantly correlated with (1) bile and blood plasma test concentration, (2) acid treatment of bile and blood plasma (hydrolysis of metal-plasma and metal-bile complexes) and (3) sediment concentration of metals during exposure of trout. In order to significantly detect the magnitude of the exposure to a xenobiotic the biomarker must respond in a dose-or time-dependent manner. Therefore, the potential use of bile toxicity as a biomarker of heavy metal exposure in fish is probably limited by the low bioconcentration of many of these toxicants in bile.

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