Ordination of the PBDE profiles in basal sources and invertebrates of the lake food webs studied.

<p>The variation of the PBDE composition was summarized by means of a principal component analysis (PCA) using the Hellinger distance <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041829#pone.0041829-Legendre1" target="_blank">[63]</a>. Biplots of the first two principal components (A) and the second and third (B) are shown. Symbols refer to each sample analyzed and vary to show the corresponding trophic level (color) and taxonomic position (shape) as indicated in the legend. With a few exceptions primary and secondary consumers are discriminated between them.</p

PBDE isotopic bromine ratios (Br⁷⁹:Br⁸¹) across trophic levels.

<p>The ratio Br⁷⁹:Br⁸¹ in nature and industrial PBDE mixtures is close to one. Deviations from that ratio can be used as indication of processes determining isotopic fractionation. Mean and standard deviation for two BDE congeners are plotted for each trophic level: BDE-209, for being the initial industrial source; and BDE-47, because is the resulting most abundant congener in the food web. The ratio differences between trophic levels for both compounds are significantly different as a whole (p<0.001); paired comparisons are indicated in the figure using lower case letters, only basal resources and fish ratios do not differ for a 95% interval of confidence. Higher Br⁷⁹:Br⁸¹ values in BDE-47 than in BDE-209 and declining values from basal resources to secondary consumers are compatible with the existence of accumulative effects of enzymatic debromination. High Br⁷⁹:Br⁸¹ values in fish indicate that some other additional process is taking place in them that discriminates against the heavier isotope, differential transport is suggested as a potential mechanisms, either at gut uptake or during within body distribution.</p

PBDE relative composition at different trophic levels of the lake food webs studied.

<p>Bars indicate average percentages of each PBDE in the lake food web components included in the respective trophic category. Error bars indicate standard deviations. Different bar colors are used to identify the trophic levels across figures. BDE-209 is the current congener produced industrially in Europe. Congeners BDE-35, BDE-77 and BDE-156 have never been present in any industrial mixture.</p

PBDE content in individual taxa and assemblages of the lake food webs studied.

<p>Mean and standard deviation are indicated, if more than one sample was available. The complete list of measured values is provided as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041829#pone.0041829.s001" target="_blank">Table S1</a>. Bar colors correspond to basal resources (green), primary consumers (yellow), secondary consumers (red), and fish (blue). Error bars correspond to standard deviation of the whole number of samples analyzed for a given species or assemblage.</p

Organisms and assemblages analyzed in this study.

<p>The evolutionary lineage and trophic information is provided. Primary consumers (PC) include herbivores and detritivores feeding on basal resources (BR), which in these lakes are mostly biofilms of varying degree of autotrophic primary producers (PP) and heterotrophic decomposers (D). Secondary consumers (SC) include organisms predating upon primary or other secondary consumers. In a few cases, we have distinguished between assemblages in different parts of the lake (e.g., littoral or bottom) or contrasting microhabitats (e.g., epilithon, epipelon). Lake occurrence is indicated by: Le, Llebreta; Lo, Llong, C, Colomina and V, Vidal.</p

PBDE concentration at different trophic levels.

<p><i>bdl,</i> below detection limit.</p

Frequency of bromine atoms at each potential site of the BDE molecule.

<p>The larger the circle, the higher the frequency. The frequency at which a potential site in the BDE molecule was occupied by a bromine atom was estimated from the formula of the respective PBDE congeners and their proportion in a trophic level. Basal resources and primary consumers of the lake food web studied are compared. Interestingly, the molecule sites with higher occupancy correspond to those that are chemically more stable. The result is compatible with a high enzymatic biotransformation capability in primary consumers.</p

Appendix A. Path diagrams and models output showing the direct and indirect effects of aquatic reliance (δ13C) and trophic position on MeHg.

Path diagrams and models output showing the direct and indirect effects of aquatic reliance (δ13C) and trophic position on MeHg

Supplement 1. R code and scripts for computing multilevel models with spatial autocorrelation for zooplankton spatial distribution data.

<h2>File List</h2><div> <p><a href="Zooplankton_Myvatn_Code.r">Zooplankton_Myvatn_Code.r</a> (MD5: 77e338006e7b29cb5a5e4d08df920736) </p> </div><h2>Description</h2><div> <p>Zooplankton_Myvatn_Code.r contains R code to create multilevel models with spatial autocorrelation, analyze the significance of random effects, and compare the best multilevel model for zooplankton spatial distribution data. Comment lines specify the inputs to the function and the outputs from the function. The code may be called from an R program as an external function, or it may be placed in-line within a R program.</p> </div