Sucralose Induces Biochemical Responses in <i>Daphnia magna</i>

<div><p>The intense artificial sweetener sucralose has no bioconcentration properties, and no adverse acute toxic effects have been observed in standard ecotoxicity tests, suggesting negligible environmental risk. However, significant feeding and behavioural alterations have been reported in non-standard tests using aquatic crustaceans, indicating possible sublethal effects. We hypothesized that these effects are related to alterations in acetylcholinesterase (AChE) and oxidative status in the exposed animals and investigated changes in AChE and oxidative biomarkers (oxygen radical absorbing capacity, ORAC, and lipid peroxidation, TBARS) in the crustacean <i>Daphnia magna</i> exposed to sucralose (0.0001–5 mg L⁻¹). The sucralose concentration was a significant positive predictor for ORAC, TBARS and AChE in the daphnids. Moreover, the AChE response was linked to both oxidative biomarkers, with positive and negative relationships for TBARS and ORAC, respectively. These joint responses support our hypothesis and suggest that exposure to sucralose may induce neurological and oxidative mechanisms with potentially important consequences for animal behaviour and physiology.</p></div

Generalized Linear Models for biomarkers of oxidative damage (lipid peroxidation, TBARS, pmol ind⁻¹), antioxidative defense (total oxygen radical absorbance capacity, ORAC, mg Trolox ind⁻¹) and neurotoxicity (acetylcholinesterase activity, AChE, nmol AcSCh min⁻¹ mg protein⁻¹) in <i>Daphnia magna</i> exposed to a range of sucralose concentrations (sucralose, 0.1–5000 µg L⁻¹); individual protein weight (protein, µg ind⁻¹) was used as a proxy for body size.

<p>(A) TBARS as a function of sucralose concentration, protein and ORAC; (B) ORAC as a function of sucralose concentration and protein; and (C) AChE as a function of sucralose concentration and ORAC. All data for the regression analysis were Box-Cox transformed; significant effects are in bold face.</p

Relationships between AChE, ORAC and TBARS in <i>Daphnia magna</i> (all data from the Experiments 1–4 are combined).

<p>The data are Box-Cox transformed and normalized to the respective controls.</p

Experimental concentrations of sucralose and biomarker values measured in <i>Daphnia magna</i>.

<p>A control using M7 medium was included in each of the four experiments (Exp I to IV). Data for the biomarkers within the experiment are shown as ranges (min-max) and for controls as mean values. Note that number of treatments differs among the experiments.</p

Metal contamination in harbours impacts life-history traits and metallothionein levels in snails

<div><p>Harbours with limited water exchange are hotspots of contaminant accumulation. Antifouling paints (AF) contribute to this accumulation by leaching biocides that may affect non-target species. In several leisure boat harbours and reference areas in the Baltic Sea, chronic exposure effects were evaluated using caging experiments with the snail <i>Theodoxus fluviatilis</i>. We analysed variations in ecologically relevant endpoints (mortality, growth and reproduction) in concert with variation in metallothionein-like proteins (MTLP) levels. The latter is a biomarker of exposure to metals, such as copper (Cu) and zinc (Zn), which are used in AF paints as active ingredient and stabilizer, respectively. In addition, environmental samples (water, sediment) were analysed for metal (Cu and Zn) and nutrient (total phosphorous and nitrogen) concentrations. All life-history endpoints were negatively affected by the exposure, with higher mortality, reduced growth and lower fecundity in the harbours compared to the reference sites. Metal concentrations were the key explanatory variables for all observed adverse effects, suggesting that metal-driven toxicity, which is likely to stem from AF paints, is a source of anthropogenic stress for biota in the harbours.</p></div

Response and explanatory variables considered in the regression models.

<p>TP = total phosphorous, TN = total nitrogen, GLM = generalized linear model, ww = wet weight.</p

Metals and organic antifouling biocides in sediment (s) and water (w) from harbours and reference sites; TS = total solids, TBT, DBT and MBT = tri, di and monobutyl tin, respectively; TN = total nitrogen, TP = total phosphorous; one sediment sample was analysed per site Concentrations in water are in μg/L and in sediment in mg/kg TS and μg/kg TS for organotins.

<p>Metals and organic antifouling biocides in sediment (s) and water (w) from harbours and reference sites; TS = total solids, TBT, DBT and MBT = tri, di and monobutyl tin, respectively; TN = total nitrogen, TP = total phosphorous; one sediment sample was analysed per site Concentrations in water are in μg/L and in sediment in mg/kg TS and μg/kg TS for organotins.</p

Regression models testing effects of environmental variables on snail life-history and biomarker responses: a) Hurdle models for zero-inflated data (mortality and fecundity rate); b) Generalized linear models (GLMs) for the growth (RGR) and MTLP responses.

<p>Regression models testing effects of environmental variables on snail life-history and biomarker responses: a) Hurdle models for zero-inflated data (mortality and fecundity rate); b) Generalized linear models (GLMs) for the growth (RGR) and MTLP responses.</p

Mortality and sublethal responses of snails exposed in different locations.

<p>For each variable, the horizontal line indicates the median, the lower and upper limits of the boxes are the 1^st and 3^rd quartile, respectively and the whiskers show the furthest point within 1.5 × the interquartile range. Harbours and reference sites are shown in black and grey, respectively. MTLP = metallothionein-like proteins, RGR = relative growth rate.</p

Map of the study locations and SMHI (Swedish Meteorological and Hydrological Institute) station that was used to retrieve the temperature data.

<p>Map of the study locations and SMHI (Swedish Meteorological and Hydrological Institute) station that was used to retrieve the temperature data.</p